Research On Laminar-premixed Combustion Characteristics Of75%Hydrous Ethanol-hydrogen Mixtures

Ethanol is one of clean alternative fuels, and much attention has been paid to it. Whenengines are fuelled with hydrous ethanol instead of pure ethanol, the energy needed fordistillation in the production process of ethanol can be considerably saved, and NOxemissionsfrom engines are also reduced. If a certain amount of hydrogen is added into hydrous ethanol, thecombustion performance of hydrous ethanol can be improved.In this dissertation, the premixed laminar combustion characteristics of75%hydrousethanol–hydrogen–air mixtures were numerically investigated by employing CHEMKIN, asoftware for analyzing gas-phase chemical kinetics. In the study, a detailed oxidation mechanismfor ethanol was selected for the modeling. The selected equivalence ratio range covers from0.6to1.6. The initial pressure range selected is0.1–0.6MPa. The initial temperatures of343K,383K,423K are selected. The hydrogen content ranges from0%to80%. Through the numericalsimulation the influences of equivalence ratio, initial temperature, pressure and hydrogenaddition on laminar burning velocity of75%hydrous ethanol–hydrogen–air mixtures wereanalyzed. The sensitivity of laminar burning velocity to elementary reactions was also conducted.The flame structures in the simulated one-dimensional planar flames and the production ofradical species were deeply investigated.The main conclusions are as follows:(1) The laminar burning velocity of75%hydrous ethanol–hydrogen–air mixtures firstincreases and then decreases with the increasing equivalence ratio. When elevating the initialpressure, the laminar burning velocity will decrease. However, when increasing the initialtemperature and the hydrogen content, the laminar burning velocity will increase.(2) In the oxidation process of75%hydrous ethanol–hydrogen mixtures, the laminarburning velocity is relatively insensitive to the elementary reactions related to ethanol. However,there is a significant influence of the elementary reactions involving radicals H, OH and O. Theelementary reaction H+O2<=>O+OH has the most significant effect on the laminar burningvelocity. When elevating the initial pressure and the mole fraction of hydrogen addition, thepeaks of net reaction rates for main elementary reactions will increase remarkably. The initialtemperature has a marginal effect on the peaks of net reaction rates for these elementaryreactions.(3) In the simulated one-dimensional planar flames, the final mole fractions of H2O andCO2and the final flame temperature weakly increase with increasing temperature and pressure, while the final mole fraction of CO has a slight decrease. When elevating the hydrogen addition,the final flame temperature remains approximately unchanged, but the final mole fraction of H2Oincreases remarkably. At the same time, the final mole fraction of CO2decreases.(4) In the oxidation process of75%hydrous ethanol–hydrogen mixtures, ethanol is mainlyconsumed via dehydrogenation reaction. The production amounts of the main radicals H, OHand H first increase and then decrease with the increasing equivalence ratio, and reach theirpeaks at equivalence ratio of about1.1. When increasing the initial pressure, the production ofthe main radical species is inhibited. However, an opposite trend is observed when elevating theinitial temperature and the hydrogen content.