Monday, 19 February 2018

Diesel Engine Components and Their Functional Applications

Introduction

In general, engines convert heat energy into mechanical energy by exploiting gas onto the piston and crankshaft assembly. The amount of energy depends on the rotational speed of crank shafts as per specifications. An internal combustion engine (ICE) is more efficient than a steam engine because an ICE is simple to start and disengage. An ICE is widely used in the field of transportation. Important components of internal combustion engines include:

1)Fuel systems
2)Lubrication systems
3)Air intake systems
4)Exhaust systems
5)Cooling systems
6)Electrical systems

Diesel Engine Components

Fuel System

In an engine, fuel reaches the cylinder bore through the following path:

Fuel tank → Water separator → Feed pump → Filter → Injection pump → Injector nozzle → Cylinder 

· The fuel tank is for storing fuel. Generally, it is made of sheet metal. Most fuel tanks have a fuel gauge to check the fuel level and a drain plug to drain fuel.

· The water separator is used for separating dirt and water from the fuel. 

· The feed pump is used to feed fuel to the filter and injection pump.

· The fuel system must pressurize the fuel to open the nozzle. The pressure required to inject fuel into the combustion chamber to offset the pressure of compression is typically 350 to 450 psi. This work is mainly done by the injection pump.

· The injector nozzle injects fuel into the combustion chamber. The injector nozzle atomizes fuel, which is the breaking up of fuel into small particles. The fuel must be atomized when it enters the combustion chamber. Atomization occurs at a pressure between 1,500 to 4,000 psi.

Lubrication System

Various purposes of lubrication include: 

1) Reduces the wear and prevents seizure of rubbing surfaces
2) Reduces the power needed to overcome frictional resistance
3) Removes heat from the piston and other parts
4) Separates piston rings and cylinders
5) Removes foreign material from the engine

In this system, the engine parts are lubricated under pressure feed. The oil is stored in the oil sump, from where an oil pump takes the oil through a strainer and delivers it through a filter to the main gallery. From the main gallery, the oil flows to the main bearings. After lubricating the main bearings, some of the oil falls back to the sump, some is splashed to the cylinder walls, and the remaining oil goes through a hole to the crankpin. From the crankpin, the oil travels to the piston pin through a hole in the connecting rod web where it lubricates the piston rings. For lubricating camshaft and timing gears, the oil is led through the separate oil line from the oil gallery. The valve tappets are lubricated by connecting the main oil gallery to the tappet guide surfaces through drilled holes. Our FE mechanical exam review course thoroughly explains the fundamental concepts and functional applications of mechanical engineering equipment parts.

Oil Cooler

An oil cooler is used for cooling lubricating oil. Higher temperatures will reduce the viscosity of oil, which causes a harmful oil film to form between moving parts. To eliminate this, an engine oil cooler is used. 

Intake System

Air flows into the cylinder bore through the following path:

Air cleaner → Turbo charger → Intake manifold → Inlet port → Inlet valve → Cylinder bore

· The air cleaner is a filter that prevents dust from entering the cylinder bore. Filters generally have pores on the surface, which are measured by microns. The lowest micron value typically has better filtration. A filter set contains outer and safety filters in heavy diesel engines for better filtration.

· The tuber charger is a very important part in an engine that compresses air from the air filter. Turbo chargers have two impellers fixed on the same shaft. These impellers are driven by exhaust air. Generally, the air sucked in by the air filter is compressed before entering the cylinder bore, which results in high efficiency. The shaft will rotate at the speed of approximately 100,000 rpm to result in a longer engine life.

· The intake manifold is a pipe that transports air from the turbo charger to the inlet port.

· The inlet valve is a valve that allows air into the cylinder bore. The opening and closing of the valve is controlled by a camshaft.

Exhaust System

Exhaust gases flow through the following path in an engine:

Cylinder bore → Exhaust valve → Exhaust port → Exhaust manifold → Turbocharger → Muffler

· To reduce engine noise, the exhaust is passed through the muffler. The exhaust gases have a higher pressure than atmosphere; if these gases were to be released directly to the atmosphere, a loud, unpleasant noise would sound, similar to the sound of firing a gun. The muffler is used to cool the exhaust gases.

Cooling System

There are many purposes of cooling an engine, including: 

1) To maintain an optimal temperature for efficient work in all conditions.
2) To avoid excess heat and to protect engine components including cylinders, cylinder head, pistons, and valves.
3) To maintain the lubricating property of the oil. 

