Piepaied and Piesenied by:Saad Alamed ioBMEio:]Aiun Kumai ioBMEio:]1nL kINCILL CI IC LNGINLn order to explain how a ic engine works we must first look at the four-stroke cycle.The four stages of the cycle commonly known as: Suction strokeCompression strokeExpansion strokeExhaust stroke5uct|on (charge exchange stroke)n a diesel or petrol injection engine, the piston moves down and air is drawn through the intake valve. n a carburettor petrol engine, the air is mixed with petrol. Compress|on (power stroke)s the piston moves back up, the air or petrol/air mixture is compressed.Lxpans|on (power stroke)n the carburettor or injected petrol engine, the fuel/air mixture is ignited by a spark plug; in the diesel engine, fuel is injected under high pressure and the mixture ignites spontaneously. n either case, the explosion drives the piston downwards.Lxhaust (charge exchange stroke)The exhaust gas is expelled through the exhaust valve when the piston moves up. n a turbocharged engine, the air is pre-compressed before being supplied to the cylinder during the suction stroke. Because it is at a higher pressure, a greater mass of air is held in the combustion chamber, which means that fuel is burned more efficiently. This increases the engine's power output, giving more torque and a higher top speed compared to a normally aspirated engine of the same swept volume, and reduces emissions.nieinal Combusiion Engineue to presence of some constituents in the gasoline used, the rate of oxidation becomes so great that the last portion of the fuel-air mixture gets ignited instantaneously, producing an explosive violence, known as knocking.NCCINGn C engines, the gasoline and air drawn into the cylinder iscompressed by the piston and ignited by an electric spark.s the flame front travels towards feed end of the combustionchamber, rapidly expanding combustion gases, compress the remaining un-burnt fuel ahead of flame front and raise its temperature.f the flame front travels rapidly at optimum speed, the combustion of un-burnt fuel takes place but smoothly. f the flame front travels too slowly, the entire last portion of the fuel-air mixture may get heated up beyond its ignition temp. and undergo instantaneous explosive combustion. This produces thermal shock wave which hits cylinder walls and piston. This result in emitting of characteristic rattling sound called knocking. NCCING MLCnANI5MThe efficiency of power production in spark ignited internal combustion (C) engines is related to the compression ratio (CR). The CR is the ratio of the cylinder volume (V1) at the end of the suction stroke to the volume (V2) at the end of the compression stroke of the piston.This ratio is always greater than one, since V1 being greaterthan V2. Theoretically, the power output and efficiency of an C engine should increase continuously with increase in the CR. The mechanism of the chemical reactions that lead to knocking is not clear. t is believed that chemical reactions that are of importance are cracking and the oxidation of the hydrocarbons.Probably the reactions proceed by a chain reaction.CCMkL55ICN kA1ICt was recognized that the structures of the fuel hydrocarbons determines largely their knocking tendency. The tendency to knock decreases as follows:straight chain paraffins>branched paraffins>olefins>cyclo-alkanes>aromaticThe tendency to knock depends not only on the fuel used but also on the engine design, location of plug, etc., and also upon the running conditions. NCCING 1LNDLNC t increases the fuel consumption. t results in decreased power output. t causes mechanical damage by overheating of the cylinder parts. The driving becomes rather unpleasant. ADVLk5L LIILC15 CI GA5CLINL NCC By a suitable change in engine design. By using critical compression ratio. By using high rating gasoline. By using anti-knocking agents.MINIMI2ING NCCING IN IC LNGINL5 Graham Edger proposed an arbitrary scale, octane rating, in order to express the anti-knock properties of gasoline's. mong alkanes, n-heptane knocks severely, while under identical conditions, 2,2,4-trimethyl pentane (iso-octane) has a high resistance to knocking. For the scale proposed to indicate the anti-knock properties of gasoline, n-heptane was arbitrarily assigned an octane number of zero and iso-octane was arbitrarily assigned a value of 100.CC1ANL NUM8LkBy blending these two hydrocarbons in various proportions, primary reference fuels were prepared. n the same engine under the same set of conditions and the same critical CR, various blends of the n-heptane and iso-octane are burnt and the percentage of iso-octane by volume in blend that knocks under these conditions is the octane number of the gasoline.nvJtocotboo Octooe Nombeteptane 02-Methylheptane 23exane252-Methylhexane441-eptene 