Qua trinh binh thaiih hda khi frong dpng CO diesel budng chay thdng nhat, ddi hdi cao doi vdi chit lupng phun, dd dam bao sy xe toi tia nhien lieu khi dupc phun vao budng chay, ngay [r]
Trang 1NGHIEN cufu - TRAO DCI
\ / A N H HU'dNG CUA CAU TRUC CHUM TIA PHUN NHIEN LIEU SINH HOC DEN QUA TRJNH HJNH THANH
H6N Hgp CHAY TRONG DONG CO DIESEL
THE INFLUENCE OF STRUCTURE OF ENGINE SPRAYS OF BIOFUEL
IN THE PROCESS OF COMBUSTION MIXTURE FORMATION IN
DIESEL ENGINE
Mai Diic Nghia, Nguydn Ngoc Canh, Nguyen Cong Minh
Khoa Ky thuat Hang khdng, Trudng ST quan Khdng quan
TOM T A T
Tinh chdt hoa, ly cUa nhien lieu sinh hgc co khdc so v&i ddu diesel O ciing thong so phun, goc non ciia tia phun nhien lieu sinh hgc nho han ddu diesel, chieu ddi phdn rd do xuyen sdu chiim tia vd nhiet do nhiin lieu sinh hgc l&n han so v&i thong so chum tia phun ddu diesel nen dnh hu&ng den qud trinh hinh thdnh hon hop chdy Vi vdy cdn xdc dmh thong sdphun hgp ly cUa he thong phun nhien lieu dgng ca diesel khi chuyen sang su dung nhiin lieu sinh hgc
Tii khoa: Nhien lieu sinh hgc, dgng ca diesel, thongsophun dgxuyensdu, chieu ddi phdn rd
ABSTRACT
Characteristic of chemical and physical ofbiofuel is different with diesel fuel At the same fuel injection parameter, spray cone angle ofbiofuel is smaller, break up length, spray tip penetration and tempreature ofbiofuel is greater than diesel oil that are effect in the process of combustion mixture formation in diesel engine So that, must determined of the optimal injection parameters of diesel engine's fiiel injection system when using biofuels
Keywords: Biofuel diesel engine, injection parameters, spray tip penetration, brack up length
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Trang 2I.MODAU
Hien nay, nhu ciu sii dung nhien lieu
gdc dau md cho ddng ca ddt frong tang manh,
dSn den phat sinh nhidu vin dd anh hudng xau
ddn mdi tiirang Trudc thyc frang frdn, ddi hdi
cac nha san suat nhien lieu, chd tgo dpng ca va
nguoi su dung tim ra bidn phap giam thidu d
nhidm khi xa Nhien lieu sinh hpc cd ngudn gdc
tft dau thuc vat va ma ddng vat, ngoai chuc nang
nhu mpt phu gia, tang cudng oxy cho qua trmh
chay, than thidn voi mdi trucmg con la ngudn
nhien lieu co thd tai sinh Dau thyc vat nguyen
gdc khdng cin tdng hap thanh Biodiesel ma pha
true tidp vao diu diesel, cd gia nhidt, dimg lam
nhidn hdu cho dpng co diesel [1] Tuy nhien, do
tinh chat hda, ly co khac so vdi diu diesel, nen
hdn hpp tao thanh khi sft dyng, se cd khdi lupng
rieng, dp nhat dpng hoc, thay ddi so vdi diu
diesel Cac yeu td nay lam cau true tia phun thay
doi gom: Chidu dai phan ra tia phun, dp xuydn
sau tia phun va goc non chiun tia phun; Dan ddn
qua trinh hinh thanh hdn hpp chay khac nhau
Vi vay, he thdng phun nhien lieu can
dupc dieu chinh, dd tao dupc qua trinh hinh
thanh hdn hop chay hieu qua nhit
2 NOI DUNG NGHIEN CUtJ
cac Id phun la ca chd phan ra chinh, su phan
