Combustion Lab I

8/6/2019 Combustion Lab I

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1st

LaboratoryEnergy Balance

Combustion Laboratory I

Prof. Dr: M.M El-Kassaby

&Eng. Ahmed Magdy


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Alexandria UniversityFaculty of Engineering

Specialized Scientific Programs

1st

LaboratoryEngine cycles and Engine parts


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1st

LaboratoryEngine cycles and Engine parts

Objective

To know the meaning of Internal Combustion Engine, get the mean of combustion

theory, and to get familiar with the Engine main parts, and also with Four Stroke Engine

Discussion

When we speak about Internal Combustion Engine, we must to take every word and see

what it means

Engine: it is a machine that with it we can take power

Combustion: so we will take this power by burning

Internal: means that we will take power in the place where we burn

Combustion Theory

From the above shape, it is obvious that to make combustion you must to have 3 sources:

Oxygen which is found in Air, Fuel, and Source of heat which is found in the spark plug.

So in the car there are 3 important systems: -

a) Air System

b) Fuel System

c) Ignition System


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A.Four stroke engine Engine parts

Internal combustion piston engineComponents of a typical, four stroke cycles, internal combustion piston engine.

E - Exhaust camshaftI - Intake camshaft

S - Spark plugV - Valves

P - PistonR - Connecting rodC - Crankshaft

W - Water jacket for coolant flow

Spark plug

The spark plug supplies the spark that ignites the air/fuel mixture so that combustion canoccur. The spark must happen at just the right moment for things to work properly.
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Valves

The intake and exhaust valves open at the proper time to let in air and fuel and to let out

exhaust. Note that both valves are closed during compression and combustion so that thecombustion chamber is sealed.

Piston

A piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston rings

Piston rings provide a sliding seal between the outer edge of the piston and the inner edgeof the cylinder. The rings serve two purposes:

They prevent the fuel/air mixture and exhaust in the combustion chamber fromleaking into the sump during compression and combustion.

They keep oil in the sump from leaking into the combustion area, where it wouldbe burned and lost.
http://auto.howstuffworks.com/question105.htmhttp://auto.howstuffworks.com/question105.htm


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Connecting rodThe connecting rod connects the piston to the crankshaft. It can rotate at both ends so that

its angle can change as the piston moves and the crankshaft rotates.

Crankshaft

The crankshaft turns the piston's up and down motion into circular motion just like acrank on a jack-in-the-box does.

Sump

The sump surrounds the crankshaft. It contains some amount of oil, which collects in thebottom of the sump (the oil pan).


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Engine operating cycle


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2nd LaboratoryEngine cycles and Engine parts (cont)


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2nd

LaboratoryEngine cycles and Engine parts (cont)

Objective

To get familiar with the Engine main parts of two strokes, and the two stroke cycle

Discussion

What is the difference between Four Stroke Engine and Two Stroke Engine?

B.Two stroke engine Engine parts

Like other types of engines, a two-stroke engine has a crankcase that surrounds andprotects all other parts of the engine. Inside, it has a crankshaft, connecting rod and single

piston. It's also got an intake port, a reed valve, an exhaust port, and a cylinder---all inaddition to the combustion chamber, where the power is produced that moves whateverthe engine is powering.


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StrokePiston

Direction

Actions

Occurringduring This

Stroke

Explanation

Stroke

1

Piston travels

up thecylinder barrel

Induction &

Compression

As the Piston travels up the barrel, fresh fuel/air mix is sucked

into the crankcase (bottom of the engine) & the fuel/air mix inthe cylinder (top of the engine) is compressed ready for ignition

Stroke

2

Piston travels

down thecylinder barrel

Ignition &

Exhaust

The spark plug ignites the fuel/air mix in the cylinder, the

resulting explosion pushes the piston back down to the bottomof the cylinder, as the piston travels down, the transfer port

openings are exposed & the fresh fuel/air mix is sucked from thecrankcase into the cylinder. As the fresh fuel/air mix is drawninto the cylinder, it forces the spent exhaust gases out through

the exhaust port.

