Bike Engines-Two Stroke/Four Stroke Engines Classification

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Technical knowledge Series Two wheelers -
BikeJinni

• Bike Engines -Two Stroke/Four Stroke Engines
  Classification

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Engine
1.Engine Classification- 1.1 Spark Ignition
Engines 1.2 Compression Ignition Engines
1.3 Two stroke Four stroke Engines 1.4
Engine Types Vertical, Horizontal,
Inline , V Engine etc 1.5 OHC and DOHC
Engines
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1.1 Spark Ignition (SI) Engines

• In Spark Ignition Engine or SI Engine- Air-fuel
  mixture enters into the combustion chamber
  together. ignition takes place with the help of
  an electric spark by spark plug.
• Usually petrol engines are SI engines.

Spark Ignition Engine
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1.2 Compression Ignition (CI) Engines

• In Compression Ignition Engine or CI Engine -Air
  and fuel enters separately into the combustion
  chamber. Ignition takes place by means of heat
  generated by the compressed air inside the
  cylinder.
• There is no spark plug
• Diesel engines are CI engines

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1.3 Two Stroke Engines

• In Two Stroke Engine -
• First stroke is combination of Intake
  Compression stroke .
• Piston moves up to compress the air/fuel mixture,
  at the same time intake port is opened which
  allows fresh mixture to move in the lower part of
  crankcase. Transfer port helps in moving this
  fresh mixture from the lower portion to the top
  of the piston.
• Second stroke This stroke is a combination of
  power and exhaust strokes. The piston moves down
  after power stroke, opening the exhaust port at
  the same time to move burnt gases out of the
  combustion space. 

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1.4 Four Stroke Engine

• In Four Stroke Engine -
• First is Intake Stroke Inlet valve is open and
  the fuel air mixture is drawn in while the piston
  goes down.
• Second is Compression Stroke Inlet valve is
  closed and piston moves up, thus compressing the
  fuel air mixture Before the piston reaches the
  top the spark plug emits a spark that combust the
  fuel air mixture.
• Third is Combustion Stroke The piston is forced
  down due to Combustion of fuel air mixture.
  Engine power is obtained from this.
• Exhaust Stroke Exhaust valve is open and the
  piston travels up making the gases to exit from
  the exhaust valve.

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1.5 Vertical , Horizontal , Inline , V-Type
Engines

• Based on the design of chassis of the bike
  different types of Engines are used.
• 1. Vertical Engine
• Piston movies vertically up down. Crankshaft is
  below the cylinder.
• Convenient to orient cylinder vertically since
  they are taller.
• Space around cannot be used.
• 2. Horizontal Engine
• Cylinder is placed horizontally.
• Less Power loss , Better handling. Packing size
  is more since very wide.
• 3. Inline Engine
• Banks of cylinder are placed one behind the
  other. Mainly six cylinder in
• one bank are used.
• Simpler, Lighter. Longer Skinny , Hard to pack.
• 4. V Engine
• Mainly Two rows of cylinder at 90 deg angle (Or
  any other angle making V)
• to each other are placed. Short length , easier
  to fir. But , separate cam shafts for each
• side of the V makes it complex.

Vertical Engine
Horizontal Engine
Inline Engine
V Engine
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1.6 OHC and DOHC Engines
A camshaft rotates and its lobes open and close
the valves in time with the piston to allow air
in and exhaust out down to enable combustion
cycle of an engine. Commonly ,there are two type
of Camshaft arrangement-
Double Cam
Single Cam
SOHC Single Overhead Camshaft DOHC Double
Overhead Camshaft
In a SOHC engine , the camshaft is installed in
the cylinder head. Valves are operated either by
the rocker arms or directly through the lobe
lifters of rotating camshaft.
DOHC engine normally has two camshafts and 4
valves per cylinder. One side camshaft operates
intake valves, while opposite side camshaft
controls exhaust valves. 
SOHC engines are less complicated in design
cheaper. DOHC engines rev much higher and
develop more power at mid to top rpms for the
same displacement engine. DOHC engines are ideal
for performance or Sports racing new bikes ,
while these are cooler ,runs more smoothly,
quietly, and efficiently.
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Engine Technical Terms and Parts
2.Engine Technical Terms Parts- 2.1
Engine Bore Stroke 2.2 Engine
Compression Ratio 2.3 Engine Maximum Power
and Torque 2.4 Capacitor Discharged Ignition
(CDI) 2.5 Spark plug 2.6 Valve 2.7
Engine- Cooling System
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Engine Bore Stroke
Bore It is the diameter of the
cylinder. Stroke It is the distance to which
piston travels.
What is cc (Cubic Centimetre) ?