ra tiep theo tao thanh nhiing gipt cd kich thudc nhd hon, dupe gpi la phan ra thft cap, gay ra do lyc khi dpng tao bdi van tdc tucmg ddi gifta cac gipt va khi bao quanh Cac luc khi ddng can frd chuydn ddng cua nhiing gipt nhd, nhiing gipt d ldp bidn tia phun chiu luc kdo mgnh nhit va di chuydn chgm han cac gipt phia frong Vi ly do nay, cac gipt nhd d bien lidn tuc dupc thay the bang nhftng gipt mdi va dp xuyen sau cua tia phun tang ldn (hmh 1) [4], Nhiing gipt co ddng nang thap dupc day ra ngoai va hinh thanh cac khu vuc ngoai bidn
Nhin chung, mdt hinh ndn phun (gdc non 9) tao ra hdn hpp cang xa mieng phun cang loang do sy van ddng cua khdng khi Hinh dgng tia nhien lieu va tdc dd van ddng ciia nd cd vai fro quan frpng ddn qiia trinh tgo hdn hpp va chay nhidn lieu Tia nhidn lieu phai xuydn qua khdng khi nen den nhung phan xa nhit cua budng chay nhung khdng dupe bam ldn thanh xy lanh va dinh piston, de franh viec chay khdng hoan toan
va tgo thanh mudi than frong qiia trinh cdng tac Bing thyc nghiem, nhieu cong trinh da xac dinh dupc sy anh hudng ciia hang loat cae yeu td ddn cau tnic tia phun nhien lieu nhu: Ap suat phun, dudng kinh Id phun, khdi lupng ridng cua nhien lieu, dp nhdt ddng hpc, ddi ap mdi trudng [6]
2.1 C4u true va sir phan r3 tia phun nhien lidu
Qua trinh binh thaiih hda khi frong dpng
CO diesel budng chay thdng nhat, ddi hdi cao doi
vdi chit lupng phun, dd dam bao sy xe toi tia
nhien lieu khi dupc phun vao budng chay, ngay
sau khi rdi khdi Id phun, tia phun bat dau tach ra
thanh hinh ndn phun, day la su phan ra dau tidn
cua chit ldng, dupc gpi la phan ra so cip, tgo
ndn ciu tiiic ciia chum tia nhidn lieu [2],[3]
Khi nhien lieu dupc phun d ap suit cao,
su xam thyc tgo bpt va nhidu loan bdn frong
Htnh 1 Cdu true vd suphdn ra cua mot tia phun nhien lieu
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Trang 3NGHIEN cufu-TRAO Ddi
2a,DACTINH CHUM TTAPHUN NHIEN LIEU
Md ta chum tia phun nhidn lidu dupc dgc
trung bdi cac thdng sd vat ly nhu hinh 1
- Chidu dai phan ra tia phun 1^ (break-up
length):
Tia nhien lieu ldng phun ra, khdng phan
ra ngay sau khi ra khdi Id vdi phun, ma ttai qua
mdt phan nao do cua chiim tia mdi phan ra thanh
hgt Chidu dai do gpi la chidu dai phan ra L^ [7]
Chieu dai L^^ la mdt dgc tinh quan trpng
dd xac dinh kha nang hda frdn khi phun nhien
lieu vao frong budng chay Cac thi nghidm xae
dinh L^ da dupe nhidu cdng trinh nghidn ciiu va
dua ra cdng thiic xac dinh dd phan tich ciu tnic
tia phun Dua ttdn ket qua thft nghidm cac tac gia
da de xuat phuong frinh sau:
Cac phuang frinh frdn cho thiy, chidu dai 1^ phu thudc vao mat dp khdng khi va khdi lupng ridng cua nhidn lidu Nhidn lidu co khdi lupng ridng cang ldn se cho 1^^ ldn Ndu Ij^ qua ldn, din den qua trinh phan tan hgt nhidn lieu kem di [7]
- Dp xuydn sau ciia tia phun s (spray penefration):
Trong chum tia phun day dac, xac suit