There are two types of cooling:

1) Air cooling 
2) Water cooling

Every cylinder in an engine is surrounded by water jackets. The water in the jackets absorb heat from the cylinders. The heated water conducted through the radiator helps cool the water.

There are three types of water cooling methods:

1) Direct or non-direct method 
2) Thermosiphon method
3) Forced circulation method

Mechanical engineers preparing for the FE exam are strongly encouraged to review heating and cooling systems prior to taking the FE Mechanical exam.

Electrical System

The electrical system of an engine is comprised of the following parts: 

1)Starter Motor
2)Alternator
3)Battery 

· The starter motor is used for rotating the flywheel. A starter motor receives its power supply from the battery. The pinion of the starter motor engages with the teeth of a flywheel ring and rotates, which then rotates the crankshaft. This rotation of crankshaft leads to the movement of pistons in the cylinders. The piston will suck air and fuel into the combustion chamber, which causes the engine to start. After reaching a specific rpm, the starter motor withdraws its pinion from the flywheel.

· The alternator is fixed on the engine and includes a pulley. The belt is used to drive the shaft of the alternator. The main job of the alternator is to charge the batteries.

· In general, two batteries, each with a 12 volt capacity, are used.

Thursday, 10 August 2017

Basic Types of Residential Drainage Systems

Introduction

Drainage is the method of removing surface or sub-surface water from a given area. Drainage systems include all of the piping within a private or public property that conveys sewage, rainwater, and other liquid waste to a point of disposal. The main objective of a drainage system is to collect and remove waste matter systematically to maintain healthy conditions in a building. Drainage systems are designed to dispose of wastewater as quickly as possible and should prevent gases from sewers and septic tanks from entering residential areas.

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Residential Drainage Systems

Residential drainage systems remove excess water from residential areas. This system helps whisk water away from walkways, driveways, and roofs to avoid flooding. Residential drainage systems are very important as they prevent rotting, mold, mildew, and structural damage in buildings from a buildup of water. Our SE exam review courses discuss the requirements and recommendations for residential structures regarding drainage systems.

The types of residential drainage systems are:
1)Surface
2)Subsurface
3)Slope
4)Downspout/gutters

Surface Drainage Systems

Surface drainage systems contain shallow ditches dug in a parallel pattern, which act as canals for run-off water. Theses ditches lead the water into the main drain to avoid water pooling and flooding.

Subsurface Drainage Systems

A subsurface drainage system is also known as a French drain. Subsurface drains are placed beneath the top layer of soil to remove excess water at the root level. Subsurface drains require the digging of deep ditches and the installation of underground pipes. A large collector drain is installed to collect water from the pipes.

Slope Drainage Systems

Slope drains allow water to flow downward from a structure with the aid of pipes moving down a slope. A pipe is installed and anchored into a small incline, which causes water to flow through the pipe and away from the structure. 

Downspout and Gutter systems

Downspouts collect water from gutters and divert it to the ground. A downspout is typically connected to a gutter system on a building and carries water away from the roof down to the ground. Downspouts empty out the water on a slope so that the water does not pool at the base of the downspout. 

Combined drainage systems use a single drain to convey both water from sanitary usage and rainwater from roofs and other surfaces to a shared sewer. This system is economical to install. Separate drainage systems use separate foul water drains that lead to a sanitary sewer. The rainwater from roofs and other surfaces is conveyed in a separate surface water drain into a surface water sewer. This system is relatively expensive to install. Our SE exam review courses thoroughly review the building and design codes to follow proper drainage system installations.

Thursday, 29 June 2017

Applications of Spread Footing and Soil Pressure Distribution

Introduction

The size and weight of a building as well as the nature of the soil structure it is built on play a critical role in foundation design. Soil pressure distribution must be addressed to ensure a sound structure. Spread footing is a crucial structural component that provides strength for a building's foundation.

Definition of footings

Footing is a structural element that transfers a building’s weight to the soil using columns, walls, and lateral loads from earth-retaining structures. Our PE Civil exam review course discusses footings and their physical characteristics for engineers preparing for the PE Civil exam.

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Importance of Spread Footings

· A spread footing foundation has a wider bottom portion compared to a load-bearing foundation; the wider bottom "spreads" the weight of the structure over a larger area for greater stability. 

· While traditional spot footings only have a single point of contact with the foundation, spread footings extend support continuously across the entire building layout. 

