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

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1 Intnal Cbustin Engins MAK 493E Gas Exchang Pcss Pf.D. C Suşbay Istanbul Tchnical Univsity Intnal Cbustin Engins MAK 493E Gas Exchang Pcss Intductin Valv chaniss Inductin in ngins Scavnging in 2-stk ngins Paats ffcting inductin and scavnging Vlutic fficincy 1

2 Intductin This sctin dals with fundantals f gas xchang pcss - intak and xhaust in 4-stk ngins, and scavnging in 2-stk ngins. Th pupus is t v th bunt gass at th nd f th pw stk and adit fsh chag f th nxt cycl. Th pw utput f an ngin at a givn spd is pptinal t th ass flw at f ai. Inducting th axiu ai ass at wid-pn thttl full lad is th piay gal f gas xchang pcss. Gas xchang pcss is chaactizzd by vall paats lik vlutic fficincy (4-stk) and scavnging and tapping fficincy (2-stk) - ths dpnd n dsign f ngin subsysts lik aniflds, valvs, pts, as wll as ngin pating cnditins. Supchaging and tubchaging a usd t incas ai flw thugh ngins and hnc pw dnsity. Intductin 2

3 Intductin Intductin 3

4 Valv Mchanis Rck a Inlt valv Exhaust valv Push d Ca fllw Cashaft Valv Mchanis 4

5 Valv-pating Systs In ngins with vhad pppt valvs, th cashaft is ith untd in th cylind blck in th cylind had (vhad cashaft -OHC). In OHC ngins, cashaft can b untd dictly v th valv sts, 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 alluiniu ally cylind had t nsu iniu wa - pppt valvs tat t vn ut any wa and t aintain gd sating. Engins with inlt and xhaust valvs nt placd in lin, can us vaius push d chaniss dubl vhad cashafts (DOHC) - n f inlt valvs and th f xhaust valvs. Valv-pating Systs 5

6 Valv Tiing 4-stk ngins p valv tiing and p ~ V diaga f gas xchang pcss Δ p Δ p p p a p ÜÖN 5 (EA) 6 (EgK) 4 1 (EgA) (EK) AÖN V 4 6 Egzz süpab aç k (EA) 5 1 (EK) Kank daisi ÜÖN (EgK) α=0-40 α= α=5-90 α= AÖN (EgA) 5 1 E süpab aç k Inductin IVO inlt valv pning 0-40 (10-25) CA BTDC whn intak valv is clsd, th p bhind th valv is th su f static and dynaic 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 gty f th intak anifld (css sctin aa tc) T b abl t us th pssu wav actin, IV can b pnd up t 5-10 CA ATDC in s ngins. With th vnt f th pistn f 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, Δp 6

7 Süpü 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 ax aunt f gass int cylind. This dpnds n th ngin spd (.p..) - 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, diu spd, high spd tc). S dn ngins hav chaniss t adjust valv tiing duing ngin patin t st th bst valv pning duatin, f bst vlutic fficincy - Hnda VTEC f xapl. Scavnging in 2-stk Engins 2-stk ngins scavnging taks plac at BDC, and pts a usd instad f valvs. (a) 4 Bas nç (p) p süp 1,6 k 5 5' Süp Haci (V) 4 5 ÜÖN A Egzz 1,6 5' 7

8 Scavnging Flw f gass is dn by a scavnging pup which pvids scavnging pssu abv at. p scav = MPa This pssu incas can b pvidd by vaius pup cnfiguatins. A) Css scavngd B) Lp scavngd C) Uniflw scavngd Scavnging A) Cankcas cpssin B) Rts blw 8

9 Paats Effcting Intak and Scavnging Intak and scavnging gas pssu Intak and scavnging gas tpatu Rsidual gas factin Paats 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 anifld. p = p Δp Wh p is pssu infnt f intak valv and Δp is th pssu dp duing inductin. p = ( ) p O 9

