Effect of Pilot Injection on Engine Noise in a Single Cylinder Compression Ignition Engine

An experimental study was performed to investigate the effect of pilot injection on engine noise using a single cylinder combustion ignition engine. The engine rotary speed was fixed at 1200 RPM and a 10-mg quantity was injected at a pilot injection ratio of 1:9, 2:8, or 3:7. The engine performance parameters were calculated from the combustion pressure data acquired by a piezoelectric transducer (6057A80, Kistler), which was placed in the location of the glow plug. Engine noise was measured at a distance and height of 1 meter each from the engine for 9-10 seconds and analyzed using a commercial sound analysis program. By analyzing in-cylinder pressure and sound quality metrics, the following conclusions were obtained. The frequency analysis showed that the combustion noise was distributed at the frequency bands from 1100 Hz to 1900 Hz and from 2100 Hz to 2900 Hz. Pilot injections lowered the maximum rate of pressure increase, and the trend of the maximum pressure rise rate varied significantly according to injection pressure. The maximum pressure rise rate exhibited a linear relationship with sound level and loudness. Thus, the pilot injection strategy appeared to improve engine noise characteristics.