REPORT of 4 Stroke Engine

REPORT 

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FOUR STROKE PETROL ENGINE 

 MR.MUHAMMAD  MR.MUHAMMAD ADNAN

 THERMODYNAMICS-|  THERMODYNAMICS-|

1. MUHAMMAD 1. MUHAMMAD ALI BHALLIZADA

13ME22

2. MUHAMMAD 2. MUHAMMAD AKHTAR

13ME42

3. MUHAMMAD 3. MUHAMMAD WASEEM

13ME16

4. USMAN SAJID

13ME40 1

Table of Contents:

INTRODUCTION …………………………………………………………………………………………….. 3 PETROL ENGINE ............................................................................................................................... 3

OTTO CYCLE ………………………………………………………………………………………………….. 3 THERMODYNAMIC PROCESS OTTO CYCLE ................................................................................... 4 FOUR STROKE ENGINE  ................................................................................................................. 5

ADVANTAGES AND DISADVANTAGES…………………………………………………………………………..... 6 CONCLUSION ……………………………………………………………………………..……………………………………………… 7 REFERENCES ………………………………………………………………………………………………………………………………. 7

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INTRODUCTION:

A four-stroke engine (also known as four-cycle) is an internal combustion engine in which the piston completes four separate strokes which comprise a single thermodynamic cycle. A stroke refers to the full travel of the piston along the cylinder, in either direction.

STROKE: The distance covered by the piston from bdc (bottom dead centre) to tdc (top dead centre) or vice versa is known as stroke. A stroke refers to the full travel of the piston along the cylinder, in either direction. PETROL ENGINE:

A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. It was invented in 1876 in Germany by German inventor Nicolaus August Otto. In most petrol engines, the fuel and air are usually pre-mixed before compression. The premixing was formerly done in a carburettor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites.

OTTO CYCLE: In 1862 a German engineer Nikolaus Augustus Otto began experimenting with different kinds of engines. His first experiment was conducted on a 4- stroke engine. 10 years later he introduced to the world the Otto engine. The 4-stroke engine consists of a 4-stroke cycle better known as the Otto cycle. The Otto engine is an internal combustion (IC) engine. The 4- stroke cycle of an IC engine is the cycle most commonly used for automotive and industrial purposes today. It is used for cars, trucks, generators and many more appliances, making this engine the most common engine type now-a-days.

Each movement of the cylinder up or down the cylinder is one

stroke of the four stroke combustion cycle or Otto cycle.

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The four stroke cycle consists of: -

Induction/suction stroke

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Compression stroke

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Ignition/power stroke

-

exhaust stroke

A single cycle requires two revolutions of the crankshaft to complete.

THERMODYNAMIC PROCESSES OTTO CYCLE (P-V DIAGRAM):

THERMODYNAMIC PROCESSES OTTO CYCLE: •

During the cycle, WORK is done on the gas by the piston between stages 2 and 3. Work is done by the gas on the piston between stages 4 and 5. The difference between the work done by the gas and the work done on the gas is the area enclosed by the cycle curve and is the work produced by the cycle. The work times the rate of the cycle (cycles per second) is equal to the POWER produced by the engine.

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The area enclosed by the cycle on a P-V DIAGRAM is proportional to the work produced by the cycle. On this page we have shown an ideal Otto cycle in which 4

there is no heat entering (or leaving) the gas during the compression and power strokes, no friction losses, and instantaneous burning occurring at constant volume. In reality, the ideal cycle does not occur and there are many losses associated with each process. These losses are normally accounted for by efficiency factors which multiply and modify the ideal result. For a real cycle, the shape of the p-V diagram is similar to the ideal, but the area (work) is always less than the ideal value.

FOUR STROKE ENGINES: 

The Four Stroke engine cycle consist of these:

1) Intake/suction

180degree

2) Compression

180 degree

3) Power/ Combustion

180 degree

4) Exhaust

180 degree



Total engine revolution

720 degree

FIRST STROKE  – INTAKE/SUCTION STROKE: •

While the inlet valve is open, the descending piston draws fresh petrol and air mixture into the cylinder. Intake valves are open to allow Air/Fuel mixture to come into the combustion chamber.

•

The Intake/Suction Stroke consist of the piston travelling down.

Spark Plug: It is an electrical device that fits into the cylinder head and ignites air fuel mixtures.

SECOND STROKE - COMPRESSION STROKE: •

While the valves are closed, the rising piston compresses the mixture to a pressure. The mixture is then ignited by the spark plug. Compression stroke consist of the piston travelling back up.

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Both intake and exhaust valves are closed.

Air fuel mixture is now being compressed.

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THIRD STROKE - POWER STROKE: While the valves are closed the pressure of the burned gases of the combustion forces push the piston downwards. •

The piston is now at the TDC.

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Spark plug ignites, creating a spark that ignites the compressed air fuel mixture.

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Explosion is created and the piston is forced back down.

•

Both valves are still closed.

FOURTH STROKE - EXHAUST STROKE The exhaust valve is open and the rising piston discharges the spent gases from the cylinder. •

Exhaust stroke the piston is travelling up.

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Exhaust valve is open.

•

Intake valve is closed.

•

Exhaust gases being pushed out by piston.

 AD VA NT AG ES OF FO UR ST RO KE ENG INES :

1. Less fuel consumption. 2. Thermal efficiency is more. 3. More volumetric efficiency. 4. Less wear and tear.

DISADVANTAGES OF FOUR STROKE ENGINES:

1. More components. 2. Separate valve operating mechanism is required. 3. More cost. 4. More complicated design.

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CONCLUSION:

Internal combustion engines are among the most important engineering applications. The theory of application either depends on Diesel or Otto cycles. They are categorized either according to the operating cycle, or due to the mechanism of working. Each type of engines has some advantages over the other one. Thus, the selection of the appropriate engine requires determining the conditions of application.

REFERENCES: http://www.cdxetextbook.com/engines/motivePower/4gasEng/engcycle.html http://biotsavart.tripod.com/ice.htm http://en.wikipedia.org/wiki/Four-stroke_engine http://www.gillcontrols.com/ignition-explained/4-stroke-engine-basic-operation/ http://www.studymode.com/essays/Four-Stroke-Engine-377583.html http://www.home.zonnet.nl/stroetmann44/second-e.htm

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