1. Heat Engines Rev. Robert Sterling and the “Air Engine”

2. History  R. Stirling minister of church of Scotland  Prolific inventor entire life  Suffered for the injuries of those in congregation

3. Invention by Need  1816 patent for air engine  Steam engines inefficient and prone to explosions  Called air engines until 1940’s use of other gases

4. How does it Work?  Sealed cylinder one side hot one side cold  Working gas is moved from hot side to cold side

5. Two Piston Type  Space above piston heated continuously  Space above cool piston is continuously cooled

6. Physics Phun  Hot gas expands on piston producing pressure (P= F/A)  Cold gas moves to cold side contracts  Two power pulses per revolution

7. Model engine

8. But is it Efficient?  Mid 1800’s Carnot determined maximum efficiency of heat engines  Temp hot side—Temp cold side Temp of hot side X 100 Equals maximum efficiency

9. Carnot Cycle

10. Efficiency  Stirling engines theoretically reach 100%  Practical examples reach 50%  Gasoline engines struggle to reach above 30%

11. Why don’t I drive a Sterling Engine  Does not start instantly, requires extensive warm up  Identical problem occurs in fuel cells  Low fuel prices work against efficient engine that does not start instantly

12. Used on SS (Swedish Subs)

13. APU’s  Auxiliary power units for electrical generation on Yachts  Quiet, smooth power  Expensive

14. Cryocoolers  Stirling engines are reversible  Heat in power out  Power in heat consumed  Extremely cold temp to 10° K

15. Micro coolers  Manufactured in large numbers to cool infrared chips  Used to cool night vision devices  May have applications for space use

16. Future?  Extensive research in Europe for efficiency advances  Application specific designs  Manufacturing methodology’s