Experimental And Model Investigation On Mechanism Of Reducingnox Emission By Flame And Vortex Interacition With An Acoustic Excitation

NOx emission of methane/air partially premixed flame under acoustic with different frequencies and amplitudes was not sysenmatic investigated before. Important engineering value and academic significance were obtained by analysis on effects of acoustic parameters and flow paremieters on partially premixed flame EINOx emission, which was based on the interaction of vortex and flame.FlameNOxemissions and dynamic behaviors with different acoustic excitations were studied through experimental studies and model researches. Influence of flow parameters and acoustic parameters on partially premixed flame EINOx emissions were analysised by experimental technologies, include thermocouple measurement, flame image acquisition and processing technologies, Particle Image Velocimetry(PIV) system andNOxmeasurement. Detailed analysis on mechanism of these influences were obtained by interaction of flame, acoustic and vortex. Finally, dynamic model of EINOx emission for partially premixed flame under acoustic was presented based on vortex motion theory and convection wave theory. Main works and achievements in this paper are as follows:1. Effects of acoustic parameters and flow paremeters onNOxemission of partially premixed flame under acoutic were obtained.Effect of equivalent ratio, coflow air velocity, jet Re number and frequency, amplitude on EINOx were studied meticulously. Results show that, ①A turning equivalent ratio at 4 was appeared. EINOx was decreased rapidly with increase of equivalent ratio when equivalent ratio was less than 4. Oppositely, EINOx was leveled off with increase of equivalent ratio when that greater than 4. ②Flame length was decreased with increase of coflow air velocity, and lead to the decrease of EINOx. ③Vortex was compressed to flame downstream with increase of Reynolds number. The mixing effect of vortex on flame was weakened, and EINOx was shorted. ④Critical frequency, [170,190]cf ?, was appeared when changing frequency influence on EINOx.When less than cf, the vortex shifted to flame upstream gradually to strengthen EINOx emission with the increase of frequency. However, EINOx variation was not obvious when greater than cf. ⑤The effects of amplitude on EINOx was consistent with frequency, cf was also existed. When less than cf, vortex effect was strengthened to reduce flame length and EINOx with the increase of amplitude. On the contrary, EINOx was gradually increased when greater than cf.2. Vortex and diffusion flame interaction under acoustic reducingNOxemission was analysised.Relationship between acoustic and vortex, vortex and EINOx were studied, and results show that, ①flame length and EINOx were both increased with strengthened fuel gas Re number. ②Oxidant went to excess after enough with the increase of coflow air velocity. Therefore,NOx reaction rate was accelerated, and EINOx was decreased after increased. ③cf was also existed when diffusion flame EINOx influenced by frequency. However, bend and fold appeared in flame during the influence of resonance frequency. It also compressed flame into burner, and EINOx was decreased significantly. ④EINOx was linear decreaseed with the enhancement of amplitude when less than cf. But EINOx was strengthened with increase of amplitude when greater than cf. ⑤Diffusion flame EINOx under acoustic was directly proportional to vortex diameter and height of the vortex, but inversely proportional to vortex life time. ⑥Amplitude was inversely proportional to vortex diameter, height of the vortex and vortex life time, and certain linear relationships was presented. ⑦Acoustic frequency was proportional to the vortex life time.3.Dynamic model for EINOx emission of partially premixed flame under acoustic was presented.Phenomenological model was presented after detail analysis on relationship between diffusion flame EINOx and vortex based on vortex motion theory. ①The vortex rotation speed and vortex was weakened to strengthen EINOx emission with the increase of vortex diameter. ②Vortex transfered to downstream with the increase of vortex height, it lead to increase of EINOx. ③EINOx was proportional to the vortex life time. Flame residence time and EINOx were weakened by enhanced vortex life time. ④EINOx,NOxgeneration space area were shrongthed with increase of diffusion flame area, flame surface area and flame volume. ⑤Error of phenomenological model was less than 10% validated through the experimental datas.EINOx dynamic model of premixed flame with an acoustic excitation were presented after study the relationship between EINOx and wavelength, pulse amplitude based on the convection wave theory. ①NOx formation space condition was improved, EINOx was increased with the increase of convection wavelength.②Pulse amplitude and flame Strouhal number was inversely proportional to EINOx. ③Model was verified by experimental datas.Diffusion flame and premixed flame EINOx generation model were combined into partially premixed flame EINOx model through proportion method as the equation 5-64. Model was verified by experiment datas and PIV images, error of model with vortexd was 10%, and error of model with S was 22.2%. Partially premixed flame EINOx model was corrected by Da number, which was chemical reaction factor. Error of corrected model with the experimental datas was reduced to less than 10%.