2.ic engine nov.dec-2013

7/23/2019 2.ic engine Nov.Dec-2013

http://slidepdf.com/reader/full/2ic-engine-novdec-2013 1/18

Question Paper Code: 31555

B.E./B.Tech. DEGREE EXA!"AT!#"$ "#%EBER/DECEBER &'13

Ei(hth )e*ester

echanica+ En(ineerin(E &',1/E -' AD%A"CED !.C. E"G!"E)

0Re(u+ation &''-

PART A 01' 2 & &' *ar4s

1. Why do we require rich mixture during idling?2. List the various factors that influence the flame speed in SI engine comustion.

!. "efine cetane numer scale.

#. What are the advantages of turo charging?$. What is green house effect?

%. "efine conversion efficiency of a catalyst.

&. What are the commonly used alternate fuels?'. What are the advantages of hydrogen as a fuel?

(. "efine charge stratification.

1). What is the function of charge amplifier?

PART B 05 2 1 -' *ar4s

11. *a+ *i+ With a neat s,etch- discuss riefly a simple caruretor.

*ii+ "escrie in detail the phenomenon of ,noc, in SI engines.*+ four / cylinder SI automotive engine of displacement volume 2.# liter operate at

wide open throttle *W0+. he engine speed is !))) rpm and the compression ratio

is (1. he mechanical efficiency and the stro,e / to ore ratio are respectively- '$3and 1.)2. Isooctane is used as a fuel with an air4fuel ratio of 1$. he fuel has a

calorific value of ## 567,g and the comustion efficiency is 1))3. t the eginning

of the compression stro,e- the conditions inside the cylinder are 1 ar and $$ )8. If

the exhaust residual left over from the previous cycle is #3 perform a complete

thermodynamics analysis of this engine. ssume the engine operates on a four 0tto

cycle.

12. *a+ What are the various factors that affect the delay period in 8I engine comustion?

"iscuss.

*+ 9xplain riefly the open comustion chamers and :icardo swirl chamer used in

8I engines.

1!. *a+ *i+ "iscuss riefly the ;8- 80 and <0 pollutant formation mechanisms in a SI engine

*ii+ With a simple s,etch- explain riefly the wor,ing principle of a particulate trap.



*+ What are the various types of instruments used for the measurement of emissions

from I8 engines? With a schematic diagram- descrie in detail the

chemiluminescence method of measuring oxides of nitrogen.

1#. *a+ *i+ ;ow does ethanol is manufactured from grains and sugarcane? 9xplain.

*ii+ 8ompare the properties of alcohol and gasoline as engine fuels.*+ *i+What are the advantages and disadvantages of hydrogen as an engine fuel?

*ii+ "iscuss riefly a hydrogen engine with a neat s,etch.

1$. *a+ write short notes on the following

i. Surface ignition engine

ii. 8ommon rail "I diesel engine.

*+ 9xplain riefly the electronic engine management system used in modern engines.



1. write short notes on the following

i. Surface ignition engine

8ommon rail "I diesel engine

)ur6ace i(nition en(ine

Surface ignition engine (Hot bulb engine)The initiation of a ame in the combustion chamber of anautomobile engine by any hotsurface other than the spark discharge. The hot bulb engine, or hot bulb or heavy oil engine is a type of internalcombustion engine. It is an engine in which fuel is ignited by being broughtintocontact with a red-hot metal surface inside a bulb followed by theintroduction of air (oxygen) compressed into the hot bulb chamber by the rising piston. There issome ignition when the fuel is introduced but it quicly uses up the availableoxygen in the bulb. !igorous ignition taes place only when su"cient oxygenissupplied to the hot bulb chamber on the compression stroe of the engine.#ost hot bulb engines were produced as one-cylinder low-speed two-stroecrancase scavenging units.Operation and working cycle The hot-bulb engine shares its basic layout with nearly all other internalcombustion engines, in that it has a piston, inside a cylinder, connected to a$ywheel via a connecting rod and cranshaft. The $ow of gases through the

engineis controlled by valves in four-stroe engines, and by the piston covering anduncovering ports in the cylinder wall in two-stroes. The type of blow-lampusedto start the %ot &ulb engine.In the hot-bulb engine combustion taes place in a separated combustionchamber,the 'vaporier' (also called the 'hot bulb'), usually mounted on the cylinderhead, into which fuel is sprayed. It is connected to the cylinder by a narrowpassage and is heated by the combustion while running an external $amesuch as

a blow-lamp or slow-burning wic is used for starting (on later modelssometimeselectric heating or pyrotechnics was used). *nother method is the inclusionof aspar plug and vibrator coil ignition.+citation needed The engine could bestartedon petrol and switched over to oil after it had warmed to runningtemperature.



