Mechanical Governor

A mechanical governor is a device used in various machines and engines to regulate and control the speed or rotational output. It operates based on the principle of centrifugal force and mechanical linkages. The main purpose of a mechanical governor is to maintain a stable speed or output, even under varying load conditions. It achieves this by automatically adjusting the fuel or energy input to the machine, ensuring that the desired speed is maintained within a predetermined range.

This blog shall delve into Mechanical Governor, Working Principle, Types, and Advantages. This article will help you prepare for exams like SSC JE ME and RRB JE Mechanical Engineering.

What is a Mechanical Governor?

A governor in mechanical engineering terms is a mechanical device utilised to automatically regulate and maintain the rotational motion of an engine or other prime mover within relatively close limits, irrespective of the load. Its primary function is to enable the engine to operate at a selected speed unaffected by variations in the load. By controlling the fuel flow into the engine, the governor ensures a consistent speed, which is why it is sometimes referred to as a speed limiter. As the load on the engine changes, causing the engine speed to decrease or increase, the governor plays a vital role in adjusting the fuel flow accordingly, ensuring optimal performance based on the requirements.

Working Principle of Mechanical Governor

The working principle of a governor is based on the equilibrium between the governor spring and flyweights. The selected spring and flyweight combination ensures that centrifugal force and spring force are balanced at the desired engine speed. When the speed increases, the centrifugal force of the flyweights increases as well, causing a reduction in fuel delivery through the system of levers. Conversely, when the speed decreases, the control rod adjusts to increase the fuel delivery rate and raise the speed to the desired level. 

Governors are designed to automatically maintain all speeds, including idling and minimum speed. They are commonly incorporated into fuel injection pump designs. Diesel engine governors should possess certain qualities or characteristics to ensure effective operation.

Types of Mechanical Governor

Governors can be broadly classified into two types:

Centrifugal Governors

These governors operate based on the principle of centrifugal force. They typically consist of rotating masses or flyweights that are driven by the engine's output shaft. As the engine speed changes, the centrifugal force on the flyweights varies, causing the governor to adjust the control mechanisms accordingly to regulate the speed.

The centrifugal governor operates by detecting changes in speed through gears and flyweights. It maintains a balance between the centrifugal force of the rotating balls and an equal and opposite radial controlling force. The flyweights play a crucial role in speed adjustment. These rotating balls are positioned opposite to each other and have the same weight.

When operating a small engine with a light load, the carburettor supplies an appropriate air-fuel mixture to the combustion chamber. As the crankshaft starts spinning, the centrifugal force causes the flyweights to open. Pressure is then applied to the governor and crank. The crank is connected to the throttle valve, resulting in the flyweights pulling the throttle valve towards the closed position.

If the load on the crankshaft increases, the flyweights spin at a slower speed, causing a decrease in centrifugal force. Consequently, the throttle valve is not fully pulled to the closed position, allowing an increased supply of air-fuel mixture.

Advantages of Centrifugal Governors

Simple and robust design, making them reliable in operation.

Cost-effective compared to electronic or hydraulic control systems.

Can handle high-speed applications efficiently.

Provide automatic speed regulation without the need for external power sources.

Disadvantages of Centrifugal Governors

Limited control precision compared to modern electronic control systems.

Response time may be slower compared to electronic or hydraulic systems.

Sensitive to external factors such as temperature and friction, which can affect their accuracy.

Require regular maintenance and adjustment to ensure proper functioning.

May not be suitable for complex control requirements or advanced applications.

Inertia Governors 

Inertia governors, also known as flywheel governors, function based on the principle of inertia. They utilise a weighted lever or pendulum mechanism that responds to changes in speed by exploiting the inertia of the rotating components. When the speed increases or decreases, the inertia governor adjusts the control mechanisms to maintain a consistent speed.

Inertia governors differ significantly from centrifugal governors as they operate on a different principle. 

In an inertia governor, the arrangement of governor balls is such that the inertia force resulting from the angular acceleration of the governor shaft tends to alter their positions. The displacement of the balls is controlled by a spring and a mechanism within the governor, which, in turn, regulates the supply of the air-fuel mixture.

The positions of the balls in an inertia governor are dependent on the rate of change of speed of the governor shaft. Consequently, these governors exhibit quick responses when load changes occur. Unlike centrifugal governors that respond to finite changes in speed, inertia governors take action based on acceleration.

