Unit 322 outcome 1,2,3 & 4

© Bonny Vocational Centre, 2013 1

Qualification: Level 3 Diploma in Engineering (IVQ) 2850-88

Module/Unit: 322 – Power Generation Systems and Ancillary Equipment

Outcomes : There are four learning outcomes to this unit. The learner will able to:

1.Be able to identify components and features of utilities2.Be able to prepare and prepare the maintenance or installation operations 3.Be able to carry out inspections and general maintenance tasks4.Be able to commission or re-commission the systems


Aim: This unit is concerned with power generation and associated systems, in terms of: planning and preparation, components, carrying out inspections, maintenance and installation tasks and commissioning the system

Lesson 01 – Identify the components and sub-systems needed for power generation units from drawings that use standard symbols

Principles of combustion of hydrocarbon fuels and the products of combustion

• Combustion is a chemical reaction between a fuel

and oxygen which is accompanied by the production of a considerable amount of heat (it is an exothermic reaction).

• The reaction has to be initiated by some source of high-temperature energy (ignition).




• Combustion Chemistry: Combining of hydrocarbon fuel with oxygen a chemical reaction between the hydrocarbon molecule and atmospheric oxygen combining at ignition temperature causes an exchange of elements that releases heat energy

The generalized combustion reaction for hydrocarbon fuels can be shown as:

CxHy + O2 = CO2 + H2O + EnergyCxHy is the hydrocarbon fuelO2 is oxygen

• The primary combustion elements of liquid heating fuel are:

o Carbon (84% - 89%)o Hydrogen (7% - 16%)

• Sulphur, generally contribute less than 1% of the total energy released

• Water, does not combust but in fact takes up energy




• Combustion of fuel can be divided into several processes:

(1) Bringing together the fuel and air (the reactants) in the correct proportions.

(2) Igniting the reactants.(3) Ensuring that the flame burns in a stable manner

and that combustion is complete.(4) Extracting useful heat from the process, and (5) Arranging for the safe disposal of the products of

combustion.



Element of combustion process

• '''Fuel''' (a combustible material)• '''Oxygen''' in sufficient quantity to support combustion• Sufficient '''heat''' to bring the fuel to its ignition

temperature and keep it there• If any of these conditions were removed, there would no

longer be a fire.


Need for the correct proportions of air and fuel for complete combustion • Oxygen is found in air

• Oxygen constitutes 20.9% of the volume of air, the balance being nitrogen 79% (and a few trace gases)

• Thus for any given amount of oxygen required, we need 4.8 times the volume of air (1 divided by 0.209)


• Complete combustion has been achieved when no further reaction takes place- all the carbon in the fuel appears in the flue gases as carbon dioxide (CO2) and all the hydrogen in the fuel is burned to water (H2O).

• As an illustration of the combustion reaction in the case of a simple but common gaseous hydrocarbon we can look at the combustion of methane (CH4).


Need for the correct proportions of air and fuel for complete combustion

• The bonding rearrangement which takes place when the fuel and air react can be regarded as producing species (carbon dioxide and water vapor) which are thermodynamically at a lower energy level than the reactants.

• The transformation to a lower energy level is responsible for the exothermic nature of the reaction.


Need for the correct proportions of air and fuel for complete combustion

Performance EvaluationPerformance Evaluation


• Combustion: rapid oxidation of a fuel

• Complete combustion: total oxidation of fuel (adequate supply of oxygen needed)

• Air: 20.9% oxygen, 79% nitrogen and other

• Nitrogen: (a) reduces the combustion efficiency (b) forms NOx at high temperatures

• Carbon forms (a) CO2 (b) CO resulting in less heat production

Emission ModellingMass of fuel burnt 1000 kg/hr

Input Mol Mass (g/mol)

Content in fuel (mass%)

Kmol/hr Mass burnt (kg/hr)

Carbon 12.01 88% 73.272 880

Hydrogen 1.01 12% 119.048 120

Sulphur 31.97 3% 0.938 30

Oxygen 8 0% 207.945 1,664

Total 1 401 2,694

Out put Mol Mass (g/mol)

Content in flue gas (mass%)

Kmol/hr Mass in flue gas (kg/hr)

CO2 28.1 76% 73.272 2,052

H2O 10.0.16 22% 59.524 596

SO2 47.97 2% 0.938 45

Total Total 2,694


Ways in which energy forms can be achieved

• Energy can be defined as the ability to do work.• Using energy to do work, objects gain energy

because work is being done on them.

• Chemical to heat: Chemical Energy is required to bond atoms together. When bonds are broken, energy is released.


Chemical to heat

• In an automobile engine, fuel is burned to convert chemical energy into heat energy.

• The heat energy is then changed into mechanical energy.

• Fuel (chemical energy) burning-heat energy-outside of boiler-water-steam-force the piston to move (mechanical energy).


Heat to mechanical• When work is done to an object, it acquires

energy. The energy it acquires is known as mechanical energy

• Conversion of heat (internal) energy to mechanical energy

• The technology to do this results in a HEAT ENGINE


Heat to mechanical

• A heat engine is a device which convert heat (internal) energy into mechanical energy.

