Master's Thesis No. 2011:03 Future Vehicle Technology and its Implementation A Study and Evaluation of Road Vehicle Propulsion Technology Kristian Näsholm Jose�ne Walker Department of Applied Mechanics CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2011 Future Vehicle Technology and its Implementation A Study and Evaluation of Road Vehicle Propulsion Technology Kristian Näsholm Jose�ne Walker © Kristian Näsholm, Jose�ne Walker 2011. Master's Thesis No. 2011:03 ISSN 1652-8557 Department of Applied Mechanics Chalmers University of Technology SE-412 96 Göteborg Sweden Telephone + 46 (0)31-772 1000 Cover: An schematic illustration of a Lotus Evora with a hybrid powertrain Chalmers Reproservice Göteborg, Sweden 2011 Future Vehicle Technology and its Implementation A Study and Evaluation of Road Vehicle Propulsion Technology KRISTIAN NÄSHOLM JOSEFINE WALKER Department of Applied Mechanics Chalmers University of Technology Abstract The automotive industry is facing several challenges right now, such as economical crisis and tough competition. At the same time the demand of alternative transportation technologies is increasing and the legislations on emissions for light duty vehicles are tightening. To be able to survive in this harsh business climate, new and creative solutions are needed and the changes have to be fast. Today's vehicle �eet is almost entirely dependent on fossil fuels and scientists are indicating that the increasing amount of CO2 in the atmosphere is contributing to the global warming. The challenge for the industry is to increase the vehicles fuel economy and make them run further on the same amount of fuel, or even better, by not using any fossil fuels at all. This master thesis's main objective is to help Lotus Engineering making up general guidelines and information for the selection of new automotive technology through analysis of several new powertrain technologies and fuels. The following technologies are being considered: � Internal combustion engine vehicles � Mechanical hybrid vehicles � Electric vehicles � Hybrid electric vehicles and plug-in hybrid electric vehicles � Fuel cell vehicles � Alternative fuels: Bio-diesel, natural gas, ethanol, methanol, hydrogen and synthetic fuels The vehicle structure and design is another important factor when it comes to fuel economy, since aerodynamic drag, weight and rolling resistance are major factors that a�ects the fuel economy. This thesis gives information about how to design and reduce weight of the car. This thesis also contains a simulation chapter, where a series and a parallel hybrid are compared in terms of fuel economy to help knowing when to use which type of system. All of this is summarized in the future vision chapter. The analysis is made to show the potential of each technology to make it in the future society and consider cost, the potential to implement it into our current society and infrastructure and how much support the technology has amongst leading governments and commissions. No full cost analysis is done since this thesis is focusing more on the technical aspects of the technology than the economic aspect. The driving behavior of the car users has also been taken in to consideration, even though in a very basic manner. The research only reaches into a feasible future, until about 2050. Acknowledgments First of all we would like to thank our examiner at Chalmers, associate professor Sven Andersson. We also like to thank Ingemar Johansson for making this thesis possible in the �rst place and for being very helpful and supportive throughout our work. A special thanks to Phil Barker - Cheif product engineer - Hybrid electric vehicles, Steve Doyle - Cheif Engineer - Hybrid electric vehicle integration, Leon Rosario - Senior Engineer - Hybrid electric vehicle integration and all the rest of the employees at Lotus engineering for their help. We would also like to give thanks to our families and friends at home, but also all our new friends at Lotus engineering and in Norwich who supported us and helped us throughout the thesis. Nomenclature APU Auxiliary Power Unit BEV Battery Electric Vehicle bmep break mean e�ective pressure bsfc break speci�c fuel consumption CVT Continuously Variable Transmission DCT Dual Clutch Transmission DI Direct Injection DfT Department for Transport DoH Degree of Hybridisation EM Electric Machine EPA Environmental Protection Agency EV Electric Vehicle FCHEV Fuel Cell Hybrid Electric Vehicle FCV Fuel Cell Vehicle GHG Greenhouse Gas HEV Hybrid Electric Vehicle ICE Internal Combustion Engine ICEV Internal Combustion Engine Vehicle KERS Kinetic Energy Recovery System MHV Mechanical Hybrid Vehicle mpg miles per gallon mph miles per hour NEDC New European Driving Cycle NGV Natural Gas Vehicle PEM Polymer Electrolyte Membrane or Proton Exchange Membrane PHEV Plug-in Hybrid Electric Vehicle rpm revolutions per minute rps rounds per second SMR Steam Methane Reforming SoC State of Charge ZEV Zero Emission Vehicle Translation of units 1 mph 1.6 km/h 1 mile 1.6 km 1 mpg 282.481 l/100km 1 lbft 0.738 Nm 1 km/h 0.625 mph 1 km 0.625 miles 1 l/100km 282.481 mpg 1 Nm 1.356 lbft List of Figures 1 Average atmospheric CO2 concentration [6, 15] . . . . . . . . . . . . . . . . . . . . . . 3 2 Predicted worldwide growth of the vehicle �eet [16] . . . . . . . . . . . . . . . . . . . . 4 3 Potential of lowering fuel consumption with hybrid technology [17-54] . . . . . . . . . 4 4 Cars sold by Lotus per model in 2008 . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Conventional vehicle with a) left: Front wheel drive b) right: Rear wheel drive . . . . 7 6 Flywheel con�gurations a) left: Series �ywheel hybrid b) right:Parallel �ywheel hybrid [59] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7 Pneumatic engine cylinder [59] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8 Schematic pneumatic powertrain layout [59] . . . . . . . . . . . . . . . . . . . . . . . . 9 9 Hydraulic hybrid con�gurations a) left: Hydraulic series hybrid b) right: Hydraulic parallel hybrid [59] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 10 Driving modes for the PHEV [16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 11 Layout of the series hybrid powertrain . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 12 Principal layout of a parallel hybrid powertrain . . . . . . . . . . . . . . . . . . . . . . 13 13 Layout of a mild parallel hybrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 14 Layout of a split hybrid drivetain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 15 FCV con�gurations a) left: FCV b) middle: FCHEV c) right: FCV with reformer [58] 15 16 Energy conversion from primary energy source to fuel cell vehicle [72] . . . . . . . . . 15 17 Engine fuel consumption map [73] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 18 Layout and machinery description of a fuel cell [65] . . . . . . . . . . . . . . . . . . . 18 19 Usable energy span for Li-ion and NiMH batteries . . . . . . . . . . . . . . . . . . . . 19 20 Speci�c energy for common battery types [75] . . . . . . . . . . . . . . . . . . . . . . . 19 21 Comparison of di�erent energy bu�er types a) left: Power output for the energy bu�ers over di�erent temperatures b) right: Cycle life depending on cycle depth . . . . . . . . 20 22 Torque at di�erent speeds for an electric motor . . . . . . . . . . . . . . . . . . . . . . 21 23 The traction force, Ft as a function of the vehicle speed, v . . . . . . . . . . . . . . . 22 24 Layout of a planetary gear in a Toyota Prius . . . . . . . . . . . . . . . . . . . . . . . 22 25 Fuel consumption compared to vehicle weight . . . . . . . . . . . . . . . . . . . . . . . 28 26 GHG emissions from transport fuels by type of energy source . . . . . . . . . . . . . . 30 27 Predicted market penetration of FCVs in a hydrogen based society . . . . . . . . . . . 37 28 Illustration of di�erent injection types a) left: Direct injection b) right: Port injection 38 29 Power demand decrease due to weight reductions over speed . . . . . . . . . . . . . . 42 30 Required road load power and the e�ects of di�erent improvements a) top: Power needed to overcome rolling resistance and aerodynamic drag at certain speeds b) mid- dle: Power demand reductions due to decrease in aerodynamic drag c) bottom: Power demand reductions due to decrease in rolling resistance . . . . . . . . . . . . . . . . . 44 31 Bene�ts from improving aerodynamic drag, rolling resistance and vehicle weight . . . 45 32 Hypothetical future distribution in the vehicle �eet in a electricity based scenario . . . 46 33 Hypothetical future distribution in the vehicle �eet in a hydrogen based scenario . . . 46 34 Hypothetical future distribution in the vehicle �eet in a mixed fuel/technology scenario 47 35 The city cycle part of the NEDC a) left: Modi ed ECE-15 b) right: Original ECE-15 . 50 36 NEDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 37 State of charge in the modi�ed ECE-15 cycle a) left:Parallel hybridb) right: Series hybrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 38 Fuel consumption of a parallel HEV with �ve di�erent weights over the spectrum of DoH from 0, ICEV to 100, pure EV a) left: In the NEDC cycle b) right: In the modi�ed European city cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 39 Fuel consumption of a series HEV compared to the original ICEV a) left: In the NEDC cycle b) right: In the modi�ed European city cycle . . . . . . . . . . . . . . . . . . . . 52 List of Tables 1 Average four-wheeled vehicle usage amongst UK drivers . . . . . . . . . . . . . . . . . 5 2 Vehicle speci�cations of Lotus's current models . . . . . . . . . . . . . . . . . . . . . . 6 3 The European emission standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 4 Comparison between diesel and HEV passenger cars . . . . . . . . . . . . . . . . . . . 28 5 Battery chemistry used in current and coming concept EVs, PHEVs and HEVs . . . . 29 6 Fuel economy improvements due to weight reductions . . . . . . . . . . . . . . . . . . 42 Contents 1 Introduction 1 1.1 Problem description and objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Report outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Background 3 2.1 Need for alternative technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Four-wheel vehicle usage in the UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Group Lotus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Vehicle powertrains and components 7 3.1 Internal combustion engine vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Mechanical hybrid vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.1 Flywheel system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.2 Pneumatic system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2.3 Hydraulic system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Electric vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.4 Hybrid-electric vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.4.1 Series hybrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4.2 Parallel hybrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.4.3 Split/combined hybrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.5 Fuel cell vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.6 Main technology characteristics of the powertrain components . . . . . . . . . . . . . . 16 3.6.1 Internal combustion engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.6.2 Fuel cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.6.3 Rechargeable energy storage systems . . . . . . . . . . . . . . . . . . . . . . . . 18 3.6.4 Electric machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.6.5 Transmissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4 Principles for selection and implementation of new technology 23 4.1 Vehicle introduction strategy and system selection . . . . . . . . . . . . . . . . . . . . 23 4.2 Summary hybrid system selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5 Future automotive propulsion technology 27 5.1 Benchmarking and research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.1.1 Methodology benchmarking and research . . . . . . . . . . . . . . . . . . . . . 