Simulation model for steady state and transient cold starting operation of diesel engines

Starting of diesel engines at low ambient temperatures presents problems, such as long cranking period, hesitation and white smoke emissions. A better understanding of the engine processes during cold starting is essential to solve these problems. In this study computer simulation models are developed for steady state and transient cold starting of a single cylinder and a turbocharged multi-cylinder diesel engine. The models are experimentally verified and used to examine the operating characteristics of diesel engines. An optimization method is employed to calibrate engine models. For transient operation, emphasis is placed on factors which affect cold starting. A fuel drop and film evaporation models were developed to analyze the effect of accumulated fuel on cold start. The engine model is applied in engine data analysis, which includes smoothing engine pressure and instantaneous engine speed data, heat release rate analysis and the effect of heat release rate on engine thermal efficiency. The effect of cranking speed on ignition delay is examined. There exists a cranking speed at which ignition delay in terms of crank angle degrees reaches minimum. By using the model for the engine, fuel drop and film evaporation, it is found that accumulated fuel in combustion chamber has a major impact on engine cold starting through increasing engine compression pressure and temperature and increasing fuel vapor concentration in the combustion chamber during the ignition delay period. An Autoignition Index (AI) is introduced to determine the diesel engine first firing cycle. In addition, the diesel engine combustion instability is analyzed in details. The simulation model indicated that misfiring after firing is caused by an imbalance between engine dynamics and combustion kinetics. The instantaneous engine speed variation and combustion instability during cold starting were predicted by using the engine models. The trend predicted by the model was observed in experimental data.