The reactivity of hydrogen enriched turbulent flames

Abstract

The use of hydrogen enriched fuel blends, e.g. syngas, offers great potential in the decarbonisation of gas turbine technologies by substitution and expansion of the lean operating limit. Studies assessing explosion risks or laminar flame properties of such fuels are common. However, there is a lack of experimental data that quantifies the impact of hydrogen addition on turbulent flame parameters including burning velocities and scalar fluxes. Such properties are here determined for aerodynamically stabilised flames in a back-to-burnt opposed jet configuration featuring fractal grid generated multi-scale turbulence (Ret=314±19) using binary H2/CH4 and H2/CO fuel blends. The binary H2/CH4 fuel blend is varied from α=XH2/(XH2+XF)= 0.0, 0.2 and 0.4–1.0, in steps on 0.1, and the binary H2/CO fuel blend from α=0.3−1.0 also in steps of 0.1. The equivalence ratio is adjusted between the mixture specific lower limit of local flame extinction and the upper limit of flashback. The flames are characterised using PIV measurements combined with a flame front detection algorithm. The study quantifies the impact of hydrogen enrichment on (i) turbulent burning velocity (ST), (ii) turbulent transport and (iii) the rate of strain acting on flame fronts. Scaling relations (iv) that correlate ST with laminar flame properties are evaluated and (v) flow field data that permits validation of computational models is provided. It is shown that CH4 results in a stronger inhibiting effect on the reaction chemistry of H2 compared to CO, that turbulent transport and burning velocities are strongly correlated with the rate of compressive strain and that scaling relationships can provide reasonable agreement with experiments.