Pulsating combustion of liquid fuel in partially closed vessels

Abstract

Two modes of combustion are possible for a liquid fuel in a vessel that is closed except for a single orifice: constant pressure diffusion burning and pulsating combustion. An experimental and theoretical investigation has been made of the pulsating mode of combustion using methanol liquid fuel. Measurements were made of liquid-fuel burning rates and of chamber pressure as a function of time in cylindrical vessels for various chamber lengths and orifice diameters. In addition, high-speed schlieren motion pictures were taken of the pulsating combustion process in order to obtain qualitative information about flow patterns, mixing, and ignition during each combustion cycle. Self-sustained pulsating combustion was found to be possible only within certain limits of chamber length and orifice diameter. Within these limits, combustion frequency ranged from about 25 to 70 c/s, and was always smaller than the Helmholtz resonator frequency by at least a factor of three. Pressure amplitudes varied from about 10 to 85 mm of mercury. Methanol burning rates were found to be as much as eight times larger than those for steady diffusion burning in open-top cylinders of the same size. Other liquid fuels, in addition to methanol, were found also to exhibit pulsating combustion. A theoretical analysis gives chamber pressure as a function of time during the pressure decay part of each cycle and agrees substantially with experimental measurements.