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NORA Oilheat Technicians Manual

Chapter 5 Nozzles and Chambers Chapter 5—Nozzles and Combustion Chambers 5-17 Introduction The flame from the oilburner is contained in the combustion chamber. A chamber must be made of the proper material to handle the high flame temperatures. It must be properly sized for the nozzle-firing rate and it must be the correct shape and the proper height. Combustion chambers have a profound effect on the first three of the four rules for good heating oil combustion: 1. The oil must be completely atomized and vaporized. 2. The oil must burn in complete suspension. 3. The mixture of air and oil vapors will burn best in the presence of hot refractory. 4. A minimum amount of air must be supplied for complete, efficient combustion. To burn the oil in suspension means that the fire must never touch any surface— especially a cold one. The cold surface will reduce the temperature of the gases turning the vaporized carbon in the fuel into smoke and soot before it has a chance to burn. For combustion to be self-sustaining, the heat produced by the flame must be sufficient to ignite the fresh mixture of oil vapor and air coming into the combustion zone from the burner. The hotter the area around the burning zone, the easier and more completely the oil will burn. The combustion chamber provides the necessary room for all the oil to burn before contacting or impinging on cold surfaces. It also reflects heat back into the burning zone, ensuring clean, quick combustion. If the chamber is too small or the wrong shape for the burner air pattern, or the nozzle is too close to the floor, there will be flame impingement, causing smoke and soot. With non-flame retention burners, an oversized chamber refractory will not reflect enough heat back into the burning zone to burn the carbon—smoke will be created. If the chamber sides are too low, combustibles will spill over the top and burn incompletely. It is your job to be able to diagnose an incorrectly built chamber as well as to build and design a correct one. Chamber materials Chambers should heat up quickly, reflect as much heat back into the burning zone as possible, and cool off quickly when the burner shuts down. There are five common types of materials used in combustion chamber construction. Insulating fire brick: The porous nature and lightness of this brick makes it highly resistant to the penetration of heat. The side of the brick facing the fire glows red hot in about 15 seconds while the rear surface remains relatively cool. (The bricks come in a variety of sizes and are available in precast chambers). For fires up to 3 GPH, you can use 2000°F firebrick. It will take up to 3000-degree temperatures, but structurally it cannot take the starting violence of a large fire. Proper refractory cement should be used with the insulating brick so the expansion of the brick and cement will be equal. Common fire brick or hard brick: This weighs more than insulating brick and it Part II: Combustion Chambers


NORA Oilheat Technicians Manual
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