1. INTERNAL COMBUSTION ENGINES LECTURER PROF.Dr. DEMIR BAYKA

2. ABNORMAL COMBUSTION KNOCK (AUTOIGNITION) SURFACE IGNITION

3. KNOCK (AUTOIGNITION) * KNOCK OCCURS AFTER SPARK IGNITION * KNOCK OCCURS IN UNBURNED MIXTURE

4. DEFINITION END GAS

5. COMBUSTION BEGINS IN THE END GAS ZONE r T p T FLAME FRONT

6. ignition During flame travelincreases

7. r T -W -Q p T For the REACTANTS

8. r T -W -Q p T -ve

9. r T -W -Q p T -ve

10. r T -W -Q p T -ve +ve ATDC

11. -ve +ve ATDC 1. Sinceis -ve increasing it will lower Tr 2. Since is -veincreases Tr therefore increasingdecreases Tr

12. IGNITION LAG WHEN PRELIMINARY REACTIONS BEGIN CHAIN CARRIERS BUILD UP TO CRITICAL VALUE REACTION RATE SUDDENLY INCREASES

13. IGNITION LAG IS THE TIME THAT PASSES FROM THE INSTANT WHEN UNTIL CONCENTRATION OF CHAIN CARRIERS REACHES THE CRITICAL LEVEL

14. IGNITION LAG VARIOUS EMPIRICAL RELATIONS

15. IGNITION LAG VARIOUS EMPIRICAL RELATIONS

18. FACTORS AFFECTING KNOCK 1. OPERATIONAL FACTORS 2. FUEL FACTORS 3. DESIGN FACTORS

19. FACTORS AFFECTING KNOCK OPERATIONAL FACTORS 1. IGNITION TIMING 2. ENGINE COOLING 3. EQUIVALANCE RATIO 4. ENGINE SPEED AND TORQUE

20. FUEL FACTORS 1. PARAFFINS n-paraffinsi-paraffins SINGLE - BONDED OPEN CHAIN STRUCTURE SATURATED

21. 1. PARAFFINS n-paraffinsi-paraffins example OCTANE H-C-C-C-C-C-C-C-C-H H H H H

22. 1. PARAFFINS example ISO-OCTANE -C-C-C-C-C- C C C THE NEW STRUCTURE IS BY THERMAL CRACKING

23. 1. PARAFFINS example ISO-OCTANE -C-C-C-C-C- C C C THIS STRUCTURE IS MORE RESISTANT TO SELF IGNITION

24. CYCLANES SINGLE BOND RING TYPE STRUCTURE UNSATURATED

25. OLEFINS ONE DOUBLE BOND OPEN CHAIN STRUCTURE UNSATURATED

26. ACETYLENES * ONE CARBON CARBON TRIPLE BOND * OPEN CHAIN STRUCTURE * UNSATURATED

27. AROMATICS * RING TYPE STRUCTURE * BENZENE HAS 3 DOUBLE BONDS C CC C C C

28. ADDITIVES * TetraEthylLead ---------------> TEL * TetraMethylLead ---------------> TML * MethylCycloPentaDienyl Manganese Tricarbonyl ------> MMT * Methyl and Ethyl Alcohols * TertiaryButyl Alcohol ---------> TBA * MethylTertiaryButylEther --> MTBE

30. OCTANE NUMBER OF GASOLINE OCTANE NUMBER (O.N.) IS THE MEASURE OF A FUEL’S RESISTANCE TO KNOCK 2 STAR (NORMAL) FUEL : 91 O.N. 4 STAR (SUPER) FUEL : 96 O.N.

31. OCTANE NUMBER OF GASOLINE IS DETERMINED BY COMPARING IT WITH A REFERENCE FUEL. THE REFERENCE FUEL IS PREPARED BY MIXING ISO-OCTANE n-HEPTANE

32. ISO-OCTANE IS ARBITRARILY ASSIGNED AN OCTANE NUMBER OF 100. n-HEPTANE IS ARBITRARILY ASSIGNED AN OCTANE NUMBER OF 0. ISO-OCTANE HAS BRANCHED STRUCTURE & n-HEPTANE HAS CHAIN STRUCTURE

33. THE OCTANE NUMBER OF THE REFERENCE FUEL IS ARBITRARILY DEFINED AS THE PERCENTAGE OF ISO-OCTANE (volume base) IN THE MIXTURE

34. GASOLINE AND REFERENCE FUEL ARE COMPARED ON A SPECIAL ENGINE

35. KNOCK SENSOR COMPRESSION RATIO CAN BE VARIED DURING OPERATION. KNOCKMETER READINGS FOR REFERENCE FUELS AND GASOLINE ARE COMPARED

36. DEPENDING ON TEST CONDITIONS RESEARCH O.N.-----> (RON) MOTOR O.N. -----> (MON) CAN BE FOUND. ROAD O.N. = a(RON) + b(MON) + c

37. DESIGN FACTORS 1. COMPRESSION RATIO 2. COMBUSTION CHAMBER SHAPE AND POSITIONING OF SPARK PLUG AND VALVES 3. COOLING OF ‘END GAS’ ZONES

38. SUMMARY 1. HIGHER COMPRESSION RATIO ENGINES NEED TO USE HIGHER OCTANE NUMBER FUELS 2. FOR A GIVEN ENGINE AND FUEL IGNITION TIMING IS IMPORTANT 3. AT HIGH LOADS HIGHER ENGINE SPEEDS WILL REDUCE KNOCK TENDENCY

39. ABNORMAL COMBUSTION KNOCK (AUTOIGNITION) SURFACE IGNITION

40. SURFACE IGNITION PRE IGNITION CAUSED BY SPARK PLUGS EXHAUST VALVES EDGES OF HEAD CAVITIES OR PISTON BOWL POST IGNITION AFTER THE SPARK