The Influence of the Temperature on Extinction and Ignition Limits of Strained Hydrogen-Air Diffusion Flames

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Abstract
Structures, extinction and ignition limits of strained diffusion flames are examined. The influence of the oxidizer stream temperature is specifically considered. Calculations are performed for diffusion flames formed by a counterflow of diluted hydrogen and air. The air temperature differs from the hydrogen temperature. The reactive flow equations are solved numerically by employing Newton iterations and adaptive continuation techniques. The model includes detailed transport and complex kinetics. Flame structures, extinction and ignition limits and characteristic flame response curves are determined for different values of the fuel-air ratio and for a set of air stream temperatures. It is shown that this last parameter strongly affects the conditions producing extinction. For an air stream temperature of 100OK, the critical extinction strain rate is ten times that found for an air stream at room temperature It is also found that a temperature exists beyond which combustion always takes place whatever the strain rate. These observations have important implications in turbulent combustion modeling and in the analysis of supersonic combustion.