Now we will find the advantage and disadvantage of Two stroke Engineswith differentiate with Four stroke Engines:

Advantages:-

Two-stroke engines do not have valves, which simplifies their construction andlowers their weight.

Two-stroke engines fire once every revolution, while four-stroke engines fireonce every other revolution. This gives two-stroke engines a significant power

boost. Two-stroke engines can work in any orientation, which can be important in

something like a chainsaw. A standard four-stroke engine may have problemswith oil flow unless it is upright, and solving this problem can add complexity tothe engine.

Disadvantages:-

Two-stroke engines don't last nearly as long as four-stroke engines. The lack of adedicated lubrication system means that the parts of a two-stroke engine wear alot faster.

Two-stroke oil is expensive, and you need about 4 ounces of it per gallon of gas.You would burn about a gallon of oil every 1,000 miles if you used a two-stroke

engine in a car. Two-stroke engines do not use fuel efficiently, so you would get fewer miles per

gallon.

Two-stroke engines produce a lot of pollution -- so much, in fact, that it is likelythat you won't see them around too much longer.


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3rd

LaboratoryIgnition system


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3rd

LaboratoryIgnition system

Objective

To know the third part of the combustion process in the spark ignition system, and to befamiliar with its consistetuent.

Discussion

What is the difference between spark ignition system (Gasoline) and compressionignition system (Diesel)?

Types of ignition systemsElectro-Mechanical Ignition (conventional system)

The ignition system is expected to give billions of sparks to the cylinders without a singlemiss, to burn the charge (air+fuel) in the combustion chamber. So we create a high

voltage on two poles between them a space so we ionized the air and spark created. Thishappen in the spark plug in the cylinder head.

Ignition system parts:-


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Schematic for Ignition system

1 Battery2 Ignition switch3 Ignition coil4 condenser5 contact breaker6 The Distributor7

Spark Plugs

Now we will take each part of the past and study it in detail

1. Battery

It is only electric source in the vehicle, it provide us with 12 Volt DC current. Lead-acidbatteries for automotive use are made with slightly different construction techniques.


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2. Ignition switch

It is the contact that with it we begin the move of the car, when we closed the circuit thecurrent flow from the battery to the rest of the circuit and give us the current that we

want.

3. Ignition coil

Primary coil Secondary coil Contact breaker Condenser

To make spark between poles of the spark plug we need to raise the volt of the batteryfrom 12 Volt to 12 Kvolt (12000 Volt) or more than it (may reach to 24000 Volt)

depending on the compression ratio. For this reason we use Ignition Coil.


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But there is a problem in converting the battery voltage to high voltage , this problem isthe battery support us with a DC current and the Ignition coil must work at AC current ,

because the Ignition coil raise or reduce the Voltage with the relation between the number

of laps in the primary coil to number of laps in the secondary coil, and the voltage in the

primary coil to the voltage in the secondary coil in case that 0.0dt

dand this

condition not satisfied except in Ac Current only.

0.0

secsec

dt

donly

V

V

n

n

ondary

primary

ondary

primary

To solve this problem we use Contact Breaker

I (Amp) I (Amp)

Time Time

With contact breaker without contact breaker

Ignition switch

Conventional coil


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The contact breaker

Its function is to open and closed the circuit with high speed to convert the DC current to

AC current. But as a result of the rate of high speed cut and contact of the current, itworks on causing spark and wears in the contact points. To prevent this we useCondenser.

Condenser function

1. Prevent contact breaker points from sparking and pitting.

2. Increase the rate of collapse of the magnetic field which increase E.M.F

Dwell angleIt is the period during which the contact breaker points are closed

Note

Cam and rotor are located on distributor shaft

Distributor shaft cam shaft speed= 1/2 crank shaft speed (4stroke)= crank shaft speed (2stroke)

4. The Distributor

To distribute the high voltage on the spark plug as a specific arrange we use Distributor.But also there is another function for the distributor as it runs the contact breaker cam.Distributor contains two integral parts that help us in overcoming the change in loads:

a. Centrifugal Advance

b. Vacuum Advance


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5. The spark plug

Contains the electrodes which are the most important parts required to generate the

ignition spark and seals off the combustion chamber


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4th

LaboratoryDiesel Engine


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4th

LaboratoryDiesel Engine

Objective

To be familiar with Diesel engine, and know the important parts in these Engine specially

the Fuel injection.

