Surveying and Types of Surveying in Civil Engineering

Surveying and Types of Surveying in Civil Engineering 

1. Introduction

Surveying is the backbone of civil engineering and infrastructure development. It is the science and art of determining the relative positions of natural and man-made features on the Earth’s surface and representing them in the form of maps, plans, or digital models. Every civil engineering project—from the construction of highways, railways, bridges, and dams to the planning of cities and irrigation systems—begins with accurate surveying.

The importance of surveying has been recognized for centuries, with historical evidence from ancient Egypt, Greece, and Rome, where surveyors played a crucial role in dividing land, building monuments, and establishing boundaries. With the advancement of technology, modern surveying has evolved from simple chains and compasses to sophisticated total stations, GPS, drones, and LiDAR systems.

This essay explores the concept, principles, objectives, classification, types, modern methods, and applications of surveying in civil engineering.

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2. Definition and Purpose of Surveying

2.1 Definition

Surveying is defined as the technique, profession, and science of accurately measuring and mapping the relative position of points on the Earth's surface or in three-dimensional space. It involves the determination of horizontal distances, vertical heights (levels), angles, and directions.

2.2 Purpose

The primary purposes of surveying include:

• Preparation of topographic, cadastral, and engineering maps.

• Determination of property boundaries and legal documentation.

• Establishment of control points and reference lines for construction.

• Calculation of earthwork quantities for excavation and filling.

• Route selection and alignment for transportation networks.

• Monitoring land deformation in dams, tunnels, and high-rise structures.

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3. Basic Principles of Surveying

Every surveying process is based on fundamental principles to ensure accuracy and reliability:

1. Working from Whole to Part
   Large areas are first surveyed to establish control points, and detailed measurements are then taken within those limits to minimize errors.

2. Location of a Point by Measurement from Two Known Points
   A new point’s location is determined by its relationship to at least two previously fixed points.

3. Control of Errors
   Errors in measurement are minimized using standardized procedures, instruments, and repeated observations.

4. Establishment of Well-defined Reference Points
   Benchmarks, triangulation stations, and permanent markers are set up to serve as reference for future work.

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4. Objectives of Surveying

The objectives of surveying in civil engineering are as follows:

• To prepare maps and plans for planning, designing, and executing engineering works.

• To establish boundaries for ownership and legal purposes.

• To determine topographical features of an area, including elevation, contours, and natural/man-made structures.

• To provide data for construction, including layout, alignment, and leveling.

• To monitor and assess land changes, such as subsidence, erosion, or settlement.

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5. Classification of Surveying

Surveying is classified based on various criteria to suit specific requirements:

5.1 Based on Nature of Field

1. Land Surveying
   Deals with determining features on land. It includes:

   • Topographical Survey: Measures natural and man-made features to prepare contour maps.

   • Cadastral Survey: Establishes property boundaries and land ownership.

   • City Survey: Used for urban planning, roads, utilities, and zoning.

2. Marine or Hydrographic Surveying
   Concerned with water bodies such as rivers, lakes, harbors, and coastal areas for navigation, port development, and underwater mapping.

3. Astronomical Surveying
   Determines latitude, longitude, azimuth, and time by observing celestial bodies.

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5.2 Based on Purpose

• Engineering Survey: Provides data for the design and construction of engineering works like highways, railways, bridges, and buildings.

• Military Survey: Used for defense planning and strategic purposes.

• Geological Survey: Involves study of rock formations, mineral deposits, and subsurface conditions.

• Archaeological Survey: Helps in exploring ancient monuments and historic sites.

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5.3 Based on Instruments Used

1. Chain Surveying

   • Uses chains or tapes to measure distances.

   • Suitable for small, open, and fairly level areas.

2. Compass Surveying

   • Uses a prismatic or surveyor’s compass to measure bearings of lines.

3. Plane Table Surveying

   • Combines field observation and map drawing simultaneously on a plane table.

4. Theodolite Surveying

   • Measures horizontal and vertical angles with high precision.

5. Tacheometric Surveying

   • Determines distances and elevations indirectly using a theodolite with a stadia diaphragm.

6. Photogrammetric Surveying

   • Uses aerial photographs and satellite images to prepare maps.

