Pressure and fuel effects on turbulent consumption speeds of H2/CO blends

This paper describes measurements and correlations of turbulent consumption speeds, S-T,S-GC, of hydrogen/carbon monoxide (H-2/CO) fuel mixtures over a range of conditions. This work is set within the broader context of understanding the sensitivity of the turbulent flame speed to chemical kinetic and diffusive properties of the reactive mixture. Turbulent consumption speed data were obtained at mean flow velocities, turbulence intensities (u'(rms)/S-L,S-0), equivalence ratios and pressures ranging from 4-50 m/s, 5-45, 0.5-0.8, and 1-10 atm, respectively. Experiments were conducted where the mixture equivalence ratio, phi, was adjusted at each fuel composition to have nominally the same calculated un-stretched laminar flame speed, S-L,S-0. Consistent with prior studies, these data show both fuel composition and pressure effects on the turbulent flame speed. For example, measured S-T,S-GC values of the 90/10 H-2/CO are about 3 times larger than CH4 blends having the same S-L,S-0, turbulence intensity, and operating conditions. Similarly, the 5 atm data have S-T,S-GC values that are consistently about 1.8 times larger than the 1 atm data, at identical conditions and fuel compositions. These data are correlated with a scaling law derived from quasi-steady leading points concepts using detailed kinetics calculations of highly stretched flames. For a given pressure, these scalings do an excellent job in scaling data obtained across the H-2/CO fuel composition and equivalence ratio range. However, the pressure sensitivities are not captured by this scaling, which may be more fundamentally a reflection of the non-quasi-steady nature of the flame leading points. In support of this argument, we show that the spread in the data can largely be correlated with the ratio of a leading point chemical time scale to a flow time scale. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.