27 5.1.2 Technology trends overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.2 Future fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.2.1 Biodiesel fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.2.2 Ethanol and methanol fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.2.3 Natural gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5.2.4 Hydrogen fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5.2.5 Synthetic fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 5.3 Future for powertrain technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 5.3.1 Future internal combustion engine vehicles . . . . . . . . . . . . . . . . . . . . 33 5.3.2 Future mechanical hybrid vehicles . . . . . . . . . . . . . . . . . . . . . . . . . 33 5.3.3 Future electrical vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 5.3.4 Future hybrid electric vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.3.5 Future plug-in hybrid electric vehicles . . . . . . . . . . . . . . . . . . . . . . . 36 5.3.6 Future fuel cell vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.4 Future for powertrain components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.4.1 Future ICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.4.2 Future fuel cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.4.3 Future electrical machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.4.4 Future energy bu�ers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 5.4.5 Future transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 5.5 Vehicle structure and design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 5.6 Summary future vision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6 Simulations 49 6.1 Methodology simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 6.2 Theory simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 6.3 Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 6.4 Summary simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 7 Discussion 53 8 Conclusions 55 9 Future work 57 A Benchmarking overview I B Simulations III 1 Introduction The transportation system today uses 26 % of the annual global energy produced and is almost entirely dependent on fossil fuels [1-2]. The large bulk of transports consist of road transports where personal transports alone are responsible for 11 % of the worlds CO2 emissions [2-3]. The current average CO2 concentration in the atmosphere is 286ppm and is increasing at a rate of 2ppm per year and will, during a business-as-usual scenario, increase to somewhere in the regions of 700ppm until 2100. A radical change in the use of fossil fuel is therefore needed to stabilize the atmospheric CO2 at a lower level [3-6]. To be able to meet the increasing emission and CO2 legislation's, vehicle manufacturers are forced to increase fuel e�ciency by both implementing new solutions and increasing e�ciency of existing parts [8-10]. Future transports are seen as zero emission vehicles and have zero or very low well-to-wheel CO2 emissions. These can be fuel cell vehicles (FCVs) with CO2 neutral H2 or pure electric vehicles (EVs) charged with CO2 neutral electricity. Depending on a number of factors this future still has many years in the making, maybe as much as 40 years [3, 5]. The technology behind hybrid electric vehicles (HEVs) has been around for more than 100 years and modern equivalents have been in production for a bit more than a decade [11-12]. The focus of the automotive industry the last 20 years have been vehicle performance with more powerful engines as a consequence. There has however been a shift in this focus the last few years, starting with the Toyota Prius in Japan 1997, towards making more fuel e�cient cars. HEVs are one of the most prominent solutions in the wait for more sustainable transports. HEVs themselves may not be the perfect solution to combat climate change, but they are a step in the right direction and will probably work as a temporary solution during the transition to the sustainable alternatives for personal transport. HEVs consist of complex system interactions that need to be optimised to achieve as high a fuel economy as possible while ful�lling requirements on performance and drive-ability [13]. How the future will turn out is still unclear, however this report aims to predict how the nearest future in HEV technology will look like. It will also attempt to make a template for the selection of which hybrid powertrain to utilize for a speci�c car with speci�c characteristics to further help streamline the development process of HEVs. 1.1 Problem description and objectives The demand for alternative transportation technologies is increasing and the emission legislations for light duty vehicles are getting narrower. It will be the vehicle manufactures that have to solve the problem of providing new technology that can meet these demands. But there are several things for a car manufacturer to take into account when introducing a new model and even more if changing the majority of the vehicles powertrain which can be both costly and time consuming. However, to be able to stay in the front line of car manufacturing, hybrids and other alternative technologies will be important to consider. It is therefore important to have as much information about new vehicle technologies as possible. This master thesis's main objective is to help Lotus Engineering set up guide lines and gather information for the selection of new automotive technology through analysis of several new powertrain technologies. The research in this report will be based on two things. First a benchmarking and literature research of di�erent road vehicle propulsion technologies, both existing and future, and secondly a systems evaluation through simulations. The literature research includes investigations of components in the di�erent powertrains and the simulation includes a study of how parameters such as weight and the extent of hybridisation can in�uence the choice of propulsion system. The main goal is to present the status of current and future automotive propulsion technologies and thereby suggest which of the technologies that has the greatest potential to make it in the industry in the nearest future. The �rst part, the investigation and benchmarking of future propulsion systems and components, will only reach into a feasible future and only consider the following technologies: � Alternative fuels: Bio-diesel, natural gas, ethanol, methanol, hydrogen and synthetic fuels produced from air � Internal combustion engine vehicles 1 � Electric vehicles � Mechanical hybrid vehicles � Hybrid electric vehicles and plug-in hybrid electric vehicles � Fuel cell vehicles The analysis of each technology is based on trends and �ndings from the benchmarking of present and coming car models and concept cars. The literature research helps to support these �ndings with facts. The analysis is made to show the potential of each technology to make it in the future automotive society and will consider cost of the technology, the potential to implement it into the current infrastructure and how much support the technology has from leading governments and commissions. But no full cost analysis is shown since the paper is focusing more on the technical aspects of the technology than the economic aspect. Even the driving behavior of the car users have been taken in to consideration, even though this analysis are very basic, see chapter 2. Both the simulations of hybrid drivetrains and the research will focus on passenger cars and not consider heavy vehicles such as buses and lorries. The simulations will only consider hybrid electric and fully electric systems, not mechanical hybrids nor fuel cell vehicles. The simulations are done using the NEDC and a modi�ed European city cycle. The simulations are mainly focused on technical aspects as fuel economy and vehicle weight and do not focus on factors such as development costs or costs of production. But since cost of the vehicle is a very important factor, both to the vehicle manufacturers and to the customers, the cost factor is brie�y discussed in the analysis from the benchmarking as described earlier. 1.2 Report outline This report is divided into 9 chapters. The �rst chapter after this introduction is the background. In the background, the need for alternative technology and car usage is presented and it also includes a presentation of Group Lotus is given, since the thesis has been carried out at Lotus Engineering. In Chapter 3 the di�erent powertrains and their components are presented. The chapter aims to give the reader more information about the vehicle technologies that has been taken into consideration in this report. But a reader that is very familiar with the subject can thereby leave this chapter out. The next chapter, chapter 4 Principles for selection and implementation of new technology, presents some guidelines for strategic implementation of vehicles with new and di�erent powertrain technology in current production. In the chapter 5 Future technology, a presentation of the analysis from both the benchmarking and the literature research is given. The potential of each technology is described individually and in the end of the chapter a summary can be found, where three hypothetical future scenarios for the technology distribution are presented. After this the results from the second part of the project are present, in chapter 6 which is the simulation section. In this chapter some of the powertrain systems that are presented in chapter 3 are validated to show where and how to use which system. Chapter 4, 5 and 6 all starts with a presentation of facts and a analysis and ends with a summary which summarises the most important �ndings from the chapter. The whole report is being summed up in the end through the discussion and conclusions in chapters 7 and 8. The last chapter, chapter 9, gives some recommendations of future work in this area. 2 2 Background Chapter 2 gives a background of this thesis and will explain the need for alternative propulsion and why alternative solutions are important and how they are linked to this work. It also gives a presentation on average car usage in the UK, since this is an important factor when investigating the possibilities for new propulsion technology. A short introduction of Group Lotus and their background is given as well since this master thesis is carried out at Lotus engineering. 2.1 Need for alternative technologies The atmospheric CO2concentration has been getting higher and higher during the last century and it is still rising at an exceptional rate, see �gure 1. If nothing is done about the global CO2emissions from fossil fuels, i.e. during a business-as-usual scenario, the CO2concentration will almost be doubled by the end of this century, see �gure 1 [2-3, 5-7].In later years the increased knowledge about the connection between atmospheric CO2, global warming and sea level rise have put environmental issues on top of everyone's agenda. The industry, energy and transport sectors are the three largest contributors of CO2and have accordingly given the main responsibility for lowering their use of fossil fuels [2]. With this in mind, the transport sector, which is responsible for 25 % of the worlds CO2emissions, has to make a drastic change in the amount of fossil fuels consumed [2]. In the personal road transport sector hybrid powertrains, alternative fuels and small fuel e�cient diesels are three of today's most used ways of attempting to reduce the environmental impact whilst at the same time trying to meet the 2020 goal of 95g-CO2/km [14]. The di�erent hybrid systems and the vehicles they are implemented in will play a signi�cant role towards lowering fuel consumption and reducing the carbon footprint until more sustainable alternatives are available on a larger market. Figure 1: Average atmospheric CO2 concentration [6, 15] The worldwide growth of the vehicle �eet is another problem to be considered, especially in the developing countries where the increase is most substantial, see �gure 2. In order to keep the increase in energy needed at an absolute minimum, cheap, fuel e�cient or zero emission vehicles (ZEV) are needed. Car manufacturers that want to be on the environmental bandwagon need to consider hybrid systems, fully electrical systems and alternative fuels as a part of their model range. 