Transient Combustion Dynamics.
Abstract
Many dump combustors exhibit low frequency longitudinal combustion instability in the frequency range of 80-300 hz. Although the exact causes of combustion instability are not known precisely, it is generally accepted that the interaction of the shock induced pressure pulsation and the coherent vortex shedding at the dump plane induces combustion instability. During this study a characteristic system frequency associated with sudden expansion steps and a resulting coherent beat phenomenon have been identified. It is also shown that combustion oscillation can occur when the induced forced frequency is approximately equal to the mean of the beat frequency. When the coherence of the shear layer at the dump plane is disrupted either by gasjets or by upstream protrusions the effect of combustion instability is found to be minimized. The control system suggested in this report is based upon the idea of disrupting the shear layer at the dump plane by means of pulsing gasjets. The control system senses the critical combination of frequency, amplitude and phase angle upstream of the combustor and actuates the gasjets at the dump plane at an appropriate combination of frequency, amplitude and phase angle to partially negate the effect of upstream pressure pulsation. Experiments in two laboratory scale dump combustors using premixed propane-air mixtures show the feasibility of reducing chamber pressure amplitude by such a technique. Keywords: Ramjets.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 22, 1985
- Accession Number
- ADA163997
Entities
People
- Melvin Gerstein
- P. R. Choudhury
- Reza Mojaradi
Organizations
- University of Southern California