Knocking , cetane and octane numer

Octane number shows the ability of a fuel to resist knock (pre-ignition of the fuel) in the Gasoline Engine that needs high compression ratios. the Cetane number is a measure of ignition delay. Higher the cetane number of fuel the shorter the ignition delay, the least time it takes to burn.

1. Chemistry Group Activity: Group Members Anurag Kumar - 20BCE11012 Anant Dubey - 20BCE11037 Vinay Gupta - 20BCE11053 Aviral Srivastava - 20BCE11027 Tanesh Parsavdiya - 20BCE10998

2. Knock Fund a mentals ‘limitations and issues’

3. Definit i ons Knock is metallic sound caused by spontaneous ignition of end gas. Occurs during compression stroke mostly in SI engine and expansion stroke in CI engines Results in pressure fluctuations in cylinder and increases temperature Surface ignition is caused due to hot spots in chamber Overheated valve, spark plug, glowing combustion chamber deposits Pre-ignition and post-ignition

4. Definitions contd… Acceleration knock produces more sound but can not cause damage due to short duration Constant speed knock can cause drastic damage pre-ignition Runway knock

5. Origin of knock Auto ignition of end gas, depends strongly on chemical composition of end- gas mixture. If the flame burns all the fresh gas before auto-ignition in the end-gas can occur then knock is avoided. Knock is a potential problem when the burn time is long. Theory of auto-ignition fuel oxidization occurs during compression of A/F mixture Theory of detonation advancing flame velocity to consume end gas is much higher

6. Limiting parameters for knocks end-gas temperature time available before flame arrival Compression ratio Spark timing Engine speed Delay period Inlet pressure and temperature, coolant temperature, fuel/air ratio

7. Fuel factor and knock scale for SI engines Octane number ON is measure of resistance to knocking. Normal heptane (n-C7H16) has an octane value of zero and isooctane (C8H18) has a value of 100. The higher the octane number, the higher the resistance to knock. Blends of these two hydrocarbons define the knock resistance of intermediate octane numbers: e.g., a blend of 10% n-heptane and 90% isooctane has an octane number of 90.

8. Fuel factor and knock scale for CI engines Ignition quality of a fuel cetane number CN. For h i gh cetane fuels i g n i tion de l ay is short so very l ittle f uel is injected before autoignition . Cetane (n-hexadecane, C 16 H 34 ) has a value of 100. In the original procedures  - methylnaphtalene (C 11 H 10 ) with a cetane number of zero represented the bottom of the scale. This has since been replaced by heptamethylnonane , (HMN) has a cetane number of 15, which is a more stable compound. The higher the CN the better the ignition quality, i.e., shorter ignition delay. The cetane number is given by: CN = (% hexadecane) + 0.15 (% HMN)

9. Knock measurement [sensors] Optical probes and Ionization detectors can be used Piezoelectric pressure transducer is used mostly Generate a voltage when vibration is applied to them utilizing the piezoelectric effect and it is proportional to the acceleration Due to the vibration, a counter weight inside the sensor is applying pressure on the piezo element, this pressure creates an electric charge in the piezo element which is the output signal of the sensor.

10. Knock damages Piston ring sticking breakage Cylinder head gasket Cylinder head erosion Piston crown erosion Piston melting and holing

11. Provide adequate cooling to the engine Use intercooler on turbo-charged engines Use high octane and cetane gasoline and diesel Anti-knock gasoline additives Fuel enrichment under severe condition Use knock sensor to control spark retard so as to operate close to engine knock limit Fast combustion system Gasoline direct injection Knock control strategies

12. FUELS & CETANE NO

13. FUELS Each substance which gives energy after burning is called fuel. Fuels are classification by sources; Natural Artificial Fuels are classification by phases; Solid – coal, wood etc. Liquid – petroleum products, alcohol, biofuel etc. Gas – methane, buthane , hydrogen, biogas etc.

14. Generally Liquid fuels are preferential Energy per gram is too high Fast conversion of chemical energy to thermal energy Easy mix with oxygen No ash after combustion Easy transport and storage Every liquid substance which provides the sufficient thermal energy can be used as a fuel for internal combustion engines.

