Nghien ciju anh hirong cua ham lirong CO2 trong nhien lieu den dac tin lam viec va khi thai dong ca mot xylanh su dung khi sinh hoc A Study on the Effect of CO2 Content on Engine Performance and Emiss[.]
Trang 1Nghien ciju anh hirong cua ham lirong CO2 trong nhien lieu den dac tin
lam viec va khi thai dong ca mot xylanh su dung khi sinh hoc
A Study on the Effect of CO2 Content on Engine Performance and Emission Characteristics ot ^mg e
Cylinder Engine with Biogas Fuel
Tran Dang Quoc
Trudng Dgi hoc Bdch khoa Ha Ngi - SS 1, Dgi CS Viet Hai Bd Trung Hd Noi
Din Toa sogn: 30-10-2017; chdp nhgn ddng: 18-01-2019
Tom tat
Sa; bao trinh bay mot nghien cou vi anh hadng cua ham logng CO2 co trong nhien lieu den dac tinh lam
doac mo phong tren phin mim AVL Boost sau do dagc hieu chinh theo si lieu thgc nghiem cua mgt dong cathgc co ty s6 nen c = 10,5 so dung nhien lieu khong co C02 Cac kit qua thu dagc to dgng CCT mo phonp vai nhien lieu 100% CH^ se doac coi la thong si ca ban di so sanh va pban tich khi logng CO2 tang dan lan loot theo tha tg 3%, 10% va 22% Dong co mo phong lam viec a diia kleri nha: lambda bang 1, buvm ga
mo hoan toan, goc danh loa sam dagc diiu chinh di dat mo men Ion nhit, tic dp dong ca tbay doi trong khoang n = 1000 - 2000 vong/phut Cac kit qua thu dagc to mo phong ch! ra ring^ anh hoang cua barn logng CO2 din mo men, cong suit va hieu suit nhiet la rit Ion Nguyen nhan chu yeu lam giam hieu suat lam viec cua ddng ca la do ca nhiet tri thip va he so nap bi giam ddng thai Tuy nhien, sg suy giam nay phan nao doac cai thien niu tang tic do cua dong ca va diiu chinh thai diim danh loa sam hon Sg gia tang ham loong COs trong nhien lieu se ia giai pbap hieu qua di giam NOx ma khong can so dgng he thing luan hii khi thai (EGR)
TLF khda Ham lugng CO2, Dgng ca mgt xylanh, Nhien lieu thay thd, Nhien li§u Biogas,
Abtract
This adicte presents the research on effect of CO2 content on engine performance and emission characteristics of the single cylinder engine with pod injection The research engine is simulated in AVL Boost software and then the simulated engine was corrected by the experimental data of the real engine has compression ratio E = 10,5 without CO2 in supplying fuel The obtained results from simulated engine with 100% CH4 were considered the basic data to compare and analyse when the proportion of C02 In Biogas fuel was progressively enhanced such as 3%, 10% and 22% The simulated engine operated in conditions as: X= 1 wide open throttle, early ignition timing was varied to obtaine maximum tourque, engine speed ' was changed into the range of n = 1000 ^ 2000 rpm The achieved results from simulation have shown that the effect of CO2 portion Into supplying fuel on the torque, power and thermal efficiency were very strong In this study, the main cause of reducing engine operation was clearly found out that was due to decreasing in low heat value and volumetric efSciency simultaneously However, the reduction of this can be , compensated by the method as increasing engine speed and adjusting early ignition timing The increase of CO2 podlon into supplying fuel will be the effective measures to decrease NOx without using EGR system
