UNIT I- CONSTRUCTION AND OPERATION Constructional details of spark ignition (SI) and compression ignition (CI) engines. Working principles. principles. Two stroke stroke SI and CI engines engines – constructio construction n and working. working. Comparison of SI and CI engines and four stroke and two stroke engines. Engine classication, ring order. order. tto, diesel and dual c!cles.
FUNDAMENTALS OF ENGINE CONSTRUCTION AND OPERATION " #eat engine is a mac#ine, w#ic# con$erts #eat energ! into mec#anical energ!. T#e com%ustion of fuel suc# as coal, petrol, and diesel generates #eat. T#is #eat is supplied to a working su%stance at #ig# temperature. &! t#e e'pansion of t#is su%stance in suita%le mac#ines, #eat energ! is con$erted into useful work. eat engines can %e furt#er di$ided into two t!pes ( i) (ii)
E'ternal com%ustion and Internal com%ustion.
In a steam engine t#e com%ustion of fuel takes place outside t#e engine and t#e steam t#us formed is used to run t#e engine. T#us, it is known as e'ternal com%ustion engine. In t#e case of internal com%ustion engine, t#e com%ustion of fuel takes place inside t#e engine c!linder itself. itself.
Engine Components T#is section descri%es t#e ma*or components of t#e engine compression s!st s!stem. em. T#e T#e compr compres essi sion on s!st s!stem em cont contai ains ns t#e t#e part parts s t#at t#at de$e de$elo lop p engin engine e compression and allow t#e #eat energ! in t#e %urning air+fuel mi'ture to %ecome Cross-section of a diesel engine mec#anical energ!.
Engine %lock. istons. -ings. Connecting rods. Cranks#aft. C!linder #eads. al$es and related components al$e train. armonic %alancers. &alance s#afts..
M.Hari Prasat!Depar Prasat!Department tment o" A#tomo$i%e Engineeri Engineering ng SSM Institute of Engineering and Technology, Dindigul.
"lt#oug# t#e e'act design and num%er of engine components $aries wit# t#e t!pe of engine and num%er of c!linders, t#e %asic components and t#eir functions are t#e same as descri%ed #ere.
&. Engine '%o() T#e engine %lock is t#e %asic support and attac#ing point for all ot#er engine parts. Engine %locks are made %! pouring molten cast iron, steel, or aluminium into molds,. "fter t#e metal cools, t#e molding sand is was#ed out and t#e %lock is mac#ined to allow ot#er parts to %e installed or attac#ed. T#e ma*or parts installed in or on t#e %lock are t#e pistons, cranks#aft, cams#aft, c!linder #eads, and manifolds.
*. Pistons an+ Rings istons transfer t#e force of e'panding com%ustion gases to t#e connecting rods. T#e! are made of aluminium to reduce weig#t. /ost automoti$e pistons #a$e two compression rings and one oil ring, as s#own in 0igure. Compression rings seal in t#e pressure created during t#e compression and power strokes. If t#is pressure is allowed to leak out, t#e engine will not start or will #a$e se$ere power and dri$ea%ilit! pro%lems. T#e compression rings are installed at t#e top of t#e piston. " lm of oil %etween t#e compression ring and c!linder wall seals pressure in t#e c!linder. T#is oil lm is onl! a%out .1123 (.1145 mm) t#ick, %ut if it is remo$ed, t#e engine will not de$elop enoug# compression to start.
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
T#e oil+control ring is installed %elow t#e compression rings to pre$ent e'cessi$e oil consumption. 6uring t#e piston7s intake stroke, $acuum in t#e c!linder tries to pull oil from t#e c!linder wall. To reduce oil loss, t#e oil+control ring scrapes most of t#e oil from t#e c!linder wall w#en t#e piston is mo$ing down in t#e c!linder. " small amount of oil passes %! t#e oil+control ring to seal t#e compression rings against t#e c!linder wall.
