Surface ignition in a steady-flow apparatus

Abstract

An experimental study is made of the temperature of a hot surface required to ignite ethanol-air mixtures of different fuel-air ratios in steady flow. The mixture at a controlled free-stream velocity, density and temperature flows over a four-inch heated surface in the test section. Temperature of the surface is increased slowly until ignition occurs. The effect on ignition temperature of varying fuelair ratio is determined at velocities of 35 and 50 ft per sec. The free-stream density and temperature were held constant at 0.0575 lhs per cu ft. and 634°R respectively. In addition,the variation of ignition temperature with the parameter V/poL was investigated for the stoichiometric fuel-air ratio. The results reveal that, at a mixture density of 0.0575 lbs per cu ft., the minimum temperature required for ignition remains essentially constant at fuel-air ratios near the stoich-iometric value. For a free- stream velocity of 35 ft per sec,the temperature required is approximately 2l|25°R from 0.73 to 1.65 times the stoichiometric fuel-air ratio. When operating at 50 ft per sec, the temperature required is approximately 2470°R over a smaller range of 0.77 to 1.32 times the stoichiometric fuel-air ratio. In both cases the temperature increases sharply as fuel-air ratios fall below the lower end of the constant range, and gradually increase as they go above the higher end. It is verified that surface temperature required for ignition plotted versus V/poL is a concave downward curve of positive slope. Lower temperatures than previously reported at the same values of V/poL were obtained. The results of these previous studies, where nozzle temperature was maintained at approximately 580°R, were reproduced.