Abstract
In order to investigate H2 rich blowout limit at different blockage ratios and flow velocities, a CFD software FLUENT was used to simulate H2 burning flow field in bluff‐body burner, and the software CHEMKIN was adopted to analyze the sensitivity of each elementary reaction. Composition Probability Density Function (C‐PDF) model was adopted to simulate H2 combustion field in turbulence flame. The numerical results show that reactions R2 and R9 possess the largest positive and negative temperature sensitivity. Temperature has a very important influence on these two reactions. When equivalence ratio is 1, the mixture is most ignitable, and the critical ignition temperature is 1550 K. There should be an optimal blockage ratio which can stabilize the flame best. When the blockage ratio remains unchanged, the relationship between H2 RBL and flow velocity is a logarithmic function. When the flow velocity remains unchanged, the relationship between H2 RBL and blockage ratio is a parabolic function. A complete extinction requires three phases: the temperature sudden decline in the main stream, the energy dissipation from the recirculation zone to the main stream, and the complete extinction of the flame.
Highlights
Bluff-body stabilized combustion with triangular or cone stabilizers is common in afterburners of military aircraft
Wright 4 performed lots of experiments to define the influence of blockage on flame stabilization by bluff-bodies in ducted flow
Bisetti and Chen 14 adopted Join-PDF/LES approach to research Sandia Flame D, and their result showed that the prediction by EMST is quite accurate near stoichiometric, but overall trend remains unpredicted at other conditions
Summary
Bluff-body stabilized combustion with triangular or cone stabilizers is common in afterburners of military aircraft. Wright 4 performed lots of experiments to define the influence of blockage on flame stabilization by bluff-bodies in ducted flow. His experiments indicated that the length of the recirculation zone varies inversely as the square root of the blockage and the flow speed past the wake increases almost linearly with blockage. Eriksson 2 investigated Zimont Turbulent Flame Closure Model TFC in conjunction with different turbulent models in simulating premixed bluff-body stabilized flame He found that the TFC model combined with k − ω model accurately captures the recirculation zone length and overall turbulent flame speed, the combined effect is not captured well in steady state RANS. The aim of the present work is to study the influence of flow velocity and blockage ratio on H2 Rich Blowout Limit RBL and summarize a formula for H2 RBL
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