3 Figure 2: Predicted worldwide growth of the vehicle �eet [16] All attempts to develop and implement more environmentally friendly technology will be of interest to the automotive industry. The potential of using hybrid technology to lower the fuel consumption can be seen in �gure 3, where conventional petrol driven internal combustion engine vehicles are compared to petrol-electric hybrids with similar engine displacement. Figure 3: Potential of lowering fuel consumption with hybrid technology [17-54] Investigating the di�erent hybrid systems and their components thereby supplies useful infor- mation to the automotive manufacturers when developing a new hybrid model. This master thesis therefore attempts to investigate the latest developments and the predicted future of hybrid propul- sion and other upcoming automotive propulsion technology. To make the introduction phase of new powertrains faster and more e�cient a strategy is needed and together with simulations for validation. The results of this work aims to be a help for Lotus engineering when dealing with these kinds of problems. The results from the future automotive propulsion technology benchmarking are presented in chapter 5 Future automotive propulsion technology and simulation results in chapter 6 Simulations. The results from the simulations aims to act as a guide to the selection of the right technology for the right car model depending on factors such as vehicle weight and degree of hybridisation, DoH, which will be further explained in section 6.2. 4 2.2 Four-wheel vehicle usage in the UK One important factor in the investigation of possibilities for current and coming vehicle propulsion systems is the average car usage amongst drivers. According to the UK department for transport (DfT), the average car mileage was 8,870 miles per year in 2007. This means that the average mileage per day is about 24.3 miles for a four-wheeled car [55]. By analysing how much time the average car user spends in their vehicles each year, an important fact is given. This information can be crucial when studying recharge times for electric based vehicles. According to the latest statistics from DfT the average time spent on travel ling by car was 232 hours per year in 2006 [55]. This means that the cars only are driven for about 40 minutes each day and is then parked for the rest of the time. A summary of the average four-wheeled vehicle usage amongst UK driver can be seen in table 1. Table 1: Average four-wheeled vehicle usage amongst UK drivers 2.3 Group Lotus As mentioned above this master thesis was made on the behalf of Lotus Engineering. Lotus is a British car manufacturer that designs and builds race and production automobiles with light weight and great handling characteristics. Anthony Colin Bruce Chapman built his �rst racing car in 1948 and founded the Lotus Engineering Company in order to build racing cars in 1952. In the year of 1966 the company moved into a purpose built factory at a former American second world war air�eld in Hethel, Norfolk, where it still remains today. The facilities include a factory, engineering o�ces and have a 2 mile test track where ride and handling can be tested. Group Lotus consists of two parts, Lotus Cars and Lotus Engineering, which 1996 was sold to the Malaysian car manufacturer Proton. Lotus Engineering is a consultancy company and the client base includes many of the world's major car manufacturers. New engineering centers have been established in the majors markets such as USA, China and south east Asia. Lotus Engineering also develops their own brand of cars produced by Lotus Cars [56]. The Lotus brand has a far going racing pedigree and a history of prestigious car models as the Lotus Esprit, the Elan and the Elite. Five di�erent car models are produced today, the Lotus Elise, Exige, Evora, Europa and 2-Eleven, where the Evora is the latest addition to the family as it was released in the spring of 2009. Figure 4 shows 2008's sales of the di�erent models [57]. 5 Figure 4: Cars sold by Lotus per model in 2008 Even though Lotus engineering are involved in several di�erent development projects, do they not yet produce any hybrids among their own brand models. Fuel consumption for the current models are presented in table 2 which summarises some important speci�cations for the current car models. The table can be used as a comparison to the vehicles analysed in the benchmarking. Table 2: Vehicle speci�cations of Lotus's current models Model Fuel Consumption Fuel Consumption Fuel Consumption CO2 Emissions Maximum Power Max Torque Acceleration Top Speed Weight Urban [l/100km] Extra urban [l/100km] Combined [l/100km] [g/km] [kW] [Nm] 0-100km/h [s] [km/h] [kg] Elise S 10.6 5.8 7.6 179 100 172 6.1 207 860 Elise R 11.6 6.2 8.2 196 141 181 5.4 222 860 Elise SC 11.8 6.4 8.5 199 163 212 4.6 233 870 Exige S 11.9 6.5 8.5 199 164 215 4.7 238 935 Europa 12.7 7.3 9.3 220 147 272 5.8 230 995 Europa SE 13.4 7.7 9.8 229 165 300 5.3 235 995 2-Eleven n/a n/a n/a n/a 142 181 4.5 225 720 Evora 12.4 6.5 8.7 205 206 350 5.1 261 1382 6 3 Vehicle powertrains and components In this section current production and R&D powertrains are presented and explained, followed by some more detailed information about the components. 3.1 Internal combustion engine vehicles The most common vehicles on the road today are petrol powered internal combustion engine vehicles (ICEVs). The powertrain is rather simple, consisting of an internal combustion engine (ICE) and some kind of transmission. The ICE produces torque which is transferred by the transmission to the wheels. The power produced in the engine corresponds to the power necessary at the wheels, including transmission losses, to propel the vehicle. A net surplus of power will accelerate the vehicle and subsequently a shortage of power will decelerate the vehicle [58]. Figure 5 schematically shows the powertrain for an ICEV with front and rear wheel drive. Figure 5: Conventional vehicle with a) left: Front wheel drive b) right: Rear wheel drive The most common transmission is the �xed-step gearbox, either as an automatic gearbox or as a manual. More about how the transmission works can be found in chapter 3.6 section 3.6.5. The downside with conventional vehicles is that it is hard to combine high performance with low fuel consumption, since the power supplied for propulsion is dependent of the engine power and size [58]. 3.2 Mechanical hybrid vehicles A mechanical hybrid vehicle (MHV) can, among other things, have a �ywheel, pneumatic or hydraulic system [59]. The main advantages with the mechanical hybrids is that they don't require a heavy and expensive battery pack as the hybrid-electric system, see section 3.4. The systems are usually quite simple and do not need that many separate devices which makes the mechanical system less expensive than an electrical system. Since the MHVs get their power from regenerative braking, the technology is very useful for vehicles traveling in urban areas such as delivery vehicles and city buses. But this is a technology that very well can be applicable to passenger cars as well and a short description will be given for each system in the following sections. 3.2.1 Flywheel system The �ywheel system usually combines an ICE with a �ywheel. The �ywheel recovers and stores the kinetic energy from deceleration and braking that would otherwise be wasted in a conventional pow- ertrain. The physics for energy storage for a rotating �ywheel can be described by the mathematical equation for a rotating solid disc or ring, see equation 1 and 2. Simply put, more mass, bigger radius and higher speed will allow more kinetic energy to be stored in the �ywheel [60-61]. Tsolid = 1 4 mr2ω2 (1) 7 Tring = 1 2 mr2ω2 (2) The �ywheel system is fully mechanical and do not need an extra battery/supercapacitor and can thereby avoid some of the problems with energy-bu�ers associated with hybrid electric powertrains, see section 3.4. The �ywheel can be coupled as a series or parallel system. In the series two continuous variable transmissions (CVTs) are needed (see section 3.6.5), one between the engine and the �ywheel and one between the �ywheel and the di�erential connecting to the wheels, see �gure 6a. In the parallel only one CVT is needed and the con�guration is basically just a conventional powertrain with a �ywheel connected to it through a CVT, �gure 6b. Figure 6: Flywheel con�gurations a) left: Series �ywheel hybrid b) right:Parallel �ywheel hybrid [59] The energy in the �ywheel will be stored as mechanical energy which means that there is no extra energy conversion between the wheels and the ICE. This makes the whole system more e�cient compared to a hybrid electric vehicle, since less energy conversions equals less energy lost. Most �ywheel systems are still under development and no vehicles have been produced beyond prototype stage [60]. But the kinetic energy recovery system (KERS) which is a mild hybrid system known from formula one racing, can be constructed with a �ywheel, more about KERS in section 3.4.2. 3.2.2 Pneumatic system In the pneumatic hybrid system a pressure tank is connected to the engine. Every cylinder is con- nected to the tank, which contains pressured air, through a fully variable charge valve, �gure 7 shows the schematic setup of the pneumatic engine cylinder [62]. 8 Figure 7: Pneumatic engine cylinder [59] With the compressed air as an extra boost the engine can be downsized, but still be able to produce the same amount of power due to the boost. If decreasing the number of cylinders it is possible to decrease the friction losses and thereby increase the average e�ciency of the engine. In the pneumatic hybrid the air is compressed during braking and is released trough electronic valves to start or drive the engine. The pressurised air can be used as an extra boost when starting from stop or just as extra boost during acceleration [62]. In �gure 8 a schematic drawing can be seen of the pneumatic powertrain. Figure 8: Schematic pneumatic powertrain layout [59] 3.2.3 Hydraulic system The hydraulic hybrid system consists of three main components; �uid stored in a low-pressure reser- voir, a high-pressure accumulator and a pump connected to the low-pressure reservoir that moves the �uid from the reservoir to the high-pressure accumulator. The system can be coupled either as a series or a parallel system. In the series hydraulic hybrid the engine is connected to the hydraulic pump, which is then connected via an high-pressure accumulator to the a hydraulic pump/motor unit at the wheels, see �gure 9a. The parallel system is more like a conventional powertrain with a hydraulic pump/motor coupled to the system between the engine and the gearbox, seen �gure 9b [59]. As the other mechanical hybrids the hydraulic system receives its energy from regenerative braking. The energy is stored in the high-pressure accumulator and is then converted through the pump/motor to the drive shaft which drives or accelerates the vehicle. This makes the system suitable for vehicles in urban areas with a lot of starts and stops. An example of implementation is an American delivery company that has some hydraulic hybrids in their vehicle �eet [63]. 