10 Pssu Dp at Inductin Bnulli quatin, p ρ v = p + ρv + ρ ζ v h v gas vlcity at inlt psitin f th valv, [/s] v gas vlcity at xit psitin f th valv, [/s] ζ cfficint indicating pssu dp at th valv ρ dnsity f gass nting th cylind, [kg/ 3 ] ρ dnsity f gass in th cylind, [kg/ 3 ] assuing, v = /s and v = /s incpssibl gass, ρ = ρ Pssu Dp at Inductin 2 2 In cpaisn t, v is ngligabl, s 2 = 0 v Bnulli qn bcs, 1 2 ( 1 ) Δ p = ρ v +ζ 2 indicating that th pssu dp is pptinal t gas vlcity squad at th valv, and th cfficint f KE lss. v Avag vlcity at th valv can b givn by, v c A a = c D d 2 D A = π 4 2 Sn c = 30 10

11 Pssu Dp at Inductin Th pssu dp will thn b, Δ p 1 D 1 ρ + 2 d D 900 d ( 1+ ζ ) c = ρ( 1 ζ ) S n 4 h A pistn sufac aa, [ 2 ] a valv pning, [ 2 ] c an pistn spd, [/s] D cylind diat, [] d valv diat, [] S stk, [] n ngin spd, [.p..] Pssu Dp at Inductin Th pssu dp is dictly pptinal t n 2 and invsly pptinal t d 4 d = ( ) D f intak valv - singl valv / cylind d = 0.4 D dubl intak valv / cylind incass th ttal flw aa by 1.25 dubl intak valv, valv ass is ducd, dynaic ffcts a ducd - allws patin at high ngin spds, valv acclatin is ducd with lw valv lift btaining th sa flw aa - liinat valv juping h ax = ( ) d axiu valv lift 11

12 Multipl Valvs Cnsidabl gain in gtic valv aa can b btaind by adpting ultipl valv cnfiguatins. F a flat cylind ngin with fixd liitatins n gaps btwn valv and cylind b, tw, th and fu valv layuts a shwn in th figu. Multipl Valvs With qual lift f intak and xhaust valvs, gtic 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 sa actual valv lift 4-valv had givs 61% incas f gtic aa v 2-valv dsign. 12

13 Valv Gty d d 1 d 2 α h had diat inn sat diat st diat sat angl lift a = πd 1 hcsα With incasing α, flw aa dcass. Gnally it is 45 O (can b ducd t 30 O ) Inc sat angl inc sating pssu, dc ducs cnting accuacy and pducs saling pbls Valv Lift Cuv Valv lift cuv f diffnt ca pfils 13

14 Flw Chaactistics at Inlt Valv Dischag cfficint Flw Chaactistics at Inlt Valv 14

15 Scavnging Pssu - tw-stk ngins Pssu f cylind chag at BDC, p = ps + p 2 xhaust at high spd ngins, p = MPa Scavnging pssu, f lw spd ngins p s = MPa f high spd ngins p s = MPa Paats Effcting Intak and Scavnging Intak and scavnging gas tpatu tpatu at th nd f inductin can b btaind f hat balanc, p ( T + ΔT ) + ϕc p T = c p ( ) T c + intak gas tpatu will b, T = ( T + ΔT ) + + ϕ T wh indics, and shw th inlt gas, fnc and sidual gas cnditins 15

16 Paats Effcting Intak and Scavnging Scavnging gas tpatu will dpnd n th cpssin pvidd by th scavnging pup, T s p = T p s n 1 n wh n is th plytpic cfficint ( ) T = ( T + ΔT ) cpss + + T T = K T = K 2-stk ngins 4-stk ngins Paats Effcting Intak and Scavnging Rsidual gas factin γ = dfins th ati f ass f siduals t th ass f cylind chag at fnc cnditins Mass f siduals is ffctd by tpatu and pssu f sidual gass, and th cpssin vlu, V c Incas f cpssin ati (with th paats bing cnstant) ducs th aunt f sidual gass 16