7. Electronic and GPS Surveying

   • Employs total stations, GPS, and GNSS for highly accurate data collection.

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5.4 Based on Method of Measurement

1. Plane Surveying

   • Assumes the Earth’s surface as flat, suitable for areas less than 250 km².

2. Geodetic Surveying

   • Considers the Earth’s curvature, suitable for large-scale surveys requiring high precision.

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6. Modern Surveying Techniques

Technological advancements have revolutionized surveying, improving accuracy, speed, and efficiency. Major modern techniques include:

1. Total Station Surveying

   • Combines electronic distance measurement (EDM) and theodolite.

   • Stores data digitally for direct processing.

2. Global Positioning System (GPS) and GNSS

   • Provides three-dimensional coordinates using satellite signals.

   • Ideal for large-scale mapping and navigation.

3. LiDAR (Light Detection and Ranging)

   • Uses laser scanning for creating high-resolution 3D models.

   • Widely used in highway design, forestry, and flood modeling.

4. Drone Surveying

   • Unmanned aerial vehicles capture aerial images and terrain data.

5. GIS Integration

   • Geographic Information System integrates spatial and non-spatial data for analysis, planning, and decision-making.

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7. Applications of Surveying in Civil Engineering

Surveying plays a critical role in various fields of civil engineering, including:

1. Transportation Engineering

   • Alignment and design of roads, railways, and airports.

2. Hydraulic Engineering

   • Planning of dams, canals, reservoirs, and irrigation systems.

3. Structural Engineering

   • Layout of buildings, bridges, and industrial plants.

4. Urban and Regional Planning

   • Land use planning, zoning, and development control.

5. Environmental Engineering

   • Flood risk mapping, land reclamation, and pollution monitoring.

6. Mining and Geological Studies

   • Exploration, excavation, and mineral resource mapping.

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8. Importance of Surveying

• Ensures accuracy in construction layouts.

• Prevents disputes related to land ownership.

• Reduces construction costs by minimizing errors.

• Provides a database for future expansion and development.

• Enhances safety and sustainability of engineering projects.

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9. Challenges in Surveying

• Terrain and weather constraints.

• High initial cost of modern equipment.

• Requirement of skilled manpower.

• Data management and security concerns in digital surveying.

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10. Future Trends in Surveying

• Integration of Artificial Intelligence (AI) and Machine Learning for automated data analysis.

• Use of Augmented Reality (AR) in field surveys.

• Real-time monitoring with IoT-enabled sensors.

• Fully automated robotic survey stations.

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11. Conclusion

Surveying is an essential discipline in civil engineering, forming the foundation for the successful planning, design, and execution of projects. With advancements in technology, the field is becoming more efficient, precise, and versatile. From traditional chain measurements to high-tech drone and satellite-based surveys, the evolution of surveying continues to shape the infrastructure of the future.

The understanding of different types of surveying and their applications allows engineers to select the most suitable method based on project requirements, terrain conditions, and desired accuracy. In an era of rapid urbanization and smart infrastructure, the importance of surveying cannot be overstated—it remains the first and most critical step in any engineering endeavor.

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Soil Mechanics and Foundation Engineering – A Comprehensive Study

download PDF Soil Mechanics and Foundation Engineering 

LINK ✔🦾

https://drive.google.com/drive/folders/15IMYunaFOcu1SYeOk3P3S0JeuJZCP90b?usp=drive_link                                                    

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1. Introduction

Civil engineering, at its very core, is about designing and constructing safe, durable, and sustainable structures. However, the strength of any structure is not just determined by the material used above ground, but also by the stability of the soil beneath. Soil Mechanics is the branch of civil engineering that deals with the behavior of soil under different conditions of loading, moisture, and stress. Foundation Engineering, on the other hand, applies soil mechanics principles to design the structural element that transfers loads from buildings, bridges, dams, and other structures to the underlying soil or rock.

The importance of these fields cannot be overstated. Around the world, structural failures often trace back to poor soil investigation or improper foundation design. Conversely, some of the greatest engineering marvels—skyscrapers in Dubai, bridges in Japan, and dams in China—stand tall today because of careful geotechnical and foundation analysis.