9 Figure 9: Hydraulic hybrid con�gurations a) left: Hydraulic series hybrid b) right: Hydraulic parallel hybrid [59] 3.3 Electric vehicles Battery electric vehicles (BEVs), or as they are more commonly called, electric vehicles (EVs), are characterised by having pure electric propulsion. They mainly consist of an electric energy bu�er, in the form of a battery or supercapacitor and an electric motor with its controller. The EV only has one energy conversion throughout the drivetrain which allows for a high overall e�ciency [64]. The EVs have a number of attractive attributes such as operating on a high e�ciency with zero exhaust-pipe emissions. It also has the possibility to regenerate most of its braking energy to recharge the battery during deceleration [16]. The EVs have a number of attractive attributes such as operating on a high e�ciency with zero exhaust-pipe emissions. It also has the possibility to regenerate most of its braking energy to recharge the battery during deceleration [65]. The range of the EV is also very short compared to the range of an ICEV. The EVs which provides the best range only reaches about 250 miles on one charge whilst an ICEV can reach up to 1000 miles on one tank [17-54, 65]. Even if a battery with high speci�c energy is used it is di�cult to reach a moderate range without adding too much weight or use too much space in the vehicle. Speci�c energy for batteries is further explained in section 3.6.3. The high cost of batteries and the maintenance needed are other reasons why EVs have not become more popular on a wider scale [16]. 3.4 Hybrid-electric vehicles Currently all the mass produced hybrid electric cars are petrol-electric system based vehicles [17-54, 59]. Hybrid-electric vehicles are characterised by having two or more types of energy sources, in contrast to ICEVs and EVs. The hybrid electric vehicle (HEV) generally includes an ICE as fuel converter or irreversible prime mover combined with an electric machine (EM) and a rechargeable energy bu�er. These components together can achieve a better fuel economy compared to an ICEV, without necessarily sacri�cing performance. The potential bene�ts of hybridisation are presented in chapter 2 �gure 3. Di�erent types of electric prime movers are used, such as standard DC or AC motors. More information regarding EMs can be found in section 3.6. One of the main advantages the HEV has is that it combines some of the advantages of previously discussed propulsion systems (ICEV and EV). The hybrid system enables the possibility of an e�cient energy management and also allows the use of some of the energy usually lost during deceleration and braking to run the vehicle [64, 66]. Another type of HEV is the plug-in hybrid electric vehicle (PHEV) which according to the IEEE have at least following characteristics [67]: � A battery system of at least 4 kWh 10 � The ability to recharge from an external electrical source � Achieve at least a fully electric range of 10 miles The PHEV essentially works in the same way as a HEV but has the ability to recharge its electric energy bu�er from the power grid. The PHEV has a moderate pure electric driving range and it usually has a small ICE that acts as a range extender when the electric energy runs out. It can thereby combine the advantages of an EV together with the less range limited behavior of a conventional HEV. The operation scheme of the PHEV, see �gure 10, can be said to have two modes. First the �charge depleting� mode, where the PHEV is run of the battery until it reaches its minimum state of charge (SoC). It then switches over to �charge sustaining� mode which has the vehicle operation functionality equivalent to a conventional HEV. In the second mode the vehicle will maintain the SoC within a limited operating range, using the stored energy to support the ICE and recharging via regenerative braking or direct charging from the ICE. The driving modes are illustrated in �gure 10. Figure 10: Driving modes for the PHEV [16] PHEVs have recently been discussed as an alternative to conventional vehicles and conventional HEVs [16]. The HEVs have several di�erent system con�gurations which can be divided into three main types, series hybrid, parallel hybrid and split hybrid. The di�erent types of system con�gurations are presented in sections 3.4.1, 3.4.2 and 3.4.3 subsequently. 3.4.1 Series hybrid One or more EMs act as the only prime movers of the vehicle in a series HEV. The electric energy is supplied from an energy bu�er which can be a battery, a supercapacitor or an ICE driven generator. In the series hybrid the ICE is utilized as a range extender to increase the range further than in an EV. A generator is connected to the ICE to convert the mechanical energy output to electrical energy that can either charge the battery or directly feed the EM driving the vehicle [64]. A schematic layout of the series hybrid can be seen in �gure 11. 11 Figure 11: Layout of the series hybrid powertrain One of the advantages of the series hybrid powertrain is the mechanical �exibility of the system, the ICE can be mounted almost anywhere since it works independently to the wheels. Subsequently the working point of the ICE is independent of the traction power, which means that it is possible to run the engine at its optimal operating point. More information with regards to the optimal e�ciency point can be found in section 3.6.1. On the other hand the e�ciency of the system is fairly low, as a consequence of all the energy conversions throughout the system. The EM by the wheels need to be relatively large, since it must handle all traction power on its own, but this on the other hand allows for more power to be recuperated during braking [58]. 3.4.2 Parallel hybrid A parallel HEV normally only have one EM that operates on the same drive shaft as the ICE, in that way the EM and the ICE can add traction power individually or simultaneously. Figure 12 shows a principal layout of the parallel hybrid drivetrain. The parallel hybrid can be seen as an ICE-based vehicle with an additional electrical path as opposed to the series hybrid where the ICE acts only as a support to generate power to the electric drivetrain [64]. 12 Figure 12: Principal layout of a parallel hybrid powertrain The parallel hybrid powertrain is much more e�cient than the series hybrid powertrain, since the ICE is mechanically connected to the wheels which results in fewer energy conversions in the system, the EM can also assist the ICE to run at a more optimal operating point. The system is less mechanically �exible compared to the series hybrid powertrain where the mechanical connection between wheels and ICE is not necessary. The ICE is not able to work completely independently from the traction power, since it is de- pendent on the gear ratio of the transmission. The ICE is therefore not able to work at its optimal operating point at all times, but it is however able to work closer to the optimal point than in a conventional ICEV. Since the EM either can assist or brake the ICE towards a higher e�ciency and thus a lower fuel consumption [58, 64]. 3.4.2.1 Mild hybrid The most simple parallel hybrid is the so called mild hybrid con�guration. The mild hybrid is characterized by having an over sized starter motor that assists the ICE and allows the ICE to be turned o� during idling, coasting or braking. The auxiliaries, such as electrical power steering, air condition etc. can run on electrical power while the engine is o� and the EM turns the engine up to operating speed before injecting fuel. In a mild hybrid about 15 % or less of total powertrain power are supplied by the EM. In a full, also called strong, hybrid the EM and ICE are of equal power and thereby have the ability to recuperate more braking energy and therefore achieve a better fuel economy than the mild hybrid [68]. Figure 13 shows a schematic layout of a mild hybrid drivetrain. The kinetic energy recovery system (KERS) is a form of mild hybrid and has been a hot topic in Formula 1 racing in the season of 2009. There are two types of KERS, one electric, with battery or supercapacitor and EM, and one that is �ywheel based. In the electric system the power from braking is stored in a supercapacitor or a battery and is then released as extra power to the wheels when needed. In the �ywheel based system the braking power is stored in a �ywheel which is then coupled through a clutch to the wheels when the extra boost is needed. In the case of Formula 1 the KERS technology is not used to improve fuel economy but is instead used to give the cars better acceleration performance to help overtaking [69-70]. 13 Figure 13: Layout of a mild parallel hybrid 3.4.3 Split/combined hybrid The split hybrid powertrain is a Toyota solution and is due to the success of Toyota/Lexus's hybrids, the worlds most common type of hybrid powertrain [71]. The split, also known as combined hybrid powertrain is a combination of the series and the parallel hybrids. The powertrain design is close to that of a parallel hybrid, but it contains some features from the series hybrid as well, such as using the engine as range extender [64]. To be able to split the power between the EM and ICE a planetary gear is used, this can be seen in �gure 14 which shows the layout of a split hybrid drivetrain. Further information about the planetary gear can be found in section 3.6.5. Figure 14: Layout of a split hybrid drivetain Since the planetary gear seamlessly can split the power independently from one source to the 14 other, it is possible for the split hybrid to run in several di�erent operating modes such as engine only mode, zero emission mode and engine power assist. The disadvantage is that the powertrain contains a large amount of components which makes it more complex and expensive compared to a series or a parallel hybrid powertrain [58, 64]. 3.5 Fuel cell vehicles A vehicle with an electric drive can utilize a fuel cell to generate electricity on demand, instead of using a battery or a supercapacitor which is normally used in the PHEV and the HEV. In a fuel cell vehicle (FCV) the fuel cell will generate an electric current which is supplied to an EM that provides mechanical power to drive the vehicle, �gure 15a. The fuel cell can also be used instead of an ICE in a HEV or PHEV application, which then becomes a fuel cell hybrid electric vehicle (FCHEV). In this case the fuel cell can both charge the energy bu�er and supply power directly to the EM, as can be seen in �gure 15b. In everyday life, it is normally this type of con�guration that is referred to when talking about fuel cell vehicles. The third fuel cell powertrain con�guration a type that uses a reformer connected to the fuel cell. The reformer allows for on-board hydrogen production from, for example methanol, �gure 15c. Figure 15: FCV con�gurations a) left: FCV b) middle: FCHEV c) right: FCV with reformer [58] In the automotive industry the proton exchange membrane (PEM) fuel cell, also known as polymer electrolyte membrane, is the most common. The fuel cell characteristics are explained further in section 3.6, subsection 3.6.2. The fuel cell uses H2 that normally is produced through electrolysis, using a primary energy source. The H2 is then compressed, and in some cases also as much as into liquid, before it is stored, distributed and �nally used in the vehicles. The entire well-to-wheel energy conversion of H2 can be seen in �gure 16. Figure 16: Energy conversion from primary energy source to fuel cell vehicle [72] The main advantage with the FCV is that the only tailpipe emissions it creates is water (H2O) and the CO2 emissions are equal to zero from the vehicle itself if running on hydrogen. If the hydrogen is produced from either nuclear power or a renewable energy source, such as wind or hydro power, 15 the entire energy conversion chain from well-to-wheel, can be CO2 neutral. The problem is if the H2 is produced from for example coal power or any other fossil fuelled energy source. In this case the well-to-wheel emissions can be equally bad or even worse than for an ICEV. Another advantage of the FCV compared to an ICEV, is that the fuel cell has an energy conversion e�ciency of about 50 % which is much higher than any ICE. The main disadvantage of the FCV is the storage of hydrogen on-board the vehicle. The problem is that hydrogen has to be highly compressed to allow enough hydrogen to be stored to get a reasonable driving range. To be able to do that, a high pressure, 350-700 bar, gas storage tank is needed, which takes up a considerable amount of space and adds a fair bit of weight compared to the usual sheet metal or plastic fuel tank used in an ICEV. This also leads to a new safety aspect, since the high pressure tank can become a considerable risk in a collision. Other factors that in�uence the FCVs from penetrating the market are the high production costs of fuel cells, which make FCVs less economically competitive, and the issue with hydrogen infras- tructure. The higher costs of a FCV can in some extent be counteracted by government incentives, but the infrastructure requires a much larger investment. What needs to be done is to create a new infrastructure for both producing and distributing H2. This problem can in some extent be avoided if using a hydrogen reformer in the vehicles. However, this will mean an extra energy conversion in the powertrain, which results in a lower e�ciency, and also adds more weight and cost since extra components are needed [58, 65, 72]. 