Investigation of flame velocities at low pressures.

Abstract

The purpose of this study is to investigate flame velocities of mixtures of oxygen and various fuel gases at low pressures. Acetylene and propane fuels were used, and flame velocities were measured by means of flat disc flames and by means of the geometry of cone-shaped flames. Flame front area was measured from the profile defined by the onset of luminosity. The pressure range from three to one hundred mm. of mercury was covered by using two burner inlet ducts of different diameters, 2.37 and 1.25 inches respectively. The equipment and characteristics of the low pressure flame limited the data in this range, so that restricted quantitative results were obtained in regard to the variation of flame velocities with pressure. Qualitatively, very definite variations were noted. There is a marked decrease of flame velocity with decreasing pressures in the regime below forty mm. of mercury. The variation in flame speed for the same pressure increments becomes greater as the pressure decreases. This is attributed to the rapid increase of the quenching effect from the inlet duct rim at these low pressures and low flow velocities. It is also found that flame velocities from flat flames are consistently lower than those obtained through the geometry of the cone flames. Similarly, flame velocities measured with the smaller inlet duct are consistently lower than those measured with the larger duct for the same measuring criteria. Both these variations appear to be explained by the large quenching effect encountered.