A study on thermal decomposition of fuels and NO_x formation in diesel combustion using a total gas sampling technique

The effects of aromatic components and distillation temperature of diesel fuel on the decomposition of hydrocarbons and NOx formation during diesel combustion were studied at different injection pressures using a rapid compression machine and a total gas sampling device. It was found that fuel injected into hot compressed air is quickly gasified and then thermally cracked, and a large amount of unsaturated light hydrocarbons, mainly C2H4, C2H2 and C3H6, are produced during the ignition delay period. It was also found that the level of the initial rate of heat release is approximately proportional to the amount of light unsaturated hydrocarbons observed. As the injection pressure is increased, both the amount of light hydrocarbons formed and the initial rate of heat release increase, which results in an NOx concentration higher than that at a lower injection pressure. As for the effects of fuel properties, it was revealed that aromatic components in the fuel enhance NOx formation over the combustion period through their higher adiabatic flame temperatures and that a high-distillation temperature of fuel yields a lower rate of heat release and lower NOx formation due to the slower rate of evaporation.