4 Stroke Petrol Enginess

8/13/2019 4 Stroke Petrol Enginess

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4 STROKE PETROL

ENGINE


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HISTORY The Otto cycle

The idealized four-stroke Otto cycle p-V diagram : the intake (A) stroke isperformed by anisobaric expansion, followed by the compression (B) stroke,performed by an adiabatic compression. Through the combustion of fuelan isochoric process is produced, followed by an adiabatic expansion,characterizing the power (C) stroke. The cycle is closed by an isochoric processand an isobaric compression, characterizing theexhaust (D) stroke.

The four-stroke engine was first patented by Alphonse Beau de Rochasin 1861.Before, in about 185457, two Italians (Eugenio Barsanti and Felice Matteucci)invented an engine that was rumored to be very similar, but the patent was lost.

"The request bears the no. 700 of Volume VII of the Patent Office of the Reign ofPiedmont. We do not have the text of the patent request, only a photo of the tablewhich contains a drawing of the engine. We do not even know if it was a newpatent or an extension of the patent granted three days earlier, on December 30,

1857, at Turin." The first person to actually build a carwith this engine

was German engineer Nikolaus Otto. That is why the four-stroke principle today iscommonly known as the Otto cycle and four-stroke engines using sparkplugs often are called Otto engines. The Otto cycle consists ofadiabatic compression, heat addition at constant volume, adiabatic expansion andrejection of heat at constant volume.
http://en.wikipedia.org/wiki/Alphonse_Beau_de_Rochashttp://en.wikipedia.org/wiki/Nikolaus_Ottohttp://en.wikipedia.org/wiki/Nikolaus_Ottohttp://en.wikipedia.org/wiki/Nikolaus_Ottohttp://en.wikipedia.org/wiki/Nikolaus_Ottohttp://en.wikipedia.org/wiki/Nikolaus_Ottohttp://en.wikipedia.org/wiki/Alphonse_Beau_de_Rochashttp://en.wikipedia.org/wiki/Alphonse_Beau_de_Rochas


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Design and engineeringprinciples Fuel octane ratingInternal combustion engine power primarily originates from the expansion of

gases in the power stroke. Compressing the fuel and air into a very small space

increases the efficiency of the power stroke, but increasing the

cylinder compression ratio also increases the heating of the fuel as the mixture is

compressed (following Charles's law).

A highly flammable fuel with a low self-ignition temperature can combust

before the piston reaches top-dead-center (TDC), potentially forcing the piston

backwards against rotation. Alternately, a fuel which self-ignites at TDC but before

the piston has started downwards can damage the piston and cylinder due to theextreme thermal energy concentrated into a very small space with no relief. This

damage is often referred to as engine knocking and can lead to permanent

engine damage if it occurs frequently.

The octane rating is a measure of the fuel's resistance to self-ignition, by

increasing the temperature at which it will self-ignite. A fuel with a greater octane

rating allows for a much higher compression ratio, virtually eliminating the risk ofdamage due to self-ignition.


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Principle of a Four StrokePetrol Engine

The principle used in a four stroke petrol engine is commonly known as OttoCycle. It states that there would be one power stroke for every four strokes.Such engines use a spark plug which is used for the ignition of thecombustible fuel used in the engine. Most of the cars, bikes and trucks usea 4 stroke engines.

In every Otto cycle there is an adiabatic compression, addition of heat atconstant volume, an adiabatic expansion and the release of heat atconstant volume. The P-V diagram for a 4 stroke engine is as follows:


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Working of a Four StrokePetrol Engine

A stroke is the movement of the piston from the top, to thebottom of the cylinder.

As the name suggest the Four Stroke Petrol Engine uses acycle of four strokes and petrol as the fuel. Each cycleincludes 2 rotations of the crankshaft and four strokes,namely:

1.An Intake Stroke

2.A Compression Stroke 3.A Combustion Stroke also called Power Stroke

4.An Exhaust Stroke


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1 Intake Stroke As the name suggests in this stroke the intake of fuel takes

place. When the engine starts, the piston descends to thecylinder's bottom from the top. Thus the pressure inside thecylinder reduces. Now the intake valve opens and the fuel andair mixture enters the cylinder. The valve then closes.


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2 Compression Stroke This stroke is known as compression stroke because the

compression of the fuel mixture takes place at this stage.When the intake valve closes (exhaust valve is alreadyclosed), the piston forced back to the top of the cylinder andthe fuel mixture gets compressed. The compression is around

1/8th of the original volume. An engine is considered moreefficient if its compression ratio is higher.


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3 Combustion/Power Stroke Now in case of petrol engine when the fuel mixture

compresses to the maximum value the spark plug producesspark which ignites the fuel mixture. The combustion leads tothe production of high pressure gases. Due to thistremendous force the piston is driven back to the bottom of

the cylinder. As the piston moves downwards, the crankshaftrotates which rotates the wheels of the vehicle.


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4 Exhaust Stroke

As the wheel moves to the bottom the exhaustvalve opens up and due to the momentum gainedby the wheel the piston is pushed back to the topof the cylinder. The gases due to combustion arehence expelled out of the cylinder into theatmosphere through the exhaust valve.


