Raymond Friedman

The Wall‐Quenching of Laminar Propane Flames as a Function of Pressure, Temperature, and Air‐Fuel Ratio

The quenching distance between plane parallel plates has been measured for propane‐air flames at eight pressures ranging from 0.0832 to 2.77 atmos., and air‐propane ratios ranging from 11 to 24. Other tests have been made at atmospheric pressure in which (a) the temperature of the quenching plates has been varied from 80° to 715°F, (b) the temperatures both of the inlet gas and the quenching plates have been varied from 80° to 545°F, and (c) a series of six different solid surfaces was tested. The minimum quenching distance is found to occur at an air‐propane ratio between 13.5 and 14.0, and is proportional to the minus 0.91 power of pressure. Lean mixtures are found to be slightly less pressure‐sensitive. When both the inlet gas and plates are heated, the minimum quenching distance is found to be proportional to the minus 0.5 power of absolute temperature. The quenching effect appears to be independent of the nature of the surface.

Measurement of Temperature Distribution in a Low‐Pressure Flat Flame

The temperature distribution in a very lean, flat propane‐air flame was measured by the thermocouple method, at a pressure of 0.0594 atmos. The temperature change occurred in a zone about 3 cm thick. Wallquenching was minimized by employing a burner tube diam of 25 cm. The thermocouple was made from 12‐micron wire, coated with ceramic to avoid catalytic effects. One hundred experimental traverse points were obtained, with a standard deviation of ±0.016 cm.The burning velocity was also measured, and was found to vary with the inverse 0.30 power of pressure. This is in agreement with Egerton and Sens result, obtained over a more limited range of pressure.The temperature pattern was analyzed mathematically to obtain the pattern of heat release rate, taking into account the variation with temperature of thermal conductivity and specific heat. It was found that the heat release began at 300°C, attained a maximum value of 1.2 cal/cm3‐sec at 1100°C, was nowhere negative, and was finite over a zone about 2 cm th...

Flame Structure Studies. III. Gas Sampling in a Low‐Pressure Propane‐Air Flame

A previous investigation of this series showed that the temperature in a very lean, low‐pressure propaneair flame continues rising for more than a centimeter downstream from the zone of blue luminosity. This suggested a two‐stage combustion process: (I) the hydrocarbon oxidizes rapidly and luminously to carbon monoxide; (II) the carbon monoxide oxidizes more slowly to carbon dioxide. The current gas‐sampling study has provided support for this hypothesis. Both water‐cooled and uncooled probes have been used to obtain gas samples from the region of the flame just beyond the luminous zone. Tests were made to insure that reaction‐quenching in the probe was effective and that flame disturbance was minimized. Gas analyses were performed both mass‐spectrometrically and by a vacuum‐freezing technique. Most of the samples were taken from a flame burning at 46 mm Hg abs pressure, with a mass air‐propane ratio of 30. Substantial proportions of CO, and about 15 as much H2, were found as much as a centimeter downstre...

A Theoretical Model of a Gaseous Combustion Wave Governed by a First‐Order Reaction

Numerical solutions are obtained for differential equations describing a hypothetical model of a laminar flame. A first‐order irreversible reaction with approximately exponential dependence of rate upon temperature is assumed, with interdiffusion of reactant and product molecules. The temperature dependence of thermal conductivity, diffusion coefficient, and gas density is taken into account. When the equations are in suitable form, the dimensionless burning velocity is an eigenvalue whose magnitude depends on two dimensionless parameters; e (the ratio of activation energy to burned gas temperature) and α (the ratio of heat flow to diffusional flow). An I.B.M. Card‐Programmed Electronic Calculator was used to obtain solutions accurate to two percent, for a wide range of values of e and α. Interdiffusion is found to reduce the burning velocity, the effect being more pronounced when e is large. The results for α equal to unity are compared with the approximate burning‐velocity equation of Zeldovich and Fran...