Study On Combustion Characteristics Of Hydrogen Adding On Methane In Micro Space

Micro power system has been widely used in various fields of life,especially in biomedicine,aerospace and other fields.The future development has been closely linked with the development of micro power system.As the core component of micro power system,whether the micro burner can achieve more stable combustion has become the main concern.The micro burner has the advantage of high energy density and has great development prospects.However,due to the influence of heat dissipation,quenching effect and other factors,the flame reaction intensity decreases or even goes out.In order to better promote the stable and efficient operation of micro burners,"super enthalpy"combustion technology and catalytic combustion,hydrogenation and other methods are mainly used to stabilize combustion.In the process of catalytic combustion,the selectivity of catalyst to oxygen affects the fuel reaction"Hydrogenation combustion stabilization"has low requirements for burner structure,simple operation and easy realization.At the same time,it does not need to consider the influence of adding catalyst on small space flow field,which can effectively avoid the influence of catalyst on oxygen selectivity.Therefore,the method of"hydrogenation combustion stabilization"is worthy of in-depth study.So it is necessary to study the heat change,free radical distribution and chemical reaction mechanism in micro space.By building a good experimental platform,it is concluded that with the decrease of spacing,the methane flame will present three states:"stable flame","FREI"and"quenching".After hydrogenation,the range of stable flame increases and the range of quenching decreases,which indicates that adding hydrogen can effectively broaden the combustible range of flame.In the stable flame region,the effects of the distance and excess air coefficient on the methane flame were investigated.With the decrease of the distance,the flame front temperature decreased gradually;At the same spacing,the larger the excess air coefficient is,the higher the flame front temperature is;The temperature decreases slightly after adding hydrogen.The addition of hydrogen will widen the limit of combustion scale and make the flame stable when the distance is 5mm.The flame propagation of"FREI"will experience the process of acceleration first and then deceleration.The period of"FREI"of methane will be smaller and the maximum velocity will be larger with the addition of hydrogen.At the same time,it will reach the peak velocity faster.Based on the numerical simulation of the experimental platform,the experimental phenomena are explained.The spacing is reduced from 15mm to 7mm,and the"surface to volume ratio"are 0.21,0.23,0.26,0.30 and 0.37 respectively.The larger the surface to volume ratio is,the stronger the heat dissipation effect is.Due to the heat loss,it is difficult to keep the flame stable in small spacing.The expansion of combustible range after hydrogenation is due to the fact that the intermediate products H and HO₂ generated by H₂ reaction can also directly participate in the elementary reaction and promote the formation of OH,and the addition of hydrogen can reduce the interaction between flame and wall and promote flame stability.When hydrogen is added,the temperature decreases mainly due to the difference of calorific value between methane and hydrogen.Meanwhile,R17:H+O₂+M<=>HO₂+M is the main formation reaction of HO₂.The flame heat release rate（HRRmax）of R17 reaction shows a negative temperature dependence.When hydrogen is added,the heat release of R17decreases,so the temperature decreases.The heat release rate of R6:O+CH₃<=>H+CH₂ and R73:CH₃+O₂<=>O+CH₃O during methane combustion is much higher than that of other reactions.The reaction rates of R6 and R73decrease gradually with the increase of"hydrogen addition ratio",and the decreasing trend slows down with the increase of"hydrogen addition ratio".The total heat release rate of hydrogen flame is mainly affected by the reaction of HO₂.R17 and R29:H+HO₂<=>2OH have great influence on the total heat release rate of hydrogen flame,and the reaction rates of R17 and R29 increase with the increase of hydrogen addition ratio.Therefore,with the increase of"hydrogen addition ratio",the flame peak temperature decreases gradually,but the decrease is not significant.With the increase of excess air coefficient,the temperature will increase because the increase of oxygen promotes the formation of a large number of more reactive o groups through R22,which promotes the oxidation heat release and makes the system temperature expand.The concentration of H and OH groups can directly determine the flame velocity,so the flame height decreases after hydrogenation.