The IC Engine: Why

1
The IC Engine Why

• By Matthew King

2
Outline

• A Short History
• Background
• Why
• How do we compare engines and their cycles?

3
History

• The internal combustion engine was first
  conceived and developed in the late 1800s
• The man who is considered the inventor of the
  modern IC engine and the founder of the industry
  is pictured to the right.Nikolaus Otto
  (1832-1891).
• Otto developed a four-stroke engine in 1876, most
  often referred to as a Spark Ignition, since a
  spark is needed to ignite the fuel air mixture.

4
History

• The impact on society is quite obvious, all most
  all travel and transportation is powered by the
  IC engine trains, automobiles, airplanes are
  just a few.
• The IC engine largely replaced the steam engine
  at the turn of the century (1900s)
• Another important cycle is the Diesel cycle
  developed by Rudolph Diesel in 1897. This cycle
  is also known as a compression ignition engine.

5
Background on IC Engines

• An internal combustion is defined as an engine
  in which the chemical energy of the fuel is
  released inside the engine and used directly for
  mechanical work, as opposed to an external
  combustion engine in which a separate combustor
  is used to burn the fuel.1
• IC engines can deliver power in the range from
  0.01 kW to 20x103 kW, depending on their
  displacement.2

6
Background on the Otto Cycle

• The Otto Cycle has four basic steps or strokes
• 1. An intake stroke that draws a combustible
  mixture of fuel and air into the cylinder
• 2. A compression stroke with the valves closed
  which raises the temperature of the mixture. A
  spark ignites the mixture towards the end of this
  stroke.
• 3. An expansion or power stroke. Resulting from
  combustion.
• 4. An Exhaust stroke the pushes the burned
  contents out of the cylinder.
• To the right is an idealized representation of
  the Otto cycle on a PV diagram.
• http//www.rawbw.com/xmwang/javappl/ottoCyc.html

7
Why

• The Otto cycle IC engine has remained
  fundamentally unchanged, besides slight
  improvements, for over 100 years. Its popularity
  has continually increased because
• Relatively low cost
• Favorable power to weight ratio
• High Efficiency
• Relative simple and robust operating
  characteristics
• Improvements are mainly lower emissions and
  higher fuel efficiency

8
Comparing Engines.

• mep work done per unit displacement volume
• Or average pressure that results in the same
  amount of indicated or brake work produced by the
  engine
• Scales out effect of engine size
• Two useful types imep and bmep
• imep indicated mean effective pressure
• -the net work per unit displacement volume done
  by the gas during compression and expansion
• bmep brake mean effective pressure
• -the external shaft work per unit volume done by
  the engine

9
BMEP

• Based on torque

(4 stroke)
(2 stroke)
10
Compare

• Brake specific fuel consumption (bsfc)
• Measure of engine efficiency
• They are in fact inversely related, so a lower
  bsfc means a better engine
• Often used over thermal efficiency because an
  accepted universal definition of thermal
  efficiency does not exist

11
bsfc

• bsfc is the fuel flow rate divided by the brake
  power
• We can also derive the brake thermal efficiency
  if we give an energy to the fuel called heat of
  combustion or, qc

12
Compare

• Volumetric Efficiency, ev
• The mass of fuel and air inducted into the
  cylinder divided by the mass that would occupy
  the displaced volume at the density ?i in the
  intake manifold
• Note its a mass ratio and for a 4 stroke engine
• For a direct injection engine

13
Other comparisons

• First law analysis- energy conservation
• For a system open to the transfer of enthalpy,
  mass, work, and heat, the net energy crossing the
  control surface is stored into or depleted from
  the control volume
• Second Law Analysis entropy conservation
• This approach takes into account the
  irreversibility that occurs in each process
• Another outcome of this analysis is the
  development of the usefulness of each type of
  energy (exergy)

14
References

• 1. Internal Combustion Engines, Colin R.
  Ferguson, John Wiley Sons, 2001
• 2. Engines An Introduction, John L. Lumley,
  Cambridge University Press, 1999