Combustion instabilities in the transition region of an unstable model rocket combustor

Stanford C Rosen, Purdue University

Abstract

Gaseous methane and 90% hydrogen peroxide at an equivalence ratio of 0.8 were used to study combustion instabilities in the region where the system transitioned from stable to unstable combustion. A variable geometry unstable rocket combustor was used at a chamber pressure of 210 psi. The combustor consists of a coaxial shear injector and a simple dump plane combustor. The oxidizer injector is mounted on a translating shaft that allows the oxidizer post length to be changed from a ½ wave resonator to a ¼ wave resonator during the course of a test. The oxidizer injector was translated forward and backward to check for hysteresis effects. A series of tests with the oxidizer injector fixed at a given location were also performed. The results indicate that the translating post moves slow enough compared to the frequency of the pressure oscillations that the system can be considered “quasi-steady.” High frequency pressure data from the oxidizer and fuel manifold, oxidizer post, and various chamber locations were obtained at a scan rate of at least 100 kHz. The physics of the combustion process were examined to determine whether or not they remained constant as the system transitioned from marginally stable to highly unstable combustion. The primary frequency of combustion, pressure mode shape, and phase angle between pressure at the head end of the chamber and pressure at the aft end of the chamber were found to change as the system transitioned to unstable combustion. The first five inches of the combustion chamber were replaceable with a quartz/acrylic housing. This allowed the combustion at the head end of the combustor to be filmed with a high speed camera. Line of sight optical images were obtained at scan rate of 10 kHz. Light intensity was used as an estimation of local unsteady heat release. The phase angles and Rayleigh index between the unsteady light and unsteady pressure oscillations were calculated and driving and damping regions identified.

Degree

M.S.A.A.

Advisors

Anderson, Purdue University.

Subject Area

Aerospace engineering

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