Using a Phenomenological Multi-Zone Model to Investigate the Effect of Injection Rate Shaping on Performance and Pollutants of a DI Heavy Duty Diesel Engine

The direct injection heavy-duty diesel engine is the main propulsion unit for trucks, lories and other heavy-duty vehicles mainly due to its superior efficiency when compared to other existing reciprocating engines. However, this engine suffers from relatively high particulate and nitric oxide emission levels. Considering current legislation for emissions and especially future limits, it seems that a great deal of research is required to satisfy these limits and maintain efficiency at a high level. As widely recognized, the fuel injection mechanism plays an important role for both engine performance and pollutant emissions. The major problem is to seek solutions that enable the control of major pollutants, nitric oxide and particulate matter. For this reason, various injection rate shapes have been proposed which require sophisticated fuel injection equipment and extremely high fuel injection pressures. Now two main categories are considered, common rail fuel injection system and PLN. Both categories have advantages and disadvantages and a great deal of research is needed before an optimum solution can be reached. Since a great number of parameters are involved, experimental investigation is extremely difficult and time consuming. For this reason, the possibility of using a phenomenological multi-zone model to examine the effect of injection rate shaping on engine performance and major emissions is examined in the present work. The task is attractive because it is extremely difficult to do a similar investigation using sophisticated 3-D CFD codes due to extremely high computational time. On the other hand, it is questionable if phenomenological models can predict the effect of injection rate shaping on the combustion mechanism. In the present investigation, four different rate shapes are examined all having the same injection duration. Of course, this will have an effect on the required peak injection pressure but this is not the purpose of this investigation. Various operating conditions are examined using a heavy duty DI diesel engine and clear conclusions are derived based on existing data, which seem to be on the correct path. A simple validation is provided using existing data for two rate shapes and the model seems to predict rather well the cylinder pressure history. From these preliminary results, it seems that such models (phenomenological) can be used to obtain at least qualitative results that may assist us during engine development and testing as far as injection rate shaping is concerned.