6 Engines 4 stroke cycle 3 by dandanhuanghuang

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									   Engines

The 4-stroke cycle
     Engines – 4 stroke cycle
• Engine needs 3 things to run
• Air – fresh air containing oxygen
• Fuel – usually gasoline – something to
  burn and cause heat
• Spark – spark to cause air and fuel to
  ignite and combust or burn
      Engines – 4 stroke cycle
• Cars use 4 stroke engines – each movement of
  the piston from up to down, or down to up is
  called a “stroke”
• Intake – air and fuel enter cylinder
• Compression – air and fuel are compressed or
  “squeezed” to make it dense
• Spark plug fires – ignites air/fuel mix
• Power – as air/fuel burns it pushes piston down,
  which turns the crankshaft
• Exhaust – gasses from burned fuel exit engine
         Engines – 4 stroke cycle
•   Terms to memorize:
•   Cylinder – chamber where piston travels up and down in (round)
•   Valves – let air into and exhaust out of engine
•   Pistons – circular pieces that the combustion explosion push down
•   Rods – connect pistons to crankshaft
•   Crankshaft – turns up/down movement of pistons into twisting
    motion for transmission
•   TDC – top dead center – piston at highest point
•   BDC – bottom dead center – pistons at lowest point
•   Spark plug – ignites air/fuel by “sparking”
•   Combustion – burning of air/fuel mixture
•   Intake – air flowing into engine
•   Exhaust – burned gasses exiting engine
Engines – 4 stroke cycle
       Engines – 4 stroke cycle
•   Intake stroke –
•   Poston at top dead center – highest point
•   Starts to move downward
•   Intake valve begins to open
•   Air drawn into cylinder
•   Piston continues moving down as intake
    valve opens fully and cylinder is filled with
    air
     Engines – 4 stroke cycle
• Compression stroke -
• Piston starts at bottom dead center –
  lowest point
• Moves upward
• Intake valve quickly closes
• Air in cylinder is compressed as piston
  continues moving upward
     Engines – 4 stroke cycle
• Ignition -
• Once piston nears or hits TDC, air and fuel
  mix is fully compressed
• Spark plug fires or “sparks”
• Spark ignites air and fuel mixture
• Explosion is called combustion
• Begins to push piston back down
     Engines – 4 stroke cycle
• Power stroke –
• As piston is moving downward from
  combustion
• Provides “power” to turn crankshaft
• Air/fuel mix burns as piston travels
  downward to BDC
• Both intake and exhaust valves remain
  closed through this stroke
     Engines – 4 stroke cycle
• Exhaust stroke –
• After piston reaches BDC from power
  stroke
• Exhaust valve opens
• Exhaust gasses are pushed from cylinder
  as piston travels upward
• Piston continues upward to TDC as
  exhaust valve is fully opened
     Engines – 4 stroke cycle
• As engine reaches TDC position from
  exhaust stroke, exhaust valve closes fully
• Cycle is ready to begin again – engine has
  completed all “4 strokes” of a 4 stroke
  engine
• Intake stroke begins again
• Crankshaft makes 2 revolutions for the 4
  strokes – only 1 of these strokes provides
  power – engines are inefficient!
4 strokes
4 stroke cycle
4 stroke in action
4 stroke cycle
4 stroke cycle
Engines – 4 stroke cycle
Engines – 4 stroke

								
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