Development of a simplified bubble growth model for flash boiling sprays in direct injection spark ignition engines

Accurate modeling of bubble growth is needed to design fuel injectors that take full advantage of the potential of flash boiling sprays to reduce drop sizes and to promote fuel vaporization in direct injection spark ignition (DISI) engines. A new simplified bubble growth model has been developed to substantially reduce the computational cost of capturing the bubble size and growth rate distributions at the fuel injector exit. These distributions have important effects on the formation and breakup of droplets. The simplified bubble growth model makes a parcel approach for simulating the bubble growth in a flash boiling fuel injector affordable. A parcel approach makes it possible to capture the distributions of large numbers of bubbles forming under different conditions within the fuel injector. The simplified bubble growth model was validated for experimental data of bubble growth in superheated water. The model showed excellent agreement with experimental data at more than 100 times less computational cost than coupling the bubble growth equation with the conservation of energy equation numerically. The model was applied to the simulation of a flash boiling spray from a swirl atomizer, and the simulated flashing spray resulted in smaller droplets and faster vaporization than a non-flashing spray at ambient conditions of 0.445 MPa and 430 K.