Experimental Investigations on High Pressure Gasoline Injection up to 800 bar for Different Combustion Modes

Authors

Andreas Stadler, MSc., Reinhardt Brunner, MSc., Dr.-Ing. Martin Härtl,
Prof. Dr.-Ing. Georg Wachtmeister, Institute of Internal Combustion Engines, Technical University of Munich, Munich;
Dr.-Ing. Henning Sauerland, Hitachi Europe GmbH, Munich

Summary

In order to meet future Particle Number (PN) emission regulations in direct-injection light duty gasoline engines, accurate mixture formation plays a key role across all combustion modes. In recent studies, increasing the injection pressure proofed to decrease PN emissions in homogenous operation. For stratified combustion, however, the higher momentum of the spray leads to strong piston wetting when injecting late in the compression stroke. The favorable effect of improved atomization with higher injection pressure can’t compensate for the stronger wetting leading to increased PN emissions. In this study, a conventional diesel injector was equipped with a designed nozzle and operated with gasoline. Both the targeting of the spray plumes and the length to diameter (l/d) ratio of the orifices were tailored to ensure a compact mixture cloud and a good mixture preparation. Investigations at a single cylinder research engine were carried out for different combustion modes. A conventional gasoline injector served as the baseline for assessing the injection pressure effect. For homogenous combustion increasing the injection pressure up to 800 bar leads to significantly reduced PN emissions, more stable combustion and reduced indicated fuel consumption without impairing other regulated gaseous emissions. In case of spray-guided stratified combustion, the improved spray atomization of the highpressure injection system shows two favorable effects:
1) PN emissions are significantly reduced by avoiding piston wetting due to shorter spray penetration,
2) a more compact mixture cloud can be placed near the spark plug leading to more stable combustion at thermodynamically optimal MFB50 timings.

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