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 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 → xO2 + N2

– 2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

– 3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O

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.

Pictures

• Metal core

• Ceramic core

Limitations

• Susceptable to lead build up, require use of lead free gasoline.

• 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

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• Compression stroke –

chamber only contains air and the piston increases the air pressure 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 back up.

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

Diesel engines-disadvantages

• Hard to start in cold weather-compression stroke can’t reach the ignition chamber. Solved with installation of a glow plug, a small heater.

• Gelling-Diesel fuel can crystalize 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 sulfur 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 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.

• 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

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

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