Investigation Concerning the Effect of Post Fuel Injection on The Performance and Pollutants of Heavy Duty Diesel Engines Using a Multi-Zone Combustion Model

As widely recognized the direct injection heavy-duty diesel engine is the most efficient powertrain system for trucks, lorries and other heavy-duty vehicles. This results from its relatively low specific fuel consumption compared to other existing thermal engines. Taking this under consideration it remains a serious problem, its relatively high, compared to future legislation, NOx and particulate emissions. Manufacturers have proposed various solutions towards this problem. Two are the main categories proposed, improvement of the combustion process to control directly the formation of pollutants inside the combustion chamber and the use of aftertreatment technologies to reduce pollutants at the engine exhaust. In the present work we will concentrate our efforts on the first category by examining the technique of post fuel injection. For this reason a multi-zone phenomenological model is used to examine the effect of post fuel injection on pollutants emissions and bsfc. The study is conducted using a single cylinder heavy-duty test diesel engine capable of withstanding relatively high peak combustion pressures. The simulation model has been used to examine the effect of post fuel injection at various operating conditions corresponding to key operation points of the engine under question. During the investigation, various injection timings are considered setting the peak combustion pressure limit to 200–220 bar. In all cases, the effect of the interval between the main and the post fuel injection is examined. From the analysis of results, important information is derived concerning the effect of post fuel injection parameters on engine performance and emissions. The results are given in the form of NO-bsfc and Soot-NO curves to obtain a clear picture of the effect of post injection. Furthermore results are provided concerning the pollutant formation mechanism i.e. Soot and NO formation history inside the combustion chamber. As revealed post injection seems to have no serious effect on NO emissions since it occurs at the late stages of combustion, but on the other hand it seems to have a serious effect on Soot emission. The effect on Soot emission depends on the interval between the main and the post fuel injection. Post injection has a small penalty on bsfc but this is compensated by the serious reduction of Soot. Comparing the results with published data concerning the effect of post injection on engine performance and emissions, they appear to be at least qualitevely correct. However it remains to verify them using experimental data. Another important outcome of the present investigation is that phenomenological modeling is a promising tool to study such cases since it is very fast and can contribute to the reduction of development cost. These models cannot be directly compared to multi-dimensional sophisticated ones since the last concentrate on the detailed modeling of the various processes occurring inside the cylinder, but in the time being it is an efficient way to conduct overall engine performance and pollutant emission studies where a great number of parameters are involved. From the experience up to now, it seems that phenomenological models can produce results that can reveal trends despite the possible differences when comparing predicted absolute values with the corresponding measured ones. For this reason we believe that the use of such models is a promising tool for engineers who want qualitative results before conducting a more detailed investigation using CFD models.