High-frequency combustion instability

Levine (Ref 22, p 1083) has studied high frequency combustion instability of LP via high speed... 

High Frequency Combustion Instability in Rockets with Distributed Combustion , in 4th Symposium on Combustion, Williams Wilkins,... 

Acoustic instabilities involve the interactions of acoustic waves with the combustion processes. These instabilities are of high frequency and can be significant in certain situations but can successfully be avoided by suitable design (11,24). 

When an energetic material burns in a combustion chamber fitted with an exhaust nozzle for the combustion gas, oscillatory combustion occurs. The observed frequency of this oscillation varies widely from low frequencies below 10 Hz to high frequencies above 10 kHz. The frequency is dependent not only on the physical and chemical properties of the energetic material, but also on its size and shape. There have been numerous theoretical and experimental studies on the combustion instability of rocket motors. Experimental methods for measuring the nature of combustion instability have been developed and verified. However, the nature of combustion instability has not yet been fully understood because of the complex interactions between the combustion wave of propellant burning and the mode of acoustic waves. 

Combustion of a propellant in a rocket motor accompanied by high-frequency pressure oscillation is one of the most harmful phenomena in rocket motor operation. There have been numerous theoretical and experimental studies on the acoustic mode of oscillation, concerning both the medium-frequency range of 100 Hz-1 kHz and the high-frequency range of 1 kHz-30 kHz. The nature of oscillatory combustion instability is dependent on various physicochemical parameters, such... 

D.W. Rice, CombstnFlame 8(1), 21-8 (1964) CA 60, 14325 (1964) (Effect of compositional variables upon oscillatory combustion of solid rocket propellants) N ) R.W. Hart F.T. McClure, "Theory of Acoustic Instability in Solid Propellant Rocket Combustion , lOthSympCombstn (1965), pp 1047-65 N2) E.W. Price, "Experimental Solid Rocket Combustion Instability , Ibid, pp 1067-82 Qi) R.S. Levine, "Experimental Status of High Frequency Liquid Rocket Combustion Instability , Ibid, pp 1083-99 O2) L. Crocco,... 

Under certain conditions, propellants may exhibit high frequency vibratory combustion. Such vibration can cause extensive hardware damage and/or a mission abort. In most instances, however, combustion instability is related principally to the physical design of the combustion chamber rather than the chemical properties of the propellants. 

Combustion instability within a furnace is characterized as a high amplitude, low frequency noise often resembling the puffing sound of a steam locomotive. This type of noise can create significant pressure fluctuations within a furnace that can cause damage to the structure and radiate high noise levels to the surroundings. 

Similar phenomena have also been observed in the combustion of composite propellants. Eisel (El) has observed that there is a unique frequency-pressure relation in a low-pressure region where nonacoustic instability results. He speculates that this preferred frequency is related to the periodic appearance and depletion of the aluminum particles on the propellant surface. High-speed pictures confirm the periodic sluffing of aluminum, but its relation to the preferred frequency is still not clear. 

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