This article provides a comprehensive overview of soil mechanics and foundation engineering, covering soil properties, classifications, foundation types, design methods, soil improvement techniques, and real-world applications.

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2. Soil Mechanics

2.1 Origin and Formation of Soils

Soil is the natural product of rock disintegration and decomposition through weathering. Weathering may be:

• Physical weathering: Breaking of rocks due to temperature variations, freeze-thaw cycles, or mechanical action.

• Chemical weathering: Alteration of minerals due to chemical reactions with water, air, or acids.

• Biological weathering: Caused by plant roots, microorganisms, or organic activity.

The type of parent rock, climate, and environmental conditions determine the soil structure and texture. For instance, sandy soils are common in arid regions, while clayey soils dominate river valleys.

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2.2 Properties of Soil

Understanding soil properties is crucial for predicting how soil will behave under structural loads.

a) Physical Properties

• Moisture content (w): Ratio of water mass to dry soil mass.

• Specific gravity (Gs): Ratio of soil particle density to water density.

• Density: Bulk density and dry density indicate soil compactness.

b) Index Properties

• Atterberg Limits: Defines consistency states of fine-grained soil.

  • Liquid Limit (LL): Water content where soil changes from plastic to liquid state.

  • Plastic Limit (PL): Minimum water content where soil remains plastic.

  • Shrinkage Limit (SL): Beyond which further drying doesn’t reduce volume.

• Consistency Index and Plasticity Index help classify soil behavior.

c) Engineering Properties

• Permeability: Ability of soil to allow water flow. Critical in dam and pavement design.

• Compressibility: Soil’s tendency to reduce volume under load.

• Shear Strength: Maximum resistance against sliding failure, governed by Mohr-Coulomb theory:

$$\tau = c + \sigma' \tan \phi$$

where c = cohesion, φ = angle of internal friction, σ’ = effective stress.

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2.3 Soil Classification

Soil classification provides a systematic way of identifying soil for engineering purposes.

• Particle Size Distribution: Gravel (>4.75 mm), Sand (4.75–0.075 mm), Silt (0.075–0.002 mm), Clay (<0.002 mm).

• Unified Soil Classification System (USCS): Widely used, identifies soil groups like GW (well-graded gravel), CL (low plasticity clay).

• Indian Standard Classification (IS 1498): Used in India, classifies soils into gravel, sand, silt, and clay.

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2.4 Soil Testing

Testing is vital to determine engineering properties.

Field Tests

• Standard Penetration Test (SPT): Provides N-value indicating soil resistance.

• Cone Penetration Test (CPT): Measures soil resistance with cone penetration.

• Vane Shear Test: Measures undrained shear strength of soft clays.

Laboratory Tests

• Proctor Compaction Test: Determines optimum moisture content for maximum dry density.

• Permeability Test: Falling head and constant head tests.

• Triaxial Test: Measures strength under controlled drainage conditions.

• Oedometer Test: For consolidation and settlement analysis.

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2.5 Soil Behavior

a) Stress Distribution in Soil

Stress beneath a loaded area decreases with depth. Boussinesq’s theory provides formulas for stress distribution beneath point loads.

b) Consolidation and Settlement

• Immediate Settlement: Elastic deformation under load.

• Consolidation Settlement: Time-dependent settlement due to expulsion of pore water.

• Secondary Settlement: Long-term creep of soil particles.

c) Flow of Water Through Soil

Darcy’s Law governs permeability:

$$q = k \cdot i \cdot A$$

where q = discharge, k = coefficient of permeability, i = hydraulic gradient, A = area.

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3. Foundation Engineering

3.1 Introduction to Foundations

A foundation is the lowest part of a structure that transfers loads safely to the soil. A good foundation ensures:

• Adequate load-bearing capacity.

• Minimal settlement within permissible limits.

• Stability against sliding and overturning.

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3.2 Types of Foundations

Shallow Foundations

• Spread Footing: Transfers load from columns to soil.

• Strip Footing: For walls and load-bearing structures.

• Mat/Raft Foundation: Large slab covering entire building area, suitable for weak soils.

• Combined Footing: Supports multiple columns.

