Experimental Analysis Of The Energy Flow In Automotive Engine Under Transient Conditions

Energy crisis and environmental pollution are among the most serious issues that threaten the living conditions and health of all humanity.As one of the most widely used thermal machines in the field of power energineering,internal comboustion engines(ICE)not only consume a large number of fossil fuels but also produce large quantities of exhaust gases.Since fossil fuels are the most common reserve until now,“Higher efficiency Energy conservation and Low emissions” is extremely necessary.Analysing energy flow in vehicles is therefore an important issue,which can obtain many benefits such as reducing fuel consumption,decreasing emission,and whittling down running cost.It is a useful tool that provides detailed information about the distribution of supplied fuel energy in the subsystems of ICE and identifies the avoidable losses precisely.Based on AVL test bench,the steady-state energy test under mapping characteristics was carried out on a turbocharged gasoline direct injection(TGDI)engine under different coolant temperatures.The influence of coolant temperatures on economic performance and in-cylinder combustion was analyzed.An Energy balance system of the effective work,the coolant losses,the exhaust losses and unaccounted losses is established.By using a diagnostic and analysis method for various operational and performance parameters of ICE under transient operating conditions,the transient energy flow test was conducted on chassis dynamometer under New European Driving Cycle(NEDC)of cold and warmed-up starting.Coupling the operational and performance parameters under transient condition,the distribution characteristics and influencing factors of energy flow under NEDC were revealed intuitively.The deviations of ICE transient performance from their steady-state values were demonstrated and their impacts were also revealed.The main research contents and results are as follows:(1)A thermodynamic model of energy flow was established,and the influence of coolant temperaturse on the performance parameters and the changing trend of the energy balance terms with the operating parameters were studied.The results on engine bench show that with higher coolant temperature,specific fuel consumption decreased;the ratio of useful work and exhaust losses increased with the rise of load;apart from full load,the energy flow of the coolant losses and unaccounted losses went to the exhaust losses and the effective work with the increasing load.(2)A mathematical method of the energy flow under transient condition was proposed.Combining the operating parameters of vehicle and engine,the distribution characteristics of the effective work,the exhaust losses,the coolant losses and the pumping losses under NEDC were revealed.The results on chassis dynamometer showed that the distributions of various kinds of energy flow terms were obviously impacted by vehicle operating conditions;in the early stage of the NEDC,the fuel mass flow of cold start was much higher than hot start;the exhaust losses are mainly determined by the exhaust temperature.(3)By comparing the calibration parameters,combustion characteristic parameters and the emission performance parameters of the engine under the cold and warmed up conditions with the steady state values,the difference between steady and transient performance and the optimization potential were revealed: later combustion phase and lower effective expansion ratio(EER)caused by too later spark timing and much leaner fuel-air mixture,resulted in poor performance of engine under cold start conditions;low coolant temperature was the secondary factor;improving the transient calibration level and optimizing the combustion phase in the cylinder were the key that would ensure the cold start performance.This paper reveals the influence of coolant temperature on engine performance,the distribution characteristics of energy flow,the difference between calibration and performance parameters under steady and transient conditions;all of which paly an important role in improving specific fuel consumption and reducing emission.