3.6 Main technology characteristics of the powertrain components There are several important components included in the powertrains presented in the sections above. In this section the theory behind each of them will be presented. 3.6.1 Internal combustion engine The internal combustion engine converts chemical energy stored in the fuel to mechanical energy through combustion. The combustion of the fuel occurs in the combustion chamber usually using air as an oxidizer [73]. The expansion of the high pressure and high temperature gasses produced by the combustion, force the moving parts of the engine (piston or turbine blades) to move and thus creating mechanical energy. The most common fuels that are used for conventional vehicles are petrol and diesel, but alternative fuels such as ethanol and bio-gas are becoming more common. The ICE has a very low thermal e�ciency, which together with the mechanical losses, gives an overall e�ciency of around 0.25-0.3 for a petrol engine and 0.4 for a diesel engine [58]. The ICE produces di�erent torque at di�erent angular velocities and at these di�erent speed/torque points the engine runs with varying e�ciency. The engine has a certain speed and load, represented by a torque, where it is operating close to its optimal e�ciency point. This can be illustrated by plotting the brake speci�c fuel consumption (bsfc) contours in a graph with brake mean e�ective pressure (bmep) as a function of engine speed in revolutions per minute (rpm). The bsfc is in this case a measure of fuel e�ciency while bmep is directly proportional to torque. Equation 3 below explains the equations behind bmep (�gure 17). bmep = Pbnr VdN (3) Where Pb is the brake power [kW], nr the number of crank revolutions for each power stroke per cylinder, which means that nr=2 in a four-stroke engine, Vd the displaced volume, [l] and N the engine speed in revolutions per second (rps). The bsfc can be used as a measure of how e�ciently the engine is converting the fuel to work. Equation 4 shows that bsfc is the fuel mass �ow per unit power output. bsfc = ṁf pb (4) where ṁf is the fuel mass �ow and Pb is the brake power output [73]. As can be seen in �gure 17 the maximum bmep, and thus the maximum torque, will occur at one engine speed and the most fuel e�cient point will in almost all cases occur at another speed and at part load. 16 Figure 17: Engine fuel consumption map [73] 3.6.2 Fuel cell The fuel cell is an energy conversion device that converts the chemical energy stored in a fuel such as hydrogen gas, H2, into electrical energy. But other fuels such as methanol, ethanol and petrol can be used as well. Even if there are several di�erent types of fuel cells, the basic principle of all of them is the same. They are supplied with hydrogen which is split into positively charged protons and negatively charged electrons through a catalyst next to the anode, see �gure 18. Since the electrons cannot pass through the negative anode they will have to take a longer way through an external circuit to re-unite with the protons and the added oxygen at the cathode on the other side of the membrane, where the protons and electrons react with oxygen to form water. If hydrogen is continuously added a stream of electrodes will �ow through the circuit and thus creating an electric current. The only exhausts from a fuel cell are water and a small amount of hydrogen that did not react at the anode [65, 72]. 17 Figure 18: Layout and machinery description of a fuel cell [65] 3.6.3 Rechargeable energy storage systems There are two main types of rechargeable, electrical energy storage systems, batteries and superca- pacitors, that both will be described in the following sections. 3.6.3.1 Battery A battery, in a vehicle with some kind of electric drive, is used to store energy used by the electric motor or motors. Batteries transform chemical energy to electrical energy during discharging and vice versa during charging [64]. The battery is usually the component responsible for 25-70 % of the increased weight, volume, and cost associated with various hybrid con�gurations compared to a standard ICEV [74]. A critical factor for batteries is their long term reliability where wear and abuse can decrease the length of the batteries life. A problem with batteries is that the practically usable energy is much less than the total energy stored, this to not shorten the battery life. To avoid shortening battery life the state of charge (SoC) of the battery should keep within a approximately 20 % span of the total capacity of the battery, see �gure 19. The SoC describes the amount of energy, or charge, remaining in the battery, expressed as percentage of its nominal capacity [64]. 18 Figure 19: Usable energy span for Li-ion and NiMH batteries Having batteries with a low weight is very important factor in keeping the overall weight of the car at a minimum and thereby using less energy during driving. The production HEVs available on the market today, utilize batteries with rated capacities of 0.6 to 2 kWh (see Appendix A), depending on which kind of hybrid con�guration used. Mild hybrids generally require smaller batteries than full hybrids. Figure 20 shows the speci�c energy (Wh/kg) and speci�c power (W/kg) for some of the most common battery types. Figure 20: Speci�c energy for common battery types [75] The early HEVs used lead acid (PbA) batteries since there was no other alternative [75]. Today the nickel-metal-hydride (NiMH) is the most commonly used battery, used in both Toyota and Honda hybrids. This is a more environmentally friendly and lighter battery with higher capacity than the PbA batteries. Lithium-ion (Li-Ion) batteries are just being introduced in production hybrids and is the most common battery type amongst PHEV concepts (see Appendix A). 19 3.6.3.2 Supercapacitor A supercapacitor is a kind of electric storage device that can be used instead, or together with, a battery in a vehicle with electric drive. The capacitor stores energy as electric charge and not as chemical energy as the battery does. This means that there are almost no losses when charging or discharging the supercapacitor [58]. The energy e�ciency of a battery is normally, depending on battery type, 50-95 % and the losses are dissipated as heat. The e�ciency losses of a typical supercapacitor are only in the range between 0.5 and 5 %, which means almost up to a hundred percent e�ciency. Another advantage with supercapacitors is their high charge and discharge times. The reason for this is that supercapacitors can allow a higher charge and discharge current than batteries. As can be seen in �gure 20 the supercapacitors has a higher speci�c power than the batteries, but due to problems with having a too high potential it is limited to having a low speci�c energy [76]. Figure 21a illustrates how e�ciently the energy bu�ers can deliver power in di�erent temperatures. The supercapacitor is only a�ected by very little by the shifts in temperature while the Li-ion battery hardly works at all until the temperature reaches 20 degrees. Another advantage with supercapacitors is illustrated in �gure 21b. As can be seen, it is possible to discharge the supercapacitor completely without decreasing the cycle life by very much, while the batteries on the contrary su�ers a huge decrease in cycle life if cycled more than 20 % of SoC. Figure 21: Comparison of di�erent energy bu�er types a) left: Power output for the energy bu�ers over di�erent temperatures b) right: Cycle life depending on cycle depth 3.6.4 Electric machines The electric machine (EM) is a key component in the hybrid-electric powertrain. The electrical machine converts electrical energy into mechanical work. The transformation is usually produced by the interaction of conductors carrying current perpendicular to a magnetic �eld. There are several di�erent types of electrical motors and they all di�er in the way the �eld and the conductors are arranged and also in the amount of mechanical output as torque, speed and power that can be achieved [77]. The torque provided at di�erent speeds by an EM is very di�erent compared to an ICE, see �gure 22. The EM provides a very high torque at low speeds which makes it very good for starting and accelerating a vehicle, but less e�ective at high speed. 20 Figure 22: Torque at di�erent speeds for an electric motor The reversed process, mechanical to electrical energy, can be also be achieved by an EM when used as a generator [78]. In hybrid vehicles the EM is in almost all cases reversible and can work both as an electric motor and a generator. It is possible for the EM to work in several di�erent ways: convert electrical energy from the battery to mechanical traction power to drive the vehicle, recharge the battery by either converting the mechanical power from the ICE or through regenerative braking. As can be seen in �gure 12 the parallel hybrid powertrain will only need one EM to provide all features such as battery charging and traction power. Whereas a series and split hybrid, �gure 11 and 14, need two separate EMs, one traction motor that can both supply traction power and recuperate braking energy and one generator that also can act as a starter motor for the ICE [64]. 3.6.5 Transmissions The transmission adjusts, transmits and distributes power between power sources, electric machines and wheels in the powertrain. A transmission is required since the di�erent components in the powertrain either need a higher or lower speed or torque compared to one another. The wheels will for example rotate slower than the ICE and are therefore in need of a step down in rotational speed. The meaning of the word transmission, in an automotive context, often refers to the gearbox. Even though simple gears, planetary gears, drive shaft, �nal gear and half shafts may be included. There are three main types of gearboxes; the manual transmission, the automatic transmission and the continuously variable transmission (CVT) [58]. The manual gearbox dominates the automotive market outside North America where the auto- matic transmission is the most common. The manual transmission has a �xed number of gears and is almost exclusively used together with a clutch. In comparison to the automatic transmission, that also has a �xed number of gears, but instead of an ordinary clutch uses a hydrodynamic torque con- verter or an automated clutch. It will also, as the name suggests, shift gears automatically without any signal or action from the driver. Both the manual and the automatic transmission gearbox have a �nite number of gears with �xed gear ratios. Another kind or gearbox is the continuously variable transmission which is becoming more common amongst both conventional vehicles and, perhaps, mainly hybrid vehicles. The CVT can be seen as having an in�nite number of gears which o�ers continuous gear ratios within a limited range. The CVT is mainly used because of its ability to get the engine to run more e�ciently, closer to its optimal e�ciency point. The CVT is able to vary the gear ratios continuously, which means that it works as an automatic transmission but with an in�nite number of gears. This makes the CVT very suitable 21 for hybrid powertrains, since the optimal gear ratio can be selected in order to keep energy e�ciency and performance as close to its maximum as possible [79]. Figure 23 shows the maximum power curve of an engine in a schematic graph with the traction force as a function of vehicle speed. With a CVT it is possible to always stay on the line repre- senting the maximum power curve. The �ve box-shaped areas illustrate the possible regions with a