Deep Foundations

• Pile Foundation: Long slender members transferring load by end bearing or skin friction.

• Caissons or Well Foundations: Used for bridges in rivers.

• Drilled Shafts: Large-diameter, cast-in-situ foundations for heavy loads.

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3.3 Bearing Capacity of Soil

Bearing capacity is the ability of soil to support foundation loads without shear failure or excessive settlement.

• Ultimate Bearing Capacity (qu): Maximum load before failure.

• Safe Bearing Capacity (qsafe): Qu divided by factor of safety (2–3).

• Net Bearing Capacity: Load per unit area beyond overburden pressure.

Terzaghi’s Equation for Shallow Foundations:

$$q_{ult} = cN_c + \gamma D_f N_q + 0.5 \gamma BN_\gamma$$

where c = cohesion, γ = unit weight of soil, Df = depth of footing, B = width of footing, Nc, Nq, Nγ = bearing capacity factors.

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3.4 Settlement of Foundations

Settlement must be within permissible limits.

• Immediate settlement: Elastic in nature, occurs quickly.

• Primary consolidation: Time-dependent due to pore water dissipation.

• Differential settlement: Uneven settlement that may cause structural cracks.

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3.5 Foundation Design Considerations

When designing a foundation, engineers consider:

• Type of load (dead, live, seismic, wind).

• Soil properties (strength, compressibility, groundwater level).

• Depth of foundation (frost depth, scour depth for bridges).

• Safety factors as per IS codes, AASHTO, Eurocode, ASTM.

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4. Special Topics in Soil & Foundation Engineering

4.1 Soil Improvement Techniques

• Compaction: Reduces voids, increases density.

• Stabilization: Using lime, cement, or chemicals to enhance soil properties.

• Grouting: Injection of cementitious material to reduce permeability.

• Geotextiles: Reinforcing soil with synthetic fabrics.

4.2 Problematic Soils

• Expansive soils: Swell/shrink due to moisture variations (e.g., black cotton soil).

• Collapsible soils: Sudden volume reduction upon wetting.

• Marine clays: High compressibility and low strength.

4.3 Earth Pressure and Retaining Structures

• Active Pressure: Exerted by soil when wall moves away.

• Passive Pressure: Resistance when wall moves towards soil.

• Coulomb and Rankine’s Theories used in retaining wall design.

4.4 Earthquake Geotechnical Engineering

• Soil liquefaction under seismic loading.

• Ground improvement methods to mitigate earthquake effects.

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5. Case Studies and Applications

5.1 Failures Due to Poor Geotechnical Investigation

• Leaning Tower of Pisa, Italy: Tilt caused by weak clayey soil and inadequate foundation depth.

• Mexico City Earthquake (1985): Many buildings collapsed due to soft clay deposits.

5.2 Successful Applications

• Burj Khalifa, Dubai: Deep pile foundation extending 50 m into the ground.

• Millau Viaduct, France: Bridge piers founded on strong limestone after extensive soil study.

• Three Gorges Dam, China: Extensive soil mechanics analysis ensured safety of world’s largest hydropower project.

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6. Conclusion

Soil mechanics and foundation engineering are the backbones of civil engineering. While soil may appear simple, its behavior under load is complex and variable. A sound understanding of soil properties, testing, and classification enables engineers to design safe and economical foundations. Foundation engineering, when executed with precision, ensures that structures can withstand not just gravity but also natural forces like earthquakes, floods, and wind.

Future trends, such as AI-based soil behavior prediction, geotechnical sensors, and sustainable ground improvement techniques, will further strengthen this field, making construction safer and more reliabiable

Four stroke engine: Definition, Working, Cycle, Applications

 

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Four stroke engine: Definition, Working, Cycle, Applications

Most of the vehicles that rush on the road are powered by four-stroke IC engines. Based on the working cycle these are further classified as petrol engines and diesel engines.

We notice four-stroke petrol engines in light or medium-duty vehicles like Motorcycles, Cars, ATVs, etc. In this detailed article, we will discuss four-stroke petrol engine

In this article, we’re going to discuss:

What is Four stroke petrol engine?