Discussion

Comparison between Gasoline Engine and Diesel Engine.Diesel Engine

In theory, diesel engines and gasoline engines are quite similar. They are both internal

combustion engines designed to convert the chemical energy available in fuel intomechanical energy. This mechanical energy moves pistons up and down inside cylinders.The pistons are connected to a crankshaft, and the up-and-down motion of the pistons,

known as linear motion, creates the rotary motion needed to turn the wheels of a carforward.

Both diesel engines and gasoline engines covert fuel into energy through a series of smallexplosions or combustions.
http://science.howstuffworks.com/gasoline.htmhttp://science.howstuffworks.com/gasoline.htm


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The major difference between diesel and gasoline is the way these explosions happen. Ina gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks

from spark plugs. In a diesel engine, however, the air is compressed first, and then the

fuel is injected. Because air heats up when it's compressed, the fuel ignites.

Remember that the diesel engine has no spark plug, that it intakes air and compresses it,

and that it then injects the fuel directly into the combustion chamber (direct injection). Itis the heat of the compressed air that lights the fuel in a diesel engine.

Injection Systems

It is important system that used for delivering the fuel to the combustion champers. Itconsists of many parts, these parts are:

Fuel tank Fuel filter Fuel pump Fuel lines injectors

All these parts are important in the system and we cannot get rid of any part of theseparts. And this system must do the following requirement:

Metering Timing Rate of fuel injection Atomization


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The most important parts in the injection system are the injection pump and the injectorso we will concern with these two parts and study them in some detail.

Injection pump

Injection pump used to increase the pressure of the fuel to push it in its path to the

injector and to meter the quantity of the fuel as the driver want.

There are many types of injection pumps such as

In-line injection pump Distributor injection pump Single barrel injection pump Common rail system

All of these types have its application that is used in it, so depend on the application we

choose the pump

We will study only one type of these pumps it is the In-line injection pump

In-line injection pump

The in-line injection pump has a pumping element (plunger-and-barrel assembly) foreach of the engine's cylinders. These pumping elements are arranged "in-line" with eachother. The pump's camshaft is driven by the engine's timing gears or chains. The in- line

pump turns at half the engine speed and is always synchronized to the diesel engine'spiston movement. The fuel is forced through high-pressure lines to the nozzle-and-holder

assemblies from where it is then injected by the nozzles (injectors).


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We will see a schematic drawing the main parts of the In-line injection pump

Fuel Pump


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Fuel tank

It contains the Fuel that we will pump and use in the injection system. It also has strainer

that is help in removing some of the impurities.

Supply pump

It is from the diaphragm Type (Diaphragm pump) it consist of spring, diaphragm, camand cam follower.

It is just used to transfer the Fuel from the fuel tank to pass through the filter and goes inall the system components

Fuel Filter

It is used in purify the fuel from any impurities or strange particle to not enter the Fuel

pump and make problems.

Fuel Pump

It is the most important part in this System; it is from the type In-line injection pump. Itconsists of plunger that takes its move from Cam and it has helical grove at the end of it,

at the end of the pump is the delivery valve that is the gate for the fuel to go through thefuel line pipe to the injector.

Also there is a rack and pinion that from it the driver can control the quantity that will beinjected.

The fuel pump as we said has two functions: to increase the fuel pressure and to meter thequantity of fuel that would be injected. The part that is responsible for this is the control

helix plunger

How does it Work?

In-line pump systems have a separate pump plunger for each cylinder of the engine, so a

4 cylinder engine has a four plunger pump; a 6 cylinder engine has a six plunger pump,

etc. The pump is run at half engine crankshaft speed and has a central shaft with four, six,etc. cam lobes attached. Each plunger is operated by its cam once every two crankshaftrevolutions, coinciding of course with the power stroke of its engine cylinder. Eachplunger also has a spiral groove or helix machined on its side and cut through to the top

of the plunger. When operating, the plunger is pushed up by its cam lobe. At a certainpoint the spiral groove will line up with a spill port on the side of the plunger cylinder

and the rest of the fuel is spilled.


