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NORA Oilheat Technicians Manual

Oilburners use one of two types of electric ignition control systems: Interrupted ignition: the ignition spark remains on for only a short time at the beginning of each burner operating cycle, and is turned off once flame is established. Intermittent ignition: the spark that ignites the oil vapors remains on as long as the burner runs. Intermittent ignition used to be called “constant ignition,” and some manufacturers call intermittent ignition “constant duty ignition.” Interrupted ignition is better Over time, the industry has switched between interrupted and intermittent ignition. Interrupted ignition has proven superior because having the spark on during the entire burn cycle detracts from performance for several reasons: • Electrode life is significantly reduced. • Ignitor or ignition transformer life is significantly reduced. • Electrical consumption is increased dramatically. • Operational noise in increased dramatically. • Intermittent ignition may hide combustion problems that can cause sootplugged boilers and oil running saturation. The constant arc keeps the flame burning even if it is belching smoke, soot, and unburned oil. With interrupted ignition, a poor flame goes out and the unit would go on safety. • NOx (nitrogen oxide) emissions are 9-4 Ignition Systems higher with intermittent ignition because the spark burns nitrogen, creating NOx. A strong spark The spark across the electrode gap at the tips of the electrodes must be strong enough to withstand the velocity of the air being blown through the air tube by the burner fan. The air being blown through the air tube forces the ignition spark to form an arc toward the oil spray. This arc extends into the spray causing the oil vapors to ignite, and the flame to establish. The ignition voltage must be high enough to create a spark that is hot enough to ignite the oil. In some cases, widening the spark will produce better ignition. The transformer The AC transformer is a device that receives electricity at one voltage and delivers it at another voltage, either higher or lower. Essentially, the transformer consists of two separate coils of wire wound on an iron core. One winding receives the electrical energy from the power source and is called the primary; and the other delivers electrical energy and is called the secondary. If the secondary winding delivers a voltage that is higher than the primary, then it is known as a step-up transformer. On the other hand, if the secondary voltage is lower than the primary voltage, then it is known as a step-down transformer. The factor that determines whether a transformer is of the step-up or step-down variety is the relative number of turns in the primary and in the secondary windings. Chapter 9 Ignition Systems


NORA Oilheat Technicians Manual
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