1-history andd classification

8/4/2019 1-History Andd Classification

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INTERNAL COMBUSTIONENGINES AND GAS

TURBINES

Prof S. K. Acharya


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IS

Gasoline-fueledreciprocatingpiston engine

Diesel-fueledreciprocatingpiston engine

Gas turbine

Rocket

IS NOT

Steam powerplant

Solar power

plant Nuclear power

plant


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ENGINES!BOON OR BANE?

Greatest invention since thewheel?

Made transportation easy! Made life easy!

OR DID IT?

Increased pollution

Increased fossil fuelconsumption


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BUT..

WHETHER WE LIKE IT OR NOT.

CAN WE DO WITHOUT IT?

DO WE HAVE VIABLEALTERNATIVES?

THINK AS OF TODAY WE HAVE NO

ANSWER

MAY BE FOR AT LEAST 20 YEARS


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SO WE STUDY IT.!

And so on to the course:


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Background on IC Engines

An internal combustion is defined asan engine in which the chemicalenergy of the fuel is released inside

the engine and used directly formechanical work, as opposed to anexternal combustion engine in whicha separate combustor is used to burn

the fuel.1 IC engines can deliver power in the

range from 0.01 kW to 20x10^3 kW,

depending on their displacement.2


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History

The internal combustionengine was firstconceived anddeveloped in the late

1800s The man who is

considered the inventorof the modern IC engineand the founder of the

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

Otto developed a four-

stroke engine in 1876,most often referred to as


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History

The impact on society is quiteobvious, almost all travel andtransportation is powered by the IC

engine: trains, automobiles, airplanesare just a few.

The IC engine largely replaced the

steam engine at the turn of thecentury (1900s)

Another important cycle is the Dieselcycle developed by Rudolph Diesel in

1897. This cycle is also known as a


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CLASSIFICATION OFINTERNAL COMBUSTION

ENGINES

VARIOUS TYPES OF ENGINES


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CLASSIFICATION OF INTERNAL COMBUSTIONENGINES

1. Application

2. Basic Engine Design

3. Operating Cycle

4. Working Cycle5. Valve/Port Design and Location

6. Fuel

7. Mixture Preparation

8. Ignition

9. Stratification of Charge

10. Combustion Chamber Design

11. Method of Load Control


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CLASSIFICATION OF INTERNALCOMBUSTION ENGINES

1. 1. Application

2. Automotive: (i) Car

(ii) Truck/Bus

(iii) Off-highway

2. Locomotive

3. Light Aircraft

4. Marine: (i) Outboard

(ii) Inboard

(iii) Ship

5. Power Generation: (i) Portable (Domestic)

(ii) Fixed (Peak Power)

6. Agricultural: (i) Tractors

(ii) Pump sets

7. Earthmoving: (i) Dumpers


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2. Basic Engine Design:

1. Reciprocating (a) Single Cylinder

(b) Multi-cylinder (I) In-

line(ii) V

(iii)Radial

(iv)Opposed

Cylinder

(v)


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Types of ReciprocatingEngines


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3. Operating Cycle

Otto (For the Conventional SIEngine)

Atkinson (For Complete Expansion SIEngine)

Miller (For Early or Late Inlet ValveClosing type SI Engine)

Diesel (For the Ideal Diesel Engine)

Dual (For the Actual Diesel Engine)


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4. Working Cycle (Strokes)

1. Four Stroke Cycle:(a) Naturally

Aspirated

(b)Supercharged/Turbocharged

2. Two Stroke Cycle: (a) Crankcase

Scavenged(b) Uniflow Scavenged

(i) Inlet valve/Exhaust Port

(ii) Inlet Port/Exhaust Valve


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5. (a) Valve/Port Design

1. Poppet Valve

2. Rotary Valve

3. Reed Valve

4. Piston Controlled Porting

5. (b) Valve Location

1. The T-head2. The L-head

3. The F-head

4. The I-head: (i) Over head Valve (OHV)


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6. Fuel

1.Conventional: (a) Crude oil derived (i) Petrol

(ii) Diesel

(b) Other sources: (i) Coal

(ii) Wood (includes bio-mass)

(iii)Tar Sands

(iv)Shale

2. Alternate: (a) Petroleum derived (i) CNG

(ii) LPG

(b) Bio-mass Derived (i) Alcohols (methyland ethyl)