va chgm gipt la rat cao Nhiing va cham nay dan ddn su thay ddi van tdc va kich thudc gipt Cac gipt nhd vi the phan ra thanh nhftng gipt nhd han, nhung chung cung cd thd kdt hpp dd tao thanh gipt ldn han, dupc gpi la gipt lien ket Trong hdn hpp loang d xa mieng phun, cac ydu
td chinh anh hudng den su phan ra va bdc hoi
la nhiing didu kidn cua budng chay nhu: nhidt
dp, mat dp va luu lupng khf (rdi, xoay) [2]
lj^=7,l5-^| (Bracco, 1983); (1-la)
lt-10dJ-ti| (Reitz vaDiwakar, 1983); (1-lb)
I, ^2,65'\d,)w^'RMn (Yule, 1995) (1-lc)
Trong do:
p/Pg - Khdi lupng ridng nhidn lieu/ khdi lupng
rieng khdng khi
R^-sd Reynolds, R,, Vl^QPl
W -sd Weber, \ .VdoP,
Pj -Dp nhdt nhien lieu;
a-Sftc cang bd mgt nhidn lieu;
V|-Van tdc cua tia nhien lieu ban diu[m/s];
^p^mj'Pc (^P suit phun-ddi ap mdi trudng)[bar];
dp-Dudng kmh Id phun [m]
Dp xuyen sau dupc gidi han bdi khoang each gifta mieng Id phun va dinh piston Trong trucmg hpp ap suat phun cao va thdi gian phun dai (day tai) hoac mat dp khi thip (phun sdm) tia phun cd thd va cham vdi vach hinh thanh mang chat ldng Mang chit ldng nay cd anh hudng xau ddn khi thai, bai bay hoi chgm hon
va khdng the ddt chay hoan toan Nhung thi nghidm ca ban va ban thyc nghidm mdi quan
he cua cac thdng sd phun cd lien quan cita ddng
ca diesel nhu: Gdc ndn, dd dai tia, chidu dai phan ra, va dudng kinh trung binh cua gipt la ham sd cua didu kidn bidn da dupe thyc hidn va cdng bd bdi nhidu tac gia khac nhau Vi nhiing thi nghiem thucmg dupc thuc hien vdi sy phun gan nhu dn dinh ndn hiu hdt cac kdt qua chi cd thd dupc su dung de md ta giai doan phun chinh (kim phun nang hoan toan) cua tia phun hinh non
Thdi gian phat frien dp xuydn sau S cua tia phun cd thd dupc chia thanh hai giai doan
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Trang 4NGHIEN cufu-TRAO D C I
Giai doan diu tien bit diu tgi diu ciia id phun (t
= 0, kim bat dau md) va kdt thuc tai thdi diem
chat long tii cac Id vdi phun bit diu phan ra (t =
t^) Do hanh ttinh nang kim nhd va khdi lupng
dong chay thip khi bit diu phun, vgn tdc phun
nhd, va sy phan ra diu tien ciia tia phun khdng
phai ludn ludn xay ra ngay sau khi chat ldng
ra khdi Id phun Trong thoi gian nay, su tang
trudng cua S tuydn tinh theo t Thdi gian tii khi
bat dau phun ddn giai doan pha va chiim tia
phun la thdi gian phan ra [2]
(l-2a)
- Gdc ndn phun 6 (spray cone angle):
Gdc hinh ndn dupc dinh nghta la gdc hinh thanh bdi hai dudng bien hinh hpc tia phun
tu mieng Id phun Gdc non thudng tft 5 ddn 30
dp, sy gia tang gdc non den mpt gia tri nhat dinh
se lam giam su xuydn sau chum tia va cd the gay
ra su hda hoi ngay midng 16 phun Mgt khac, neu gdc ndn giam thap han gia tri nhit dinh, lam tang dp xuyen sau tia phun dan den va chgm tia phun vdi vach [7]
Trong cac nghidn cftu trudc day da cd mpt loat cac dd xuat de xac dinh gdc hinh ndn nhu sau:
Theo Hiroyasu va Arai (1990), dp xuyen
