Effect of ambient fuel vapour concentration on the liquid length and air-fuel mixing of an evaporating spray

Mixing of the injected fuel with the in-cylinder gas controls the evaporation process in direct injection engines and hence influences spray parameter like the liquid length. Injected fuel density, surrounding gas density, characteristics of the nozzle and spray parameters like cone angle etc. influence this mixing procedure. Presence of fuel vapour in the surrounding gas can also change the air-fuel mixing ratio and liquid length. The previous works by the present author showed that the presence of fuel vapour in the surrounding gas changed the properties of the entrained gas and hence influenced the heating and evaporation of the injected fuel. In the present paper, the effect of fuel vapour in the entrained gas on liquid length are studied experimentally. The results showed that the higher fuel concentration in the ambient gas increases the liquid length. However, at a lower concentration, this effect is missing. A model is also presented to study the effect of the presence of fuel vapour in the surrounding gas on air-fuel mixing. The model is able to predict the axial and radial variation of the fuel-ambient gas ratio in a spray considering that the entrained gas is a mixture of fuel vapour and dry gas. The results showed that, air-fuel mixture fraction along the spray axis and radial direction are greatly influenced by the presence of fuel vapour in the entrained gas.