Study of turbulent flame characteristics of water vapor diluted hydrogen-air micro-mixing combustion

Hydrogen has been regarded as an important alternative fuel, especially in gas turbine applications. However, the premixed combustion of pure hydrogen has problems such as easily flashback and high NO_x emissions. A more reasonable method of combustion is to use micro-mixing technology combined with water vapor dilution. This work experimentally investigated the influences of dilution rate (D) and equivalence ratio (φ) on the flame characteristics of hydrogen-air micro-mixing combustion diluted with water vapor. Results show that increasing D reduces the flame area by reducing the downstream OH radical signal, which is contrary to the effect of CO₂ dilution. The flame local curvature radius shows that the micro-mixing combustion is a high turbulence intensity combustion, and the convex structure is more frequent. Moreover, increasing φ or decreasing D leads to a decrease in the instantaneous average curvature radius (R_ave), indicating more small-scale wrinkle structures are generated. D and φ have a similar influence on the fluctuations of R_ave and flame area in the time domain, while the fluctuation of the flame area is more evident near the lean-burn limit. When D = 25%, the frequency characteristics of the flame structure and chemical reactions are synchronized.