1. Announcements 9/21/11 Prayer Exam 1 starts a week from Saturday! a. a.Doodle survey about exam review times, vote for times before Friday If you emailed me about Mathematica issues on HW 7 and still need to turn it in, do so by Friday Regarding showing your work for the TA: (Foxtrot)

2. Video Adiabatic cotton burner Mist from pressurized bottle

3. Special Processes: Review Constant volume (isovolumetric) Constant pressure (isobaric) Constant temperature (isothermal) No heat added (adiabatic) General process? a. a.  E int = ? b. b.W on gas = ? c. c.Q added = ? A B P V

4. Last Special Case: Cyclical Processes  E int = ? Is it W by gas or W on gas ? Q added = ? P V State 1

5. Engines: Energy Transformation Q in = work by gas + Q out Notation: Q h, Q c, T h, T c, |W| Q h = |W| + Q c engine heat in (higher T) work exhaust out (lower T)

6. (a) - piston at room temp and atmospheric pressure P V a Heat Engine Example

7. (a-b) - gas heated to keep volume constant as cart rolls onto piston P V a b Heat Engine Example

8. (b-c) - gas heated to increase volume and lift the cart P V a b c Heat Engine Example

9. (c-d) - gas cooled to keep volume constant at cart rolls off piston P V a b c d Heat Engine Example

10. (d-a) - gas cooled to reduce volume back to initial level P V a b c d Heat Engine Example

11. Efficiency How good is your engine? Definition

12. Worked Problem A car engine produces 5000 W of power, at 20 cycles/second. Its efficiency is 20%. What are |W net |, Q h, and Q c per cycle? What do those quantities represent?

13. Reading Quiz (graded) What is the name we use for the cycle which models how a gas engine works? a. a.Brayton cycle b. b.Carnot cycle c. c.Diesel cycle d. d.Otto cycle e. e.Tri cycle

14. Otto Cycle: Gas Engines (Starting at 2) Piston is com- pressed quickly Heat is then added quickly by igniting fuel (const volume) Piston then expands quickly Heat is then expelled quickly (by getting rid of old air) → We pretend heat is added without changing gas Image credit: http://www.grc.nasa.gov/WWW/K-12/airplane/otto.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/otto.html “Compression ratio” r = V max /V min Derived in book:

15. Thought Question If I replaced all of the nitrogen (N 2 ) in the air with carbon dioxide (CO 2 ), what do you think would happen to the efficiency of car engines? a. a.They would get more efficient b. b.They would get less efficient c. c.The efficiency would not change

16. Diesel Cycle: Diesel Engines What’s the main difference between gas and diesel engines? Change to our PV-diagram model Diesel cycle details… done in HW problem

17. Worked problem: Class designed Make up a “three-legged cycle”. What is the efficiency of this cycle? Game plan: a. a.Calculate Q for each leg b. b.Calculate Q in, Q out, |W| c. c.e = |W|/Q in d. d.[Next class period: Test to make sure e < e max ]