The pre-heating time depends on the engine design, the type of heatingused andthe ambient temperature, but generally ranges from / minutes (for mostenginesin a temperate climate) to as much as half an hour (if operating in extreme

coldor the engine is especially large). The engine is then turned over, usually byhand but sometimes by compressed air or an electric motor.

0nce the engine is running, the heat of compression and ignition maintainsthehot-bulb at the necessary temperature and the blow-lamp or other heatsource canbe removed. 1rom this point the engine requires no external heat andrequires onlya supply of air, fuel oil and lubricating oil to run. %owever, under low powerthebulb could cool o2 too much, and a throttle can cut down the cold fresh airsupply. *lso, as the engine3s load increased, so does the temperature of thebulb,

causing the ignition period to advance to counteract pre-ignition, water isdrippedinto the air intae. 4qually, if the load on the engine is low, combustiontemperatures may not be su"cient to maintain the temperature of the hot-bulb.#any hot-bulb engines cannot be run o2-load without auxiliary heating forthisreason.



Co**on rai+ D! diese+ en(ine

Common ail !irect "n#ection !iesel $ngine

Common rail direct fuel in#ection is a modern %ariant of direct fuel

in#ection system for petrol and diesel engines.

• * diesel fuel in5ection system employing a common pressure

accumulator,called the rail, which is mounted along the engine bloc.

• The rail is fed by a high pressure fuel pump. The in5ectors, which are fedfrom the common rail, are activated by solenoid valves.

• The solenoid valves and the fuel pump are electronically controlled. In the

common rail in5ection system the in5ection pressure is independent fromengine speed and load. Therefore, the in5ection parameters can be freelycontrolled.

• 6sually a pilot in5ection is introduced, which allows for reductions in enginenoise and 70x emissions. This system operates at 8,/99 psi (:;99&*<).

• The in5ectors use a needle-and seat-type valve to control fuel $ow and fuel

pressure is fed to both the top and bottom of the needle valve.

• &y bleeding some of the pressure o2 the top, the pressure on the bottom

will push the needle o2 its seat and fuel will $ow through the nole holes.

1. 07 E2p+ain 7rie6+8 the e+ectronic en(ine *ana(e*ent s8ste* used in *odern

en(ines.

$lectronic $ngine &anagement*n engine control unit (4=6), most commonly called the powertrain controlmodule (>=#), is a type of electronic control unit that controls a series of



actuators on an internal combustion engine to ensure the optimum running.It doesthis by reading values from a multitude of sensors within the engine bay,interpreting the data using multidimensional performance maps (called ?oo-up

tables), and ad5usting the engine actuators accordingly.$ngine management Sensors O'ygen sensor The oxygen sensor provides information about the fuel mixture. The >=#uses thisto constantly re-ad5ust and @ne tune the airAfuel ratio. This eeps emissionsandfuel consumption to a minimum. * bad 0 sensor will typically mae anenginerun rich, use more fuel and pollute. 0 sensors deteriorate with age and maybecontaminated if the engine burns oil or develops a coolant lea.

Coolant sensor The coolant sensor monitors engine temperature. The >=# uses thisinformation toregulate a wide variety of ignition, fuel and emission control functions. Bhenthe

engine is cold, for example, the fuel mixture needs to be richer to improvedrivability. 0nce the engine reaches a certain temperature, the >=# startsusingthe signal from the 0 sensor to vary the fuel mixture. This is called 'closedloop' operation, and it is necessary to eep emissions to a minimum.Throttle position sensor (TS) The throttle position sensor (T>C) eeps the >=# informed about throttleposition.



The >=# uses this input to change spar timing and the fuel mixture asengineload changes. * problem here can cause a $at spot during acceleration (lieabad accelerator pump in a carburetor) as well as other drivability complaints.

irow Sensor The *ir$ow Censor, of which there are several types, tells the >=# how muchairthe engine is drawing in as it runs. The >=# uses this to further vary the fuelmixture as needed. There are several types of air$ow sensors including hotwiremass air$ow sensors and the older $ap-style vane air$ow sensors. *ll areveryexpensive to replace&anifold absolute pressure (&) The manifold absolute pressure (#*>) sensor measures intae vacuum,

which the>=# also uses to determine engine load. The #*> sensor3s input a2ectsignitiontiming primarily, but also fuel delivery.*nock sensorsDnoc sensors are used to detect vibrations produced by detonation. Bhenthe>=# receives a signal from the noc sensor, it momentarily retards timingwhilethe engine is under load to protect the engine against spar noc.$+ position sensor

The 4E< position sensor tells the >=# when the exhaust gas recirculation(4E<)valve opens (and how much). This allows the >=# to detect problems withthe4E< system that would increase pollution.