Four stroke petrol engine working cycle:

Parts:Construction of four stroke petrol engine:

Terms used in 4 stroke petrol engine:

What are Four Strokes in Four Stroke Petrol Engine:

Working of four stroke petrol engine:

Valve timing diagram:                           

Advantages of four stroke petrol engine:

Disadvantages of four stroke petrol engine:

Applications of four stroke petrol engine

What is Four stroke petrol engine?

The four stroke petrol engine is and I.C Engines that works on a petrol cycle and completes a single power cycle within four strokes of the piston or two revolutions of the crankshaft.

The term “four-stroke” indicates the engine in which a single working cycle is completed within four strokes of the piston (suction, compression, expansion, exhaust) while “Petrol” indicates the engine that works on a petrol cycle (Otto cycle).

As these engines use spark plugs for the combustion of the air-fuel mixture, these are also referred to as 4-stroke spark ignition (SI) engines. It runs on the fuels like gasoline, CNG, methanol, LNG, etc.

These engines are generally lighter and smaller in size than the four-stroke diesel engines as it uses a lower compression ratio (8 to 12) in comparison with 4 stroke diesel engines (14 to 24). Thus these engines are used to run low to medium-duty automobiles.

Four stroke petrol engine working cycle:

The four stroke petrol engine works on the principle of the Otto cycle. The cycle was invented by the German engineer Nicolaus Otto and mainly consists of two adiabatic and two isochoric processes.

It comprises the following processes:-

a) Process (0-1):- During this process, the piston sucks (pulls) the air-fuel mixture inside the cylinder at constant pressure P1.

b) Process (1-2):- It is an adiabatic compression process in which the piston compresses the air-fuel mixture inside the cylinder from pressure P1 to P2.

c) Process (2-3):- It is a constant volume heat addition process. In this process, a spark plug produces a spark, to ignite the fresh charge (Air + Fuel) which causes the pressure inside the combustion chamber to rise from P2 toP3.

d) Process (3-4):- It is an adiabatic expansion in which the high-pressure gases expand inside the cylinder from P3 to P4.

e) Process (4-1):- It is a constant volume heat rejection, during which the heat is rejected outside of the cylinder.

f) Process (1-0):- It is a constant pressure process in which burn gases are released from the cylinder into the exhaust Pipe.

Parts:                                                    

The Four Stroke Petrol Engine Consists of Cylinder, Piston, Connecting Rod, Crank, Inlet Port, Connecting Rod, Exhaust Port & Spark Plug.

These engines basically consist of the following parts:-

1) Intake Port and intake valve:- Inlet Port connects the cylinder to the intake manifold and its opening is controlled with the help of the intake valve. During the open period of the intake valve, a fresh charge from the intake manifold enters the engine cylinder.

2) Exhaust Port and exhaust valve:- Exhaust Port connects the cylinder to the exhaust manifold and its opening is controlled with the help of the exhaust valve. Burn gases from Cylinder are released into the exhaust pipe through the exhaust port.

3) Spark Plug:- Spark Plug is connected to the cylinder head. The spark plug produces a spark in the cylinder which helps to initiate the burning of fuel.

4) Cylinder:- The cylinder guides the movement of the piston and also helps to form the enclosed cavity for the combustion of the air-fuel mixture. It is connected between the cylinder head and the crankcase

The size of the cylinders used in automobiles varies as per power requirements.

The capacity of the engine is specified by the volume inside the cylinder when the piston is at the bottom dead center.

5) Cylinder head:- The cylinder head helps to form the upper enclosure of the combustion chamber. The inlet and exhaust ports are constructed on the cylinder head and it also has a provision for mounting the valves, spark plug, and valve actuating mechanism.

6) Piston: The piston reciprocates inside the cylinder to continuously change the volume enclosed in the cylinder which helps to perform the operations like suction, compression, expansion, and exhaust.

7) Connecting Rod: The connecting Rod connects the piston to the crank. One end of the connecting rod is connected to the piston while another end of the connecting rod is connected to the crank.

8) Crank and crankshaft:- The big end of the connecting rod is connected to the crank. The crank and crankshaft along with the connecting rod convert the reciprocating motion of the piston into the rotary motion.

