5. Modelling and Experimental Studies of NO_x and Soot Emissions in Common Rail Direct Injection Diesel Engines

Diesel engines have sustained with stringent emission limits and increased power demands due to the advancement in the fuel-injection systems. The injection process plays a major role in diesel engine combustion. In this regard, the common rail injection system has the potential of providing flexibilities in injection pressure and timing over a wide range of engine operating conditions. Common rail system is one of the modern variants of electronically controlled injection systems and offers flexibility in injection scheduling with sharp start and cut-off in injection process. It is reported that while the pilot injection is capable of reducing the initial rate of heat release and hence the NO_x emission, the post injection enhances the rate of air fuel mixing in the later stages of combustion which promotes soot oxidation. Hence, multiple-injection offers simultaneous reduction of NO_x and soot emission. However, the reduction in NO_x and soot emission depends on the judicious selection of the multiple injection schedules which comprise injection timing, fuel quantities in each pulse and the intervening dwell between the pulses for a given engine at a particular operating condition. This necessitates a great deal of parametric investigations to analyze the performance and emission characteristics. In this regard, modelling of diesel engines serves as a beneficial tool for the first order design estimates by avoiding exhaustive experimental works. Hence, this article addresses both the modelling and experimental investigations on CRDI engines. Further, this study highlights the effect of biofuel and their blends on NO_x and soot emission of a common rail direct injection diesel engine. The potential of alcohols as oxygenated additives for realizing the emission reduction is also covered in this chapter.