IC ENGINES

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Internal Combustion Engine
2F1 - 16/02/2017
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Introduction

• Heat engine It can be defined as any engine
  that converts thermal energy to mechanical work
  output. Examples of heat engines include steam
  engine, diesel engine, and gasoline (petrol)
  engine.
• On the basis of how thermal energy is being
  delivered to working fluid of the heat engine (or
  as to where the combustion of fuel takes place),
  heat engine can be classified as an internal
  combustion engine and external combustion engine.
  

Thermal energy
Mechanical work
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Internal Combustion Engine

• In an Internal combustion engine, the combustion
  of fuel produces heat energy inside the engine
  cylinder. The products of combustion directly act
  upon the piston and develop power, which is used
  to rotate the crank shaft.
• Petrol engine is an example of internal
  combustion engine, where the working fluid is a
  mixture of air and fuel.
• IC Engines are used as main prime movers in
  commercial vehicles.

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External Combustion Engine

• External combustion engines are those in which
  combustion takes place outside the engine
  cylinder.

For example In steam engine or steam turbine,
the heat generated due to combustion of fuel is
employed to generate high pressure steam,which is
used as working fluid in a reciprocating engine
or turbine.
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I.C. ENGINE
E.C. ENGINE
Combustion is outside engine cylinder. Working
fluid steam Requires large space. Capital cost
is high. Starting of engine takes more time and
isn't easy.

• Combustion is inside engine cylinder.
• Working fluid petrol, diesel and other gases.
• Requires less space.
• Capital cost is low.
• Starting of engine is easy and quick.

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I.C. ENGINE
E.C. ENGINE
Thermal efficiency is low, Power developed per
unit weight of these engines is low. Fuel cost is
relatively lower. Not convinient and economical
for small power range. Limited applications -
Railway locomotives, power generation etc.

• Thermal efficiency is high.
• Power developed per unit weight of these engines
  is high.
• Fuel cost is relatively higher.
• Used for small capacity power.
• Wide application for road vehicles, locomotives,
  machine practices, aircrafts etc.

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Engine Classification

• Even though basic parts are the same, design
  differences can change the way engines operate
  and how they are repaired
• For this reason, you must be able to classify
  engines

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Engine Classification

• According to type of fuel used.
• Petrol engine.
• Diesel engine.
• Gas engine.
• Bi-fuel engine.
• According to number of strokes per cycle.
• 4 stroke engines.
• 2 stroke engines.
• According to method of cooling
• Air cooled engine.
• Water cooled engine.

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Engine Classification

• According to method of ignition.
• Spark ignition.
• Compression ignition.
• According to the cycle of combustion.
• Otto cycle.
• Diesel cycle.
• Duel combustion.
• According to the number of cylinders.
• Single cylinder.
• Multi cylinder.

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Acc. to cylinder arrangement
(Refers to the position of the cylinders in
relation to the crankshaft)

• Inline Engines The cylinders are arranged in a
  line, in a single bank.

• V Engines The cylinders are arranged in two
  banks, set at an angle to one another.

• Opposed cylinder Engines The cylinders are
  arranged in two banks on opposite sides of the
  engine

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Acc. to cylinder arrangement

• Radial Engines The cylinders are arranged
  radially, in a circle.

• Opposed piston Engines The pistons are
  arranged in two different cylinders on opposite
  sides of the engine

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Engine Details
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Engine Details
Cylinder Head

• Cylinder Heart of the engine, where fuel is
  burnt and power is developed. It has to withstand
  high pressure and temperature, because combustion
  of fuel is carried out within the cylinder.
  Therefore, cylinder at times is covered via
  cooling towers. The piston reciprocates indise
  the cylinder.
• Cylinder Head covers the top of cylinder and
  provides space for valve mechanism, sparks plug,
  fuel injector etc.

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Engine Details

• Piston It's a close fitting hollow cylinderical
  plunger reciprocating inside the cylinder. Power
  developed via combustion of fuel is transmitted
  by piston to the crank shaft through connecting
  rods.
• Piston Rings Metalic rings inserted into
  circumferential grooves provided at the top of
  piston. These help in maintaining a gas-tight
  joint between piston and cylinder.
• Piston Pin or Gudgeon pin It's the pin joining
  small end of connecting rod and piston. It's made
  of steel.

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Engine Details

• Connecting Rod Member connecting piston
  (through piston pin) and crank shaft (through
  crank pin). It converts the reciprocating motion
  of the piston into rotary motion of the
  crankshaft.
• Crank and crank shaft Crank is a lever that is
  connected to big end of connecting rod and other
  end is rigidly connected to a shaft, called
  crankshaft. Crank rotates about the axis of
  crankshaft and causes the connecting rod to
  oscilliate.
• Valves These are devices which control the flow
  of intake and exhaust gases.

