Elementary reaction models and correlations for burning velocities of multicomponent organic fuel mixtures

This computational study uses elementary reaction mechanisms to interpret the trends in a database of burning velocities for multicomponent organic fuel mixtures derived from coal. These mixtures contain CO, H2, CH4, C2H2, oils, and, in some cases, appreciable amounts of C2H4, C2H6, C3H6, and C3H8. The database represents fuel equivalence ratios from 0.5 to 1.5, two unburned gas temperatures, and two diluent: O2 ratios. Predicted burning velocities are based on a one-dimensional laminar flame code with the Miller-Bowman mehanism without nitrogen conversion chemistry or oxidative pyrolysis of any higher hydrocarbons. The initial amounts of oils and higher hydrocarbons are expressed as additional amounts of C2H4 and C2H6 and reduced levels of H2. Burning velocities of multicomponent fuel mixtures at high temperatures can be interpreted with only oxyhydrogen and C1/C2 chemistry without any fuel decomposition steps for the higher hydrocarbons. This approach rationalizes the trends due to higher extents of secondary volatiles pyrolysis, which means increasing CO and H2 levels and diminishing hydrocarbon levels in the fuel mixtures. It also rationalizes the variations with coals of higher rank, which means diminishing CO levels and H2 and hydrocarbon levels that pass through maxima. Predictions from the elementary reaction mechanism are quantiatively accurate for nearly all lean mixtures, but discrepancies are substantial for rich mixtures, especially those with abundant CO and H2. Systematic overpredictions for rich mixtures are probably due to defects in steps for the attack of C1 or C2 species by O2 or H atoms.