Construction of four stroke petrol engine:

The 4 stroke petrol engine consists of stationary as well as moving components.
The stationary components of the petrol engine are the cylinder, cylinder head, crankcase, intake and exhaust manifold, spark plug, etc.Advertisements

The moving components of the petrol engine are piston, connecting rod, crank and crankshaft, intake and exhaust valves, etc.

The cylinder head is mounted over the cylinder block and the piston is placed inside the cylinder to form a cylinder cavity or combustion chamber.

The piston easily reciprocates inside a cylinder and it is connected to the crankshaft with the help of connecting rod. This helps to convert the reciprocating motion of the piston into the rotary motion of the crankshaft and vice versa.

The inlet and exhaust valves are mounted into the cylinder head. The inlet valve actuates to control the entry of fresh charge from the intake manifold into the engine cylinder and the exhaust valve actuates to control the removal of exhaust gases from a cylinder to the exhaust manifold.

 

Terms used in 4 stroke petrol engine:

Following are some of the vital terms used in the case of the 4-stroke petrol engine, which will provide ease to understand the topic:-

TDC (Top Dead Centre):- It is the nearest position of the piston from the cylinder head. When the piston is at TDC, the volume inside the cylinder enclosed by the piston is minimum.

BDC (Bottom Dead Centre):- It is the farthest position of the piston from the cylinder head. When the piston is at BDC, the volume inside the cylinder enclosed by the piston is maximum.

Stroke:- The travel of the piston from the TDC to BDC or vice versa is known as stroke.

Stroke volume:- The volume of the cylinder from the position TDC to the BDC is known as a stroke/swept volume. It is also known as the volume swept by the piston from TDC to BDC.

Clearance volume:- When the piston is at TDC, the Volume enclosed by the cylinder and piston is known as clearance volume. It is the minimum volume inside the cylinder in the whole cycle.

A/F ratio (Air-fuel ratio):- It is the ratio of the mass of air to the mass of fuel present in the air-fuel mixture.

What are Four Strokes in Four Stroke Petrol Engine:

The working of the 4-stroke petrol engine comprises of the following 4 important strokes:-

1) Suction Stroke:- While suction stroke, the piston moves from TDC to BDC with the intake valve in open condition and the exhaust valve in closed condition.

During this stroke, as the piston moves from TDC to BDC, a partial vacuum is created inside a cylinder that helps to suck (pull) the air-fuel mixture from the intake manifold into the cylinder.
At the end of the suction stroke when the piston reaches the BDC, the inlet valve becomes closed.

2) Compression Stroke:– During the compression stroke, the piston compresses the air-fuel mixture to high pressure {inside the cylinder←Remove}. For this purpose, the piston moves from the BDC toward TDC. During a compression stroke, both valves (Inlet and Exhaust) remain in a closed condition.  At the end of the compression stroke, the spark plug produces the spark to ignite the air-fuel mixture.

Power Stroke / Expansion Stroke:- In this stroke, the high-pressure combustion products push the piston downward (toward BDC) to get expand. Hence, the piston gets power due to the expansion of combustion products. During the power, stroke piston moves from the TDC toward BDC. At the end of the power stroke, the exhaust port becomes open.

4) Exhaust Stroke:- In Exhaust stroke, the piston moves from BDC to TDC. During this stroke, burn gases are released to Exhaust Pipe through an exhaust port. The exhaust valve becomes closed when the exhaust stroke is completed.

Working of four stroke petrol engine:

 

At the start of the combustion cycle, when the piston is at TDC, the intake valve becomes open and the exhaust valve remains in closed condition.

The first stroke is the suction stroke during which the piston moves from TDC to BDC. As the intake valve is in an open situation, the piston pulls the fresh charge from the intake manifold, thus the cylinder gets filled with the fresh charge. At the end of the suction stroke, when the piston reaches BDC, the intake valve becomes closed.

Now the piston moves from the BDC to TDC to compress the fresh charge trapped inside the cylinder. During this stroke, both the intake and exhaust valve remains in closed situation.

At the end of the compression stroke, the spark plug produces the spark to ignite the compressed air-fuel mixture. The combustion of the compressed charge results in the generation of high-pressure combustion products inside the combustion chamber.

