Gas Exchange Process. Gas Exchange Process. Internal Combustion Engines MAK 493E. Prof.Dr. Cem Soruşbay Istanbul Technical University

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1 Intnal Cmbustin Engins MAK 493E Gas Exchang Pcss Pf.D. Cm Suşbay Istanbul Tchnical Univsity Intnal Cmbustin Engins MAK 493E Gas Exchang Pcss Intductin Valv mchanisms Inductin in ngins Scavnging in -stk ngins Paamts ffcting inductin and scavnging Vlumtic fficincy 1

2 Intductin This sctin dals with fundamntals f gas xchang pcss - intak and xhaust in 4-stk ngins, and scavnging in -stk ngins. Th pupus is t mv th bunt gass at th nd f th pw stk and admit fsh chag f th nxt cycl. Th pw utput f an ngin at a givn spd is pptinal t th mass flw at f ai. Inducting th maximum ai mass at wid-pn thttl full lad is th pimay gal f gas xchang pcss. Gas xchang pcss is chaactizzd by vall paamts lik vlumtic fficincy (4-stk) and scavnging and tapping fficincy (-stk) - ths dpnd n dsign f ngin subsystms lik maniflds, valvs, pts, as wll as ngin pating cnditins. Supchaging and tubchaging a usd t incas ai flw thugh ngins and hnc pw dnsity. Gas Exchang in a Tubchagd Engin

3 Gas Exchang Intductin 3

4 Intductin Intductin 4

5 Intductin Valv Mchanism 5

6 Valv Mchanism Valv Mchanism 6

7 Valv Mchanism Rck am Inlt valv Exhaust valv Push d Cam fllw Camshaft Valv Mchanism 7

8 Valv Mchanism Valv-pating Systms In ngins with vhad pppt valvs, th camshaft is ith muntd in th cylind blck in th cylind had (vhad camshaft - OHC). In OHC ngins, camshaft can b muntd dictly v th valv stms, it can b ffst - ffst valvs a patd by cks and valv clancs can b adjustd by alting pivt hight. Th div is by chain tthd blt. Valv sat insts a usd, spcially f ngins with alluminium ally cylind had t nsu minimum wa - pppt valvs tat t vn ut any wa and t maintain gd sating. Engins with inlt and xhaust valvs nt placd in lin, can us vaius push d mchanisms dubl vhad camshafts (DOHC) - n f inlt valvs and th f xhaust valvs. 8

9 Valv-pating Systms Valv Timing 4-stk ngins p valv timing and p ~ V diagam f gas xchang pcss p p p p a p Ü Ö N 5 (EmA ) 6 (EgK ) 4 1 (EgA ) (EmK ) A Ö N V 4 6 Egzz süpab aç k (Em A ) 5 1 (Em K ) K ank daisi Ü Ö N (EgK ) =0-40 = =5-90 = A Ö N (EgA ) 5 1 Emm süpab aç k 9

10 Inductin IVO inlt valv pning 0-40 (10-5) CA BTDC whn intak valv is clsd, th p bhind th valv is th sum f static and dynamic pssus. Whn th valv is pnd, th pssu p is gat than cylind pssu and gass flw int th cylind. This aly pning dpnds n th gas vlcitis and th gmty f th intak manifld (css sctin aa tc) T b abl t us th pssu wav actin, IV can b pnd up t 5-10 CA ATDC in sm ngins. With th mvmnt f th pistn fm TDC t BDC, p in cylind dps and gnally is lw than th fnc pssu, p O - gas flw is btaind by this pssu diffnc, p Inductin IVC inlt valv clsing 5-90 (40-60) CA ABDC th kintic ngy f th gass pvid th gas flw int cylind - accding t th lvl f th KE, intak valv is kpt pn t allw max amunt f gass int cylind. This dpnds n th ngin spd (.p.m.) - as th ngin spd, n incass, this dlay is incasd. Usually valv pning and clsing is st at ngin dsign, accding t th spcificatins f th ngin (lw spd, mdium spd, high spd tc). Sm mdn ngins hav mchanisms t adjust valv timing duing ngin patin t st th bst valv pning duatin, f bst vlumtic fficincy - Hnda VTEC f xampl. 10

11 B as nç (p) Egzz Süpüm Scavnging in -stk Engins -stk ngins scavnging taks plac at BDC, and pts a usd instad f valvs. (a) 4 k Süp p süp 1,6 5 5' H aci m (V ) 4 5 Ü Ö N A 1,6 5' Scavnging Flw f gass is dn by a scavnging pump which pvids scavnging pssu abv atm. p scav = MPa This pssu incas can b pvidd by vaius pump cnfiguatins. A) Css scavngd B) Lp scavngd C) Uniflw scavngd 11

12 Scavnging A) Cankcas cmpssin B) Rts blw Paamts Effcting Intak and Scavnging Intak and scavnging gas pssu Intak and scavnging gas tmpatu Rsidual gas factin 1

