Very low soot formation with modulated liquid length and lift-off length of diesel spray flame

Abstract

The vehicle diesel engine has entered the ultra-high injection pressure era. In order to study the spray and combustion characteristics under ultra-high pressure, the liquid length and combustion characteristics of multi-hole injectors (10 holes) with different hole diameters and different injection pressures were studied via experimental methods. The results show that increasing the injection pressure can effectively increase the slope of liquid length, while the hole diameter has little effect on it. However, during the stable stage, increasing hole diameter increase the liquid length, while the injection pressure has little effect on it. Different from the liquid length, the lift-off length during the stable stage is mainly affected by the injection pressure. F. Dos Santos’ model and the parameters of Siebers can more accurately predict the liquid length and lift-off length, even if the injection pressure has been increased to 300 MPa. Increasing injection pressure and reducing hole diameter can reduce the interference between liquid length and lift-off length. When the liquid length is less than the lift-off length, it can effectively inhibit soot formation. The value of LL/LOL has a fine linear relationship with stoichiometric air percentage. An equation of the relationship between the injection pressure and the hole diameter was established by the predicted model. Using this equation, we can get the range of LL/LOL less than 1 under different hole diameters or different injection pressures. The determination of this equation provides guidance and suggestions for the selection of hole diameters and injection pressure for diesel engines.