Auto 1

1. 4-Stroke Engine Theory

2. The 4 Stroke Cycle
 The 4 strokes
• Intake
• Compression
• Power
• Exhaust
 Engine speed is measured in RPM
(revolutions per minute)
• The number of times the crank shaft
makes one revolution

3. Intake Stroke
 Exhaust valve is
closed.
 Intake valve
opens.
 Piston goes down
and atmospheric
pressure pushes
the air/fuel mixture
into cylinder.

4. Compression Stroke
 After piston
reaches lowest
point in it’s stroke
(BDC) it starts to
move up.
 Intake and exhaust
valves are closed.
 The piston
compresses air/fuel
mixture to just
below it’s self
ignition point.

5. Power Stroke
 The spark plug fires
near the top of the
stroke at TDC (Top
Dead Center).
 The piston starts it’s
downward stroke
turning the
crankshaft.
 Intake and exhaust
valves are still closed.

6. Exhaust Stroke
 The exhaust valve
opens.
 The piston starts
it’s upward stroke
and forces out
exhaust gasses
 (HC, CO, CO2, O2,
and NOx).

7. Four things engines need to run
Air
Fuel
Compression
Ignition

8. So…what is air?
Air is a mixture of
various gas
compounds that
are completely
mixed in the
atmosphere

9. A little more detail, please…
By volume
 Nitrogen (N2) 78.1%
 Oxygen (O2) 20.1%
 Argon (Ar) 0.93%
 CO2 0.038%
 Trace gases <0.03%

10. I’m still having a little trouble…
 Ok, let’s say that air is a football field

11. How long is Air?
 N2 would go from goal to 78yd line

12. How long is Air?
 O2 from 78yd line to 99yd line

13. Argon would be almost 1yd
CO2 would be 1.3 inches
All other trace gases would be 1 inch

14. Fuel
Well, that takes
care of air, what is
in fuel?
Making BP fuel in the Gulf>

15. Fuel

16. Well, it’s a witches brew…
Over 500 other
compounds make
up gasoline.
It’s probably best
if you just pay
your $3-$4 and
don’t ask
questions.

17. Air and Fuel go in…
…what comes out?
CO2
H2O
Catalytic
ConverterNOx

18. Whew! My brain hurts!
Can we stop now?