conventional �xed �ve step gearbox [64]. Figure 23: The traction force, Ft as a function of the vehicle speed, v To be able to split power between di�erent components in the split hybrid powertrain, a planetary gear can be used, as done in for example the Toyota Prius. The planetary gear can be de�ned as an assembly of meshed gears consisting of one sun gear, three or more planet gears held together by the planet carrier and one ring gear. In the Prius the ICE is connected to the carrier, the traction motor to the ring gear and the generator to the sun gear, a schematic drawing of the planetary gear can be seen in �gure 24 [58]. The full layout of the split hybrid can be seen in �gure 14, section 3.4.3 . Figure 24: Layout of a planetary gear in a Toyota Prius 22 4 Principles for selection and implementation of new technol- ogy Several things need to be taken into consideration when putting a new car model into production. Furthermore, if the new model has an entirely di�erent powertrain, like a hybrid system, there are several additional aspects that need to be taken into account. This section will include a discussion regarding these signi�cant factors involved in selecting and implementing a new system, and relevant factors will be assigned observing the process from a manufacturer's point of view. 4.1 Vehicle introduction strategy and system selection From a car manufacturer's view, there are more issues to be considered when introducing a HEV than solely the environmental aspect. The manufacturer needs to have a well planned roll-out strategy, and there is also a need for building up supplier partnerships and having a clear path throughout the entire development phase. Also, it is important to have a long-term goal, so that the �rst introduction becomes a stepping stone in the implementation of future forms of propulsion systems, such as PHEVs, EVs or FCVs. The �rst factors that need to be regarded are saleability and cost, and the introduction step involving these factors could be summarised as follows: � The competitiveness possessed by the new system, and the ICEV competition already present in the same market segment � The customer needs and knowledge regarding the new technology � Compatibility and di�erentiation, i.e. to what extent the base vehicle can be used and which changes are required if a base vehicle is available � Benchmarking of available technology � Supplier availability and pricing � The legislative driven needs To summarise, it is important to have a good knowledge about the market and the customers, but also to highlight the base vehicles if the new system is meant to be based on an existing model. Benchmarking of the available market and spotting trends are important initial steps before selecting a new technology. Although, even if there are plenty of new solutions on the market, these will only be available if a supplier can deliver the technology to the manufacturer at the right price. Further information regarding technology trends and benchmarking can be found in section 5.1.2. Taking a closer look at the legislative needs, the European commission have decided on emissions standards for all newly produced light-duty vehicles regardless of the powertrain technology being used. The currently used emission standard is the Euro 4, but already in September 2009 the Euro 5 will come into force. The di�erence between Euro 4 and Euro 5 is denoted in table 3 where an overview of the European standards for emissions from Euro 1-6 is given. 23 Table 3: The European emission standards The saleability of the vehicle also needs to be balanced with the vehicle attributes and features. This can be approached in di�erent ways, focusing on one hand on performance such as speed and power and on the other hand on fuel economy. When considering the selection of a new system technology and choosing market segment, the o�set between performance and fuel economy is very central. Regarding this aspect, there are three main approaches that can be applied: � Performance only approach � Performance/fuel economy approach � Fuel economy only approach In a premium customer approach the performance is the most essential part and the production cost can be considered less. The performance orientated systems usually have a minimal e�ect on the lowering of CO2 emissions since the new technology is used to add power to the vehicle rather than making it more environmentally friendly. The customer segment is rather small, since the strategy is usually applied only to luxury car models which already lie within the high priced segment. To get a broader customer appeal, the focus on the aspects of performance gain versus economy needs to be equal. The vehicle production cost has to be considered to a greater extent to approach a bigger market segment than that approached by the performance oriented vehicle. In the third approach listed, economy is the most important and the vehicle is to approach a big market with cheap a�ordable cars. Still, even if the segment has a big customer base there will also be more competition, meaning that the system needs to be rather cheap to be competitive. Subsequently, the cost of production is a very important factor. In conclusion, the �rst step in the development process is knowing the market situation and deciding which segment to aim for [80]. After choosing in which implementation segment one is to place the vehicle, it is rather easy to decide upon which propulsion technology to use, since choice of segment basically determines the budget for the new introduction. If a HEV propulsion system is chosen, this system needs to be complemented with the right degree of hybridisation (DoH). The degree of hybridisation basically de�nes the relationship between ICE and EM power in a HEV, see section 6, equation 6. To be able to know which DoH that will result in the desired performance and fuel economy some kind of validation, such as simulations, is needed. Using simulations is always a good way of validating the selection of system and to establish the improvements actually contributed to the vehicle by usage of the selected hybrid system. Rather simple simulations can give a good indication of performance and fuel economy of the new system and this data can easily be compared to the original model. Through the simulations one is able to see to what extent previous decisions in performance and fuel economy will be a�ected by various properties such as weight and DoH. The simulations performed to validate the test vehicles used as a basis for this report are presented in chapter 6 Simulations. 24 4.2 Summary hybrid system selection The system selection can be summarised in six main steps, all of equal importance. � Gather information about your market, customer and legislations � Investigate validity of the current vehicle base model � Choose implementation segment: Performance oriented, performance-economy oriented or econ- omy oriented � Select propulsion technology � Choose desired vehicle properties that match up with the implementation segment and tech- nology � Validate selections through usage of simulations 25 26 5 Future automotive propulsion technology This chapter contains a review of the prospects and prognosis' of old and upcoming technologies, technologies which was described in previous chapters. Most of the technologies can easily be im- plemented into the current vehicle �eet without any major e�orts from politicians or manufacturers. However some technologies, which have been presented in previous chapter and which will now be further highlighted, might stand or fall with designs and e�orts from the governments. The future of transports can be described in the three possible scenarios: an �electrical based� society, a �hydrogen based� society or a third society with a mix of technologies. In the third society, no radical government decisions are made and the manufacturers have to �nd their own approach to implement new technologies into the current infrastructure. Regardless of which future scenario that will occur, all of the mentioned technologies have a potential to make a change in the �ght against CO2 emissions from transports. Thereby all future prospects will be discussed as possibilities due to the potentials of technologies, even though they may rely on governmental support to a larger extent, and less on knowledge and availability. 5.1 Benchmarking and research In this section the results from the benchmarking and technology research will be presented. An overview of the information about the vehicles studied for the benchmarking can be found in Appendix Aand the references for the research can be found at the end of the report. 5.1.1 Methodology benchmarking and research To be able to investigate and get an indication of the hybrid technology and components suitable in future production, benchmarking is of great importance. The aim of this research is to identify trends in the development of technologies, to describe currently available powertrains, but also to try identifying which coming technologies that will be available for future vehicles. The benchmarking performed is based on a total of 54 vehicles, mainly consisting of HEVs, EVs and PHEVs, although ICEVs and FCVs are also included. [17-54, 81-84], see Appendix A. The literature study is based on information from several articles, papers and books. Databases mainly used in the study are the IEEE (institute of electrical and electronic engineers) and SAE (Society of automotive engineers). For the benchmarking, several internet sources have been used to gather information about the vehicles concerned in the study. Bibliography and other references used as basis for this thesis can be found in the reference list at the end of the report. 5.1.2 Technology trends overview This section will present the trends found when performing the benchmarking of a number of di�erent production, upcoming and concept vehicles. The benchmarking is made to identify trends in concepts and existing vehicle powertrains on the market, and thereby giving an indication of how the future in automotive engineering will turn out. Figure 25 shows how vehicle weight in�uences fuel consumption. This fact might seem obvious, however it is still important to highlight since weight savings can be done in almost every application of the vehicle. Thus, to keep the weight of the vehicle body down, it is important to keep the weight in mind during production of its separate components. In section 5.5 more information can be found on how to construct the vehicle, with the aim towards a lower weight. 27 Figure 25: Fuel consumption compared to vehicle weight Table 4 present a comparison between three fuel e�cient diesel sedans and three petrol-electric HEVs. They are all �ve seat passenger vehicles with similar size and weight. Table 4: Comparison between diesel and HEV passenger cars In previous chapters, a similar comparison between petrol-electric HEVs and petrol ICEVs have been presented in �gure 3, section 2. It can be concluded that the petrol-electric HEVs have a huge advantage in fuel consumption in comparison to petrol ICEVs, although, when it comes to e�cient diesel ICEVs and petrol-electric HEVs the scenario is very di�erent. In the case presented, all the ICEVs are using a supercharged, direct injected four cylinder diesel engines. Moreover, it can be seen in the comparison study that the ICEVs have an equally good or slightly better fuel economy than the HEVs. These results from the benchmarking indicates that diesel ICEs may become more common amongst ICEV �green car� models. Also, this is a possibility for HEVs and PHEVs, since a diesel ICE can be used in these powertrains as well. Furthermore, the benchmarking shows that the HEVs and EVs available on the market mostly use NiMH batteries whilst almost every concept are using Li-ion battery packs. This is a strong indication that NiMH batteries belong to the past and that future models of EVs, HEVs and PHEVs with all certainty will depend on the usage of Li-ion batteries. This development is due to the fact that most concept cars are EVs and PHEVs which depend on an all-electric driving mode and thereby demands more energy stored onboard. Li-ion batteries have a much higher speci�c energy than other battery types (see �gure 20) and are therefore a better choice for this application. 