Autoignition of H2/CO at Elevated Pressures in a Rapid Compression Machine
Authors: G. Mittal, C. J. Sung, and R. A. Yetter
Direct link to the paper: http://onlinelibrary.wiley.com/doi/10.1002/kin.20180/full DOI: 10.1002/kin.20180
Autoignition of H2/O2 and H2/CO/O2 mixtures has been studied in a rapid compression machine at pressures from 15 to 50 bar, temperatures from 950 to 1100 K, and equivalence ratios from 0.36 to 1.6. In addition, the effect of change in relative concentrations of H2 and CO is investigated by replacing H2 with CO, while keeping the total fuel mole fraction of the combined H2/CO fuel constant. Under the experimental conditions of intermediate temperature and high pressure, reactions involving formation and consumption of HO2 and H2O2 are important. Results show that for H2 autoignition, the mechanism of O’Conaire et al. agrees well with the experimental data, although some improvements can still be made. At all the pressures investigated, replacement of some amount of H2 by CO in a reacting mixture leads to an increase in ignition delay, even with small amounts of CO addition. The inhibition effect of CO addition is also observed to be much more pronounced with increasing pressure. For H2/CO mixtures, the existing mechanisms of Li et al., Davis et al., and GRI-Mech 3.0 fail to describe the experimental trend of ignition delay. At a pressure of 50 bar, ignition delays are seen to decrease monotonically with O2 addition, although such an effect is rather weak. Kinetic analysis further demonstrates that under the present experimental conditions, CO + HO2 = CO2 + OH is the primary reaction responsible for the mismatch of experimental and calculated ignition delays. Significant improvements in the ignition delay predictions can be made by reducing this reaction rate.
Citation: G. Mittal, C. J. Sung, and R. A. Yetter, “Autoignition of H2/CO at Elevated Pressures in a Rapid Compression Machine,” International Journal of Chemical Kinetics 38, 516-529 (2006).