Kinetic study of the effects of hydrogen blending to toluene reference fuel (TRF)/air mixtures on laminar burning velocity and flame structure

Because of its high reactivity, rapid flame speed, and low ignition energy, hydrogen is an excellent additive in gasoline to improve the combustion performance and reduce pollutant formation. In this study, we conducted a numerical study of the effect of hydrogen blending into TRF (toluene/iso-octane/n-heptane)/air mixtures on laminar burning velocity and flame structure at the initial pressure of 1 bar, initial temperature of 453 K, equivalence ratio of 0.8–1.4 and hydrogen addition ratio range from 0% to 50%. The adiabatic flame temperature increases slightly and the thermal diffusion coefficient increases significantly with hydrogen addition. The peak values of H + OH + O mole fractions are correlated nearly linearly with the laminar burning velocity, indicating a direct correlation relationship between the peak mole fraction of H + OH + O and the laminar burning velocity. The increase of reaction rate of R361 (H + O₂ = O + OH) is one of the main reasons for the enhanced laminar burning velocity due to hydrogen addition. The rate-of-production analysis of fuel shows that hydrogen promotes the consumption of hydrocarbons. The thermal/dilution and chemical effects of hydrogen addition were numerically quantified. The chemical effect is the dominant effect on laminar burning velocity. In the last part of the study, we separated the thermal, chemical and dilution effects of hydrogen addition and the results demonstrate that the relative importance of these effects follow the order of chemical > dilution > thermal under the conditions of our study.