,ehicle speed sensor (,SS) The vehicle speed sensor (!CC) eeps the >=# informed about how fast thevehicle is traveling. This is needed to control other functions such as torqueconverter locup. The !CC signal is also used by other control modules,includingthe antiloc brae system (*&C).Crankshaft position sensor The cranshaft position sensor serves the same function as the picupassembly inan engine with a distributor. It does two thingsF It monitors engine rpm andhelps

the computer determine relative position of the cranshaft so the >=# cancontrolspar timing and fuel delivery in the proper sequence. The >=# also uses thecran sensor3s input to regulate idle speed, which it does by sending a signaltoan idle speed control motor or idle air bypass motor. 0n some engines, anadditional camshaft position sensor is used to provide additional input to the>=#



about valve timing.

1!.*a+ *i+ "iscuss riefly the ;8- 80 and <0 pollutant formation mechanisms in a SI engine

&echanism of -O formation The nitric oxide formation during the combustion process is the result of

group of elementary reaction involving the nitrogen and oxygen molecules.Gi2erentmechanism proposed is discussed below.a. Simple reaction between -/ and O/

7 H 0 70 This mechanism proposed by 4yat and Euibet predicts 70 concentrationsmuch lower that those measured in I.= engines. *ccording to thismechanism, theformation process is too slow for 70 to reach equilibrium at peatemperatures andpressures in the cylinders.

b. 0eldo%ich Chai eaction mechanism0 0 ------------- (:)0 H 770 H 7 ------ ()

7 H 070 H 0 ------ ()

The chain reactions are initiated by the equation () by the atomic oxygen,formed in equation (:) from the dissociation of oxygen molecules at the hightemperatures reached in the combustion process. 0xygen atoms react withnitrogenmolecules and produces 70 and nitrogen atoms. In the equation () thenitrogenatoms react with oxygen molecule to form nitric oxide and atomic oxygen.

*ccording to this mechanism nitrogen atoms do not start the chain reactionbecause their equilibrium concentration during the combustion process isrelativelylow compared to that of atomic oxygen. 4xperiments have shown thatequilibriumconcentrations of both oxygen atoms and nitric oxide molecules increasewithtemperature and with leaning of mixtures. It has also been observed that 70formed at the maximum cycle temperature does not decompose even duringtheexpansion stroe when the gas temperature decreases.

In general it can be expected that higher temperature would promote theformation of 70 by speeding the formation reactions. *mple 0 supplieswould alsoincrease the formation of 70. The 70 levels would be low in fuel richoperations,i.e. *A1 :/, since there is little 0 left to react with 7 after the hydrocarbonshad reacted. The maximum 70 levels are formed with *1< about :9 percent above



stoichiometric. #ore air than this reduces the pea temperature, sinceexcess airmust be heated from energy released during combustion and the 70concentrationfall o2 even with additional oxygen.

#easurements taen on 70 concentrations at the exhaust valve indicate thatthe concentration rises to a pea and then fall as the combustion gasesexhaustfrom the cylinder. This is consistent with the idea that 70 is formed in thebulgases. The @rst gas exhausted is that near the exhaust valve followed by thebulgases. The last gases out should be those from near the cylinder wall andshould

exhibit lower temperatures and lower 70 concentration.

Hydrocarbons formation

%ydrocarbon exhaust emission may arise from three sources asa. Ball quenchingb. Incomplete combustion of chargec. 4xhaust scavenging in -stroe enginesIn an automotive type J-stroe cycle engine, wall quenching is thepredominantsource of exhaust hydrocarbon under most operating conditions.a. 1all 2uenching The quenching of $ame near the combustion chamber walls is nown as wallquenching. This is a combustion phenomenon which arises when the $ametries to

propagate in the vicinity of a wall. 7ormally the e2ect of the wall is a slowingdown or stopping of the reaction.&ecause of the cooling, there is a cold one next to the cooled combustionchamber walls. This region is called the quench one. &ecause of the lowtemperature, the fuel-air mixture fails to burn and remains unburned.Gue to this, the exhaust gas shows a mared variation in %= emission. The @rst gas that exits is from near the valve and is relatively cool. Gue tothis itis rich in %=. The next part of gas that comes is from the hot combustionchamber and hence a low %= concentration. The last part of the gas thatexits is

scrapped o2 the cool cylinder wall and is relatively cool. Therefore it is alsorichin %= emission.b. "ncomplete combustion6nder operating conditions, where mixtures are extremely rich or lean, orexhaust gas dilution is excessive, incomplete $ame propagation occursduringcombustion and results in incomplete combustion of the charge.



