1Finish reading Chapter 3 (textbook).Homework #4 due today.Inquire/Inform Assignment #1 due in class on Friday.Homework #5 due next Wednesday.••Fuel is burned inside the cylinder. Fuel is burned inside the cylinder. Typically it is vaporized and mixed Typically it is vaporized and mixed with air first.with air first.••Rapid increase in pressure and Rapid increase in pressure and temperature exerts force on piston. temperature exerts force on piston. Often rapid burning (explodes!).Often rapid burning (explodes!).••Smaller for comparable output Smaller for comparable output powerpower••Conflicting requirements hard to Conflicting requirements hard to satisfy in a single cylindersatisfy in a single cylinderInternal Combustion EnginePistonConnecting rodFlywheel/crankshaftIntake strokeAir/gasdrawn inFlywheelDrives pistonGasAirBurning happens at higher temperature and pressure with less air. More CO and NOx pollution. Typical efficiency ~ 20%.Clicker QuestionFor a given heat engine, heptane is used as the fuel.It is observed that when heptane is burned C7H16 +11 O2Æ 7CO2+8H2O it produces carbon dioxide water and heat. If one were to double the amount of oxygen present for the reaction but keep the same amount of heptane, how would the resulting amounts of carbon dioxide, water, and heat differ?A. double everything B. reduce quantity of carbon dioxide by some factorC. double water only D. no changeE. impossible to tell/ something elseIf the heptane is kept fixed, you can't get more product out. The extra oxygen will just hang around and not participate, it won't change the CO2, H2O or heat produced.Clicker QuestionWhich of the following are a heat engine?A) A coal fired electric generatorB) A car engineC) A steam engine in an old fashioned train.D) A nuclear power plant's turbinesE) All of the aboveThey all are. They are all devices which convert thermal energy (from a fuel, or from nuclear materials) and convert (some of) it into mechanical work.2Diesel EnginePhysics is similar to standard internal combustion engine, but many details are different.• Much higher pressures (and thus no spark required).••Higher compression for a diesel implies higher efficiency Higher compression for a diesel implies higher efficiency (typical efficiency ~ 30%).(typical efficiency ~ 30%).••Fuel injection makes engine less sensitive to fuel Fuel injection makes engine less sensitive to fuel characteristics (can run on cheaper fuel).characteristics (can run on cheaper fuel).••Higher combustion temperature makes Higher combustion temperature makes NOxNOxworse, but worse, but much lower CO output.much lower CO output.••Fuel smells, more noise, heavier weight, harder to start in Fuel smells, more noise, heavier weight, harder to start in cold weather, and slower response. cold weather, and slower response. “The fuel economy of hybrid transit buses is all over themap, but all are improvements over technology. There are reports from transit agencies of fuel economy improvements of 10 percent all the way up to 50 percent, depending on variables such as series or parallel hybrid design, system optimizations, and the type of bus route. Some over-the-road tests are being carried out by the National Renewable Energy Laboratory (NREL), but final results have not yet been released. However, preliminary results are promising with fuel economy tests showing a 25 percent to 50 percent increase for the hybrid buses being evaluated, depending in part on the conventional diesel used in the comparison.).How much do hybrid buses cost? Hybrid buses can cost up to $500,000, a significant increase over a standard diesel transit bus, the cost of which is closer to $300,000. Natural gas buses, a lower-emission alternative to conventional diesel transit buses, are generally $20,000 to $50,000 more than a diesel bus. Natural gas buses will likely continue to be able to meet lower NOx emission standards than even diesel hybrid buses until at least 2010 when stronger diesel emission standards go into effect.”http://www.hybridcenter.org/hybrid-transit-buses.html- Rolls-Royce- General ElectricGas Turbines (Jets)Expanding gas serves two functions:1) It rotates the turbine to compress the air/fuel on its way in2) Then it exits the chamber to give thrust !• Typically 20-30% efficient.• Needs high temperatures.• More “high tech”Engines generate mechanical energy (e.g. turning turbines or crank shaft).How do we use this to generate electricity?Electromagnetic Induction (Faraday’s Law)Amazing discovery in 1830’s that says that a moving metal in a magnetic field creates an electrical current.Michael Faraday was asked by a British government official “of what use is electricity” and he replied “someday you can tax it.”Generator DemonstrationSomehow it converts mechanical motion (turning the crank) into electrical energy (that lights the bulb)!By turning a wire coil in a magnetic field (from a permanent magnet in this case), there is a “changing magnetic flux” and this induces an electrical current.Faraday’s Law of Induction3Faraday Flashlight (No Batteries)The first electrical power generator station using this idea.Where is this?At Niagara Falls, the energy from the falling water turns a set of wire coils inside of permanent magnets and this creates an alternating electrical current (AC).This was a great success by Westinghouse and Tesla. In fact, at the time there was a great rivalry between Edison (promoting direct current DC) and Tesla (promoting AC).In this arrangement, is the efficiency for generating electricity limited by a Carnot Maximum Efficiency?A) Yes B) NoClicker QuestionNo, it is not a heat engine.A heat engine can also turn a coil. And thus you can generate alternating current electricity. That is how most power plants work.Note that most plants are 35% efficient at converting heat energy into mechanical energy and then into electrical energy.However, this is at the power plant. One then loses another 1-10% in transporting the electricity in power lines into cities or wherever it is used.4If we want to generate 100 If we want to generate 100 MegaJoulesMegaJoulesof energy in of energy in electricity, we typically need to burn 300 electricity, we typically need to burn 300 MegaJoulesMegaJoulesworth of worth of chemical energy of coal (i.e. 33% efficiency chemical energy of coal (i.e.
View Full Document
Unlocking...