Study On Flame And Emission Characteristics From Ammonia/Methane Partial Premixed Combustion Under Ultrasonic Excitation

As a high energy density hydrogen-rich carrier,ammonia（NH₃）is a highly promising carbon-free fuel.The use of NH₃ offers a new idea for the development and use of clean alternative fuels.However,the large-scale industrial application of NH₃ is limited by its low reactivity and high nitrogen oxide（NO_X）emission.Combustion enhancement and emission reduction of NH₃ combustion process was research objectives,flame and emission characteristics of partial premixed ammonia/methane（NH₃/CH₄）combustion under ultrasonic excitation were studied by integrating experimental exploration and numerical simulation.An experimental system was designed and built,including partial premixed combustion system,loading ultrasonic system,and multi-parameter measurement system.Combustion and measurement experiments at different ultrasonic frequencies and NH₃/CH₄ blending ratios were carried out.Flame images,Moiréfringes,and flue gas species concentrations under different working conditions were acquired.The influence of ultrasonic excitation at different frequencies on flame characteristics,flame temperature field and emission characteristics of the combustion process was analysed.Based on experimental conditions,large eddy simulation research was conducted.The effects of various acoustic parameters on emission characteristics and flame response characteristics were investigated.The distribution of key radicals and transport characteristics of species within the flame under different working conditions were obtained to reveal the emission reduction mechanism under ultrasonic excitation.At the same time,the variation rules of parameters in time series under different working conditions were obtained for spectral characteristics studies.The flame response mechanism was clarified.Results showed that part of the hydrocarbon fuels was replaced by NH₃ to reduce CO₂ and unburned CH₄ emission.Meanwhile the flame colour was changed from light blue to brownish yellow,and the maximum temperature of flame was decreased.As ultrasonic excitation was added to the combustion flow field,the flame colour was changed from brownish yellow to orange,the flame brightness was enhanced,the combustion temperature was increased,and the unburned CH₄ and NO in the flue gas emissions was reduced.Results of numerical simulation showed that H-abstraction reactions of NH_i（i=1,2,3）was promoted and the recombination reaction of NH₂ with NH was accelerated when the flame was excited by ultrasonic wave.Pathway where NH and N respectively react with NO to directly generate N₂ was promoted.When the flame was excited by ultrasonic wave of different frequencies,the nonlinear response of flame was found.As the amplitude of the ultrasonic wave increased,the flame oscillates at the response frequency increased.