Watt

’

s Steam Engine

• • • • Improvement upon Newcomen ’ s 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.

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

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 CO 1000 C.

2 and water vapor. Since the nitrogen in the air is not part of the reaction to burn hydrocarbons, it also heats up to over 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 stroke internal combustion engine cycle.

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.

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 → xO 2 + N 2 – 2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O 2 → 2CO 2 – 3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: C x H 2x+2 + 2xO 2 → xCO 2 + 2xH 2 O

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.

• Metal core

Pictures

• Ceramic core

Catalytic converter flow diagram

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 and emit more CO In fact most of emission is CO 2 gas “ richer ” fuel mixture, burn more fossil fuels 2 which is a greenhouse The manufacturing of catalytic converters requires palladium and/or platinum for which there are environmental effects from the mining of these metals

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.

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.

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 CO 2 than CO is formed

Diesel engines-disadvantages

• • • Hard to start in cold weather-compression stroke can ’ t 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.

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).

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.

Gas turbine

Gas Turbines

• • For electricity generation, the power output turbine turns the shaft.

For aircraft, the gas is expelled out the jet nozzle.

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

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

Electromagnetism

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

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.

Generator

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

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

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

Van de graf generator

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

Van de graaff generator

• Video: http://www.youtube.com/watch?v=sy05B32X TYY