Carburetors, the heart of automobiles, are described along with its definition, parts, diagrams, how carburetor works along with its various types. We all know vehicles need to run on combustion principles.
It needs fuel gasoline to be mixed with correct proportions of air to cause combustion. This combustion helps to generate the power to move the vehicle.
So how the air-fuel mixture is managed? Here comes the carburetor’s role for managing the air-fuel mixtures for correct quantity.
Though these are not found in modern cars but they were used in almost every vehicle type from commercial to racing. The main goal of the carburetor is to mix just the right amount of air-fuel mixture to get the desired and optimum combustion possible.
We all know that in the case of gasoline or petrol engine, fuel is used and with the help of spark ignition along with air, combustion happens in the combustion chamber. The component which is used to mix the fuel with air for combustion is defined as a carburetor.
Simply, the carburetor supplies fuel for the combustion. It mixes with the air and fuel mixtures at the correct quantity needed for optimum combustion processes.
The optimum air-fuel mixtures are known as stoichiometric ratios. It’s the ideal ratio of air-fuel mixture which is 14.7:1.
It denotes for every 1 gram of fuel you need about 14.7 grams of air for ideal combustion.
That’s where the role of carburetors role kicks in.
The invention of carburetors was going through a very big cycle, let us glance in brief,
Let’s know more about the functions and the parts of the carburetor.
So, what are the parts of the simple carburetors? Let’s try to understand. There are various parts of carburetor.
It has the followings,
A simple carburetor diagram is indicated below, so have a basic idea before the description of carburetor parts.
Let’s check the components one by one.
We have already learned venturi meter, and here, carburetor venturi also works based on the same philosophy. It is basically a passage that has a gradual decrease in its cross-section area.
Function & Working Process
This venturi is narrow in the middle and air is passed through this narrow tube. Airflow is the same within this tube and air velocity is varied based on the cross-sectional area. Air velocity is maximum in the narrowest section.
It reduces pressure and creates slightly low pressure.
Based on the variation of the cross-sectional area, air quantity is adjusted in the mixture.
Based on the shape or function, carburetor venture can be many types,
Check out a very basic understanding of a simple carburetor, by ADTW [a door through a window],
The throttle valve is a major part of the carburation system. We have already learned that there is carburetor venturi is to adjust the airflow. Below the venturi, there is a butterfly valve known as the throttle valve.
It just acts as our home water tap. Just like the water tap the flow can be controlled as fully open or close same happens in case of the throttle valve. It controls the air which can be passed to mix with the fuel.
The throttle valve link is connected to the accelerator of the vehicle.
The strainer is filtering equipment used to filter the fuel.
The function of the strainer is to filtrate. Here, it filters the fuel before entering the float chamber.
How Does Strainer Works
It has a wire mesh structure that is responsible for removing dust and suspended particles. If these particles are not removed it can serious blockage issues and the vehicle will not start.
When the engine is going to be in idle condition, the throttle valve will be almost closed. Airflow through will not be able to create enough vacuum in the carburetor venturi which will not be able to pull the fuel.
In this case, the idle system comes into the picture. This system or circuit helps to feed fuel into the air.
Normally, at below 800 rpm, the carburetor idle system provides the air-fuel mixture.
Off idle or sometimes called part throttle is the main part used to feed more fuel. When the throttle valve is slightly open from the closed position, fuel delivery holes are uncovered.
The idle system alone is not able to meet the fuel requirements in the air stream of the carburetor. When the engine changes from idle condition to high speed, the off idle system is able to supply the fuel.
The low-pressure area is created by the throttle valve which blocks the airflow. Thus, allowing more fuel to enter to compensate reduced vacuum pressure and to smoothing the operation to a regular open circuit.
The idle system will not be able to supply a sufficient amount of fuel alone, and an off idle system is required.
It supplies fuel when the vehicle changes its idle condition to high speed.
The operation of the Off idle system, as follows:
When the throttle valve is getting slightly opened the manifold vacuum gets weakened because of less restriction to airflow. This results in reducing the fuel flow through off-idle circuits. Now the role of Venturi components kicks in.
We know Bernoulli’s principle, where the velocity increases pressure will fall.
As the name suggests it controls the flow of fuel into the nozzle. It is responsible to get the correct mixture of air and fuel.
It has two parts,
As we have already seen low pressure is generated when the air passes through the venturi. Due to this fuel gets discharged into the air stream.
The main function of the metering system shall be as follows,
Hence, the quantity of fuel is controlled by the metering orifice and discharge hole at the exit of the nozzle.
This is for the storage of the fuel so as to maintain the continuous supply of the fuel.
To avoid the heating of the fuel in the float chamber in hot climates the heat deflectors and insulating gaskets are used.
It reduces the “heat soak” effect.
Gasoline is denser than air, so obviously, air will react more and travel quickly compared to Gasoline. When the driver accelerates suddenly the throttle valve opens up immediately tries to admit the mixture even more.
But the air pressure inside the manifold increases which decreases the evaporation of the fuel, this results in less fuel gets entered into the engine.
When the quantity of air is more the mixture is called a lean mixture. When the too lean mixture is transferred to the engine, the engine causes misfiring.
All this problem is corrected by the use Accelerator pump.
The choke valve is most useful in cold climatic conditions. In cold conditions, the fuel is present in less quantity in the cylinders and makes difficult the starting of the engine. So to counter this situation more rich mixture needs to be provided.
In short, more fuel should be supplied compared to the air to start the engine. So the choke controls the flow of air at the entrance of the carburetor.
You may have tried opening up the choke valve mostly on two-wheeler bikes.
Since there are many disadvantages of the simple carburetor, it is modernized and added a few additional modern components, like
Automatic mixture control means a plunger-shaped valve, which is operated by a solenoid and Spring.
When the throttle valve is open completely, the engine will run at a very high speed. It may create a high intake manifold vacuum.
Now, to avert this problem, the throttle return check valve is connected in modern Carburetors with the help of linkages.
Now a day, vehicles are used various modern emission control engines. These engines are normally working at high temperatures.
To avert this pre-ignition, a modern carburetor is provided with an anti-dieseling solenoid and turns off the pre-ignition. Now we have seen all the parts present in the basic carburetor structure.
There are some additions to the newest carburetors like throttle return check, anti-dieseling solenoid, and automatic mixture controls.
Now let’s see how the Carburetor works.
The structure of the carburetor may seem a bit complex but the working is pretty much easy to understand.
Let’s know the working pointwise to understand it easily.
This cycle runs continuously till the vehicle is switched on. There are various types of carburetors used let’s know more about them they are very easy to understand.
There are three types of carburetors namely,
These types are differentiated on the basis of air intake.
The use of carburetors was stopped due to introduction of the fuel injection technology. There are some advantages and disadvantages of the carburetor let’s know them now.
The advantages of carburetors are as follows,
There are disadvantages of carburetors as well, these are,
There are various disadvantages compared to fuel injection. Carburetors are now becoming obsolete as even the small bikes are incorporating fuel injection technology because of advantages and advancements in fuel injection technology.
There are a lot of carburetors manufacturers across the globe, few of them are listed below,
Hence, from this lesson, we have learned the basics of the carburetor, its working principle, types, and many more. If you have any doubt, please write to us.
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