Ignition by moving hot spheres in H_2-O_2-N_2 environments
A combined experimental and numerical study was carried out to investigate thermal ignition by millimeter size (d=6 mm) moving hot spheres in H_2-O_2-N_2 environments over a range of equivalence ratios. The mixtures investigated were diluted with N_2 to keep their laminar flame speed constant and comparable to the sphere fall velocity (2.4 m/s) at time of contact with the reactive mixture. The ignition thresholds (and confidence intervals) were found by applying a logistic regression to the data and were observed to increase from lean (Φ=0.39; T_(sphere) = 963 K) to rich (Φ=1.35; T_(sphere) = 1007 K) conditions. Experimental temperature fields of the gas surrounding the hot sphere during an ignition event were, for the first time, extracted using interferometry and compared against simulated fields. Numerical predictions of the ignition thresholds were within 2% of the experimental values and captured the experimentally observed increasing trend between lean and rich conditions. The effect of stoichiometry and dilution on the observed variation in ignition threshold was explained using 0-D constant pressure delay time computations.
© 2018 The Combustion Institute. Published by Elsevier Inc. Received 30 November 2017, Revised 3 July 2018, Accepted 6 July 2018, Available online 30 July 2018. Special thanks to Stephanie Coronel for her development of the interferometry processing software and the experimental apparatus, and to Lorenz Boeck for his design of the gate valve. Research carried out in the Explosion Dynamics Laboratory and supported by The Boeing Company (CT-BA-GTA-1). This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562.
Accepted Version - h2o2n2_ign_preprint.pdf
Supplemental Material - 1-s2.0-S1540748918304644-mmc1.pdf