Combustion with humid air is a key process of humid air turbine (HAT) cycle. In the present study, the influence of humid air on gas turbine combustion was studied both experimentally and numerically. Performance of a full-scale can-type combustor equipped with a diffusion burner was investigated when burning propane and syn-gas with various humidity of intake air. The results indicate that the effect of humid air on pollutant emission depends on fuel type due to the difference of chemical mechanisms. For the syn-gas flames, moisture addition can effectively reduce NO emission without increasing CO. A numerical model was developed to simulate the 3D flow field in the combustor when burning syn-gas. The mixture fraction approach and the laminar flamelet model were applied to simulate the diffusion flame. The thermochemical quantities of the flamelets were computed by adopting a detailed chemical reaction mechanism for the H2-CO-N2-O2 system. The numerical results show that an oval hot zone above 2100 K is formed near the axis of the combustor due to flow recirculation. The hot zone mainly accounts for the thermal NO in the syn-gas flames. With the moisture addition into intake air, the volume of this zone is substantially decreased, and, therefore, the NO production is suppressed. This explains the NO reduction due to humid air observed in the experiment.

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