Combustion behaviour of a heavy duty common rail marine Diesel engine fumigated with propane

This paper presents results from the testing of a heavy duty common rail marine Diesel engine with electronically controlled two stage liquid fuel injection, operating under load on a test bench with propane mixed into the inlet air at various rates. Results are presented for a range of engine loads, with brake mean effective pressure up to 22. bar at 1800. rpm. The electronic engine control unit is not modified and allowed to respond to the addition of propane according to its inbuilt map. This results in retarded injection timing with increased propane addition at some test points. At each test point, constant engine speed and brake torque are maintained for various rates of propane addition. Cylinder pressure and the injector activation voltage are recorded with a high speed data acquisition system. Apparent heat release rate is calculated from the measured cylinder pressure. At high rates of propane addition very high pressure rise rates and severe knock are measured. At the high brake mean effective pressure conditions tested, knock limits propane supply rates to less than 20% by energy. Small increases in thermal efficiency are indicated with moderate rates of propane addition. Exhaust emissions of NO_x, CO, HC and smoke are measured. CO, HC and smoke emissions increase significantly with increasing propane addition. For high propane supply rates, two distinct peaks in heat release rate are measured. Analysis is made of the flammability of the propane-air mixtures at the elevated temperatures at the end of the compression stroke, using the modified Burgess-Wheeler Law. At propane supply rates greater than 25%, the propane-air mixture is flammable in its own right at compression temperature. The apparent heat release rate, fuel injection timing and flammability data allow analysis of the mechanism of the combustion process with propane fumigation.