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Basics of Carburetor:
A carburetor is a device which mixes air and fuel in a proper ratio(as per requirement) for combustion process in Internal Combustion engine. It works on the principle of pressure difference.( Bernoulli’s principle). It is an essential part of the engine and sometimes it is also refereed as heart of a engine( like heart pumps blood to our body). The carburetion or to carburate is the process to mix the air and fuel and then feed it to the Internal combustion Engine.
The carburetor controls the required quantity of fuel and breaks it up into minute globules. This afterward being mixed with the correct quantity of air.
The main purpose of a carburetor is to supply the required quantity of petrol and air mixture. The strength must be correct as per requirement of load conditions of the engine.
Carburetor were widely used in automobile industries in earlier time but with changing time with implementation of new technologies the carburetor is mostly discontinued and is not used. However its not like that , they are still used on small engines like commuter motorcycles, lawn movers and other equipment.
Construction of a Carburetor:
Simple carburetor consists of a venturi and a fuel jet located there-in. For maintaining the level of fuel in the jet, a float chamber is usually required.
A throttle valve in the form of a flat circular metal disc mounted on a spindle. This is provided for controlling the flow of air-fuel mixture to the induction manifold.
A rotary type valve also can be used instead of disc type. The level of fuel is just kept slightly below the top of the jet to prevent the leakage when not in operation. Normally 1.5 mm difference is kept between the top of the jet and the surface of the fuel in the float chamber.
Also there are 2 screws provided in the construction one is for setting air fuel mixture and another one is for setting idle speed of engine also known as idle screw.
Choke: It restricts air flow into the carburetor causing extra fuel to be drawn. Thus creating a Richer Air/Fuel Ratio, which is necessary in an engine cold start .
Types of Carburetors:
- Vertical or up drought
- Inverted or down drought
- Horizontal drought
The carburetor combines fuel and air in the engine by using an intake vacuum supply ( suction created inside cylinder during intake stroke) The air is pulled down by the intake vacuum through to the carburetor passing through the venturi , the increased velocity creates Low Pressure Area causing the fuel to flow from fuel blow through a passage into the venturi, then into the air flow, atomizing and making an air/fuel charge. From here, the fuel and air form a combustible mixture that powers the engine. At high engine speeds, fuel is pulled through the metering jets into the narrowest part of the carburetor throat. It then travels down to the intake manifold where it is burned to produce power in the cylinder/cylinders(if multiple).
If there is not enough fuel in the mixture, the engine could be damaged or the vehicle will not run at all. This is called running lean. If there is too much fuel, the engine can flood, run poorly. Or it may have bad fuel economy, or become very smoky while running. This is called running rich. However, these both problem can be rectified by achieving optimum tuning( correct air /fuel mixture). It can be done by adjusting it through A/F screw.
As the throttle continues to open to obtain normal driving speed and the Venturi are exposed to vacuum, fuel flows. When the throttle is opened completely or if the engine is under a “Load”, the vacuum will drop, which allows a spring loaded valve to open and more fuel to flow to give power and prevent “Detonation”. The carburetor plays an important part in keeping your vehicle in smooth operating condition.
- Earlier used in cars, Bikes(almost all).
- Commuter bikes(50-125 cc), lawn-movers,etc.
- Simple design.
- Cheaper to manufacture.
- Easy to service , repair.
- Spares are easily available.
- Any roadside mechanic can fix all types of carburetor problems.
- Cannot provide a perfect air fuel ratio consistently.
- If not serviced for a long time the vehicle will give problem. The problems may be engine stalling, low fuel efficiency, rough idling, not starting in a single self/ kick, etc.
- Needs to be serviced after a period of time.
- Fuel wastage cannot be controlled.
Popular Manufacturers of Carburetors:
|Fig: Popular manufacturers of carburetor Source: Bing search|
Future of Carburetor:
Carburetors being widely used before 1990’s , are now being replaced by its rival and more efficient device called Fuel Injection commonly known as FI. It is electronically controlled by ECU. But the carburetors are still being used on small bikes ( 50-125 cc). Today no car uses carburetor to power its engine. But with implementation of new technology and strict pollution norms carburetors might be fully replaced by FI in automobile industry. But it may continue to power other applications like lawn-movers,etc.