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Combustion stability in liquid propellant gun.

Verbrennungsstabilitäten in Flüssigtreibstoffkanonen
: Lawton, B.; Klingenberg, G.
: Fraunhofer-Institut für Kurzzeitdynamik, Ernst-Mach-Institut -EMI-, Freiburg/Brsg.

Freiburg/Brsg., 1991, 128 pp. : Abb.,Lit.
EMI-Berichte, 4/91
Fraunhofer EMI ()
Druckoszillation; Flüssigtreibstoff; liquid gun propellant; Oszillationskriterium; pressure oscillation; pressure oscillation criterion; regenerative system; Regenerativsystem; suppression of oscillation; unstable combustion; Unterdrückung von Oszillation; Verbrennungsinstabilität

The onset of pressure oscillations in 28-mm-, 30-mm- , and 40-mm-caliber liquid propellant (LP) guns firing 10 or more different propellants are analyzed. Two indicators of combustion driven oscillations are modified and used, namely, the impulse frequency and the stability number. It is shown that both these numbers may be calculated from the heat release rate which is itself calculated from the measured chamber pressure history of the gun. Pressure oscillations start when the stability number exceeds a value which varies from 0.4 to 0.55 depending on the type of propellant. The impulse frequency, at onset of oscillations, varies from 150 to 900 Hz. Stability number displays less variation with change in gun size than the impulse frequency. Fourier transforms of the pressure signals reveal random frequencies of low amplitude during combustion. Out of these random frequencies a fundamental frequency of about 18 kHz (wavelength about 56 mm), with up to five harmonics, grows. This well d efined harmonic structure always appears in the 28-mm and 30-mm LP guns and also in a 20-mm gas gun. Oscillations in the 40-mm LP gun remain random.