Effects of Multiple Injections in a HSDI Diesel Engine Equipped with Common Rail Injection System 2004-01-0127

Diesel fuel injection system is the most important part of the direct-injection diesel engine and, in recent years, it has become one of the critical technologies for emission control with the help of electronically controlled fuel injection. Common rail injection system has great flexibility in injection timing, pressure and multi-injections. Many studies and applications have reported the advantages of using common rail system to meet the strict emission regulation and to improve engine performance for diesel engines.

The main objective of this study is to investigate the effect of pilot-, post- 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 power output by controlling the premixed combustion. The post-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.