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Because the groove is a spiral shape, the point in the plunger stroke when it uncovers thespill port will vary as the plunger is rotated a few degrees either way. This adjusts thespill point and hence, the volume of its fuel charges to the engine cylinder. Since all of

the engine cylinders receive the same sized fuel charge, all of the plungers are rotatedtogether.


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The pump increase the pressure of the fuel to range (50-100 bar) then it goes to theinjector to be injected.

Injector

The fuel injected by the injector in range (200 to 1700 bar) and sometimes it reaches(2000 and 2500) bar, these large pressure difference across the injector nozzle arerequired so that the injected fuel jet will enter the chamber at sufficiently high velocity to

1- Atomize into small sized droplets to enable rapid evaporation2- Traverse the combustion chamber in the time and fully utilize the air chargeThe task of fuel injected

1- To meter the appropriate quantity of fuel at given engine speed.2- Inject fuel at the appropriate time in the cylinder at the desired rate with high

pressure to ensure good atomization and proper penetration and good fuel air mixture

If penetration is weak, poor mixing will result If penetration is strong, the fuel is impingement with walls

3- To avoid low injection pressure which will result dribblingInjector cross section


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1. Leak off port 7. Fuel Gallery 13. Needle Valve

2. Leak off cap 8. Tapered needle shoulder 14. One of 3 feed holes

3. Injector Spring 9. Nozzle Body 15. Supply Hole

4. Lower spring plate 10. Spray Holes 16. Spindle

5. Clamping Flange 11. Nozzle Tip 17. Inlet Port

6. Nozzle Holder 12. Needle and Nozzle seat 18. Spring cap adjustment nut

No.1 - Leak off Port, a hole to release pressure from the injector if/ when it needs

changing.

No.2Leak off cap, a cap which screws on to the top of the keep the spring compressed.

No.3 Injector Spring, a helical coil compression spring, which is in- between the springcap adjustment nut (No.18) and the Spindle (No.16). It is held in place by both upperand lower spring plates. The springs job is to keep the Needle Valve (No.13) closed

until the appropriate fuel pressure is reached, also to close the Needle Valve (No.13)when the fuel pressure drops.

No.4Lower Spring Plate, retains the injector spring

No.5Clamping Flange, the injector is supported by this flange

No.6 Nozzle Holder, this is a forged-steel flanged housing which supports various

parts; it is bolted to the engines cylinder head. It has a threaded inlet port to support aninlet adaptor; a supply hole is drilled to intersect the pressure face junction between the

Nozzle Holder (No.6) and the Nozzle Body (No.9). The upper end has a largethreaded countersunk hole made to support the spring cap adjustment nut.

No.7 Fuel Gallery, the storage chamber to hold the fuel which has been pumped to theinjector before injection

No.8 Tapered Needle Shoulder, the tapered needle shoulder is actually tapered so that

the fuel can smoothly and quickly pass by when being injected.

No.9 Nozzle Body, this supports the Needle Valve (No.13), it is cylindrical in shapeand has a centrally bored steel body. The bottom of the centrally blind hole is conically

ground to form the Nozzle Valve Seat (No.12).


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No.10 Spray holes, these are the holes in the end of the nozzle. These are drilled atvarious angles to suit the combustion chamber on a multi-hole type nozzle.

No.11Nozzle Tip, The extreme end of the nozzle body containing spray holes.

No.12 Needle and Nozzle seat, this determines how much fuel flows to the combustion

chamber.

No.13 Needle Valve, this has two sections of different diameters. The bigger of the twodiameters forms a lapped fit with the Nozzle Body (No.9). The smaller diameter has alarge clearance between it and the Nozzle Body (No.9), its 60 inclusive angle conical

ground end forms the Needle valve seat (No.12).

