Simulation of Diesel Engines Cold-Start

Diesel engine cold-start problems include long cranking periods, hesitation and white smoke emissions. A better understanding of these problems is essential to improve diesel engine cold-start. In this study computer simulation model is developed for the steady state and transient cold starting processes in a single-cylinder naturally aspirated direct injection diesel engine. The model is verified experimentally and utilized to determine the key parameters that affect the cranking period and combustion instability after the engine starts. The behavior of the fuel spray before and after it impinges on the combustion chamber walls was analyzed in each cycle during the cold-start operation. The analysis indicated that the 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. Also, diesel engine combustion instability is analyzed in details. The model indicated that misfiring after firing is caused by an imbalance between engine dynamic and combustion kinetics. The model predictions of the instantaneous engine speed variation during cold-start showed the same tend as the experimental results.