A study on engine efficiency and performance improvements through hybrid turbocharging assisting

Abstract

Engine efficiency and transient performance carry a major importance in the automotive industry as they incorporate the two major requirements: fuel consumption and drivability. A major inconvenience for turbochargers constitutes the low response in the low speed region of the engine creating the so called “turbo lag” affecting drivability. Also a large portion of the fuel energy is lost through exhaust gas in a SI engine affecting engine efficiency, fuel consumption implicitly. A hybrid turbocharging assist system is a promising technology for improving both transient response and engine efficiency. This paper studies the possibility of implementing a hybrid turbocharging assisting system on a VEP 2.0 L SI engine. Two modules are studied: electrically assistance for the turbocharger which regards the transient performance and exhaust gas energy recovery which regards the engine efficiency. An electric machine is connected to turbocharger’s shaft through a planetary gear, enabling two operating modes: motor in electrical assistance and generator in energy recovery mode. Transient simulations are performed for the electrical assistance module having three configurations: a standard and a bigger compressor (HP Compressor) and a bigger turbine (HP Turbine). Steady state simulations are performed for the exhaust gas energy recovery module at full load and part load conditions having two turbine configurations: standard turbine and bigger turbine (HP turbine). As a last step of the thesis, a take-off simulation where both modules work together is done for the Volvo XC90. All the modelling and simulations are carried within the framework of GT-Suite. Results from the electrically assistance module show that transient performance is improved by 30% at 1400 rpm, 20 % at 1600 rpm and 16% at 1800 rpm by using the standard compressor configuration. When using the exhaust gas energy recovery system the engine efficiency is significantly improved by using a bigger turbine configuration.