The Diesel Cycle

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The Diesel Cycle

• Avinash Jayakumar

Objective To introduce and explain the basic
concepts of the diesel cycle
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If you Dare to Care

• The diesel cycle is the combustion process of a
  type of internal combustion engine
• The burning of the fuel is triggered not by a
  spark plug as in the Otto cycle, but rather by
  the heat generated in compressing the fuel-air
  mixture.
• Used in automobiles, emergency power generation
  and diesel-electric submarines.

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If you Still Dare to Care

• Only air is drawn into the engine and compressed.
  
• The fuel is then injected directly into the
  cylinder with a high-pressure fuel injector when
  the piston reaches the top of its motion.
• The fuel is thicker and burns more slowly than
  petrol, so the piston is already moving down by
  the time the combustion completes.
• Compression Stroke - Adiabatic compression of
  gas fuel mixture in the cylinder. Ignition of gas
  fuel mixture. Fuel is ignited by high temperature
  due a large compression. Burning takes places
  while the pressure is essentially constant.
• Expansion Stroke. Adiabatic, isentropic expansion
  of gases. This is the part of the cycle that does
  positive work. Exhaust of the spent gases and the
  intake of a new fuel mixture into the cylinder.
  The volume is the same at beginning and ending of
  the exhaust and intake stroke.

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Bringing it into Focus
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An example
The four cycles of the diesel engine are   1 - 
The piston is moved away from the cylinder head
by the crankshaft, drawing only air into the
cylinder.   2 -  The piston moves towards the
cylinder head, compressing the air. At the end of
the stroke vaporized fuel is injected
into the cylinder and is ignited by the high
temperature of the air.   3 -  The piston is
forced away from the cylinder head by the gas,
expanding after the ignition of the fuel.   4 - 
The exhaust valve is opened and the piston moves
towards the cylinder head, driving the exhaust
gases from the cylinder.
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Finally(!)

• A thermodynamic cycle in which only air is
  admitted in the intake stroke.
• The air is then adiabatically compressed, and
  fuel is injected into to the hot air in the form
  of many small drops (not a vapor).
• Each drop burns over a small time, giving an
  approximation of a isobaric explosion.
• The explosion pushes the cylinder outwards.
• The power stroke, valve exhaust, and exhaust
  stroke which follow are identical to those in the
  Otto cycle.

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Sources of Knowledge

• http//www.ac.wwu.edu/vawter/PhysicsNet/Topics/Th
  ermLaw2/Entropy/GasCycleEngines.html
• http//scienceworld.wolfram.com/physics/DieselCycl
  e.html
• http//science.howstuffworks.com/two-stroke1.htm
• http//en.wikipedia.org/wiki/Diesel_cycle