Numerical Study on the Effect of CH_4 Addition to H_2 Flames Flashback

摘要

Swirl flame stabilization of lean premixed fuels is one of the most important technologies used in gas turbine combustors. It gives considerable benefits in terms of flame stabilization and NO_x pollutant emissions reduction. However, there are still problems that can occur during the combustion process including those related to flashback especially with hydrogen enriched fuels. Pure hydrogen or hydrogen enriched fuels give rise to especial problems owing to the high flame speed of hydrogen, potential for flashback in conventional or simply modified combustors and often requirement for multi fuel operation. CFD modeling is thus used to simulate the combustion of H_2/CH_4 hybrid fuel. Flashback limits were defined and determined for H_2/CH_4 blends ranging from 0% (pure methane) up to 100% (pure hydrogen) based on the volumetric composition at atmospheric pressure and 300K for various equivalence ratios. The results show that the use of up to 50% blends - by volume - of methane and hydrogen causes fewer problems with flame stability and flashback compared with the use of pure hydrogen. The flashback study is extended to investigate the effect of operating pressure and premixed gases initial temperature on flashback. The stability limits of methane-dominated combustion (up to 50% blends of methane and hydrogen) is extensively studies at different pressures and temperatures to show the effect of the combustion conditions on H_2/CH_4 blends flame stability. It was found that the stability limits depend on the pressure and raw mixture temperature.