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Combustion noise reduction in a kerosene burner : investigations in the spray characteristics of the fuel nozzle

Installing a small cylindrical tube, a short distance away from the fuel nozzle, successfully reduced the combustion noise generated in a small cooking burner. To investigate the mechanism, the characteristics of the fuel spray were examined with and without the tube insert. Laser-sheet flow visualizations provided a qualitative description of the spray. Droplet size and velocity measurements were carried out close to the fuel nozzle (< 2 in) using a Phase Doppler Particle Analyzer (PDPA). The experiments were performed in a cold-flow spray rig with optical access using MIL-C-7024 as fuel surrogate. The geometry of the preheating chamber of the burner is replicated using quartz windows. The spray cone angle, estimated from the flow visualization photographs, suggests interaction with the inner wall of the cylindrical tube. This is consistent with previous findings from a CFD simulation. The PDPA measurements show that the wall interactions resulted in large droplets being formed in the middle of the spray. This change in the average droplet size due to the inserted tube is believed to alter the drop evaporation time, which in turn will affect the transient characteristics of the burner and ultimately suppress combustion instabilities.