Effect Of Hydrogen Addition On Laminar Combustion Characteristics Of Ethanol-Air Mixture

China’s 14th Five-Year Plan points out the need to accelerate the green transformation of development methods,with special emphasis on vigorously developing a green economy and resolutely curbing the blind development of high energy-consuming and high-emission projects.Due to the shortage of fossil resources such as oil in China and the pollution problems caused by the burning of fossil energy,the National 14th Five-Year Plan strongly supports the development of new energy vehicles,and the most important of these is to find green and clean energy sources that can be replaced.Bioethanol is a renewable,green and clean energy source,but the ignition limit of bioethanol is not low enough,making it difficult to ignite and cold start pure ethanol engines.Researchers at home and abroad have found that a small amount of hydrogen can be blended into an internal combustion engine to give the fuel mix better burning characteristics.Since hydrogen is a clean energy source and China’s 14th Five-Year Plan states that the economics of hydrogen fuel production,storage and transportation should be improved and hydrogen refuelling infrastructure should be promoted,this thesis blends a certain amount of hydrogen into ethanol as a way to improve the burning characteristics of bioethanol.In order to make more efficient use of the ethanol-hydrogen fuel mixture,experimental and numerical simulations of the laminar flow burning characteristics of the ethanol-hydrogen mixture are carried out in this thesis.The main research elements are as follows:The laminar burning characteristics of ethanol-hydrogen gas mixtures containing 0%,10%,30%,50%,70%and 90%hydrogen at an initial temperature of 400 K and an initial pressure of 0.1 MPa were first investigated experimentally in a constant volume combustion chamber with an equivalence ratio of0.7-1.4.A new image processing method has been developed which combines the advantages of Laplace and sobel operators and uses a hybrid spatial enhancement method for the accurate extraction of flame contours from the images.Secondly,the experimentally obtained flame shadow images,flame radius,unstretched flame propagation velocity,laminar burning velocity,Markstein length,flame thickness and internal pressure of the capacitor bomb were investigated in depth.The results show that the addition of hydrogen can increase the laminar burning velocity of ethanol under the same initial conditions,especially in the hydrogen-rich state than in the hydrogen-poor state;with the increase of the equivalent ratio,the maximum laminar burning velocity of ethanol-hydrogen mixture with different hydrogen content appears between 1.2 and 1.3 of the equivalent ratio,with the increase of the hydrogen content,the velocity peak tends to move towards the high equivalent ratio;in the In the hydrogen-poor state,the Markstein length decreases with increasing equivalence ratio,while in the hydrogen-rich case,it shows the opposite characteristics;at a certain hydrogen content,the flame thickness first decreases and then increases with increasing equivalence ratio,and reaches a minimum around equivalence ratio 1.2;in addition,the addition of hydrogen can also reduce the dilute combustion limit of ethanol.Finally,based on the experiments,the chemical reaction mechanism of the ethanol-hydrogen mixture was collated and optimised based on the oxidation mechanism of ethanol proposed by Marinov and the hydrogen-oxygen reaction mechanism proposed by GRI-Mech 3.0,and the combustion process of the ethanol-hydrogen mixture was simulated.The laminar combustion rate,adiabatic flame temperature,temperature sensitivity and H,O and OH radical concentrations of the fuel mixture were also analysed.The results show that:the simulation model can predict the laminar combustion rate well;the adiabatic flame temperature of the mixture with different hydrogen contents increases and then decreases with the increase of the equivalence ratio,and reaches the maximum at the equivalence ratio of 1.1;the temperature sensitivity analysis of the ethanol-hydrogen mixture reveals that the radical reaction H+O₂=O+OH（R1）has the greatest promotion effect on the fuel combustion The laminar combustion rate of the mixture was found to increase with the increase of hydrogen content in the mixture and the higher the molar fraction of H,O and OH radicals produced;it was found that the trend of the maximum molar fraction of H,O and OH radicals with the equivalence ratio directly influenced the trend of the laminar combustion rate of the mixture with the equivalence ratio.