Gasoline Engines
Operation
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.
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.
Four-Stroke Cycle Engines
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All modern automotive engines utilize a four
stroke design.
The four strokes are:

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
Intake
Compression
Power
Exhaust
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
Four-Stroke Cycle Engines

Compression stroke
– the intake valve
closes and the piston
travels upward in the
cylinder

this compresses the
air/fuel mixture.
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
Four-Stroke Cycle Engines

Exhaust stroke – as
the piston travels up
tow

This expels the spent
exhaust gasses
The downward movement of
the piston draws the air-fuel
mixture into the cylinder
through the intake valve on
the intake stroke.
On the compression stroke,
the mixture is compressed by
the upward movement of the
piston with both valves
closed.
Ignition occurs at the
beginning of the power
stroke, and combustion
drives the piston downward
to produce power.
On the exhaust stroke, the
upward-moving piston forces
the burned gases out the
open exhaust valve.
Crankshaft

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
Mounted at the “centerline” 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
720 Degree Cycle
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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.
Engine Classification

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Number of cylinders.
Number of strokes.
Cylinder arrangement

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Inline engine
V-type engine
Horizontal (opposed)

boxer or pancake
design
Automotive
engine cylinder
arrangements.
Engine Classification (cont.)
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Longitudinal – the engine is mounted parallel
with the length of the vehicle.
Transverse – the engine is mounted
crosswise to the length of the vehicle.
Longitudinal
front engine,
rear-wheel
drive.
Two types of
front engine,
front-wheel drive.
Valves and Camshafts

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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.
Valves and Camshafts

Valve opening and
closing is
performed by the
camshaft.
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.
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.
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
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 airfuel mixture that can be
drawn into the cylinder.
 The greater the A/F
mixture, the greater
the force when the
mixture is ignited.
The bore and
stroke of pistons
are used to
calculate an
engine’s
displacement.
TECH
TIP
Engine Displacement
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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.
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
Engine Displacement
Engine Displacement


If an engine is said to be ‘bored” or “boredout” 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.
Engine Displacement Formula
Bore X Bore X Stroke X 0.7854 X number of cylinders
For example, take a 6-cylinder engine where
Bore = 4.000 in., Stroke = 3.000 in.
Applying the formula,
4.000 in. X 4.000 in. X 3.000 in. X 0.7854 X 6 = 226 cu. in.
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.
Compression
ratio is the ratio
of the total
cylinder volume
(when the piston
is at the bottom
of its stroke) to
the clearance
volume (when the
piston is at the
top of its stroke).
Compression Ratio

= PV+DV+GV+CV
DV+GV+CV

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PV = piston volume
DV = deck clearance volume
GV = head gasket volume
CV = combustion chamber volume (pg.298)
Combustion
chamber volume
is the volume
above the piston
with the piston at
top dead center.
The Four Stroke Cycle Video
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).
Torque is a twisting force equal to
the distance from the pivot times
the force applied expressed in
units called pound-feet (lb-ft) or
Newton-meters (N-m).
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.
Horsepower

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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.
One horsepower is equal to
33,000 foot-pounds (200 lbs.
X 165 ft.) of work per minute.
TECH
TIP
H.P. vs. Torque
Engine Power Video
Engine Aspiration
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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
Engine Aspiration

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Turbocharged – an exhaust driven turbine forces the A/F
mixture into the engine.
Exhaust driven
Engine Aspiration

Supercharged – an
engine driven airpump.

Crankshaft driven
Turbochargers and Superchargers
A turbocharged (exhaust-driven) system is designed to
provide a pressure greater than atmospheric pressure in the
intake manifold. This increased pressure forces additional
amounts of air into the combustion chamber over what would
normally be forced in by atmospheric pressure. This
increased charge increases engine power.
The amount of “boost” (or pressure in the intake manifold) is
measured in pounds per square inch (psi), inches of mercury
(in. Hg), in BAR’s, or in atmospheres. The higher the level of
boost (pressure), the greater the horsepower potential.
A supercharged system is an engine-driven system designed
to provide pressure greater than atmospheric pressure in the
intake manifold. A supercharger is used on some engines
from the factory including the General Motors 3800 cc, V-6,
which uses an Eaton-built unit.