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Combustion

Combustion. Detonation and Pre-ignition. Normal Combustion. Controlled burn of air/fuel mixture Lasts between .0005 and .004 seconds Flame front propagates at approx. 50 mph Combustion chamber temperature reaches between 2000 and 3000 degrees Fahrenheit. Detonation (post-ignition).

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Combustion

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  1. Combustion Detonation and Pre-ignition

  2. Normal Combustion • Controlled burn of air/fuel mixture • Lasts between .0005 and .004 seconds • Flame front propagates at approx. 50 mph • Combustion chamber temperature reaches between 2000 and 3000 degrees Fahrenheit

  3. Detonation (post-ignition) • The heat from compression along with the radiated heat from the initial flame front causes a secondary flame front to develop • This second flame front can propagate at supersonic speeds • This second flame front collides with the first creating extremely high cylinder temperatures (3500 F)and pressures (800 PSI)

  4. Detonation Causes • Excessive compression • Insufficient fuel octane • Carbon deposits

  5. Pre-ignition • Like detonation, pre-ignition causes two flame fronts to propagate and collide causing a dramatic increase in cylinder temperatures and pressure • When the second flame front occurs before the spark plug fires the abnormal combustion is called pre-ignition • Pre-ignition will cause excessive cylinder pressures (1200 PSI) and temperatures (4000 F)

  6. Pre-ignition Causes • Excessive compression – as the temperature of compression approaches 1700 Fahrenheit fuel will spontaneously combust (depending on octane) • Abnormal heat in the cylinder – caused by: • Detonation • Inoperative EGR valve • Faulty cooling system • Faulty intake air temperature control system • Low octane fuel

  7. Pre-ignition Causes • Hot spots • Sharp edge on combustion chamber or piston • Carbon deposits • Too high heat range plug • Overheated valve (insufficient valve margin) • Head gasket fire ring protruding into cylinder • Plug wire crossfiring

  8. Abnormal Combustion Effects

  9. Abnormal Combustion Effects • Piston damage • Cracks in piston head • Cracks in ring lands • Melted piston head (aluminum spattered spark plug) • Micro-melting of ring lands causing stuck rings • Broken rings • Blown head gasket • Spark plug damage • Connecting rod, bearing, and crankshaft damage

  10. Abnormal Combustion Effects

  11. Abnormal Combustion Effects

  12. Abnormal Combustion Effects

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