Keyword: CO2 proportion, Single cylinder engine, Alternative fuel, Biogas fuel,
1 Gidi thieu = 25-50%, H2S - 0-3%, H2 = 0-3% va H2O = 0-3%
Nhien heu khi sinh hgc hay con ggi la E [2], Sii dung khi sinh hgc lara nhien heu cho dgng ca
INlllCIl l i e u Mil 311 til IIV- ""J • - " " 5V" ' " UIUBUJ ICI A'> ~ I' - " , , , " - - , - mot trong rfiimg ngiik nmg luong tai tao (tiy tiSm ™ """"B f ' " " ? ' E"" P^^P ^^ >* <te co the cap
nans tren thS g,6i va o nuoc ta, sii dnng nhien lieu T " <=''° nh™g/ung sau, vung xa va hai dao, nhitng Idti smh hoc cho dong CO d6t trong se khong lam tang ™°.S ™ ' > " ' ' * ? " I " ? ' S'", '^t'ua den duoc [3] Tay
luong c o ; trong khi quySn [1], Khi smh hoc duoc ta, ??'.•=" T™!, • S ^ ''?''° ? ' J ' * ^'^ ' ° " ' ^ ' '"'V'^ tao S, nguSn ra^c tha, smh hoat hoac rac thai trong l*™? I™ "'.' ^ ^ rat eo h,, do, vol moi truong song Chan nudi o d i k kien khong co oxi, thanh phin cae ™.^',<" «•'!> 4™E •;°.''."" I' !*• ,1« chay H^S se tao ra
f J ^ den sue khoe con ngua, ma con lam hong cac chi tiit
eua dong co d5t trong cu the la he thSng nap-thai va
• Dia chi lien he: Tel.: (+84) 963.915.476 xylanh ciia dong co, [4] Mot aia, phjp g^g^ j]j„ ij
Trang 2thfing dung va tiSt kiem, do la gidi phap sir dung phoi
sdt lam chdt khu dg loai bo H2S vd hieu sudt khii co
cdn dugc loai bo do la khi CO2, day la loai khi khong
nhign lieu vd lara cdn tra toe dg lan tran mang lira
Hinh 1 Dgng ca rao phong
Dieu nay duac du bao rang lugng khi thai NOx se
dugc gidm di nhung thanh phdn khi thai H-C khong
chay hgt cd thg tang ten Mgt trong nhUng yeu cdu
can thiet de khac phuc dugc nhugc diera tren cua khi
sinh hgc, dac biet la ham lugng C O : cd trong nhign
lieu tang len khi raa higu qua bg lge giara [6], yeu cau
do la tang dong nang ciia dong khi truac va trong suot
qua trinh chay Phuong an ky thuat co the phdn nao
dap img dugc yeu cdu tren do Id tang toe do lara viec
va thai diem ddnh lira sdra Tuy nhign, cac anh hucmg
CO2 CO trong nhien lieu den dac tinh lam viec vd khi
thai cua dgng co la chua ro rang hoac rat kho co the
tim hieu dugc Vi vay, uen hanh "Nghien ciru dnh
huatig ciia hdm lugng CO2 den dac tinh ldm viec vd
khi thdi dong ca mot xylanh hinh thdnh hon hgp ben
ngoai sic dung khi sinh hoc''' la rdt can thiet Dg xem
xet moi quan hg giiia hdra lugng CO2 vdi cong sudt,
hieu sudt nhiet (rje), gdc ddnh lira sdm toi uu vd cac
khi thai, thuc hien nghign ciiu rao phong tren phdn
mem AVL Boost se co tinh khoa hgc va cd the tiet
kiem dugc chi phi nghien ciiu thir nghiem
2 Bieu kien va phirong p h a p thii' nghifim
2.1 Thanh phan nhien lieu thir nghiem
Nhien lieu se sii dung trong nghien ciiu ndy la
nhiSn lieu khi sinh hgc sau khi da Igc bo hodn toan
diroc thanh phdn H2S va H2O, thanh phdn cua nhign