,. Conne(ting Ro+s an+ Cran)sa"t T#e connecting rods are forged steel rods t#at connect t#e piston to t#e cranks#aft. T#e! transfer t#e force from t#e piston to t#e cranks#aft. Eac# connecting rod is connected to a piston %! a piston pin. T#e rod is attac#ed to t#e cranks#aft %! a %earing cap and %earing inserts t#at surround t#e cranks#aft *ournal. T#e piston pin and cranks#aft %earings allow t#e rod to mo$e in relation to %ot# t#e piston and cranks#aft.
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
T#e cranks#aft con$erts t#e straig#t+line force from t#e piston and connecting rod into rotar! force. It is attac#ed to t#e engine %lock %! %earing caps and %earings t#at surround t#e cranks#aft *ournal8 T#is design allows t#e cranks#aft to rotate inside of t#e %earings wit# minimal friction. T#e %earing caps are #eld to t#e engine %lock %! two, four, or si' %olts tor3ued to specications.
. C%in+er Hea+s T#e c!linder #ead contains t#e com%ustion c#am%er for eac# c!linder and forms t#e top of t#e c!linder. C!linder #eads contain t#e intake and e'#aust $al$es and, in some cases, t#e cams#aft and lifters. T#e! also contain oil galleries, coolant passages, and openings to allow t#e 9ow of intake and e'#aust gases. C!linder #eads are made from eit#er cast iron or aluminium. " s#eet metal, cast aluminium, or plastic $al$e co$er is installed o$er t#e upper $al$e train components. Coolant passages %etween t#e c!linder #eads and engine %lock must %e sealed to pre$ent coolant leakage. "lso, t#e pressure of e'panding com%ustion gases must %e contained wit#in t#e c!linder. ead gaskets are used %etween t#e #ead and engine %lock for t#ese purposes. T#e! are t#in and made from steel, copper, and %ers. T#e c!linder #ead and #ead gasket are secured to t#e %lock wit# #ead %olts. T#ese must %e tor3ued to specications. " few engines #a$e studs and nuts, rat#er t#an #ead %olts.
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
/. C%in+er T#e c!linder of an IC engine constitutes t#e %asic and supporting portion of t#e engine power unit. Its ma*or function is to pro$ide space in w#ic# t#e piston can operate to draw in t#e fuel mi'ture or air (depending upon spark ignition or compression ignition), compress it, allow it to e'pand and t#us generate power. T#e c!linder is usuall! made of #ig#+grade cast iron. In some cases, to gi$e greater strengt# and wear resistance wit# less weig#t, c#romium, nickel and mol!%denum are added to t#e cast iron.
/. 0a%1es an+ Re%ate+ Components ne or more intake $al$es are used to control t#e 9ow of t#e air into eac# c!linder. ne or more e'#aust $al$es are used to control t#e 9ow of e'#aust gases out of eac# c!linder. al$es also seal t#e c!linder during t#e compression and power strokes. T#e! are occasionall! called mus#room $al$es due to t#eir resem%lance to a mus#room. Intake and e'#aust $al$es are identical in s#ape, %ut intake $al$es are usuall! larger. pening and closing of t#e $al$es are controlled %! t#e $al$e train. T#e $al$e spring #olds t#e $al$e against its seat, keeping it closed. al$e springs are alwa!s slig#tl! compressed w#en installed. T#is ensures t#at t#e $al$e closes tig#tl!. T#e spring is #eld to t#e $al$e %! $al$e spring retainers. T#e retainer is a cap w#ic# co$ers t#e spring. " locking de$ice, usuall! called a split keeper, locks t#e cap to t#e $al$e stem. " $al$e and spring assem%l! is s#own in 0igure. T#e assem%l! is #eld toget#er %! t#e pressure of $al$e spring acting against t#e c!linder #ead. T#e $al$e stem slides up and down in a $al$e guide. T#e guide ma! %e integral to t#e c!linder #ead or a remo$a%le insert. It keeps t#e $al$e stead! and pro$ides a smoot# surface on w#ic# t#e stem can slide. T#e oil seal at t#e top of eac# $al$e stem pre$ents engine oil from entering t#e com%ustion c#am%er. Wit#out a seal, oil would %e pulled from
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
t#e c!linder #ead, %etween t#e $al$e stem and guide, and into t#e com%ustion c#am%er. T#e $al$e seal ma! %e an um%rella t!pe or an +ring installed %etween t#e $al$e stem and $al$e retainer. W#en t#e $al$e is in contact wit# its seat, #eat is transferred from t#e $al$e to t#e c!linder #ead. T#is transfer is most critical for e'#aust $al$es, since t#e! a%sor% more #eat of com%ustion. If t#e #eat is not transferred to t#e #ead, t#e $al$e ma! melt. Some $al$es are lled wit# metallic sodium to furt#er aid in #eat transfer. T#e intake $al$es are cooled %! t#e incoming air and are not as prone to damage. T#e $al$e+to+seat contact is controlled %! t#e $al$e clearance.
