Measurements and analysis of turbulent consumption speeds of H2/CO mixtures

This paper describes measurements of global turbulent consumption speeds, ST,GC, of hydrogen/carbon monoxide (H2/CO) mixtures. The turbulent flame properties of such mixtures are of fundamental interest because of their strong stretch sensitivity, and of practical interest since they are the primary constituents of syngas fuels. Data are reported at mean flow velocities and turbulence intensities of 4 < U0 < 50 m/s and 1 < u rms ′ / S L , 0 < 100 , respectively, for H2/CO blends ranging from 30% to 90% H2 by volume. Two sets of experiments are reported. In the first, fuel blends ranging from 30% to 90% H2 and mixture equivalence ratio, ϕ, were adjusted at each fuel composition to have nominally the same un-stretched laminar flame speed, SL,0. In the second set, equivalence ratios were varied at constant H2 levels. The data clearly corroborate results from other studies that show significant sensitivity of ST,GC to fuel composition. In particular, at a fixed u rms ′ and SL,0, values of ST,GC increase by a factor of almost 2 when H2 levels are increased from 30% (at ϕ = 0.61) to 90% (at ϕ = 0.48). Moreover, ST,GC in the 90% H2 case is three times larger than the ϕ = 0.9 CH4/air mixture with the same SL,0 value. An important conclusion from this work is these fuel effects are not simply a low turbulence intensity phenomenon – they clearly persist over the entire range of turbulence intensities used in the measurements. We also describe physics-based correlations of these data, using leading points concepts and detailed kinetic calculations of the stretch sensitivity of these mixtures. These results are used to develop an inequality for negative Markstein length flames that bounds the turbulent flame speed data and show that the data can be collapsed using the maximum stretched laminar flame speed, SL,max, rather than SL,0.