Importance of Combustion Chamber Geometry in High Frequency Oscillations in Rocket Motors

Osborn, J. R.; Bonnell, J. M.

doi:10.2514/8.5536

Cited by 12 publications

(5 citation statements)

References 4 publications

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“…The latter assumption is consistent with experimental observations of tangentialmode behavior in a cylindrical combustor with a short length/ diameter ratio. 8 If the measurements of the wave amplitude taken close to the injector and the nozzle are nearly the same (with negligible phase difference) in combustors up to 6 in. long (see Fig.…”

Section: Discussionmentioning

confidence: 96%

“…4 7 There is general agreement among these researchers that the pressure oscillations are sustained by a chemical reaction, rate-controlled mechanism. Although extensive experimental studies of transverse-mode oscillations 8 " 10 have been conducted utilizing cylindrical combustors burning premixed gases, the only theoretical treatment of the latter modes is the attempt by Culick 3 to extend his linearized analysis of the transverse modes in a liquid-propellant rocket to the case of a gas-burning combustor.…”

Section: Nomenclaturementioning

confidence: 99%

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Combustion stability in an annular gas combustor.

Bonnell

1968

AIAA Journal

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The conditions for either stable or oscillatory combustion are determined analytically for a burning mixture of ideal gases in an annular combustion zone. The mixture, flowing steadily in the axial direction, is perturbed by a small-amplitude, tangentially propagating pressure disturbance. The rate of energy release is described by an Arrhenius function. The stability of the system is governed by an amplif cation coefficient that reflects the effects due to the rate of energy release and the convective transport of energy. The stability criterion is employed to evaluate the effects of changes in the system parameters on the combustion stability. A critical value of the Arrhenius exponent is determined which exists at a line demarcating regions of stable and oscillatory combustion; it is a function of the flowfield variables, the specific-heat ratio, and the reaction rate frequency factor. A partial, qualitative verification of the stability trends predicted by the analysis is provided by the known stability behavior of premixed gases burned in cylindrical and annular combustors.Mach number m = mean molecular weight n = wave number for tangential mode of oscillation p -static pressure p i} p. 2 = amplitude constants r = mean radius of annulus, radial coordinate R -gas constant R u -universal gas constant t = time T = static temperature v = velocity vector v$j v z = tangential and axial velocity components, respectively Xij Xj = mass fractions of components i and j z = axial coordinate & = na/r Sij 5 2 = constant phase angles e = activation energy 0 = angular coordinate p = density

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Section: Discussionmentioning

confidence: 96%

Section: Nomenclaturementioning

confidence: 99%

Combustion stability in an annular gas combustor.

Bonnell

1968

AIAA Journal

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“…In this paper, however, the major emphasis will be placed upon the effect of the fuel composition. The influence of differences in combustion chamber geometry is presented in (1). 3 .…”

Section: Amplitude Of Oscillations Of the Longitudinal Mode Vs Chambmentioning

confidence: 99%

Effect of Fuel Composition on High Frequency Oscillations in Rocket Motors Burning Premixed Hydrocarbon Gases and Air

Osborn¹,

Bonnell²

1961

ARS Journal

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The experiments reported herein were concerned with the determination of some of the factors which contribute to the occurrence of transverse and longitudinal modes of combustion oscillation in rocket motors burning gases. Three rocket motors having different combustion chamber geometries were employed, using gaseous hydrocarbon fuels premixed with air as propellants; the fuels were methane, ethane, superheated propane, ethylene and hydrogen. The findings indicated that the incidence and amplitude of the combustion pressure oscillations were profoundly influenced by the coupled effects of the chemical composition of the fuels and the aspect ratio of the cylindrical combustion chamber. The results also indicated that the following measures of the behavior of combustion oscillations were functions of the chemical differences of the fuels: 1) the relative ability of the different gaseous propellant combinations to support combustion oscillations; 2) the shape and origin of the instability region of the transverse modes, and the amplitudes of the oscillations within that region; 3) the combustion chamber length below which longitudinal oscillations will not occur (the lower critical length) , * 4) the tendency for interactions between transverse and longitudinal modes to occur; and 5) the mode of oscillation.

