Numerical Investigation on Combustion Instability in a small MMH/NTO Liquid Rocket Engine

摘要

Three dimensional two-phase reaction turbulent flow in a small MMH/NTO Liquid Rocket Engine is investigated numerically. Four cases with different droplet size are calculated. The pressure oscillations are strengthened firstly and then weakened with the increase of the droplet size. Self-excited combustion instabilities are captured without any artificial pressure disturbances or simulation bombing. The enhancement of evaporation of MMH and NTO droplets at the downstream region adjacent to impingent points result in abrupt peak of mass fraction of MMH and NTO at the same time, which indicates local concentration combustible pre-mixture is formed there. This leads to local violent chemical reaction, accompanied with high amplitude increase of pressure. The pressure peaks occur occasionally and frequently at the head of the chamber, and their propagation and reflection in the chamber excite combustion instability. An increase of droplet size in 10-30 microns indicates an increased tendency to instability, while an increase of droplet size in 30-70 microns indicates an increased stability margin.