7ormally, the carburetor supplies air fuel mixture in the combustible range. Thus incomplete combustion usually results from high exhaust gas dilutionarisingfrom high vacuum operation such as idle or deceleration. %owever duringtransient operation, especially during warm up and

deceleration it is possible that sometimes too rich or too lean mixture entersthecombustion chamber resulting in very high %= emission.1actors which promote incomplete $ame propagation and mis@re includeFa. >oor condition of the ignition system, including spar plugb. ?ow charge temperaturec. >oor charge homogeneityd. Too rich or lean mixture in the cylindere. ?arge exhaust residual quantityf. >oor distribution of residuals with cylinder=arburetion and mixture preparation, evaporation and mixing in the intae

manifold,atomiation at the intae valve and swirl and turbulence in the combustionchamberare some factors which in$uence gaseous mixture ration and degree ofchargehomogeneity including residual mixing. The engine and intae system temperature resulting from prior operation oftheengine a2ect charge temperature and can also a2ect fuel distribution.!alve overlap, engine speed, spar timing, compression ratio, intae andexhaust

system bac pressure a2ect the amount and composition of exhaustresidual. 1uel

volatility of the fuel is also one of the main reasons.

Carbon mono'ide 3ormation co=arbon monoxide remains in the exhaust if the oxidation of =0 to =0 isnot complete. This is because carbon monoxide is an intermediate product inthecombustion process. Eenerally this is due to lac of su"cient oxygen. Theemission levels of =0 from gasoline engine are highly dependent on *A1ratio. The amount of =0 released reduces as the mixture is made leaner. The

reason that the =0 concentration does not drop to ero when the mixture ischemically correct and leaner arises from a combination of cycle to cycle andcylinder to cylinder mal distribution and slow =0 reaction inetics. &ettercarburetionand fuel distribution are ey to low =0 emission in addition to operating the

engine at increased air-fuel ratio.



1!*a+ ii.With a simple s,etch- explain riefly the wor,ing principle of a particulate trap.

!iesel particulate 4lter (articulate Trap)* diesel particulate @lter (or G>1) is a device designed to remove dieselparticulate matter or soot from the exhaust gas of a diesel engine. Ball-$owdieselparticulate @lters usually remove K/L or more of the soot and under certainconditions can attain soot removal e"ciencies of close to :99L. Come @ltersaresingle-use, intended for disposal and replacement once full of accumulatedash.

0thers are designed to burn o2 the accumulated particulate either passivelythroughthe use of a catalyst or by active means such as a fuel burner which heatsthe@lter to soot combustion temperatures engine programming to run when the@lter isfull in a manner that elevates exhaust temperature or produces high

amounts

0f 70x to oxidie the accumulated ash, or through other methods. This isnown

as '@lter regeneration'. =leaning is also required as part of periodicmaintenance,and it must be done carefully to avoid damaging the @lter. 1ailure of fuelin5ectorsor turbochargers resulting in contamination of the @lter with raw diesel orengine oilcan also necessitate cleaning.



1!. *+ What are the various types of instruments used for the measurement of emissions from I8

engines? With a schematic diagram- descrie in detail the chemiluminescence method of

measuring oxides of nitrogen.

Three way catalytic con%erter* catalytic converter is a vehicle emissions control device which converts

toxic by-products of combustion in the exhaust of an internal combustionengine toless toxic substances by way of catalysed chemical reactions. The speci@creactionsvary with the type of catalyst installed. #ost present-day vehicles that run ongasoline are @tted with a Mthree way‛ converter, so named because itconverts thethree main pollutants in automobile exhaustF carbon monoxide, unburnedhydrocarbonand oxides of nitrogen

* three way catalyst is a mixture of platinum and rhodium. It acts on allthree of the regulated pollutants (%=, =0 and 70x) but only when the air-fuel ratio isprecisely controlled. If the engine is operated with the ideal or stoichiometricairfuelratio of :J.8F:. The three way catalyst is very e2ective. It strips oxygen awayfrom the 70x to form harmless water, carbon dioxide and nitrogen. %owevertheair-fuel ratio must be precisely controlled, otherwise the three way catalystdoes

not wor.!iesel particulate 4lter (articulate Trap)* diesel particulate @lter (or G>1) is a device designed to remove dieselparticulate matter or soot from the exhaust gas of a diesel engine. Ball-$owdieselparticulate @lters usually remove K/L or more of the soot and under certainconditions can attain soot removal e"ciencies of close to :99L. Come @ltersare



single-use, intended for disposal and replacement once full of accumulatedash.0thers are designed to burn o2 the accumulated particulate either passivelythroughthe use of a catalyst or by active means such as a fuel burner which heats

the@lter to soot combustion temperatures engine programming to run when the@lter isfull in a manner that elevates exhaust temperature or produces high

amounts

0f 70x to oxidie the accumulated ash, or through other methods. This isnownas '@lter regeneration'. =leaning is also required as part of periodicmaintenance,and it must be done carefully to avoid damaging the @lter. 1ailure of fuelin5ectors

or turbochargers resulting in contamination of the @lter with raw diesel orengine oilcan also necessitate cleaning.

