The impact of H2 2-enrichment on flame structure and combustion characteristic properties of premixed hydrocarbon-air flames

The addition of hydrogen to fossil fuels has a great impact on their combustion, changing the characteristic parameters of flame ignition and propagation. Thus, hydrogen addition to hydrocarbon-air gaseous mixtures results in an increase in the laminar burning velocity as well as in an increase in the radical pool, accounting for an increase in the reaction rate of the more slowly combusting hydrocarbons. The present paper studies this effect on propane-air combustion under various initial conditions. It reports the laminar burning velocities (LBVs) of hydrogen-blended propane-air mixtures with various hydrogen/fuel mixing ratios (rH r H = 0...0.3) ... 0.3) obtained from p ( t ) records registered during explosions in a spherical vessel with central ignition at various initial pressures between 0.3 and 1.0 bar. The kinetic modelling of flame propagation under adiabatic conditions delivered the LBVs for these mixtures and for the other two hydrogen-blended fuel-air mixtures (fuels: methane and n-heptane). The LBVs of these ternary mixtures are discussed in correlation with the rates of heat release and with the concentrations of the most abundant radical species in the flame front. Hydrogen addition to fuel-air mixtures determined the increase in H, O, and OH mass fractions and of the rate of heat release in the flame front, resulting in the enhancement of laminar burning velocities. Sensitivity analyses in respect to LBVs revealed the most important elementary reactions for each examined system.