No.14Feed hole, where the fuel is fed from.

No.15

Supply Hole, the hole that is responsible for taking the fuel from the inlet port toone of three feed holes.

No.16 Spindle, the spindle relays the spring thrust to the needle valve from the spring,

it is placed in- between the spring-cap adjustment nut (No.18) and the countersunkthreaded hole in the Nozzle holder (No.6), it forces the Needle Valve (No.13) onto the

nozzle body seat.

No.17Inlet Port, the port in which the fuel is fed into one of the three feed holes.

No.18 Spring Cap Adjustment Nut, to adjust the amount of pressure in which the

injector injects fuel into the combustion chamber or the swirl chamber.


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5th

LaboratoryGas Turbine


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5th

LaboratoryGas Turbine

Objective

To be familiar with Gas Turbine, studying its parts and know some of Gas Turbine types.

Discussion

Some of the application that Gas turbine are used Comparison between Reciprocating Engine and Gas turbine

Gas Turbine

The gas turbine is a power plant, which produces a great amount of energy for its size and

weight. Gas turbine engines derive their power from burning fuel in a combustionchamber and using the fast flowing combustion gases to drive a turbine in much the same

way as the high pressure steam drives a steam turbine.

Gas turbine Parts

In gas turbine also we change the chemical energy of the fuel into thermal energy thatgive energy of the compressed air then we make it Expands in the turbine so Mainly inAny Gas Turbine we will need three main Parts:-

Compressor Combustion chamber Turbine


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We will take each part and discuss its operation:-

CompressorIn compressor we raise the pressure of air, and there are 2 main types of compressors thatused in Gas Turbine: centrifugal compressor and Axial compressor and depend on theapplication we choose the type of compressor.

Combustion chamberCombustion chamber is placed between compressor and turbine and as the velocity of the

air exit from the compressor is high, so we use diffuser to reduce the velocity and do thatthe flame does not stop. It also contains the injector which injects the fuel in the path of

the air.


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Injection pressure

The fuel is injected continuously in the combustion chamber by using the atomizer atpressure approximately (50 bar).

Combustion Zones

Combustion chamber consists of three major zones:

1. Primary Zone2. Intermediate Zone3. Dilution zone


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a) Primary ZoneThe air enter in these region approximately (15:20%) from the total air and at these time

the combustion in these region start as the mixture is rich with fuel. excess air factor ()1

b) Intermediate ZoneThe air which enter in these region is approximately (30%) from the total air to completethe combustion process of the outlet gases from the primary zone. excess air factor ()

(2:3)

c) Dilution ZoneThe rest of air (50%) from the total air enter these region where late combustion happen

and the air mix with the combustion product to reduce its temperature , because if thetemperature is high it may cause melting the parts of the turbine. excess air factor () (4:5).

Combustion chamber types

There are three common types for the combustion chamber

1. Annular type

2. Cannular type


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There are two types

a) open circuit (loop)b) closed circuit (loop)

Our choice to one of the above circuit will depend on the medium we use, if we use cheapmedium (like air) it will not be efficient to reticulate it. But if we use expensive medium(like Ar or He) it is not efficient to lose it in the atmospheric so we use heat exchanger to heat

it and after expansion we use heat exchanger to cold it. Also in heat exchanger we may usenuclear reactor so in closed loop we cannot make the medium go out of circuit for safety

operation.

According to turbine shaftThere are many types of these specification but we will focus on two types:

a) Single shaft turbineb) Double shaft turbine


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In single shaft turbine the shaft is coupling between compressor and turbine , so thepower from the turbine is used to operate the compressor and to give us power

In double shaft turbine there are two shafts: one between the high pressure turbine and

compressor and these only to operate the compressor, and the other shaft between the lowpressure turbine and the load where it gives us the power.

Application on Gas Turbine

power stationWhere we use the power from the output shaft to generate electricity, but mostly it isused with steam turbine in Combined Cycle

Jet EngineWhere the power from the shaft is used to operate propeller as in helicopter, or to makethe exhaust gas expand through nozzle to give us thrust force


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Documents

Combustion Lab I