-ondispersi%e infrared sensor (Carbon mono o'ide)* nondispersive infrared sensor (or 7GI<) sensor is a simple spectroscopicdeviceoften used as gas detector. It is called nondispersive because wavelengthwhichpasses through the sampling chamber is not pre-@ltered instead a @lter isusedbefore the detector.



3lame ioni5ation detector (Hydro Carbon) The operation of the 1IG is based on the detection of ions formed duringcombustion of organic compounds in a hydrogen $ame. The generation of

theseions is proportional to the concentration of organic species in the sample gasstream. %ydrocarbons generally have molar response factors that are equaltonumber of carbon atoms in their molecule, while oxygenates and otherspecies thatcontain heteroatoms tend to have a lower response factor. =arbon monoxideandcarbon dioxide are not detectable by 1IG.

In order to detect these ions, two electrodes are used to provide a potentialdi2erence. The positive electrode doubles as the nole head where the$ame isproduced. The other, negative electrode is positioned above the $ame. Bhen@rst



designed, the negative electrode was either tear-drop shaped or angularpiece of platinum. Today, the design has been modi@ed into a tubular electrode,commonlyreferred to as a collector plate. The ions thus are attracted to the collector

plateand upon hitting the plate, induce a current. This current is measured with ahigh-impedancepicoammeter and fed into an integrator. The manner inwhich the@nal data is displayed is based on the computer and software. In general, agraphis displayed that has time on the x-axis and total ion on the y-axis. The current measured corresponds roughly to the proportion of reducedcarbonatoms in the $ame. Cpeci@cally how the ions are produced is not necessarilyunderstood, but the response of the detector is determined by the number of

carbon atoms (ions) hitting the detector per unit time. This maes thedetectorsensitive to the mass rather than the concentration, which is useful becausetheresponse of the detector is not greatly a2ected by changes in the carrier gas$ow rate.

!etector (-O' measurement)=hemiluminescence (sometimes 'chemoluminescence') is the emission oflight(luminescence), as the result of a chemical reaction. There may also belimited

emission of heat. Eiven reactants * and &, with an excited intermediate ◊,+* H +& → +◊ → +>roducts H light1or example, if +* is luminol and +& is hydrogen peroxide in the presence ofasuitable catalyst we haveF?uminol H %0 → -*>* +◊ → -*>* H lightBhereFBhere -*>* is -aminophthalate-*>* +◊ is the vibronic excited state $uorescing as it decays to a lowerenergylevel.



0ne of the oldest nown chemoluminescent reactions is that of elementalwhite

phosphorus oxidiing in moist air, producing a green glow. This is a gas-phasereaction of phosphorus vapour, above the solid, with oxygen producing theexcitedstates (>0) and %>0.*nother gas phase reaction is the basis of nitric oxide detection incommercialanalytic instruments applied to environmental air-quality testing. 0one iscombinedwith nitric oxide to form nitrogen dioxide in an activated state.70H0 → 70 +◊ H 0

The activated 70 +◊ luminesces broadband visible to infrared light as itrevertsto a lower energy state. * photomultiplier and associated electronics countsthephotons that are proportional to the amount of 70 present. To determine theamount of nitrogen dioxide, 70, in a sample (containing no 70) it must @rstbeconverted to nitric oxide, 70, by passing the sample through a converterbeforethe above oone activation reaction is applied. The oone reaction producesa

photon count proportional to 70 that is proportional to 70 before it wasconverted to 70. In the case of a mixed sample that contains both 70 and70,the above reaction yields the amount of 70 and 70 combined in the airsample,assuming that the sample is passed through the converter. If the mixedsample is



not passed through the converter, the oone reaction produces activated70+◊only in proportion to the 70 in the sample. The 70 in the sample is notactivated by the oone reaction. Though unactivated 70 is present with theactivated 70 +◊, photons are emitted only by the activated species that is

proportional to original 70. 1inal stepF Cubtract 70 from (70 H 70) to yield70.

2.ic engine nov.dec-2013

Documents