Mechanisms of Exciting Pressure Oscillations in Ramjet Engines.
Abstract
During the past two years, we have been able to understand, in principle, the mechanism of one predominant mode of combustion instability in dump combustors for ramjet engines. The objectives of further experiments have been to provide a quantitive, physical basis for elements of this mechanism which will allow application of the results to a wide class of combustor sizes, fuels and mixture ratios, and to more complex acoustic environments. One mode of unsteady combustion in dump burners, which under certain circumstances may lead to combustion instability, involves the periodic formation of a large vortex in the separated shear layer and its subsequent movement toward the combustor wall. When oscillations appear, the frequency of the vortex shedding coincides with that of some natural acoustic mode of the apparatus. Detailed experiments show that the heat release which drives the oscillation occurs predominantly as the result of an interaction between this vortex and the wall. Recent experiments and calculations have shown that the time delay between vortex formation and the wall encounter is strongly dependent on the pressure amplitude of the oscillation and, consequently, and acoustic mode of particular frequency will be excited to an amplitude required to produce the suitable phase of the heat release. Experiments have been performed to assess the role of chemical time in the overall time delay. The results provide means for using the results for different mixture ratios and fuel types. Keywords: Combustion, Instability, Pressure oscillations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1986
- Accession Number
- ADA174608
Entities
People
- Frank E. Marble
Organizations
- California Institute of Technology