• In most practical devices heat is used to boil a liquid and increase the pressure of a gas that is then arranged to provide a force on a surface which can be used to perform mechanical work– (force x distance in direction of the force)


Schematic Diagram of Heat Engine


Heat flow from hot reservoir

Heat flow to cold reservoir

kinetic to mechanical• The energy of motion is

called kinetic energy.• The faster an object

moves, the more kinetic energy it has.

• The greater the mass of a moving object, the more kinetic energy it has.

• Kinetic energy depends on both mass and velocity.


Principles and factors affecting heat transfer by conduction, convection and radiation


• Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy and heat between physical systems.

• There are three method of transporting heat energy– Conduction– Convection– Radiation

conduction, convection and radiation


Conduction

• Conduction: Collisions between adjacent particles result in an increase in heat energy at a distance from a heat source

E.g.

o A poker in a fireo Transfer of heat through the base of a saucepan from an

energy sourceo Transfer of heat from a furnace to a boiler


Radiation

• Radiation: Transfer of heat energy by generation of electromagnetic waves by any substance above absolute zero temperature

E.g. o Transfer of heat energy from the sun to the eartho Transfer of heat energy from an electric fire to a persono Transfer of heat energy from the atmosphere to the universe


Convection• Convection (Passive or Forced): Transfer of heat

energy by physical movement of material in bulk.

E.g. • Distribution of heat energy in water from the base of a

saucepan (passive)• Distribution of hot air in a domestic heating system (forced)• Cooling of a computer by a fan (forced)


Basic four stroke


• The Four (4) stroke takes 4 cycles to fire once.

• Intake, compression, combustion and exhaust to fire once. the cycles happen individually.

Two stroke cycle for spark• Two stroke engines fire

once every two (2) cycles. There intake and combustion cycle happen at the same time and there exhaust and compression cycle happen at the same time allowing it to fire every 2 cycles.


Compression ignition (CI) systems



• Cycle consists of four distinct strokes (processes) as in the case of SI engines, except that the spark plug is replaced by a fuel injector- Intake- Compression stroke- Power stroke- Exhaust


First stroke: SUCTION (Intake)


• Inlet Valve: OPEN• Outlet Valve: CLOSE• Piston Movement: DOWN• Combustion: NONE

First stroke: SUCTION (Intake) BDC


Second stroke: COMPRESSION

• Inlet Valve: CLOSED• Outlet Valve: CLOSED• Piston Movement: UP• Combustion NONE


Third stroke: POWER [ignition]

• Inlet Valve: CLOSED • Outlet Valve: CLOSED • Piston Movement: DOWN • Combustion: YES


Third stroke: POWER [expansion]


Fourth stroke: EXHAUST

• Inlet Valve: CLOSED • Outlet Valve: OPEN • Piston Movement: UP • Combustion: NONE




Valve timing diagrams defining lead


Valve timing

• Valve timing is the time a valve opens and closes during the four stroke cycles.

• Exhaust opening to let out exhaust gases,

• Inlet opening to let in the Air/fuel mixture and then both of them closing to keep the mixture in for compression.


Other example: Valve timing


Valve timing diagrams


Valve timing diagrams

• Valve timing (in previous slide) is a system developed for measuring valve operation in relation to crankshaft position (in degrees), particularly the points when the valves open, how long they remain open, and when they close.

• Valve timing is probably the single most important factor in tailoring an engine for special needs.


Opening and closing points of the valve

• An engine can be made to produce its maximum power in various speed ranges by altering valve timing.


Lead, lag and overlap


Lead, lag and overlap• The modified valve and ignition timings, the

following terms are used:• “Valve lead” means that the inlet valve opens before

the piston has reached TDC, and that the exhaust valve opens before BDC.

• “Valve lag” means that the inlet valve closes after the piston has passed BDC and that the exhaust valve closes after the piston has passed TDC.

• “Valve overlap” means that both inlet and exhaust valves are open together.It is a period when the inlet valve opens before TDC and the exhaust valve does not close until after TDC


NOTE !• “Ignition advance” describes the fact that ignition occurs

before the piston reached TDC on the compression stroke. (Note that timings of all these events (ie ignition, and the valves opening or closing) are all measured in degrees of crankshaft rotation - eg “120 before TDC” etc.)

• Increasing the efficiency of the engine by using valve lead, lag and overlap is made possible by a natural feature of the piston engine called “ineffective crank angle”.

• This means that near TDC and BDC a fairly large rotation of the crankshaft causes only a small linear movement of the piston.



Ignition and combustion requirements

• Combustion is the process in which air and fuel are burned after being mixed at a correct ratio of 14.7 parts of air to 1 part of fuel.

• The specific requirement for combustion including such as:

o air, o fuel and o ignition requirements, o timing, o air-fuel ratios, o compression ratio and engine efficiency

obtaining the correct air pressures and temperatures

• The internal combustion engine has certain requirements for efficient operation.

o There must be sufficient air for combustiono Correct amount of fuel mixture with air and o Ignition to start combustion.


obtaining the correct air pressures and temperatures

• For the engine to operate efficiently, the air and fuel mixture must enter the cylinder at the correct time.

