Abstract
An ultra lean mixture (empty set <= 0.5) of methane-hydrogen-air was experimentally investigated to explore the effect of fuel flexibility on the flame stability and emission of a non-premixed swirl stabilized combustor. In order to isolate the effect of hydrogen addition to methane, experiments were carried out at fixed fuel energy input to the combustor while increasing the hydrogen content from 0% up to 50% in the methane-hydrogen mixture on volume basis. The combustor fuel energy was then increased up to the range of typical gas turbine combustors. Equivalence ratio sweep was carried out to determine the lean stability limit of the combustor. Results show that the hydrogen content in the fuel mixture and fuel energy input have a coupled effect on the combustor lean blow off velocity (LBV), temperature and emissions. The LBV increases by similar to 103% with the addition of 30% H-2. On the other hand, the LBV increases by similar to 20% as the fuel energy increases from 1.83MW/m(3) to 2.75 MW/m(3). Burning under ultra lean condition serves two purposes. (1) The excess air supplied reduces the overall combustor temperature with its ensuing effect on low NOx formation. (2) It increases the overall combustor volume flow rate which reduces the residence time for NOx formation. The axial temperature profile presented along with the emission data can serve as basis for the validation of numerical models. This would give more insight onto the effect of hydrogen on the turbulence level and how it would improve the localized extinction of methane in a cost-effective way.