Carburetor used inAutomobiles

Automobile:
Which Carburetor used inAutomobiles?
A carburetor is a device used in petrol or similar
liquid fuel engines by means of which the fuel mixed
with air, is supplied into the induction manifold of the
engine. An engineering or automobile field connected
people will better know this. The main object of the
carburetor is to supply the required quantity of fuel
and air mixture of the correct strength as dedicated
by the load condition of the engine. For this purpose
different types of carburetorsare available in the
market. Out of that, you will find here the details of
Zenith Carburetor, as below. Zenith carburetor is also
known as “British Carburetor” and used by various
famous car manufacturers. This carburetor has also
number of designs available for different purposes.
Construction and Working
In this, float chamber is supplied with fuel from the
fuel tank through a pipe.Whenever the float chamber
falls short of fuel, the fuel from the fuel tank flows
into the chamber at a fastest speed than is consumed
by the engine with the result that, the float rises up, till
it reaches a certain level. At this time, a needle valve
moves down and rest against the seat, resulting the
stoppage of fuel supply from fuel tank.
The main jet is directly connected to the float
chamber while the auxiliary jet which is also called as
compensating jet draws fuel from auxiliary chamber
(Reservoir).Thi s auxiliary chamber is connected to
the float chamber through an orifice. Both, main and
auxiliary jet is openedup in the venturi.
The air to the carburetor is supplied through the
passage. The throttle valve is located at the end of
the carburetor and connected to the engine suction
pipe. The opening andthe closing of the throttle valve
controls the quantity of air-fuel mixture supplied to
the engine suction manifold. An auxiliary nozzle from
auxiliary chamber (Reservoir) is located at one end of
the by-pass and the other end of this nozzle, opens
upnear the throttle valve.
Working at Starting and Low Speed Running
Because of lower velocity of air at the time of starting
or slow speed of the engine, the suction produced at
the venturi is quite insufficient to operatethe main and
the auxiliary jet in nozzle. To improve the velocity of
air, the throttle valve is closed to such an extent that
there is only a small contracted passage is provided
near the end of by-pass. By this, the velocity of air,
passing through the region increases, producing the
high suction, which operates the nozzle at auxiliary
chamber and the air-fuel mixture supplied through
the holes.
There is starting and slow running device is fitted in
reservoir (Auxiliary Chamber).To vary the supply of
air to the nozzle, the set screw given is slackened
and whole assembly is taken out. By the suitable
number of rotation of screw joint, the position
ofauxiliary nozzle is set. The whole device is then
again fitted to the carburetor and tightened the screw.
Working at Normal Running
At this condition, the throttle valve is opened about
66% and as the air entering through the passage,
passes through the venturi, its velocity increases due
to smaller area consequently its pressure drops,
resulting the suction effect. The fuel is sprayed in the
venturi by main and auxiliary nozzle. As the speed of
engine increases, there by producing the greater
suction. Due to this, greater fuel being supplied by the
main nozzle. Since the compensating jet (Auxiliary
Jet) draws fuel from reservoir (Auxiliary Chamber),
which is subjected to atmospheric pressure, through
the air, the quantity of fuel supplied by it to the venturi
does not change to an appreciable extent. This has
the effect of supplying a weaker solution than if only
one jet were provide in which case, the air-fuel
mixture supplied at high speed will be richer then
desired.
Thus the compensating jet enables the air-fuel
mixture of the desirable strength to be supplied. In
fact with correctly proportioned design of various
parts of this carburetor, the fuel supplied by the main
and compensating nozzle can be made to bear
almost a constant ratio to the air supplied.