Effect of shock waves on the evolution of high-pressure fuel jets

Highlights: • A new criterion of shock wave generation for high-pressure fuel jets is proposed according to the experiments. • Penetration characteristics of shock wave and non-shock wave fuel jets are acquired and major difference is found. • A modified numerical model, which has wide application range from subsonic state to supersonic state, is introduced. - Abstract: In the modern diesel engine, with increasingly higher injection pressures, shock waves will appear with high velocity fuel jets. To better understand the effect of shock waves on the atomization of fuel sprays, diesel fuel injected at a pressure of 60 to 120 MPa was studied using a schlieren imaging visualisation system. The initiation and boundary conditions of the shock wave initiated by fuel jets were examined. A clear difference of spray penetration between the shock-wave state and the non-shock-wave state was recorded in a nitrogen (N₂) and sulphur hexafluoride (SF₆) gas atmosphere. By eliminating the other potential explanations, such as pressure drop differences and the enhancement of gas density, it is shown that the shock wave itself had a predominant effect on the evolution of high-pressure fuel jets. Additionally, a computational model considering the Mach number was developed to predict the spray penetration. The model was found to have excellent agreement with the presented experimental results.