sau tia phun dupc xac dinh theo hai giai dogn: n^ = o,i3|i + ^|(Reit2, 1979); (l-3a)
Trudc khi phan ra:
0<t<t,,S-0,39p^.t;
Sau khi phan ra:
t > V S = 2 9 5 ^ |
.(d,.t)«'^-(l-2b)
(l-2c)
2 \^-dpPgAp
2 (Hiroyasu, 1980) (l-3b)
- Cf bidu thuc 1-2 cho thay, dp xuyen
sau chum tia phun phu thudc rat ldn vao ap suat
phun
- Dp xuydn sau chum tia phun cang
16n, nang lupng va van tdc cac hat vimg bidn
cang nhd, kha nang hoa ttdn se tdt han (Dent
J.C.,1971)- Vi vay, didu chmh ap suit phun hop
ly la mdt frong so cac giai phap giiip cho qua
trinh hda frdn nhidn lidu-khdng khi dupc hidu
qua han
O cac bidu thftc 1-3 thay rang, gdc ndn chum tia hi anh hudng bdi nhidu yeu td Trong
do, khdi lupng rieng nhidn lieu, ap suat phun va ddi ap mdi trudng (Ap) gan nhu chi phdi gia tri cua 9
2.3 Blln thien tia phun nhien li^u trong bu6ng ch^y dong co diesel
Theo Woschni (1974, [6]), khi nhidn lieu dupc phun tryc tiep vao budng chay, su phan
bd mat dp nhidn lieu trong tia phun la nhu nhau frong tit ca cac hudng, tuang iing vdi dp gdc quay true khuy va tdng thd tieh cua chiim tia nhien lieu phun vao budng chay (Vt) dupe xac dinh theo md hinh bidn thien tia nhien lidu nhu fren hinh 2 "^
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Hinh 2 Bien thien tia nhien heu trong buong chdy
dgng ca diesel
t^ ' l3 l^ctge + lj ^•'1^ ctge + lj 3 [clge + lj (l-4a)
Phuang trinh l-4a, thd hidn thd tich hic
thdi cua chum tia nhidn lieu, khi xet ca qua tiinh
phun, su thay ddi thd tich (Vt) bidn thien theo dp
gdc quay true khuy Khi do;
dtp
•4^f
'- = i.n.s{<?f
(ctge+i)2 (ctge+i)^
1 1
(ctg0+i)^
(ctge+i)-6s_
'dp (l-4b)
•vs(q>)
Oday:
i-S6 Id tia phun;
V^((p)-T6ng tiid tich tuc tiidi chum tia [m^]; dV/dcp-Bidn thidn cua tdng thd tich [mVdeg]; G-Goc ndn tia phun [rad];
(p-Gdc quay true khuyu [deg];
v/tp)- Van tdc tia phun [m/deg];
s((p)-Dd xuyen sau tia phun[m];
n-Tdc dp quay true khuyu [vong/phut]; (p^j-Thdi diem phun nhien lieu [deg]; a^-He sd cua dong xoay frong tia phun [-]; c^-Hd sd xa vol phun
Tu phuang trinh l-4f cho thiy, d cung didu kidn vd kdt cau budng chay va cae thdng
sd cudi ky nen, mftc dp hda frpn cua cac loai nhidn lieu ttong budng chay phu thudc rat ldn vao cac thdng sd hinh hpc chum tia phun Trong
do, goc ndn chiim tia 0 va dp xuyen sau s chiu anh hudng bdi ap suat phun va thdi didm phun nhu da phan tich ttong cac ndi dung frdn
2.4 Tinh toan thdng so chum tia phun nhien lieu sinh hoc (diu diesel - d i u thwc vat)
v,=c,
s(<p) =
dep 2,/2.a„
l2Ap
V Pl
I 1
6n 1
.s(<p)
mj|
Phuong trinh l-4b tra thanh:
c =
Ttongiac phucmg trinh tren:
Vdi nhung thugn lpi vd ngudn diu dfta (l4e) a Viet Nam; Bai bao chpn hdn hop diu diesel -dau dira lam nhidn lieu va chpn thdng sd ddng ca (l-4d) ^^^^^^ 4CHE Yanmar [1], dd tinh toan thdng sd chum tia nhidn lieu sinh hpc va so sanh vdi diu diesel
(l-4e)
(l-4f)
Quan he giua cac thdng sd ca ban cua hdn hop nhidn lieu d i u diesel-diu dfta duac thd hidn frdn hinh 3 [1] Nhu da phan tich vd ciu tiiic chiim tia phun d phin fren Theo hmh 3 nhan tiiiy
