Common rail injection system has a great flexibility in injection timing, pressure and multiple-injection. The main objective of this study is to investigate the effect of pilot, after and multiple fuel injection strategies on engine performance and emissions. The study was carried out on a single cylinder optical direct injection diesel engine equipped with a high pressure common rail fuel injection system. Spray and combustion evolutions were visualized through a high speed charge-coupled device (CCD) camera.
Tests were performed at fixed engine speed with various injection and flow parameters. Engine performance, emissions and cylinder pressure were obtained and analyzed to investigate the effect of fuel injection and engine operations. It was found that pilot-injection reduced the ignition delay of main injection, then contributed to the improvement of indicated mean effective pressure (IMEP) by controlling the premixed combustion. The after-injection was found to be very effective in completing the oxidation process and reducing the particulate emissions even when small fuel quantities were injected. It was also found that multiple injection could reduce particulate emissions by more than 40% in some cases. It was believed that a reduction of particulates using after- or multiple-injections resulted from improved particulate oxidation in the later combustion cycle due to increased in-cylinder bulk temperature and enhanced fuel-air mixing during an additional combustion event.
