In order to investigate the performance and emissions behavior of a high compression ratio compression ignition (CI) engine operating in partially premixed charge compression ignition (PPCI) mode, a series of experiments were conducted using a single-cylinder engine with a high-pressure rail fuel injection system. This included a moderately advanced direct injection strategy to attempt PPCI combustion under low load conditions by varying the injection timing between 25 deg and 35 deg before top dead center (BTDC) in steps of 2.5 deg. Furthermore, during experimentation the fuel injection pressure, engine speed, and engine torque were kept constant. Performance parameters and emissions were measured and analyzed using a zero-dimensional heat release model. Compared to the baseline conventional 12.5 deg BTDC injection, in-cylinder pressure and temperature were higher at advanced timings for all load conditions considered. Additionally, NOx, PM, CO, and total hydrocarbon (THC) were higher than conventional results at the 0.5 N·m load condition. While PM emissions were lower, and CO and THC emissions were comparable to conventional injection results at the 1.5 N·m load condition between 25 deg and 30 deg BTDC, NOx emissions were relatively high. Hence, there was limited success in beating the NOx-PM trade-off. Moreover, since the start of combustion (SOC) occurred BTDC, the resulting higher peak combustion pressures restricted the operating condition to lower loads. As a result, further investigation including exhaust gas recirculation (EGR) and/or variance in fuel cetane number (CN) is required to achieve PPCI in a high compression ratio CI engine.
Effect of piston bowl geometry and compression ratio on in-cylinder combustion and engine performance in a gasoline direct-injection compression ignition engine under different injection conditions