Features of low-temperature oxidation of hydrogen in the medium of nitrogen, carbon dioxide, and water vapor at elevated pressures

The article discusses novel research results on combustion features of high-density H-2/O-2 mixtures (p(H2) = 0.70-1.89 mol/dm(3), P-O2 = 0.32-0.81 mol/dm(3)) diluted with nitrogen, carbon dioxide, or water vapor (from 46 to 76% mol.) at the uniform heating (1 K/min) of tubular reactor. Based on time dependencies of temperature increment in the reaction mixtures caused by the heat release during oxidation of H-2, it is found that the self-ignition temperature of H-2/O-2/N-2 and H-2/O-2/H2O mixtures is by = 30 K lower than that of the H-2/O-2/CO2 mixture. Unlike combustion of H-2 in the N-2 medium, in the CO2 and H2O media a chain thermal explosion is observed at a certain concentration of reagents. The influencing mechanisms of diluents on the H-2 oxidation dynamics, as well as the contribution of homogeneous and heterogeneous reactions in the heat release are revealed. It is established that high heat capacity of H-2/O-2/CO2 mixture, chemical interaction between its components, and presence of CO2 molecules adsorbed on the reactor inner surface, are the factors determining the H-2 oxidation dynamics in CO2 medium. At oxidation of H-2 in the H2O medium, the process takes place against the background of water evaporation and, as a consequence, is characterized by increased heat capacity and thermal conductivity of the H-2/O-2/H2O reaction mixture. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.