Parts of carburetor and function

A carburettor consists of the following main parts :

• Fuel strainer
• Float chamber
• Main fuel metering and idling nozzles 
• Chock and throttle 

Parts that mentioned above are discussed briefly below : 

• The fuel strainer :

As the petrol has to pass through a narrow nozzle exit there is every possibility that the nozzle may get clogged prolonged operation of the engine. To prevent this possibility of blockage of the nozzle by dust particles, the petrol is filtered by installing a fuel strainer at the inlet of the float chamber. 

The strainer made of a fine wire mesh or another type of filtering device. The fuel strainer is an either cone-shaped or cylindrical shape. 

• The float chamber :

The float chamber is to supply the fuel to the nozzle at a constant pressure head. This is possible by maintaining a constant level of fuel in the float bowl. The float in a carburettor is provided to control the level of fuel in the float chamber. In order to provide the correct amount of fuel and to prevent the leakage of fuel from the nozzle fuel level must be maintained slightly below the discharge nozzle outlet holes. 

• The main fuel metering and idling system :

The main fuel metering system of the carburettor controls the fuel feed for cruising and the full-throttle operations. 

It consists of three principles:

• The fuel metering orifice through which fuel is drawn from the float chamber.
• The main discharge nozzle.
• The passage leading to the idling system. 

The main three functions of the main metering system are :

• To proportion the air-fuel mixture.
• To decrease the pressure at the discharge nozzle exit.
• To limit the airflow at full throttle. 

• Chock and throttle :

When the vehicle is kept stationary for a long period during cold whether it may be overnight too then starting of the vehicle becomes more difficult. 

For low cranking speeds and intake temperatures, a very rich mixture is required to initiate the combustion. The main reason is that a very large fraction of fuel may remain as liquid suspended in the air even in the cylinder. The most popular method of providing such mixture is by the use of chock valve.

Throttle valve controlled the speed and the output of an engine. The more the throttle is closed the greater is the obstruction to the flow of the mixture placed in the passage and the less is the quantity of mixture delivered to the cylinders. 

As the throttle is opened, the output of the engine increases. But this is not always the case as the load on the engine is also a factor.  

As we discuss the throttle is simply a means to regulate the output of the engine by varying the quantity of charge going into the cylinder.

Simple carburetor | Construction | Working | Drawback

Construction and working of simple carburettor:

Carburettors are highly complex provides an air-fuel mixture for cruising or normal range at a single speed. Later, other mechanisms to provide for the various special requirements like starting, idling, variable load and speed operation and acceleration will be included. Below Figure shows that the details of the simple carburettor. 

The simple carburettor mainly consists of a float chamber, fuel discharge nozzle and a metering orifice, a venturi, a throttle valve and a choke. The float and a needle valve system maintains a constant level of gasoline in the float chamber. 

If the amount of fuel in the float chamber falls below the designed level, the float goes down, thereby opening the fuel supply wire and admitting fuel. The float closes the fuel supply valve thus stopping additional fuel flow from the supply system when the design level has been reached. The float chamber is vented either to the atmosphere or to the upstream side of the venturi. 

During suction stroke air is drawn through the venturi. Now the first question arise in your mind that what is venturi?

It is a tube of decreasing cross-section with a minimum area at the throat. Venturi tube is also known as the chock tube and is shaped that it offers minimum resistance to the airflow. The velocity increases and reaching a maximum at the venturi throat when the air is passing through the venturi.

Correspondingly, the pressure decreases and reaches a minimum. From the float chamber, the fuel is fed to a discharge jet, the tip of which is located in the throat of venturi. Fuel is discharged into the airstream because of differential pressure known as carburettor depression. The fuel discharge is affected by the size of the discharge jet and it is used to give the required air-fuel ratio. As the throttle is fully opened the pressure lies between 4 to 5 cm of HG, below atmospheric and sometimes exceeds 8 cm Hg below atmospheric. 

To avoid overflow of fuel through the jet, the level of liquid in the float chamber is maintained at a level slightly below the tip of the discharge jet. It is also known as the tip of the nozzle. The difference in the height between the top of the nozzle and the float chamber level is marked as h. 

The gasoline engine is quantity governed, which means that when the power output is to be varied at a particular speed, the amount of charge delivered to the cylinder is varied. This is achieved by means of a throttle valve. All the parts and its functions are described below. 

