0-2103471 introduction to engine design

8/7/2019 0-2103471 Introduction to Engine Design

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Introduction

2103471 Internal Combustion Engine



Definition of Engine

• Historically, the definition of ENGINE is any

machine that does work, no matter how it ispowered. This definition covers wind mills, waterwheels, muscle-operated machinery, etc. The

origin of the word engine is from Latin andGreek roots meaning invention. In modern times,

the meaning has shifted to describe prime

movers that operate automatically andcontinuously to convert some form of energy intouseful mechanical power.



Heat Engine

• 1824 Sadi Carnot -Noted that work could be converted to heatand vice versa and there must be a fixed ratio between the two.

However, the efficiency with which heat could be turned to work byany engine was limited by the degree of heat. Thus, he hasessentially stated the first and second laws of thermodynamics.

• 1850 James Joule -Measured the fixed ratio between work andheat thus defining the first law.

• 1889 Wm. Rankine -Having already developed Carnot's ideas tolead to an "absolute" temperature scale, Rankinewrites the firstformalized thermodynamics textbook thus defining the second law

• Alternatives to steam engines were being developed in the 19thcentury (1800's).



SEARCH FOR NEW ENGINES: Mid-19th century.

Steam was not satisfactory for all purposes, despite generally goodrecord of engineering development.

• Thermodynamics one reason. Allowed calculation of efficiencyagainst theoretical standard.

– a. Steam looked poor, < 12%

– b. Somewhat unfair, idealistic view.

• Opportunity presented by new fuel. "Gas" (from coking ovens) in

pipes. – a. Supplied to cities as illuminant.

– b. Use as engine fuel tempting, but in steam engine?

• Market advantages. Steam required: – a. Licensed operators.

– b. Lead & lag times for boilers.

– c. Fairly large size installations.

– d. Any machine avoiding these had possible market.



Stanley Steamer



Hot air engine

• 1807 George CayleyBuilds a working hot air engine, then goes off and has a brilliant career in

• 1837 aerodynamics. In 1837, he patents an improved hot air engineand it is commercially produced in the 1860's and 1870's. -basically,the engine has an enclosed coal burner. Air is pumped into the

combustion chamber and, by burning with the coal, it expands to hotcombustion gases which raise engine pressure, forcing a piston upits cylinder. This internal combustion engine suffers from seriouswear problems with coal cinders in the working cylinder.



Hot air engine

• 1826 John Ericsson External combustion, open cycle hot air engine.These engines were less efficient and noisier than the Stirling

engines but better marketed and were fairly successful, with engines

ranging from small portable to a 300 hp ship engine.



Hot air engine

• The hot air engines were actually more efficient than steam engines

but were not sufficiently reliable and long lasting due to poor

materials for the hot end and poor lubricating & sealing materials for

metal/metal/air joints. Also, with atmospheric air as the working fluid,

it was hard to get high specific power.



Why Internal Combustion?

• IC engines were thought to have a bleak

future when first invented

“You can’t get people to sit over an explosion”

“The automobile industry will surelyburgeon…but this motor will not be a factor.”

- Col. Albert A. Pope, largest

automobile manufacturer at the turnof the century



• 1794 Robert Street Patented a reciprocating ICengine burning a gaseous fuel-air mixture (heatedturpentine / air)

• 1801-1860 Philippe Lebon, Samuel Morey, and manyothers experimented with engines that burned fuel inside

the piston/cylinder arrangement to produce work. All oftheir engines were failures but they gradually built up thebasic technology necessary for engines.

History of I.C. Engine



• Most of the earilest practical internal combustion engine ofthe 17th and 18th centuries can be classified as AtmosphericEngine.

• It drew in the fuel-air mixture during the first half of thestroke, then ignited the mixture which expanded during thesecond half of the stroke.

• Gunpowder was often used as the fuel.

• The trapped exhaust products was allowed to cool. As the

gas cooled, it created a vacuum within the cylinder. Thiscaused a pressure differential across the piston. As thepiston move because of this pressure differential, it woulddo work by being connected to an external system.

EARLY ATTEMPTS.



Atmospheric Engine

Process 1-2: Fuel air mixture introduced into cylinder atatmospheric pressureProcess 2-3: Constant pressure combustion (cylinder open

to atmosphere)Process 3-4: Constant volume cooling (produces vacuum)Process 4-5: Isentropic compression (vacuum pulls piston)Process 5-1: Exhaust process

31

2

5

Po

4

P

V

VALVEPatm



EARLY ATTEMPTS.

