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Diesel Engines

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Title: Diesel Engines


1
Diesel Engines
  • Found mostly in large trucks, locomotives, farm
    tractors and occasionally cars.
  • An internal combustion engine
  • Does not mix the fuel and air before they enter
    the combustion chamber
  • Does not use a spark for emission
  • Heavier and bulkier than gasoline engine
  • Slower speed and slower response to driver
  • More efficient than gasoline engines,
    efficiencies of over 30 of converting fuel
    energy to mechanical energy.

2
Diesel Engines
  • Piston moves down, drawing air into the cylinder
  • Compression stroke chamber only contains air and
    the piston pushes up, increases the air pressure
    and temperature until ignition can occur when the
    fuel is introduced.
  • Short burst of fuel is sent into the chamber when
    this pressure is reached.
  • Explosion heats gases in chamber and causes them
    to expand, pushing the piston down.
  • Piston pushes up, expelling the exhaust gasses.

3
Diesel engines-advantages
  • Ignition occurs at a higher T, resulting in
    higher efficiency than gasoline engines (more
    than 30 efficient in converting chemical to
    mechanical energy).
  • Can run on low grade fuels and diesel fuels have
    10 more BTU per gallon.
  • CO emissions are lower more air in the chamber
    means more CO2 than CO is formed

4
Diesel engines-disadvantages
  • Hard to start in cold weather-compression stroke
    cant reach the ignition chamber. Solved with
    installation of a glow plug, a small heater.
  • Gelling-Diesel fuel can crystallize in cold
    weather clogging fuel filters and hindering fuel
    flow. Solved via electric heaters on fuel lines.
  • Fuel injection is critical, if timing is off,
    combustion is not complete and results in excess
    exhaust smoke with unburned particles and excess
    hydrocarbons.

5
Diesel engine disadvantages
  • Noisy
  • More expensive initially
  • Smell
  • Diesel fuel has become routinely more expensive
    than gasoline
  • Why?-rising demand, cheap gas due to decreased
    demand, environmental restrictions (need for
    lower sulfer emissions and higher taxes on diesel
    fuel than gasoline).

6
Gas turbines
  • Newer type of internal combustion engine.
  • Used in jets and some electric power plants
  • Air pulled in the front and compressed in a
    compressor. (The rotating fan-like structure you
    see when you look into a jet engine).
  • Air is mixed with fuel and ignited, this heated
    mixture expands.
  • Expanding gas moves through the turbine, which is
    connected to the compressor by a rotating shaft.
  • Hot gases are expelled with a greater velocity
    than the intake air, giving the engine is thrust.

7
Gas Turbines
  • For electricity generation, the power output
    turbine turns the shaft.
  • For aircraft, the gas is expelled out the jet
    nozzle.

8
Gas Turbines
  • 20-30 efficiency converting thermal energy to
    mechanical energy
  • Lightweight
  • Respond quickly to changing power demands
  • Relatively cheap for public utilities
  • Limitations are the need for materials to
    withstand T 1000 C and the high rotation speeds

9
Generating Electricity
  • 1831 Michael Faraday discovers that by moving a
    magnetic bar near a loop of wire, an electric
    current can be induced in the wire.
  • Known as electromagnetic induction
  • This allowed the generation and transmission of
    electricity possible, along with electric motors
    and modern communications and computer systems
  • Electromagnetic induction animation

10
Electromagnetism
  • It was already known that the opposite was true,
    that a metal placed inside a current loop could
    become magnetized.

11
Generators
  • Coil of copper wire mounted on a rotating
    armature
  • Coils are rotated through a magnetic field
  • This induces a current in the coils.
  • But, the induced current resists the rotation of
    the coils, so we need an external energy source
    to rotate the coils.
  • The current exits the rotating coil via slip
    rings that are in contact with carbon brushes.
  • The direction of current flow changes as the coil
    rotates in the magnetic field. This produces an
    alternating current.

12
Generator
13
Before Faraday
  • Electricity was generated via electrostatic means
  • used moving electrically charged belts, plates
    and disks to carry charge to a high potential
    electrode.
  • Charge was generated using either of two
    mechanisms
  • Electrostatic induction or
  • The triboelectric effect, where the contact
    between two insulators leaves them charged.
  • Generated high voltage but low current, not good
    for commercial use

14
Wimshurst Machine
  • two large contra-rotating discs mounted in a
    vertical plane, two cross bars with metallic
    brushes, and a spark gap formed by two metal
    spheres.
  • two insulated disks and their metal sectors
    rotate in opposite directions passing the crossed
    metal neutralizer bars and their brushes.
  • imbalance of charges is induced, amplified, and
    collected by two pairs of metal combs with points
    placed near the surfaces of each disk.
  • The positive feedback increases the accumulating
    charges exponentially until a spark jumps across
    the gap.
  • The accumulated spark energy can be increased by
    adding a pair of Leyden jars, an early type of
    capacitor suitable for high voltages

15
Van de graf generator
  • an electrostatic machine which uses a moving belt
    to accumulate very high electrostatically stable
    voltages on a hollow metal globe.

16
Van de graaff generator
  • Video http//www.youtube.com/watch?vsy05B32XTYY

17
Faradays Disk
  • A copper disc rotating between
  • the poles of a horseshoe magnet.
  • produced a small DC voltage,
  • and large amounts of current.
  • First electromagnetic generator

18
Dynamos
  • First generator able to produce electricity for
    industrial purposes
  • First dynamo was built by Hippolyte Pixii in
    1832.
  • a stationary structure, which provides a constant
    magnetic field, and a set of rotating windings
    which turn within that field.
  • Magnetic field may be provided by one or more
    permanent magnets or by one or more
    electromagnets, which are usually called field
    coils.

19
Pixii's dynamo
20
Dynamos
  • Produce a direct current
  • Basis for later devices such as the electric
    motor, the alternating-current alternator, and
    the rotary converter.
  • Developed as a replacement for batteries

21
Modern electrical power plants
  • Boiler Unit Almost all of power plants operate
    by heating water in a boiler unit into super
    heated steam at very high pressures. The source
    of heat from combustion reactions may vary in
    fossil fuel plants from the source of fuels such
    as coal, oil, or natural gas. Biomass, waste
    plant parts, solid waste incinerators are also
    used as a source of heat. All of these sources of
    fuels result in varying amounts of air pollution,
    as well as carbon
  • In a nuclear power plant, the fission chain
    reaction of splitting nuclei provides the source
    of heat.

22
Modern electrical power plants
  • The super heated steam is used to spin the blades
    of a turbine, which turns a coil of wires within
    a circular arrangements of magnets.

23
Modern Electric power plants
  • Cooling Water After the steam travels through
    the turbine, it must be cooled and condensed back
    into liquid water to start the cycle over again.
    Cooling water can be obtained from a nearby river
    or lake. An alternate method is to use a very
    tall cooling tower, where the evaporation of
    water falling through the tower provides the
    cooling effect.
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