• Volume of Cylinder Normally more the Volume of
  Cylinder of an Engine,
• more Power it can produce.
• Displacement/Swept Volume of an engine (V) pi
  S B2 / 4
• Larger the bore and stroke, the bigger the 
  displacement and thus a
• more power of engine.
• Unit is CC or Litre . CC stands for Cubic
  Centimetres. 1000 cc 1 litre.

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Engine Compression Ratio

• Compression Ratio
• It's the ratio of the volume of the combustion
  chamber and bore when the piston is at bottom
  dead centre (BDC) versus when it is at top dead
  centre (TDC).
• Formula - (Swept Volume Clearance Volume) /
  Clearance Volume
• Swept Volume pi S B2 / 4
• Clearance Volume Above the piston at TDC is
  the volume contained in the cylinder head gasket
  and combustion chamber - this volume is called
  the "Clearance Volume".

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Engine Maximum Power and Torque

• Torque Twisting or turning force
• Automotive terms - It is a rotating force
  produced by an engines crankshaft.
• Unit is Newton metre (Nm)
• The more torque an engine produces, the greater
  its ability to perform work.
• Formula Torque 5252 x Horsepower / RPM
• RPM (Revolution per Minute) Speed at which the
  crank shaft is rotating , if you accelerate the
  RPM will increase.
• Power How fast can engine do work
• Normal used Units are BHP , Ps ,Kw.
• I Ps 735.5 newtonm/s 735.5 W 0.7355 kW
  0.98632 hp

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Capacitor Discharged Ignition (CDI)

• The capacitor discharged ignition uses capacitor
  discharge current output to power the spark plug
  for a powerful ,high spark.
• It stores current. Stored current is divided to
  give it to other parts of the vehicle .
• If current exceeds the limit in the battery, CDI
  becomes hot and vehicle stops. After CDI cools
  vehicle may or may not start.

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Spark plug

• A device for delivering electric current from
  an ignition system to the combustion chamber of
  a spark-ignition engine to ignite the compressed
  fuel/air mixture by an electric spark.

Spark Plug
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Valve

• Two types-
• 1.It allows mixture into the cylinder is the
  inlet valve.
• 2.The one through which the spent gases escape is
  the exhaust valve.
• They are designed to open and close at precise
  moments, to allow the engine to run efficiently
  at all speeds.

An OHC (or DOHC) Engine cylinder head will have
at least two valves per cylinder (1 inlet and 1
exhaust), but multi-valve engines may have three
(2 inlet and 1 exhaust), or four (2 inlet and 2
exhaust), five (3 inlet and 2 exhaust) or even
more . Multi-valve engines rev higher and make
more , while have more components resulting
higher cost.
Two Valve Engine
Three Valve Engine
Four Valve Engine
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Engine- Cooling System
Cooling System It prevents engine breakdown
due to overheating. 1. Air cooled Engines
Engine of the motorcycle is cooled naturally by
the outside atmosphere air. 2. Liquid cooled
Engines Engine is surrounded by the liquid
cooling system. It uses a coolant to keep the
temperature of the engine at an optimum level.
3. Oil Cooled Engines In Oil Cooled Engines
the oil is circulated between the radiator and
the engine case, the radiator takes off the heat
from the oil, thus bringing down the temperature,
hence helping in maintaining the viscosity of the
oil.
Oil Cooled Engine
Air Cooled Engine
Liquid Cooled Engine
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