1. Heat Engines
How do we get the heat energy of the fuel and turn it into mechanical energy?
Simply put we combine the carbon and hydrogen in the fuel with oxygen.
2 reactions that occur are
C + O2  CO2 + heat energy
H2 + O  H2O + heat energy
This process is just the reverse of photosynthesis.

2. Just a little chemistry
For example, the the equation for burning heptane looks like:
C7H O2  7CO2 + 8 H2O X 106 calories per 100g of Heptane
1.15 x106 is called the heat of combustion for heptane. Every hydrocarbon has such a number
It is the maximum amount of energy for a certain amount of mass of a substance you can extract.
It represents the energy from the sun stored in the fuel since ancient times

3. So what is a heat engine?
A heat engine is any device that can take energy from a warm source and convert it to mechanical energy
Efficiency: not all of the energy from the burning of the fuel goes into the production of energy. Heat is lost as waste heat and needs to be disposed of.
For example, most energy generating plants are located near bodies of water or have cooling towers which are used to carry off waste heat.

4. How well does one work?
Your car often carries off waste heat via its cooling system. But your car recycles some of that heat—how?
No heat engine will perfectly convert all the heat energy to mechanical energy.
We need to quantify the efficiency and designers of heat engines work to maximize this efficiency.

5. Carnot and his cycle
Sadi Carnot created an efficiencey measure for a heat engine, now named after him (Carnot Efficiency).
Always less than 100%
Simply put it is the percentage of the energy taken from the heat source which is actually converted to mechanical work.

6. Diagram of a heat engine

7. Carnot Efficciency Efficiency = work done/energy put into the system
In terms of the flow of heat (Q) energy this becomes : [(Qhot - Qcold)/Qhot ]X 100%
Now energy is not easy to quantify, but temperature is, and since we know the Kelvin T scale is true measure of energy, we can express the efficiency in terms of temperature.

8. Carnot Efficciency So our efficiency, in terms of T becomes:
Carnot Efficiency = [(Thot - Tcold)/Thot ]X 100%
Or with some algebraic wizardry we get
Carnot efficiency = [1- (Tcold/Thot) ]X 100%
Example: for a coal fired electric power plant, the boiler temperature = 825K and the cooling tower temperature is 300k. So [1-(300/825)] X 100% = 64%

9. Carnot Cycle Figure 1 Figure 2
From an initial stat A, the gas is placed in contact with the hot temperature reservoir (Th) and expands isothermally (keeping T = Th = constant) to some state B. During this isothermal expansion heat Qh flows into the gas from the hot temperature Th.
From state B, the gas undergoes an adiabatic expansion to state C. No heat is exchanged during this expansion. Expanding an insulated gas means work is done at the "expense" of the internal energy. That means the gas will have a lower temperature. This is the cold temperature Tc.
At state C, we place the gas in contact with the cold temperature heat reservoir (like a large tank of water) and do an isothermal compression to state D. In compressing the gas, work is done on the gas by the outside. But the temperature remains constant -- meaning the internal energy U of the gas remains constant. For this to happen, heat Qc is given out to the cold temperature heat reservoir.
From state D we do an adiabatic compression back to state A. Remember, "adiabatic" means insulated so there is no heat exchange.
Figure 1
Figure 2

10. So how can we make this work for us: The Steam Engine
Concept of a heat engine was revolutionary-if the heat energy could be turned into mechanical energy, human and labor could be replaced cheaply and more efficiently.

11. Simple steam engine
Water is heated in the boiler and steam forces piston up
At the valve, steam escapes into the cooling tower, where it cools and condenses.
Cool water is pumped back into boiler, T drops and piston drops, until sufficient steam is created to cause the process to repeat.

12. A little history
First writings on the power of steam are from Hero of Alexandria (10-70 CE).
The aeolipile (known as Hero's engine) was a rocket-like reaction engine and the first recorded steam engine.
He also created an engine that used air from a closed chamber heated by an altar fire to displace water from a sealed vessel; the water was collected and its weight, pulling on a rope, opened temple doors.
Taqi al-Din in 1551 and Giovanni Branca in 1629 both created experimental steam engines.

13. More History
Thomas Savery ( ), in 1698, patented the first crude steam engine.
Based on Denis Papin's Digester or pressure cooker of 1679.
Savery had been working on solving the problem of pumping water out of coal mines
Thomas Newcomen created the atmospheric engine, which was relatively inefficient, and in most cases was only used for pumping water out of deep mines

14. Newcomen’s atmospheric engine

15. Watt’s Steam Engine Improvement upon Newomen’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.

16. 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.

17. 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.

18. 4 stroke internal combustion engine cycle.

19. 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.

20. 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

21. 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.

22. Pictures
Metal core
Ceramic core

23. 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

24. 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.

25. 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.

26. 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

27. 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.

28. 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).