| In today’s society,environmental degradation and the depletion of energy resources have attracted widespread attention from countries and various fields,which has led to the urgent need to find clean fuels to replace traditional fossil fuels.Ammonia,as a carrier of hydrogen,is a highly promising carbon-free renewable fuel with advantages such as high energy density,low cost,and safe storage and transportation.Its cost is much lower than that of methane.Therefore,in recent years,it has received a lot of attention from scholars and has become a research hotspot.However,the low chemical reactivity of NH3 makes it difficult to self-ignite or be ignited by a spark,and it has disadvantages such as a narrow flammable range,slow combustion speed,and instability,which pose challenges to the application of NH3 fuel in gas turbines.However,with the development of multi-fuel combustion regulation theory,many research institutions have begun to consider using ammonia as the main fuel and have conducted simulation studies of ammonia/hydrogen combustion under different parameters such as hydrogen mixing ratio and turbulence intensity,in order to provide theoretical support for the application of ammonia/hydrogen fuel and the design of a new generation of carbon-free burners.The use of a high-pressure pre-mixed combustion chamber for ammonia/hydrogen binary fuel is described in the dissertation.By simulating and exploring the effects of the equivalence ratio,hydrogen mixing ratio,and total flow rate on the lean flammability limit,turbulent combustion characteristics,and NOx emissions of the premixed binary gas,it was found that the addition of hydrogen can significantly improve the stability of ammonia/hydrogen combustion,and within a certain range,as the hydrogen mixing ratio increases,the turbulent combustion speed increases and the combustion reaction intensifies.The larger the total flow rate of the premixed gas,the narrower the range of the flame limit.The formation of ammonia/hydrogen strip flames can be observed near the lean flammability limit.Using the Workbench simulation and calculation platform,based on the FGM small flame model and using the Gotama mechanism,the simulation of the lean combustion limit of ammonia/hydrogen binary fuel was carried out and compared with relevant experimental results to explore the combustion limit characteristics and NOx emissions of ammonia/hydrogen flames.The effects of equivalence ratio,hydrogen mixing ratio on the combustion characteristics of ammonia/hydrogen binary fuel were elucidated.With the increase of hydrogen mixing ratio,the lean flammability limit equivalence ratio continuously decreases.When the fuel composition is fixed,with the increase of equivalent ratio,the combustion is more full,the steady combustion temperature is constantly increasing,NO is constantly increasing,the concentration of NO2 decreases,and the thermal NOx is signiticantly reduced.Based on a large number of numerical calculations,relevant conclusions are as follows:(1)When the mixing ratio of ammonia/hydrogen binary fuel is 40%,the initial temperature is 300 K,and the equivalent ratio is 1,the relationship between laminar flame propagation speed and temperature is given by:SL=-40.42+0.218T,R2=0.99.(2)According to the change of laminar flame propagation speed with pressure,the relationship between equivalent ratio of 1 and hydrogen mixing ratio of 40%-60%is given by:SL=1.0172P-0.445,R2=0.996.(3)The laminar flame propagation velocity of fuel with 40%hydrogen blending ratio at five equivalence ratios Φ=0.75,0.875,1,1.125,1.25 and initial temperatures of 300 K,350 K,400 K and 450 K,it is correlated with the maximum molar fraction[H+NH+NH2]and the maximum molar fraction[NH+NH2]respectively.The relation is SL=9.676+7979.272×(XNH2+XNH+XH)max,R2=0.943;SL=-15.2+22966.34×(XNH2+XNH)max,R2=0.88093,where XNH2,XH and XNH are mole fractions of NH2,H and NH respectively.It is found that H radical plays a dominant role in laminar flame propagation velocity. |
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