Oil burner

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Oil Burner for Asphalt Plant[1]
An oil burner for domestic central heating

An oil burner is a heating device which burns #1, #2 and #6 heating oils, diesel fuel or other similar fuels. The fuel is atomized into a fine spray usually by forcing it under pressure through a nozzle which gives the resulting flame a specific flow rate, angle of spray and pattern (variations of a cone shape). This spray is usually ignited by an electric spark with the air being forced through around it at the end of a blast tube, by a fan driven by the oil burner motor.[2] The fuel pump is typically driven via a coupling connecting its shaft to that of the motor's. Oil burners also include combustion-proving devices to prevent out-of-control combustion - Primary Control; Safety Control; Cad Cell Control; Master Control; Fire-Eye Control are all common names for the 'combustion safety control'.

Fuel injection[edit]

Used nozzles from an oil burner

Fuel is injected into the combustion chamber by a spray nozzle.

The nozzles are usually supplied with high pressure oil. Because erosion from friction with the oil, and possible blockage due to lumps in it, they need replacement when worn. Fuel nozzles are usually rated in fuel volume flow per unit time e.g. USGal/h (U.S. Gallons per hour).

A fuel nozzle is characterized by three features:

  • Flow at 100psi pump pressure (e.g. 0.65 USGal/h)
  • Spray characteristic (e.g. "S")
  • Spray angle (e.g. 60 °)

Alternatively fuel may be passed over a tiny orifice fed with compressed air. This arrangement is referred to as Babington atomiser/nozzle, named after its inventor Robert Babington.[3] As the oil flows over the nozzle, the fuel needn't be under any great pressure. If the pump can handle such the oil may even contain lumps such as scraps of food. Because it is only compressed air that passes through the orifice hole, such nozzles do not suffer much from erosion.

Oil pump[edit]

Oil pump

A gear pump of two parts:

Gear pump assembly[edit]

This pumps the oil in and increases the pressure in the nozzles to 15 bar maximum (217.5 psi). Usually a gerotor of the sickle type is used. Gear pumps are used frequently in oil burners because of their simplicity, stability and low price.

Pressure regulator[edit]

To set the heat output of the burner, the rate of fuel delivery via the nozzle must be adjustable. This is often achieved by an adjustable pressure relief valve between the pump and the nozzle. When the set pressure is reached (usually 100psi), this valve opens and allows excess oil to flow through a bypass back to the fuel tank or the pump suction side.

Electromagnetic valve[edit]

A small two-stage industrial burner. The blue cubes are the coils of the two electromagnetic valves.

This allows fuel to be shut off from the sprayer by electrical control. It helps avoid drips when the valve is closed. It also eases the purging of the burner (and any boiler) of fuel mist during start up, or while restarting after a misfire. If the burner were not purged the oil/air mixture could explode dangerously.

Fan[edit]

The fan blows air into the combustion chamber. The rotor of the fan is powered by an electric motor.

Igniters[edit]

Some oil burners use glow bars which operate much like the glow plugs of a diesel engine.

Many use high voltage generated by a voltage-step up transformer to create a spark for ignition, somewhat similar to a spark plug.

Original oil burner transformers were copper wire conductors wrapped around an iron core. A standard type of transformer to this day. In the mid 90s electronic igniters replaced the copper and iron transformer,solving many problems related to the old style transformer. This new technology in igniters would soon replace all old style transformers throughout the oil burner industry. The new igniters would run cooler so the output voltage could be increased from 10,000 to 20,000 VAC.

This increase of voltage would be more reliable, reduce delayed ignition, run cooler and all while using less energy. The voltage is high, but a standard igniter will only pull around 35 milliamp.

Safety control[edit]

LDR

Oil-fired burners are fitted with a safety mechanism for determining if the fuel has ignited and a flame present. The terms "primary control", "safety control", "cad cell control", "master control", and "fire-eye control" are variously used to describe a light dependent electrical resistor (LDR) which detects the flame whose value changes by the amount of light it is exposed to. The resistance decreases as the LDR is exposed to more light. The material is usually cadmium sulfide, hence the name "cad cell" for this component. In darkness the resistance is around 1 MΩ, while when exposed to light from a properly ignited flame the resistance is significantly lower, around 75-300 Ω.

Older oil burners were equipped with a primary control installed on the exhaust stack with a bimetallic heat sensing element protruding into the stack, such a control was referred to as a "stack relay" or a "stack control". It performed the same function as the newer cad-cell control but instead of sensing light from the burner flame it sensed heat from the flame exhaust gases to prove that ignition took place.

Capacitor start motor[edit]

Schematic of a capacitor start motor.

The motor which drives the fan and the oil pump is usually a capacitor start motor. It is a vortex shortage tank motor because it also contains a short cage or cage holds. The difference with a three-phase motor is in the stator. Where the vortex power motor has three coils aligned at 120° in the stator, the capacitor start motor holds one main winding and one auxiliary winding aligned at 90°. The phase shift of 90° between the main winding and the auxiliary winding is achieved by a connected capacitor which feeds the auxiliary winding and is connected on the single-phase AC mains. The capacitor will achieve a phase shift of 90° between the main and the auxiliary winding, producing an acceptable initial torque. This motor is intended for continuous operation.

See also[edit]

References[edit]