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The acoustic kinetic energy and soot suppression efficiency of acetylene diffusion flame under acoustic excitation at varying resonant frequencies in Rijke tube is investigated experimentally. The acoustic kinetic energy is introduced for the first time to explain the mechanism of soot suppression by acoustic oscillation. The soot suppression efficiency and acoustic kinetic energy is investigated by changing the acoustic parameters and the length of the Rijke tube. The results show that the efficiency of the soot suppression and the acoustic pressure increase significantly at the resonant fundamental frequency (167 Hz and 185 Hz) and resonant frequency (346 Hz and 373 Hz). The standing wave at the resonant fundamental frequency is a half wave, while the standing wave at the resonant frequency is a full wave. Soot suppression efficiency and acoustic kinetic energy reach the maximum at the wave nodes. When the efficiency of soot suppression is the same, the acoustic kinetic energy at the resonant frequency is twice that at the resonant fundamental frequency at the wave nodes. The flame brush, flame fluctuation velocity and the flame temperature are studied in detail by changing the acoustic parameters. The results show that the efficiency of soot suppression increase with the increase of flame fluctuation velocity and flame temperature. This is considered that the acoustic kinetic energy accelerates the flame fluctuation velocity which enhances the heat and mass transfer in the combustion field, resulting in an increase in the flame temperature, thereby soot is re-oxidized. This study can provide some reference for the practical application of acoustic oscillate combustion in soot suppression. • The efficiency of soot suppression at the wave node is the highest. • Suppression of acetylene diffusion flame soot by acoustic kinetic energy. • The Effect of Acoustic Kinetic Energy on the Efficiency of Carbon Smoke Suppression at Different Resonance Frequencies. • Different flame fluctuations and flame temperature in different phases. [ABSTRACT FROM AUTHOR]

• The method of inserting wire mesh into the flame to suppress soot described in this manuscript is simple and easy to operate. • The method described in this manuscript achieves the highest soot suppression efficiency of nearly 100%. • The method described in this manuscript is simple and widely applicable to a wide range of burners and fuels. A simple and efficient strategy to suppress soot from acetylene diffusion flames is reported for the first time. Horizontally insertion of metal wire mesh into the acetylene diffusion flame is found to greatly suppress the soot emission. The effects of experimental parameters such as acetylene flow rate, wire mesh height above nozzle (WHAN), material of wire mesh, mesh number, and inner diameter of the burner nozzle on soot suppression in acetylene diffusion flames are investigated. In addition, the collected soot samples are characterized by TEM, HRTEM, XRD, BET and Raman. The soot suppression efficiency can reach 100 % by horizontal insertion of the metal wire mesh in the acetylene diffusion flame. The WHAN has a great influence on the effect of soot suppression. In the first 210 s of horizontally inserting the metal wire mesh into the flame, the total mass of collected soot first decreases and then increases with the increase of WHAN. The minimum total mass of soot is achieved when the normalized WHAN (obtained by dividing the wire mesh height above nozzle by flame height without insertion of the wire mesh) is at 0.1. This position corresponds to the soot particle inception zone of the acetylene diffusion flame. The flame is divided into two parts when the metal wire mesh is horizontally inserted into the flame. The temperature of the flame below the metal wire mesh decreases from 1770 K to 1480 K. The temperature of the flame above the metal wire mesh increases from 1590 K to 1780 K. The soot collected on the metal wire mesh grows into a volcano-shaped carbon (VSC) structure. The results of the schlieren imaging experiments show that this structure can promote the mixing of air and fuel in the lower region of the flame thereby suppressing the formation of soot particles. The soot analysis shows that the horizontal insertion of metal wire mesh into the flame leads to high amorphous feature and low degree of structural order of the soot, which means that the oxidation reactivity of the soot increases. [ABSTRACT FROM AUTHOR]

• The TSDWSC grows naturally from the protrusion at the outlet of the nozzle without external influence, resulting in a stable structure. • Interestingly, the soot is completely oxidized, and no soot is emission when the TSDWSC is generated. • The large dimensional carbon material with fine structure from acetylene diffusion flame is rarely reported. • The structure of the TSDWSC is similar to that of the flame damper installed at the muzzle. This paper reports the formation of a self-formed three-stage dual-wing-shaped carbon (TSDWSC) from acetylene diffusion flame for the first time. The TSDWSC grows naturally from the protrusion at the outlet of the nozzle, while the emission of soot can be greatly reduced. The evolution of the TSDWSC involves three stages: the first unclosed dual-wing, the second unclosed dual-wing and the unmatured third dual-wing. The effects of protrusion, the flow rate of acetylene and various burner nozzle diameters on the formation of the TSDWSC are investigated. The experimental results show that with the increase of the protrusion height, the time when the first stage begins to appear decreases. With the increase of the acetylene flow rate, the stage number of the final dual-wing-shaped carbon increases. The TSDWSC can only be generated when the nozzle inner diameter is 2 or 3 mm. Using a two-color thermometer, the flame temperature distribution along the flame centerline is measured after the complete growth of the TSDWSC. The results show that the temperature of the TSDWSC area in the lower part is remarkably lower than that of the flame area in the upper part. The efficiency of reducing soot emission increases gradually with the evolution of the TSDWSC and reaches 100%, while the temperature of the flame area in the upper also rises gradually. X-ray diffraction (XRD) result indicates the formation of carbon crystals. [ABSTRACT FROM AUTHOR]

The effect of the energy of forced acoustics on the soot suppression from an acetylene-air diffusion flame is experimentally investigated. The acoustic energy is calculated by integrating the acoustic power in the positive period. Results show that the suppression efficiency of soot increases linearly with the increase of acoustic energy. In addition, the acoustic energy is similar under different acoustic waveforms when achieving the same soot suppression effect. The acoustic waves cause the flame to periodically stretch and compress, and the flame brush shows the range of fluctuations in the flame front. When the fluctuation velocity is greater than 2 m/s, the suppression efficiency reaches 50%. However, as the premixed level increases, the flame height decreases, resulting in a decrease of fluctuation velocity. [ABSTRACT FROM AUTHOR]