- Tri sd cetance hdn hpp giam, din ddn thdi gian chay ttd tang theo ty 16 pha ttdn
- Khdi lupng ridng tang theo ty Id pha
ttpn, din den gia tang chidu dai phan ra, dp xuydn
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sau tia phun va lam giam gdc non ehiim tia
- Dp nhdt ddng hpc hon hpp tang theo
ty Id pha ttdn, d i n ddn gia tang dudng kinh hat
nhien lieu
P
Tii««latnl(K«*iKi4
Hinh 3 Quan he giua cdc thdng sd
nhiit ddng cua nhien liiu hdn hgp theo ty li
Nhihig nhgn xet nay hoan toan phii hop
vdi ket qua tinh toan thdng sd chiim tia phun
nhidn lieu hdn hpp dupc thd hidn tren hinh 4
Chu y rang, cac kdt qua ttdn hinh 4 chi 6LQ xem
xet quy luat bien thien cau tnic tia nhien lieu hdn
hpp theo ty le pha frdn so vdi dau diesel Day
cung la c a sd, de giai thich va bd sung ly thuyet
cho qua trinh hinh thanh hdn hop chay cua nhien
lieu d i u diesel-diu thuc vat ndi chung va ddi vdi
rieng hdn hpp d i u diesl-dau dfta
diu diesel (3 ty Id pha ttdn thap, su chenh lech nay khdng dang kd, khi tang ty le fren 10%, cac gia tri thay ddi ro ret, mac du sy chenh lech khdng ldn Tuy nhien, a cimg dieu kidn phun, cac thdng sd tten se lam xu hudng phat tridn tia phun hdn hpp dau diesel-diu'dfta cd khac so vdi diu diesel Ben canh do, vide gia nhidt cho hdn hpp nhim giam dp nhdt, se lam giam dp xuydn sau cua chiim tia, anh hudng jxau ddn qua trinh hinh thanh hdn hpp chay
2.5 Md phong anh huong cua ap s u i t phun den cau true tia phun d i n diesel - d a u dva trong buong chay ddng co diesel 4CHE Yanmar
Dimg phan mem Ansys Fluent 14.0, md phdng tia phun nhidu lieu diu diesel-diu dfta (B15: 85% diu diesel-15% d i u dfta) dupc gia nhidt ddn 750c, voi sy thay ddi ap suat phun theo phuang trinh l-4d Ludi md phdng nhu hinh 5
Ket qua md phdng dupc thd hidn frdn
Nhung phuong trinh ca ban frong md phdng [8]:
- Phuang trinh bao toan khdi lupng
— 1
(l-5a)
Phucmg trmh bao toan dong luong
5pu,
—(pu,u-t,,) = —— + i„
a Sx, ' ' " Sx,
(l-5b)
Hinh 4 Thong sd chilm tia phun nhien lieu hdn hop
theo ty te
TrSn hinh 4, do xuyen sSu tia phun va
chidu dai phan la tia phun nhien lieu hon hgp
ldn ban diu diesel, goc non chtei tia nho boo
- Phuong trinh bao toan nang lugng
aph
T ' ^ ^ + ^ h j ) - ^ * " dp_
au 'liaT l i ^ - h C1-5C)
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Trong do: a^ va a,, dugc xac dinh nhu sau: €,_ = 1.44; C^
1.92; Cu = 0.09 ; o^ = 1.0; o = 1.3 [9]
= 2|.is,j -2 S u - puiu;
1 5u au
y 21 5x ax
T , s , s , F J, s., p, u, u, h, u', la cac thanh phan
ling suat, trudng bien dgng, ngudn khdi lupng,
thdng lupng khuech tan theo phuong j , ngudn
nang lupng, khdi lupng ridng, van tdc theo cac
phucmg, dp nhdt, enthalpy, cae thanh phan van
tdc mgch dpng
c a c phuang trinh fren khdng du khdp kin
de giai do sd an ldn hem sd phuong trinh Vi vgy,
bd sung them md hinh rdi k-8 Md hinh k-e la
