Oil burner

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This article is about the heating device. For a meaning related to engines, see Oil burner (engine).
Oil Burner for Asphalt Plant[1]
An oil burner for domestic central heating

An oil burner is a heating device which burns fuel oil. The oil is atomized into a fine spray usually by forcing it under pressure through a nozzle. This spray is usually ignited by an electric spark with the air being forced through by an electric fan.[2]

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 of problems with erosion, and blockage due to lumps in the oil, they need frequent replacement typically every year. 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 3 features:

  • A flow of 7 bar pump pressure (0.65 (USGal / h))
  • The spray characteristic (S)
  • The spray angle (60 °)

Alternatively fuel may be passed over a tiny orifice fed with compressed air. This arrangement is referred to as babington atomiser/nozzle after its inventor. 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 fuel oil pump consists of two parts:

  • Gear pump type

This sucks the oil and increases the pressure in the nozzles to 15 bar maximum. Usually a gear pump of the sickle type is used. This type of pump is a simple and therefore cheap pump consisting of one or more radical pairs of gears and with a very small space between the gears and the pump casing. Gear pumps are used frequently in oil burners because of their simplicity, stability and low price.

  • Pressure regulator

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 reaches usually 10 - 11 bar, this valve opens and allows excess oil through a bypass back to the fuel tank or pump suction.

Electromagnetic valve[edit]

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

This enables fuel to be shut off from the sprayer by electrical control. This helps avoid drips when it is inactivated. 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.

Ignitors[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 and use a spark plug to initiate ignition

Photocell[edit]

LDR

A light sensitive resistor (LDR) detects the flame. The LDR (or Light Dependent Resistor) resistor is an electrical resistor whose value changes by the amount of light that is present. The resistance value of an LDR becomes smaller, as the LDR is more and more exposed. The material is usually cadmium sulfide, the dark resistance is 1.10 MΩ resistor while the light resistance is about 75-300 Ω. LDR's have a relatively slow response time.

Capacitor start motor[edit]

Schematic of a capacitor start motor.

The fan and motor which drives 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.

Order for starting an oil burner[edit]

  • Connect the oil burner to a power source.
  • Turn off the 'Emergency Shut Down' located on the furnace.
  • Purge the burner/boiler with air
  • Atomize the fuel oil
  • Deflagrate the Atomized fuel oil with a high voltage between two electrodes
  • Check with flame detection whether the fuel oil fires up

If the burning does not catch on, the burner will go into alarm and must then be manually reset.

See also[edit]

References[edit]