SI and CI Engines

7/27/2019 SI and CI Engines

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MENG422 AUTOMOTIVE

SPARK & COMPRESSION

IGNITION ENGINES

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There are two kinds of piston engines:

1. Spark-Ignition Engine

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SPARK IGNITION ENGINE

INTRODUCTION

The actions in the spark-ignition engine can be dividedinto four arts. Each art consists of a piston stroke.

This is the movement of the piston from BDC to TDC,

or from TDC to BDC. The complete cycle of events inthe engine cylinder requires four piston strokes. These

are intake, compression, power and exhaust. The

the four piston strokes. This makes the engine a four-

stroke-c cle en ine. It is also called a our-stroke or

four-cycle engine.


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Intake Stroke:

During the intake stroke of a spark-

gn on eng ne, e p s on s mov ng own.

The intake valve is open. Air-fuel mixtureows roug e n a e por an n o e

cylinder. The fuel system supplies the

m x ure. s e p s on passes rougBDC, the intake valve closes. This seals off

e upper en o e cy n er.


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SPARK IGNITION ENGINE OPERATION Compression Stroke:

After the piston passes BDC, it startsmoving up. Both valves are closed. The

upward moving piston compresses the air-

fuel mixture into a smaller space, betweenthe top of the piston and the cylinder head.

This space is combustion chamber. The

mixture is compressed 1/8 or less of itsoriginal volume. The amount that the

mixture is compressed is compression

ratio.


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SPARK IGNITION ENGINE OPERATION

Power Stroke:

As the piston nears TDC at the end of the

,

gap at the spark plug. The heat from the spark

i nites the com ressed air-fuel mixture. The air-

fuel mixture then burns rapidly. These high

temperatures cause very high pressure which

pushes down the piston. The connecting rod carriesthis force to the crankshaft, which turns to move

.


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Exhaust Stroke:

As the piston approaches BDC on the

power stroke, the exhaust valve opens.

After passing through BDC, the pistonmoves up again. The burned gases escape

through the open exhaust port. As the

piston nears TDC, the intake valve opens.When the piston passes through TDC and

starts down again, the exhaust valve

closes.


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DIESEL ENGINE

INTRODUCTION

Diesel engines are similar to sparkignition engines in construction. Both have

pistons, with piston rings, moving up and

down in cylinders. Both burn fuel incombustion chambers in the upper part of

the cylinders. The high pressure produced

by the burning fuel pushes the pistonsdown. This rotates the crankshaft and the

rotary motion is carried through shafts and

gears to the drive wheels.


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Common Rail

System


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DIESEL ENGINE OPERATION

Intake Stroke:

The diesel engine takes in air alone.

No throttle valve impedes the airflow.

-mixture of air and fuel enters the

stroke. The throttle valve controls the

amoun a en ers.


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ompress on tro e:

In the diesel engine, the upward-

alone. On the other hand, in the

spark ignition engine, the piston- .


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Power Stroke:

diesel fuelis injected into thecompresse an o a r. e ea

of com ression i nites the fuel. In

the spark-ignition engine, a spark

compressed air-fuel mixture.


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Exhaust Stroke:

The exhaust stroke is the same for

both engines. The exhaust valveo ens and the burned ases flow

out as the piston moves up the.


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SPARK & COMPRESSION

IGNITION ENGINES

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The way the fuel gets into the

cyclinders.

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Compression Ratios

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SI and CI Engines