Further study on the ignition delay times of propane-hydrogen-oxygen-argon mixtures: Effect of equivalence ratio

Using a shock tube facility, measurements on ignition delay times of propane/hydrogen mixtures (hydrogen fraction X-H2 is from 0% to 100%) were conducted at equivalence ratios of 0.5, 1.0 and 2.0. Results show that when X-H2 is less than 70%, ignition delay time shows a strong Arrhenius temperature dependence, and the ignition delay time increases with the increase of equivalence ratio. When X-H2 is larger than 95%, the ignition delay times do not retain an Arrhenius-like temperature dependence, and the effect of equivalence ratio is very weak when the hydrogen fraction is further increased. Numerical studies were made using two selected kinetic mechanisms and the results show that the predicted ignition delay times give a reasonable agreement with the measurements under all test conditions. Both measurements and predictions show that for mixtures with X-H2 less than 70%, the ignition delay time is only moderately decreased with the increase of X-H2, indicating that hydrogen addition has a weak effect on the ignition enhancement. Sensitivity analysis reveals the key reactions that control the simulation of ignition delay time. Further investigation of the H-atom consumption is made to interpret the ignition delay time dependence on equivalence ratio and X-H2. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.