COMBUSTION CHARACTERISTICS AND HYDROGEN ADDITION EFFECTS ON THE PERFORMANCE OF A CAN COMBUSTOR FOR A MICRO GAS TURBINE

To better understand the combustion performance by using hydrogen/methane blended fuels for an innovative micro gas turbine which is designed originally as a natural gas fired engine, the combustion characteristics of a can type combustor has been modeled and the effects of hydrogen amount were investigated. The simulations were performed using the commercial code STAR-CD, in which the three-dimension compressible k-epsilon turbulent flow model and presumed probability density function for chemical reaction between methane/hydrogen/air mixtures were used. The results showed the detailed flame structures including the flow fields, distributions of flame temperature, major species and gas emissions. A variable volumetric fraction of hydrogen from 0% to 80% and the fuel injection velocities of this blended fuel ranging from 20 m/s to 60 m/s were studied. When hydrogen amount is higher, the flame temperature and exit gas temperature increase; high temperature region becomes wider and shifts to the intermediate zone. As fuel inlet velocity decreases from 60 m/s to 20 m/s, the high temperature region shifts to the side of the combustor due to the high diffusivity of hydrogen. Compared to the combustion using pure methane, NOx emissions increase with blended fuel, but the increase of hydrogen amount does not produce any significant effect over emission level of NOx. However, CO emission reduction is more remarkable at low hydrogen fraction, but the level of CO emission increases drastically when the fuel injection velocity is lower. Further modifications of the combustor designs including the fuel injection and cooling strategies are needed to improve the combustion performance for the micro gas turbine engine with hydrogen blended fuel as an alternative.