A carburettor consists of the following main parts :

• Fuel strainer
• Float chamber
• Main fuel metering and idling nozzles 
• Chock and throttle 

Parts that mentioned above are discussed briefly below : 

• The fuel strainer :

As petrol has to pass through a narrow nozzle exit there is every possibility that the nozzle may get clogged prolonged operation of the engine. To prevent this possibility of blockage of the nozzle by dust particles, the petrol is filtered by installing a fuel the strainer at the inlet of the float chamber. 

The strainer made of a fine wire mesh or other types of filtering device. The fuel strainer is either cone-shaped or cylindrical shape. 

• The float chamber :

The float chamber is to supply the fuel to the nozzle at a constant pressure head. This is possible by maintaining a constant level of fuel in the float bowl. The float in a carburettor is provided to control the level of fuel in the float chamber. In order to provide the correct amount of fuel and to prevent the leakage of fuel from the nozzle fuel level must be maintained slightly below the discharge nozzle outlet holes. 

• The main fuel metering and idling system :

The main fuel metering system of the carburettor controls the fuel feed for cruising and the full-throttle operations. 

It consists of three principles:

• The fuel metering orifice through which fuel is drawn from the float chamber.
• The main discharge nozzle.
• The passage leading to the idling system. 

The main three functions of the main metering system is:

• To proportion the air-fuel mixture.
• To decrease the pressure at the discharge nozzle exit.
• To limit the airflow at full throttle. 

• Chock and throttle :

When the vehicle is kept stationary for a long period during cold weather, it may be overnight too then starting of vehicle becomes more difficult. 

For a low intake temperatures and cranking speed a very rich mixture is required to initiate the combustion. The main reason is that a very large fraction of fuel may remain as liquid suspended in the air even in the cylinder. The most popular method of providing such mixture is by the use of chock valve.

Throttle valve controlled the speed and the output of an engine. The more the throttle is closed the greater is the obstruction to the flow of the mixture placed in the passage and the less is the quantity of mixture delivered to the cylinders. 

As the throttle is opened, the output of the engine increases. But this is not always the case as the load on the engine is also a factor.  

As we discuss the throttle is simply a means to regulate the output of the engine by varying the quantity of charge going into the cylinder.

Drawback of simple carburettor:

• A fundamental drawback is providing the required A/F ratio only at one throttle position.
• While at the other throttle positions the mixture is either leaner or richer depending on whether the throttle is opened less or more. 

What are the advantages of dual carburetor over single barrel carburetor?

The single-barrel carburettor has only one barrel, whereas a dual carburettor has two-barrel. Engine with higher displacement requirement is large-bore to provide adequate airflow makes throttle response too fast so some automobile manufacturer used two-barrel used in carburettor in this type of engine. Let us have a deep insight into the advantages of used dual carburettor over single barrel carburettor?

Advantages of dual carburettor : 

• The duel carburettor supplies a charge of a mixture to the cylinders which are uniform in quality. 
• Volumetric the efficiency of the dual carburettor is higher than a single barrel carburettor. 
• The charge of the air-fuel mixture is distributed to each cylinder in a better manner. 
• The dual a carburettor is compact in its design. 

Why are double barrel used in the carburettor?

The fight is only and only efficiency and performance when the question comes to the carburettor. Many older carburettors are single barrel which is fine for low HP applications. The problem is that higher displacement engine as we have seen in the first paragraph. To getting a fairly constant fuel-air ratio across the engine double-barrel carburettor can be optimised. At low RPM and low power demand, only one provides a fuel-air mix to the engine. When more RPM or power is required, the second barrel comes into play and allowing the different fuel-air ratio to be used and provide a better fuel-air mix to the engine. 

Carburetor size

The size of a carburettor is generally given in terms of the diameter of the venturi tube in mm and the jet size in hundredths of a millimetre. 

The calibrated jets have a stamped number which gives the flow in ml/min under ahead of 500 mm of pure benzol. 

Jet size is usually one-sixteenth of venturi size. 

For a venturi of 30 to 35 mm size, the pressure difference (p1-p2) is about 50 mm of Hg. The velocity at the throat is about 90 - 100 m/s and the coefficient of discharge for venturi Cda is usually 0.85. 

Normally the size of carburettor 1 or 2, 3 or 4 barrel, a little bit of confuse about the size so there is a formula for choosing a proper size in cfm for your engine.

Formula :

First step: CC full form is cubic displacement divided by 2.

