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NORA Oilheat Technicians Manual

Chapter 5 Nozzles and Chambers How a nozzle works Figure 5-2: Fuel pressure vs. droplet size 5-4 Nozzles and Combustion Chambers pattern and angle best suited to the requirements of each specific burner and combustion area. Effects of pressure on nozzle performance Historically, 100 PSI was considered satisfactory for the fixed oil pressure supplied to the nozzle, and all nozzle manufacturers calibrate their nozzles at that pressure. Many burner and appliance (boilers, furnaces, and water heater) manufacturers are recommending higher pressures for their products. Higher pressures create better atomization, i.e. smaller droplets. See Figure 5-2. Heating oil, under pressure (100 psi) passes through the strainer to remove contamination, then through a set of slots, cut at an angle into the swirl chamber. The angle of the ejected oil creates a high velocity swirl, like a tornado. As the oil swirls against the swirl chamber walls it creates an area of low pressure in the center. This pressure differential moves the oil out through the orifice in a hollow tube shape where it spreads into a film that stretches until is ruptures into billions of tiny droplets. Mean Drop Size (Micron) Greater Oil Pressure Will Make the Average Atomized Drop Smaller Oil Pressure (psi) 2. Metering: A nozzle delivers a fixed amount of atomized fuel to the combustion chamber. The amount of fuel is measured in gallons-per-hour (GPH) at 100 pounds pressure. For burning rates below five GPH, there are more that 25 different flow rates each in 6 different spray angles and six or more spray patterns. 3. Patterning: A nozzle is expected to deliver the fuel to the combustion area in a uniform spray


NORA Oilheat Technicians Manual
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