• The intake valve must be opened and closed at the correct time. The exhaust valve must be opened and closed at the correct time too. The ignition must also be timed.

• The timing of the ignition can change with speed and load; if the processes is correctly timed, maximum power will be obtained in converting chemical energy into mechanical energy.


Obtaining the correct air pressures and temperatures

• Air-fuel ratio: is defined as the ratio of air to fuel mixed by the carburetor or fuel injectors.

• The term fuel ratio is also called stoichiometric ratio


Uniform mixtures of air and fuel in the required proportions

• The mass of air per kilogram of fuel in a mixture of air and fuel gives the air/fuel ratio of the mixture and, as already noted, the air/fuel ratio for complete combustion- called the chemically correct mixture is about 15 in the case of petrol.

• A mixture having greater proportion of fuel, i.e. lower air/fuel ratio than 15, is called a rich mixture, while one having a greater proportion of air, i.e. a higher air/fuel ratio than 15, is a weak mixture. Within limits both rich and weak mixtures will burn, but produce different results.


Air-Fuel-RatioAir-Fuel-Ratio • Best power at AFR of 12.5 (rich) • Best mileage at 15.5 (lean) • ARF above 17 causes misfiring • ARF below 10 causes flooding and plug fouling


Effects of incorrect mixtures

• The air and fuel must be thoroughly mixed. Each molecule of fuel must have enough air surrounding it to be completely burned.

• If the two are not mixed in the correct ratio, the engine efficiency will drop, and exhaust emission level will increase.


Use of pressure/volume and crank angle/pressure diagrams



• Crank angle, advance vs. retard (delay or hold back)

• Combustion takes time, about 5 ms.

• Combustion should occur at Top Dead Center (TDC), therefore spark must precede piston.

• The higher the engine speed (RPM's) the more advanced the spark must be. Vacuum or centrifugal advance.

• As lower octane fuel is used, the spark must be retarded. Effectively reduces compression thus reducing power and fuel economy.

• Retarding the spark reduces the max. and end temps of combustion and thus reduces both CO and NO formation.

Use of pressure/volume and crank angle/pressure diagrams


Lesson 02- Identify the function of the essential components needed for power generation plant or sub-systems

General layouts of types of engine:

• An inline engine (ICE)is long and narrow. In small cars in particular, a long, narrow engine mounted transversely can allow a very short hood.

• In an air-cooled engine, the inline configuration is sometimes harder to cool



The in-line engine

• Inline -- the cylinders are arranged in a line in a single bank:

INLINE 4 V6

INLINE 4 V6

FLAT 4

FLAT 4

Vee engine


Vee engine

• This is a more complex design using two camshafts that are synchronized through timing belt.

• Each camshaft is responsible for either the intake or the exhaust valves of the engine. It’s important to note here that on a V shaped engine, having two camshafts doesn’t make it Double Over-Head Camshaft (DOHC).

• You need two on each cylinder bank (one for intake valves and another for exhaust valves). This type of camshaft design is usually harder to repair but it provides additional performance and efficiency.


Vee engine


Methods of supplying air to IC engines • An air injection system forces

fresh air into the exhaust ports of the engine to reduce HC and CO emissions.

• The exhaust gases leaving an engine can contain unburned and partially burned fuel. Oxygen from the air injection system causes this fuel to continue to burn.

• The major parts of the system are the air pump, the diverter valve, the air distribution manifold, and the air check valve


• The AIR PUMP is belt-driven and forces air at low pressure into the system. A hose is connected to the output of the diverter valve.

• The DIVERTER VALVE keeps air from entering the exhaust system during deceleration. This prevents backfiring in the exhaust system. Also, the diverter valve limits maximum system air pressure when needed, releasing excessive pressure through a silencer or a muffler.

• AIR DISTRIBUTION MANIFOLD directs a stream of fresh air toward each engine exhaust valve.

• Fittings on the air distribution manifold screw into a threaded hole in the exhaust manifold or cylinder head.

• AIR CHECK VALVE is usually located in the line between the diverter valve and the air distribution manifold. It keeps exhaust gases from entering the air injection system.


Basic operation of the air injection system is as follows:

– When the engine is running, the spinning vanes of the air pump force air into the diverter valve. If not decelerating, the air is forced through the diverter valve, the check valve, the air injection manifold, and into the engine. The fresh air blows on the exhaust valves.

– During periods of deceleration, the diverter valve blocks air flow into the engine exhaust manifold. This prevents a possible backfire that could damage the exhaust system of the vehicle. When needed, the diverter valve will release excess pressure in the system.



Main features of electrical systems

• The control unit (ECU or ECM) is a small, dedicated computer which has the ability to read input signals from the engine, such as speed, crank position, and load. These readings are compared with data stored in the computer memory and the computer then sends outputs to the ignition system.