md hinh co ban dua frdn cac phuong trinh van
chuyen cho ddng ddng nang roi (k) vatdc dp tidu
tan rdi (e) [9]:
-(pk) + V.pku = V
- ^
+ G -ps
(l-5d)
-{p£)+V,peu=V
Trong dd:
h C , - G > - C , p - ^ j _ 5 ^ j
Hinh 5 Lu&i mo phdng budng chdy dgng ca 4CHE-YANMAR
Hinh 6 Anh huang cua dp sudtphun din cdu true tia phun trong budng chdy dong ca
Trdn hinh 6, trinh bay cau friic cua tia
He sd nhot rdi \i^ = pC^, — va hing sd thd phun nhidn lieu sinh hpc (B15) tiieo ap suit phun
khac nhau Cac kdt qua eho thiy, dp xuydn sau
va gdc non chum tia nhidn lieu tang len khi tang
ap suit phun Tuy nhidn, ddn gia tri 225kg/cm^
cd xu hudng giam dp xuydn sau Didu nay minh chiing, viec gia nhidt cho hdn hpp (nhien lieu cd Cac hing sd C,^, C^^, Cp, va sd Prandti nhiet dp cao) khi phun vdi ap suit phun cao, se
hidn su phu thupc cua sy hinh thanh nang lupng
rdi ddng hpc (k) G,, = jdH:
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lam^ giam sy phan tan efta chiim tia ttong khdng gian budng chay Do dd, tang ap suat phun cho nhien hdu hdn hpp, phai kdt hpp cftng vdi didu chinh gdc phun sam, de tao ra eiu trftc chum tia phun phu hpp vai budng chay ddng ca
3 KET LUAN
Trdn co sd tinh toan va mo phdng su thay ddi cau tnic chiim tia phun nhidn lieu hdn hpp dau diesel-dau tiiuc vat (diu dfta), co anh hudng ldn ddn qua trinh hmh t h ^ hdn hpp chay Vi vay, dpng CO diesel phun nhien lidu tryc tidp, can didu chinh thdng sd phun khi chuydn sang su dung nhien li?u hdn hop:
- Tang ap suat phun ddn mdt gia tii nhit dinh, dd giam dudng kinh hat nhidn lieu va tang gdc ndn chum tia
- Giam ddi ap mdi truang (tang goc phun som) 6 mpt gia hi nhit dinh, dd tang dp xuyen sau tia phun nhidn lieu •>
Ngay nhan bai: 15/9/2015
Ngay phan bidn: 14/10/2015
Tai Ufu tham khao:
[1] Mai Diic NghTa, Phung Minh L^c; Nghien euu chi tgo thiit hi phoi tron ddu diesel-ddu thuc vgt ldm
nhien lieu cho ddng ca diesel, T?.p chi Khoa hpc Cong nghe Thuy san, s6 2, 2011
[2] Carsten Baumgarten, Mixture Formation in Internal Combustion Engines 2006
[3] G Stieseh Modeling engine spray and combustion processes Springer, Beriin, 2003
[4] Rolf D Reitz, spray technology short course, mechanical engineering department university ofwisconsin,
may 7,1996
[5] PA Lakshminarayanan, Yogesh V Aghav, Modelling Diesel Combustion, Springer Science Business
Media B.V 2010
[6].Kaz\mwTzLG}dzmidPawe\Wos,Fuel Injection in AutomotiveEngineering,Editedhy,lSBN
978-953-51-0528-2, Publisher: InTech, Chapters published April 20, 2012 under CC BY 3.0 license, DOI: 10.5772/2553 [7] Daniela Siano, Fuel Injection, ISBN 978-953-307-116-9, Publisher; Sciyo Chapters published August
17 2010 under CCBY-NC-SA 3.0 license DOI: 10.5772/55402
[8] T J Chung, Computational Fluid Dynamics, Cambridge, England 2002
[9] ANSYS Fluent Tutorial Guide Release 15.0 ANSYS, Inc November 2013
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