File Seminar

8/13/2019 File Seminar

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DEPARTMENT OF MECHANICAL ENGINEERING

SEMIN R ON

SPARK IGNITION ENGINE

Submitted To Submitted By

Mr. Yogesh Vikram Srivastav Kumar Suman

Roll No. 1119540023


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Acknowledgement

I would like to extend my heartfelt thanks and deep sense ofgratitude to all those who helped us in preparing for thisseminar. First and foremost, I would like to express sincerethanks to all my faculty members from the core of my heartbecause they encouraged and persuaded us to prepare on

this topic.


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Contents

Introduction Two Stroke Engine Four stroke EngineOtto Cycle

Flame propagation

Flame developmentKnockingCarburetor

SuperchargerAdvantages & disadvantagesFuture trend in si engine


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Two Stroke Engine

A two-stroke, two-cycle, or two-cycle engine is a typeof internal combustion engine which completes a powercycle in only one crankshaft revolution and with two strokes,or up and down movements, of the piston in comparison toa "four-stroke engine ", which uses four strokes to do so.This is accomplished by the end of the combustion strokeand the beginning of the compression stroke happeningsimultaneously and performing the intake and exhaust(orscavenging ) functions at the same time.

Two-stroke engines often provide high power-to-weightratio , usually in a narrow range of rotational speeds calledthe "power band", and, compared to 4-stroke engines, havea greatly reduced number of moving parts, are morecompact and significantly lighter.

The first commercial two-stroke engine involving in-cylindercompression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having aseparate charging cylinder. The crankcase-scavengedengine, employing the area below the piston as a chargingpump, is generally credited to Englishman Joseph Day. Gasoline (spark ignition ) versions are particularly useful inlightweight (portable) applications such as chainsaws andsmall, lightweight and racing motorcycles, and the concept

is also used in diesel compression ignition engines in large
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and weight insensitive applications, such as ships,locomotives and electricity generation. The heat transferfrom the engine to the cooling system is less in a two-stroke

engine than in a traditional four-stroke, a fact that adds tothe overall engine efficiency; however, traditional 2-strokeshave a poor exhaust emissions feature.

The two-stroke petrol engine was very popular throughoutthe 19th-20th century in motorcycles and small-enginedevices, such as chainsaws and outboard motors, and wasalso used in some cars, a few tractors and many ships. Partof their appeal was their simple design (and resulting low

cost) and often high power-to-weight ratio. The lower cost torebuild and maintain made the two stroke engine incrediblypopular, until for the USA their EPA mandated morestringent emission controls in 1978 (taking effect in 1980)and in 2004 (taking effect in 2005 and 2010). The industrylargely responded by switching to four-stroke petrol engines,which emit less pollution .[1] Most small designs

use petroil lubrication, with the oil being burned in the
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combustion chamber, causing "blue smoke" and other typesof exhaust pollution. This is a major reason why two-strokeengines were replaced by four-stroke engines in many

applications.Simple two-stroke petrol (gas) engines continue to becommonly used in high-power, handheld applications suchas string trimmers and chainsaws. The light overall weight,and light-weight spinning parts give important operationaland even safety advantages. For example, a four-strokeengine to power a chainsaw operating in any position would

be much more expensive and complex than a two-strokeengine that uses a gasoline-oil mixture.These engines are still preferred for small, portable, orspecialized machine applications such as outboard motors, high-performance, small-capacity motorcycles , mopeds , underbones , scooters , tuk-tuks, snowmobiles , karts, ultralights , model airplanes (andother model vehicles) and lawnmowers and dirt bikes.The two-stroke cycle is also used in many diesel engines, most notably large industrial and marine engines, as well assome trucks and heavy machinery.

