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Abstract
This research involves a theoretical analysis of the propagation of sound within chemically reacting hydrocarbon combustion products. A procedure for determining the sound speed and absorption coefficient was developed. Analyses for other chemically reacting gas mixtures can be done by using a similar approach.
The ideal gas mixture of hydrocarbon combustion products was considered spatially infinite, uniform, stationary, and initially in chemical equilibrium. One dimensional (i.e., plane wave) sound propagation was assumed. Molecular diffusion effects, such as viscous stress, heat conduction, and mass diffusion were appropriately neglected along with possible effects due to vibrational non-equilibrium. In this way, only the effects of chemical reactions on sound propagation was considered.
The expressions for sound speed and absorption coefficient were derived as a function of frequency. Required background property information, such as equilibrium composition and equilibrium thermodynamic properties, were evaluated using standard thermodynamics procedures. Published sources and standard chemical kinetics theory were used to calculate the forward and backward rate constants for the chemical reactions controlling the chemical kinetics. The theory was also extended to do the phase shift analysis of the change of properties with respect to change in pressure.
A computer program, using FORTRAN, was written to calculate the values of different parameters related to acoustic propagation within a chemically reacting gas mixture. Calculations were performed for different temperatures and pressures. The variation of the values of the parameters with frequency, equivalence ratio, and different thermodynamic properties were observed. The low frequency (equilibrium) and high frequency (frozen) limits were evaluated. Equilibrium values and frozen values were also calculated independently to check the validity of the method developed in this project.
Practical applications of the method were also discussed. Acoustic pyrometers and other acoustic sensors will in general provide better results if the theoretical method is used for calculating sound speed propagating within chemically reacting gas mixtures.
