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Transcript of I.C. ENGINES
I.C. ENGINESLECTURE NO: 09(24 Mar, 2014)
Combustion FormulasCombustion is a chemical reaction in which certain elements of the fuel combined with oxygen causing an increase in temperature of the gasesMain combustion elements areCarbon HydrogenSulphurOxygen is necessary for combustion and chiefly diluted by Nitrogen
CHEMICAL SYMBOLSElement Symbol Atomic MassMolecular Massor CompoundHYDROGENH12CarbonC1224NitrogenN1428OxygenO1632SulphurS3264Combustion FormulasHydrogen HAtomic mass of hydrogen = 1One molecule of hydrogen contains 2 atom of so it is written as H2Since atom of Hydrogen has an atomic mass 1, the molecular mass = 22 H2 means 2 molecules of hydrogen each consisting of 2 atoms Mass would be 2 x 2 = 4Combustion FormulasOxygen OAtomic mass of Oxygen = 16One molecule of contains 2 atom of so it is written as O2Since atom of Oxygen has an atomic mass 16, the molecular mass = 322 O2 means 2 molecules of Oxygen each consisting of 2 atoms Mass would be 2 x 32 = 64Combustion Formulas Water H2 OAtomic mass of hydrogen = 1One molecule of hydrogen contains 2 atom of so it is written as H2H2 O = ( 1 x 2) + ( 16 x 1)= 18Combustion Formulas C8 H18Molecular mass of C8 H18 = (12 x 8) + (1 x 18) = 114C6 H18Molecular mass of C6 H6 = (12 x 6) + (1 x 6) = 78FuelCn H2n+2
Combustion Formulas H2 + O = H2 O Two atom of Hydrogen combined with one atom of Oxygen to form one molecule steam H2 + O2 = H2OTwo atom of Hydrogen combined with one atom of Oxygen to form two molecule water 2H2 + O2 = 2H2O
+ + = =1 V + 1 V + 1 Vol = 3 V mixed= 3 V combinedCombustion Calculation C8 H18Molecular mass of C8 H18 = (12 x 8) + (1 x 18) = 114C6 H18Molecular mass of C6 H6 = (12 x 6) + (1 x 6) = 78FuelCn H2n+2
Combustion CalculationCombustion CalculationAir Required to burn HydrogenAir Required to Burn HydrogenAir Required for complete Combustion of CarbonAir Required to Burn Carbon to Carbon MonoxideAir Required to Burn Carbon Monoxide to Carbon DioxideAir Required to Burn SulphurAir Required to Burn Fuel1 kg of H requires 8 kg O1 kg of C requires 2.66kg O1 kg of S requires 1kg O 1 kg of O is contained in 4.35kg air
Problem No 1A certain petrol consists of 84 % C and 16 % H by mass. What mass of air is required for complete combustion?
Problem No 2A fuel oil contains, by mass, 87 % C, 11 % H, 1 % S and 1 % O. What mass of air is required for complete combustion?
Problem No 3What is mass of air is required to burn complete 1 kg of benzole C6 H6 ?
Problem No 4What is mass of air is required to burn complete 1 kg of ethyl alcohol C6 H6 ?
Determination of Calorific ValueWhen 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 C6 H14 This fuel contain 84 % C and 16 % HHeat liberated by 1 kg C = 33830 kJHeat liberated by 0.84 kg C = 28417 kJ
Determination of Calorific ValueHeat liberated by 1 kg H = 144600 kJHeat liberated by 0.16 kg H = 23136 kJ
Therefore H.C.V. of fuel = 28417+23136 = 51553 kJ/kg
DIESEL FUEL SYSTEMSCABEDPressureVolumeTheoretical Diesel cycle
P V diagram for C.I. Engine / Diesel Cycle EngineDTDCBDCDiesel Cycle
Diesel CycleAt Constant pressure per kg of air
At constant volume per kg of air heat rejected
THE C.I. ENGINES FUEL SYSTEMThe 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.THE C.I. ENGINES FUEL SYSTEMThe fuel system consists basically of a Fuel tankOne or more filtersLow pressure fuel (lift) pumpHigh pressure injection pumpInjector 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.TYPICAL C.I. FUEL SYSTEM LAYOUTFuel TankWaterTrapLift PumpFuelFiltersFuelInjectionPumpFuel InjectorsLeak OffEngine combustionChamberFUEL 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.
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
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
FUEL INJECTORSEach injector is fitted in the cylinder head above each combustion chamberFuel 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 cylindersEach injector sprays atomized fuel in to the combustion chamber to insure complete combustion
COMBUSTION CHAMBERS In the C.I. engine the fuel is injected intothe combustion chamber, it the has to mixthoroughly with the air, ignite and burn all at the same time. To insure this happens, twotypes of combustion chamber have beendeveloped.DirectInjectionIndirect Injection