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Valves
Connecting Rod
Cam Shaft
Connecting rod
Connecting Rod
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Engine Details

• Flywheel It's a heavy wheel, mounted on the
  crankshaft of the engine and minimizes cyclic
  variation in speed.
• Crank case It's the lower part of the engine,
  serving as an enclosure to crankshaft and also as
  a sump for lubricating oils.

Flywheel
Flywheel
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Engine Details
Spark Plug

• Carburetor It's used in petrol engine for
  proper mixing of air and fuel.
• Fuel Pump It's used in diesel engine for
  increasing pressure and controlling of fuel
  supplied to the injector.

• Fuel Injector It's used to inject diesel fuel
  in the form of fine atomised spray under
  pressure.
• Spark Plug It's used in petrol engine to
  produce a high intensity spark for ignition of
  air and fuel mixture in the cylinder.

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I.C. ENGINE TERMINOLOGY

• Bore (D) The inner diameter of the engine
  cylinder is termed as bore.
• Stroke (L) It's the linear distance travelled
  by piston, as it moves from one end of the
  cylinder to the other end. It's equal to twice
  the radius of crank.

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I.C. ENGINE TERMINOLOGY

• Dead Centres In vertical engines, the top most
  position of the piston is termed as Top Dead
  Centre (TDC) and bottom most position of piston
  is Bottom Dead Centre (BDC).

In horizontal engine, the extreme position of the
piston, close to the cylinder head is called
Inner Dead Centre (IDC) and extreme position of
piston near crank is called Outer Dead Centre
(ODC).
ODC
IDC
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I.C. ENGINE TERMINOLOGY

• Clearance Volume (Vc) It's the volume contained
  between top and cylinder head, when the piston
  is at TDC or IDC.
• Swept Volume (Stroke Volume, Vs) It's the
  volume displaced by the piston in one stroke.

Compression Ratio (r) The ratio of total
cylinder volume (Vc Vs) to the clearance volume
(Vc).
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I.C. ENGINE TERMINOLOGY

• Piston speed (VP) It's the average speed of
  piston.

The unit of Piston Speed (VP) is m/s, whereby, L
Stroke Length N Speed of Crank shaft (RPM)
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OTTO FOUR STROKE CYCLE(FOUR STROKE PETROL ENGINE
or SPARK IGNITION FOUR STROKE ENGINE)
A Four Stroke Internal Combustion Engine is an
engine whose working cycle consists of an intake
(or suction) stroke, a compression stroke, a
power stroke and an exhaust stroke.
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Suction or Intake stroke

• Inlet valve opens and the exhaust valve is
  closed.
• Presure in the cylinder will be atmospheric.
• As piston moves from TDC to BDC, volume in the
  cylinder increases and simultaneously the
  pressure decreases.
• This creates a pressure difference b/w atmosphere
  and inside of the cylinder. Due to this pressure
  difference, petrol and air mixture enters the
  cylinder through carburetor.
• This stroke is represented by horizontal line 1-2
  on the P-V diagram.
• The crankshaft has now made a half rotation,
  i.e., 180 of crank angle.
• At the end, the cylinder will be completely
  filled with petrol and air mixture, called
  charge, and the inlet vavle is closed.

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Compression stroke

• Both the inlet valve and the exhaust valve are
  closed.
• As piston moves from BDC to TDC, the petrol and
  air mixture contained in the cylinder will be
  compressed.
• Thus pressure and temperature of the mixture
  increases.
• The process of compression is shown is shown by
  2-3 on the p-v diagram.
• Near the end of the stroke, petrol and air
  mixture is ignited by electric spark, which is
  given out by spark plug.
• Combustion of fuel releases hot gases, which will
  increase the pressure at constant volume.
• This constant volume combustion process is
  represented by vertical line 3-4 on the p-v
  diagram.

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Power (expansion) stroke

• Both the inlet valve and the exhaust valve are
  closed.
• As piston moves from TDC to BDC, the high
  pressure and high temperature burnt gases force
  the piston to perform the stroke, called Power
  Stroke (Expansion or working stroke).
• The engine produces mechanical work or power,
  during this stroke.
• As the piston moves from TDC to BDC, the pressure
  of the hot gases gradually decreases and volume
  increases (curve 4-5 on p-v diagram).
• Near the end of stoke the exhaust valve opens,
  which releases the burnt gases to atmosphere.
• This drop of pressure at constt. volume is
  represented by vertical line 5-6 on the p-v
  diagram.

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Exhaust stroke

• During this stroke the exhaust valve opens and
  the inlet valve is closed.
• The piston moves from BDC to TDC.
• During this stroke, the piston pushes the exhaust
  gases (combustion product) out of the cylinder at
  constant pressure.
• This stroke is represented by horizontal line 2-1
  on the P-V diagram.