· Spread footings are used to support a foundation or set of piers below a building. 

· To add additional support, spread footings are constructed with concrete and reinforced with steel. Since spread footing transfers the weight of the building over a large area, spread footings have little risk of failure compared to spot footers. 

· Spread footing extends the life of a building by minimizing structural damage. Footings must be designed to carry the column loads and transmit them to the soil safely. 

· Spread footings may be circular, square, or rectangular. 

· Spread footings are common in residential construction.

Mode of Distribution of Soil Pressure in a Spread Footing

Column loads act at the center of the footing, creating a uniform surface for the soil underneath the footing area. The distribution of pressure depends on the composition of the soil and on the degree of flexibility of the footing. 

Types of Spread Footings:

· Isolated Footing
When columns are spaced far apart, isolated footings are used to support single columns. 

· Combined Footing
When two columns are close to each other and their individual footings overlap, a combined footing is required. A combined footing supports two columns so that the load is evenly distributed. A combined footing may be rectangular or trapezoidal.

· Strap Footing (Cantilever)
In strap footing, two isolated footings are connected with a structural strap (rigid beam) or lever. 

· Mat Foundation (Raft)
A mat foundation is a large slab that supports several columns and walls under the entire structure. If several columns overlap each other, then a single footing for all columns is provided. This type of footing is known as mat footing. Mat foundations are used to reduce the differential settlements on non-homogeneous soils. 


Wednesday, 21 June 2017

Basic Principles and Classifications of Pile Foundations

Introduction

Shallow and deep foundations signify the relative depth of the soil on which buildings are founded. When the depth of a foundation is less than the width of the footing and is less than ten feet deep, it is a shallow foundation. Shallow foundations are used when surface soils are strong enough to support the imposed loads. If the depth of a foundation is more than the width of the building foundation, it is a deep foundation. Deep foundations are often used to transfer building loads deeper into the ground. 

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Conditions where deep foundations are used

· Soil near the surface that has relatively weak bearing capacities (700 pounds per square foot or less)
· Soils near the surface that contain expansive clays (shrink/swell soils) 
· Surface soils that are vulnerable to being removed by erosion or scour

Classification of deep foundations 

Deep foundations are classified into three categories:
· Pile foundations
· Well foundations
· Caisson foundations

Types of foundations and basic mechanisms involved in the classification of deep foundations are reviewed in our FE Civil exam review course for those preparing to become an engineer in training.

Pile foundations

A pile foundation is defined as a series of columns constructed or inserted into the ground to transmit loads to a lower level of subsoil. A pile is a long cylinder made up of a strong material, such as concrete. Piles are pushed into the ground to act as a steady support for structures built on top of them. Piles transfer the loads from structures to hard strata, rocks, or soil with high bearing capacity. The piles support the structure by remaining solidly placed in the soil. As pile foundations are set in the soil, they are more tolerant to erosion and scour.

Installation of pile foundations 

Piles are first cast at ground level and then hammered or driven into the ground using a pile driver. A pile driver is a machine that holds the pile vertical and hammers it into the ground. Blows are repeated by lifting a heavy weight and dropping it on top of the pile. Piles should be hammered into the ground until the refusal point is reached, which is the point where a pile cannot be driven into the soil any farther. The method of installing a pile is a major consideration in the structural integrity of pile foundations. The driven-pile method is an ideal option because it least disturbs the supporting soil around the pile and results in the highest bearing capacity for each pile. Since every pile has a zone of influence on the soil around it, piles must be spaced far enough apart from each other so that the loads are distributed evenly.

Categories of piles

· Depending on their function, piles are classified as bearing piles, friction piles, friction-cum-bearing piles, batter piles, guide piles, and sheet piles.

· Based on the composition of materials, piles are classified as timber piles, concrete piles, sand piles, or steel piles. 

1)Bearing piles are driven into the ground until a hard stratum is reached. Bearing piles rest on hard strata and act as pillars to support the structure. Bearing piles allow vertical loads and transfer the building load to the hard stratum underneath. 

2)Friction piles are used when the soil is soft and there are no hard strata available. These piles are long, and the surfaces are roughened to increase surface area and increase frictional resistance. They bear on frictional resistance between their outer surface and the soil in contact. Friction piles do not rest on hard strata. 

3)Batter piles are driven inclined to resist inclined loads.

4)Guide piles are used in the formation of cofferdams to provide stable foundations for under-water construction.

