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NORA Oilheat Technicians Manual

tertiary opening. See Figure 1-9. The center opening is the orifice in the center of the head that allows clearance for the oil spray and the electrode spark to pass through the head without interference. The secondary slots are the slots that radiate out from the center opening towards the outside of the head. The tertiary opening is a slot that is concentric to the center opening and follows the circumference of the combustion head. All three openings affect the way air is delivered to the oil spray. • The primary air is the air that exits through the center opening hole in the flame retention ring where the oil from the nozzle is sprayed. Primary air has the least desirable effect on combustion. Air will always take the path of least resistance, so the larger the center opening, the more the air will tend to pass through this opening and push the flame out away from the face of the head. This air travels in a forward motion only. The smaller the center opening, the more air will be forced to seek its passageway through the other openings in the combustion head. (Figure 1-9). • The secondary air is the air that exits through the slots cut into the flame retention ring. The secondary slots are where the most important mixing of oil and air occurs. The slot width regulates the velocity of the air passing through the slot. This is where the air acquires a spinning action. The air moves mostly in a rotary motion with little forward movement. Narrow slots will cause the air to spin faster and move forward less. This will cause the best mixing of oil and air and create a compact, intense, and efficient flame. The secondary slots also aid in keeping the surface of the head clean and free of carbon. This air is turbulated by the flame retention ring and it is this Secondary Air that creates the flame retention effect. By spinning this secondary air, the flame is actually pulled back toward the flame retention ring. (Figure 1-9). • The tertiary air is the air that exits around the outside of the flame retention ring or through the tertiary slots. For clean oil combustion, every droplet of atomized oil MUST be completely blanketed with air in order to provide total combustion. Tertiary Air ensures that any droplets of atomized oil escaping the oil spray pattern will contact this air and burn. Creating an envelope or curtain of air between the main swirl area of the flame and the walls of the combustion area or the chamber. The width of the slots in the outside ring control the amount of tertiary air entering the combustion area. The larger the slots the more tertiary air and less secondary air, thus the size of the slots affects the firing rate of the burner. (Figure 1-9). Fixed and adjustable heads Flame retention heads fall into one of two categories: fixed or adjustable (sometimes called variable heads). The difference between them is the method by which they control the tertiary opening and hence, the firing rate of the burner. The fixed head group’s tertiary opening is pre-set to a specific opening size for a specific firing rate range. There are a variety of one-piece heads available with fixed tertiary slots sized according to the firing rate for which it was designed. To change firing rates, you have to change the head. With an adjustable head burner, the head is designed to move against or away from a ring, thus closing or opening the tertiary Chapter 1 Intro to Oil Burners Chapter 1—Introduction to Oil Burners 1-9


NORA Oilheat Technicians Manual
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