An Experimental Study of High-Frequency Combustion Pressure Oscillations

Zucrow, M. J.; Osborn, J. R.

doi:10.2514/8.7420

Cited by 32 publications

(7 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…length again occurs at a higher chamber pressure. 5 The shift of the instability region is also evident for the 14-in. diameter motor.…”

Section: Experimental Results For Methane and Airmentioning

confidence: 84%

“…Therefore, it receives a greater share of the available energy. It should be noted, however, that the longitudinal mode oscillations eventually reach a limiting amplitude which is to be expected (5).…”

Section: Experimental Results For Ethylene and Airmentioning

confidence: 93%

“…Those curves, plotted for both the 7-and 14-in. diameter motors, 5 The shortest chamber length at which the transverse mode instability region shifts to a lower chamber pressure will be referred to as the "shifted length." length.…”

Section: Experimental Results For Methane and Airmentioning

confidence: 99%

See 2 more Smart Citations

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

Osborn¹,

Bonnell²

1961

ARS Journal

Self Cite

View full text Add to dashboard Cite

The experiments reported herein were concerned with the determination of some of the underlying factors which contribute to the occurrence of transverse modes of combustion pressure oscillation in rocket motors. Two rocket motors having different diameters and several different lengths were employed in the experiments using a gaseous hydrocarbon fuel and air as propellants. The investigation indicated that changes in the aspect ratio and volume of the rocket motor combustion chamber had a profound effect on the incidence and amplitude of the transverse modes. These effects were modified by interactions of the transverse modes with the longitudinal mode. The transverse modes present in the experiments were determined to be the "spinning" and the radial modes.

show abstract

“…length again occurs at a higher chamber pressure. 5 The shift of the instability region is also evident for the 14-in. diameter motor.…”

Section: Experimental Results For Methane and Airmentioning

confidence: 84%

Section: Experimental Results For Ethylene and Airmentioning

confidence: 93%

See 1 more Smart Citation

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

Osborn¹,

Bonnell²

1961

ARS Journal

Self Cite

View full text Add to dashboard Cite

show abstract

“…When these values of p', P', u f , w f are introduced in Equations [5 and 6], and terms of the order of M e 2 are neglected, we obtain the following linear ordinary differential equations for the amplitudes [15] [16]…”

Section: Linearization Of the Equations For Smallmentioning

confidence: 99%

Theory of Liquid PropelIant Rocket Combustion Instability and Its Experimental Verification

1960

View full text Add to dashboard Cite

A straightforward theoretical formulation of the longitudinal high frequency rocket stability criteria is presented. Based on Crocco's sensitive combustion time lag theory, the derivation ii considerably simpler, although somewhat less rigorous, than previously published detailed treatments. A series of rocket motor experiments is described, demonstrating that there exists ar upper limit to the chamber length at which each mode of longitudinal high frequency pressure oscillations will occur, and that this limit is accurately predicted by the theory over a wide rang* of mixture ratios on two different injectors. The method used to compare experimental result! with the theoretical stability limit predictions (including a simple experimental technique fo] determination of the sensitive time lag) is described. Phenomenon of Rocket Combustion InstabilityE XCEPT for starting and cutoff transients, rocket motors are designed for steady operation. Two kinds of unsteadiness have nevertheless been observed to be present. First, the combustion in a rocket is always more or less "rough"; that is, random pressure fluctuations of larger or smaller amplitude cannot be avoided. Second, under proper conditions organized pressure oscillations at well-defined frequencies and distributions may appear. The latter form of unsteady operation is given the general title of "combustion instability."There are three recognized types of combustion instability. The first, the "low frequency instability" (1-3,6,7) 5 is due to interaction between the processes taking place in the combustion chamber and the propellant feed system; it is now sufficiently understood and comparitively easy to avoid or cure.The second, the "intermediate frequency instability" (4,5), results from a so-called "entropy wave" produced C3^clically in the chamber and interacting with the exhaust nozzle. Of the three, it is the least frequent.The third, the "high frequency instability," consists of the excitation of acoustic vibrational modes of the combustion chamber. This is by far the most destructive kind of instability and the hardest to control. The present paper deals with certain theoretical and experimental results concerning this third type of instability.A possible cause for high frequency instability was first advanced in 1950 (6). It was speculated that if pressure waves are produced in the chamber, they must produce an effect on Presented at the rates of the various physico-chemical processes leading tc combustion. These modified rates, in turn, by causing periodic intensification or weakening of the local gas evolutior. or heat release, could sustain the pressure waves under the appropriate conditions. A somewhat oversimplified model introduced to express quantitatively the sensitivity of the combustion rates to the pressure oscillations, was able tc demonstrate that high frequency instability could indeed be produced (6). This simple model was refined over the years in order to treat the problem in a more realistic manner. The results of these theoretical t...