al$e clearance is t#e amount of looseness in t#e $al$e train %etween t#e cams#aft and $al$e stem. al$e clearance can sometimes %e ad*usted. al$e clearance #as more e:ect on $al$e life t#an on engine performance.
0a%1e Train T#e $al$e train is t#e group of components t#at control t#e opening and closing of t#e $al$es. al$e train operation is similar in %ot# o$er#ead cams#aft and cam+in+%lock engines. T#e engine cranks#aft turns cams#aft $ia a c#ain, %elt, or gear set. T#e cams#aft controls t#e distance t#e $al$es open and t#e duration of time o$er w#ic# t#e! are open. T#ere is one cams#aft lo%e for eac# $al$e. In a cam+in+%lock engine, t#e cams#aft lo%es pus# on $al$e lifters installed into %ores mac#ined into t#e %lock. T#e motion is transferred t#roug# pus# rods and rocker arms to t#e $al$es. T#e $al$e spring pressure is o$ercome and t#e
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
$al$es are forced open. T#e $al$e remains open until t#e cams#aft lo%e allows t#e $al$e spring to reseat t#e $al$e. n o$er#ead cams#aft engines, t#e cam lo%es usuall! pus# directl! on t#e $al$e rocker arm.
Valve Timing T#e $al$es must open and close in proper relation to t#e mo$ement of t#e piston or t#e engine will not run. T#is relations#ip is called $al$e timing, not to %e confused wit# ignition timing. al$e timing is determined %! t#e relati$e positions of t#e cranks#aft and cams#aft. T#e intake $al$e must also open wide enoug# and long enoug# to allow t#e air+fuel mi'ture to get into t#e c!linder. T#e e'#aust $al$e must do t#e same to allow t#e e'#aust gases to get out of t#e c!linder. ;ift is #ow wide t#e $al$e opens. 6uration is t#e amount of time t#at t#e $al$e sta!s open. $erlap is t#e amount of time t#at %ot# intake and e'#aust $al$es are open. ;ift and duration are determined %! t#e s#ape of t#e cams#aft lo%es. al$e timing, lift, and duration #a$e a %ig e:ect on engine dri$ea%ilit!. T#e cranks#aft alwa!s turns two complete re$olutions for e$er! one re$olution of t#e cams#aft. T#is is %ecause an! c!linder in a four+stroke c!cle engine, w#et#er gasoline or diesel, re3uires two complete re$olutions of t#e cranks#aft to complete all four c!cles. owe$er, eac# $al$e in t#e engine opens onl! once during all four strokes. To accomplis# t#is, t#e dri$ing gear on t#e cranks#aft alwa!s #as #alf t#e num%er of teet# as t#e dri$en gear on t#e cams#aft.
