What is Carburetor – Parts and Working?

Today we will learn about what is carburetor – parts
and its working
. As we know that spark ignition engines used volatile liquid
fuels such as petrol for its working. Petrol is high volatile and its ignition
temperature is quite below the temperature occurs in engine cylinder before
full compression. Hence, mixing of air and fuel can’t possible inside the
engine cylinder of SI engines. But we require properly mixed, homogenous
mixture of air-fuel in correct ratio for proper combustion. This needs a device
which can mix air-fuel in correct ratio and form a homogenous mixture outside
the cylinder. This device is known as Carburetor.

What is Carburetor?

Carburetor is a device which is used in spark
ignition engine to mix air-fuel in correct ratio outside the cylinder. This
process is known as carburation.

Carburetor Parts

What is Carburetor - Parts and Working?

1. Float Chamber:    

The float chamber serves as a storage tank of
fuel for continuous supply of fuel. It contains a float valve which maintains
the level of fuel in float chamber. When the level of fuel decreases in float
chamber the float moves downward, which open the fuel supply valve and allow
flow of fuel into float chamber. As the fuel level increases, the float moves
upward which close and stop the fuel supply. This fuel level is maintained
below the discharge nozzle outlet hole to prevent overflow.

2. Strainer:

It is a device which is used to filter the fuel
before entering into float chamber. It consist a fine wire mesh which filters
the fuel and removes dust and other suspended particles from it. These
particles if not removed can cause blockage of nozzle.

3. Metering System:

The metering system controls the flow of fuel
into nozzle. It is responsible to form correct mixture of air fuel.  It
consist two main parts, first one is known as metering orifice and other one is
known as fuel discharge nozzle.
When the air passes through venturi, it
generates a low pressure field across throat compare to pressure at float
chamber. Due to this pressure difference, fuel is discharge into the air
stream. The quantity of fuel is control by the metering orifice and discharge
hole at the exit of fuel discharge nozzle.

4. Idling System:

It consist a passage directly from the float
chamber to venturi tube. It provides rich mixture during idling and at low
speed. It works during idling or when the throttle is open below 15%.

5. Throttle Valve:

It is a butterfly valve situated at the exit of
the venturi tube. It controls the speed of the vehicle by providing control
amount of mixture. It controls the quantity of air fuel mixture. If throttle is
fully opened, than more mixture drawn into cylinder and thus gives high output.
But if it is little opened, less mixture is drawn into the cylinder, which
gives less power.

6. Choke Valve:

It is same as throttle valve in construction but
situated at the entrance of venturi tube. It is used to provide very rich
mixture during starting in cold season. It controls the quantity of air flow
through the venturi tube. If the choke is fully open, normal amount of air flow
through venturi, which forms a normal mixture. But if the choke is partially
closed, it results low amount of air flow through venturi and large amount of
fuel flow through discharge nozzle. It gives rich mixture.

Working of Carburetor:

Now we know about basic parts of carburetor and
its function. These all parts work together to perform a common function of
providing homogenous air-fuel mixture in proper ratio. Its working can be
summarized into following points.
  • First fuel is supplied into the float chamber through
    strainer. Strainer works as a filter. It does not allow dust and other
    suspended particles into the float chamber which can choke any fuel
    passage.
  • The float maintains a constant level of fuel into float
    chamber. If the amount of fuel in the float chamber goes down below
    designed limit, the float goes down which opens the fuel supply valve and
    allow fuel to flow into float chamber. If the fuel reaches designed limit,
    the float goes up, which closes the fuel supply valve and thus stop fuel
    supply into float chamber.
  • The fuel discharge nozzle connects float chamber to
    venturi tube. The one end of fuel supply nozzle connected to the bottom of
    the float chamber and other one is to the venturi tube slightly above the
    designed fuel level in the float chamber. This will avoid overflow when
    engine is not running.
  • During suction stroke air is drawn into cylinder
    through venturi tube. Venturi is a tube of decreasing cross section and
    has a minimum area at throat. The fuel supply nozzle connects at the
    throat of venturi tube.  This air has maximum velocity at throat. Due
    to this high velocity, the pressure at the throat goes down below float
    chamber pressure.
  • This will create a pressure difference between float
    chamber and venturi tube. This pressure difference is known as carburetor
    depression. It acts as driving force for fuel. It drives fuel from float
    chamber to venturi tube through fuel supply tube and the fuel is discharged
    into the air stream.
  •  The
    fuel-air ratio depends on the size of discharge jet and metering system. So
    they are chosen as such, they can give desired air-fuel ratio.
  • This air fuel mixture provided to the cylinder through
    throttle valve. The SI engine is a quantity governed engine. So the
    quantity of the mixture provided into the cylinder is controlled by the
    throttle valve and hence control output power.
  • For idling or when required rich mixture, extra fuel is
    supplied by the idling system into venturi tube.
This is all about what is carburetor main parts and
working
. If you have any query regarding this article, or you find anything
missing or wrong, ask by commenting.   

Author Bio:

Mitesh Bairwa is Mechanical Engineer by profession and blogger by hobby. He is owner of www.mech4study.com.

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