show abstract

“…1 are not capable of yielding the limits of Ref. 2. It is noted at the beginning that we shall confine subsequent discussions to second-order controlled elements with positive static stability, namely, with positive stiffness, unless otherwise stated.…”

mentioning

confidence: 97%

Combustion Instability in Gas Rockets

1965

View full text Add to dashboard Cite

T HE objective of the comment by R. H. Smith seems to point out that the controllability limits as given by Refs. 1 and 2 disagree widely because of the difference of practice, and that predictions of the limits of manual control made by Ref. 1 are not capable of yielding the limits of Ref. 2. It is noted at the beginning that we shall confine subsequent discussions to second-order controlled elements with positive static stability, namely, with positive stiffness, unless otherwise stated.Replying to the first part of the comment, we agree that practice is an essential factor for explaining the discrepancy, although it should be remembered that no system input is present in the experiment of Ref. 1, whereas random inputs are present in that of Ref. 2. As mentioned in Ref. 1, we conducted experiments for obtaining the difference between the controllability limits at one trial and at three trials and concluded that the results indicated, evidently, the effect of practicing.The controllability limit of a human operator may depend on many factors such as practice, his naivete, or experience as an airplane pilot, and so forth. Consequently, it is considered indispensable when presenting data on the controllability limit to prescribe conditions fully under which experiments have been conducted. We believe that our data show a controllability limit under the prescribed test program of Ref. 1, namely, a controllability limit at one trial and at three trials. We note that our data agree very well with those obtained by NASA in Ref. 3.On the other hand, we find in Ref. 2 that the two controllability limits, the establishment of which required nearly 900 trial runs, show clearly the effect of heavy practice. This is a controllability limit established by Smith. It seems probable that a more sophisticated technique would further improve the controllability limit established by him. We note here that unpublished data obtained recently at National Aerospace Laboratory of Japan also show that the controllability limit can be improved by heavy practice far beyond that of Ref. 1.In replying to the second part of the comment, we agree that a transfer function, which is more complicated than Eq.(3) of Ref. 1 must be employed in predicting the limits of Ref. 2. The purpose of writing Ref. 1 was this: we assumed that the transfer function of a human pilot was given by Eq.(3) and that the pilot could conduct a self-adaptive control. Then, we made a speculation to find how our prediction could correlate with our experimental data. During the prediction, we were satisfied with obtaining a rough idea of the controllability limit by taking T L = °°, although it was possible to take an assigned value for T L . We believe that Eq. (3) is an appropriate transfer function of a human pilot who is trying to find a controllability limit on a "first-encounter basis.' 7 A brief mention is made here on an operator's behavior under heavy practice. Since there exists a periodicity in transient response of the controlled element with positive static s...

show abstract

An Experimental Study of High-Frequency Combustion Pressure Oscillations

Cited by 32 publications

References 1 publication

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

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

Theory of Liquid PropelIant Rocket Combustion Instability and Its Experimental Verification

Combustion Instability in Gas Rockets

Contact Info

Product

Resources

About