Numerical Simulation On Hydrogen-blended High Octanenumber Fuel Premixed Laminar Flame Characteristics

Three hydrogen-blended fuel premixed laminar flame models were built throughcombining the premixed laminar flame and chemical kinetic theories, which werehydrogen-blended methanol, ethanol and PRF(primary reference fuel) premixedlaminar flame models, respectively. In terms of hydrogen-blended methanol premixedlaminar flame model, C1mechanism was used to calculate hydrogen and methanollaminar flame speeds under specified conditions, respectively. And the calculatedlaminar flame speeds were compared with experimental ones. In this way, thehydrogen-blended methanol premixed laminar flame model was validated. As forhydrogen-blended ethanol premixed laminar flame model, the ethanol methanismcombined with NOx reaction mechanism was used to calculate ethanol-hydrogen-airmixture premixed laminar flame speeds at equivalence ratios of0.8,1.0and1.2. Thecalculated flame speeds at different hydrogen blending fractions were compared withthe experimental ones in present literatures. It showed that the model used in thisstudy could reflect ethanol-hydrogen-air premixed laminr flame speed variation atdifferent hydrogen blending fractions. As for hydrogen-blended PRF premixedlaminar flame model, the reduced PRF mechanism for high temperatures was updatedwith H2sub-mechanism. The experimental and empirical equation data were bothused to validate PRF-hydrogen-air premixed laminar flame model. In detail, thehydrogen-iso-octane-air premixed laminar flame speed measured in experiments wascompared with the calculated one in model, with the error lower than10%. Besides,the PRF-hydrogen-air premixed laminar flame speed calculated by the empiricalequation was5%away from the one calculated by the model.Simulation results show that it is effective to raise methanol, ethanol and PRFfuel laminar flame speeds by hydrogen blending at the same initial temperature,pressure and equivalence ratio. Moreover, the dominant reaction influencing laminarflame speed changes. Apart from that, as hydrogen blending mole and energyfractions increase, the main reactant hydrogen’s role changes from the intermediate toreactant; main intermediate H, O and OH radical mole fractions rise up; mainproducts CO and CO2mole fractions fall down, and H2O mole fraction goes up. Someconclusions on hydrogen-blended high-octane fuel premixed flames are revealedbelow: CH2OH and CH3O are consumed faster after hydrogen blending in methanol-hydrogen-air premixed laminar flame; C2H4as soot precursor descendsremarkably while hydrogen enrichment mole fraction ascends at equivalence ratios of0.8,1.0and1.2in ethanol-hydrogen-air premixed laminar flames; CH3CHO asaldehyde precursor declines heavily as well, especially at equivalence ratio of0.8inethanol-hydrogen-air premixed laminar flame; In the PRF-hydrogen-air premixedlaminar flame, C7H16and C8H18decompose firstly through dehydrogenation reactionswith H, O and OH radical, whose concentrations are increased, thus promote thedecomposition of C7H16and C8H18.