FOUR STROKE ENGINE

A four-stroke engine (also known as four-cycle) is an internalcombustion engine in which the piston completes fourseparate strokes intake, compression, power, andexhaust during two separate revolutions of theengine's crankshaft, and one single thermodynamic cycle.There are two common types of four-stroke engines. Theyare closely related to each other, but have major differencesin design and behaviour. The earliest of these to bedeveloped is the Otto cycle engine developed in 1876
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by Nikolas August Otto in Cologne, Germany, after theoperation principle described by Alphonse Beau deRochas in 1861. This engine is most often referred to as

a petrol engine or gasoline engine, after the fuel that powersit. The second type of four-stroke engine is the Dieselengine developed in 1893 by Rudolph Diesel, also ofGermany. Diesel created his engine to improve efficiencycompared with the Otto engine. There are several majordifferences between the Otto cycle engine and the four-stroke diesel engine. The diesel engine is made in both

a two-stroke and a four-stroke version. Otto'scompany, Deutz AG, now primarily produces diesel engines.The Otto cycle is named after the 1876 engine of Nikolas A.Otto, who built a successful four-stroke engine based on thework of Jean Joseph Etienne Lenoir .[1] It was the thirdengine type that Otto developed. It used a sliding flamegateway for ignition of its fuel a mixture of illuminatinggas and air. After 1884, Otto also developed the magneto tocreate an electrical spark for ignition, which had beenunreliable on the Lenoir engine.

Today, the internal combustion engine (ICE) is usedin motorcycles, automobiles, boats, trucks, aircraft, ships ,heavy duty machinery, and in its original intended use asstationary power both for kinetic and electrical powergeneration. Diesel engines are found in virtually all heavyduty applications such as trucks, ships, locomotives, powergeneration, and stationary power. Many of these dieselengines are two-stroke with power ratings up to 105,000 hp(78,000 kW).

The four strokes refer to intake, compression, combustion(power) and exhaust strokes that occur during two
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crankshaft rotations per power cycle. (Risqu slang amongsome automotive enthusiasts names these respectively the"suck," "squeeze," "bang" and "blow" strokes.) The cycle

begins at Top Dead Centre (TDC), when the piston isfarthest away from the axis of the crankshaft . A stroke refersto the full travel of the piston from Top Dead Centre (TDC) toBottom Dead Centre.

STROKES IN SI ENGINE

1.INTAKE or INDUCTION stroke: onthe intake or induction stroke of the piston, the pistondescends from the top of the cylinder to the bottom of thecylinder, increasing the volume of the cylinder. A mixture offuel and air, or just air in a diesel engine, is forced byatmospheric (or greater) pressure into the cylinder through

the intake port. The intake valve (s) then closes. The volumeof air/fuel mixture that is drawn into the cylinder, relative tothe maximum volume of the cylinder, is called the volumetricefficiency of the engine.

2. COMPRESSION stroke: with both intake and exhaustvalves closed, the piston returns to the top of the cylindercompressing the air or fuel-air mixture into the combustionchamber of the cylinder head. During the compressionstroke the temperature of the air or fuel-air mixture rises byseveral hundred degrees.

3. POWER stroke: this is the start of the second revolutionof the cycle. While the piston is close to Top Dead Centre,the compressed air fuel mixture in a gasoline engine isignited, usually by a spark plug , or fuel is injected into a
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diesel engine, which ignites due to the heat generated in theair during the compression stroke. The resulting pressurefrom the combustion of the compressed fuel-air mixture

forces the piston back down toward bottom dead centre.

4. EXHAUST stroke: during the exhaust stroke, the pistononce again returns to top dead centre while the exhaustvalve is open. This action expels the spent fuel-air mixturethrough the exhaust valve(s).
http://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Combustion


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The I deal Air Standard Otto Cycle


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Most production carbureted (as opposed to fuel-injected) engines have a single carburetor and a matching intakemanifold that divides and transports the air fuel mixture to

the intake valves, though some engines (like motorcycleengines) use multiple carburetors on split heads. Multiplecarburetor engines were also common enhancements formodifying engines in the USA from the 1950s to mid-1960s,as well as during the following decade of high-performance muscle cars fueling different chambers of theengine's intake manifold .

