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Combination of High Injection Pressure and EGR to Control Nitric Oxide and Soot in DI Diesel Engines
Published September 07, 2004 by CMT in Spain
Event: Thiesel 2004
The diesel engine seems to be the most efficient powertrain for propulsion of truck engines and vehicles. Its superiority against the main competitor the spark ignition engine is widely recognized despite the improvements achieved in the last, i.e., direct injection gasoline engines. But considering current and future emissions legislation diesel engine pollutant emissions mainly NO and Soot have to be reduced considerably. Towards this direction, two main solutions are available, control of pollutants emissions using internal measures or aftertreatment technology. The last introduces various difficulties such as increased bsfc, complexity, and increase of cost and volume of the entire system. For this reason research is conducted to control pollutants emissions using internal measures. This offers the possibility to introduce aftertreatment technologies that are less demanding. A promising technology is the use of increased injection pressure. Experimental and computational investigations reveal that the use of increased injection pressure can result to extremely low soot emissions that satisfy EURO V or even more strict emission legislation. Unfortunately, the use of increased injection pressure results to a considerable increase of NO emissions. For this reason a computational study is conducted on a heavy-duty truck engine to estimate up to what point it is possible to control both NO and Soot, using increased injection pressure and EGR. Two EGR strategies are examined, one using a constant boost pressure resulting in a reduction of the overall AFR and a second using increased boost pressure to maintain the AFR the same as in the zero EGR case. The last is considered to minimize the negative effect of EGR on soot emissions. The simulation model used is a multi-zone one which is initially validated using experimental data revealing the effect of increased injection pressure on performance and emissions. Then it examined the use of various EGR rates using constant BP and AFR for various injection pressures. From the computational investigation it is estimated the combined effect of increased injection pressure and EGR on engine performance and emissions. The effect on engine performance is focused mainly on bsfc and peak combustion pressure. As revealed there is a possibility to control considerably both pollutants (NO and Soot) using increased injection pressure and EGR. Furthermore, it is revealed that the use of phenomenological modelling can be beneficial for engine development, resulting to the acceleration of the development process and the reduction of its cost.