Engines
Sancho McCann
Types of Engines
Inline
Horizontally Opposed
Radial
Inline Engine
• Pistons all lie along
the same line
• Small frontal area
• Low drag
http://auto.howstuffworks.com/engine-inline.htm
Horizontally Opposed Engine
• Pistons arranged in
opposing banks
• Flat
• Low drag
• Most common
general aviation
engine
http://auto.howstuffworks.com/engine-flat.htm
Radial Engine
• Odd number of
cylinders
• Cylinders arranged
radially around a
central crankshaft
• High power to
weight ratio
• Lots of drag
http://en.wikipedia.org/wiki/Image:Radial_engine.gif
Parts of an Engine
• This is a cut-away of an individual
cylinder in an engine
http://auto.howstuffworks.com/engine.htm
Parts of an Engine
(M) Piston
• Forced up and down
within the cylinder
Parts of an Engine
(N) Connecting Rod
• Connects the piston
to the crankshaft
Parts of an Engine
(P) Crankshaft
• The purpose of the
engine is to turn the
crankshaft
• Each piston is
connected to the
crankshaft by a
connecting rod
Parts of an Engine
(C) Intake Port
• The fuel-air mixture
enters here
• Opened and closed
by the intake valve
Parts of an Engine
(L) Exhaust Port
• The burnt mixture
exits here
• Opened and closed
by the exhaust valve
Parts of an Engine
(K) Spark Plug
• Two per cylinder
(only one shown in
diagram)
• Delivers the spark to
ignite the mixture
Parts of an Engine
(I) Camshaft
• Lifts the intake and
exhaust valves open
• Controls the timing
of the intake and
exhaust valves
• Rotates at half the
speed of the
crankshaft
4 Stroke Cycle
(1) Intake (induction)
(2) Compression
(3) Combustion (power)
(4) Exhaust
1. Intake Stroke
• Intake valve is open
• Fuel-air mixture enters the cylinder
• Piston is moving downward from Top
Dead Centre to Bottom Dead Centre
2. Compression Stroke
• Piston is moving upward from Bottom
Dead Centre to Top Dead Centre
• Both valves (intake and exhaust) are
closed
• Fuel-air mixture is compressed
3. Combustion (Power) Stroke
• Spark fires when piston approaches top
of cylinder
• Both valves (intake and exhaust) are
closed
• Fuel-air mixture is ignited and expands
• Piston is forced downward from Top
Dead Centre to Bottom Dead Centre
4. Exhaust Stroke
• Exhaust port opens
• Piston moves upward from Bottom
Dead Centre to Top Dead Centre
• Burnt fuel-air mixture is expelled
through the exhaust port
4 Stroke Cycle Again
http://en.wikipedia.org/wiki/Four-stroke_cycle
Definitions
• Top Dead Centre - The highest possible
position of the piston during the cycle
• Bottom Dead Centre - The lowest
possible position of the piston during
the cycle
Definitions
• Compression Ratio - The ratio of
– the volume in the cylinder when the piston
is at bottom dead centre to,
– the volume in the cylinder when the piston
is at top dead centre
• A higher compression ratio produces
more power
Valve Timings
• Valve Lead: When a valve opens
slightly before the beginning of a stroke
• Valve Lag: When a valve stays open
slightly longer than the entire stroke
• Valve Overlap: When both valves are
open at the same time
Valve Timings Example
• There is valve lead on the intake valve
• There is valve lag on the exhaust valve
• This gives valve overlap at the end of
the exhaust stroke and beginning of the
intake stroke
A Valve Timing Chart
Where is
the lag?
Where is
the lead?
Where is the
overlap?
http://www.compcams.com/Base/Images/Technical/800-615-ValveTimingIllustration-002.gif
A Valve Timing Chart
Where is
the lag?
Where is
the lead?
Where is the
overlap?
http://www.compcams.com/Base/Images/Technical/800-615-ValveTimingIllustration-002.gif
A Valve Timing Chart
Where is
the lag?
Where is
the lead?
Where is the
overlap?
http://www.compcams.com/Base/Images/Technical/800-615-ValveTimingIllustration-002.gif
A Valve Timing Chart
Where is
the lag?
Where is
the lead?
Where is the
overlap?
http://www.compcams.com/Base/Images/Technical/800-615-ValveTimingIllustration-002.gif