A Nondimensional Correlation of Flame Propagation at Subatmospheric Pressures

The effect of ambient pressure on the propagation rate of Bunsen flames in propane-air and ethylene-air mixtures is described. It is concluded that the normal flame speed for the fuels studied varies inversely with the logarithm of the pressure from atmospheric pressures to as low as 1 in. Hg abs. A nondimensional parameter, the Peclet number, is established that correlates the results with four burner sizes, two fuels, and for the range of pressures investigated. It is concluded that the Peclet number must be kept large to avoid considerable reductions in flame speeds at subatmospheric pressures.