SOC Detection of Diesel Engines Based on Online Estimation of Motored Pressure

In this paper, a diesel SOC (Start of Combustion) online detection method is developed in a diesel engine equipped with serial produced in-cylinder pressure signal sensors. Motored pressure trace is estimated in real time and the difference between the measured actual cylinder pressure and the estimated motored pressure is calculated. SOC is defined as the separation point of the two different pressure traces. In order to realize accurate motored pressure estimation, a thermodynamic analysis of the motored process of engines is done and a new concept “equivalent adiabatic exponent” is proposed. The pressure difference 0.2 MPa is taken as the criteria of combustion start. The SOC detection algorithm is executed in a MCU based electronic control unit. Engine tests are done in steady states as well as dynamic states.