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“…The combustion is focused in a certain cross section, i.e., the perturbation wavelength is much greater than the length of the combustion region. 4. The squared values of perturbations can be neglected, as compared with the values of perturbations proper.…”

mentioning

confidence: 99%

“…It is difficult to interpret the results of numerous available experiments because it is next to impossible to retain the regime parameters affecting the mixing processes unchanged when using another propellant. In addition, when some species of the propellant is changed, the physical parameters (evaporation heat, vapor elasticity, viscosity, and surface tension) also become different, and it is difficult to reveal the role of the kinetic factor [4]. Narrje and Reardon in their book dealing with unstable combustion [3] noted that the role of physicochemical properties of the propellant species in the high-frequency combustion mechanism was still unclear.…”

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confidence: 99%

Diagnostics of acoustic properties of the combustion zone by means of periodic changes in the nozzle throat area

Lisochkin

2008

Combust Explos Shock Waves

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A mathematical model is proposed, which allows calculating the amplitude of forced pressure oscillations in the combustor of a liquid-propellant rocket engine, caused by periodic changes in the nozzle throat area, with allowance for acoustic properties of the combustion zone. Results calculated for some particular cases are given.The development of highly forced combustors is associated with ensuring stability of the operation process. As the combustion zone is capable of sustaining self-induced high-intensity pressure oscillations, which may lead to structural failure, it is necessary to increase the amount of validation tests and, sometimes, to avoid using the previously chosen scheme of mixing of the species. Self-induced oscillations are usually divided into low-frequency, intermediate, and high-frequency oscillations. Studying and finding means of suppression of high-frequency oscillations are the most difficult tasks. This phenomenon has been most comprehensively studied for liquid-propellant rocket engines. A large amount of experimental data has been accumulated (see the monographs [1-3]). The emergence of oscillations is dangerous not only because of higher thermal and mechanical loads on structural elements of the combustor, but also because of worse mixing, which reduces the combustion efficiency.A completed theory of this phenomenon has not yet been developed. The theoretical progress is mainly based on the phenomenological approach and involves an analysis of the delay between the moment when the species enter the combustor and the end of the combustion process. As the delay is sensitive to regime parameters of the combustor, there appears a feedback between the energy release in the combustion region and pressure oscillations. As there is no complete understanding of steady combustion of liquid propellants, there are no grounds for the development of a physical theory of vibrational combustion. It should be noted 1 Russian Research Center "Applied Chemistry," St. Petersburg 197198; office@cisp.spb.ru.that the attempts to transfer the laws of steady combustion to the processes of unsteady combustion may turn to be ineffective because a minor fraction of the total energy released in the combustion region is sufficient to initiate developed pressure oscillations in the case of low acoustic losses in the combustor. Though the available phenomenological theories [1] allowed a scientifically grounded approach to planning and analyzing experiments on vibrational combustion to be developed, the effect of physicochemical and kinetic properties of the liquid propellant on stability of the operation process has not been adequately studied. It is difficult to interpret the results of numerous available experiments because it is next to impossible to retain the regime parameters affecting the mixing processes unchanged when using another propellant. In addition, when some species of the propellant is changed, the physical parameters (evaporation heat, vapor elasticity, viscosity, and surface tension) also become...

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Importance of Combustion Chamber Geometry in High Frequency Oscillations in Rocket Motors

Cited by 12 publications

References 4 publications

Combustion stability in an annular gas combustor.

Combustion stability in an annular gas combustor.

Effect of Fuel Composition on High Frequency Oscillations in Rocket Motors Burning Premixed Hydrocarbon Gases and Air

Diagnostics of acoustic properties of the combustion zone by means of periodic changes in the nozzle throat area

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