Multi-Zone Combustion Modeling as a Tool for DI Diesel Engine Development – Application for the Effect of Injection Pressure

During the recent years, extensive research conducted worldwide in the field of Heavy Duty Diesel engines has resulted to a significant improvement of engine performance and emissions. These efforts have been assisted from simulation models providing good results. Towards this direction a multi-zone model developed by the authors has been used in the past to examine the effect of injection pressure on DI diesel engine performance and emissions. The attempt was challenging since no experimental data existed when the calculations were conducted, to support the findings. Eventually, experimental data concerning engine performance and emissions became available using slightly different operating conditions and injection pressure data. In the present study an attempt is made to evaluate the prediction ability of the multi zone model by comparing the theoretical results with experimental data and explain any discrepancies between them. The simulation code used is essentially the same while a calibration has been made only for the soot model, to obtain at one operating point (low injection pressure) similar absolute values. It is promising that the simulation manages to predict for all examined cases the effect of injection pressure on engine performance and emissions. It is confirmed that the increase of injection pressure results to fast combustion and a serious reduction of soot especially at part load and high engine speeds but at the same time to a considerable increase of NO emissions. Predictions from the present study using actual injection rate data and operating conditions are qualitatively similar to the ones of the initial investigation while absolute values are closer to the experimental ones. But since the most important role of modeling is not to capture accurately absolute values but trends, its validity as a prediction tool is revealed.