Older engines used updraft carburetors, where the airenters from below the carburetor and exits through the top.This had the advantage of never "flooding" the engine , asany liquid fuel droplets would fall out of the carburetorinstead of into the intake manifold; it also lent itself to use ofan oil bath air cleaner , where a pool of oil below a meshelement below the carburetor is sucked up into the meshand the air is drawn through the oil-covered mesh; this wasan effective system in a time when paper air filters did notexist.

Beginning in the late 1930s, downdraft carburetors were themost popular type for automotive use in the United States. In Europe, the side draft carburetors replaced downdraft asfree space in the engine bay decreased and the use ofthe SU -type carburetor (and similar units from othermanufacturers) increased. Some small propeller-drivenaircraft engines still use the updraft carburetor design.
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Outboard motor carburetors are typically sidedraft, becausethey must be stacked one on top of the other in order tofeed the cylinders in a vertically oriented cylinder block.

1979 Evinrude Type I marine sidedraft carburetor

The main disadvantage of basing a carburetor's operationon Bernoulli's principle is that, being a fluid dynamic device,the pressure reduction in a venturi tends to be proportionalto the square of the intake air speed. The fuel jets are muchsmaller and limited mainly by viscosity, so that the fuel flowtends to be proportional to the pressure difference. So jetssized for full power tend to starve the engine at lower speedand part throttle. Most commonly this has been corrected byusing multiple jets. In SU and other movable jet carburetors,it was corrected by varying the jet size. For cold starting, adifferent principle was used in multi-jet carburetors. A flowresisting valve called a choke, similar to the throttle valve,was placed upstream of the main jet to reduce the intakepressure and suck additional fuel out of the jets.
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FLAME SPEED

The flame speed is the measured rate of expansion ofthe flame front in a combustion reaction. Whereas flamespeed is generally used for a fuel, a related termis explosive velocity, which is the same relationshipmeasured for an explosive. Combustion engineers differentiate between the laminarflame speed and turbulent flame speed. Flame speed is

typically measured in m/s, cm/s, etc.

KNOCKING

Knocking (also called knock, detonation, spark

knock, pinging or pinking) in spark-ignition internalcombustion engines occurs when combustion of the air/fuelmixture in the cylinder starts off correctly in response toignition by the spark plug, but one or more pockets of air/fuelmixture explode outside the envelope of the normalcombustion front.

The fuel-air charge is meant to be ignited by the spark plugonly, and at a precise point in the piston's stroke. Knockoccurs when the peak of the combustion process no longeroccurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging"sound, and cylinder pressure increases dramatically. Effectsof engine knocking range from inconsequential tocompletely destructive.
http://en.wikipedia.org/w/index.php?title=Flame_front&action=edit&redlink=1http://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Explosive_velocityhttp://en.wikipedia.org/wiki/Explosivehttp://en.wikipedia.org/wiki/Engineerhttp://en.wikipedia.org/wiki/Laminar_flame_speedhttp://en.wikipedia.org/wiki/Laminar_flame_speedhttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Air-fuel_ratiohttp://en.wikipedia.org/wiki/Air-fuel_ratiohttp://en.wikipedia.org/wiki/Spark_plughttp://en.wikipedia.org/wiki/Four-stroke_cyclehttp://en.wikipedia.org/wiki/Four-stroke_cyclehttp://en.wikipedia.org/wiki/Spark_plughttp://en.wikipedia.org/wiki/Air-fuel_ratiohttp://en.wikipedia.org/wiki/Air-fuel_ratiohttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Turbulenthttp://en.wikipedia.org/wiki/Laminar_flame_speedhttp://en.wikipedia.org/wiki/Laminar_flame_speedhttp://en.wikipedia.org/wiki/Engineerhttp://en.wikipedia.org/wiki/Explosivehttp://en.wikipedia.org/wiki/Explosive_velocityhttp://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/w/index.php?title=Flame_front&action=edit&redlink=1


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Knocking should not be confused with pre-ignition . They aretwo separate events, however, pre-ignition is usuallyfollowed by knocking.

