Theoretical, Numerical Simulation And Experimental Investigations Of Combustion Instability In Liquid Rocket Engine

Combustion instability in liquid rocket engine is investigated with theoretical analyses, numerical simulations and experiments. Nonlinear science, such as Nonlinear Dynamics, Non- equilibrium Thermodynamics, and Wavelets, is introduced in the studies.Nonlinear oscillation equation of chamber pressure is established. The first three coefficients of combustion Vs pressure play different roles in combustion instability.Continuous Stirred Tank Reactor Acoustic Model is put forward. The heat transfer is the important Hopf bifurcation parameter. The self-catalyze mechanism may drive the combustion oscillate at an inherent frequency, and can provide frequency-draught and nonlinear inspiration behaviors.Temporal-spatial interaction model is established. The concept of competition and cooperation of the acoustic modes is introduced. Different acoustic modes can shares oscillation energy if the nonlinear interaction coefficient is little. Otherwise, only one mode gets instability.Non-equilibrium Thermodynamics is used to analyze the combustion instability. The vaporization models controlled by diffusion process can not include driving mechanism. General thermodynamics stability criterion of combustion is got.The nonlinear acoustic process is numerically simulated. It is found that the pressure and velocity disturbances run at sound speed, the entropy and components at flow speed, the temperature and density partly at sound speed, partly at flow speed.Gas combustion instability is numerically simulated with EBU model. The standard EBU model can not drive combustion to oscillate. The amendatory EBU model including ignition and extinguish mechanism can drive the combustion to oscillate. However, the oscillation can not last for a long time.Combustion instability of gas and spray flame in a lab-scale O₂/Kersene/H₂ tripropellant rocket engine is numerically studied. The diffusion and premixed gas flame are always stable in our simulations, though the premixed gas flame will oscillate for a period of time when the activation energy is artificially enlarged.The spray flames can self-oscillate from startup sequence with large amplitudes, and eventually reach limited cycles. The LO₂/Kerosene biproprellant spray flame is the most unstable case, and its stability is improved when gas hydrogen is injected and the velocity of gas oxygen is increased. Correlation of the numerical results on the basis of flow visualization and theoretical analyses indicate chemical kinetic play an important role in the combustion instability.During the experiments on the coaxial swirl injector of YF-75 engine, the injector can self-oscillate. This behavior is the result of the coupling between the gas vortex and the gas channel. It can affect the droplet distribution.Different inspiring methods are used to experimentally study the acoustic characteristics of the small chamber.Combustion instability of tripropellant rocket engine under different condition is experimentally studied. It is not absolute to improve the hydrogen/oxygen combustion stability by adding hydrogen.The experiment method to determinant the driving mechanism is put forward. The third control method of combustion instability besides the passive control and the active control is also brought forward.The research of the author shows that the chemistry dynamics can explain well almost all the combustion instability phenomenon, and the chemistry dynamics may be the driving mechanism of combustion instability in liquid rocket engine.