A ?GA optimization code was applied experimentally to a HSDI single-cylinder diesel engine equipped with a common rail fuel injection system in order to reduce NOx, soot, and BSFC simultaneously. Four important control factors were used in this research to optimize engine emissions and fuel consumption, namely, start-of-injection (SOI) timing, intake boost pressure level, cooled exhaust gas recirculation (EGR) rate, and fuel injection pressure. The engine testing was done at two different operating conditions, which are 1757 rev/min and 45% load and 1550 rev/min, 25% load.
In order to investigate the characteristics of the optimum obtained during the optimization process, more fundamental research was done on the nature of the low-temperature combustion regime. Visualization tests using a transparent engine at the Sandia National Laboratory were performed. Based on these, combustion characteristics were examined by comparing with traditional heat release analysis. Finally, the factors that influence turbulent mixing rates, such as injection pressure, swirl ratio and post injection strategies were thoroughly explored through parametric study. Two different versions of the engine were used in the research, which are the optical engine for the visualization tests and combustion analysis, and an all-metal engine for emissions measurements. The representative operating condition considered for low-temperature combustion was 1500 rev/min, 3bar IMEP with 800 bar injection pressure and 50% EGR rate.