Effect of a split-injections strategy on the atomisation rate for charge stratification using a high pressure gasoline multi-hole injector 2019-01-2248
Some of the challenges of optimising the gasoline direct-injection engines are achieving high rates of atomisation and evaporation of fuel sprays for effective fuel-air mixture formation. This is especially important for the stratified charge when operating under cold-start and part-load conditions. Poorly mixed charge results in the increased production of total Hydrocarbons and Nitrogen Oxides.
Many studies have previously focused on improving the spray characteristics of a single fuel injection strategy from direct-injection gasoline injectors, with fuel rail pressures of up to 20MPa. The current study focuses on a split injections strategy and its influence on the spray's structure, fuel-air mixing and atomisation rates. Short pulse widths in the range of 0.3ms to 0.8ms are employed. In particular, the effects of dwell times between the two injections on the second injection's spray characteristics are evaluated.
The experiments are carried out inside a constant volume spray chamber with a latest high pressure multi-hole piezo injector. The fuel rail pressures range between 5MPa and 35MPa. The effect of increasing fuel rail pressures on the evaporation and mixing rates of the split injections strategy are investigated. High speed flow visualisation techniques are employed to measure and analyse the sprays' characteristics, velocity profiles of the flow field, and the droplets' sizes.
The results show that large injection ratios with large dwell times had pronounced effects on the penetration lengths and spray angles. So large pulse widths for the first injection, early in the intake stroke, would aid in achieving a pre-mixed homogenous charge, specifically at high rail pressures. Short pulse widths would be ideal for second injection as the charge would be locally rich and the injection quantity low.
Citation: Dhanji, M. and Zhao, H., "Effect of a split-injections strategy on the atomisation rate for charge stratification using a high pressure gasoline multi-hole injector," SAE Technical Paper 2019-01-2248, 2019. Download Citation
Meghnaa Dhanji, Hua Zhao
Brunel University London
2019 JSAE/SAE Powertrains, Fuels and Lubricants