To overcome the trade-off between NOx and particulate emissions for future diesel vehicles and engines it is necessary to seek methods to lower pollutant emissions. The desired simultaneous improvement in fuel efficiency for future DI (Direct Injection) diesels is also a difficult challenge due to the combustion modifications that will be required to meet the exhaust emission mandates.
This study demonstrates the emission reduction capability of split injections, EGR (Exhaust Gas Recirculation), and other parameters on a High Speed Direct Injection (HSDI) diesel engine equipped with a common rail injection system using an RSM (Response Surface Method) optimization method. The optimizations were conducted at 1757 rev/min, 45% load. Six factors were considered for the optimization, namely the EGR rate, SOI (Start of Injection), intake boost pressure, and injection pressure, the percentage of fuel in the first injection, and the dwell between injections. In addition, the effects of swirl were investigated.
The benefit of the combined effects of EGR with supercharging was well realized by the RSM optimization, which resulted in simultaneous reductions in both NOx and PM emissions, while even improving BSFC (Brake Specific Fuel Consumption). Through the present optimization process, it was shown that RSM optimization is an effective and powerful tool for realizing the full advantages of the combined effects of combustion control techniques. In addition, observation of the optimization process provides a more thorough understanding of HSDI diesel combustion since the observed trends can be explained by monitoring the effects of the operating parameters.