However, centrifugal governors are generally preferred over inertia governors due to practical difficulties in arranging and achieving the expected balance of the revolving parts in inertia governors. The design and implementation of inertia governors can be more challenging, making centrifugal governors a more common choice in various applications.

Advantages of Inertial Governors

Provide precise and accurate speed control.

Quick response time to changes in load or speed variations.

Can handle sudden and transient loads effectively.

Offer stable and reliable speed regulation even in harsh operating conditions.

Do not require external power sources for operation.

Disadvantages of Inertial Governors

Complex design and construction, resulting in higher costs.

Require regular maintenance and adjustment for optimal performance.

May not be suitable for high-speed applications.

Can be sensitive to external factors such as vibration and shock.

Limited control range compared to electronic control systemsAdvantages of Mechanical Governor

The multiple advantages of Mechanical governors are:

Simplicity: Mechanical governors are relatively simple in design and construction, consisting of mechanical components and linkages.

Reliability: They tend to be robust and reliable, with fewer electronic components that could be prone to failure.

Cost-effectiveness: Mechanical governors are generally less expensive compared to their electronic counterparts.

Easy maintenance: Maintenance and repairs of mechanical governors are often simpler and can be performed without specialised electronic expertise.

Well-established technology: Mechanical governors have been used for a long time, and their principles of operation are well-understood, making them familiar to many technicians and engineers.

Suitable for low-tech applications: They are commonly used in simpler applications where precise control and advanced features may not be necessary.

Disadvantages of Mechanical Governors

The advantages of Mechanical Governors include:

Limited speed control: Mechanical governors may have limited responsiveness in regulating engine speed, leading to difficulties in maintaining precise speed control, especially under varying loads and conditions.

Sluggish response: Mechanical governors often suffer from sluggish response times, causing delays in adjusting the engine speed when there are sudden changes in load or demand.

Wear and tear: The mechanical components of governors can experience wear and tear over time, leading to reduced efficiency and accuracy in speed control.

Maintenance requirements: Mechanical governors require regular maintenance and calibration to ensure they function correctly. Failure to maintain them properly can result in performance issues or even engine damage.

Sensitivity to environmental factors: Mechanical governors can be affected by external factors like temperature, humidity, and vibrations, which may affect their performance and accuracy.

Size and complexity: Mechanical governors can be relatively bulky and complex, taking up valuable space and adding weight to the engine.

Lack of versatility: Some mechanical governors are designed for specific engine models or applications, limiting their versatility for use in different settings.

Inefficient fuel consumption: Due to their limited responsiveness, mechanical governors may not optimise fuel consumption as effectively as more advanced electronic systems.

Kinematic Pair is the combination of two kinematic links ( a link is a resistant body that constitutes part of the machine ) that have relative motion with respect to each other and relative motion between them is completely or successfully constrained.

Examples of Kinematic Pairs are :-

i) Rectangular bar in a rectangular hole.

ii) Wheel rolling on a flat surface.

iii) Ball and Socket Joint

Kinematic Pair can be classified into different types based on the following criteria:-

1.Type of relative motion between the different elements of the pair.

2. Type of contact

3. Type of Mechanical Constraint

Kinematic Pair – Its types and examples

Kinematic Pair is the combination of two kinematic links ( a link is a resistant body that constitutes part of the machine ) that have relative motion with respect to each other and relative motion between them is completely or successfully constrained.

Examples of Kinematic Pairs are :-
i) Rectangular bar in a rectangular hole.
ii) Wheel rolling on a flat surface.
iii) Ball and Socket Joint

Kinematic Pair can be classified into different types based on the following criteria:-

1.Type of relative motion between the different elements of the pair.
2. Type of contact
3. Type of Mechanical Constraint

1. Type of relative motion between the elements of pair.

Based on the relative motion between the elements of kinematic pair are classified into following types :-
i) Sliding Pair
ii) Rolling Pair
iii) Turning Pair
iv) Screw pair
v) Cylindrical Pair
vi) Spherical Pair

i) Sliding Pair:-
In sliding pair, the two elements of the kinematic pair in which each elements has sliding contact with respect to the other element.

ii) Rolling Pair:-

The kinematic pair in which elements of the pair have rolling contact with each other is known as Rolling Pair.

The main examples of rolling pair are:-

i) Ball bearings

ii) Belt and pulley

iii) Wheel rolling on a flat surface.

iii) Turning Pair:-

In a kinematic pair if one element of pair can only turn or revolve about a fixed axis of another element, then this type of kinematic pair is known as turning pair.Example of turning pair are:-

i) Shaft with a collar at both ends in a circular hole.

ii) Cycle wheel revolving about their axles.

iv) Screw Pair:-

When two elements of a kinematic pair have both turning as well as sliding motion between them by means of screw threads, then this type of kinematic pair is called screw pair.

