Combustion Stability Control of Dieseline PPCI Based on In-Cylinder Pressure Signals

This paper investigates on cycle-to-cycle variation of dieseline fueled PPCI engine and introduces a closed-loop control method based on in-cylinder pressure sensor. Experiments are performed on a four-cylinder compression ignition engine. Results show that pmax (maximum in-cylinder pressure) and θpmax (crank angle where pmax occurs) cannot be properly identified by the control system. Thus, COV (coefficient of variation) of pmax and θpmax cannot reflect the real combustion fluctuation level. IMEP (indicated mean effective pressure) contains information about the whole combustion process for it is calculated by all the sampled pressure of the current cycle. Therefore, COVimep can be chosen as the combustion stability indicator to evaluate cycle-to cycle variation. Besides, sweep experiments of injection timing (IT) and exhaust gas recirculation (EGR) are conducted to investigate the influence of these control parameters on COVimep and MPRR (maximum pressure rise rate). COVimep is the indicator of combustion stability while MPRR is related to the noise level. Based on detailed analysis of experimental results, a model-based combustion stability closed-loop control algorithm is proposed in order to ensure good combustion stability on the premise that the noise of engine can also be limited (which means COVimep and MPRR can be restrained below their threshold) by an acceptable level. The simulation results show that COVimep and MPRR can be restrained simultaneously under different loads.