What is Carburetor? & 9 Different Types of Carburetor with Explanation

In this post, you will learn what is carburetor and its working principle, Eight different types of carburetors with its functions.

Carburetor and Types of Carburetors:

A carburetor is a device for atomizing and vaporizing the fuel and mixing it with the air in varying proportions to suit the changing condition of spark ignition engines. The air-fuel mixture so obtained from the carburetor known as the combustible mixture.

The carburetor is the most important part of the fuel system of spark ignition engines. the carburetor is attached between the fuel filter and the induction manifold. If supplies the air-fuel mixture of varying proportions to suit engine operating conditions.

The liquid fuel enters the float chamber of the carburetor. And the air enters the air horn of the carburetor. Mixing of the fuel and air takes place when both pass through the venturi in the mixing chamber of the carburetor. This air and fuel mixture then goes to the intake manifold.

Types of Carburetors

Following are the different types of carburetors:

1. According to the arrangement of the float chamber:
   1. Eccentric
   2. Concentric
2. According to the direction of air flow:
   1. Downdraft.
   2. Side draft.
   3. Up draft.
   4. Semi-down draft.
3. According to the number of units:
   1. Single
   2. Dual
   3. Four-barrel.
4. According to the type of metering system:
   1. Air-bleed jet.
   2. Metering rod type.
5. According to the types of venturi:
   1. Plain venturi.
   2. Double venturi
   3. Vane venturi
   4. Nozzle-bar venturi
   5. Triple venturi.
6. According to the pressure above the fuel in the float chamber:
   1. Unbalanced.
   2. Balanced.
7. According to the type of power system:
   1. Manually operated
   2. Vacuum controlled
8. According to the method of varying the mixture strength:
   1. Constant choke carburetor.
   2. Constant vacuum carburetor.
9. Typical Carburetors
   1. SU Carburetor
   2. Solex Carburetor
   3. Zenith Carburetor
   4. Carter Carburetor

Carburetor

The process of mixing the gasoline the fuel with air to get the combustible mixture known as carburetor.

Understanding The Terms Vaporization and Atomization

1. Vaporization- It is the change of state of the fuel from liquid to vapour.
2. Atomization- It is the mechanical breaking-up of the liquid fuel into small particles so that every particle of the fuel is surrounded by air.

To produce quick vaporization of the liquid fuel, it is sprayed into the air passing through the carburetor. Spraying of the liquid turns it into many fine particles so that the vaporization occurs almost instantly.

A carburetor supplies the air-fuel mixture of varying proportions to suit the changing conditions of the engine. The mixture must be rich (have a higher percentage of fuel) for starting, acceleration, and high-speed operation.

The mixtures should be mean (have a lower percentage of fuel) for operation at intermediate speed with a warm engine. The theoretically perfect mixture of air and gasoline contains 15 parts of air and 1 part fo gasoline by weight. An ideal carburetor passes the mixture off completely vaporized fuel and air, in the proper proportion to the intake manifold and cylinder.

But in the present-day carburetors, the complete vaporization of fuel is not achieved, due to the heavy nature of the fuel and other limitations. The heated intake manifold and hot-spots in the manifold vaporise part of atomized fuel.

Even until the end of the compression stroke in the cylinder, the gasoline does not vaporize completely. Although the heat and pressure during the compression stroke are applied to it.

1. A Carburetor According to The Arrangement of Float Chamber

1. Eccentric
2. Concentric

• In eccentric float chamber types of carburetors, the float chamber is placed at a side of the venturi tube.
• In concentric float chamber types of carburetors, the float chamber is placed around the venturi tube.
• The eccentric float chamber type carburetor does not provide correct air-fuel mixture when the vehicle is ascending a grade.
• When the vehicle is running on a horizontal road, the level of the gasoline in the float chamber and the discharge jet is normal, as at (A). The carburetor correct air-fuel mixture to the engine.

• When the vehicle is ascending or descending a grade, the carburetor is tilted and the level of the gasoline changes in the discharge jet as at (b) and (c). This causes too much or too little gasoline to be supplied by the jet giving incorrect mixtures. The concentric float chamber type carburetors do not have this difficulty.

The level of the gasoline in the discharge jet remains approximately constant, which provides the correct air-fuel mixture to the engine in all positions of the level.

2. The Carburetor According to the direction of Air-Flow:

1. Downdraft.
2. Side draft.
3. Up draft.
4. Semi-down draft.

• In downdraft carburetor types of carburetors, the air enters the top of the carburetor rettor and leaves at the bottom, as in the figure.

• A side-draft carburetor types of carburetors, the air enters the top of the carburetor and leaves at the side, as at (b).

• In updraft carburetor types of carburetors, the air enters the bottom or side of the carburetor and leaves at the top, as in the figure.

• The semi-downdraft carburetor types of carburetors, the direction of air flow is inclined from top to bottom, as at (d).

