The Effect of the LPG Injector Distance from an Inlet Valve on the Combustion Process in a SI Engine

This paper seeks to examine the effect of distance of the gas injector from an inlet valve on the combustion process in a LPG fuelled SI engine under varied injection timing. Tests were conducted at an engine test stand, where the operating conditions of the engine were maintained stable. The tests were undertaken on an indirect injection spark ignition engine under partial load and at a constant speed. Holes in the inlet pipes were drilled in order to test for four variants of injection nozzle distance from the combustion chamber into which 4 mm diameter nozzles were successively mounted. Each given distance was measured along the symmetry axis of the inlet port, which represents a real path of the fuel-air mixture.

The results show that the engine performance is affected more by the injector distance from the inlet valve than by varied LPG injection timing. Consequently, cycle-to-cycle variations of main combustion parameters and engine performance parameters were analyzed. The results show that the distance between the injection nozzle and the combustion chamber affects the unrepeatability of engine operation. To evaluate the cycle-to-cycle variations of the combustion parameters, the coefficient of variation (COV) and return maps of the IMEP were calculated for each engine operating condition. The increase of CO and HC emission were recorded in some cases because of the nozzle distance impact on combustion. The maximum distance between the nozzle and the inlet valve caused a significant increase of hydrocarbon in exhaust gases.