Study of Cyclic Variability in Diesel Dual Fuel Engine with Different Fuel Volatility

Compressed natural gas (CNG) is one of the alternative fuels that has a great potential in the near future. The cyclic variation of a diesel engine combustion fueled with CNG and ignited by pilot fuel with different fuel volatility was investigated and presented in this study. To investigate the combustion characteristics of diesel dual fuel engine, a single cylinder diesel engine has been modified to use CNG as fuel. CNG was fed into the intake manifold by a mixer before entering the combustion chamber. The engine was operated at a constant speed of 1400 rpm and variable loads. An engine indicating system was used to sample and record the engine cylinder pressure for 100 consecutive cycles. The combustion data were then analyzed for the maximum cylinder pressure for each cycle and its derivative parameter (rate of heat release). The cyclic variation is indicated by the mean value, standard deviation, and coefficient of variation of the maximum pressure. In higher engine load operation, the cyclic variability is found to be reduced. In addition, volatile pilot fuel resulted in more stable combustion especially at low load.