Second step: Maximum RPM is divided by 1728.

Third step: Multiple above two step figure. 

Fourth step: Multiply third step answer with volumetric efficiency for that engine depending on what you have done with your heads and exhaust. 

Fifth step: Final Answer in cfm.

Factor affecting carburetion

The process of carburetion is influenced by various factors following below :

• The engine Speed 
• The vaporization characteristics of the fuel 
• The temperature of the incoming air 
• The design of the carburettor 

Since modern engines are of high-speed type, the time available for mixture formation is very limited. 

For example, An engine running at 2500 RPM has only about 10 milliseconds for mixture induction during the intake stroke. When the speed become 5000 RPM the time available is only 5 millisecond.

therefore in order to have high-quality carburetion, the velocity of the airstream at the point where the fuel is injected has to be increased. This is achieved by introducing a venturi section in the path of the air. The fuel is discharged from the main metering jet at the minimum cross-section of venturi. 

Other factors which ensure high-quality carburetion within a short period are the pressure of highly volatile hydrocarbons in the fuel. Therefore, suitable evaporation characteristics of the fuel indicated by its distillation curve are necessary for efficient carburetion, especially at high engine speeds. 

Also, another parameter like the temperature and pressure of the surrounding area has a large influence on efficient carburetion. Higher atmospheric air temperature increases the vaporization of fuel and produces a more homogeneous mixture. An increase in atmospheric temperature leads to a decrease in power output of the engine when the air-fuel ratio is constant due to reduces mass flow into the cylinder or in other words reduced volumetric efficiency. 

The design of carburetor, the intake system and the combustion chamber have influence on uniform distribution of mixture to the various cylinders of the engine. proper design of carburetor elements alone ensures supply of desired composition of the mixture under different operating condition of the engine.

Advantages of multiple venturi carburetion system

When one or more secondary venturi enclosed inside the main venturi of a carburettor is called multiple venturi carburettor and this carburetion system is called a multiple venturi carburetion systems. Benefits of using this and results of multiple venturi carburetion system are listed below. 

Advantages of multiple venturi carburetion system : 

• Reducing condensation of the fuel :

The main jet discharges the fuel into the primary venturi in an upward direction against the downward airstream in a multiple venturi system. The airflow atomizes the fuel. The primary venturi keeps the fuel thus atomized in the primary venturi centrally located in the air stream.

In addition, a blanket of air surrounding the primary venturi and passing into the secondary venturi keeps the atomized fuel in the air stream centrally located. Through this process, the carburettor walls are protected for a certain distance from coming into contact with fuel, thus reducing condensation.

• High-speed system : 

The throttle valve is sufficiently opened when the speed is to be increased from low to high. The air flows faster through the primary venturi when the throttle valve is wider open. In the portion of the jet orifice, this airflow produces a vacuum. Because of this increase in a vacuum, the main jet will discharge additional fuel. The high-speed system maintains an almost constant air-fuel ratio.

• Due to high depression created at the region of fuel nozzle better automatization, and better control of fuel.
• The excellent air-fuel mixture is achieved without any reduction in volumetric efficiency.  
• The excellent low-speed full throttle operation is provided.

Chemical structure of petroleum

Petroleum, as obtained from the oil wells, is predominantly a mixture of many hydrocarbons with differing molecules structure. It also contains a small amount of sulphur, oxygen, nitrogen and impurities such as water and sand. 

The carbon-hydrogen atoms may be linked in different ways in a hydrocarbon molecule and this linking influences the chemical and physical property of different hydrocarbon groups. Most petroleum fuels tend to exhibit the characteristics of that type of hydrocarbon which forms a major constituent of the fuel. 

The carbon and hydrogen combine in different proportions and molecular structure to form a variety of hydrocarbons. The carbon to hydrogen ratio which is one of the important parameters and their nature of bonding determine the energy characteristics of the hydrocarbon fuels. Depending upon the number of carbon and hydrogen atoms the petroleum product is classified into different groups. 

