Numerical Investigation On Flame Characteristics Of CH₄ And CO Mixed Fuel Including Hydrogen Under O₂/H₂O Conditions

Because of the serious environmental problems caused by fossil fuel combustion,the development of new combustion technology with high efficiency,low emission and clean fuel has become a hot topic.O₂/H₂O combustion has a bright prospect for low operation cost and NOx emissions.But so far the related researches have been mainly focused on single fuel such as coal or hydrocarbons.In addition,as the clean energy,hydrogen has a unique advantage in reducing CO₂ emissions.This paper studies the combustion charactersistics of methane/hydrogen and carbon monoxide/hydrogen O₂/H₂O combustion numerically,and mainly discusses the effects of the addition of hydrogen and the chemical properties of H₂O on combustion characteristics.First,this paper studies the effects of H₂ addition on the mole fraction profiles and NO emission in methane/hydrogen O₂/H₂O combustion.The results show,the addition of hydrogen promotes the ignition and combustion,NO emissions are also reduced.In addition,the importance of thermal,prompt,NNH and N₂O NO also changes.Next,this paper discusses the heat release rate from three aspects:the equivalence ratio,the H₂addition and the chemical properties of H₂O,which is important in the combustion process.The results reveal,the heat release rate is the maximum when the equivalence ratio is 1.0,and the heat release increases obviously with the addition of hydrogen.The chemical effects of H₂O are different in different temperature regions.In low temperature region H₂O inhibits the production of H radical,which causes the decrease of heat release,while in high temperature H₂O promotes the enhancement of the third-body reaction and OH radicals,conversely causes the increase of heat release.Last,this paper studies the effects of chemical properties of H₂O on the combustion characterisitcs in carbon monoxide/hydrogen O₂/H₂O combustion.The results suggest,the H₂O effects have great differences in the two kinds of fuels.When the hydrogen is in low concentration,chemical properties of H₂O promote the flame propagation and heat release,while in high concentration the properties inhibit the flame propagation and promote the heat release.In addition,in carbon monoxide/hydrogen flame,the paths of NO formation have thermal NO,NNH NO and N₂O NO.In the low hydrogen combustion,the chemical properties of H₂O increase the conversion ratio of thermal NO,N₂O?NO,NH?HNO,and reduce the conversion ratio of NNH NO,N₂O NO,N₂?NNH,NNH?NO,NH?NO,NH?N.The addition of hydrogen reduces the conversion ratio of thermal NO,increase the conversion ratio of NNH NO,N₂O NO.What's more,the chemical effects of H₂O in high hydrogen flame enhance the conversion ratio of N₂O NO,which is different from low hydrogen flame.