Push Rods and Rocker Arms us# rods are used onl! on cam+in+%lock engines. T#e! transmit t#e lifter motion to t#e rocker arm. /an! pus# rods are #ollow. il from t#e lifter 9ows t#roug# t#em to lu%ricate t#e rest of t#e $al$e train. -ocker arms are pi$oting le$ers t#at con$ert t#e upward mo$ement of t#e pus# rod or lifter into downward mo$ement of t#e $al$e. n o$er#ead cam engines, t#e cams#aft is installed on top of t#e c!linder #ead. It opens t#e $al$es from a%o$e. In some o$er#ead cam engines, t#e lifter is placed %etween t#e cam lo%e and t#e rocker arm. In man! cases, t#e rocker arm is directl! operated %! t#e cams#aft. " #!draulic las# ad*uster, similar in operation to a #!draulic lifter, maintains t#e proper $al$e clearance
2. 0i$ration Damper W#en t#e engine c!linders re, force is transmitted to t#e cranks#aft. W#en it recei$es t#is force, part of t#e cranks#aft tends to rotate %efore t#e rest of t#e
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
cranks#aft. T#is causes a twisting of t#e cranks#aft. W#en t#e force is remo$ed, t#e partiall! twisted s#aft unwinds. T#is unwinding action, alt#oug# minute, causes w#at is known as torsional $i%ration. To stop t#e $i%ration, a $i%ration damper, sometimes called a #armonic %alancer, is attac#ed to t#e front of t#e cranks#aft. It consists of two #ea$! rings connected %! ru%%er plugs, spring+ loaded friction discs, or a com%ination of t#e two. W#en a c!linder res and t#e cranks#aft speeds up, t#e outer ring of t#e damper #as a tendenc! not to rotate. "s a result, t#e ru%%er connecting t#e two rings of t#e damper 9e'es. "s t#e cranks#aft tries to unwind after t#e c!linder #as red, t#e outer ring of t#e damper again tends not to rotate in t#e opposite direction and t#e ru%%er 9e'es. T#e unwinding force of t#e cranks#aft is cancelled out %! t#e damper. n some newer engines, t#e cranks#aft pulle! is an integral part of t#e %alancer. T#e engine 9!w#eel also a%sor%s $i%ration. T#e 9!w#eel used wit# manual transmissions is #ea$! and a%sor%s $i%ration. "utomatic transmission 9!w#eels are lig#tweig#t steel stampings. T#e tor3ue con$erter a%sor%s most of t#e $i%ration.
3. 'a%an(e Sa"ts In some engines, one or more %alance s#afts are added to counter%alance $ertical and torsional $i%rations. " %alance s#aft #as o:set weig#ts t#at rotate in t#e opposite direction of t#e cranks#aft. T#ese s#afts are eit#er turned %! t#e cams#aft t#roug# direct gearing or %! t#e cranks#aft t#roug# a %elt or c#ain. &alance s#afts #elp to pro$ide a smoot#er idle and less $i%ration from t#e engine.
FOUR-STRO4E C5CLE ENGINE OPERATION ne power c!cle in an automoti$e engine is a four+stroke process, w#ic# is w#! t#ese engines are known as four+stroke c!cle engines. T#e piston mo$es up twice in t#e c!linder and down twice in t#e c!linder for eac# power+producing c!cle. T#is re3uires two re$olutions of t#e cranks#aft.
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
T#e downward mo$ement of t#e piston on t#e intake stroke draws t#e air+ fuel mi'ture into t#e c!linder t#roug# t#e intake $al$e(s). W#en t#e piston reac#es t#e %ottom of t#e intake stroke, t#e intake $al$es are closed. T#e piston t#en mo$es up in t#e c!linder, compressing t#e air+fuel mi'ture. T#is is called t#e compression stroke. W#en t#e air+fuel mi'ture in t#e c!linder is ignited, t#e %urning fuel and o'!gen produce #eat. T#e #eat causes t#e gases in t#e c!linder to e'pand, forcing t#e piston down under pressure. T#is is called t#e power stroke. T#e downward motion of t#e piston is transferred to t#e connecting rod, w#ic# in turn pus#es on t#e cranks#aft. T#e connecting rod and cranks#aft arrangement c#anges t#e linear piston mo$ement into rotation of t#e cranks#aft. T#is rotational mo$ement is used to mo$e t#e $e#icle. W#en t#e piston reac#es t#e %ottom of t#e power stroke, t#e e'#aust $al$e is open. T#e e'#aust stroke t#en %egins as t#e piston mo$es up t#e c!linder, pus#ing t#e e'#aust gases out of t#e open e'#aust $al$e. ne c!cle is now complete. T#e c!cle t#en repeats.
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
M.Hari Prasat!Department o" A#tomo$i%e Engineering SSM Institute of Engineering and Technology, Dindigul.