60Pentane 621-Pentene 84Butane91Cyclohexane972,2,4-Trimethylpentane (isooctane)100Benzene101Toluene112le compounds wlicl aie mixed wiil C fuels iend io impioveociane numbeiaie called Anii Knocling Compounds.EX: Anii Knocling piopeiiies of gasoline aie incieased by adding"EL"ieiia eilyl lead].ANTIKNOCKING1L1kA L1nL LLADbout 0.5 ml of TEL per liter is added for motor fuel and about1 ml of TEL per liter is generally added for aviation petrol. t is believed that during combustion of gasoline, TEL forms Pb and PbO. These species act as free-radical chain inhibitors and thus curtail the propagation of the explosive chain reaction and thereby minimizing knocking. f TEL alone is used, the species Pb and PbO may get deposited on engine parts and cause mechanical damage.The vapours of Pb and PbO may pollute the air.n order to minimize the air pollution and damage to engine parts, TEL is always used along with ethylene dibromide or ethylene dichloride. The functions of these ethylene derivatives is to convert the less volatile Pb and PbO into more volatile PbBr2 or PbCl2 which escapes into air along with exhaust gases.The suitability of diesel fuel deteremined by its cetane value which is a percentage of hexadecane in a mixture of hexadecane and 2-methyl naphthalene which has sane ignition characteristics as a diesel fuel in the question .CL1ANL NUM8LkThe cetane number of a diesel fuel can be raised by addition of small quantity of certain pre-ignition dopes like ethyl nitrite,isoamyl nitrite,acetone peroxide..etc.CETANE RATINGCetane kat|ng Measure of Lhe lanlLlon delav of Lhe fuel and ablllLv Lo selflanlLeCetane Number 1`(Percentage of Cetane) + 0.15`(Percentage of heptmethynonae))lanlLlon uelav hvslcal uelav + Chemlcal uelavrem|x Combust|on CombusLlon of all fuel LhaL ls alreadv mlxed when combusLlonsLarLs verv hlah raLe of pressure rlseD|ffus|on Combust|on CombusLlon as rlch fuel core mlxes wlLh alrLaLe 8urnlna LvaporaLlon of cvllnder walls eLcLow Cetane NumberLaLe 8urnlna durlna expanslon sLroke dlfflculL sLarLlna whlLe smoken|gh CetanelanlLlon delav Loo shorL more dlffuslon combusLlon wlLh lower cvcle efflclencv lncompleLecombusLlon black smoke- hvslcal uelav 1emperaLure and denslLv of alr ln cvllnder ALomlzaLlon peneLraLlon and shape of ln[ecLlon sprav luel properLles such as volaLlllLv and vlscoslLv whlch affecL sprav characLerlsLlcs 1urbulence whlch lncreases mlxlnaIgnition Delay decreases with:- lncrease ln 1emperaLure Compresslon raLlo lnleL alr Lemp coolanL Lemp load lncorrecL ln[ecLlon Llmlna- lncrease ln ressure lnleL ressure compresslon raLlo- lncrease ln speed 1urbulence decreases phvslcal delav Compresslon 1emp lncreases decreases phvslcal and chemlcal delav- lncrease ln CeLane 8educe Chemlcal delavThe usual diesel engine fuel is diesel oil or gas oil,a fraction obtained 250-320 degree Celsius during the fractional distilation of crude petroleum.This oil,generally,contains 85%carbon and 12% hydrogen.ts calorific value is about 11,000kcal/kg.DIL5LL IULL5gnition quality order among hydrocarbon constituents of a diesel fuel is as follows:n-alkanes>naphthalenes>alkenes>branched alkenes>aromatics.Thus hydrocarbons which arepoor gasoline fuels are quite good diesel fuels.DIL5LL5n|gh 5peed Low 5peedOn a high speed diesel engine,the time lag in getting the droplets heated to ignition point is very brief,about1/500 th of a second.OSuch diesel engines require diesel with cetane numbers in excessof 45(upto 60).OOn the other hand ,low speed diesel requires cetane number of about 25.OCetane number of medium speed diesel is about 35.UNLLADLDL1kCLPetrol wherein the enhancement of octane rating is accomplished without the addition of lead compounds is referred to as unleaded petrol.To improve its octane number, Concentration of high octanecomponents (like isopentane, isooctane, ethylbenzene, isopropyl benzene, etc) is increased by the process of reforming.Compounds like methyl tertiary butylether (MTBE) can also be added to improve octane number of unleaded petrol. MTBE provides oxygen (of ether group) for combustion of petrol in C engines, thereby reducing considerably the formation of peroxy compounds (which causes knocking).The harmful effects of discharge of poisonous lead and its compounds through the exhaust of automobiles is avoided. One of the major advantages of using unleaded petrol is that it permits the attachment of a catalytic converter to the exhaust pipe in automobiles.ADVAN1AGL5 CI UNLLADLD L1kCLCatalytic converter contains rhodium catalyst. t converts the toxic gases such as CO and NO to harmlessCO2 and N2. t also oxidizes hydrocarbons into CO2 and 2O. Leaded petrol cannot be used in automobiles equipped with catalytic converter as the lead present poisons the catalyst thus destroying the active sites.