Numerical simulation of diesel spray characteristics based on air-assisted atomization injection

To numerically analyse the process of air-assisted atomization for diesel spray，the computational fluid dynamics simulation tool Fluent was applied.Three-dimensional fluid calculation model considering diesel injection process in fuel/air premixing chamber was established without changing the injector structure.The air-assisted injection process of diesel/air two-phase flow was investigated in constant volume chamber.The effects of air injection pressure，ambient backpressure and fuel temperature on diesel spray characteristics were investigated.The results showed that the air injection pressure had a great influence on the spray penetration distance.As the air injection pressure increased from 0.65 MPa to 0.75 MPa，the penetration distance increased by 12.2%，while the Sauter mean diameter （SMD） of diesel only decreased by 5.2%.When maintaining the SMD of fuel spray at an optimal level，the pressure ratio of 7.5 was beneficial to reduce the air consumption.Ambient backpressure had significant influence on penetration distance and SMD of fuel spray，as the pressure ratio was 1.875，the flow field at injector outlet almost did not produce supersonic flow，and the decrease of aerodynamic force significantly affected the breaking process of fuel droplets，making the SMD increase to 40.7 μm at the injection time of 4 ms.Fuel temperature had little effect on spray penetration distance，while it had a great effect on SMD.The SMD of fuel decreased significantly with the increase of temperature，and the SMD corresponding to 323 K decreased by 12.3% compared with that of 293 K.At the injection time of 4 ms，the overall SMD of fuel was 14.9 μm and the evaporated mass fraction of fuel reached 36.93%.