(ii) Vegetable oils


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7. Mixture Preparation

1. Carburetion

2. Fuel Injection (i) Diesel(ii) Gasoline

(a) Manifold

(b) Port

(c) Cylinder


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8. Ignition

1. Spark Ignition

(a) Conventional(i) Battery

(ii) Magneto

(b) Other methods

2. Compression Ignition


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10. Combustion Chamber Design

1. Open Chamber: (i) Disc type

(ii) Wedge

(iii) Hemispherical

(iv) Bowl-in-piston

(v) Other design

2. Divided Chamber: (For CI): (i) Swirlchamber

(ii) Pre-chamber

(For SI) (i) CVCC

(ii) Other designs


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11.Method of Load Control

1. Throttling: (To keep mixturestrength constant) Also called

Charge Control

Used in the Carbureted S.I. Engine

2. Fuel Control (To vary the mixture

strength according to load)

Used in the C.I. Engine

3. Combination

Used in the Fuel-injected S.I. Engine.


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12. Cooling

1. Direct Air-cooling

2. Indirect Air-cooling (Liquid

Cooling)

.


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Basic Piston Engine Definitions

TDC

BDC

Stroke

Bore

Intake valve

Exhaust valve


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Nomenclature for Engines


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Basic Engine Definitions

Clearance volume

Displaced volume

Compression ratio

r

V

V

V

V

BDC

TDC

= =max

min


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Background on the OttoCycle

The Otto Cycle has fourbasic steps or strokes:

1. An intake stroke thatdraws a combustiblemixture of fuel and air intothe cylinder

2. A compression strokewith the valves closedwhich raises thetemperature of themixture. A spark ignites themixture towards the end ofthis stroke.

3. An expansion or powerstroke. Resulting fromcombustion.

4. An Exhaust stroke thepushes the burned

contents out of thecylinder.


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Why

The Otto cycle IC engine has remainedfundamentally unchanged, besides slightimprovements, for over 100 years. Itspopularity has continually increased

because Relatively low cost

Favorable power to weight ratio

High Efficiency

Relative simple and robust operatingcharacteristics

Improvements are mainly lower emissions


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Common terms used tocompare engine performance

Brake power (bp): net power outputof an IC engine

Torque: A force acting through aradius

RPM: engine speed, in rotations perminute

Specific fuel consumption (sfc): rateof fuel consumption per unit of brakepower


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Mean Effective Pressure

MEP: a fictitious pressure that, ifacted on the piston during the entirepower stroke, would produce the

same amount of net work as thatproduced during the actual cycle(Cengel & Boles, 2006)

If the MEP goes up, the cylinder

volume can go down and still achievethe same power output


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Mean Effective Pressure,cont.

Indicated MEP (imep): uses the totalpower output minus the powerneeded for the intake and exhaust

stokes (indicated power) Brake MEP (bmep): the power used

to overcome friction in the cylinder isalso subtracted; this term is usedmore often than the imep


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Brake Thermal Efficiency

Brake thermal efficiency: brakepower/rate of heat output forcomplete combustion

Brake thermal efficiency=indicatedthermal efficiency* mechanicalefficiency

Mechanical efficiency: related to theamount of power used to overcomefriction


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Carnot Efficiency

To see how well our engine is doing, wecan compare our brake thermal efficiencyto the Carnot efficiency

Remember that the Carnot efficiency is thebest we can do!

=1-(Tlow/Thigh), where Ts are in absolute

scale We could estimate Thigh as our exhaust

temperature

Tlow is our ambient temperature


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P

v

1

2

3

4

rr( )cycle 3 4 1 234 12 4 1in 23 3 2 3 2

4 14 1 1 4 1v

3 2 3 2 2 3 2

4 1

Thermal efficiency of the system:

W [ ( )] ( )= 1

Q ( ) ( )

( )( ) / 1For an ideal gas, u=C , =1 1 1

( ) ( ) / 1

Since /

v

v

m u u u uW W u u

Q m u u u u

C T Tu u T T T T

u u C T T T T T

T T

+ + = = =

= =

3 2

1

2

1

1 2 1

1

2 1 2

/ (why?)

1 . From isentropic compression relation for an ideal gas

1, where r= is the volume compression ratio

k

k

T T

T

T

T V V

T V r V

=

=

= =

1-2 isentropiccompression 2-3 constant volumeheat transfer 3-4 isentropicexpansion 4-1 constant volumeheat rejection


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0 3 6 9 12 15

0

20

40

60

80

100

compression ratio

thermalefficie

ncy

( )r

r

Thermal efficiency of an Ottocycle,

= 1

11

rk

Typical value of r for a realengine: between 7 and 10

The higher the compression ratio, the higher the thermal

efficiency. Higher r will led to engine knock (spontaneous ignition)problem.