15. CETANE NO . Cetane number (diesel fuel) and octane number (gasoline) both measure the tendency of the fuel to ignite spontaneously. The cetane number refers to the ea s e with which desel fuel ignites easily at a relatively low temperature.

16. Fuel Research Octane Number (ROM) Motor Octane Number (MON) Cetane number Boiling point (ºC) Gasoline 92-98 80-90 0-5 37-205 Diesel -25 - 45-55 140-360 Methanol 106 92 5 65 Ethanol 107 89 5 79 Propane (LPG) 112 97 -2 -42.15 Methane (CNG) 120 120 -161.6 Octane and Cetane number of fuel

17. CE T ANE NUMBE R S Higher cetane related with: improved combustion improved cold starting reduced noise, white smoke, HC, CO and particulate emissions.

18. Cetane Rating Indicates the cold starting ability of diesel fuel Most automakers recommend a cetane rating of about 45 High cetane rating means the fuel will ignite easily from heat and pressure and burn quickly

19. Cetane Rating

20. Fuel Ignition Quality The ignition characteristics of the fuel affect the ignition delay. The ignition quality of a fuel is defined by its cetane number. For low cetane fuels For high cetane fuels 

21. Key points for Cetane Number

22. OCTANE NUMBER

23. I N T R O D U C TION It’s a standard measure of the performance of an engine. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). This number can be counted by representing with a mixture of 2,2,4-trimethylpentane ( iso - octane)which has high resistance from early ignition and n-heptane which have fast detonation. For example 90 octane means that the fuel has the same knocking characteristics as a mixture of 90% iso -octane and 10% n-heptane. The fist scientist who made that definition and put the standards was Marker Russell.

24. WHY DO WE CARE ABOUT OCTANE NO. ? octane ratings measure a fuel's ability to resist the spontaneous ignition. So the higher octane rating means that your car will burn slower. In addition that every single engine has a specific octane number and when it use a lower number the engine can be damaged for a short term.

25. OCTANE RATING METHOD RON Method MON Method OCTANE ENGINE SYSTEM

26. OCTANE RATING METHOD Research Octane Number (RON) is most commonly used octane number and it is determined by burning the fuel in a test engine under controlled conditions and variable compression ratios. Then the results are compared with mixtures of iso -octane and heptane. Motor Octane Number (MON) testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed (900 RPM instead of 600 RPM used for RON, Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON.

27. Octane number and suitable engine When fuel is exposed to high temperature or pressure, automatic ignition may occur. the higher the octane number of the fuel, the higher the temperature and pressure at which automatic ignition occurs. rising the octane number increases the efficiency of engine against pressing fuel.

28. IMPROVING OCTANE NUMBER How to improve it decreas i ng factors

29. Decreasing Factors Octane number decreases when increasing carbon chain length. Normal Paraffin have low Octane number as the molecular weight increases. Some impurities such as lead and sulfur can decrease the Octane rate.

30. How to improve it. o There is an improving and reforming unit in every refinery processing company and its mission is to improve the quality of the product (specially fuel products). By putting some additives into the fuel which discourage auto ignition such as : Aromatics, organometals and oxygenates. By some treating and reforming processes that changes the properties of the fuel like: catalytic reforming, cracking, isomiration and alkylation.

31. Key points for Octane Number

32. LATEST UPDATES

33. Octane boosters Octane booster can be added to the fuel in the car and it has the ability to improve the fuel and increase its Octane number. These octane boosters use anti-knock additives which, when added to the fuel, prevent the onset of knock (detonation or pre-ignition). By preventing the knock, the effective octane of the fuel is raised.

34. SHELL V-POWER Shell's Friction Modification Technology, or lube, helps the engine turn more freely. Less friction means less wasted energy and more power from the fuel can be transmitted to the wheels. Also, whereas ordinary unleaded fuels have a research octane number of 95 RON, V-Power Nitro+ is rated at 99 RON. Shell says it'll work in anything, old or new. It can help maintain the performance levels of a new car and help restore lost performance to older motors.

35. REFE R ENCES  http://www.richardwheeler.net/  http://www.automotive.com/ .  "Octane Explanation" . runyard.org .  http://www.fuelexpert.co.za/  https://recombu.com  http://www.shell.us/motorist/shell-fuels.html

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