A quantitative study on deposited fuel film and microscopic droplet characteristics of gasoline surrogate fuel and ethanol spray impingement

Abstract

By applying down-sizing and high-pressure injection on gasoline direct injection (GDI) and dual-fuel spark ignition (DFSI) engines, the deposited fuel film caused by spray impingement would significantly increase engine soot emissions. In this study, laser-induced fluorescence (LIF) was used to initially explore the difference in deposited fuel film of gasoline surrogate fuel (GSF) and ethanol spray impingement. And, phase doppler anemometry (PDA) was used to further reveal the difference in deposited film formation mechanisms by analysing microscopic droplet characteristics quantitatively. The study could contribute novel insights to the fuel injection strategy optimisation, spray modelling research, pollution reduction and thermal efficiency improvement for GDI and DFSI engines. The results showed that 60% to 70% mass of the ethanol spray would deposit on the wall when vertical impingement, while that of GSF only is 40% to 60%. Moreover, due to ethanol's high viscosity, ethanol film is at least 39% thicker than GSF under the same injection condition. Thicker average film thickness easily results in pool fire and high soot emissions. Inclined impingement angle and high injection pressure could help reduce the deposited film mass of both fuels. Particularly, the film mass of GSF would decrease by 36% by increasing injection from 7 MPa to 15 MPa. Regarding microscopic droplet characteristics, a considerable difference can be seen for the incident droplets in different radial positions. Compared to ethanol, GSF spray droplet velocity is at least 13% higher, which would further enhance the reflection and secondary breakup.