Effects of pressure oscillations on impinging-jet atomization and spray combustion in liquid rocket engines

Combustion dynamics are a critical factor in determining the performance and reliability of a chemical propulsion engine. The underlying processes include liquid atomization, evaporation, mixing, and chemical reactions. This paper presents a high-fidelity numerical study of liquid atomization and spray combustion under high-pressure conditions, emphasizing the effects of pressure oscillations on the flow evolution and combustion dynamics. The theoretical framework is based on the three-dimensional conservation equations for multiphase flows and turbulent combustion. The numerical solution is achieved using a coupling method of volume-of-fluid and Lagrangian particle tracking. The Zhuang-Kadota-Sutton (ZKS) high-pressure evaporation model and the eddy breakup-Arrhenius combustion model are employed. Simulations are conducted for a model combustion chamber with impinging-jet injectors using liquid oxygen and kerosene as propellants. Both conditions with and without inlet and outlet pressure oscillations are considered. The findings reveal that pressure oscillations amplify flow fluctuations and can be characterized using key physical parameters such as droplet evaporation, chemical reaction, and chamber pressure. The spectral analysis uncovers the axial variations of the dominant and secondary frequencies and their amplitudes in terms of the characteristic physical quantities. This research helps establish a methodology for exploring the coupling effect of liquid atomization and spray combustion. It also provides practical insights into their responses to pressure oscillations during the occurrence of combustion instability. This information can be used to enhance the design and operation of liquid-fueled propulsion engines.