Shock-tube study of the ignition of methane/ethane/hydrogen mixtures with hydrogen contents from 0% to 100% at different pressures

The ignition delay times of diluted hydrogen/reference gas (92% methane, 8% ethane)/O-2/Ar mixtures with hydrogen contents of 0%, 40%, 80% and 100% were determined in a high-pressure shock tube at equivalence ratios phi = 0.5 and 1.0 (dilution 1:5). The temperature range was 900 K <= T <= 1800 K at pressures of about 1, 4 and 16 bar. The reference gas and the 40% hydrogen/60% reference gas data showed typical characteristics of hydrocarbon systems and can be represented by: tau(ign)/mu s = 10-2.75 +/- 0.13 exp(20,450 +/- 442K/T)(p/bar)(-0.51 +/- 0.02)phi(0.59 +/- 0.06) (reference gas) and tau(ign)/mu s = 10(-2.07 +/- 0.09) exp(16,350 +/- 299K/T)(p/bar)(-0.49 +/- 0.02)phi(0.75 +/- 0.06) (40% H-2/reference gas). The pure hydrogen data exhibit a more complex pressure dependence with the 16 bar values having the slowest ignition delay times at lower temperatures and the fastest ignition delay times at higher temperatures. No dependence on the equivalence ratio was observed. The 80% hydrogen/20% reference gas data display characteristics of hydrocarbon and hydrogen systems. The comparison of the measurements to MPFR-CHEMKIN II simulations with different mechanisms shows that the predictions of all tested mechanisms with the exception of the GRI3.0 agree well with the experimental values for reference gas, 40% hydrogen/60% reference gas and partly for 80% hydrogen/20% reference gas and 100% hydrogen. None of the mechanisms can represent the observed reduction of the activation energy at low temperatures of pure hydrogen and of 80% hydrogen/20% reference gas at p >= 4 bar. The literature mechanisms which were developed for H-2 or for mixtures with a dominating H-2 subsystem cannot predict the observed reduction of the activation energies, either. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.