Pilot injection and two other forms of auxiliary fuel introduction have been studied for their effects on diesel engine combustion and emissions. A two-stroke diesel has been equipped with an electronic solenoid-controlled unit injector such that the injector can operate with pilot injection. In addition, the engine has been fitted with experimental air-blast atomizing injectors in the inlet port and intake manifold. In-cylinder pressure, Bosch smoke, exhaust hydrocarbons, NO and NOx emissions measurements have been made for a range of engine conditions. In addition, two fuels have been tested to observe the effects of fuel blend on the auxiliary fuel behavior.
In general, the effect of auxiliary fuel introduction is to reduce ignition delay and rate-of-pressure rise. This tends to result in a decrease in NO emissions. Unburned hydrocarbons and smoke tend to increase, although not in every case. With 20 cetane, Army Type 1 Referee fuel, extreme rates of pressure rise limit the load at which the engine can be operated with normal injection. With pilot it is possible to operate at high loads.
Heat-release analysis shows that the pilot or preliminary fuel introduction can influence the main combustion event in a variety of ways. In some cases, there is evidence of heat release from the pilot. In other cases, the pilot seems to reduce the overall temperature in the chamber before the main injection event, due to evaporation of the spray, while still reducing the ignition delay of the main charge.