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NORA Oilheat Technicians Manual

• Pipe or duct insulation • Heating systems tune-up • Thermostat set back • Combining equipment modifications Flame retention burners The main difference between old nonflame retention and flame retention burners is the way the combustion air and fuel are combined. The flame retention burner has a specially designed burner head (end cone) and a high-pressure fan that produces more recirculation within the flame for better fuelair mixing. The swirling air pattern increases the contact between the fuel droplets and the air. In addition, a recirculation zone is formed within the flame. This recirculation pattern draws some of the hot combustion gases back toward the burner head. This helps to vaporize the oil droplets by direct contact with hot gases. Recirculation also provides a longer path length through the flame. This adds to the time available for the fuel and air to react, promoting complete combustion. This swirling and recirculation pattern also reduces smoke formation, requires less excess combustion air, and provides higher efficiency. The flame is more stable in flame retention burners. It forms a tight shape that is held near the burner head. That’s where the name “flame retention” comes from. Flame retention burners can operate efficiently in heating units where marginal chimney draft or where oversized combustion chambers could cause problems with older burner designs. With flame retention, the flame is stabilized by the high velocity airflow and it does not need radiant heat reflected back from the combustion chamber for stable operation. This eliminates some of the flame problems experienced by older burner designs. A drawing of non-flame retention and flame retention combustion is shown in Figure 16-8. Chapter 16 Energy Conservation Figure 16-8: Non-flame retention and flame retention combustion. Non-Flame Retention Combustion Flame Retention Combustion Nozzle Combustion Air Non-Flame Retention (Optional) Combustion Head Rear View Cast Iron 16-12 Energy Conservation Nozzle Combustion Air Flame Retention Combustion Head Rear View Stainless Steel Combustion Chamber Circumferential Slots Radial Vanes Air Vanes Combustion Chamber Target Wall


NORA Oilheat Technicians Manual
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