28 Table 5: Battery chemistry used in current and coming concept EVs, PHEVs and HEVs The analysis of the HEVs and the PHEVs in the benchmarking indicates that split and parallel systems are mostly used in HEVs, but in PHEVs, where the ICE works more as a range extender, the series powertrain is the most common. Regarding the trends concerning fuels, all HEVs on the market are petrol-electric, although one can identify an increasing amount of diesel-electric amongst the concepts. Amongst the new �green car� concepts analysed, the majority of vehicles are using battery based system while the alternate hydrogen based systems are used only in a few vehicles. Thus when analysing the �ndings from the benchmarking, it seems like the electric based vehicles are more attractive on the automotive market compared to the hydrogen cars. 5.2 Future fuels As highlighted in previous chapters, the amount of produced cars will increase in an exponential rate in the upcoming years, with a resulting energy need that has to be satis�ed and fuel needs that somehow will have to be provided. The uncertainty regarding the lasting of oil reserves of the earth as well as the increasing environmental awareness has established a demand for a fuel and energy source that is cleaner and more environmental friendly. As discussed in previous chapter, the European commission implemented emission standards and the Euro 4 standard is currently in force, but already in September 2009 the Euro 5 will come to pass as the new standard and in January 2014 even tougher standards will be implemented as Euro 6 enters as the new emissions standard. To preserve the air quality, new cars will have to stand more extensive testing before being approved for sale in the European Union. In table 3 in chapter 4, section 4.1 one can see the new light-duty vehicle emission standards of Euro 5 and 6 which new petrol and diesel cars have to live up to [85]. The future fuels needs to be cleaner and more e�cient to satisfy the demand of new vehicles and tougher legislation's. In sections below, some future alternative fuels will be presented which can create a higher variety of fuels and make the world less oil dependent. 5.2.1 Biodiesel fuel Biodiesel is a form of diesel produced from vegetable oil, animal fat or recycled restaurant grease waste. The biodiesel is cleaner and produces less air pollutions than the conventional petrol based diesel, since it is produced by renewable sources such as new and used vegetable oils. Biodiesel is currently used as a mix with petrol diesel, with 2, 5 and 20 % biodiesel in the blend (B2, B5 and B20). One problem with the biodiesel is that the e�ciency of the blends is not as good as for pure petrol-based diesel. Another drawback is that the biodiesel currently on the market is more expensive than conventional fuels, which becomes a problem when trying to get it accepted by the consumers. Also, another major issue is that even if most of the emissions (PM, CO, HC) decrease when more biodiesel goes into the blend, the NOx will increase. This problem can be diminished by usage of a catalyst which absorbs the NOx. For now, present engine manufacturers do not recommend usage of blends greater than B5, since a higher blend can damage the engine. This means that the use of biodiesel will be very much dependent on conventional fossil fuel based diesel. Conclusively, biodiesel is not a substitute for conventional fossil-based diesel at the moment and thus it will not solve the dependence of fossil-fuels. However, if engines are developed to manage a higher blend of biodiesel this can be a good complement to fossil-based diesel and thereby decrease the overall oil dependence [86-88]. 29 5.2.2 Ethanol and methanol fuels The two alcohols ethanol (ethyl alcohol) and methanol (methyl alcohol) can be used as alternative fuels in internal combustion engines. Ethanol is available as E85, which means 15 % fossil petrol and 85 % ethanol, which can be used to power �ex-fuel vehicles. The ethanol fuel can be made from starch and sugar based feedstock or from cellulose feedstock such as crops, grass and wood [89]. Brazil is a very good example of a society using alternative fuels, where all the petrol sold the last 15 years has contained about 22 % ethanol. The �eet has about 4 million fully dedicated ethanol vehicles and about 13.5 million vehicles which are using an ethanol-petrol blend [90]. The main reason for Brazil to be a less oil-dependent society was a consequence of the oil shocks that occurred almost 40 years ago. This event launched the usage of ethanol as a replacement for oil based petrol, and it is a good example not just when it comes to the use of ethanol fuels but also when it comes to proving that it is possible to actualise the decisions that are made regarding such a large societal change. When looking at the capacity of reducing CO2 emissions with the usage of ethanol it is necessary to examine the whole production chain for ethanol. This chain includes the following steps: growing the crops, transporting the crops to the production plant, producing the ethanol, distributing and transporting the ethanol and �nally burning it in the vehicle. In a place like Brazil where they use sugar canes to produce the ethanol they have obtained a very good performance for the ethanol vehicles due to several reasons. Because of the local sugar cane agriculture, the transportation distance is minimal and the usage of these canes for ethanol production gives a high reduction in CO2 emissions. Because of the local mass production in Brazil they have also been able to keep down the cost of the fuel and have made it competitive to the conventional fuel. In contrast, if a country do not have the possibility to produce the corps locally, the cost of producing ethanol fuel can be much higher and the gain in CO2 emissions reduction will not be as high as desirable due to the increased need of transportation. In �gure 26 is it possible to see the di�erence between some of the energy sources used to process ethanol fuel [91]. Figure 26: GHG emissions from transport fuels by type of energy source Methanol can also be used in a blend with petrol. It is produced by the fermentation of biomass 30 and has therefore got the name �wood alcohol�. Methanol as a substitute to conventional petrol has not received the same attention as ethanol, even though it has similar potential. However, the production of methanol is being discussed more when it comes to on-board reformers in fuel cell vehicles. On a methanol fuel cell the reformer will transform methanol into hydrogen which in turn will run the fuel cell. In this case it will be possible to refuel the vehicle with methanol while still having a hydrogen-based fuel cell vehicle. This will be further discussed in a coming section. 5.2.3 Natural gas Running vehicles on natural gas can also be used as a substitute to conventional fuels such as petrol and diesel. Today, there are about 8.7 million natural gas powered vehicles worldwide. Natural gas is a fossil fuel, though the Natural Gas Vehicles (NGVs) CO2 emissions are much lower than those from a petrol-powered vehicle. The natural gas contains less carbon and produce less CO2 per mile travelled, however when comparing NGVs to diesel-powered vehicles the CO2 emissions are only 3 % less and might even be lesser if looking at a well-to-wheel scenario. However, NGVs do perform very well in �ghting local pollutants and can thereby contribute to cleaner air in urban areas [90, 92]. Honda have produced a NGV in its Honda Civic GX which was awarded �Americas greenest car� 2008 by the American council for energy-e�cient economy. The Civic GX is a commercially available NGV sold mostly in Southern California, where an adequate natural gas infrastructure is already developed [93]. Otherwise it is �eets, usually operating a number of vehicles in city areas such as taxis and buses, which represents the highest potential for NGVs. A concern when it comes to natural gas is the methane emissions, where the loads of methane released through the exhaust have a much greater impact in terms of greenhouse gases. To sum up the potential for natural gas, it can �rst of all be seen as an insurance of future energy supply, making the world less dependent of the availability of oil. Also, it is a good substitute for oil based fuel in urban areas where air pollutions is a major problem, but it does not necessarily produce less greenhouse gas (GHG) emissions than an fuel e�cient diesel engine. Finally, the introduction of a natural gas infrastructure can be the gateway towards the introduction of a hydrogen based society, since they need a similar infrastructure. Also, natural gas can be used in FCVs that converts it to hydrogen through an onboard converter. The potential of hydrogen as fuel well be further discussed in the next section. 5.2.4 Hydrogen fuel Hydrogen, H2, is one of the two elements in water and it is not an energy source itself, but functions more as an energy carrier. This is due to the amount of energy that can be realized when extracting H2 from water. Currently H2 is mostly used as an industrial gas, but during the past years the discussion of using hydrogen as a fuel for road vehicles has increased. H2 is usually thought of as a fuel linked to the use of FCVs, but H2 can be used as fuel in ICEs as well. The idea of using hydrogen in ICEs is not a new invention, experiments with H2 have been made for more than a hundred years and have been used as fuel for rocket engines for decades. The idea of using hydrogen in road vehicles has lately been brought up to the surface again when trying to �nd alternatives to fossil fuel. The exhausts created in an ICE running on hydrogen are water vapour and NOx and can achieve an about 20 % increased energy e�ciency compared to an ICE running on petrol. The downside with running an ICE on hydrogen is that it typically cost more than a conventional ICE and it requires a turbo or supercharger to get the air needed to achieve full power. The fact that the NOx emissions tends to get rather high is also a challenge for the hydrogen ICE. Nevertheless, if developing the technology and overcoming these challenges, the hydrogen ICE have great potential to make a change in the future vehicle �eet [94]. H2 can also be used to run a vehicle through the powering of a fuel cell. In the same way as EVs, FCVs are able to run as a zero emission vehicles (ZEV), since the only emission created is water. The fuel cell technology have been highlighted as an alternative to the conventional ICEV and Honda for example have introduced a commercial fuel cell vehicle with its FCX clarity, see Appendix A. On the downside, the cost of fuel cell technology is rather high and the H2 fuel availability is quite limited [83,90, 95]. There are only a few currently used methods for producing hydrogen, although new methods are under development. Of the existing production methods the two main ones are steam methane 31 reforming (SMR) and electrolysis. SMR consists of two steps; reformation of natural gas and shift reaction. The �rst step involves methane reacting with steam at high temperatures (750-800°C) to make a synthesis gas which is a mixture of carbon monoxide, CO, and hydrogen. The second step is a water gas shift reaction, which includes a reaction of carbon monoxide (from the �rst step) and water steam over a catalyst forming hydrogen and carbon dioxide, CO2. If using natural gas in the production of hydrogen, an energy e�ciency of 78 % can be reached. Although, in performing this process in a non-CO2 adding fashion, the capturing of carbon dioxide results in an 20 % e�ciency decrease down to 58 %. To make the SMR into a sustainable process, biomass can be used to produce methane. Still, this is not a very likely scenario since six times more biomass is needed for one unit of hydrogen, meaning that the biomass would have to cover large areas and make the whole process very costly [90, 95]. In electrolysis, electricity