Examples of screw pair are:-

i) Nut and Bolt

ii) Lead Screw of Lathe and Nut

v) Cylindrical Pair:-

Cylindrical Pair is a kinematic pair in which the elements of pair undergoes rotational as well as translational motion with respect to each other. These pairs have 2 degrees of freedom.An example of a cylindrical pair is a Cylindrical bar inside a hollow shaft.

vi) Spherical Pair:-

The kinematic pair in which one of element of the pair is spherical and turns inside the other element which is stationary element is called spherical pair. A spherical pair has 3 degrees of freedom.An example of a spherical pair is a ball and socket joint.

2. Type of contact-

Based on the type of contact the kinematic pair is classified into two types:-

i) Lower Pair

ii) Higher Pair

i) Lower Pair:-

When two links of a kinematic pair have surface contact between them and two links which have surface contact slides over each other is known as Lower Pair.

Eg – i) Rectangular bar in a rectangular hole.

ii) Nut and bolt.

iii) Bolt and Socket Joint.

iv) Piston inside a reciprocating cylinder.

ii) Higher Pair:-

When only one point or line contact is responsible to form a kinematic pair, then this type of pair is called higher pair.

The elements of a higher pair is always curve in its shape. Higher pairs are generally found in cylinders or spheres of the same or different radius and their axes are parallel to each other.

Eg -i) Contact between cam and its follower is a higher pair with line contact.

ii) Pivot on a plate is a higher pair with point contact.3. Type of Mechanical Constraint:-

Based on Mechanical Constraint, kinematic pairs are classified into following types:-

i) Self Closed Pair

ii) Force Closed Pair

i) Self Closed Pair:-

When two elements of a kinematic pair have direct mechanical contact even without the application of external force in such a way that only required type of relative motion occurs then it is called Self Closed Pair.

Example – All lower pairs are self closed pairs.

ii) Force Closed Pair:-

When two elements of a kinematic pair are kept in contact by the application of external forces then this type of kinematic pair is called force closed pair.

Example:-

i) Cam and spring-loaded follower pair.

ii) Ball and roller bearings.

IC Engine.

Internal combustion engine (IC engine) is the heart and soul of countless machines that power our modern world. IC engines have revolutionised transportation and provided unprecedented mobility, from cars and motorcycles to ships and airplanes. Combustion reaction within these engines involves a complex interplay of fuel, air, and ignition, releasing energy that propels vehicles forward.

In this article, readers shall be apprised of the Internal Combustion Engine and its working principle.

What is an Internal Combustion Engine?

An internal combustion engine (IC engine) is a type of heat engine that converts the chemical energy stored in fuel into mechanical energy. It is commonly used in vehicles, power generators, and various industrial applications. Fuel and air are mixed, combusted, and burned in an IC engine within a combustion chamber. The resulting high-pressure gases exert force on a piston, which translates the pressure into rotational motion through a crankshaft. This mechanical energy is then used to power the vehicle or operate machinery. IC engines come in different variations, such as gasoline engines and diesel engines, each with its own combustion process and characteristics.

Components of IC Engine

Fig: Components of IC Engine

The main Components of IC Engine are:

Exhaust camshaft

Exhaust valve bucket

Spark plug

Intake valve bucket

Intake camshaft

Exhaust valve

Intake valve

Cylinder head

Piston

Piston pin

Connecting rod

Engine block

Crankshaft

These are explained below:

Exhaust camshaft: A rotating shaft that controls the opening and closing of the exhaust valves.

Exhaust valve bucket: A component that sits on top of the valve stem and transfers the motion from the camshaft to open and close the exhaust valve.

Spark plug: A device that ignites the air-fuel mixture in the combustion chamber to initiate the combustion process.

Intake valve bucket: Similar to the exhaust valve bucket, it transfers the motion from the camshaft to open and close the intake valve.

Intake camshaft: A rotating shaft that controls the opening and closing of the intake valves.

Exhaust valve: A valve that opens to allow the exhaust gases to exit the combustion chamber during the exhaust stroke.

Intake valve: A valve that opens to allow the fresh air-fuel mixture to enter the combustion chamber during the intake stroke.

Cylinder head: The topmost part of the engine that houses the combustion chambers, valves, and spark plugs.

