motors (3,450 RPM) and air pattern shaping to create the high static air pressure needed to make the high velocity air swirl and the internal recirculation needed for clean, efficient combustion. This recirculation is created by the drop in pressure in the center of the air swirl, like the eye of a tornado. This pulls some of the hot flame gases toward the burner head, the way the spray from a showerhead pulls in the shower curtain. These hot gases add heat to the fuel droplets coming out of the nozzle speeding up their vaporization and burning rates, which gives us a nice clean, stable fire close to the burner head. New oilburners should not produce smoke Smoke and soot, which are nothing more than unburned carbon, are created by outdated burner designs and incorrect burner service and adjustment. Smoke production is unnecessary and must be Chapter 7 Combustion Figure 7-4: Soot affects fuel consumption Effect of Soot on Fuel Consumption Soot Layer on Heating Surfaces 7-6 Combustion eliminated, because it reduces efficiency, increases service calls, and is a nuisance to homeowners. It can be prevented using modern burners and by careful adjustment of burners using combustion test equipment. Excessive smoke wastes fuel because it deposits soot on the heat exchanger surfaces, Figure 7-4. This insulates the heat exchanger, limiting its ability to extract the heat from the combustion gases. A layer of soot only 1/8" thick can reduce heat absorption by over 8%. Efficiency loss caused by a smoky burner occurs as the soot slowly builds up. Soot also affects the reliable operation of the burner. If it builds up on the cad cell or the bimetal of the stack relay, it can act like a flame failure and cause the control to lock out on safety, creating an unnecessary service call. Overfiring can cause smoke: If a unit is overfired, the burner will create heat faster than the heating system can distribute to the building. When this happens, the burner short cycles (goes on and off frequently for short periods of time). The problem is that older oilburners create smoke when they start and stop. Up to two thirds of all the smoke produced by burners made before the year 2000 is produced on start up and shut down. Therefore, properly sized nozzles will produce less frequent burner cycling and less smoke. Sulfur Sulfur exists in varying degrees in all fossil fuels. The sulfur content of heating oil ranges from 0.5% to 0.05% by weight. When burned, the sulfur mixes with oxygen to form sulfuric oxide (SOx). It reacts with the water vapor in the combustion gases to create sulfuric acid aerosol.
NORA Oilheat Technicians Manual
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