Lenoir (1822-1900) designed and innovated first sufficient and useful engine
during the 1860s. Then, many researchers try to invent many different engine
design. But, most of the engine only produce power about 4.5kW (6hp) and
reached mechanical efficiency up to 5%. Nicolaus A. Otto (1832-1891) and Eugen
Langen (1833-1895) were most famous engine creators at that period. Otto-Langen
engine reached mechanical efficiency up to 11% compared to any other engine
design.  During this decade, the engine
was functioning on the same basic four-stroke cycle (Otto cycle) as advanced
automobile engine start to grow. Otto engine was built in 1876 and given
recognition as best engine prototype. 1



following is an explanation of spark ignited four-stroke cycle engine:

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1.      Intake
Stroke- As the exhaust valve closed and intake valve open, the piston moves
from TDC to BDC. The vacuum generated the volume increase in the cylinder.
Air-thrust into cylinder due to the pressure difference between intake system
which has atmospheric pressure and vacuum inside the cylinder. Gasoline will be
added to the air flow through the intake system.


2.      Compression
Stroke- The intake valve closed as the piston passes BDC. Then, the piston moves back to TDC while intake and exhaust
valve closed. During this process, the air-fuel
mixture is compressed, increasing
temperature and pressure of the cylinder. 
In a normal present spark-ignited gasoline engine, the compression ratio is about 8:1 to11:1.


3.      Expansion
or Power Stroke- Spark ignited as the piston nears the TDC and combustion
process started to occur.  Combustion
process alters the air-fuel mixture into exhaust gas and increases the cylinder
pressure and temperature.  High pressure
is generated by the combustion process push the piston from TDC to BDC. This
cycle produces useable work and cylinder pressure and temperature start to


4.      Exhaust
Stroke- Exhaust gasses fill the cylinder as the piston reached BDC. Then,
exhaust valve opened to enable the exhaust gases to travel to the exhaust
manifold. The piston travels from BDC to TDC in the exhaust stroke. This
process pushes remaining exhaust gases out of the cylinder.


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