A digital ignition system




• Primary and Secondary SystemThe ignition switch allows the driver to turn the system on and off. Turning the key to the on position closes the circuit and allows current to flow. As current flows around the primary coil, a magnetic field is created. The strength of the magnetic field is determined by how long the points are closed. The points act as a mechanical switch that is controlled by the distributor's cam. When the points open, the circuit is broken; this instantly collapses the magnetic field and induces a high voltage into the secondary windings. The voltage is so intense that in its path to ground, it is able to ionize the air gap of the spark plug, thus igniting the fuel air mixture in the combustion chamber



Lesson 03- Select components or equipment to meet specified functions in terms of required volumes (fuel, air and steam), pressures and temperatures using manufacturers’ catalogues or other data

Components : Parts of cooling water supply systems • In a liquid cooled system, heat is carried away by the

use of a heat absorbing coolant that circulates through the engine, especially around the combustion chamber in the cylinder head area of the engine block.

• The coolant is pumped through the engine, then after absorbing the heat of combustion is circulated to the radiator where the heat is transferred to the atmosphere. The cooled liquid is then transferred back into the engine to repeat the process.



Water treatment for preventing scaling• Scaling and rust • Heat is conducted from the combustion chamber through the

surrounding metal to the coolant passages where the coolant picks up the heat and carries it to radiator.

• Keeping them clean internally (coolant replacement) is the best way to ensure trouble-free .


Water treatment for preventing scaling


Tips

1. Insufficient coolant

1.1 No coolant or very low coolant levels will obviously prevent heat transfer.

1.2 Coolant losses are normally caused by burst hoses, leaking seals, gaskets etc.


Tips 2 Restriction of coolant flow

2.1 A faulty thermostat can cause restriction of coolant flow; radiator tubes blocked internally, faulty water pump etc.

2.2 Also due to air bubbles admitted to the system by low coolant levels or pin-sized holes at the suction side of the water pump. These bubbles displace coolant at heat transfer surfaces and can also cause air locks at the water pump, thus reducing coolant flow.


Tips

3. Restriction of air flow3.1 An unkempt radiator exterior reduces

airflow.3.2 Also slipping fan belts, wrong type of fan or

blades at an incorrect angle etc.3.3 Position of radiator in relation to the fan or

vent is also important factors that can affect the airflow.


Corrosion and freezing • Water is used because of its ability to absorb and

carry heat efficiently, but it provides no corrosion protection, and has a limited operating range due to its freezing and boiling temperatures (32 degrees F and 212 degrees F).

• Various types of corrosion inhibitors are added to antifreeze to prevent oxidation and corrosion inside the cooling system.

• Corrosion occurs when oxygen and dissolved minerals or salts in the coolant react with metal surfaces.


Antifreeze


• Antifreeze is a material, such as ethylene glycol, that is added to water to lower its freezing point and bring up the boiling point as well.

• When adding coolant for warm temperatures, mix 50% water to 50% antifreeze. NEVER JUST USE WATER – Antifreeze will bring up the boiling point as

well.• For freezing temperatures, refer to the

chart on the antifreeze container. This should be done before the temperatures get down that low.– A frozen cooling system will damage the

radiator and the engine block.


Water

Vapor

pressure

Air

pressure

Water

Vapor

pressure

Air

pressure

Relationship between pressure and boiling point and resultant danger

Pressure – boiling point relationship


• As energy is transferred from a heating device to the water, the kinetic energy of the water molecules increases and the molecules become more mobile. If the kinetic energy is large enough to break the intermolecular forces of attraction between water molecules in the liquid phase then the molecules can escape in the form of water vapor. This is indicated by bubbles forming near the bottom of the container of water, nearest to the heat source. These gaseous water molecules exert a force on the atmosphere, called the vapor pressure. The vapor pressure is opposed by another force, created by a column of air pushing down on the surface of the water. This pressure is the atmospheric pressure.




• The atmospheric pressure will initially squash the pressure of the water vapor causing the bubbles to burst, but as more energy is provided the pressure exerted by the bubbles will exceed the atmospheric pressure and the bubbles of water vapor will escape the surface of the liquid. A diagram of these forces is provided. Water begins to boil. The temperature at which water boils is related to the vapor pressure required for boiling, which is equal to the atmospheric pressure. The implication of this is that as the atmospheric pressure changes, the boiling point of water changes as well. When you go up a mountain, the air pressure is lower (the column of air pushing downward is less) and water boils at a lower temperature.


Parts of lubricating systems


Lubrication System Components

Sump bolts to the bottom of the engine and holds the oil supply sealed by a gasket.

Dipstick measures level of oil in the sump.

Drain plug, to change oil.

Oil pickup linkssump to oil pump.

Oil pump mounted at front.

Oil filtermounted on cylinder block.



Oil Filter

Keeps impurities out of the engine.

Spin-on oil filter with O-ring seal.

Centre outlet tube.

Paper elements trap impurities.

Input feed holes.



Oil Filter Housing

Oil pressure switch.

May have oil cooler adapter.

Fed by oil cooler hoses.

Oil filter.

Heat shield.

Bolts to cylinder block.





All oil goes through filter



Gear Pump

Pump shaft drives one gear.

Other gear turned.

Low pressure at input.

High pressure at output.



