A computational study of hydrogen substitution effects on the combustion performance for a micro gas turbine

The effects of hydrogen substitution on methane/air combustion in a micro gas turbine were studied in this work. The combustion performance and emission characteristics of a can type combustor were investigated with model simulations using the commercial code STAR-CD, in which the three-dimension compressible k-? turbuent fow mode and presumed probability density function for chemical reaction between methane/hydrogen/air mixtures were used. With hydrogen being the substituent, not a supplement to methane, the detailed flame structures, distributions of flame temperature and flow velocity, and gas emissions were presented and compared by using a fraction of hydrogen to substitute methane in the combustor. For the scenarios from pure methane to pure hydrogen, results show the flame temperature and exit gas temperature increase when only 10% methane is substituted. But as hydrogen substitution percentage increases, the flame temperature and exit gas temperature decrease because of a power shortage caused by lower mass flow rate and heating value of the resulting blended fuels, although the pattern factor drops drastically compared to that of pure methane. As the fuel inlet velocity decreases from 100 m/s to 20 m/s, the high temperature region shifts to the side of the combustor due to the high diffusivity of hydrogen. Increasing hydrogen substitution percentage at a fixed fuel injection velocity reduces NO_x emission due to lower flame temperature, but CO emissions increase continually with increasing hydrogen substitution percentage because oxygen depletion for methane/air combustion. Before hydrogen blended fuels or pure hydrogen are used as an alternative fuel for the micro gas turbine, further experimental testing are needed as the CFD modeling results provide a guidance for the improved designs of the combustor.