• Lenoir in France produced the first practical internalcombustion engine in 1860.

• By firing in every stroke on the piston, an internal-

combustion engine on model of steam engine by EtienneLenoir (2-stroke) led to more efforts.

• Lenoir-cycle engines were not very efficient and because

the piston was double acting, and therefore was heatedfrom both sides, they were limited to relatively small sizesthat could be cooled by the cylinder water jacket.



• 1860 JeanJosephLenoir The first commerciallyproduced internalcombustionengine. -non-compression ... theenginesucked inair /fuel

mixtureduringhalf the intakestrokeand then ignited it. Theexpandingmixtureshut the intakevalveandproducedenoughpressuretopush thepistondown, rotate theengine through itsexhaust stroke, andstart the intakestrokeagain. In fact, theenginewas alsodouble-actingwith a combustionchamber oneachsideof thepiston. -due to lackof compression, his engines wereveryinefficient ... includingmechanical inefficiencies, theconsumptionwas

givenas 100cu ft/ hp.hr of 500-600btu/scf gas. This would beabout4 to5 % efficient whichwas not badcompared tosteam. (However ,remember it nowusedcoal gas (a refined fuel) rather than rawcoal.Someenergy hadbeenused toproduce thecoal gas.)




1860 Lenoir’s

engine (a converted

steam engine)

combusted naturalgas in a double

acting piston, using

electric ignition


Two stroke Lenoir Engine



Two-stroke Lenoir Engine

Process 1-2: Fuel air mixture introduced into cylinder at

atmospheric pressureProcess 2-3: At half-stroke inlet valve closed and combustion

initiated constant volume due to heavy pistonproducing high pressure products

Process 3-4: Products expand producing workProcess 4-5: At the end of the first stroke exhaust valve opens

and blowdown occurs

Process 5-1: Exhaust stroke

3

1 2Po

4

5

P

V



• 1876 Nikolaus Otto patented the 4 cycle engine; it usedgaseous fuel

• 1882 Gottlieb Daimler, an engineer for Daimler, left towork on his own engine. His 1889 twin cylinder V was

the first engine to be produced in quantities. It usedliquid fuel and Venturi type carburetor, engine wasnamed “Mercedes” after the daughter of his majordistributor

• 1893 Rudolf Diesel built successful IC engine whichwas 26% efficient (double the efficiency of any other

engine of its time)





• The internal combustionengine was first conceivedand developed in the late

1800’s• The man who is considered

the inventor of the modernIC engine and the founder

of the industry is pictured tothe right….Nikolaus Otto(1832-1891).

• Otto developed a four-stroke engine in 1876, mostoften referred to as a SparkIgnition, since a spark is

needed to ignite the fuel airmixture.



Two-stroke Otto-Langen Engine



Two-stroke Otto-Langen Engine

Process 1-2: Fuel air mixture introduced into cylinder at

atmospheric pressureProcess 2-3: Early in the stroke inlet valve closed and

combustion initiated constant volume due toheavy piston producing high pressure products

Process 3-4: Products expand accelerating a free pistonmomentum generates a vacuum in the tube

Process 4-5: Atmospheric pressure pushes piston back,

piston rack engaged through clutch to output shaftProcess 5-1: Valve opens gas exhausted

Disengagedoutput shaft

Engagedoutput shaft



1885 Schleicher-Schumm Built in Philadelphia, PA by theAmerican licensee of Otto and the second oldest American,operating internal combustion engine. Two-horsepower at 180rpm, single-cylinder, horizontal design.



Historical IC Engines

EARLY ATTEMPTS



• The impact on society is quite obvious, all most all traveland transportation is powered by the IC engine: trains,automobiles, airplanes are just a few.

• The IC engine largely replaced the steam engine at theturn of the century (1900’s)

• Another important cycle is the Diesel cycle developed by

Rudolph Diesel in 1897. This cycle is also known as acompression ignition engine.

EARLY ATTEMPTS.

EARLY ATTEMPTS : summary



Atmospheric engines

• Huygens proposed using gunpowder for providingmotive power (1680)

• Papin described an engine design to the Royal Society

of London (1688)• Newcomen (1712) - first steam engine

Engines with compression• Lenoir (1860)

• Otto and Langen (1866)

• Otto silent engine - four stroke (1876)• Robson - two stroke (1877)

• Daimler - workable power-to-weight ratio (1884)

• Diesel - diesel engine (1892)

EARLY ATTEMPTS : summary



Background on IC Engines

• “An internal combustion is defined as an engine

in which the chemical energy of the fuel isreleased inside the engine and used directly formechanical work, as opposed to an external

combustion engine in which a separatecombustor is used to burn the fuel.”

