Systematic Investigation of Fuel Film Evaporation 2018-01-0310

To meet future particulate emission limits is quite ambitious for gasoline engines working with direct injection. It was found that there is a relationship between the fuel deposited on the combustion chamber surfaces due to spray impingement and the soot emissions. To understand and avoid the fuel film formation, measurements of the fuel film thickness and mass are important. However, in practical applications fuel films in general are not always problematic as long as they evaporate in time before ignition. Therefore, a systematic investigation of the evaporation duration of fuel film resulting from spray/wall interaction using high-speed visualization was performed. The investigation focused on the influence of engine related operating parameters on the film evaporation duration under the typical homogeneously charged gasoline engines conditions. To distinguish the effects of different operating parameters on the evaporation duration, the measurements were performed inside a conditioned pressure vessel. By varying the vessel pressure, vessel temperature and rail pressure a wide range of injection conditions were studied. The spray was generated by a standard high-pressure, six-hole nozzle. The measurements were carried out using three liquid fuels (gasoline, iso-octane and a 3-component surrogate fuel), to investigate the effect of the fuel on film evaporation. The resulting evaporation durations of iso-octane were discussed using the results of laser-induced fluorescence measurements of the corresponding film masses. It was found that under several conditions, the evaporation duration does not correlate with the values of the deposited film mass. Hence, smaller amounts of fuel deposited as film do not necessarily lead to shorter evaporation times. Additionally, it is shown that the 3-component fuel used in the measurements can be recommended as gasoline surrogate in measurements and simulations, as the evaporation duration agrees well with that of gasoline.