1. I.C. ENGINES LECTURE NO: 08 (24 Mar, 2014)

2. Combustion Formulas Combustion is a chemical reaction in which certain elements of the fuel combined with oxygen causing an increase in temperature of the gases Main combustion elements are Carbon Hydrogen Sulphur Oxygen is necessary for combustion and chiefly diluted by Nitrogen

3. CHEMICAL SYMBOLS Element Symbol Atomic MassMolecular Mass or Compound HYDROGENH12 CarbonC1224 NitrogenN1428 OxygenO1632 SulphurS3264

4. Combustion Formulas Hydrogen H Atomic mass of hydrogen = 1 One molecule of hydrogen contains 2 atom of so it is written as H 2 Since atom of Hydrogen has an atomic mass 1, the molecular mass = 2 2 H 2 means 2 molecules of hydrogen each consisting of 2 atoms Mass would be 2 x 2 = 4

5. Combustion Formulas Oxygen O Atomic mass of Oxygen = 16 One molecule of contains 2 atom of so it is written as O 2 Since atom of Oxygen has an atomic mass 16, the molecular mass = 32 2 O 2 means 2 molecules of Oxygen each consisting of 2 atoms Mass would be 2 x 32 = 64

6. Combustion Formulas Water H 2 O Atomic mass of hydrogen = 1 One molecule of hydrogen contains 2 atom of so it is written as H 2 H 2 O = ( 1 x 2) + ( 16 x 1) = 18

7. Combustion Formulas C 8 H 18 Molecular mass of C 8 H 18 = (12 x 8) + (1 x 18) = 114 C 6 H 18 Molecular mass of C 6 H 6 = (12 x 6) + (1 x 6) = 78 Fuel C n H 2n+2

8. Combustion Formulas H 2 + O = H 2 O Two atom of Hydrogen combined with one atom of Oxygen to form one molecule steam H 2 + O 2 = H 2 O Two atom of Hydrogen combined with one atom of Oxygen to form two molecule water 2H 2 + O 2 = 2H 2 O + + = = 1 V + 1 V + 1 Vol = 3 V mixed= 3 V combined

9. Combustion Calculation C 8 H 18 Molecular mass of C 8 H 18 = (12 x 8) + (1 x 18) = 114 C 6 H 18 Molecular mass of C 6 H 6 = (12 x 6) + (1 x 6) = 78 Fuel C n H 2n+2

10. Combustion Calculation

12. Air Required to burn Hydrogen

13. Air Required to Burn Hydrogen

14. Air Required for complete Combustion of Carbon

15. Air Required to Burn Carbon to Carbon Monoxide

16. Air Required to Burn Carbon Monoxide to Carbon Dioxide

17. Air Required to Burn Sulphur

18. Air Required to Burn Fuel 1 kg of H requires 8 kg O 1 kg of C requires 2.66kg O 1 kg of S requires 1kg O 1 kg of O is contained in 4.35kg air

19. Problem No 1 A certain petrol consists of 84 % C and 16 % H by mass. What mass of air is required for complete combustion?

20. Problem No 2 A fuel oil contains, by mass, 87 % C, 11 % H, 1 % S and 1 % O. What mass of air is required for complete combustion?

21. Problem No 3 What is mass of air is required to burn complete 1 kg of benzole C 6 H 6 ?

22. Problem No 4 What is mass of air is required to burn complete 1 kg of ethyl alcohol C 6 H 6 ?

23. Determination of Calorific Value When the composition of a fuel is known. This method is not so accurate as burning fuel in a calorimeter, so the answers are only approximate. Hexane C 6 H 14 This fuel contain 84 % C and 16 % H Heat liberated by 1 kg C = 33830 kJ Heat liberated by 0.84 kg C = 28417 kJ

24. Determination of Calorific Value Heat liberated by 1 kg H = 144600 kJ Heat liberated by 0.16 kg H = 23136 kJ Therefore H.C.V. of fuel = 28417+23136 = 51553 kJ/kg

25. DIESEL FUEL SYSTEMS

26. THE C.I. ENGINES FUEL SYSTEM The C.I. engine demands that the fuel supplied is:- –Timed to inject when the piston is near the end of the compression stroke. –The fuel is atomised (broken up) into fine particles if efficient combustion and reduced pollution are to be obtained. –The fuel is forced with sufficient pressure into to the hot air in the combustion engine. –All C.I.engines require some form of cold start device, this is because when the engine is cold, heat loss can result in the heat generated by the compression stroke insufficient to ignite the fuel. To overcome this, most C.I.engine inject addition fuel when cold (excess fuel) and use some form of electrical heating device, to raise the temperature of the air (glow plugs). –If theses demands are not met, the engine will produce excessive noise (combustion knock) and pollution.

27. THE C.I. ENGINES FUEL SYSTEM The fuel system consists basically of a fuel tank, one or more filters, a low pressure fuel (lift) pump, a high pressure injection pump and a injector for each cylinder. Air must not be allowed to get into the fuel injection system, the engine will not run, some systems require bleeding if air is present e.g. when the fuel filter is replaced, or the vehicle runs out of fuel.

28. TYPICAL C.I. FUEL SYSTEM LAYOUT Fuel Tank Water Trap Lift Pump Fuel Filters Fuel Injection Pump Fuel Injectors Leak Off Engine combustion Chamber

29. FUEL LIFT PUMP (LOW PRESSURE) Typically a diaphragm pump driven off of the engine camshaft, or built into the injection pump or electrically driven in later systems May Have manual priming Function is to supply steady flow of fuel to injection pump. May incorporate a strainer filter which requires cleaning at service intervals.

30. MAIN FUEL FILTERS Maybe of replaceable element or cartridge type. Filter material must be of large enough surface area to allow for fuel flow, which will stop very small partials of dirt reaching the injection system Maybe large single units or consist of a ‘primary’ & ‘secondary’ filter. Must be changed at the correct service interval Incorporate the water trap

31. HIGH PRESSURE FUEL INJECTION PUMPS Can be of ‘Rotary’ or ‘In line’ design. Driven by the engine at half crankshaft speed Pressurises the fuel and delivers it to the injections at the correct time for combustion Accurately meters the fuel quantity to match engine load demands Incorporates a governor to control engine speed and prevent the engine over speeding and damaging itself

32. FUEL INJECTORS Each injector is fitted in the cylinder head above each combustion chamber Fuel is delivered to the injectors via thick walled high pressure steel pipes Injector pipes are of equal volume/length to ensure accuracy of timing between cylinders Each injector sprays atomized fuel in to the combustion chamber to insure complete combustion

33. COMBUSTION CHAMBERS In the C.I. engine the fuel is injected into the combustion chamber, it the has to mix thoroughly with the air, ignite and burn all at the same time. To insure this happens, two types of combustion chamber have been developed. DirectInjection Indirect Injection