CARBURETTOR AND THE PROCESS OF CARBURETION

 

CARBURETOR                                                                                  Subhankar Karmakar

DEFINITION: A carburetor is a device that mixes air and fuel in the correct proportion for combustion in an internal combustion engine. The process of mixing air and fuel in a carburetor is known as carburetion.

STRUCTURE: The carburetor has a narrow opening called the throttle, which controls the amount of air that enters the engine. When the throttle is opened, air is drawn into the carburetor and mixed with fuel. The amount of fuel that is mixed with the air is controlled by a valve called the fuel valve, which regulates the flow of fuel into the carburetor.

 

Once the air and fuel are mixed, the resulting mixture is drawn into the engine through the intake manifold. The fuel and air mixture is then ignited by a spark plug, which causes the fuel to burn and produce energy. This energy is used to power the engine and propel the vehicle.

 

The carburetor must be adjusted to ensure that the fuel and air mixture is correct for the specific engine and driving conditions. If the mixture is too lean (too much air and not enough fuel), the engine will run poorly and may even overheat. If the mixture is too rich (too much fuel and not enough air), the engine may run rough and produce excessive emissions.

 

Carburetors were commonly used in older cars, but they have been largely replaced by fuel injection systems in modern vehicles. However, they are still used in some small engines, such as those found in lawnmowers and chainsaws.

 

CARBURETOR IN PETROL ENGINE:

 

A carburetor is a device that mixes air and fuel in the correct ratio before it enters the engine's combustion chamber. It was commonly used in older petrol (gasoline) engines before the advent of electronic fuel injection systems.

 

The basic principle of operation of a carburetor is that it uses a venturi, a narrow section of the carburetor through which air is forced to flow at high speed. As the air moves through the venturi, it creates a vacuum that draws fuel into the airflow, which mixes with the air and forms a combustible mixture.

 

The carburetor consists of several components, including a throttle valve, a choke, an idle speed adjustment screw, and a fuel bowl. The throttle valve controls the amount of air entering the engine, while the choke is used to enrich the air-fuel mixture when starting the engine. The idle speed adjustment screw regulates the engine's idle speed, while the fuel bowl stores the fuel that is drawn into the carburetor.

 

While modern petrol engines typically use electronic fuel injection systems, carburetors are still used in some older engines, as well as in small engines such as those used in lawnmowers, chainsaws, and other small equipment.

 

CARBURETOR IN DIESEL ENGINE:

 

A carburetor is a device used in gasoline engines to mix air and fuel in the correct proportions before it enters the engine cylinders for combustion.

 

However, diesel engines do not use carburetors. Instead, they use a fuel injection system, which injects fuel directly into the combustion chamber at the appropriate time, under high pressure.

 

In a diesel engine, air is compressed in the cylinder, causing it to heat up. When the air is hot enough, fuel is injected into the combustion chamber, where it ignites spontaneously due to the high temperature and pressure, without the need for a spark plug.

 

The fuel injection system in a diesel engine is more complex than a carburetor and requires precise control over the amount and timing of fuel injection to optimize combustion efficiency and reduce emissions.

COMPONENTS OF A CARBURETOR:

Carburetor in Petrol (Gasoline) Engine:

A carburetor is a crucial component in older petrol engines, responsible for mixing air and fuel in the correct ratio before it enters the engine's combustion chamber. Here's a more detailed breakdown of its components and operation:

1. Venturi Principle: The core principle behind a carburetor's function is the Venturi effect. A venturi is a narrow section within the carburetor where air is forced to flow at high speeds. As air passes through the venturi, it accelerates, creating a region of low pressure. This low-pressure area effectively "sucks" fuel from a reservoir into the air stream.
2. Throttle Valve: The throttle valve, also known as the butterfly valve, controls the amount of air entering the engine. When you press the accelerator pedal, it opens the throttle valve wider, allowing more air to pass through, and vice versa.
3. Choke: The choke is a mechanism used to enrich the air-fuel mixture when starting a cold engine. By restricting the airflow, it increases the fuel-to-air ratio, making it easier for the engine to start in cold conditions.
4. Idle Speed Adjustment Screw: This screw allows adjustment of the engine's idle speed. By controlling the amount of air allowed to bypass the closed throttle valve, it regulates the engine's speed when it's not under load.
5. Fuel Bowl: The fuel bowl is a reservoir that stores fuel. Fuel is drawn from the bowl into the venturi as needed to maintain the correct air-fuel mixture.

Carburetor in Diesel Engine:

Diesel engines operate differently from petrol engines, and they do not use carburetors. Instead, they employ a fuel injection system, which works as follows:

1. Compression Ignition: Diesel engines rely on high compression ratios to generate the heat needed for ignition. As air is compressed within the cylinder, its temperature increases significantly. When the piston reaches the top of its compression stroke, fuel is directly injected into the hot, highly compressed air.
2. Fuel Injection System: Diesel fuel injection systems are highly precise and operate under high pressure. They consist of injectors that spray a fine mist of diesel fuel directly into the combustion chamber at the precise moment required for ignition. The injection timing and quantity are controlled electronically or mechanically for optimal efficiency and emissions control.
3. No Spark Plugs: Unlike petrol engines, diesel engines do not require spark plugs because the high temperature and pressure in the cylinder are sufficient to ignite the fuel without the need for an external spark.

While carburetors were widely used in older petrol engines, diesel engines operate on a different principle altogether, using fuel injection systems to introduce fuel directly into the combustion chamber. Modern petrol engines have also largely transitioned to electronic fuel injection systems due to their efficiency and emissions control advantages. Carburetors are still found in some older engines and small equipment, but they are becoming increasingly rare in automotive applications.