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Space Technology Research Grants

Measurement of Combustion Response to Transverse Modes at High Pressure

Completed Technology Project

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Project Image Measurement of Combustion Response to Transverse Modes at High Pressure

The coupling between acoustics and unstable combustion has been a prime concern and unsolved problem over the entire modern history of chemical propulsion. These instabilities are extremely complicated due to the myriad potential coupling mechanisms and multiple length and time scales of the combustor and combustion processes. With frequencies greater than 1000 Hz, high-frequency combustion instabilities can impact combustor performance and lead to catastrophic failure due to overheating. Experimental work at Purdue is part of a larger effort to integrate experimentation, high order models, and engineering level models to better predict combustion instability and to better serve future engine design and performance. An absolutely unique experiment is being used to provide a representative unstable flowfield to which the response of propellant combustion can be measured. Imaging processing techniques are used to identify combusting structures in injector flowfields and their response to pressure and velocity instabilities. Combustion light intensity as measured by a filtered high speed camera is used as an indicator of local unsteady heat release. Combining heat release and high frequency pressure measurements, the damping and driving effects of an injector shall be identified based on Rayleighís criterion of instability. These data are compared to high fidelity computer models to distill combustion response functions that can be used in engineering-level models. When fully developed this diagnostic method could be deployed on operational rocket engines to actively control against unstable behavior or implemented on research combustors for more standardized, complete experimental results. More »

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When fully developed this diagnostic method could be deployed on operational rocket engines to actively control against unstable behavior or implemented on research combustors for more standardized, complete experimental results. More »

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Primary U.S. Work Locations and Key Partners

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Organizations Performing Work	Role	Type	Location
Purdue University-Main Campus	Lead Organization	Academia	West Lafayette, Indiana
Glenn Research Center (GRC)	Supporting Organization	NASA Center	Cleveland, Ohio

Primary U.S. Work Locations

Indiana

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Transition Events

August 2011: Project Start

July 2015: Closed out More »

Closeout Summary:

A two-dimensional Transverse Instability Combustor (TIC) capable of producing varying levels of transverse instabilities was tested. A seven element array of gaseous CH4 and decomposed H2O2 ox centered shear coaxial elements was used. The center Study element design was kept from the single element longitudinal Continuously Variable Resonance Combustor (CVRC). The other six Driving elements were simplified versions of this design and were used to initiate and sustain the unstable flowfield. The Study element was subjected to this unstable flowfield and its response recorded through high frequency pressure transducers and OH* chemiluminescent imaging. The instability amplitude was controlled by the length of the oxidizer posts of the ox-centered shear coaxial injectors. Identical test conditions were tested between tests with the only significant difference between tests being the length of the Driving element oxidizer post lengths. Phase lag measurements between ox post inlet and local chamber pressure showed a linear scaling of phase lag as a function of post length. Response speed calculations identified this as an acoustic response. The highest amplitude post length configuration had a phase lag of 180 degrees of the full 1W period. Consistent phasing between oxidizer posts and the chamber flowfield of near half the 1W acoustic mode period is necessary to sustain a high amplitude limit cycle. The results indicate that the oxidizer post length in the multi-element transverse combustor has a significant effect in modulating unsteady pressure amplitude. This correlates with the modulating effect of the varying oxidizer post length in the CVRC. With post length scaled based on frequency and Mach number, stable and unstable behavior as a function of oxidizer post length was consistent between the TIC and the CVRC. Chemiluminescent imaging of the OH* emissions is still under analysis and will support determination of the combustion response of the observed Study element as a function of unsteady pressure amplitude.

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Co-Investigator:

Matthew K Wierman

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Start:	2
Current:	3
Estimated End:	3

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Measurement of Combustion Response to Transverse Modes at High Pressure

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Primary U.S. Work Locations and Key Partners

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