A car’s internal combustion engine depends on the mixture of fuel and air. The key is regulating the amount of fuel air mixture from the moment you start your engine till you reach the destination. This is either achieved by carburettors or fuel injectors.
Modern cars have phased out carburettors as they are replaced by electronically controlled fuel injectors. Older and especially classic cars still rely on carburettors. The fuel system is known for its simplicity and understanding how a carburettor works has an interesting science behind it.
How Carburettor Works
A carburettor usually consists of a vertical chamber with a float chamber to disperse fuel. The air enters into the carburettor from the top through air filters to remove the contaminants. It passes through the choke valve, which controls the amount of air entering the system.
The centre chamber, known as venturi, has a narrow zone to speed up the flow of air and reduce the pressure. This creates a pressure difference between the air and fuel in the float chamber.
The float chamber is designed to keep a certain amount of fuel with the help of a fuel supply valve. The chamber is usually ventilated to keep it at atmospheric pressure. Hence, when air flows through the venturi, the drop in pressure creates a suction for fuel at the atmospheric pressure.
The pressure difference between the venturi and float chamber is known as carburettor depression. The small discharge nozzle from the float chamber at the venturi allows fuel to atomise and mix with the air.
Since the amount of mixture needs to be controlled based on engine power, the throttle valve below the venturi manages it. For instance, an open throttle valve will allow more fuel and air to pass through, which leads to more power production in the engine. If the throttle valve is partially open, less air will flow across the chamber. This in turn reduces the pressure drop and allows less fuel to discharge from the nozzle. Hence, a controlled mixture reaches the engine based on the requirement.
When the engine is not in motion, the throttle valve shuts off. A separate nozzle below the throttle valve allows a small amount of fuel air mixture to enter the engine to keep the engine running while it is idling.
Types of Carburettor
There are three main types of vehicle carburettors for automotive engines depending on flow direction of fuel and air mixture.
- Up-draught Carburettor: The air enters the carburettor from the bottom and goes upward against the gravity. Since the air has to lift the atomized fuel, the carburettor cannot supply the mixture to the high speed engine rapidly.
- Downdraught Carburettor: The carburettor is commonly used as air flow across the chamber with the assistance of gravity. The carburettor functions well for low and high speed engines. Since the downdraught carburettor is installed higher than the intake manifold, leakage from the float chamber can enter the inlet manifold.
- Horizontal Carburettor: The carburettor is basically a rotated downdraught carburettor. The layout is ideal when there is constraint space in the engine.
FAQs
How often do you clean a car carburettor?
For maximum efficiency of the engine in the dry weather of the UAE, the car maintenance schedule must include cleaning of carburettor after every six months.
Do cars still have carburettors?
With the advent of fuel injections, vehicle carburettors are now a history. Various manufacturers stopped using carburettors by the late 1980s. Some cars continued to use it till 1990’s. Nowadays, fuel injectors have replaced the carburettors.
Carburettors are no longer standard in most cars as fuel injectors were found to be a better alternative. The electronic fuel injectors give more precision in mixing air fuel, resulting in reduced fuel consumption, improved efficiency and better power delivery. However, when it comes to maintenance, it’s cheaper to replace a mechanical carburettor than an electronic fuel injector.
If you are facing problems with car fuel system or requires frequent visits to auto workshops, explore your options with used cars for sale in the UAE to find some affordable replacement.
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