Assessment of gasoline direct injector coking effects on fuel injection, engine performance and emissions
2016
Badawy, Tawfik | Attar, Mohammadreza Anbari | Xu, Hongming | Ghafourian, Akbar
Experimental optical and thermal tests were carried out to obtain a comprehensive understanding of gasoline direct injector coking effects on fuel injection, engine performance and emissions. A robust injector fouling cycle was employed to produce coked injectors in a multi-cylinder thermal engine. Deposit build-up in the coked injectors and fouling cycle repeatability was first examined by measurements of fuel flow rate. Macroscopic spray characteristics of the clean and the coked injectors were carried out using high-speed imaging and Planar Laser Induced Fluorescence (PLIF) of sprays’ foot print. Fuel droplets’ size and velocity were characterised with a two-dimensional Phase Doppler Particle Analyser (PDPA). It was observed that the deposit build-up inside injectors’ nozzles and on the injectors’ tip reduced ‘plume cone angle’ while increased ‘plumes’ penetration length’, ‘plumes’ angles’, mean droplets’ velocity and size for the coked injector. Impact of injector coking was further investigated by PLIF measurements of in-cylinder charge stratification and repeatability in mixture preparation. The coked injectors showed higher degree of stratification and poorer repeatability in mixture preparation. These were in agreement with combustion analysis results where the coked injectors showed lower load and lower combustion stability compared with the clean injector under same operating conditions. Significantly higher unburned hydrocarbon emissions and particulate number concentration were also observed for the coked injectors. This work was carried out to obtain a broad picture of injector cooking effects in GDI engines.
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