Global Turbulent Consumption Speeds (ST,GC) Of H2/CO Blends

Abstract

This paper describes measurements of the global turbulent consumption speed, ST,GC, of atmospheric pressure H2/CO flames at mean flow velocities and turbulence intensities up to U = 50 m/s and u′/SL = 100, respectively. The particular emphasis of the paper is to characterize H2/CO mixture properties upon turbulent flame speeds — a number of prior studies have noted that different fuels, with the same laminar flame speed and combusted in the same turbulent flow, can have widely different turbulent flame speeds. This effect is believed to be due to flame speed sensitivities to stretch and possibly thermo-diffusive instabilities. While this effect is widely known, little data are available for syngas blends. Turbulent flame speeds were obtained with blends ranging from 30–90% H2, with the mixture equivalence ratio, φ, adjusted at each fuel composition to have nominally the same laminar flame speed, SL. In addition, equivalence ratio sweeps at constant H2 level were also performed. The data clearly corroborate results from other studies that show significant sensitivity of ST,GC to fuel composition. In particular, at a fixed u′ and SL, values of ST,GC increase by almost a factor of 1.5–2 when H2 levels are increased from 30% (at φ = 0.59) to 90% (at φ = 0.46). Moreover, ST,GC in the 90% H2 case is 3 times larger than the φ = 0.9 CH4/air mixture with the same SL value. An important conclusion from this work is that fuel effects on ST,GC highlighted above are not simply a low turbulence intensity phenomenon — they clearly persist over the entire range of turbulence intensities used in the measurements.