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Increase the compression ratio

Increase the engine displacement: more power

Compress more air into the cylinder duringintake: using supercharger and turbocharger.

Cool the air before allowing it to enter thecylinder: cooler air can expand more, thus,increase the work output.

Reduce resistance during intake and exhauststages: multiple valve configuration: 4 cylinders/16valves engine

Fuel injection: do away with the carburetor andprovide precise metering of fuel into the cylinders.
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Diesel Cycle

T

s

1

2

3

4

P

v

2 3

4

1

2-3: a constantpressure process

(instead of a constantvolume process) andis the only differencebetween an idealizedDiesel cycle and anidealized Otto cycle.

Fuel injection for an extended period during the power strokeand therefore maintaining a relatively constant pressure. Diesel cycle has a lower thermal efficiency as compared toan Otto cycle under the same compression ratio. In general, Diesel engine has a higher thermal efficiencythan spark-ignition engine because the Diesel engine has amuch higher compression ratio. Compression-ignition: very high compression ratio 10 to 20or even higher.


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CI vs. SI Engines

SI engines draw fuel and air into thecylinder.

Fuel must be injected into the cylinder atthe desired time of combustion in CIengines.

Air intake is throttled to the SI engine -- nothrottling in CI engines.

Compression ratios must be high enoughto cause auto-ignition in CI engines.

Upper compression ratio in SI engines islimited by the auto-ignition temperature.


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CI vs. SI Engines

Flame front in SI engines smooth andcontrolled.

CI combustion is rapid anduncontrolled at the beginning.


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Diesel vs Otto engine

qHigher thermal efficiencyas a consequence of a higher compression ratio (16-20 vs9-12) needed for the self ignition of the mixture

q Higher efficiency at part load condition (city driving) because of the different loadcontrol with much inferior pumping loss for aspirating air into the cylinder: load controldirectly by varying the fuel delivery, while in the Otto engine by varying the air through anintake throttle

qLess energyspent to produce Diesel fuel

q Higher weight for same power delivery, because of higher thermal and mechanicalstresses due to higher temperatures and pressures , almost double vs Otto engine, at theend of compression and combustion phases

q Lower maximum engine speed because a slower combustion process and higherweight of the rotating an oscillating masses

qEngine roughness that generates higher structural and airborne vibration/noise.

Advantages

Disadvantages

4141


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4-stroke engine

High volumetric efficiency over a wideengine speed rangeLow sensitivity to pressure losses in theexhaust systemEffective control of the chargingefficiency trough appropriate valve timingand intake system design

2-stroke engine

Very simple and cheap engine designLow weightLow manufacturing costBetter torsional forces pattern

2-stroke engine

Higher fuel consumption

Higher HC emissions because of aproblematic cylinder scavengingLower mean effective pressure becauseof poorer volumetric efficiencyHigher thermal load because no gasechange strokePoor idle because of high residual gaspercentage into the cylinder

4-stroke engine

High complexity of the valve control

Reduced power density because thework is generated only every secondshaft rotation

Four stroke vs Two-stroke cycle

Advantages

Disadvantages

4242


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EXHAUST GAS RECIRCULATION (EGR) -SI AND CI ENGINES

Dilutes Air/Fuel mixture with exhaust gases therebyreducing peak combustion temperatures and NOxformation

There are limits to how lean an air-fuel-exhaust gas

mixture can be for ignition

Ignition systems (spark plugs etc.) and combustionchambers can be designed to improve performance withthese lean mixtures


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Exhaust Gas Recirculation

Returns ~ 5% of Exhaust toIntake Charge

Displaces Air/Fuel ChargeWithout Affecting Ratio

Reduces Peak Temperature

Reduces NOx Emissions

HCCI


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HCCI

Importance

SI engines have very low NOx and PM emissions

CI engines have high efficiency

Homogeneous Charge Compression Ignition(HCCI) is

a promising alternative combustion technologywith high efficiency and lower NOx andparticulate matter emissions

P i i l


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Principle

HCCI is characterized by the fact that the fueland air are mixed before combustion starts andthe mixture auto-ignites as a result of the

temperature increase in the compression stroke

Optical diagnostics research shows that HCCI

combustion initiates simultaneously at multiple

siteswithin the combustion chamber and that thereis no discernable flame propagation.