Basic principles of pile foundations and their classifications are recommended topics to review prior to taking the FE Civil exam. 

Types of piles based on shape and composition


Wednesday, 14 June 2017

The Conduction Process and its Importance in Mechanical Engineering Applications

Introduction

Regions with greater molecular kinetic energy pass their thermal energy into regions with less molecular energy through direct molecular collisions. This process is known as conduction. In metals, a significant portion of the transported thermal energy is carried by conduction-band electrons.

Definition of Conduction

Conduction is the transfer of thermal energy that does not have any flow of material medium and is the main process by which thermal energy is transferred from one solid to another. Our PE Mechanical course reviews the physical properties of heat.

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Importance of Heat Transfer Conduction

· Sticking a metal pole into a fire is an example of heat transfer conduction. Particles at the heated end vibrate vigorously. They collide with the neighboring particles and transfer their energy. Eventually, the particles at the cooler end are set into vigorous vibration, which causes the entire metal pole to become hot.

Types of conduction

There are two types of conduction:
1)Molecular vibration
2)Free electron diffusion

Molecular Vibration

· When heat is supplied to one end of an object, the molecules at that end start to vibrate vigorously. During this process, they bump into their neighboring molecules, which transfers some energy. The receiving neighbor molecule gains energy and starts to vibrate more vigorously. The cycle continues.

Free Electron Diffusion

· This form of conduction takes place only in metals because only metals have free electrons. Electrons are freed from a molecule when heat is applied, which forces the electrons to travel toward the colder end of the metal. At the colder end, the electrons collide into many molecules, and therefore, pass energy to the molecules at the other side.

Conduction in Metals

· In solids, thermal energy is transferred through the vibration and collision of particles. However, in metals, due to the presence of free electrons, thermal energy is spread through electron diffusion. Electrons gain kinetic energy and move rapidly and collide with the atoms in the cooler parts of the metal to pass on their energy.

The process of conduction in metals is important for engineers to understand when preparing to pass the PE Mechanical exam.

Fourier’s Law of Heat Conduction

The law of heat conduction, or Fourier’s law, states that the time rate of the heat transfer through the material is proportional to the negative gradient in the temperature and to the area.

Q = -kA(dT/dx)
‘Q’ - heat flow rate by conduction (W)

‘k’ - thermal conductivity of body material (W m-1 K-1)

‘A’- cross-sectional area normal to direction of heat flow (m2) and ‘dT/dx’ is the temperature gradient (k-m-1)

· The negative sign in Fourier’s equation indicates that the heat flow is in the direction of negative gradient temperature, which makes the heat flow positive

· The thermal conductivity “k” refers to the transport properties 

· Thermal conductivity “k” provides indication of the rate at which heat energy is transferred through the medium by the conduction process 

Applications of Conduction Phenomena in Engineering

· Mechanical Engineering Equipment
· Home Appliances
· Boilers

Wednesday, 7 June 2017

Types and Sources of Air Pollution

Introduction

Air pollution is defined as the presence of any particle or gas found in the air that is not part of the original composition. Air pollution is a change in the physical, chemical, and biological characteristics of the air surrounding us. The substances that cause air pollution are called air pollutants, and they may be in the form of a gas, liquid, or solid.

PE Environmental Exam Course

Air pollutants are transboundary in nature as they travel and affect areas far away from their point of origin. Air pollution causes adverse effects on humans and other living organisms. Our PE Environmental exam review course thoroughly reviews the types and sources of air pollution for those preparing for the PE Environmental exam.

Air Quality Index

Air quality index (AQI) indicates whether pollutant levels in the air may cause health concerns. AQI ranges from 0 to 500, with a higher number meaning a lower air quality.

The table below provides the AQI limits for human health.


Air Quality Index
Air Quality
Air Quality Index Range
Good
0-50
Moderate
51-100
Unhealthy for sensitive groups
101-150
Unhealthy
151-200
Very unhealthy - ALERT
201-500

The air quality index table is a useful reference for environmental engineers preparing to take the PE exam.

Types of Air Pollutants

Air pollutants may be natural, such as wildfires, or may be synthetic (manmade). Air pollutants are classified as primary pollutants and secondary pollutants. 

· Primary air pollutants are emitted directly into the atmosphere by the original source
· Secondary air pollutants are formed because of reactions between primary pollutants and other elements in the atmosphere, such as the ozone.

