Abstract
A new countermeasure against injection-coupled combustion instabilities in liquid propellant rocket engines is presented. Whereas the problem is usually addressed by adding damping elements such as baffles or resonators to the combustion chamber, this approach directly damps the acoustic eigenmodes of the injector instead. The principle of the damping method is described in this article, as well as the implementation of such a device in a sub-scale rocket thrust chamber operated with liquid oxygen and hydrogen at conditions representative of upper stage engines. Test results are presented which show that flame and pressure oscillations were successfully reduced by the modification. The absorbers had no measurable influence on thrust chamber performance, and so the solution lends itself to retrofitting in existing engines, as well as integration during the design phase.
Highlights
Since the development of the first large liquid propellant rocket engines (LPRE) high-frequency combustion instabilities have been one of the major challenges facing designers [1]
Research combustor model “D′′ German Aerospace Center Liquid Oxygen Load Point Liquid Propellant Rocket Engine Photomultiplier Power Spectral Density Ratio Oxidizer to Fuel Selective Laser Melting acoustic resonators connected to the chamber wall
The level of flame oscillation is inferred by the dynamic content of the optical probe signals
Summary
Since the development of the first large liquid propellant rocket engines (LPRE) high-frequency combustion instabilities have been one of the major challenges facing designers [1]. Due to the extreme power density in rocket combustors, only a small fraction of the total heat release needs to be transferred into the acoustic field to get rapidly growing amplitudes which can lead to the destruction of the engine by increased mechanical and thermal loads on the walls [14]. In a real system with acoustic dissipation, the energy transfer from combustion into the acoustic field must overcome the damping of the system in order to excite combustion instabilities. This balance can be described by Eq (1), where Li represents the ith damping process [16,17]. The driving mechanisms are often difficult to be identified, and so the most common approach to eliminate combustion instabilities is to add acoustic damping features to the combustion chamber
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