Integration of Thermal and Performance Models - Complete Engine Model

Abstract

The demand for reducing energy expenditure and increasing efficiency have been two of the main driving forces behind the research and development in many major industries today. It is the case even with the automotive industry. The need for higher efficiency propulsion systems is further intensified by the fact that the automotive industry is one of the largest contributor to air pollution. Increasing efficiency allows not only to save energy but also to decrease the emissions per unit of work derived. This push for efficiency has seen development of various solutions such as electric and hybrid powertrains, downsizing of combustion engines while increasing the specific power output etcetera. While focusing on energy efficiency in any system, it is critical to keep accurate track of the flow of energy in it. Energy in a combustion engine is input into the system as chemical potential energy. This is transformed into heat energy and then mechanical energy. Parts of both heat and mechanical energies are lost in various ways in the system - thermodynamic inefficiency, friction etcetera. Mono dimensional models to predict the flow of heat in an engine, predict the performance of an engine, predict the friction load on the engine, simulate the oil flow in an engine and simulate the cooling system of the engine have all been developed. But they work independently with main boundary conditions being input by the user using experimental data. In this thesis, all the models mentioned above are integrated to obtain one single model with two way coupling between the models allowing dynamic boundary conditions to be input. This allows more accurate tracking of energy in the system, especially in transient cases like engine start up. The model is configured for three operational modes - steady state full load, steady state part load and transient part load. The steady state models are run and the results are used to verify energy conservation and to see the deviation from the stand alone models. The transient model is setup for various warm up strategies and study their effect on friction, temperature profiles and fuel consumption. The strategies considered in this thesis are the coupling, decoupling and timed decoupled of the engine oil cooler and variation of the oil quantity. The model was also used to conduct a parametric study of the dependency of friction on oil and coolant temperatures.