Chapter 5 Nozzles and Chambers Figure 5-10: Viscosity vs. temperature change Viscosity vs. Temperature No. 2 Fueloil Viscosity, SSU Temperature °F Chapter 5—Nozzles and Combustion Chambers 5-11 most important factor. This is unfortunate, because you cannot control or adjust air pattern; it is fixed by the burner design. Also, you cannot see the burner air pattern; you must rely on trial and error in our quest for perfection. See Figure 5-9. Your tools in your search for the perfect flame are: the smoke tester, stack thermometer, draft gauge, pressure gauge, CO2 or O2 tester, the manufacturer’s recommendations and the experience of the person who was there before you. Always use the condition of the unit as you found it as your best guide to what needs to be done. If you find the unit running well and reasonably clean, the nozzle installed in the unit is probably pretty close to being the right one. However, if the unit is not running well, it may be time for some changes. The single greatest factor in combustion inefficiency is excess air. It absorbs large quantities of heat and carries it wastefully up the chimney. It also reduces the flame temperature, decreasing the rate of heat transfer to the heat exchanger. Both of these raise stack temperatures, which lower efficiency. The best burner adjustment is one that allows a smokeless, sootless operation with a minimum of excess air. We determine excess air by measuring the percentage of oxygen (O2) in the flue gases. You will learn more about this in the combustion chapter. Nozzle application procedure If the manufacturer’s recommendations are not available, or if you are upgrading an old unit with a new burner, the following is a step-by-step procedure you may use for selecting the best nozzle. 1. Set the over-the-fire draft to -.02", check the oil pressure, and install a nozzle that does not exceed the rating of the appliance. 2. Start with an 80-degree hollow nozzle, and adjust for a 1 smoke and mark the air band opening. 3. Try an 80-degree solid nozzle and take another smoke test. If it is lighter, you have a solid air pattern; if the smoke is heavier, it is hollow. 4. Try a 60-degree hollow or solid nozzle as indicated by the previous two tests. 5. Select the nozzle that creates the lowest smoke and highest efficiency. 6. Once the tests are completed, record the results. Post the results near the burner and report them to the office where they should become a permanent part of the customer’s service history. Effects of viscosity on nozzle performance One of the important factors affecting nozzle performance is the viscosity of the fuel. Viscosity is the resistance to flow— the thickness of the fuel. Thus, gasoline is “thin”, having a lower viscosity, while grease is “thick”, having a higher viscosity.
NORA Oilheat Technicians Manual
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