Carbone-dioxide (CO2) Hdm lugng CO2 cd trong
nhien hgu dugc gid dinh se thay ddi idn lugt la 0%,
3%, 10% va 22%, cac gid tri ndy duoc nhap vao phdn
ham lugng CO2 = 0 dugc coi la nhien lieu g6c dg hieu chuan mo hrah ban dau, Nhiet tri thdp cua nhien lieu cdc gia tri nhiet tri thdp dugc phdn mira AVL Boost tinh ra kgt qua nhu bang 1 [7]
Bang 1 Ham lugng CO2 trong nhien lieu STT
1
2
3
Thiinh p h a n nhien lieu
(%)
CH4 = 100 CH4 - 97 CH4 = 90 CH4 - 88
CO2 = 0
C O j - 3
CO, = 10
CO, - 22
Nhiet t r i t h a p Qi.n(kJ/kG)
50000 49473,344
39699
2.2 Mo phong va hieu chuan mo hinh
Dgng CO nghign ciiu duge rag phdng bdi phdn mgm AVL Boost (Hinh 1) vdi cac thong s6 ca bdn dugc lay ni dgng co mgt xylanh QTC2015 thugc dg tai cap Bg ma so B2015-01-106 Cdc thong s6 dgng
CO rad phong dugc trinli bdy trong bdng 2 Co sd ly khao va lua chon tir tai lieu hudng dan cua AVL Boost [8] nhu:
Dinh luat nhiet dgng hgc thu nhat dig hign moi quan he giUa sir bien thien cua ngi nang (entanpi) vdi
su bien thien cua nhigt va c6ng
He so truyen nhiet dugc tinh theo rao hinh Woschni 1978
Mo hinh chay Fractal dimg cho ddng ca ddnh lira cudng buc va khi nap dong nhdt
Gia tri CO dugc tinh todn dua vao giai phuang trinh vi phan doi vdi hai phdn ung: CO + OH = CO2 +
H v a C 0 2 + 0 = CO + 02, Gia tri cua H-C duoc xdc dinh tir cac nguon chfnh cua H-C chua chay Uieo phuang phap ciia D'Errico
Trang 3Co che hinh thanh N O , trong mo phong
BOOST dua tren ca sd cua Pan:as vd Hafner Qud
trinh hinh thdnh cua chiing dugc the hien qua sau
phugng trinh phdn ung theo co chg Zeldovich
Hieu chuan dgng co rao phong dugc tign hdnh
dua tren eo sd so iieu thuc nghiera ciia dgng co
QTC2015 (Hinh 2) tai ty s6 nen e = 10,5 vd nhien heu
ihuc nghiem ldn nhat khodng 3 % , vdi kgt qua sai lech
cac phuang phap thi nghiem khac tdiau
Bang 2 Thong so ky thuat cua dgng ca rao phong
Thong so
Dudng kinh xylanh (mra)
Hanh trinh piston (mm)
Sd xylanh
Toe do dinh miic (v/ph)
Ty so nen (-)
So ky (-)
Ky hieu
D
S
1 ridm
s
T
Gia tri
103
115
1
2200 10,5
4
2.3 Phuffng phdp thi nghiem
Dg thu dugc cac kgt qua nghien cim vg dnh
hucmg cua ham lugng COi dgn dac tinh lam viec va
kb) thai dgng ca mgt xylanh, cac digu kien thi nghiem
se dugc thuc hien nhu sau:
Hudng den dieu kien hoa trgn ly tudng giCra
khdng khi va nhien lieu truoc khi hinh thdnh raang
lua, gid tri larabda duac chgn 'k = I
Do md cua budm ga (WOT: Wide Open
Throttle) Id 100% nhdm giara t6i da ton that trgn
dudng ong nap,
Thdi dilra ddnh lira sora (IT: eariy Ignited
Timing) dugc thuc hien trudc digra chet tren va thay
ddi trong khoang tir 10 ^ 20 do gdc quay true khuyu,
AIT = 2
Ddi tdc do dgng co mo phong thay doi trong
khoang n = 1000 -^ 2200 vdng/phut, budc thay doi
trong suot qua trirdi thir nghiera la An = 200 tCet qud
thu dugc se dugc xem xet vg miic do dnh hudng ciia
tdc do ddng CO va hdra lugng CO2 den cac chi tigu
lara viec cua dong ca
Dg ddnh gid miic do dnh hudng cua hdra lugng
CO2 cd trong nhien lieu, khdi Iugng nhien lieu se
