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NORA Oilheat Technicians Manual

Chapter 2—Heating Oil and Its Properties 2-5 for No.1 and No.2 oil is 100°F minimum. When oil is heated to its flash point, some of the hydrogen flashes off but the fuel will not continue to burn. Ignition point The ignition or fire point is lowest temperature at which rapid combustion of a fuel will take place in air. It is the temperature at which all the fuel has been sufficiently heated and vaporized to the point where it continues to burn for at least 5 seconds. For No. 2 oil, the ignition point is over 500°F. Pour point Pour point is the lowest temperature at which fuel will flow. Below this, it turns to waxy gel. The ASTM standard for untreated No. 2 oil is 17°F. Additives or kerosene are added to heating oil during the winter to ensure that it flows. Cloud point Cloud point is the temperature at which wax crystals begin to form in the fuel— typically 10 to 20 degrees above the pour point. These crystals can clog filters and strainers, restricting fuel flow. Raising the temperature causes the crystals to go back into solution. ASTM does not list a specification for cloud point for heating oil. Both pour point and cloud point affect winter performance, and could cause problems if the fuel is not properly treated. Viscosity Viscosity is the thickness of the fuel and its resistance to flow. Grease has a high viscosity. Gasoline has a low viscosity—it flows easily. Heating oil’s viscosity changes dramatically with temperature. As the Heating Oil’s Physical Properties (No. 2 oil) ASTM Specification: D 396 Flashpoint: 100°F minimum (37.8°C) Ignition Point: >500°F (260°C) Pour Point: 17°F (8.3°C) Cloud Point: Pour point temp. plus 10-20° (F) Viscosity: Varies: increases as temp. drops Water/Sediment: ASTM allowable amount of H2O: 0.1% (Water content is usually much lower in practice) Sulfur Content: Ranges from 0.5% to 0.05% (5000 to 500 parts per million); ASTM maximum allowable amount is 0.5%. Color: Colorless, but heating oil is dyed red for tax compliance reasons. Color resembles cranberry juice. BTU Content: 139,000 (approx.) temperature decreases, viscosity increases. Normally the temperature of oil in a basement tank is 60°F. In the winter, you might get a delivery of 5°F oil. The colder oil will have a higher viscosity and burner Chapter 2 Heating Oil


NORA Oilheat Technicians Manual
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