Nozzle is that part of an injector through which the liquid fuel is sprayed
into the combustion chamber. It is used in Diesel engine in which fuel is drawn separately through
injector at end of compression stroke and air is drawn into cylinder in suction
stroke.
The nozzle used in IC engine should follow following functions.
- It should automate fuel. This is a very important function since it is the first phase in obtaining proper mixing of the fuel and air in the combustion chamber.
- Distribute the fuel in require area within the combustion chamber.
- To prevent fuel from impinging directly on the walls of combustion chamber or piston. This is necessary because fuel striking the walls decomposes and produces carbon deposits. This causes smoky exhaust as well as increase in fuel consumption.
- To mix the fuel with air in case of non-turbulent type of combustion chamber.
Pintle
Nozzle:
In
this type of nozzle, the stem of nozzle valve is extended to from a pin or
Pintle which protrudes through the mouth of the nozzle.
The
size and shape of the Pintle can be varied according to the requirement.
It
provides a spray operating at low injection pressures of 8-10MPa.
The
spray cone angle is generally 60 degree.
The
main advantage of this nozzle is that it avoids weak injection and dribbling.
It
prevents the carbon deposition on the nozzle hole.
Single
Hole Nozzle:
In
this type of nozzle, at the center of the body there is a single hole which is
closed by the nozzle valve.
The
size of the hole is usually of the order of 0.2 mm.
Injection
pressure is of order of 8-10MPa and spray cone angle is about 15 degree.
One
of the major disadvantages of this nozzle is that they tends to dribble.
Besides,
their spray angle it too narrow to facilitate good mixing unless higher
velocities are used.
Multi
Hole Nozzle:
This
nozzle consists of a number of holes bored in the tip of the nozzle.
The
number of holes varies from 4 to 18 and the size from 35 to 200 micro meters.
The
hole angle may be from 20 degree upwards.
These
nozzles operate at high injection pressure of the order of 18 MPa.
Their
advantage lies in the ability to distribute the fuel properly even with lower
air motion available in open combustion chambers.
Pintaux
Nozzle:
This
is a type of Pintle nozzle which has an auxiliary hole drilled in the nozzle
body.
It
injects a small amount of fuel through this additional hole which is called
pilot injection in upstream direction slightly before the main injection.
The
needle valve does not lift fully at low speeds and most of the fuel is injected
through the auxiliary hole.
The
main advantage of this nozzle is better cold starting performance.
A
major drawback of this nozzle is that its injection characteristics are poorer
than the multi hole nozzle.