Normal combustion

Under ideal conditions the common internal combustionengine burns the fuel/air mixture in the cylinder in an orderlyand controlled fashion. The combustion is started by thespark plug some 10 to 40 crankshaft degrees prior to top

dead centre (TDC), depending on many factors includingengine speed and load. This ignition advance allows time forthe combustion process to develop peak pressure at theideal time for maximum recovery of work from theexpanding gases.

The spark across the spark plug's electrodes forms a smallkernel of flame approximately the size of the spark plug gap.

As it grows in size, its heat output increases, which allows itto grow at an accelerating rate, expanding rapidly throughthe combustion chamber. This growth is due to the travel ofthe flame front through the combustible fuel air mix itself,and due to turbulence which rapidly stretches the burningzone into a complex of fingers of burning gas that have amuch greater surface area than a simple spherical ball offlame would have. In normal combustion, this flame frontmoves throughout the fuel/air mixture at a rate characteristicfor the particular mixture. Pressure rises smoothly to a peak,as nearly all the available fuel is consumed, then pressurefalls as the piston descends. Maximum cylinder pressure isachieved a few crankshaft degrees after the piston passesTDC, so that the force applied on the piston (from theincreasing pressure applied to the top surface of the piston)
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can give its hardest push precisely when the piston's speedand mechanical advantage on the crank shaft gives the bestrecovery of force from the expanding gases, thus

maximizing torque transferred to the crank shaft.

Abnormal combustion

When unburned fuel/air mixture beyond the boundary of theflame front is subjected to a combination of heat andpressure for a certain duration (beyond the delay period of

the fuel used) ,detonation may occur. Detonation ischaracterized by an instantaneous, explosive ignition of atleast one pocket of fuel/air mixture outside of the flame front.

A local shockwave is created around each pocket and thecylinder pressure may rise sharply beyond its design limits.

If detonation is allowed to persist under extreme conditionsor over many engine cycles, engine parts can be damagedor destroyed. The simplest deleterious effects are typicallyparticle wear caused by moderate knocking, which mayfurther ensue through the engine's oil system and causewear on other parts before being trapped by the oil filter.Severe knocking can lead to catastrophic failure in the formof physical holes punched through the piston or cylinderhead (i.e., rupture of the combustion chamber ), either ofwhich depressurizes the affected cylinder and introduceslarge metal fragments, fuel, and combustion products intothe oil system. Hypereutectic pistons are known to breakeasily from such shock waves.

Detonation can be prevented by any or all of the followingtechniques:
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1. The use of a fuel with high octane rating, whichincreases the combustion temperature of the fuel andreduces the proclivity to detonate.

2. Enriching the air-fuel ratio which alters the chemicalreactions during combustion, reduces the combustiontemperature and increases the margin abovedetonation.

3. Reducing peak cylinder pressure by decreasing the

engine revolutions (e.g., shifting to a higher gear, there isalso evidence that knock occurs more easily at high rpmthan low regardless of other factors).

4. Decreasing the manifold pressure by reducing thethrottle opening, boost pressure orreducing the loadon the engine.

Because pressure and temperature are strongly linked,knock can also be attenuated by controlling peakcombustion chamber temperatures by compressionratio reduction, exhaust gas recirculation , appropriatecalibration of the engine's ignition timing schedule, andcareful design of the engine's combustion chambers and

cooling system as well as controlling the initial air intaketemperature.

The addition of certain materials such as leadand thallium will suppress detonation extremely well whencertain fuels are used . The addition of tetraethyl lead (TEL),a soluble salt added to gasoline was common until it was

discontinued for reasons of toxic pollution. Lead dust addedto the intake charge will also reduce knock with various
http://en.wikipedia.org/wiki/Octane_ratinghttp://en.wikipedia.org/wiki/Air-fuel_ratiohttp://en.wikipedia.org/wiki/Manifold_pressurehttp://en.wikipedia.org/wiki/Compression_ratiohttp://en.wikipedia.org/wiki/Compression_ratiohttp://en.wikipedia.org/wiki/Exhaust_gas_recirculationhttp://en.wikipedia.org/wiki/Ignition_timinghttp://en.wikipedia.org/wiki/Thalliumhttp://en.wikipedia.org/wiki/Thalliumhttp://en.wikipedia.org/wiki/Ignition_timinghttp://en.wikipedia.org/wiki/Exhaust_gas_recirculationhttp://en.wikipedia.org/wiki/Compression_ratiohttp://en.wikipedia.org/wiki/Compression_ratiohttp://en.wikipedia.org/wiki/Manifold_pressurehttp://en.wikipedia.org/wiki/Air-fuel_ratiohttp://en.wikipedia.org/wiki/Octane_rating