Piston: A cylindrical component that moves up and down inside the cylinder, driven by the force generated by the combustion process.

Piston pin: Also known as a wrist pin, it connects the piston to the connecting rod, allowing the piston to pivot.

Connecting rod: Connects the piston to the crankshaft and transfers the linear motion of the piston into rotational motion.

Engine block: The main housing of the engine that contains the cylinders and provides support for various engine components.

Crankshaft: Converts the reciprocating motion of the pistons into rotational motion, which drives the transmission and, ultimately, the wheels.

Working Principle of IC Engine

A schematic description of the working principle of IC Engine is given below:

Intake Stroke 

At the start of the intake stroke, the piston is near the top dead center (TDC). The intake valve opens, initiating the piston's downward movement towards the bottom dead center (BDC). During this stroke, the cylinder draws in fresh air or an air-fuel mixture. This phase is known as the intake stroke, as it involves the intake of new air/mixture into the engine. The intake stroke concludes when the piston reaches the BDC. Throughout the intake stroke, the engine expends energy as the crankshaft rotates due to the inertia of its components.

Compression Stroke

The compression stroke commences after the completion of the intake stroke, with the piston positioned at the Bottom Dead Center (BDC). During this stroke, both the intake and exhaust valves remain closed as the piston moves towards the Top Dead Center (TDC). As the air or mixture becomes compressed, the pressure within the cylinder increases, reaching its maximum when the piston nears the TDC. Just before the piston reaches the TDC (in close proximity), specific actions occur depending on the engine type:

For gasoline engines, a spark is generated to initiate the combustion process.

For diesel engines, fuel is injected into the highly compressed air to trigger combustion.

Power Stroke

The power stroke commences with the piston positioned at the Top Dead Center (TDC). During this stroke, both the intake and exhaust valves remain closed. At the end of the compression stroke, combustion of the air-fuel mixture begins, resulting in a substantial rise in cylinder pressure. This increased pressure forcefully drives the piston downward towards the Bottom Dead Center (BDC). During the power stroke, the engine generates energy, converting the force exerted by the pressure into mechanical work.

Exhaust Stroke

The exhaust stroke commences as the piston reaches the Bottom Dead Center (BDC), following the completion of the power stroke. Throughout this stroke, the exhaust valve opens, allowing the movement of the piston from BDC to Top Dead Center (TDC). This piston motion effectively expels the majority of the exhaust gases from the cylinder, directing them into the exhaust pipes. Similar to the previous strokes, the engine expends energy during the exhaust stroke as the crankshaft rotates due to the inertia of its components.

Ranking Power Cycle

The Rankine cycle or Rankine Vapor Cycle is the process widely used by power plants such as coal-fired power plants or nuclear reactors. In this mechanism, a fuel is used to produce heat within a boiler, converting water into steam which then expands through a turbine producing useful work. This process was developed in 1859 by Scottish engineer William J.M. Rankine.[1] This is a thermodynamic cycle which converts heat into mechanical energy—which usually gets transformed into electricity by electrical generation.

 

Figure 1. A simple schematic with components for the Rankine Cycle

Figure 2. The pressure volume diagram of the Rankine cycle. This illustrates the changes in pressure and volume the working fluid (water) undergoes to produce work. [3]

The steps in the Rankine Cycle as shown in Figure 1 and the corresponding steps in the pressure volume diagram (figure 2) are outlined below: [1]

Pump: Compression of the fluid to high pressure using a pump (this takes work) (Figure 2: Steps 3 to 4)

Boiler: The compressed fluid is heated to the final temperature (which is at boiling point), therefore, a phase change occurs—from liquid to vapor. (Figure 2: Steps 4 to 1)

Turbine: Expansion of the vapor in the turbine. (Figure 2: Steps 1 to 2)

Condenser: Condensation of the vapor in the condenser (where the waste heat goes to the final heat sink (the atmosphere or a large body of water (ex. lake or river). (Figure 2: Steps 2 to 3)

The efficiency of the Rankine cycle is limited by the high heat of vaporization by the fluid. The fluid must be cycled through and reused constantly, therefore, water is the most practical fluid for this cycle. This is not why many power plants are located near a body of water—that's for the waste heat.

As the water condenses in the condenser, waste heat is given off in the form of water vapour—which can be seen billowing from a plant's cooling towers. This waste heat is necessary in any thermodynamic cycle. Due to this condensation step, the pressure at the turbine outlet is lowered. This means the pump requires less work to compress the water—resulting in higher overall efficiencies.