Internal combustion engines mix fuel right, do you know this mixture takes place in the carburetor? Well, the component is often called the heart of an automobile engine but of an old model version. 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!
The primary function of carburetors in an automobile is to mix the exact amount of fuel and air needed to produce power. Thinking of the exact fuel and air an engine needs from time to time will be determined by how long it has been working, how fast the engine is running, and some other factors that will be covered in this article.
Today we’ll be looking at the definition, history, functions, applications, parts, types, and working principle, as well as the advantages and disadvantages of carburetors. This topic is so broad I urge you to stay with us and attain the knowledge.
What is a Carburetor?
A carburetor is a component in an automobile engine that 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.
The working of this component is quite complex in car engines but let me explain. If you have enough atoms of oxygen to burn all your atoms of fuel, that is known as a stochiometric mixture. The term is used in chemistry to ensure there is enough of each ingredient before a recipe is cooked. In the case of an automobile engine, the ratio is usually around 14.7 parts of air to 1 part of fuel.
Although it’s determined by what the fuel is made of. When an engine burns “lean” it’s the cause of too much air and lesser fuel, while too much fuel and less air are called burning “rich.” Note that having slightly too little air (a slightly rich mixture) will offer better performance. Slightly too much air (a slightly lean mixture) will give better fuel economy.
Too much air is not good for engines so having too little, so there should be a proper amount of air intake. So, a simple definition of the carburetor is that it is a device for mixing air with fuel in a system for proper burning of fuel. It’s only seen in gasoline engine that works with spark ignition. Apart from a spark ignition engine, the carburetor is found in small engines for lawnmowers, generators, rototillers, and other equipment.
Functions of Carburetor
Below are the functions of a carburetor in an automobile engine as well as other equipment:
- As earlier mentioned, the primary function of a carburetor is to allow a suitable amount of air and fuel needed to produce power. It’s done at the correct strength under all conditions of load and speed of the engine.
- It regulates the air-fuel ratio and also mixes the fuels.
- Controls the engine speed.
- According to the engine speed and load changes, carburetors increase or decrease the amount of mixture.
- It vaporizes the fuel and mixes the air into a homogeneous air-fuel mixture.
- Also, helps to keep a certain head of fuel in the float chamber all the time.
- Helps the fuel to burn smoothly and properly without any problem.
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:
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.
This part controls the flow of fuel into the nozzle making it responsible for the exact mixture of air-fuel. It consists of a metering orifice and a fuel discharge nozzle.
When air passes through the venturi, the low-pressure field is produced across the throat because of the pressure difference between air and fuel. The fuel is then discharged into the air stream. The metering orifice and a discharge hole at the exit of the fuel discharge nozzle control the quantity of the fuel.
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.
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.
A venturi is a cross-sectional hollow that gradually decreases to reduce the air pressure of the chamber. From it, fuel comes out from the fuel pipe to mix.
A choke valve is another part of the carburetor that controls the mixture of air/fuel. Its purpose is to control the quantity of air inside the mixing chamber. It is a valve that normally stays in semi-open condition, but when a rich mixture is required the valve is operated. The inlet of the air within the chamber is closed so the rich mixture can be obtained. This is a result of the quantity of fuel in the mixture being more because of less air in the chamber. This valve is also helpful in the winter season when engines hardly start. It is used to supply a mixture of rich air-fuel to the engine cylinder.
Float chambers are storage tanks for fuel that aid 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. Also, when the level of fuel decreases in the float chamber the float moves downward. This opens the fuel supply valve and allows more flow of fuel into the float 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 to 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.
In modern engines, a throttle return check v/v is connected to the throttle linkage to avoid this issue.
Automatic Mixture Control:
There is a plunger-shaped valve in a carburetor which 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 supply to the jet. When the solenoid is turned off the spring pushes the valve down to decrease fuel supplied. This solenoid is a computer control system that receives signals from the engine’s speed, and coolant temperature. carburetor with this feature is also called feedback-controlled calculators.
Because modern emission control engine usually runs hotter, resulting 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:
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 the combustion.
There is a limitation with this type of carburetor that makes others more preferred which is that the sprayed fuel droplet must be lifted by air friction.
This makes the carburetor to be designed with a small mixing tube and throat so that even at low engine speeds fuel particles can be lifted by the air velocity. Else, the fuel droplet will separate out providing only a lean mixture to the engine.
On the other hand, the mixing tube is limited and small which makes it insufficient to supply mixture to the engine rapidly at high speeds.
The down-draft carburetor is the most used and 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 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 and in which 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 make the engine speed high and the possibility of high outputs.
There is only one drawback in this type of carburetor which is the possibility of leakage going directly into the inlet manifold if the float is defective and the jet is overflowing.
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 Principle of a Carburetor
The working of a carburetor is 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 airflow 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”, 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.
Below the venturi, the second valve is known as the “Throttle”. It determines the amount of air that enters the carburetor and the amount of fuel it drags in from the pipe to the side. As the throttle is opening the air and fuel flowing in makes the engine release more energy and makes more power making the vehicle move faster. Thus, the throttle makes the car accelerate. The throttle is connected to the accelerator pedal in a car and on the handlebar of a motorcycle.
Watch the video to have a better understanding of how carburetors work:
Advantages and Disadvantages of a Carburetor
Below are the benefits of carburetors in an automobile engine:
- Carburetor parts are less expensive when compared to that of the fuel injector.
- The air and 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 denser mixture in the chamber.
Despite the great benefits of carburetors some limitations still occur. Below are the disadvantages of a carburetor in an engine:
- 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 more fuel when compared with fuel injectors.
- More air emissions than fuel injectors.
- Higher maintenance than fuel injectors.
In summary, the carburetor is an important component in an automobile engine. it allows the exact air/fuel mixture to occur and helps to control the engine speed. its functional components include a metering system, idling system, strainer, venturi, etc. We said the various types of carburetors available out there are known by the direction of airflow.
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