Influence of Combustion Process on Stability
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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The relative importance of various steps in the combustion process on combustion instability was compared theoretically by assuming that individual steps controlled the growth of a disturbance. The combustion steps involved the time dependence of 1 propellant injection, 2 accumulation of unburned propellant, 3 propellant atomization, 4 propellant vaporization, and 5 chemical reaction. The calculation gave stability limits minimum disturbance that will grow to instability with various steps considered to control the combustion rate. The calculations show that chemical reaction is the most sensitive mechanism, but if accumulation of unburned propellants is included, the chemical reaction step is likely to be important only for low conversion rates that do not occur in most rocket combustors. With realistic combustion conditions the physical processes of vaporization and atomization appear to be the most important in determining instability limits, the limits for each step depending on the accumulation of unburned propellant and vortex velocity. Experimental instability studies with an 8-foot torus combustor, which is similar in geometry to that used for the theoretical calculations, confirmed the calculated results. Experiments also confirmed qualitatively the fluctuations that occur during instability.
- Combustion and Ignition
- Liquid Rocket Propellants