• “IC engines can deliver power in the range from

0.01 kW to 20x10^3 kW, depending on theirdisplacement.”

B k d IC E i



Internal combustion engines are so called because theheat required to drive them is released by burning a fuelinside the engine itself.

This approach has advantages and disadvantages, but

is still the most popular for transport and small powergeneration plant. We will be looking at some commontypes of engine, examining some ways of analyzing theirperformance parameters, and some of the problems

encountered in improving efficiency and output.All the engines we will examine contain the same basicactivities:

• invest some work to compress a working fluid,• inject heat into the fluid,• recover a greater amount of work,

• return to initial conditions by removal of some heat.


Backgro nd on IC Engines



Actual processes by which this is done vary. Internalcombustion engines "use up" the charge of working fluideach cycle.

They therefore need to induce a fresh charge of workingfluid and get rid of the spent gases at the end of thecycle.

Internal combustion engines vary, and include systemswhich function like "closed" systems (e.g. petrol engines)or as "open" systems (e.g. gas turbines). All essentiallyperform the following basic processes


T i l P



Typical Processesfor an Internal Combustion Engine



Cl ifi ti f I t l C b ti E i



Classification of Internal Combustion Engine

Type of Ignition

1. Spark Ignition

• Generally homogeneous mixture

• Ignition by external source such as a spark

• Orderly flame propagation-premixed flame

• Controlled energy release• Intake air throttled

• Limited variation in A/F ratio

• Distinct fuel requirements• Limitations on compression ratio





Type of Ignition

1. Spark Ignition

The Otto cycle SI engine has remained fundamentally unchanged,besides slight improvements, for over 100 years. Its’ popularity has

continually increased because…

• Relatively low cost• Favorable power to weight ratio

• High Efficiency

• Relative simple and robust operating characteristics

• Improvements are mainly lower emissions and higher fuel efficiency





Type of Ignition

2. Compression Ignition

• Nonhomogeneous mixture

• Ignition due to high temperature

• May not have flame propagation

• Uncontrolled burning (varies for engines)• No throttling of intake air

• Wide range of A/F ratio

• Distinct fuel requirements• Needs high compression ratio



Differences between design and operating

Characteristics of SI and Diesel Engine

Spark Ignition Diesel

1. Premixed charge drawn into cylinders Only air drawn into cylinders

2. Mixture formed in intake system Fuel injected into cylinder prior

to combustion

3. Load control by throttling Load control by fuel metering;no throttling in diesel engines

4. Ignition by spark Spontaneous ignition of mixture;

no external ignition source

5. Generally volatile fuel (gasoline); Generally distillate oil. Must ignite

does not ignite spontaneously at at lower temperatures.

Lower temperatures.




Engine Cycle

1. Four Stroke Cycle

• Four strokes to complete the thermodynamic cycle :

– Intake process - one stroke (fresh mixture inducted in, work done by piston toinduct mixture)

– Compression process - one stroke (mixture compressed almost adiabatically,

work done by piston on mixture; process Pv= constant)

– Combustion and expansion -one stroke (mixture is ignited and burned through

flame propagation in SI engine and the high pressure gases then expand

producing work. In CI engine, ignition occurs after fuel injetionand a delay

period, mixture is burned, and high pressure gases expand producing workoutput)

– Exhaust process - one stroke (the burned gases are purged out by opening the

exhaust valve and moving the piston from BDC to TDC)

4-Stroke Engines



4-Stroke Engines exhaustintake



Four-Stroke SI Engine



IVO - intake valve opens, IVC – intake valve closesEVO – exhaust valve opens, EVC – exhaust valve opens

Xb – burned gas mole fraction

Exhaust gasresidual



CompressionStroke

ExhaustStroke

PowerStroke

AI

R

CombustionProducts

IntakeStroke

Air

Fuel Injector

Four stroke Compression Ignition (CI) Engine

Stroke 1: Air is introduced into cylinder through intake valveStroke 2: Air is compressedStroke 3: Combustion (roughly constant pressure) occurs and

product gases expand doing workStroke 4: Product gases pushed out of the cylinder through theexhaust valve

