Investigation of the fuel distribution in a two-stroke engine with an air-assisted injector

Results of experiments performed on a direct-injection two-stroke engine using an air-assisted injector are presented. Pressure measurements in both the engine cylinder and injector body coupled with backlit photographs of the spray provide a qualitative understanding of the spray dynamics from the oscillating poppet system. The temporal evolution of the spatial distribution of both liquid and vapor fuel were measured within the cylinder using the Exciplex technique with a new dopant which is suitable for tracing gasoline. However, a temperature dependence of the vapor phase fluorescence was found that limits the direct quantitative interpretation of the images. Investigation of a number of realizations of the vapor field at a time typical of ignition for a stratified-charge engine shows a high degree of cycle to cycle variability with some cycles exhibiting a high level of charge stratification. Laser diffraction droplet sizing was performed in the motoring engine and shows that the air-assist injector produces a very finely atomized spray under conditions of early injection when the ratio of injector pressure to cylinder pressure is high. However, when the air rail pressure was decreased larger drop sizes were observed.