Effect of Injection Pressure on the Performance and Exhaust Emissions of a Heavy Duty DI Diesel Engine 2003-01-0340

During the recent years, extensive research is conducted worldwide for the purpose of tailpipe emission reduction from diesel engines. These efforts resulted in the achievement of very low emission levels for today's diesels. But considering the future legislation it is required a further drastic reduction. Towards this direction, a multi-zone combustion model is used in the present study to investigate the effect of fuel injection pressure level on the performance and pollutant emissions from a Heavy Duty DI diesel engine. For this purpose it is made use of injection pressure histories obtained from a detailed simulation model at various engine operating conditions. The increase of injection pressure is accomplished by increasing the injector opening pressure from 400 up to 1600 bar. Using this technique peak injection pressures up to 1900 bar are obtained without significant modifications of the existing FIE, depending on engine load and operating speed while injection duration is considerably reduced. Three different operating points are considered corresponding to the low and high operating speed of the engine at 50% and 100% load. A series of injection timings are examined at each operating condition to produce the relevant bsfc-NO and Soot-NO tradeoff curves. Furthermore it is also examined the effect of injection pressure on the peak combustion pressure and the heat release rate mechanism. From the analysis it is revealed that the increase of injection pressure results to fast combustion, a serious reduction of soot especially at part load and low engine speeds but at the same time to a considerable increase of NO emissions. The last can be possibly controlled using after-treatment technologies or EGR and thus benefits of soot reduction can be partially maintained. The increase of injection pressure results to a penalty in bsfc at low injection timings but as injection timing is advanced a slight improvement is observed. But a more thorough investigation is required to consider for the power required to drive the fuel pump at elevated injection pressure levels. Using the simulation code it is determined the required increase of peak injection pressure at various operating conditions to obtain the previously mentioned benefits as far as soot emission and bsfc is concerned. As revealed from the analysis a higher increase of injection pressure, on a percentage basis, is required at low engine load and engine speed. On the other hand it is observed a penalty in peak combustion pressure that increases considerably at low engine speed and high load.