13 Paamts Effcting Intak and Scavnging Intak and scavnging gas pssu Pssu f gass in cylind at BDC is spcifid as p, intak gas pssu scavnging gas pssu - this dpnds n ngin spd, lsss at intak manifld. p p p Wh p is pssu infnt f intak valv and p is th pssu dp duing inductin. p = ( ) p O Pssu Dp at Inductin Bnulli quatin, p 1 v 1 p v 1 v h v gas vlcity at inlt psitin f th valv, [m/s] v gas vlcity at xit psitin f th valv, [m/s] cfficint indicating pssu dp at th valv dnsity f gass nting th cylind, [kg/m 3 ] dnsity f gass in th cylind, [kg/m 3 ] assuming, v = 10-0 m/s and v = m/s incmpssibl gass, 13

14 Pssu Dp at Inductin v In cmpaisn t, is ngligabl, s Bnulli qn bcms, 1 p v 1 v 0 v indicating that th pssu dp is pptinal t gas vlcity squad at th valv, and th cfficint f KE lss. Avag vlcity at th valv can b givn by, v c m A c a m D d D A 4 Sn c m 30 Pssu Dp at Inductin Th pssu dp will thn b, p 1 D d cm 1 S n 4 D d h A pistn sufac aa, [m ] a valv pning, [m ] c m man pistn spd, [m/s] D cylind diamt, [m] d valv diamt, [m] S stk, [m] n ngin spd, [.p.m.] 14

15 Pssu Dp at Inductin Th pssu dp is dictly pptinal t n invsly pptinal t d 4 and d = ( ) D d = 0.4 D f intak valv - singl valv / cylind dubl intak valv / cylind incass th ttal flw aa by 1.5 dubl intak valv, valv mass is ducd, dynamic ffcts a ducd - allws patin at high ngin spds, valv acclatin is ducd with lw valv lift btaining th sam flw aa - liminat valv jumping h max = ( ) d maximum valv lift Multipl Valvs Cnsidabl gain in gmtic valv aa can b btaind by adpting multipl valv cnfiguatins. F a flat cylind ngin with fixd limitatins n gaps btwn valv and cylind b, tw, th and fu valv layuts a shwn in th figu. 15

4-valv layut is pfabl, pviding spac at cnt f ful injct spak plug.

16 Multipl Valvs With qual lift f intak and xhaust valvs, gmtic xhaust valv aa is 80% f intak. 3-valv layut givs incnvnintly lag xhaust valv. 4-valv layut is pfabl, pviding spac at cnt f ful injct spak plug. F sam actual valv lift 4-valv had givs 61% incas f gmtic aa v -valv dsign. 5-valv layut Fai ngin Valv Sat 16

17 Valv Gmty d d 1 d h had diamt inn sat diamt stm diamt sat angl lift a d h 1 cs With incasing, flw aa dcass. Gnally it is 45 O (can b ducd t 30 O ) Incasing sat angl : incass sating pssu, dcasing : ducs cnting accuacy and pducs saling pblms Valv Lift Cuv Valv lift cuv f diffnt cam pfils 17

Vaiabl Valv Timing Vaiabl Valv Timing BMW VANOS : Vaiabl Cam Timing cmbind

systm Adjustmnt mchanism that can mdify th psitin f th intak camshaft vsus

Dubl-VANOS adjustmnt f bth intak and utlt camshafts - cntinuusly vaiabl

18 Vaiabl Valv Timing Vaiabl Valv Timing BMW VANOS : Vaiabl Cam Timing cmbind hydaulic and mchanical camshaft cntl dvic managd by lctnic ngin managmnt systm Adjustmnt mchanism that can mdify th psitin f th intak camshaft vsus th cankshaft - th timing f th intak cam is changd at tw distinct pm pints Dubl-VANOS adjustmnt f bth intak and utlt camshafts - cntinuusly vaiabl thughut th majity f th pm ang intnal xhaust gas -ciculatin, quick waming up 18

19 Vaiabl Valv Timing Vaiabl Valv Timing 19

20 Flw Chaactistics at Inlt Valv Dischag cfficint Flw Chaactistics at Inlt Valv 0

21 Scavnging Pssu - tw-stk ngins Pssu f cylind chag at BDC, p p p s xhaust at high spd ngins, p = MPa Scavnging pssu, f lw spd ngins f high spd ngins p s = MPa p s = MPa Paamts Effcting Intak and Scavnging Intak and scavnging gas tmpatu Tmpatu at th nd f inductin can b btaind fm hat balanc, c m T T c m T c m m T p p p intak gas tmpatu will b, T m T T m m m T wh indics shw, inlt gas, fnc, sidual gas cnditins 1