In most passenger cars, the downdraft carburetor is used. This type of carburetor, The gravity assists the flow of the mixture. Thus, the engine sucks it better at lower speeds under load. the higher volumetric efficiency of the engine is achieved. The location of the carburetor above the engine is more accessible for inspection change or repair. An air entering the carburetor is cooler.

Read also: Types of Cooling System In Automobile Engines (I.C Engine)

3. Carburetor According to The Number of Units:

1. Single
2. Dual
3. Four-barrel.

• Single barrel carburetor has only one barrel.

• Dual barrel carburetor has two barrels, each containing a fuel jet, venturi tube idling system, choke and throttle. It may have a single air inlet, choke and float chamber, although it frequently has two floats one for each jet. It has only an accelerating pump.

Usually, the passenger car engines of eight or more cylinders are provided with of the dual carburetor having the dual intake manifold. Each barrel of the dual carburetor feeds one branch of the intake manifold. This arrangement provides uniform distribution of the fuel mixture to the cylinders.

• Four the barrel, the carburetor is made up of two dual carburetor in one unit. The primary side to a complete dual carburetor containing a choke, an accelerating pump, a power valve and a complete main metering and idle system. The secondary unit has its one float bowl and a dual carburetor main metering system and idle system.

4. Carburetor According to The Type of Metering System:

1. Air-bleed jet.
2. Metering rod type.

• In the air bleed jet types of carburetors, the fuel is supplied to the main discharge nozzle through the main metering jet at low speeds.

The air bleeds are connected to a vent tube located inside the main discharge nozzle so that air is mixed with fuel as it is drawn into the carburetor venturi.

As the suction of the main discharge nozzle increases at higher speeds, more air is drawn through the main air bleed and the correct air-fuel mixture is maintained.

In the metering rod types of carburetors, the amount of fuel is controlled by a rod which extends into the jet. The metering rod has three steps of different diameter. Which opens the space in the jet through which the fuel passes.

The metering rod is connected to the throttle shaft by the suitable linkage. so that it is raised when the throttle valve is opened and lowered when the throttle valve is closed.

When the rod is raised up, it provides more area between the jet and the rod and more fuel passes to match the flow of ait at high speeds.

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5. Carburetor According to the type of Venturi

1. Plain venturi.
2. Double venturi
3. Vane venturi
4. Nozzle-bar venturi
5. Triple venturi.

• Different types and number of venturies are used in the carburetor design, according to which the carburetors are classified.
• The carburetor may have plain, double, vane, nozzle-bar and triple venturi.
• Each type of the venturi is designed to provide the decreased pressure of air flow so that it may draw fuel from the discharge jet.
• Multiple venturies help to keep the fuel away from the carburetor walls to reduce condensation.

6. Carburetors According to the Pressure above the Fuel in the float chamber:

1. Unbalanced.
2. Balanced.

• If the pressure above the fuel in the float chamber is atmospheric pressure, the carburetor is said to be unbalanced.
• If the pressure above the fuel in the float chamber is equal to the air intake in the air horn, the carburetor is said to be balanced.

The balanced carburetor contains a balance tube and passages that connect the air-horn with the top of the float chamber so that the pressure in the air horn and the float chamber remains the same.

In the case, if the air intake is restricted by a clogged air cleaner, the mixture ratio of the carburetor is not affected. Also, it prevents discharge of the fuel through the pump discharges jet at high speeds.

Read also: What is Air Cooling System and How It Works In Vehicle

7. Carburetor According to the Types of Power System:

1. Manually operated
2. Vacuum controlled.

According to the type of power system, the carburetor may be either manually operated or vacuum controlled.

• In the manually operated carburetor. the power jets for enriching the mixture are operated by mechanical linkage to the throttle shaft.
• In vacuum controlled carburetor a vacuum controlled power jet (called a step-up system) is used for enriching the mixture.

When the engine is operating normally at cruising speed, no-load, a high vacuum is produced in the vacuum passages connected to the intake manifold. It pulls the vacuum piston down against the spring so that it holds the step up the rod in the step-up (power) jet to keep it closed.

When the engine is operating on load the intake manifold vacuum falls off, and the spring pushes the piston up which raises the step up the rod out of the jet to allow extra fuel to flow from the float chamber to the discharge nozzle. The extra fuel supplements the normal supply furnished by the main metering jet. Thus enriching the mixture.

8. Carburetor According to the method of Varying the Mixture Strength:

1. Constant choke carburetor.
2. Constant vacuum carburetor.

In the constant choke carburetor, the mixture strength is determined by the varying depression of a fixed tube or venturi.

• Solex and zenith carburettor are of this type.

In the constant vacuum carburetor, depression in the choke tube is reasonably constant. And the size of the jet is varied to provide the correct mixture for all engine operating conditions.

• S.U. the carburetor is an example of a constant vacuum carburetor.

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