Sound Pressure Level Analysis of a Liquid-Fueled Lean Premixed Swirl Burner with Various Quarls

Abstract

Swirl burners are widely used in numerous practical applications since they are characterized by low pollutant emission and a wide operating range. Besides reliable operation, a burner must fulfill noise emission regulations, which is often a sound pressure level in dB(A) when people are affected. Therefore, the present paper evaluates the overall sound pressure level (OASPL) variation of a 15-kW liquid-fueled turbulent atmospheric swirl burner at various setups. Firstly, the combustion air flow rate was adjusted, which induced a swirl number modification due to the fixed swirl vanes. Secondly, the atomizing pressure of the plain-jet airblast atomizer was modified, which also affected the swirl number. High atomizing air jets notably increased combustion noise by intensifying the shear layer. Thirdly, a geometrical modification was performed; 0°–60° half cone angle quarls in 15° steps were installed on the lip of the baseline burner for extended flame stability. By filtering the OASPL to the V-shaped flames, a linearly decreasing trend was observed as a function of swirl number. Their derivative also has a linearly decreasing characteristic as a function of the atomizing pressure.

Experimental Comparison of Diesel and Crude Rapeseed Oil Combustion in a Swirl Burner

“…The straight flame was dominated by higher frequencies, and its overall sound pressure level was also higher, as discussed in a previous work [46]. The noise emission of the transitory flame was similar, however, the V-shaped flame was characterized by lower noise, which decreased until blowout.…”

“…However, it was used for comparison only in the case of diesel oil combustion, since crude rapeseed oil combustion was principally limited by low fuel evaporation through the swirl number, S [41]. The calculation of S is detailed in reference [46] for the present setup, while its definition is shown by Equation (1)…”

“…The acoustic spectrum of V-shaped turbulent flames is confined below 1.5-2 kHz [42,43]; the dominant frequencies are located at a few hundred Hz [44,45]. However, with weak swirl, when the flame is straight, the combustion-related frequencies can also be found at higher frequencies [46]. In engineering practice, temporal signals are typically evaluated by using Fast Fourier Transform (FFT) [44].…”