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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&deg, &ndash, 60&deg, half cone angle quarls in 15&deg, 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.

The potential of biodiesel as an alternative fuel for various applications leads to an investigation to understand the combustion characteristics of pure and blended biodiesel. The concept of internal recirculation of combustion products is employed in a high swirl and low emission burner to reduce emissions. Due to high boiling point (613 K) and SMD (37 mu m) of biodiesel, air preheating with minimum temperature above the boiling point of biodiesel is considered. Air at different temperatures of 623, 673 and 703 K is injected tangentially. Swirl flow pattern in the combustor creates the central low pressure zone due to vortex breakdown and improves the recirculation of combustion products. Results in improved mixing and high residence time of reactants. Biodiesel is blended with diesel to reduce the surface tension and viscosity and improve the combustion characteristics. Literature has little consensus on NOx emissions from the combustion system operating with biodiesel. Therefore, the present study aims to reduce the thermal NO formation through the concept of exhaust gas recirculation. The CO, HC, NOx emissions and soot-volume fraction from biodiesel (100B0D), 50% blending (50B50D), diesel and kerosene are compared at different air preheating temperatures. A drastic reduction in emissions is observed in 50B50D as compared with pure biodiesel. (C) 2013 Elsevier B.V. All rights reserved.

In this paper, numerical and experimental investigations have been carried out to delineate the effect of various spray parameters on CO and NOx emissions in a combustor operating in flameless combustion mode with kerosene fuel. Thermal input was varied in the range of 20-41 kW (Heat release density similar to 5-10 MW/m(3)) with different fuel injectors and various fuel injection pressures. Spray parameters were varied by employing two separate conditions (i) same fuel flow rate with different solid cone pressure swirl spray nozzles (N1 - N4) and injection pressures (2.5-14 bar) to achieve varying spray parameters at same thermal input (ii) same fuel injection nozzle at different fuel flow rates and injection pressures (5-13 bar) to understand their effect on combustion and emissions. In both the cases, Sauter Mean Diameter (SMD) varied in the range of 34-58 mu m with spray cone angle varying from 42 degrees to 56 degrees using different nozzles and fuel injection pressures. Tangential air injection helped achieve higher recirculation of hot combustion products in the primary zone of the combustor for all thermal inputs. The finer sprays obtained at higher injection pressures helped achieve improved recirculation and better mixing, resulting in uniform temperature and hence reduced CO and NOx emissions. The measured CO and NOx emissions were in the range of 28-70 ppm and 2-10 ppm for all heat inputs with global equivalence ratio varying from phi = 0.6 to 1, respectively. Measured acoustic emission levels were in the range of 98-101 dB and 104-107 dB for the flameless and transition mode respectively. The measured CO, NOx and acoustic emissions are an order of magnitude smaller those corresponding to conventional combustion mode. It was observed that coarser sprays led to a significant increase in acoustic emissions, relatively non-uniform temperature distribution and higher CO, NOx emissions during flameless combustion mode. (C) 2017 Elsevier Ltd. All rights reserved.

This paper presents the experimental and numerical results for a two stage combustor capable of achieving flameless combustion mode with 20 kW thermal input and heat release density up to 5 MW/m(3). The fuel and oxidizer are supplied at ambient conditions. The concept of high swirl flows has been adopted to achieve high internal recirculation rates, residence time and increased dilution of the fresh reactants in the primary combustion zone, resulting in flameless combustion mode. Air is injected through four tangential injection ports located near the bottom of the combustor and liquid fuel is injected through a centrally mounted pressure swirl injector. Preliminary computational analysis of the flow features shows that decrease in the exit port diameter of the primary chamber increases the recirculation rate of combustion products and helps in achieving the flameless combustion mode. Based on preliminary computational studies, a 30 mm primary chamber exit port diameter is chosen for experimental studies. Detailed experimental investigations show that flameless combustion mode was achieved with evenly distributed combustion reaction zone and uniform temperature distribution in the combustor. The CO and NOx emissions are reduced from 350 to 11 ppm and 45 to 12 ppm respectively at an equivalence ratio of 0.92, as operation of the combustor changes from conventional to flameless combustion mode. Measurement of CO and NOx emissions show that these emissions are reduced by an order of magnitude when operated in flameless combustion mode. The acoustic emission levels are reduced by 6-8 dB as combustion mode shifts from conventional mode to flameless combustion mode. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.