The differences in physical and chemical properties between different types of hydrocarbon depend on the chemical composition and affect mainly the combustion process and hence, the proportion of fuel and air required in the engine. The basic families of hydrocarbons, their general formula and their molecular arrangement are shown below :

1. Paraffin :

• General formula: C_nH_2n+2
• Molecular structure: Chain 
• Saturated / Unsaturated : Saturated 
• Stability: Stable 

2. Olefin :

• General formula: C_nH_2n
• Molecular structure: Chain 
• Saturated / Unsaturated : Unsaturated 
• Stability: Unstable 

3. Naphthene :

• General formula: C_nH_2n
• Molecular structure: Ring 
• Saturated /Unsaturated: Highly saturated 
• Stability: Most stable 

4. Aromatic : 

• General formula: C_nH_2n-6
• Molecular structure: Ring 
• Saturated / Unsaturated : Unsaturated 
• Stability: Unstable 

Classification of fuels | Fuel and its classification

The fuel can be classified mainly into three types one is a liquid fuel, the second one is gaseous fuel and another one is a solid fuel. Based on the type of fuel used by engines are classified as follows. Let us check out the detailed information on the classification of fuels here in this article. 

Classification of fuels: 

• Engine using volatile liquid fuels for example - gasoline, alcohol, kerosene, benzene etc. The fuel is generally mixed with air to form a homogeneous charge in a carburettor outside the cylinder and drawn into the cylinder in its suction stroke. By an externally applied spark, the charge is ignited near the end of the compression stroke. These engines are called spark-ignition engines. 
• Engine using gaseous fuels like CNG full form Compressed Natural Gas, LPG full form Liquefied Petroleum Gas, blast furnace gas and biogas. Gaseous fuels are comparatively better compared to liquid fuels because of reduced ignition delay. The gas is mixed with air and the mixture is introduced into the cylinder during the suction process. The working of this type of engine is similar to that of the engines using liquid fuels called SI gas engines.
• Engine using solid fuels like charcoal, powdered coal etc. Solid fuels are generally converted into gaseous fuels outside the engine in a separate gas producer and the engine works as a gas engine. 
• Engine using viscous liquid fuels like heavy and light diesel oils. The fuel is generally introduced into the cylinder in the form of minute droplets by a fuel injection system near the end of the compression process. Combustion takes place because of the fuels coming into contact with the high temperature compressed air in the cylinder. Therefore, these engines are called compression-ignition engines. 
• Engines using two fuels. A gaseous fuel or a highly volatile liquid fuel is supplied along with air during the suction stroke or during the initial part of compression through a gas valve in the cylinder head and the other fuel is injected into the combustion space near the end of the compression stroke. These are called dual-fuel engines.  

Definition of heat engine

What is a heat engine?

In thermodynamics and engineering a device for producing motive power from heat. 

A heat engine is a system that converts thermal and chemical energy into mechanical energy which can be used to do mechanical work.  

Heat engine can be classified into two categories :

1. Internal combustion engine 
2. External combustion engine

Engines are also classified into two types :

1. Rotary engines 
2. Reciprocating engines 

Definition of Engine

What is the engine?

A machine that converts any of various form of energy into mechanical force and motion. 

A mechanism which can serve as an energy source. 

Normally, most the engines convert thermal energy into mechanical work and therefore they are called Heat Engine. 

The engine can be broadly classified into two categories :

1. Internal combustion engine
2. External combustion engine 

Difference between spontaneous and stimulated emission

What is called spontaneous emission?

Spontaneous emission is electron drops from an excited state to a lower state. 

Example - emitting a photon.

What is called stimulated emission?

Stimulated emission is a photon of the same frequency that interacts with an electron in an excited state which drops to a lower state. The emitted photon is coherent with the incoming photon.

Example - Laser 

Let us have deep insight into the difference between spontaneous and stimulated emission to know more about this concept. 

Differences between spontaneous and stimulated emission :

• Where quantum system undergoes a change and jumps to a lower energy state, emitting quanta of energy is called the spontaneous emission Whereas stimulated emission is the process where an external photon of a certain frequency, reacts with the excited electron in an atom and this results in dropping to lower energy state.
• Spontaneous emission found in LEDs, Fluorescent tubes and stimulated emission found in laser it is the key process for the formation of a laser beam. 
• There is no population inversion of electrons in LEDs in spontaneous emission whereas population inversion is achieved by various pumping techniques in stimulated emission. 
• In spontaneous emission, external stimuli are not required and stimulated emission is caused by external stimuli. 
• Spontaneous emission depends only on the upper level of the electron whereas stimulated emission depends upon the electron being in the upper level but the electron must be started at the upper level. 
• Only one energy wave is released during spontaneous emission while two energy waves are released during stimulated emission. 
• Spontaneous emission is the self-emission process of radioactive materials without any influence of radiation whereas a single particle or group of particles initiated emission in radioactive material is called stimulated emission.

