Watt

1
Watts Steam Engine

• Improvement upon Newcomens
• Used 75 less coal than Newcomen's, and was hence
  much cheaper to run.
• Watt developed his engine further, modifying it
  to provide a rotary motion suitable for driving
  factory machinery.
• This enabled factories to be sited away from
  rivers, and further accelerated the pace of the
  Industrial Revolution.

2
Steam Engines

• Efficiencies were only 1 for converting heat to
  mechanical energy.
• Now they are above 30.
• Class of engine known as external combustion
  engines. Fuel is burned outside the pressurized
  part of the engine
• Results in low CO and NO emissions
• Particulate and sulfur oxides emissions depend
  upon the fuel being burned.
• Eventually replaced in transportation by the
  internal combustion engine which has higher
  power-to-weight ratio, lower maintenance and
  lower space requirements

3
Gasoline Engines

• Use internal combustion fuel is vaporized and
  mixed with air inside a closed chamber
• Mixture is compressed to 6-10 times atmospheric
  pressure and ignited with a spark
• Fuel burns explosively forming a gas of CO2 and
  water vapor. Since the nitrogen in the air is not
  part of the reaction to burn hydrocarbons, it
  also heats up to over 1000 C.
• Now when a gas heats it expands and exerts a
  force. The expanding gases exert the force on a
  piston, which pushes it downward and causes the
  crankshaft to rotate.

4
4 stroke internal combustion engine cycle.
5
Gasoline engines

• Efficiency of converting chemical to mechanical
  energy of about 25.
• Produces carbon monoxide (CO), nitrogen oxides
  and hydrocarbons. All are considered pollutants
• Enter the catalytic converter.

6
Catalytic converter

• Starting in 1975, catalytic converters were
  installed on all production vehicles via
  increasing government controls on pollutants from
  gasoline powered vehicles.
• Catalytic converters have 3 tasks
• 1. Reduction of nitrogen oxides to nitrogen and
  oxygen 2NOx ? xO2 N2
• 2. Oxidation of carbon monoxide to carbon
  dioxide 2CO O2 ? 2CO2
• 3. Oxidation of unburnt hydrocarbons (HC) to
  carbon dioxide and water CxH2x2 2xO2 ? xCO2
  2xH2O

7
Catalytic converters

• The catalytic converter consists of several
  components
• 1. The core, or substrate. In modern catalytic
  converters, this is most often a ceramic
  honeycomb however, stainless steel foil
  honeycombs are also used.
• 2. The washcoat. In an effort to make
  converters more efficient, a washcoat is
  utilized, most often a mixture of silica and
  alumina. The washcoat, when added to the core,
  forms a rough, irregular surface which has a far
  greater surface area than the flat core surfaces,
  which then gives the converter core a larger
  surface area, and therefore more places for
  active precious metal sites.
• 3. The catalyst itself is most often a
  precious metal. Platinum is the most active
  catalyst and is widely used. However, it is not
  suitable for all applications because of unwanted
  additional reactions and/or cost. Palladium and
  rhodium are two other precious metals that are
  used. Platinum and rhodium are used as a
  reduction catalyst, while platinum and palladium
  are used as an oxidization catalyst. Cerium,
  iron, manganese and nickel are also used, though
  each has its own limitations. Nickel is not legal
  for use in the European Union (due to reaction
  with carbon monoxide). While copper can be used,
  its use is illegal in North America due to the
  formation of dioxin.

8
Pictures

• Metal core
• Ceramic core

9
Catalytic converter flow diagram
10
Limitations

• Susceptible to lead build up, require use of lead
  free gasoline. Lead in gas would coat the
  washcoat and render it useless. Lead had been
  added to gas since the 1920s to reduce engine
  knock(auto-ignition of gas), and increase octane
  level of the gas.
• Require richer fuel mixture, burn more fossil
  fuels and emit more CO2
• In fact most of emission is CO2 which is a
  greenhouse gas
• The manufacturing of catalytic converters
  requires palladium and/or platinum for which
  there are environmental effects from the mining
  of these metals

11
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.

12
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.

13
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

14
Diesel engines-disadvantages

• Hard to start in cold weather-compression stroke
  cant reach the ignition temperature. 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.

15
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).

16
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.

17
Gas turbine
18
Gas Turbines

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

19
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

20
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.
• The magnetic field produced by the magnet applies
  a force on the electrons in the wire, causing
  them to move.
• When the north end of the magnet enters the coil,
  a current is induced that travels around the coil
  in a counterclockwise direction producing a
  positive current when the magnet is then pulled
  out of the coil, the direction reverses to
  clockwise producing a negative current.
• 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

21
Electromagnetism

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

22
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.

23
Generator
24
Alternating vs direct current

• Direct current flow of current in one direction.
  Produced by batteries, solar cells, dynamos
• Alternating current when the flow of current
  periodically changes direction(50-60 times per
  second). This is what is delivered to homes and
  businesses

25
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

26
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

27
Van de graf generator

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

28
Van de graaff generator

• Video http//www.youtube.com/watch?vsy05B32XTYY