The combustive sound source: Combustion and bubble dynamics theory and experiment

Abstract

In combustion systems, characteristics such as adiabatic flame temperature and laminar flame speed are highly dependent on the equivalence ratio, which is defined as the actual fuel/oxidizer ratio divided by the stoichiometric fuel/oxidizer ratio. Experimental results indicate that the acoustic output of the combustive sound source (CSS) also shows equivalence ratio dependency. Peak acoustic pressure produced by CSS is low for lean mixtures, rises to a maximum for near stoichiometric mixtures, and falls for rich mixtures. Experiments were also conducted to compare the acoustic output of CSS with the predictions of Rayleigh–Willis bubble theory. The measured acoustic output of CSS follows the trend of Rayleigh–Willis bubble theory but always falls below the absolute values. Energy losses that are not accounted for in the theory are probably responsible for the high predictions. Other factors that affect the acoustic output of CSS are discussed, including the shape of the combustion chamber, the source of ignition, the type of oxidizer and fuel, the presence of high-pressure bubble collapses, and the generation of high-frequency components. [Work supported by ONR.]