Influence Of Forced Acoustic Field On Soot Suppression In Diffused Flame

In recent years,with the increase of car ownership year by year,increasing efforts to control air pollution,stricter emission standards for internal combustion engines have been put forward,and the design and manufacture of cleaner engines has become a top priority.Pulsating combustion caused by the coupling of oscillating combustion process and acoustic wave can strengthen mass and heat transfer and enhance thermal efficiency,which attracts more and more people’s attention.However,the existing research has not fully revealed the mechanism of pulsating combustion inhibiting soot formation,and the relationship between the combustion response of flame and the law of acoustic parameters is not enough.Therefore,the research on the mechanism of pulsating combustion inhibiting soot generation is helpful to find a new design method of internal combustion engine,which can effectively inhibit the generation of soot during combustion of internal combustion engine,improve the combustion thermal efficiency of internal combustion engine,and has important academic significance and industrial application value for environmental protection and clean use of energy.In this paper,the flame dynamics and soot suppression effect under transverse acoustic excitation are studied theoretically and practically.On the basis of in-depth analysis of the response of acetylene diffused flame under acoustic excitation,the relationship between sound energy and soot suppression efficiency is estimated according to the sonic-force-electric analogy method.By changing the frequency,amplitude,initial phase and waveform of acoustic wave,the standing wave field at the flame location is changed,and the soot suppression efficiency and flame fluctuation response of acetylene diffusion flame are studied and analyzed.The time synchronization of sound pressure signal and flame fluctuation provides a reliable basis for in-depth theoretical analysis of flame response to sound field,and the change of flame temperature reflects the state of combustion oxidation reaction.The main conclusions are as follows:(1)The application of transverse acoustic field can effectively suppress the amount of soot generation,and with the flame position from the belly of the standing wave to the nodule,the soot suppression efficiency will gradually improve.The soot suppression efficiency of the flame at the standing wave node is better than that at the belly of the wave.In addition,at the same frequency,with the increase of sound pressure,soot suppression efficiency will also improve.Low sound pressure at low frequency can greatly improve soot suppression efficiency.(2)In a flame wave dominated by acoustic radiation,the flame moves up and down.As the flame position moves from the ventral point to the node,the flame fluctuation is a mixture of up and down fluctuation and left and right fluctuation,and the flame will tilt,and its tilt direction is always towards the pressure ventral point.The flame is located at the pressure node,and the flame only fluctuates left and right,which is related to the dominant situation of acoustic radiation force and acoustic wave velocity.And as the sound pressure increases,the strain of the flame will also increase.(3)The effect of sound field will raise the flame temperature,and the harmonic frequency with periodic fluctuations.At the standing wave node,the flame temperature increases the most,and its peak and trough values and average values are much higher than those at other phase differences.And with the increase of sound pressure,flame temperature will gradually increase.(4)After the flame is excited by sound,the wave response of flame has hysteresis,and the periodic stretching and compression of flame shape is related to the direction of sound pressure.In the positive period of sound wave,the flame is compressed by sound pressure and becomes longer,while in the negative period of sound wave,the flame is stretched by sound pressure and becomes shorter.(5)There is a linear relationship between soot suppression efficiency and sound energy,and with the increase of frequency,more sound energy is required to achieve the corresponding soot suppression efficiency.At the same acoustic frequency,sound waves of different waveforms need different sound pressures to achieve the same soot suppression efficiency,but sound energy is similar.The sound energy variance of different waveforms is less than 5.17E-09.