Diesel engine cold start combustion instability and control strategy

Diesel engine combustion instability during cold starting period is characterized by unstable engine speed and large amount of white smoke emissions caused by misfiring cycles sandwiched with firing cycles. Previous investigations have proved that combustion instability increases as ambient temperature gets lower. White smoke is undesirable in military diesel engines particularly in the field. In this investigation, the mechanism of combustion instability has been studied with both theoretical analysis and engine experiment. The experiment was conducted at different ambient temperature, with a 4-cylinder heavy-duty direct injection diesel engine, in a temperature controlled cold room.; A new method of data analysis has been used to reveal the mechanism of misfiring. Based on detailed cycle-by-cycle analysis of the experimental results to check on the successfulness of autoignition of every cycle during cold transient period, the sequential cycles were then compared in the injection timing - engine speed plane with its firing or misfiring information. This new viewing angle revealed the existence of two zones on this timing - speed plane: the firing and misfiring zones divided by a boundary line. The area of misfiring zone increases and firing zone decreases at lower ambient temperatures.; A new autoignition model based on global reaction rate has been developed to predict the misfiring during cold start transient. The new autoignition model takes consideration the effect of piston motion in real engine on the autoignition process which has not been accounted for in previous investigations.; New diesel engine cold start control strategy has been developed. The new strategy is to maintain the engine stay in the firing zone during cold start transient period. Cycle-by-cycle level control in both injection timing and fueling during cold start transient are required.