Stimulated emission

The concept of stimulated emission was first put forward by Albert Einstein in 1917.

Let us consider two energy levels E₁ and E₂ in a material. Let us assume that the atom is initially at energy level E₂. Also, consider that an electromagnetic wave of frequency v is incident on a given material. This wave has the same frequency as that of the specific material. Therefore, there is a high degree of probability that this wave will force the atom to undergo a change from energy level E₂ to energy level E₁. In this case, the energy difference E₂ - E₁ is received in the form of an electromagnetic wave which adds to the incident wave. Here, it is to be noted that the atom is already in the excited state E₂. Before it could come to the ground state, due to the spontaneous emission process, if it is irradiated with a photon, whose energy is exactly equal to E₂ - E₁. The incident photon will stimulate the excited atom to emit one photon of exactly the same energy, as that of the incident photon. Thus, two photons will be emitted in this process. This phenomenon is known as Stimulated Emission. 

Note: The most remarkable feature of the stimulated emission is both the emitted photons will have the same frequency, phase direction and polarization, as that of the incident photon. So, in this process, we give the input of one incident photon and obtain the two photons identical in all respects as an output. Thus, amplification of radiation takes place by the stimulated process. 

You can also look at the difference between spontaneous and stipulated emission. 

Spontaneous emission

Let us consider two energy levels E₁ and E₂ in a material. For convenience, E₁ is taken to be the ground level. E₂ is greater than E₁. ( E₂ > E₁ ) The two levels of energy under consideration can be any two of the unlimited numbers of levels of energy that can be possessed by any material. 

E₁ = Energy level 1 ( Ground state )

E₂ = Energy level 2 ( Excite state ) 

h = Plank's constant

v = Frequency of radiated energy 

When the particle or atom of the material is excited, it can remain in the excited state for a limited time known as a lifetime. The lifetime of the excited hydrogen atoms is of the order of 10^-8 sec. Usually, the number of excited particles in a system is smaller than the non-excited particles. The time during which a particle can exist in the ground state is unlimited. The particle at the excitement level is more unstable as compared to that at the ground level. Naturally, there is a tendency for the particle to come back to ground level. When it comes back to ground level, the particle releases some amount of energy. When this energy is released in the form of electromagnetic waves, we call it spontaneous emission of energy. The frequency of the radiated wave is given by :

v = ( E₂ - E₁ / h ) 

OR 

hv = ( E₂ - E₁ ) 

Note: Radiative emission is just one of the two possible ways for the atom to decay. The decay can also occur in a non-radiative manner. In the non-radiative transition, the difference in energy levels E₂ and E₁ can be experienced in regions other than electromagnetic. 

You can also look at the difference between spontaneous and stipulated emission. 

Types of mechanical vibration

There are mainly three basic types of vibration according to the axis of body move : 

1. Longitudinal vibration 
2. Transverse vibration 
3. Torsional vibration 

Now we can check it out in detail below. Let us check out the different types of mechanical vibration here in this article. Before you start you can check some basic introduction of mechanical vibration. 

• Longitudinal vibration :

If the shaft is elongated and shortened so that the same moves up and down resulting in tensile and compressive stresses in the shaft, the vibrations are said to be longitudinal. The different particles of the body move parallel to the axis of the body. 

• Transverse vibration :

When the shaft is bent alternately and tensile and compressive stresses due to bending result, the vibrations are said to be transverse. The particles of the body move approximately perpendicular to its axis. 

• Torsional vibration :

When the shaft is twisted and untwisted alternately and torsional shear stresses are induced, the vibrations are known as torsional vibrations. 

There are also some more vibrations that are following below :

1. Free and Forced vibration 
2. Linear and non-linear vibration 
3. Damped and Un-damped vibration 
4. Deterministic and Random vibration 

Now we can check it out in detail below : 

• Free vibration : 

After distributing the system, the external excitation is removed, then the system vibrates on its own. This type of vibration is known as free vibration. 

Example - Simple pendulum 

• Forced vibration 

The vibration which is under the influence of external force is called forced vibration. 

Example - Machine tools, electric bells

• Linear vibration : 

In a system, if mass, spring and damper behave in a linear manner, the vibrations caused are known as linear in nature. 