Rotary Oil Pump

May be shaft, gear or chain driven.

Inner rotor driven by pump shaft.

Inner rotor drives outer rotor.

Oil is forced from input,

to output.



Crankshaft-Driven Pump

Drive splineson crankshaft.

Outer gear (rotor) driven by inner gear.

Inner gear (rotor) driven by crankshaft.

Pump housing at front of engine.

Pump insert holds drive within housing.

Main seal.



Lubrication SystemOil is held in the sump.

Drawn into engine throughthe pickup.

Forced round by a pump.

Protected by a pressurerelief valve.

Carried aroundin galleries.

Particulates removed by a filter.


Galleries

Cylinder bores.

To and from oil filter.

Carry oil to all parts of engine.

Lubricates valve gear, crank and camshaft.

From pickup to pump.


Splash methods of lubricating cylinder walls and valve mechanisms


Oiling Methods

Pressure-fed systems feed upper parts of engine.

Splash and drip-feed feeds down to the lower parts.


The Oil Is Pumped Through Passages In The Engine

Types of oil and grease used specifically for IC engines

• Oil-The lubricant, cools, separates and protects the engine components. The quality of the oil, i.e. – how good it is ,– confirmed by the industry standards and – printed on the container, e.g. SAE 10w/40 API SJ/CF

ACEA A3-96/B3-96.




Viscosity-Multi-Grade Oils


• The higher the viscosity number the thicker the oil is- if the oil is too thick it will not allow the engine components to rotate or slide easily, it will also be more difficult to pump around the engine.

• The lower the viscosity number the thinner the oil- if the oil is too thin it will not separate the engines moving components.

• 10W/40 engine oil i.e W means winter, therefore the oil is not too thick when cold and does not become too thin when hot thus providing all year round protection



Oil Viscosity (Weight)• Thickness or fluidity of engine oil• High viscosity number - SAE 30

– thick oil• Low viscosity number - SAE 5

– thin oil• Viscosity number is printed on container

(standardized by SAE)


Temperature Effects

• Cold oil is very thick and resists flow• When heated, oil thins and becomes runny• If it becomes too hot and thin, the oil film

can break down and part contact can result


Single and Multi-viscosity Oils

• Single viscosity —SAE 20, 30 or 40– limited range of operating temperatures– not as stable as multiviscosity oil

• Multiviscosity—SAE 10W-30, 20W-50– exhibits characteristics of a thin light oil when

cold and a thicker, heavy oil when hot



GreaseA. Their composition• Lubrication oils dispersed in a soap material• During operation , soap acts as a velvety surface which

carries the lube oil.


B. When to use them?1. In places where it is hard to make an oil cycle.2. When lubricated locations are exposed to water and dust.

C. Kinds of greases• Greases differ in the kind of oil used , and the kind of acidic and mineral radicals of the used soap , and their percentages.




• Grease• Lithium grease or white lube.• Used on mist. parts• Used in manual transmissions

and differentials on rear drive cars.


• Starter : Several methods are used to start IC engines. Most are started by use of an electric motor (starter) geared to the engine flywheel. Energy is supplied from an electric battery.

• Glow plug (heater plug) : Small electrical resistance heater mounted inside the combustion chamber of many CI engines, used to preheat the chamber enough so that combustion will occur when first starting a cold engine.

– The glow plug is turn off after the engine is started.


Starting methods for IC engines

Starting methods for IC engines


• What is the purpose of a glow plug on a diesel engine? A:To heat up the combustion chamber to prepare for firing.

General construction details of reciprocating IC engines

• A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion.

• The main types are: 1. the internal combustion engine, used extensively in motor

vehicles; 2. the steam engine, the mainstay of the Industrial Revolution;

and 3. the niche application Stirling engine.




Stirling Engine 4 Stroke Engine 2 Stroke Engine


• Block : Body of the engine containing cylinders, made of cast iron or aluminium.

• Cylinder : The circular cylinders in the engine block in which the pistons reciprocate back and forth.

• Head : The piece which closes the end of the cylinders, usually containing part of the clearance volume of the combustion chamber.

• Combustion chamber:Combustion chamber: The end of the cylinder between the head and the piston face where combustion occurs.– The size of combustion chamber continuously changes from

minimum volume when the piston is at TDC to a maximum volume when the piston at BDC.


• Crankshaft Crankshaft :: Rotating shaft through which engine work output Rotating shaft through which engine work output is supplied to external systems. is supplied to external systems.

– The crankshaft is connected to the engine block with the main bearings.

– It is rotated by the reciprocating pistons through the connecting rods connected to the crankshaft, offset from the axis of rotation. This offset is sometimes called crank throw or crank radius.

• Connecting rod : Rod connecting the piston with the rotating crankshaft, usually made of steel or alloy forging in most engines but may be aluminum in some small engines.

• Piston rings: Metal rings that fit into circumferential grooves around the piston and form a sliding surface against the cylinder walls.


• Camshaft : Rotating shaft used to push open valves at the proper time in the engine cycle, either directly or through mechanical or hydraulic linkage (push rods, rocker arms, tappets) .