Four-Stroke CI Engine



SOI – start of injectionEOI – end of injection

SOC – start of combustionEOC – end of combustion

Fuel massflow rate

Fuel massburn rate

F t k C i I iti (CI) E i



CompressionStroke

PowerStroke

ExhaustStroke

AI

R

CombustionProducts

IntakeStroke

Air

Fuel Injector

Four stroke Compression Ignition (CI) Engine

Stroke 1: Air is introduced into cylinder through intake valveStroke 2: Air is compressedStroke 3: Combustion (roughly constant pressure) occurs and

product gases expand doing workStroke 4: Product gases pushed out of the cylinder through the

exhaust valve





Engine Cycle

2. Two Stroke Cycle

• In a two-stroke engine all the processes are the same but the cycle

is completed in two strokes of the piston.

• Since there is one power stroke per revolution, one would expect the

power output of a 2-stroke engine to be twice that of a 4-stroke

engine for the same displacement.



Two Stroke Spark Ignition Engine

Stroke 1: Fuel-air mixture is introduced into the cylinder andis then compressed, combustion initiated at the end ofthe stroke

Stroke 2: Combustion products expand doing work and thenexhausted

* Power delivered to the crankshaft on every revolution

2-StrokeEngines



2 StrokeEngines

2-stroke

Reed

Valve

intake

Two Stroke Spark Ignition Engine



Intake (“Scavenging”)

Compression Ignition

ExhaustExpansion

Fuel-air-oilmixture

Fuel-air-oil

mixturecompressed

Crankshaft

Checkvalve

Exhaustport

Scavenging in Two-Stroke Engine



Cross Loop Uniflow

Two-Stroke CI Engine



EPO – exhaust port openEPC – exhaust port closedIPO – intake port openIPC – intake port closed

Exhaust area

Intake area

scavenging



49

Advantages of the two stroke engine:

• Power to weight ratio is higher than the four stroke engine since thereis one power stroke per crank shaft revolution.• Simple valve design

Most often used for small engine applications such as lawn mowers,marine outboard engines, motorcycles….

Disadvantages of the two-stroke engine:

• Incomplete scavenging or to much scavenging

• Burns oil mixed in with the fuel




Valve Location• Valves in Head (overhead valve), also called I Head Engine.

• Valve in Block (Flat head), also called L Head Engine or T Head

Engine.

• One valve in Head and one valve in Block, also called F Head

engine.




Inlet Valve and Head Configurations

‘L’ head Wedge chamber Hemispherical Head Blow-in-piston chamber

Bath-Tub Head Squish Zone Head May Fireball-high Turbulence chamber




Basic Design1. Reciprocating Engines

• Linear motion of piston in a cylinder and conversion of linear into

rotary motion using crankshaft.• Advantages - better sealing of high pressure gases; ease of

lubrication; lower surface area; less wear on rings/seals.

• Disadvantages - reciprocating mass and force unbalance; vibrations,lower power density (based on mass); larger physical size.




Basic Design2. Rotary

• Rotary motion of rotor-direct output at the shaft.

• Advantages - compact size power plant; higher power density;

smooth, vibration-free operation; lower height.

• Disadvantages - sealing of high pressure gases and leakage; cost

and durability of seals; lubrication of seals; larger surface area.

Wankel Engines



intakeexhaust

+: No valves needed

Continuous motion

less vibration

-: Leaks through

seals

low compression

ratio

pollution

(high levels of HCand CO)




Posit ion and Number of Cylinders of Reciprocating Engines• Single Cylinder.

• In-Line

• V Engine

• Opposed Cylinder Engine

• W Engine

• Opposed Piston Engine

• Radial Engine



Air Intake Process• Naturally Aspirated

• Supercharged

• Turbocharged

• Crankcase Compressed

Supercharger and Turbocharger



These devices are used to increase the power of an IC engine by raisingthe intake pressure and thus allowing more fuel to be burned per cycle.

Knock or autoignition phenomenon limits the amount of precompression.

Superchargers are compressors that are mechanically driven by the enginecrankshaft and thus represent a parasitic load.

Compressor

Pint > Patm

Patm

Turbochargers couple a compressor with a turbine driven by the exhaustgas The compressor pressure is proportional to the engine speed



gas. The compressor pressure is proportional to the engine speed

Compressor also raises the gas temperature, so aftercoolers are usedafter the compressor to drop the temperature and thus increase the airdensity.



