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 + O 2  CO 2 + heat energy – H 2 + O  H 2 O + 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: – C 7 H 16 + 11O 2  7CO 2 + 8 H 2 O +1.15 X 10 6 calories per 100g of Heptane 1.15 x10 6 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 : [(Q hot - Q cold )/Q hot ]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 = [(T hot - T cold )/T hot ]X 100% – Or with some algebraic wizardry we get Carnot efficiency = [1- (T cold /T hot ) ]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 1. Reversible isothermal expansion of the gas at the "hot" temperature, TH (isothermal heat addition). During this step (A to B on Figure 1, 1 to 2 in Figure 2) the expanding gas causes the piston to do work on the surroundings. 2. Isentropic (Reversible adiabatic) expansion of the gas. For this step (B to C on Figure 1, 2 to 3 in Figure 2) we assume the piston and cylinder are thermally insulated, so that no heat is gained or lost. The gas continues to expand, doing work on the surroundings. The gas expansion causes it to cool to the "cold" temperature, TC. 3. Reversible isothermal compression of the gas at the "cold" temperature, TC. (isothermal heat rejection) (C to D on Figure 1, 3 to 4 on Figure 2) Now the surroundings do work on the gas, causing quantity Q2 of heat to flow out of the gas to the low temperature reservoir. 4. Isentropic compression of the gas. (D to A on Figure 1, 4 to 1 in Figure 2) Once again we assume the piston and cylinder are thermally insulated. During this step, the surroundings do work on the gas, compressing it and causing the temperature to rise to TH. At this point the gas is in the same state as at the start of step 1. Figure 2 Figure 1

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 (1650-1715), 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 CO 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 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 → 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

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 CO 2 In fact most of emission is CO 2 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