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

Abstract

The article discusses novel research results on combustion features of high-density Н2/О2 mixtures (ρH2 = 0.70–1.89 mol/dm3, ρO2 = 0.32–0.81 mol/dm3) 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 H2, it is found that the self-ignition temperature of Н2/О2/N2 and Н2/О2/H2O mixtures is by ≈ 30 K lower than that of the Н2/О2/СО2 mixture. Unlike combustion of H2 in the N2 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 H2 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 H2/O2/CO2 mixture, chemical interaction between its components, and presence of CO2 molecules adsorbed on the reactor inner surface, are the factors determining the H2 oxidation dynamics in CO2 medium. At oxidation of H2 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 H2/O2/H2O reaction mixture.