Abstract
Based on the URANS equation, a numerical simulation is carried out for acoustic properties of the thruster chamber with coaxial injectors and plenum chamber in a liquid rocket engine. Pressure oscillations with multiacoustic modes are successfully excited in the chamber by using the constant volume bomb method. FFT analysis is applied to obtain the acoustic properties of eigenfrequencies, power amplitudes, and damping rates for each excited acoustic mode. Compared with the acoustic properties in the model chamber with and without an injector as well as with and without the plenum chamber, it can be found that the injector with one open end and one half-open end still can work as a quarter-wave resonator. The power amplitudes of the acoustic mode can be suppressed significantly when its eigenfrequency is close to the tuning frequency of the injector, which is achieved by Cutting down the pressure Peak and Raising up the pressure Trough (CPRT). Compared with the acoustic properties in the model chamber with and without the plenum chamber, it can be found that 1L acoustic pressure oscillation is inhibited completely by the plenum chamber and other acoustic pressure oscillations are also suppressed in a different extent. The injector and plenum chamber have a little effect on the eigenfrequencies and damping rate of each acoustic mode. For multimode pressure oscillation, it is better for tuning frequency of the injector closing to the lower eigenfrequency acoustic mode, which will be effective for suppression of these multiacoustic modes simultaneously.
Highlights
Gas-liquid coaxial injectors have been widely used in liquid rocket engines for their good properties on the mixing of fuel and oxygen, atomization of liquid propellant, and combustion stability of the thruster chamber
The numerical method applied in this paper for acoustic properties of a combustion chamber has been validated for a small thrust liquid rocket engine chamber by experimental results [18]
Unidentified frequency peaks increase not dramatically. 1L and 2T acoustic modes, which are mostly concerned by engineering, are significantly controlled by coaxial injectors. Such a coaxial injector with one open end and another half-open end still can work as a quarter-wave resonator. It is better for tuning frequency of the injector closing to the lower eigenfrequency acoustic mode, which will be effective for suppression of these multiacoustic modes simultaneously
Summary
Gas-liquid coaxial injectors have been widely used in liquid rocket engines for their good properties on the mixing of fuel and oxygen, atomization of liquid propellant, and combustion stability of the thruster chamber. Shear coaxial injector elements are prone to such instability because the resonant acoustic frequencies of the LOX post are often close to the resonant frequencies of the combustion chamber [1]. A phenomenon on combustion instability in a subscale combustor for a LOX/methane rocket engine has been conducted by JAXA [2], in which the effects of five types of single shear coaxial injector on the combustion instability were observed. The injection-coupled response of a LOX post was predicted by Lin et al based on the finite element model (FEM) [3], in which the observed instability was a result of the interaction of combustion chamber resonance frequencies with injector resonance frequencies. The acoustic properties and decay rate of coaxial injectors have got much investigation
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