The effect of hydrogen enrichment of methane fuel on flame stability and emissions

The effect of hydrogen enrichment of methane fuel in a premixed flame configuration is studied experimentally. A laboratory scale 30 kW thermal power swirl stabilized atmospheric test rig was built for this purpose. Hydrogen enrichment increases the adiabatic flame temperature and NOx emissions through the Zeldovich (thermal) pathway. On the other hand hydrogen addition extends lean flammability limits of methane considerably. Therefore through lean combustion, since adiabatic flame temperature is reduced, it becomes possible to reduce NOx emissions as an overall effect. Static stability limits are investigated through blowout correlations. For low hydrogen percentages lean blowout data correlates better with the flamelet based reactor loading parameter. With increasing hydrogen content correlation is better with regards to a well reactor model. There is a great mismatch between methane and hydrogen flame speeds. Increasing hydrogen content also poses significant challenges in terms of flame flashback due to increased propagation speeds. Furthermore, it is also concluded that Wobbe index, which is often used as a measure of gaseous fuel interchangeability by the power generation industry, is not an appropriate scaling parameter for methane/hydrogen mixtures. Due to profound changes in flame behavior, a novel design methodology is needed in order to burn hydrogen rich fuels in premixed gas turbine combustors.