Experimental Investigation of ultra-high fuel injection pressure spray for GDI engines

Licentiate thesis, 2020

Gasoline Direct Injection Engines (GDI) for passenger cars currently use fuel injection systems operating at pressures of up to 350 bar. Injection pressures have increased over time, and there is evidence that particulate emissions could be reduced by raising them further, up to 500 bar. However, it is not clear whether further beneficial effects would be achieved by using higher injection pressures exceeding 600 bar. This thesis presents experimental studies on sprays and combustion conducted to assess the benefits and downsides of substantially increased fuel injection system pressures (between 200 and 1500 bar) in GDI engines. Experiments on spray characteristics and spray-air interaction revealed that raising the injection pressure from 200 to 600 bar significantly improved spray atomization. This pressure effect on atomization became less significant when the injection pressure was over 800 bar. High pressure sprays also evolved much faster than low pressure ones, but the spray tip penetration at the end of injection did not vary greatly with the injection pressure. High pressure sprays induced more air flow because of their high velocity and good atomization, which increased the likelihood and strength of spray-air interactions. These results indicate that high injection pressures result in better mixture formation because they accelerate evaporation and induce stronger air flow. However, spray impingement caused by high spray velocities and penetration may cause problems during engine operation.