is used to split water into hydrogen and oxygen. The reaction takes place in a so called electrolyser, which consists of an anode and a cathode separated by a membrane in the same way as in a fuel cell. This form of hydrogen production can result in zero GHG emissions depending on how the electricity is produced. If the electricity is produced by wind or nuclear power for example, the GHG emissions get close to zero. The problems with the electrolysis are the rather low overall e�ciency (about 30 %) and the high cost of the electrolyser. However, researchers are now working on improving the e�ciency and lowering the investment costs. They are also trying to imply the compressing of hydrogen into the process, since the hydrogen needs to be stored under high pressure in the vehicle [90, 94]. The production step is not the only obstacle for H2 to enter the market as a commercial fuel. An entirely new infrastructure would be needed for storing and distributing of the fuel. This is a major problem since the hydrogen based infrastructure would compete with the electrically based infrastructure and also the current one for petrol and diesel. One option is to combine production with the �lling stations to minimise the transports, but this still means building numerous new refuelling stations which thereby does not avoid the problem with infrastructure. Perhaps a better solution will be the on-board reforming, with the transformation of for example methanol into hydrogen. Even though solving some problems with this approach, the problem of reducing the GHG emissions still remains. Thus this is not a solution to the problem, although it can be a �rst step in the introduction of hydrogen and fuel cell vehicles. Conclusively, even if the technology exists for production of H2, this is a very new approach which is still in the development phase, and it will probably be several years until the H2 becomes an accepted and widespread alternative to fossil fuels. 5.2.5 Synthetic fuels Synthetic fuels are usually de�ned as liquid fuels obtained from the processing of for example coal or natural gas. Using these kind of materials for processing always result in fossil CO2 emissions, but there is a way of reducing the net CO2 emitted. For example by processing biomass that almost, depending on a number of factors, can achieve zero net CO2 emissions. The main advantage of these fuels is that it allows for a greater variety in fuel sources which will make the transports less oil dependent. One problem with ethanol, methanol and biodiesel when it comes to producing enough, is the competition over land areas that normally could be used for food production instead of producing biomass. However, all the building blocks for making methanol, ethanol and even petrol can be taken directly from the atmosphere as well. Recently other approaches have been made to obtain synthetic fuels. One of the research projects are �Sun to petrol� which is the name of a ongoing project run by the American research corporation Sandia [96]. The goal is to produce petrol with help from sun energy and synthesis. This project is still only in the research phase, but might act as an alternative in the future fuel mixture. 5.3 Future for powertrain technologies Even though cleaner fuels is one step towards less emissions and air pollution, future powertrain tech- nology may be an even more important step. The basics of the powertrain technology was presented 32 in chapter 3 section 3.1 to 3.5. This chapter will present the predicted future and introduction of a number of di�erent powertrain technologies 5.3.1 Future internal combustion engine vehicles Internal combustion engine vehicles utilize the most common and known technology presently on the market, the combustion engine. Although the technology has not, after more than a hundred years, reached the end of its development and there are still things that can be done to improve the e�ciency and emissions of the ICEVs. An example are the new DRIVe vehicles from Volvo, which still use ICE technology but presents impressive mileage and CO2 emission numbers. The new Volvo s40 DRIVe use a small diesel engine, and a comparison to the Toyota Prius can be found in table 4 [97]. The Volvo is a little less powerful but the cars have similar dimensions and are de�nitely in the same market segment. In section 5.1.2 Technology trends overview table 4 are more examples showing that small and light vehicles using e�cient diesel engines can be almost as fuel e�cient as HEVs in the same segment. A big advantage that speaks for the ICEVs is the cost. If looking at fuel e�cient sedans in the same segment as the HEVs, the price can di�er with up to $10 000 (see Appendix A) The future market of ICEVs will stand or fall with the development if the internal combustion engine, as will be further discussed in section 5.4. Nevertheless, the ICEV will as mentioned still play a large role in the next decades. Also, the development of e�cient ICE systems will be important for the introduction of alternative fuels, HEVs and PHEVs. Diesel engines combined with e�ective after-treatment will, according to the trends increase its market shares together with HEVs, since they both have proved to deliver very good fuel economy. Also, the vehicle structure has played a part in the promising fuel consumption numbers presented by the fuel e�cient diesel ICEVs. The importance of shape, weight and tires are discussed in more detail in chapter 5.5 Vehicle structure. 5.3.2 Future mechanical hybrid vehicles The mechanical hybrid systems are good alternatives to boost the fuel e�ciency of ICEVs. The mechanical hybrid vehicles (MHV) might be an e�ective solution to the problems with high costs of batteries, which have been one of the largest obstacles for the EVs and HEVs to make it in a wider scale. The di�erent mechanical systems can play di�erent roles in di�erent vehicle segments depending on their size and weight. Considering the �ywheel mechanical hybrid, this type of hybrid is not a new invention. A �ywheel assisted bus was developed and used as early as in the 1940s, and the early applications had a lot of advantages. The �ywheel hybrid added a bit of fuel e�ciency, but the disadvantage however was that a very big and heavy �ywheel was required to be able to recover a reasonable amount of kinetic energy during braking. This fact made it hard for the �ywheel hybrids to compete with pure ICEVs. Nevertheless, during recent years, the �ywheel hybrids have returned as an alternative which can support the ICE instead of an electric hybrid with a battery pack. The �ywheel system is more e�cient than the electric system since it has less energy conversions. The possibilities of this system are that it is very applicable under conditions when short periods of boost are required, and may thereby be very e�ective for city tra�c with many starts and stops. On the contrary, a highway situation requiring long distance cruises, a long and even boost is needed and the �ywheel support will not be satisfactory due to the limited amount of energy stored in it. In this case a battery electric system will be better suited. One suggestion is to use a �ywheel hybrid where both �ywheel and battery electric drive are combined. This would protect the battery from shock loads, since the �ywheel can provide energy at fast and sudden accelerations and the battery can take over the boosting when the vehicle demands an even and constant load. This hybrid system in an ICE vehicle might have the ability to increase the range with hundreds of miles [98]. The pneumatic hybrid is not a new technology either. The option to run a car with a compressed air motor has existed in many di�erent applications and forms during the last two centuries [99]. This system is quite similar to the �ywheel system in the sense of having an extremely low energy density, making it rather ine�cient during highway driving. In urban driving on the other hand, the system can make a huge improvement in fuel e�ciency. In a city with start and stop environment, the system will be able to build up a storage of compressed air, and then releasing it again when 33 needed. According to research made by Lino Guzella, a professor at ETH in Zürich, a pneumatic air hybrid can obtain a fuel economy that is 32 % better compared to a convectional ICEV and it can also o�er about 80% of the fuel saving currently o�ered by the HEVs.�. Despite the fact that the pneumatic system cannot reach the same fuel economy levels as the HEV, the cost is much less. The biggest potential for the pneumatic hybrid might then be as a more a�ordable alternative to the current HEVs. Providing almost as good fuel economy as the HEVs to a lesser cost it is possible for the pneumatic system to enter the �green car� market [99]. The �rst hydraulic hybrid ever was constructed by the US Environmental Protection Agency (EPA) and its partners in June 2006. The vehicle was a delivery-van with a full series hydraulic hybrid drivetrain. As described in previous examples this technology is also very well suited for urban driving. Therefore the implementation and choice of a delivery truck as testing vehicle for the hydraulic hybrid was very successful. According to the EPA, the vehicle have achieved a 60-70 % better fuel economy in laboratory tests, with a 40 % reduction in carbon-dioxide emissions and an ability to recover the additional cost for the new technology in less than 3 years. Furthermore, EPA states that design breakthroughs have been made to make the accumulator and pump/motor more e�cient, allowing the system to be used in light-duty vehicles as well. All the mechanical hybrids are quite simple solutions and can also be implemented easily to the current ICEV powertrains. Another advantage that the systems have compared to HEV is that the critical factor of battery cost can be ignored. On the other hand the electric hybrids have a greater potential when it comes to fuel savings, so if the mechanical hybrid is to have a fair chance in the green vehicle market, this chance is probably at the time being while they can still act as a more a�ordable alternative to the HEVs. The price of battery packs (lithium-ion) will with all certainty decrease as the technology becomes more of common use, thereby diminishing this impact of the cost di�erence in the future [74]. The mechanical systems are probably best suited for heavy vehicle applications, since the components in some of the powertrains tends to be rather heavy in order to deliver and store a reasonable amount of energy. 5.3.3 Future electrical vehicles Two of the greatest obstacles to overcome for the EVs are range limitations and recharging times for the batteries. Another issue for the EVs is the mentioned high cost of battery packs. This issue combined together with the insu�cient availability of recharging stations have prevented the EVs from penetrating the market on a larger scale. The question is whether it always will be a necessity for vehicle to provide a range greater than 250 miles. According to the UK department for transport (DfT), the average car mileage was 8,870 miles per year in 2007. This corresponds to the average mileage of 24.3 miles per day for a 4-wheeled car [55]. Hence, the average UK driver travels 225.7 miles shorter than the possible range of presently available EVs. Analysing the second problem with recharging times being too long, it can be compared to how much time people actually spend in their cars on average each year. According to the latest statistics from DfT the average time spent travelling by car per year was 232 hours during 2006 [55]. Thus, the cars are only driven for about 40 minutes each day and stay parked for the rest of the time. Since the cars are parked most of the time during a day there will be plenty of time for charging the car whilst it is parked, and the time of recharging should therefore not be such a big problem. Nonetheless, there will be travels exceeding 250 miles where the driver spends several hours in the vehicle. However for the everyday driver, who goes back and forth to work, the EV and will be a very good substitute for the ICEV with the bene�t o