Passenger car Diesel engines not only have to fulfill stringent emissions legislation, it is also necessary to significantly reduce fuel consumption. Additionally the targets for drivability and noise have to be reached. From these often conflicting interests, ambitious requirements were derived for the future fuel injection system and these led to the development of the new direct drive piezo injector (PCR-NG) of the Continental Automotive GmbH. Essential parameters, which have to be considered for the development of the combustion system are the EGR rate, the boost and injection pressures. High EGR rates serve to suppress NO(x), high boost pressures to provide the necessary oxygen concentration. The resulting high charge density demands the adaptation of the injection pressure for a globally suitable fuel distribution in the combustion chamber. For this the injection pressure needs to be raised, but only to the optimum level for good engine thermal efficiency. The current study investigated the optimum combination of EGR rate, boost and injection pressure to achieve the best compromise in NO(x) and PM reduction, focussing on lowest fuel consumption. One particularly important issue was the reduction of combustion noise. The measures showed the following results: minimum fuel consumption was found at a rail pressure of app. 900 bar, irrespective of changes in other parameters; for high in-cylinder gas mass the gas temperature reduces. This effects a reduction in NO(x) and indicated specific fuel consumption. The reduction in indicated specific fuel consumption is due to the reduced heat rejection from the working cycle. The air path parameters have a profound effect on fuel consumption of a full engine, which cannot be investigated on a single cylinder engine with external boosting. However, the general method of optimisation was equally applicable on a full engine, as derived from the single cylinder engine. The reduction of PM, NO(x) and fuel consumption usually incurs a significant penalty in combustion noise this can be improved by the suitable modification of the injection strategy, e.g. the application of 'dwell zero'. The reduction of NO(x) and CN are prerequisites for an advance of HR50 for improvements in fuel consumption
Efficient combination of EGR, boost and injection pressure for the reduction of CO2 and lowest emissions
Emission Control, 5 ; 69-88
2010
20 Seiten, 14 Bilder, 8 Quellen
Aufsatz (Konferenz)
Englisch
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