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QUESTIONS

QUESTIONS. Performance. Typical thermal efficiency: ~25% Mechanical friction Rolling friction Exhaust Radiator Driving auxiliaries: fan, water pump, etc. Practice problem.

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QUESTIONS

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  1. QUESTIONS

  2. Performance • Typical thermal efficiency: ~25% • Mechanical friction • Rolling friction • Exhaust • Radiator • Driving auxiliaries: fan, water pump, etc

  3. Practice problem • A four-cylinder, four-stroke engine has 3.75-in cylinder. Clearance volume of 17% of cylinder volume at BDC. Stroke is 3.45 in. Crankshaft rotates at 2600rpm. Otto cycle begins at 14.6psi and 100oF. Maximum cycle temperature is 5200oR. What horsepower developed by the engine?

  4. Diesel Cycle • Rudolph Diesel • Improve efficiency of power generation vs steam engine: new approach • Overcome deficiency of SIIC • CIIC

  5. Diesel cycle • Higher molecular weight fuel; less volatile. Less refined fuel. • Air compressed before fuel addition; no autoignition • No spark plug • Higher pressures; sturdier construction

  6. Diesel cycle • Air standard • Constant specific heat • Variable specific heat • Otto cycle: compression ratio - 1/2 • Diesel cycle • Compression ratio - 1/2 • Cut-off ratio - 3/2

  7. Diesel cycle • 1→2 isentropic compression • 2→3 constant pressure heat addition • 3→4 isentropic expansion • 4→1 constant volume heat rejection

  8. Performance • Approximate “rule” • >300hp SIIC preferred for performance • < 300hp efficiency & costs favor CIIC • Thermal efficiency • SIIC 25 – 30% • CIIC 35 – 40%

  9. Cycle analysis • Heat • Work • Thermal efficiency: related to ratios • Specific heats: fixed or variable

  10. Practice Problem • The compression ratio of an air standard Diesel cycle is 17.At the beginning of compression, conditions are 14.0 psi, 2ft3, & 520oR. Maximum cycle temperature is 4000oR. • Find • Cycle work, Btu • Thermal efficiency • mep, psi • Cut-off ratio

  11. Dual cycle

  12. Dual cycle analysis • Heat • Work • Thermal efficiency

  13. Two stroke engine • Simple; inexpensive; light weight • No valves • Power stroke every revolution • Any orientation

  14. Two stroke engine • No lube system; mix with oil. More costly fuel. More wear. • Purging of exhaust inefficient; some mixing with fresh fuel. • Noise & pollution; local regulations?

  15. Wankel • Rotary; smooth torque curve • Relatively simple & light-weight • High power:weight ratio • Chambers “rotate” in engine casing

  16. Wankel • Difficult to seal compartments • Mixing of fuel & exhaust • Fuel consumption; short duration of combustion • Low compression ratio • Replace vs repair

  17. Cycles • Stirling • Ericsson

  18. Stirling

  19. Ericsson

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