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An experimental facility for measuring burning velocity has been designed and built. It consists of a spherical constant volume vessel equipped with a dynamic pressure transducer, ionization probes, thermocouple, and data acquisition system. The constant volume combustion vessel allows for the determination of the burning velocity over a wide range of temperatures and pressures from a single run. A new model has been developed to calculate the laminar burning velocity using the pressure data of the combustion process. The model solves conservation of mass and energy equations to determine the mass fraction of the burned gas as the combustion process proceeds. This new method allows for temperature gradients in the burned gas and the effects of flame stretch on burning velocity. Exact calculations of the burned gas properties are determined by using a chemical equilibrium code with gas properties from the JANAF Tables. Numerical differentiation of the mass fraction burned determines the rate of the mass fraction burned, from which the laminar burning velocity is calculated. Using this method, the laminar burning velocities of methane–air–diluent mixtures have been measured. A correlation has been developed for the range of pressures from 0.75 to 70 atm, unburned gas temperatures from 298 to 550 K, fuel/air equivalence ratios from 0.8 to 1.2, and diluent addition from 0 to 15 percent by volume.

Burning velocities of methane-oxygen-argon mixtures have been measured in two matched constant-volume chambers, one spherical and one cylindrical. Burning velocities in the spherical chamber were determined from the pressure rise using a thermodynamic model based on the conservation of mass and energy. Photographic observations made through end windows in the cylindrical chamber at early times were used to study the effects of flame curvature and stretch on the flame speed under constant pressure conditions. The cylindrical chamber was also used to investigate flame shape, cracking and wrinkling. Substitution of argon for the nitrogen in air increased the range of pressure and temperature at which measurements could be made. A correlation for the burning velocity of methane-oxygen-argon mixtures has been developed for the range of pressures from 1 to 40 atmospheres, unburned gas temperatures from 298 to 650 K and fuel-air equivalence ratios from 0.8 to 1.2. Using this correlation and previous results for methane-air mixtures, the burning velocities of methane-air mixtures have been extended to higher temperatures. The results are compared to other experimental measurements and theoretical predictions.

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