Variations in heat release rates and NO_x formation of indirect injection (IDI) diesel engine fueled with fatty acid methyl esters (FAME)

摘要

Due to concerns over fossil fuel shortages as well as the greenhouse effect of engine exhaust, biodiesel use in the transportation sector is being promoted. Biodiesel and fossil diesel have distinct physical and chemical properties. These deviations in fuel properties can result in different combustion characteristics and engine exhaust emissions. It has been reported that the emissions of CO, HC, and PM are reduced with biodiesel blends, but NO_x emissions are increased and the increment is roughly proportional to the amount of biodiesel mixed in the fuel blend. Comparing the heat release rates of D100, B5, and B20 we found that the heat release rate increases as more biodiesel is mixed in the fuel blend. Ignition delay was shortened. The maximum pressure increase rate and the maximum heat release rate also increased for B20. A two-zone combustion model was developed to estimate the burned gas temperature. The extended Zeldovich mechanism was then used to calculate the NO formation in the burned zone. It was found that the calculated NO concentration for B20 is 15% higher than that of D100. The calculated NO formation corresponds to the uncertainty in heat loss. It is evident that the uncertainty in the heat transfer model would have a significant effect on the NO calculation. The trend of variation in NO formation is consistent for both the measured data and the calculated results no matter what heat transfer model was used.