17 Rsidual Gas Factin 4-stk ngins CI ngins γ = SI ngins γ = stk ngins uniflw scavngd ngins γ = css scavngd ngins γ = cankcas scavngd ngins γ = Vlutic Efficincy Vlutic fficincy is an vall asu f th ffctivnss f an IC ngin and its intak and xhaust syst. It is dfind as th ati f th ass f intak chag t th ass f th sa chag at fnc cnditins. ηv = g 4-stk ngins at pint, bginning f inductin Vc p = R T 17

18 Vlutic Efficincy at pint, nd f inductin V p = R T ass f chag ntd th cylind η v = g = 273 p p η = v ε 1 T T g = with T = 273 K and p = 1 ba vlutic fficincy is ffctd by pssu and tpatu at th nd f inductin, sidual gas pssu and tpatu, and cpssin ati. SI ngins η v = CI ngins lw spd η = high spd = v η v Vlutic Efficincy 2-stk ngins at th bginning f cpssin, at pint 1 ttal gas ass is, 1 = g + η g 1 v = = p V pv 1 1 c T T 1 η v = Vh p T usful vlu is (V 1, V p, V c f figu) V = V + V V 1 h c p V1 = V + V (1 S') c h a V S ' = = S V p h a is xhaust pt hight S is stk 18

19 Vlutic Efficincy V 1 V p 4 Bas nç (p) p süp p 1 V c V h 1 Haci (V) η = v T p p1 p T1 T 1 S' ε 1 ηv 2stk ηv 4stk(1 S') = Vlutic Efficincy In 2-stk ngins, p 1 > p thf vlutic fficincy can b gat than 1.0 uniflw scavngd ngins η v = css scavngd ngins η v = cankcas scavngd ngins η v =

20 Vlutic Efficincy Vlutic fficincy is affctd by th ful, ngin dsign and ngin pating vaiabls, Ful typ, F/A ati, factin f ful vapizd in intak syst and ful hat f vapizatin Mixtu T as influncd by hat tansf Rati f xhaust t inlt anifld pssu Cpssin ati Engin spd Intak and xhaust anifld and pt dsign Intak and xhaust valv gty, siz, lift and tiing Vlutic Efficincy Inlt anifld pssu Is ffctd by th dsign f intak anifld and th intak valv. This p is ffctd by th ngin spd - dcass pptinally with n 2. η v n (d/dak) 20

21 Vlutic Efficincy At lw spds, dynaic pssu f th incing gass is lw - s vlutic 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 η v C [/s] Vlutic Efficincy Intak gas tpatu Inc th hat tansf t th incing gass ducs vlutic fficincy. All paats that ffct gas T, ffcts vlutic ff. This is dinant with Disl ngins - incas in ngin lad chang in λ changs vlutic ff. In SI vlutic ff is ducd with a thttl valv intnsinally f pat lad patins. 21

22 Vlutic Efficincy Rsidual gas pssu and tpatu Inc th sidual gas pssu and tpatu ducs vlutic fficincy. Inc in adynaic lsss, inc th aunt f siduals (cbustin pducts f th pvius cycl) and thi pssu. This ducs th aunt f fsh chag nting th cylind, vl ff. is ducd. Exhaust valvs a sall in diat than inlt valvs - xhaust syst css sctin aa shuld b 0.6 t 0.7 f th inlt syst. Vlutic Efficincy Cpssin ati Whn CR is incasd with all th paats bing kpt cnstant, vlutic fficincy shuld b ducd thatically. In pactic, incasing CR incass tpatus - ducs vl ff, and dcass th ass f sidual gass - inc vl ff. S in s ngins ths tw ffcts cancl ut ach th - th is n appant ffct f CR n vlutic fficincy. 22

23 Vlutic Efficincy Scavnging syst In tw-stk ngins, vlutic ff is influncd by th scavnging pup. Effctiv scavnging can vn incas th vlutic ff t a valu gat than