Research and Development Trends in Combustion and Aftertreatment Systems for Next-Generation HSDI Diesel Engines

Recently, the performance and exhaust emissions of high-speed direct injection (HSDI) diesel engines for passenger cars have been rapidly improved. In these engines, the power and torque densities have reached 50-60 kW/l and 160-170 Nm/l, respectively. In addition, the noise, vibration and harshness (NVH) and exhaust emissions have been decreasing toward a level that is comparable to that of gasoline engines. Furthermore, the maximum brake thermal efficiency has reached 42-43% and both city and highway fuel economy is excellent. Therefore, the percentage of diesel passenger cars in Europe has been increasing remarkably and is forecasted to reach 48% in 2007. The developments of common-rail (CR) injection systems, high-efficiency aftertreatment devices such as the diesel particulate filter (DPF) and catalysts, and advanced electronic control systems are listed as major technical backgrounds of the progress in HSDI diesel engines. In the present review, recent trends in research and development of the above-listed component technologies, primarily regarding combustion and aftertreatment systems, are outlined. Finally, critical technical areas that must be addressed in order to realize an ultra-clean and highperformance diesel engine are presented.