Gasoline Engines

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Gasoline Engines

• Operation

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Energy and Power

• Energy is used to produce power.
• Chemical energy is converted to heat energy by
  burning fuel at a controlled rate.
• This is called Combustion
• If engine combustion occurs within the power
  chamber (combustion chamber) it is an internal
  combustion engine.

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Energy and Power

• The chemical to heat energy conversion within the
  combustion chamber causes a pressure increase
  within the combustion chamber.
• This pressure is applied to the head of the
  piston to produce mechanical force.
• This mechanical force is converted into
  mechanical power.

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Four-Stroke Cycle Engines

• All modern automotive engines utilize a four
  stroke design.
• The four strokes are
• Intake
• Compression
• Power
• Exhaust

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Four-Stroke Cycle Engines

• Intake stroke - the intake valve opens as the
  piston inside the cylinder travels downward.
• This draws the air/fuel mixture into the cylinder

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Four-Stroke Cycle Engines

• Compression stroke the intake valve closes and
  the piston travels upward in the cylinder
• this compresses the air/fuel mixture.

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Four-Stroke Cycle Engines

• Power stroke as the piston travels toward the
  top of the cylinder (top dead center) a spark
  plug ignites the compressed A/F mixture.
• This forces the piston downward

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Four-Stroke Cycle Engines

• Exhaust stroke as the piston travels up tow
• This expels the spent exhaust gasses

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Crankshaft

• Mounted at the center-line of the engine
• The pistons are mounted to the crank via
  connecting rods
• As the crank rotates the pistons move up and down
  in the engine bore
• http//quadhub.com/wiki/images/a/ac/Cshaft.gif

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720 Degree Cycle

• Each cycle of a four stroke engine requires two
  complete revolutions of the crankshaft.
• The greater the number of cylinders, the more
  frequently power strokes occur.
• This is why an eight cylinder engine runs
  smoother than a four cylinder.

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Engine Classification

• Number of cylinders.
• Number of strokes.
• Cylinder arrangement
• Inline engine
• V-type engine
• Horizontal (opposed)
• boxer or pancake design

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Engine Classification (cont.)

• Longitudinal the engine is mounted parallel
  with the length of the vehicle.
• Transverse the engine is mounted crosswise to
  the length of the vehicle.

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Valves and Camshafts

• A traditional style of engine uses one intake and
  one exhaust valve per cylinder.
• Newer designs use two intake and two exhaust
  valves per cylinder.

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Valves and Camshafts

• Valve opening and closing is performed by the
  camshaft.

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Valves and Camshafts

• If the camshaft is located in the engine block,
  valve operation will also utilize lifters,
  pushrods, and rocker arms.
• This arrangement is called a pushrod engine.

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Valves and Camshafts

• If the camshaft is located over the valves, in
  the cylinder head, it is considered an overhead
  cam engine.
• Single overhead cam (SOHC) engines utilize a
  common cam to operate the intake and exhaust
  valves per cylinder head.

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Valves and Camshafts

• Double overhead cam (DOHC) engines utilize a
  separate camshaft for the intake and exhaust
  valves per cylinder head.
• Note a v-type DOHC engine will have four
  camshafts per engine!
• Cam Operation

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Bore Stroke

• The diameter of the cylinder is the bore.
• The distance that the piston travels within the
  bore between TDC and bottom dead center (BTC) is
  the stroke.
• The longer the stroke, the greater the amount of
  air-fuel mixture that can be drawn into the
  cylinder.
• The greater the A/F mixture, the greater the
  force when the mixture is ignited.

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Engine Displacement

• Displacement is generally referred to in terms of
  cubic inches (cu. in.) cubic centimeters (cc) or
  liters (l).
• Displacement the volume of the cylinder x the
  number of cylinders.
• Displacement B x B x S x 0.7854 x cyls.

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Engine Displacement

• An over-square displacement engine has a larger
  bore than stroke.
• Transversely, an under-square engine has a larger
  stroke than bore.

Over-square displacement
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Engine Displacement
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Engine Displacement

• If an engine is said to be bored or bored-out
  the stock engine bore has been increased.
• If an engine is said to be stroked the stock
  engine stroke has been increased.
• This is achieved at the crankshaft
• Either event effectively increases the stock
  displacement of the engine.

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Engine Displacement

• If an engine is bored larger diameter pistons
  must be installed.
• If an engine is stroked the height of the piston
  must be compensated for and the engine may need
  to be clearanced.
• This is generally done by decreasing the length
  of the connecting rod
• And/or raising the wrist pin bore in the piston.

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Compression Ratio

• PVDVGVCV
• DVGVCV
• PV piston volume
• DV deck clearance volume
• GV head gasket volume
• CV combustion chamber volume (pg.298)

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The Four Stroke Cycle Video
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Torque

• Torque twisting force
• Torque the amount of force multiplied by the
  length of the lever through which it acts.
• Torque is measured in foot pound (ft. lbs.) or
  Newton-meters (N-m).

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Work Power

• Work the applied force x distance of movement
• Power the rate of doing work
• If a 550 lb. object is moved one foot in 10
  seconds or 10 minutes the same amount of work is
  performed.
• More power is exerted to move the object in ten
  seconds.

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Horsepower

• Horsepower the power required to move 550lbs.
  one foot in one second.
• Or
• 33,000lbs. one foot in one minute.
• Horsepower torque x RPM / 5,252
• SAE gross H.P vs. SAE net H.P. pg.58.

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H.P. vs. Torque
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Engine Power Video
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Engine Aspiration

• If the air-fuel mixture is introduced into the
  cylinder solely through vacuum it is considered
  to be a naturally aspirated engine.
• Turbocharged an exhaust driven turbine forces
  the A/F mixture into the engine.
• Supercharged an engine driven air-pump.
• Roots-type
• centrifugal

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Engine Aspiration

• Turbocharged an exhaust driven turbine forces
  the A/F mixture into the engine.
• Exhaust driven

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Engine Aspiration

• Supercharged an engine driven air-pump.
• Crankshaft driven

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