The common air pollutants are discussed below:
· Carbon Monoxide - Carbon monoxide is a colorless, odorless gas. Carbon monoxide can be present in car exhaust and smoke. Carbon monoxide deprives humans of their oxygen supply, which causes headaches, fatigue, impaired vision, and even death.

· Sulfur Dioxide - Sulfur dioxide is produced when coal and fuel oils are burned and is also present in power plant exhaust. Exposure to sulfur dioxide narrows the airways in the respiratory system, which causes wheezing and shortness of breath. 

· Nitrogen Dioxide - Nitrogen dioxide is both a primary and secondary air pollutant. Nitrogen dioxide is created when nitrogen reacts with oxygen in the atmosphere. Nitrogen dioxide can cause respiratory infections and other respiratory problems.

· Particulate Matter - Particulate matter contains particles of different sizes that are released into the atmosphere from various sources, including fossil fuels, dust, smoke, and fog. Particulate matter can accumulate in the respiratory system, which can aggravate the heart and lungs and increase the risk of respiratory infections.

· Ground-Level Ozone – Ground-level ozone is formed from automobile, power, and chemical plant exhausts. Ground-level ozone irritates the respiratory system and causes asthma by reducing lung function.

· Smog - Smog is the combination of gases with water vapor and dust and forms when heat and sunlight react with gases, which is known as photochemical smog. 



Tuesday, 30 May 2017

FUNDAMENTALS OF KIRCHHOFF’S LAWS FOR ELECTRICAL ENGINEERS

Introduction

Kirchhoff’s laws are basic analytical tools used to obtain solutions for currents and voltages in an electrical circuit. Circuits may be from a direct-current system or from an alternating current system. The following diagram depicts a simple resistive network.
Figure: Simple Resistive Network

Kirchhoff’s laws of circuit analysis are reviewed in our FE Electrical exam review course. Kirchhoff’s Current Law (KCL) and Kirchhoff’s Voltage Law (KVL) are important for both DC and AC steady states, and they are important to understand for the FE exam.

fundamentals of kirchhoff's law

Parts of an Electrical Circuit

Node: In an electrical circuit, a node is the point where two or more components are connected. This point is usually marked with a dark circle or dot when being depicted on diagrams. The circuit in the diagram above includes nodes, which are labeled as “b” and “g.” A point, or a node in a circuit, specifies a certain voltage level with respect to a reference point or node.

Branch: A branch is a traversing path between any two nodes in a circuit that have electrical elements. The above diagram shows that the circuit has seven branches, of which four are resistive branches (a-c, a-b, b-c, and b-g), and the other three branches contain voltage and current sources (a-b, a-g, and c-g).

Loop: A loop is any closed path in an electrical circuit. A loop in a circuit consists of branches that have a beginning point and an end point for tracing the path of electricity. In the above diagram, loops/closed paths include a-b-g-a and a-c-b-a. Further, it may be noted that the outside closed paths are a-c-g-a and a-b-c-g-a.

Mesh: A mesh is a special loop that does not include any other loops within it. The above diagram indicates that the three loops (a-b-g-a, b-c-g-b and a-c-b-a) are also considered meshes, while the loops a-c-g-a and a-b-c-g-a are not considered meshes.

Kirchhoff’s Current Law:

KCL states that at any node in a circuit, the algebraic sum of currents entering and leaving a node at any instant of time must be equal to zero. Currents entering and currents exiting the node must be assigned opposite algebraic signs to assure the resultant equates to zero. Example: In the following figure, I1 – I2 + I3 – I4 + I5 – I6 = 0. 
Figure: Kirchhoff's Current Law

Kirchhoff’s Voltage Law

KVL states that in a closed circuit, the sum of all source voltages must be equal to the sum of all voltage drops. Voltage drops occur when the current flows from the higher potential terminal toward the lower potential terminal. Voltage rise occurs when current flows from a lower potential terminal toward the higher potential terminal or positive terminal of voltage source. 

Kirchhoff’s Voltage Law from the figure: in clockwise direction starting from the voltage source is: V1 – IR1 – IR2- V2 – IR3 – IR4 + V3 – IR5 – V4 = 0, V1 – V2 + V3 – V4 = IR1 + IR2 + IR3 + IR4 + IR5
Figure: Kirchhoff’s Voltage Law

Engineers preparing for the Fundamentals of Engineering Electrical and Computer exam should review Kirchhoff’s laws prior to the exam in order to be able to estimate currents and voltages in an electrical circuit.