• Push rods : The mechanical linkage between the camshaft and valves on overhead valve engines with the camshaft in the crankcase.

• Crankcase : Part of the engine block surrounding the crankshaft.

– In many engines the oil pan makes up part of the crankcase housing.

• Exhaust manifold : Piping system which carries exhaust gases away from the engine cylinders, usually made of cast iron


• Intake manifold :Piping system which delivers incoming air to the cylinders, usually made of cast metal, plastic, or composite material.

– In most SI engines, fuel is added to the air in the intake manifold system either by fuel injectors or with a carburetor.

– The individual pipe to a single cylinder is called runner.• Carburetor : A device which meters the proper amount of

fuel into the air flow by means of pressure differential.– For many decades it was the basic fuel metering system

on all automobile (and other) engines.• Spark plug : Electrical device used to initiate combustion in

an SI engine by creating high voltage discharge across an electrode gap.


• Exhaust System: Flow system for removing exhaust gases from the cylinders, treating them, and exhausting them to the surroundings.– It consists of an exhaust manifold which carries the

exhaust gases away from the engine, a thermal or catalytic converter to reduce emissions, a muffler to reduce engine noise, and a tailpipe to carry the exhaust gases away from the passenger compartment.

• Flywheel : Rotating mass with a large moment of inertia connected to the crank shaft of the engine.– The purpose of the flywheel is to store energy and furnish

large angular momentum that keeps the engine rotating between power strokes and smooths out engine operation


• Fuel injector : A pressurized nozzle that sprays fuel into the incoming air (SI engines )or into the cylinder (CI engines).

• Fuel pump : Electrically or mechanically driven pump to supply fuel from the fuel tank (reservoir) to the engine.


Bearing types and application• The main function of a rotating shaft is to transmit

power from one end of the line to the other. – It needs a good supportsupport to ensure stabilitystability and

frictionless rotation. The supportsupport for the shaft is known as “bearing”.

• The shaft has a “running fit” in a bearing. All bearing are provided some lubrication arrangement to reduced friction between shaft and bearing.


Bearing types and application


S O L ID S P L IT H A L F T IL T IN G P A D

JO U R N A L B E A R IN G(R A D IA L L O A D )

G . C Y L IN D E R &R ID E R R IN G

G U ID E B E A R ING(B A C K & F O R T H )

M O T IO N

G . V E R T IC A L F A N

T H R U S T B E A R IN G / T IL T IN G P A D(A X IA L L O A D)

(A R E A C O N T A C T )

P L A IN B E A R ING

(P O IN T O R L IN E C O N T A C T )

R O L L IN G E L E M E NTO R

A N T I F R IC T IO N B E A R IN G

B E A R IN G

Bearings are classified under two main categories:

– Plain or slider bearing : -• In which the rotating shaft has a sliding contact with the

bearing which is held stationary . Due to large contact area friction between mating parts is high requiring greater lubrication.



– Rolling or anti-friction bearing : -• Due to less contact area rolling friction is much

lesser than the sliding friction , hence these bearings are also known as antifriction bearing.




Rolling or anti-friction bearing

Load direction and name



Ball bearings


Roller bearings


Needle roller bearings


Types of rolling bearing• Single row deep-groove ball bearing:

– Incorporating a deep hardened raceway which makes them suitable for radial and axial loads in either direction, provided the radial loads are greater than the axial loads.

• Single row roller bearing:– Roller bearing have a greater load-carrying capacity than

ball bearing of equivalent size as they make line contact rather than point contact with their rings.

• Not suitable for axial loading, cheaper to manufacture, used for heavy and sudden loading, high speed and continuous service.


Ball and Roller bearing

Races and balls are high carbon chrome steel (to provide resistance to wear) machined and ground to fine limits of 0.0025 mm, highly polished and hardened.

The cages are made of low-carbon steel, bronzes or brasses, though for high temperature application case-hardened and stainless steels are used.


Bearing designation


Bearing designation


Types of bearing



Types of ball bearings






Prelubricated sealed ball bearing



Thrust ball bearings




Solid bearing

Solid bush


• Bush bearing– In this the bush of soft material like brass or gun

metal is provided and the body or main block is made of cast iron.

– Bush is hollow cylindrical piece which is fitted in a housing to accommodate the mating part. When the bush gets worn out it can be easily replaced.


Bushed bearing

Bushed bearing• The outside of the bush is a driving fit (interference fit) in the

hole of the casting where as the inside is a running fit for the shaft.

• The bearing material used may be white metal (Babbit – Tin/Cu/Lead/antimony) , copper alloy (brass, gunmetal) or aluminum alloy.

• Solid bushes are entirely made of bearing material and find the general application. In lined bush as the bearing material is applied as a lining to a backing material .

• Applications: turbines, large diesel engines etc



• Direct lined housings: directly by means of metallurgical bonding.

• Low-melting point white metal is used as a lining on the cast iron housing

Bush and Direct-lined housing

Split bearings• Plummer block or Pedestal bearing is a split type of

bearing. This type of bearing is used for higher speeds, heavy loads and large sizes.