These high-pressure combustion products push the piston from TDC to BDC. The movement of the piston due to the expansion of the combustion products is known as expansion stroke or power stroke. At the end of this power stroke (at BDC), the exhaust valve becomes open.

Now in the next stroke, the exhaust gases are expelled outside of the cylinder through the exhaust port due to the upward motion of the piston from BDC to TDC. At the end of this stroke, after reaching the piston to TDC, the exhaust valve get closed.

After Exhaust valve closes, the intake valve again becomes open and the fresh Air-fuel mixture again enters the cylinder Therefore cycle continues.

As the piston is connected to the crankshaft with the help of connecting rod, the reciprocating motion of the piston gets converted into the rotary motion of the crankshaft.

Valve timing diagram:

The valve timing diagram for four stroke petrol engine indicates the position of the piston or the position of the crankshaft during the opening and closing of the intake and exhaust valves, and generation of spark.

The valve timing diagram is different for the theoretical cycle and for the actual cycle. Lets discuss about each of them.

Theoretical valve timing diagram:-

The above figure shows the valve timing diagram for a theoretical 4 stroke petrol engine. As shown in the above figure, at the start of the suction stroke, the intake valve opens exactly when the piston is at TDC and closes exactly when the piston reaches to BDC.

The spark generation in this theoretical cycle occurs when the piston is at TDC (starting of the expansion stroke). During the exhaust stroke, the exhaust valve opens when the piston is at TDC and it closes when the piston reaches to TDC

Actual valve timing diagram:-

In the actual operation of the four stroke petrol engine, the inlet valve opens a few degrees before the piston reaches TDC, thus due to the valve overlap, the intake charge from the intake manifold helps to push the exhaust gases outside of the cylinder.

The inlet valve closes a few degrees after the BDC. During the suction stroke, when the piston reaches the BDC, the intake charge not completely enters into the cylinder and still the negative pressure is present in the cylinder.
Thus for completely feeding the intake charge into the cylinder, the closing of the intake valve is delayed by a few degrees after the TDC.

AdvertisementsThe spark generation occurs just a few degrees before the piston reaches to TDC. The combustion of intake charge and building of pressure is not an instantaneous process and takes a certain time. To avoid the delay in the building of pressure, the spark is generated a few degrees before the piston reaches TDC so that the building of pressure starts just after the piston reaches TDC.

The exhaust valve opens a few degrees before the piston reaches to BDC. It occurs to release the excessive pressure from the cylinder (at the end of the expansion stroke) and thus it helps to avoid pumping losses during the upward movement (exhaust stroke) of the piston.

The exhaust valve closes a few degrees after the TDC. Thus the intake and exhaust valve remains open for better scavenging

 

Advantages of four stroke petrol engine:

The four stroke petrol engine has the following advantages:-

1.      The 4-stroke petrol engines work at high speed and low torque.

2.     The 4-stroke petrol engines work at a comparatively lower compression ratio.

3.     It does not require a high-pressure fuel injection system and fuel injectors.

4.     The engines are light in weight.

5.     The working of 4 stroke petrol engine is less noisy.

6.     Because of the spark plug, cold starting is easier in 4-stroke petrol engines.

7.     The initial cost of 4 stroke petrol engine is less.

8.    It has a lower maintenance cost.

9.     The engine creates fewer vibrations.

Disadvantages of four stroke petrol engine:

The four stroke petrol engine has the following disadvantages:-Advertisements

1.      It requires an external device like a carburetor for the mixing of air and fuel.

2.     The fuel used by the four stroke petrol engine is highly volatile.

3.     The spark ignition system is required to ignite the compressed mixture.

4.     The cost of fuel used in four stroke petrol engine is comparatively high.

5.     It creates less torque than diesel engines.

6.     The 4 stroke petrol engine has lower thermal efficiency.

7.     It is not suitable for heavy load applications due to the less torque generation.

8.    This engine consumes more fuel for a unit amount of power generation, Thus it has lower specific fuel consumption.

9.     Applications of four stroke petrol engine:

The four stroke petrol engine has applications in the following vehicles:-

       Auto-rickshaw

• Scooter
• Motorcycle
• ATVs
• Petrol Cars
• Generators
• Light-duty transport vehicle