They are governed by linear differential equations. 

They follow the law of superposition. 

• Non-linear vibration : 

If any of the basic components of a vibratory system behaves non-linearly that type of vibration is called non-linear in nature. 

Linear vibration becomes non-linear for a very large amplitude of vibrations. 

They do not follow the law of superposition. 

• Damped and Un-damped vibration : 

If the vibratory system has a damper and the motion of the system will be opposed by the damper also the energy of the system will be dissipated in friction is called damped vibration. 

On the other hand, the system that has no damper is known as un-damped vibration. 

• Deterministic and Random vibration :

In the vibratory system, the amount of external excitation is known in magnitude, it causes deterministic vibration is called deterministic vibration.

The non-deterministic vibration is known as random vibrations. 

Introduction to mechanical vibration

A body is said to vibrate if it has a to and fro motion. A pendulum swinging on either side of a mean position does so under the action of gravity. When the pendulum swings through the mid position, its centre of mass is at the lowest point and it possesses only kinetic energy. At each extremity of its swing, it has only potential energy. In the absence of any friction, the motion continues indefinitely. It can be shown that if the swings on either side of the mean position are very small, it approximates to simple harmonic motion. 

Usually, vibrations are due to elastic forces. Work is done on the elastic constraints of the forces on the body when a body is displaced from its equilibrium position and is stored as strain energy. Now, if the body is released, the internal forces cause the body to move towards its equilibrium position. If the motion is frictionless, the strain energy stored in the body is converted into kinetic energy during the period the body reaches the equilibrium position at which it has maximum kinetic energy. The body passes through the mean position, the kinetic energy is utilized to overcome the elastic forces and is stored in the form of strain energy. 

The vibration is mainly three types :

1. Longitudinal vibrations
2. Transverse vibrations
3. Torsional vibrations 

Terms related to vibration :

1. Free vibration 
2. Damped vibration 
3. Forced vibration 
4. Period
5. Cycle
6. Frequency 
7. Resonance 

All the terms are used in vibrations are explain below :

Free vibration is also called natural vibration. Elastic vibration in which there are no friction and external forces after the initial release of the body is known as free vibration.

Damped vibrations are when the energy of a vibrating system is gradually dissipated by friction and other resistances is called damping. The vibrations gradually cease and the system rests in its equilibrium position.

Forced vibration is when a repeated force continuously acts on a system. The vibration is said to be forced. The frequency of the vibrations is that of the applied force and is independent of their own natural frequency of vibrations. 

The period is the time taken by a motion to repeat itself and is measured in seconds. 

The cycle is the motion completed during one time period. 

Frequency is the number of cycles of motion completed in one second. It is expressed in hertz ( Hz ) and is equal to one cycle per second. 

Resonance is the frequency of the external forces is the same as that of the natural frequency of the system. A state of resonance is said to have been reached. 

It results in large amplitudes of vibrations and this may be dangerous. 

Explore more information: 

1. Types of mechanical vibration

Watt governor application

Let us check out the Watt governor application here in this article. 

Application of Watt governor:

• Watt governor used to maintain the engine's speed of the truck.
• It is also used in ships and trains.
• It is used in a steam turbine, the internal combustion engine and variously fueled turbines. 
• Watt governor is also used in AC generators to maintain the electricity supply with the load increase on it. 
• It is used in automobiles to restrict engine RPM and total speed. 
• It also protects the engine from excessive rotational speed.
• We also used it in that system where working fluid and speed of the system are the main issues. 

Watt governor | Working | Limitations | Height calculation

Watt governor is the simplest form of a centrifugal governor. It is also called a simple conical pendulum governor. It is basically a conical pendulum with a link attached to a sleeve of negligible mass. This governor is used by James Watt in his steam engine and it also has many applications. 

Working of Watt governor :

The upper sides of arms are pivoted with the governor balls so the governor balls can move upward and downward as they revolve with a vertical spindle. Bevel gears drive the engine. A bevel gear is driven by the spindle. The lower arms are connected to the sleeves and are keyed to the spindle in such a way that revolves around the spindle. At that time, it can slide up and down according to the spindle speed. Two stoppers are provided at the bottom and top of the spindle to limit the movement of the sleeve.

If the load on the engine decreases, the speed of the engine and then the angular velocity of the governor spindle increase. The centrifugal force on the ball increases that tends balls to move outward and the sleeve to move upward thus sleeve actuates a mechanism that operates the throttle valve at the end of the bell crank lever to decrease the fuel supply. Thus the power output is reduced.

