Prediction of flame blowoff limits for hydrogen-air mixtures over an isolated vee-gutter flameholder using a well-stirred reactor model

The purpose of this research was to begin initial development of an analytical tool to predict flame blowoff limits for hydrogen-air mixtures over vee-gutter flameholders. A specific geometric configuration of an isolated vee-gutter was selected to represent a flameholder test apparatus described in the literature. An analytical tool was developed by treating the recirculation zone behind the vee-gutter as a homogeneous chemical reactor, modeling the recirculation zone as a well-stirred reactor and using LSENS, a chemical kinetics code, to solve the governing equations of the reacting flow. The well-stirred reactor was assumed adiabatic and operated under steady-state conditions. The well-stirred reactor model was applied to premixed, turbulent hydrogen-air mixtures over the vee-gutter configuration. To calibrate the well-stirred reactor model, appropriate values of the recirculation zone volume from existing experimental data for hydrogen-air mixtures at given freestream static pressures were determined. The freestream, blowoff velocities were predicted for static pressures fi-om 1.5 psia to 6 psia and static temperatures from 530 °R to 930 °R.

The blowoff limits predicted by LSENS were compared to existing experimental data on axisymmetrical disks corrected for two-dimensional flameholders at a given pressure. A parametric study of the model predictions was conducted to analyze the effects of pressure, temperature, fuel-air equivalence ratio and Reynolds number on flame stability. Conclusions were drawn regarding the accuracy and potential use of the model. The well-stirred reactor model developed in this study provides a useful preliminary survey of flame blowoff limits for premixed, turbulent hydrogen-air mixtures over the specific geometric configuration.