Basic Carburetor



Venturi

Throttle

Air Flow

Mixture to manifold

Fuel

Sketch of a Carburetor



Fuel InjectionSystem



System

ECU: Electronic

Control Unit

Throttle



Diesel Fuel Injection System

With di l i f l i d di tl i t th li d



With diesel engines fuel is sprayed directly into the cylinders

power is varied by metering the amount of fuel added (no throttle)

Diesel fuel injection systems operate at high-pressure, e.g., 100 MPa• fuel pressure must be greater than the compression pressure• need high fuel jet speed to atomize droplets small enough for rapidevaporation

Direct Injection (DI) Engine

Hybrid engines that combines the best features of SI and CI engines:



Hybrid engines that combines the best features of SI and CI engines:

• operate at optimum compression ratio (12-15) for efficiency byinjecting fuel directly into engine during compression (avoiding knockassociated with SI engines with premixed charge)• ignite the fuel as it mixes (avoid fuel-quality requirement of diesel fuel)

• control engine power by fuel added (no throttling no pumping work)

Need bowl in piston design with highswirl in order to achieve rapid fuel-airmixing

Direct-Injection Stratified-Charge Engines



• Create easily ignitable fuel-air mixture at the spark plug and a leanerfuel-air mixture in the rest of the cylinder.• Lean burn results in lower emissions.

Following is an example of a torch or jet ignition engine




Fuel Used• Gasoline

• Diesel Oil of Fuel Oil

• Gas, Natural Gas, Methane

• LPG

• Alcohol –Ethyl, Methyl

• Dual Fuel

• Gasohol




Application• Automobile, Truck, Bus

• Locomotive

• Stationary

• Marine

• Aircraft

• Small Portable, Chain Saw, Model Airplane




Type of Cooling• Air Cooled.

• Liquid Cooled, Water Cooled.

Introduction to the Internal CombustionEngine’s Components



Engine s Components

Keys components• Combustion chamber

• Intake and exhaust

• Ignition

• Conversion to rotary motion

I C Engine’s Components

Air cleaner

Cylinder head

Breather cap



Choke

Throttle

Intake manifold

Exhaust manifold

Piston ringsPiston

Wrist pin

Cylinder blockConnecting rod

Oil gallery to piston

Oil gallery to head

Crankcase

CrankpinCrankshaft

p

Rocker arm

Valve spring

Valve guide

Pushrod

Sparkplug

Combustion chamber

Tappet

Dipstick

Cam

CamshaftWater jacket

Wet liner

Connecting rod bearing

Main bearing

Oil pan or sump

CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE

CamshaftCarburetor

Air cleaner



Intake valve

Rocker arm

Piston

Connecting rod

Crankshaft

Oil pump

Exhaust valve

Crank sprocket Oil pickup

Timing belt

Cam sprocket

Timing belttensor

Crankshaft



• Originally steel forged; however,

large stiff crankshafts with relatively

low stresses allowed cast iron to be

substituted as a means to reduce

cost

• How is crankshaft supported?

Piston Assembly



• Piston: aluminum, cast steel or cast iron

• Wrist pin: machined steel

• Connecting rod: forged-steel or cast iron

Cylinder Head and Crankcase



• Crankcase and cylinder block are

usually cast iron; however, some

have been assembled from welded

steel plate

• Crankcase and cylinder are usuallyintegral for greater rigidity

• How is cylinder head made?

Cylinder block

Crank case

Cylinders



• How are cylinders fabricated?

– Gray cast iron with cylinder bores machined to meet tolerance

• Why must a new engine be “run-in / broken in”?

– Cast iron forms a hard glazed surface when subject to sliding friction

– When first assembled, slow speeds and light loads should be usedtofacilitate forming this protective coating to give long engine life



Camshaft and Cams



• Camshaft and cams are usually made

from steel

• How are cams fastened?



Valves• Intake valve: a chromium-nickel

alloy

• Exhaust valve: a silicon-chromealloy since it operates at higher

temperatures (about 1200oF)

Engine Temperature Profiles



• What two purposes doesengine lubrication serve?

– minimize friction

– dissipate heat



Automotive Fuel Needs

x1.1 x2.2 x2.5

After combustion and friction losses are considered, onlyabout 1/6 of energy available in gasoline is actually used

After combustion and friction losses are considered, only

about 1/6 of energy available in gasoline is actually used

0-2103471 introduction to engine design

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