If the speed of the engine decreases as the load on the engine increase, the centrifugal force decreases. So that the inward movement fly balls and downward movement of the sleeve cause a wide opening of the throttle valve. Engine speed increase with increasing the fuel supply.

Types of Watt governor :

The Watt governor was classified based on the position of upper arms. The arms can be connected by the way we describe below :

1. Pivot is on the axis of the spindle 
2. Pivot is offset from spindle
3. The pivot is offset, and arms cross the axis.

Based on this Watt governors are classified into three types :

1. Simply pinned type governor 
2. Open arm type governor 
3. Crossed arm type governor 

Simply pinned type governor: The upper arms are joined to a point O on the axis of the spindle, where both arms intersect the spindle axis.

Open arm type governor: The upper arm of Watt governor is hinged on a collar attached to the spindle or joined by a horizontal link as shown in fig below instead of connecting directly to the spindle. The arms, when produced, meet the axis of the spindle at O. 

Crossed arm type governor: The upper arms o governor in hinged on a collar on the axis of the spindle or arms are joined through a fixed horizontal link as shown in fig below. The arms intersect the axis at a point O.

Limitations of Watt governor :

• Its use is limited up to vertical position applications. 
• It is used in a very slow speed engines because, at a higher speeds, the sensitivity of the governor will decrease. 

Height Calculations :

The vertical distance from the plane of rotation of the balls to the point of intersection of the upper arms along the axis of the spindle is called the height of the governor. 

The height of the governor decreases with an increase in speed and increases with a decrease in speed. 

Let, 

m = mass of each ball

h = height of governor

w = weight of each ball ( w = mg )

ω = angular velocity of the balls, arms and the sleeve

T = Tension in the arm

r = radial distance of ball-centre from spindle-axis 

For the finding h, the height of governor the equilibrium of the mass provides 

Tcosθ = mg and Tsinθ = mrω²

Tanθ = mrω² / mg = rω² / g

r / h = rω² / g

h = g / ω² = g / ( 2πN / 60 ) = ( 60 / 2π )² * 9.81 / N²

h = 859 / N² m

h = 859000 / N² mm

Thus, the height of a Watt governor is inversely proportional to the square of the speed. 

Explore more information: 

1. Application of Watt governor

Hunting of governor | Definition | Process

Definition of hunting of governor:

You know that the function of the governor is to keep the speed constant so the hunting of a governor is the condition in which the speed of the engine can fluctuate continuously above and below the mean speed and which are controlled by the governor.

In other words, hunting is said to occur in a governor when it is not able to find a stable position for a change in load at a new value of speed and oscillates around it due to the tendency of balls and sleeve to restore original speed and inertia effect leading to an overshoot of the desired position.

Process of hunting:

The sensitiveness of a governor and the hunting of a governor both are desirable qualities. If a governor is too sensitive, it may fluctuate continuously, because when the load on the engine falls, the sleeve rises rapidly to a maximum position. This shuts off the fuel supply to the extent of effect a sudden fall in speed. As the speed falls below the mean value, the sleeve again moves rapidly and falls to a minimum position to increase the fuel supply. The speed subsequently rises and becomes more than the average with the result that the sleeve again rises to reduce the fuel supply. This process is continuing and it is known as hunting of the governor. 

Hunting is directly proportional to sensitiveness. If more sensitive the governor, more is the hunting.

Sensitiveness of governor | Definition | Formula

Definition of sensitiveness : 

The ratio of the difference between the maximum and minimum equilibrium speed to the mean equilibrium speed is called sensitiveness of governor.

A governor is said to be sensitive when it readily responds to a small change of speed. The movement of the sleeve for a fractional change of speed is the measure of sensitivity. 

Explanation of sensitiveness :

As a governor is used to limit the change of speed of the engine between minimum to full-load conditions, the sensitiveness of a governor is also defined as the ratio of the difference between the maximum and the minimum speeds to the mean equilibrium speed. 

Sensitiveness = Range of speed / Mean speed 

                       = N₂ - N₁ / N 

                       

                       = 2 ( N₂ - N₁ ) / N₁ + N₂ 

Where, 

N = Mean speed

N₁ = Minimum speed corresponding to full load condition 

N₂ = Maximum speed corresponding to no-load condition