You do realise that fuel is mixed in internal combustion engines? This mixing occurs in the carburetor. New automobiles now use fuel injection for the same process. Nevertheless, the scientific secret behind most transportation, either by land, sea, or sky, is that fuel is turned into power. This is achieved when it burns with air to cause a small explosion, but that is not our purpose here, but maybe!
Contents
Recap
A carburetor is a device in an internal combustion engine for mixing air with a fine spray of liquid fuel. The primary function of carburetors in an automobile is to mix the exact amount of fuel and air needed to produce power.
Parts of a car’s carburetor include the throttle valve, metering system, idling system, strainer, venturi, choke valve, float chamber, mixing chamber, idle and transfer port, throttle return check, automatic mixture control, and anti-dieseling solenoid.
Up-draft carburetors, down-draft carburetors, and horizontal carburetors are the three basic types of carburetors.
Let’s get into more detail!
What is a carburetor?
A carburetor is designed to take in the exact air and fuel needed for proper combustion. The part has been the heart of a vehicle’s engine, making it run smoothly and give better horsepower. Carburetors are so perfect that even at cold starting or running hot at high speed, getting the exact fuel/air mixture is the job of the mechanical gadget.
Functions of Carburetor
Below are the functions of a carburetor in an automobile engine as well as other equipment:
- It regulates the air-fuel ratio and also mixes the fuels.
- Controls the engine speed.
- According to engine speed and load changes, carburetors increase or decrease the amount of mixture.
- It vaporises the fuel and mixes the air into a homogeneous air-fuel mixture.
- It also helps to keep a certain amount of fuel in the float chamber all the time.
- It helps the fuel burn smoothly and properly without any problems.
A brief history of the invention of a carburetor is that carburetors have been around since the 19th century. It was first developed by an automobile pioneer, Karl Benz who is the founder of Mercedes. This, which has become an unforgettable history was designed in 1888 and still, and date carburetors are still in application.
Functional Parts of Carburetors
Below are the major parts of a carburetor:
Throttle Valve: The function of a throttle valve in a carburetor is to control the air/fuel mixture (charge) that enters the engine cylinder. This throttle valve is opened when the accelerating pedal is pressed.
Metering system: This part controls the flow of fuel into the nozzle, making it responsible for the exact mixture of air and fuel. It consists of a metering orifice and a fuel discharge nozzle.
Idling system: The passage from the float chamber to the venturi tube is called an idling system. It offers a rich mixture during idling and at low speed. It works when the throttle is open below 15% or during idling.
Strainer: A strainer is a device that filters the fuel before entering the float chamber. It is made of a fine wire mesh, which filters the fuel from dust and other suspended particles. Nozzles get blocked if particles are not removed from the surface of the strainer.
Venturi: A venturi is a cross-sectional hollow that gradually decreases to reduce the air pressure in the chamber. From it, fuel comes out of the fuel pipe to mix.
Choke Valve: A choke valve is another part of the carburetor that controls the mixture of air and fuel. Its purpose is to control the quantity of air inside the mixing chamber. It is a valve that normally stays in a semi-open condition, but when a rich mixture is required, the valve is operated.
Float Chamber: Float chambers are storage tanks for fuel that aid in the continuous supply of fuel. It features a floating valve that maintains the level of fuel in the float chamber. When the fuel level increases, the float moves upward, which closes and stops the fuel supply.
Mixing Chamber: The mixing chamber is where the air and fuel mixture takes place, which is then transferred to the engine cylinder.
Idle and transfer port: In the carburetor’s venturi, there are two nozzles or ports that help deliver fuel to the engine cylinder. In modern automobile engines, there are some additional parts that feature their carburetors to improve efficiency. These parts include:
Throttle Return Check: The fact that the total throttle on an engine running at a very high speed causes a very high intake manifold vacuum. This will draw exhaust into the engine intake during v/v overlap. The intake chart will be diluted, causing misfiring or stalling.
Automatic Mixture Control: There is a plunger-shaped valve in a carburetor that is controlled by a solenoid and spring. It operates the separate jet in the float chamber. The solenoid is turned on, and the v/v is lifted to increase the amount of fuel supplied to the jet.
Anti-dieseling solenoid: Because modern emission control engines usually run hotter, this results in some hot spots in the combustion chamber. These hot spots cause pre-ignition in the chamber. Carburetors are designed with an anti-dieseling solenoid in modern engines to prevent pre-ignition.
Types of Carburetors
Below are the various types of carburetors which are considered according to the direction of airflow:
Up-draft carburetor:
In the up-draft types of carburetor, air enters through the bottom side and leaves through the top. This is to let the direction of its flow upward. The fuel comes from the float chamber and the pressure difference within the two-chamber is achieved by venturi. Fuel comes out from the fuel pipe and mixes with the inlet air to make the fuel-air mixture. The fuel passes through the throttle valve, which is directly connected to the accelerator. This mixture then goes into the engine cylinder to perform combustion.
Down-draft Carburetor:
The down-draft carburetor is the most common because of its advantages. It supplies air from the top portion of the mixing chamber. Some of its advantages include:
- The gravity assists the flow of the mixture, making the engine pull better at lower speeds under load.
- The position of the carburetor is easily accessible.
- A higher value of volumetric efficiency can be achieved with an engine with such a part.
Though some disadvantages still occur, before that, let me explain why it is considered better than the up-draft type:
To prevent the limitation of down-draft carburetors revealed above, up-draft is the only option. It is placed at a level higher than the inlet manifold, where the air and mixture will generally follow a downward course.
The fuel is not lifted by air friction like the first type; it moves into the cylinders by gravity even if the air velocity is low. Thus, the design of the mixing tube and throat can be made large, which will increase the engine speed and the possibility of high outputs.
Horizontal Carburetor:
The horizontal carburetor is the third type, which is known when a down-draft carburetor is in a horizontal direction. Its working principle is very simple. The carburetor stays in a horizontal position where the air is coming in through one end of it. it mixes the fuel before going into the engine cylinder for combustion.
Working Principles of a Carburetor
The workings of a carburetor are quite simple but complex, depending on the design. However, the simplest is the one with a large vertical air pipe above the engine cylinders. It has a horizontal fuel pipe joined into one side. As air flows down the pipe, it passes through a narrow kink in the middle.
This kink makes it speed up and causes its pressure to fall. The kink is known as venturi. The sucking effect that draws air in through the fuel pipe at the side is caused by the falling pressure of the air. The airflow pulls the fuel along, causing their mixture, which is its intended purpose. The mixture is caused in the carburetor by two swivelling valves, which are located above and below the venturi.
The valve at the top is called “Choke,” and it regulates the amount of air that flows in the carburetor. If this choke is closed, a little amount of air flows down through the pipe, and the venturi sucks in more fuel. This caused the engine to get a rich fuel mixture, which is helpful when the engine is cold, first starting up, and running slowly.
Watch the video to get a better understanding of how carburetors work.
Advantages and Disadvantages of a Carburetor
Advantages:
- Carburetor parts are less expensive when compared to that of the fuel injector.
- The air-fuel mixture is perfectly done with the components.
- It has more power and precision than the air-fuel mixture.
- The engine component is not restricted by the amount of gas pumped from the fuel tank. This is to say, the cylinders may pull more fuel through the carburetor, leading to greater power and a denser mixture in the chamber.
Disadvantages:
- The mixture supplied at a very low speed is weak, making the engine not perfectly ignite.
- The engine part can be affected by changes in atmospheric pressure.
- More fuel is consumed when compared with fuel injectors.
- More air emissions than fuel injectors.
- Higher maintenance than fuel injectors.
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