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Knocking is more or less unavoidable in diesel engines, where fuel is injected into highly compressed air towards theend of the compression stroke. There is a short lag between

the fuel being injected and combustion starting. By this timethere is already a quantity of fuel in the combustion chamberwhich will ignite first in areas of greater oxygen density priorto the combustion of the complete charge. This suddenincrease in pressure and temperature causes the distinctivediesel 'knock' or 'clatter', some of which must be allowed forin the engine design.

Careful design of the injector pump, fuel injector, combustionchamber, piston crown and cylinder head can reduceknocking greatly, and modern engines usingelectronic common rail injection have very low levels ofknock. Engines using indirect injection generally have lowerlevels of knock than direct injection engine, due to the

greater dispersal of oxygen in the combustion chamber andlower injection pressures providing a more complete mixingof fuel and air. Diesels actually do not suffer exactly thesame "knock" as gasoline engines since the cause is knownto be only the very fast rate of pressure rise, not unstablecombustion. Diesel fuels are actually very prone to knock ingasoline engines but in the diesel engine there is no time forknock to occur because the fuel is only oxidized during theexpansion cycle. In the gasoline engine the fuel is slowlyoxidizing all the while it is being compressed before thespark. This allows for changes to occur in thestructure/makeup of the molecules before the very criticalperiod of high temp/pressure.
http://en.wikipedia.org/wiki/Diesel_enginehttp://en.wikipedia.org/wiki/Common_railhttp://en.wikipedia.org/wiki/Indirect_injectionhttp://en.wikipedia.org/wiki/Fuel_injection#Direct_injectionhttp://en.wikipedia.org/wiki/Fuel_injection#Direct_injectionhttp://en.wikipedia.org/wiki/Indirect_injectionhttp://en.wikipedia.org/wiki/Common_railhttp://en.wikipedia.org/wiki/Diesel_engine


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An unconventional engine that makes use of detonation toimprove efficiency and decrease pollutants is the Bourkeengine.

Pre-ignition

Pre-ignition (or preignition) in a spark-ignition engine is atechnically different phenomenon from engine knocking, anddescribes the event wherein the air/fuel mixture in thecylinder ignites before the spark plug fires. Pre-ignition is

initiated by an ignition source other than the spark, such ashot spots in the combustion chamber, a spark plug that runstoo hot for the application, or carbonaceous deposits in thecombustion chamber heated to incandescence by previousengine combustion events.

The phenomenon is also referred to as 'after-run', or 'run-on'

or sometimes dieseling , when it causes the engine to carryon running after the ignition is shut off. This effect is morereadily achieved on carbureted gasoline engines, becausethe fuel supply to the carburetor is typically regulated by apassive mechanical float valve and fuel delivery can feasiblycontinue until fuel line pressure has been relieved, providedthe fuel can be somehow drawn past the throttle plate. Theoccurrence is rare in modern engines with throttle-bodyor electronic fuel injection , because the injectors will not bepermitted to continue delivering fuel after the engine is shutoff, and any occurrence may indicate the presence of aleaking (failed) injector.