• The component of the bearing:– Cast iron pedestal or block with a sole– Brass or gun-metal or phosphorus-bronze

“Brasses”, bushes or steps made in two halves.– Cast iron cap.– Two mild steel bolts and nuts.


Split bearings• Care is taken that the brasses do not move axially • nor are allowed to rotate. For preventing this• rotation , usually a snug at the bottom fitting inside • a recess at the bottom of the pedestal is provided.

• This bearing facilitates the placements and removal• of the shaft from the bearing. Unlike the solid • bearing which are to be inserted end-wise and • hence are kept near the ends of the shaft, these • can be placed anywhere. This bearing ensures a • perfect adjustment for wear in the brasses by• screwing the cap.


Split/Sleeve bearings


• A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between.

• Energy is added to the gas stream in the combustor, where fuel is mixed with air and ignited. In the high pressure environment of the combustor, combustion of the fuel increases the temperature.


Gas Turbine engine

Principles and construction of turbines

• The products of the combustion are forced into the turbine section.

• There, the high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades, spinning the turbine which powers the compressor and, for some turbines, drives their mechanical output.

• The energy given up to the turbine comes from the reduction in the temperature and pressure of the exhaust gas.





• Gas turbine engines are, theoretically, extremely simple. They have three parts:

• Compressor - Compresses the incoming air to high pressure

• Combustion area - Burns the fuel and produces high-pressure, high-velocity gas

• Turbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber



Power-to-weight ratio• Power-to-weight ratio (or specific power or power-

to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources. It is also used as a measurement of performance of a vehicle as a whole, with the engine's power output being divided by the weight (or mass) of the vehicle, to give a metric that is independent of the vehicle's size.


Power-to-weight ratio

• Power-to-weight is often quoted by manufacturers at the peak value, but the actual value may vary in use and variations will affect performance.

• The inverse of power-to-weight, weight-to-power ratio (power loading) is a calculation commonly applied to aircraft, cars, and vehicles in general, to enable the comparison of one vehicle performance to another. Power-to-weight ratio is equal to powered acceleration multiplied by the velocity of any vehicle.


Power-to-weight ratio• The power-to-weight ratio (Specific Power) formula

for an engine (power plant) is the power generated by the engine divided by weight of the engine as follows:


Stages of gas turbine engine and the associated components


Compressor Combustion area Turbine


Turbine3 stages Impulse Type

Combustor10 cansReverse Flow Type

Compressor17 stagesAxial Type

Combustor10 cansReverse Flow Type

Stages of gas turbine engine and the associated components

Can type: Individual liners and cases mounted around the engine each with its own fuel nozzle.

• Can-annular type- Designed to deal with split spool compressor.

• Individual cans are placed inside an annular case. Combines the strength of annular design with the convenience of maintenance of the can.

• Also keeps high temperatures in the inner can.



Working Cycle • Brayton cycle is the ideal cycle for gas-turbine

T

P= Const.

1

2

3

4

QH

1-2isentropic compression (in compressor) 2-3 const. pressure heat-addition (in combustion chamber) 3-4 isentropic expansion (in turbine) 4-1 const. pressure heat rejection (exhaust)

s

Basic components


Basic components


Basic components Gas turbine engines are, theoretically, extremely

simple. They have three parts: • Compressor - Compresses the incoming air to high

pressure

• Combustion area - Burns the fuel and produces high-pressure, high-velocity gas

• Turbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber



Combustion chamber Fan – low pressurecompressor

6 stage high pressurecompressor

8 stage intermediate pressure compressor


Inlet system


CompressorThe compressor is basically a cone-shaped cylinder with small fan blades attached in rows. Assuming the light blue represents air at normal air pressure, then as the air is forced through the compression stage its pressure rises significantly. The high-pressure air produced by the compressor is shown in dark blue.


RRAADDIIAAL L

FFLLOOWW

AXIAL

FLOW


Modern Compressor Designs are Extremely Efficient

gas turbine performance rating depends greatly on the compressor efficiency

High Performance Made Possible by Advanced Aerodynamics, Coatings, and Small Blade Tip Clearances

Even Small Amounts of Deposits on Compressor Blades May Cause Large Performance Losses

Inlet Guide Vane

Rotor Blades(rotating)

Stator Vanes (fixed to case)

Axial compressor


Axial vs. Radial

• Axial• Advantages:

• simple and inexpensive

• light weight• Disadvantages:

• less efficient• large frontal area• limited compression

ratio (4:1 ratio)

• RadialRadial– Advantages:Advantages:

• efficientefficient• high high

compression compression ratios (20:1)ratios (20:1)

– DisadvantagesDisadvantages::• complexcomplex• expensiveexpensive


Air Flow in Combustor

• Combustion air, with the help of swirler (twist or spiral) vanes, flows in around the fuel nozzle and mixes with the fuel.