HCCI


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HCCI

POTENTIAL1. High efficiency, no knock limit on compression

ratio.2. Low NOx and no NOx after treatment systems

required.3. Low PM emissions, no need for PM filter.4. HCCI provides up to a 15-percent fuel savings,

while meeting current emissions standards.5. HCCI engines can operate on gasoline, diesel fuel,

and most alternative fuels.6. In regards to CI engines, the omission of throttle

losses improves HCCI efficiency.

HCCI


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HCCI

BARRIERS1. The auto-ignition event is difficult to

control, unlike the ignition event in spark

-ignition(SI) and diesel engines which arecontrolled by spark plugs and in-cylinderfuel injectors, respectively.

2. HCCI engines have a small power range,constrained at low loads by leanflammability limits and high loads by in-cylinder pressure restrictions

3. High HC and CO emissions.


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Multi-Port Fuel Injection

One injector percylinder

Mounts in intakemanifold, spraysdirectly at intake valve

Fired in groups orindividually (SFI)

Ram Tuning for denserair charge

Lower A/F temps

Leaner mixture during

warm-up


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M it f F l I j ti i


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Merits of Fuel Injection inthe SI Engine

Absence of Venturi NoRestriction in Air Flow/HigherVol. Eff./Torque/Power

Hot Spots for Preheating cold aireliminated/Denser air enters

Manifold Branch Pipes Notconcerned with MixturePreparation (MPI)

Better Acceleration ResponseMPI


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Merits (Continued)

Use of Greater Valve Overlap

Use of Sensors to MonitorOperating Parameters/Gives

Accurate Matching of Air/fuelRequirements: Improves Power,Reduces fuel consumption andEmissions

Precise in Metering Fuel in Ports

Precise Fuel DistributionBetween Cylinders (MPI)


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Merits (Continued)

Fuel Transportation in Manifoldnot required (MPI) so no WallWetting

Fuel Surge During Fast Corneringor Heavy Braking Eliminated

Adaptable and Suitable ForSupercharging (SPI and MPI)

Limitations of Petrol


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Limitations of PetrolInjection

High Initial Cost/HighReplacement Cost

Increased Care and

Attention/More ServicingProblems

Requires Special Servicing

Equipment to Diagnose Faultsand Failures

Special Knowledge of Mechanicaland Electrical Systems Neededto Dia nose and Rectif Faults



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Limitations of PetrolInjection (Continued)

Injection EquipmentComplicated, Delicate to Handleand Impossible to Service by

Roadside Service Units Contain More Mechanical and

Electrical Components Which

May Go Wrong Increased Hydraulic and

Mechanical Noise Due to

Pumping and Metering of Fuel



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Limitations of PetrolInjection (Continued)

Very Careful Filtration NeededDue to Fine Tolerances ofMetering and Discharging

Components More Electrical/Mechanical

Power Needed to Drive FuelPump and/or Injection Devices

More Fuel Pumping/InjectionEquip-ment and Pipe PlumbingRequired- May be Awkwardly

Placed and Bulky


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Dual Fuel SystemMechanical KitComponents

Electronic KitComponents

n Converts vehicle to run on up to 80% natural gas and 20%

dieseln Meets or exceeds CARB/EPA emission standards

n Retro fit for older engines


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Dual Fuel SystemCharacteristics

No mechanical or electrical modifications to theoriginal diesel engine

Diesel system can be either mechanical or electroniccontrolled

Electronic Control Unit provides completemanagement of natural gas

and diesel simultaneously, for reliable power andemissions control over a wide range of operatingconditions.

ECU contains 64-bit core micro-controller for fastcalculations of

required engine control parameters. The program isstored entirely in flash memory.

No ower loss or loss of milea e


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Lean Burn EngineLean Air/Fuel mixture as high as 65:1can be used.Engine can employ higher CR for betterperformance

Efficient fuel use.Low exhaust hydrocarbon emissionCan be achieved by GDIIt can not reduce Nox

Used in heavy duty natural gas ,biogas,LPG engines


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Stratified Charge Engine

In the cylinder air /fuel mixture is layeredUsed in direct injection systemFuel injection is at the cylinder head or at

peripheryRich charge in that area ignites and burnsCombustion proceeds to lean areaFlame front cools rapidly.

Nox is not formed.Extra O2 in lean area combines with CO toform CO2Also applied to diesel engineFuel economy 20%

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