In the case of highly supercharged or high compressionmulti-cylinder engines particularly ones that use methanol(or other fuels prone to pre-ignition) pre-ignition can quickly
http://en.wikipedia.org/wiki/Bourke_enginehttp://en.wikipedia.org/wiki/Bourke_enginehttp://en.wikipedia.org/wiki/Spark_plughttp://en.wikipedia.org/wiki/Incandescencehttp://en.wikipedia.org/wiki/Dieselinghttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/Float_valvehttp://en.wikipedia.org/wiki/Throttlehttp://en.wikipedia.org/wiki/Electronic_fuel_injectionhttp://en.wikipedia.org/wiki/Electronic_fuel_injectionhttp://en.wikipedia.org/wiki/Throttlehttp://en.wikipedia.org/wiki/Float_valvehttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/Dieselinghttp://en.wikipedia.org/wiki/Incandescencehttp://en.wikipedia.org/wiki/Spark_plughttp://en.wikipedia.org/wiki/Bourke_enginehttp://en.wikipedia.org/wiki/Bourke_engine


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melt or burn pistons since the power generated by other stillfunctioning pistons will force the overheated ones along nomatter how early the mix pre-ignites. Many engines have

suffered such failure where improper fuel delivery is present.Often one injector may clog while the others carry onnormally allowing mild detonation in one cylinder that leadsto serious detonation, then pre-ignition. The challenges associated with pre-ignition have increasedin recent years with the development of highly boosted and

"down speeded" spark ignition engines. The reduced enginespeeds allow more time for auto ignition chemistry tocomplete thus promoting the possibility of pre-ignition andso called "mega-knock". Under these circumstances, thereis still significant debate as to the sources of the pre-ignitionevent. Pre-ignition and engine knock both sharply increasecombustion chamber temperatures. Consequently, eithereffect increases the likelihood of the other effect occurring,and both can produce similar effects from the operator'sperspective, such as rough engine operation or loss ofperformance due to operational intervention by apowertrain-management computer. For reasons like these,a person not familiarized with the distinction might describeone by the name of the other. Given proper combustionchamber design, pre-ignition can generally be eliminated byproper spark plug selection, proper fuel/air mixtureadjustment, and periodic cleaning of the combustionchambers

.


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technologies have been developed which can identifyengine design or operating conditions in which knock mightbe expected to occur. This then enables engineers to design

ways to mitigate knocking combustion whilst maintaining ahigh thermal efficiency.

Since the onset of knock is sensitive to the in-cylinderpressure, temperature and autoignition chemistryassociated with the local mixture compositions within thecombustion chamber, simulations which account for all of

these aspects have thus proven most effective indetermining knock operating limits and enabling engineersto determine the most appropriate operating strategy.


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Two Stroke Advantages

Advantages

Requires fewer moving parts to accomplish the same amount

of output as four stroke engines. Cheaper to maintain than four stroke engines. Smaller and simple in construction than four stroke engines. Can work in any orientation.

Two Stroke Disadvantages Disadvantages

Less fuel efficient than four stroke. Quicker wear of the engine s moving parts. More polluting than four stroke engines since oil isburnt with the fuel and air mixture .


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Future of Spark-Ignition Engine

The similar targets of future spark-ignition (SI) andcompression-ignition (CI) engines consisting in the noticeableincrease of specific power concomitantly with the drasticreduction of fuel consumption and pollution in a wideoperation range lead to similar development ofthermodynamic functions and technical solutions. Theachieved modular level of implementation of functions andsolutions in advanced piston engines allows to establishcommon development platforms for both SI and CI engines.Such functions are the scavenging management, the spray-guided mixture formation by fuel direct injection, the exhaustgas recirculation and the homogeneous charge compressionignition. Under the technical solutions to their generationthere are the super- or turbocharging, the variable control ofintake- and exhaust valves and the direct injection techniquesby common rails or by high pressure modulation. Betweenthe common platforms of the future SI and CI engines andtheir several individual peculiarities there are somedevelopment milestones of particular interest.

Similar development targets of future SI and CI engines suchas high specific power, low specific fuel consumption andextremely low pollutant emissions must not leadautomatically to their convergence: There are alternativeways to the power by speed (SI) or by torque (CI). There arealso different trade off aspects sound versus fuelconsumption or hydrocarbon emissions versus particulates.


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Reference

1. IC by Rogowsky International Book Co.

2. IC Engine Analysis & Practice by E.F. Robert

3. IC Engine by V.Gnesan

4.WWW.Wikipedia.com

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