• This air is called primary air and represents approximately 25 percent of total air ingested by the engine. The fuel-air mixture by weight is roughly 15 parts of air to 1 part of fuel. The remaining 75 percent of the air is used to form an air blanket around the burning gases to lower the tempera

Compressed Air Distribution:


Primary Air - 30% of the compressed air is supplied directly to the combustion chamberSecondary Air - 65% of the air provides cooling for the combustion chamberFilm Cooling Air - 5% of the air provides cooling directly to the turbine blades


Combustion AreaThe high-pressure air then enters the combustion area, where a ring of fuel injectors injects a steady stream of fuel. The special piece that located in combustion area called a "flame holder," or sometimes a "can." The can is a hollow, perforated piece of heavy metal. The injectors are at the right. Compressed air enters through the perforations. Exhaust gases exit at the left.

Combustor


Can



TurbineAt the far left is a final turbine stage, shown here with a single set of vanes. It drives the output shaft. This final turbine stage and the output shaft are a completely stand-alone, freewheeling unit. They spin freely without any connection to the rest of the engine. And that is the amazing part about a gas turbine engine.


Compressor blade materials

• Stainless steel materials


Changes in air pressure and temperatures



Changes in air pressure and temperatures

Compression chambers


• What do you understand about power plant? Explain. • How do you classify internal combustion (IC) engines? Explain. • Describe the working of two stroke petrol engine with neat diagrams. • Describe the working of four stroke petrol engine with neat diagram. • Describe the working of two stroke diesel engine with neat diagram. • What's the difference between an two stroke and four stroke petrol engine?• What is meant by the terms S.I and C.I in a four stroke engine?• Why do we have valve clearance?• What is the purpose of the thrust washers on the crankshaft?• On a diesel engine what's the difference between direct injection and a indirect

injection type?• What is taper and ovality in the bore, how is it caused how do you check it?• What is side clearance on a piston and how is it checked?• How can you tell the difference between a inlet and exhaust valve and why?


Advantages of gas turbine engines

• Very high power-to-weight ratio, compared to reciprocating engines;• Moves in one direction only, with far less vibration than a reciprocating

engine.• Fewer moving parts than reciprocating engines.• Waste heat is dissipated almost entirely in the exhaust. This results in a

high temperature exhaust stream that is very usable for boiling water in a combined cycle, or for cogeneration.

• Low operating pressures.• High operation speeds.• Low lubricating oil cost and consumption.• Can run on a wide variety of fuels.


;

• What is the purpose of the thrust washers on the crankshaft?

•A:The thrust washers stop the play of the conrods on the crankshaft, and the crank itself.


• On a diesel engine whats the difference between direct injection and a indirect injection type?

•A: Direct is injected directly into the combustion chamber while Indirect in injected into a Pre-combustion chamber before being ignited.



• Why do we have valve clearance?A:Valve clearance is the gap between the camlobe and the top of the valve. You can damage your engine if you set your clearances too tight causing it to wear and after prolonged wearing it can stop the valves from seating properly.



• Whats the difference between an two stroke and four stroke petrol engine? A: Two storke engines fire once every 2 cycles. There intake and combustion cycle happen at the same time and there exhaust and compression cycle happen at the same time allowing it to fire every 2 cycles.


• The 4 stroke takes 4 cycles to fire once. Intake, compression, combustion and exhaust to fire once. the cycles happen individually.


• What is taper and ovality in the bore, how is it caused how do you check it?•

A:Ovality is the wear in the cylinder bore. The ovality is caused by the main friction of the piston's movement up and down the cylinder bore. Though it may seem the piston moves straight up and down, the pull from the conrod going back and forth by the motion of the crank causes the piston to do the same but since the piston follows up and down the bore, it moves up and down.


• What is side clearance on a piston

and how is it checked? A:The side clearance is the distance between the piston and the cylinder wall. The piston rings are used to close the gap when under pressure to help contain the compression in the cylinder. To check the side clearance on the piston, place the ring into the piston and use a feeler gauge to measure the clearance in between.


• How can you tell the difference between a inlet and exhaust valve and why?A:The inlet valve is bigger, it lets in plenty of Air/fuel mixture. The exhaust valve is smaller, it lets out the exhaust gases, not a higher priority.


• What sort of tempatures do the inlet and exhaust valves get up to?A:the inlet valves can get up to round 250 degrees celsius and the exhaust valves can get up to around 750 degrees celsius.

What temperatures and speeds must the piston be able to cope with?A:Most pistons handle temperatures up to 300 degrees celsius and handle speeds up to 7500rpm which is the common "redline" for most vehicles.

•Why do we have piston ring end gap clearance?A:To allow the ring to expand when pressure gets underneath it to increase the strength of the seal.

What could the result be if the piston ring end gap is too small?A:Not much pressure would be able to get underneath it and make an adequate seal.

Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the cylinder head surface ?A:To prevent damage to the head as the head is made by a softer/lighter alloy and after time the spring loses tension, the shim would also bring it back to normal.


What is meant by the terms S.I and C.I in a four stroke engine?A: SI means spark ignition and CI means Compression ignition


• http://www.fao.org/docrep/v8966e/v8966e05.htm• http://www.prochemagencies.com/pdfs/products/spill_response/OIl

%20Eater%20Products.pdf


Documents

Unit 322 outcome 1,2,3 & 4