22 Paamts Effcting Intak and Scavnging Scavnging gas tmpatu will dpnd n th cmpssin pvidd by th scavnging pump, T s p T p s n1 n wh n is th plytpic cfficint ( ) T m T cmpss m T m m T T = K T = K -stk ngins 4-stk ngins Paamts Effcting Intak and Scavnging Rsidual gas factin m m dfins th ati f mass f siduals t th mass f cylind chag at fnc cnditins Mass f siduals is ffctd by tmpatu and pssu f sidual gass, and th cmpssin vlum, V c Incas f cmpssin ati (with th paamts bing cnstant) ducs th amunt f sidual gass

23 Rsidual Gas Factin 4-stk ngins CI ngins = SI ngins = stk ngins uniflw scavngd ngins = css scavngd ngins = cankcas scavngd ngins = Vlumtic Efficincy Vlumtic fficincy is an vall masu f th ffctivnss f an IC ngin and its intak and xhaust systm. It is dfind as th ati f th mass f intak chag t th mass f th sam chag at fnc cnditins. m v m g 4-stk ngins at pint, bginning f inductin Vc p m R T 3

24 Vlumtic Efficincy at pint, nd f inductin V p m R T mass f chag ntd th cylind m v m g 73 p v 1 T m m p T m g m m with T = 73 K and p = 1 ba vlumtic fficincy is ffctd by pssu and tmpatu at th nd f inductin, sidual gas pssu and tmpatu, and cmpssin ati. SI ngins v CI ngins lw spd high spd v v Vlumtic Efficincy -stk ngins at th bginning f cmpssin, at pint 1 ttal gas mass is, m1 m g m m g 1 v m m m m p V pv 1 1 c T T 1 v Vh p T usful vlum is (V 1, V p, V c fm figu) V V V V 1 h c p V1 Vc Vh (1 S') S' a S V V p h a is xhaust pt hight S is stk 4

25 B a s n ç ( p ) Vlumtic Efficincy V 1 V p 4 p sü p p 1 V c V h 1 H a c i m ( V ) v T p p1 p T T 1 1 S' 1 (1 v stk v 4stk S ') Vlumtic Efficincy In -stk ngins, p 1 > p thf vlumtic fficincy can b gat than 1.0 uniflw scavngd ngins v = css scavngd ngins v = cankcas scavngd ngins v =

26 Vlumtic Efficincy Vlumtic fficincy is affctd by th ful, ngin dsign and ngin pating vaiabls, Ful typ, F/A ati, factin f ful vapizd in intak systm and ful hat f vapizatin Mixtu T as influncd by hat tansf Rati f xhaust t inlt manifld pssu Cmpssin ati Engin spd Intak and xhaust manifld and pt dsign Intak and xhaust valv gmty, siz, lift and timing Vlumtic Efficincy Inlt manifld pssu Is ffctd by th dsign f intak manifld and th intak valv. This p is ffctd by th ngin spd - dcass pptinally with n. v n (d/d ak ) 6

27 Vlumtic Efficincy At lw spds, dynamic pssu f th incming gass is lw - s vlumtic fficincy is ducd. At high spds, pssu lss is incasing with th squa f ngin spd (cank shaft vlutin) Man pistn spd can als b usd t indicat th chang v C m [ m /s] Vlumtic Efficincy Intak gas tmpatu Incasing th hat tansf t th incming gass ducs vlumtic fficincy. All paamts that ffct gas T, ffcts vlumtic ff. This is m dminant with Disl ngins - incas in ngin lad chang in changs vlumtic ff. In SI vlumtic ff is ducd with a thttl valv intnsinally f pat lad patins. 7

28 Vlumtic Efficincy Rsidual gas pssu and tmpatu Inc th sidual gas pssu and tmpatu ducs vlumtic fficincy. Inc in adynamic lsss, inc th amunt f siduals (cmbustin pducts fm th pvius cycl) and thi pssu. This ducs th amunt f fsh chag nting th cylind, vl ff. is ducd. Exhaust valvs a small in diamt than inlt valvs - xhaust systm css sctin aa shuld b 0.6 t 0.7 f th inlt systm. Vlumtic Efficincy Cmpssin ati Whn CR is incasd with all th paamts bing kpt cnstant, vlumtic fficincy shuld b ducd thatically. In pactic, incasing CR incass tmpatus - ducs vl ff, and dcass th mass f sidual gass - incass vl ff. S in sm ngins ths tw ffcts cancl ut ach th - th is n appant ffct f CR n vlumtic fficincy. 8

29 Vlumtic Efficincy Scavnging systm In tw-stk ngins, vlumtic ff is influncd by th scavnging pump. Effctiv scavnging can vn incas th vlumtic ff t a valu gat than 1.0 9

Physics 111. Lecture 38 (Walker: ) Phase Change Latent Heat. May 6, The Three Basic Phases of Matter. Solid Liquid Gas

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