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MAIN COMPONENTS OF ENGINE

ENGINE BLOCK

ENGINE HEAD

SUMP

PISTON

PISTON RINGSCRANK SHAFT

CAM SHAFT

CONNECTING ROD

VALVE

FLYWHEEL INTAKE MANIFOLD

EXHAUST MANIFOLD

TIMING CHAIN AIR FILTER


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Design and engineering

principles Power output limitations

The maximum amount of power generated by an engine isdetermined by the maximum amount of air ingested. The amount ofpower generated by a piston engine is related to its size (cylindervolume), whether it is a [[two-stroke]] or four-stroke design,[[volumetric efficiency]], losses, air-to-fuel ratio, the calorific value ofthe fuel, oxygen content of the air and speed ([[RPM]]). The speed isultimately limited by material strength and [[lubrication]]. Valves,pistons and [[connecting rod]]s suffer severe acceleration forces. Athigh engine speed, physical breakage and [[piston ring]] flutter canoccur, resulting in power loss or even engine destruction. [[Pistonring]] flutter occurs when the rings oscillate vertically within the pistongrooves they reside in. Ring flutter compromises the seal between thering and the cylinder wall, which causes a loss of cylinder pressure andpower. If an engine spins too quickly, valve springs cannot act quicklyenough to close the valves. This is commonly referred to as '[[valvefloat]]', and it can result in piston to valve contact, severely damagingthe engine. At high speeds the lubrication of piston cylinder wallinterface tends to break down. This limits the piston speed forindustrial engines to about 10m/s.


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Intake/exhaust port flow

The output power of an engine is dependent onthe ability of intake (airfuel mixture) andexhaust matter to move quickly through valve

ports, typically located in the [[cylinder head]]. Toincrease an engine's output power, irregularitiesin the intake and exhaust paths, such as castingflaws, can be removed, and, with the aid of an

[[air flow bench]], the radii of valve port turnsand [[valve seat]] configuration can be modifiedto reduce resistance. This process is called[[cylinder head porting|porting]], and it can be

done by hand or with a [[CNC]] machine.


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Supercharging One way to increase engine power is to force more air into

the cylinder so that more power can be produced fromeach power stroke. This can be done using some type of aircompression device known as a [[supercharger]], which canbe powered by the engine crankshaft.

Supercharging increases the power output limits of aninternal combustion engine relative to its displacement.Most commonly, the supercharger is always running, butthere have been designs that allow it to be cut out or run atvarying speeds (relative to engine speed). Mechanically

driven supercharging has the disadvantage that some ofthe output power is used to drive the supercharger, whilepower is wasted in the high pressure exhaust, as the air hasbeen compressed twice and then gains more potentialvolume in the combustion but it is only expanded in one

stage.


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Turbocharging A [[turbocharger]] is a supercharger that is driven by the engine's exhaust

gases, by means of a [[turbine]]. It consists of a two piece, high-speedturbine assembly with one side that compresses the intake air, and theother side that is powered by the exhaust gas outflow.

When idling, and at low-to-moderate speeds, the turbine produces littlepower from the small exhaust volume, the turbocharger has little effect

and the engine operates nearly in a naturally aspirated manner. Whenmuch more power output is required, the engine speed and throttleopening are increased until the exhaust gases are sufficient to 'spin up' theturbocharger's turbine to start compressing much more air than normalinto the intake manifold.

Turbocharging allows for more efficient engine operation because it isdriven by exhaust pressure that would otherwise be (mostly) wasted, butthere is a design limitation known as [[turbo lag]]. The increased enginepower is not immediately available due to the need to sharply increaseengine RPM, to build up pressure and to spin up the turbo, before theturbo starts to do any useful air compression. The increased intake volume

causes increased exhaust and spins the turbo faster, and so forth untilsteady high power operation is reached.


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Rod and piston-to-stroke ratio

The rod-to-stroke ratio is the ratio of the lengthof the [[connecting rod]] to the length of thepiston stroke. A longer rod reduces sidewisepressure of the piston on the cylinder wall and

the stress forces, increasing engine life. It alsoincreases the cost and engine height and weight.

A "square engine" is an engine with a bore

diameter equal to its stroke length. An enginewhere the bore diameter is larger than its strokelength is an [[oversquare]] engine, conversely, anengine with a bore diameter that is smaller than

its stroke length is an undersquare engine.


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Valve train

The valves are typically operated by a [[camshaft]]rotating at half the speed of the [[crankshaft]]. It has aseries of [[cam]]s along its length, each designed toopen a valve during the appropriate part of an intake

or exhaust stroke. A [[tappet]] between valve and camis a contact surface on which the cam slides to openthe valve. Many engines use one or more camshaftsabove a row (or each row) of cylinders, as in theillustration, in which each cam directly actuates a valve

through a flat tappet. In other engine designs thecamshaft is in the [[crankcase]], in which case each camcontacts a [[push rod]], which contacts a [[rocker arm]]that opens a valve. The [[overhead cam]] designtypically allows higher engine speeds because it

provides the most direct path between cam and valve.


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Valve clearance

Valve clearance refers to the small gap between avalve lifter and a valve stem that ensures that thevalve completely closes. On engines with

mechanical valve adjustment, excessive clearancecauses noise from the valve train. A too smallvalve clearance can result in the valves notclosing properly, this results in a loss of

performance and possibly overheating of exhaustvalves. Typically, the clearance must bereadjusted each {{convert|20000|mi|km}} with afeeler gauge.


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Energy balance

Otto engines are about 30% efficient; in other words,30% of the energy generated by combustion isconverted into useful rotational energy at the outputshaft of the engine, while the remainder being losses

due to waste heat, friction and engine accessories.

The use of a Turbocharger in Diesel engines is very effective

by boosting incoming air pressure and in effect provides the

same increase in performance as having more displacement.


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Applications Of 4 StrokeEngines

Lawn Moweres, Compressors, Pump

Sets, Gensets, Vibrators, Sugar Cane

Crushers,

HTP Sprayers, Rail Cutting Machine,Road Markers, Power Trolleys,

Threshers,

Silk Reeling Machines, ConcreteMixers, Alternators, Etc.

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4 Stroke Petrol Enginess