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Write a short note on: Types of diesel fuel injection nozzles.

The types of diesel fuel nozzles used with different types of combustion chambers are:

1. Single hole nozzle:

• These are used in open combustion chambers. In these a single injection hole whose size is greater than 0.2 mm is drilled through the nozzle body.

• The hole may be drilled centrally or at an angle. Its main disadvantages include:

  • need for very high injection pressure
  • dribbling tendency of single hole nozzle
  • narrow spray angle leading to unsatisfactory mixing.

1. Multi-hole nozzles:

• This type of nozzle mixes fuel properly even with low air velocities available with many open combustion chambers.
• The number of holes ranges from 4 to 18 and size from 1.5 to 0.35 mm. The holes may be drilled symmetrically or asymmetrically depending on the application.
• However the injection rate characteristics of this nozzle are not very good compared to other types of nozzles.

1. Pintle nozzles:

• This type of nozzle is provided with a projection called pintle which sticks out of the mouth of the nozzle body. The projection is cylindrical or conical in shape.
• The projection aids in avoiding weak injection and dribbling. The pintle does not allow pressure drop to be high by partially blocking the orifice when the valve lifts. The orifice is uncovered as the lift increases and area of flow opens.
• The fuel pressures are lower than single or multihole nozzles.
• Pintle nozzle are used in pre-combustion chambers or high swirl chambers due to good atomization and reduced penetration.

1. Pintaux nozzles:

• This nozzle is used to improve cold starting performance without ant detrimental effect on efficiency.
• It is an advanced design of the pintle type and has an auxiliary hole drilled in nozzle body which allows a small amount of fuel injection in upstream direction of air flow in advance of the main downstream injection.
• The needle valve does not lift at low speeds leading to very good cold starting performance.
• Its main disadvantage is the tendency of side hole to choke due to which a filtering unit is needed.