Investigations on Low Pressure Gasoline Direct Injection for a Standard GDI Combustion System

In the course of the last few years a continuous increase of the injection pressure level of gasoline direct injection systems appeared. Today's systems use an injection pressure up to 200bar and the trend shows a further increase for the future. Although several benefits go along with the increased injection pressure, the disadvantages such as higher system costs and higher energy demand lead to the question of the lowest acceptable injection pressure level for low cost GDI combustion systems. Lowering injection pressure and costs could enable the technological upgrading from MPFI to GDI in smaller engine segments, which would lead to a reduction of CO2 emission.

This publication covers the investigation of a low pressure GDI system (LPDI) with focus on small and low cost GDI engines. The influence of the injection pressure on the fuel consumption and emission behavior was investigated using a 1.4l series production engine. Baseline tests on the vehicle dynamometer and the engine test bed were followed by experimental and simulation investigations of the system behavior using lowered injection pressure. These investigations were concluded by experimental tests with adapted and optimized engine operating parameters, e.g. valve timing or injection and ignition timing. The general focus was the determination of the lowest acceptable injection pressure and the assessment of benefits and disadvantages of the reduced injection pressure in terms of the main issues, i.e. fuel economy, emission and engine operation stability.