dugc giir nguygn ddi vdi ca bon loai nhien lieu
(0,4569 g/s),
3 Pban tich sd lieu
3.1 Anh hudng cua hdm lugng CO2 den dac tinh
Hrah 3 Xhh hien su bign ddi cong suat dieo toe
do ddng ca d digu kien ^ = 1, bdra ga mo h o ^ " / ° ^ " gia tri rao-raen ldn nhdt (MBT) Nhin chung sir bien thien cong sudt theo t6c do dpng co cua bon ty l_e CU2 d6u cd xu hudng diay ddi nhu nhau, tuy nhien,_ t^i radi tdc do ddng co gid tri cong sudt lai co ty^ le
tu 1000 vdng/phut dgn 1800 vong/phiit, cong suat dong ca cd thg coi la raot hdm ddng bien vdi bien so chuygn thanh hdm nghich bign khi toe do dgng ca Ion hon 1800 vdne/phut vd cue tri cua ham so nay dugc tira thdy tai tdc do 1800 vong/phut.^ Nguygn nhdn lam cho cdng sudt cua dgng co thay doi khi toe dg dgng cua hon hgp ben trong xylanh ddng co, Nhung khi tang tdc do dgng co ldn hon nua se lam tang dnh hudng ciia dp sudt ngugc dgn he so nap, va ket qua la cdng sudt ciia dgng co c6 xu hudng gidm d tdc do ldn hon 1800 vong/phut Quan sat cac kgt qua tiiu dugc ciia hdn hgp trong dgng co da dugc cai thien dang ke ngay ca khi ty le CO2 tang KSt qua nay cd thi thdy ro
d toe do dinh miic ciia dgng co (2200 vong/phiit), cong sudt dong co vdi 22% CO2 co Uong nhign lieu biogas xdp xi bang cong sudt cua ddng ca tai 1400 vong/phut khi da loai bo hoan toan CO2 ra khoi nhien lieu De Idra ro hon dnh hudng cua CO2 den cdc thdng sd Idra viec cua dgng co cdn phai xet den suat tieu hao nhien heu ciia bdn loai nhien lieu I khde nhau khi thay doi toe do dpng co
Hinh 3 Anh huang cua toe do dgn cong sudt cua
dgng ca
Trang 4Toe d ; dJDg ccr D (kdng/pbiil]
Hinh 4 Bien ddi cua suat tieu hao nhien heu theo tdc
do dgng ca
Hinh 4 the hien dnh hudng cua toe do dgng co
den sudt tieu hao nhign lieu ddi vdi bdn ty le CO2
cna toe do dpng cg, sudt Hgu hao nhien lieu co xu
hudng giam va sau dd lai cd xu hudng tang d toe do
Ion hon Gid tri nho nhat cua sudt tigu hao nhign lieu
dugc tira thdy d tdc dd 1400 vong/phiit md khdng phu
dan den su suy gidra cua sudt tieu hao nhign lieu la do
cai thien dugc phan nao cua hieu sudt nhiet Tuy
nhien, muc do cdi ihien ndy dudng nhu vdn chua du
khi toe do ddng co ldn han 1400 vong/phiit, Nguyen
nhan lam cho suat tieu hao nhign lieu cd xu hudng
tang chii yeu la do ty le CO2 co trong nhien Iteu Dieu
nay co the de dang chirng rainh bang ket qua thu
dugc tren hinh ve, tai radi tdc dd ddng cg sudt tieu
hao nhign heu tang khi ty le CO2 cd trong nhien lieu
tang
De lara ro hon anh hudng cua thanh phan CO2
CO trong nhien heu dgn cdc thdng so ky thudt cua
phong tai tdc do n = 1400 vdng/phut Khdi lugng
nhign lieu cdp cho radt chu trinh dugc giir nguygn vdi
15n lugt la 3%, 10% vd 22%, Hinh 5 thi hien anh
hudng ciia ty le CO: co trong nhien heu den rad raen
va hieu sudt nhiet ciia ddng co khi cd dinh lugng
nhien lieu cdp tai 1400 vong/phiit Tu cac ket qua thu
CO trong nhien lieu din md men va hieu suat nhiet cua
dpng CO, cd rao raen va hieu sudt nhiet deu cd xu
hudng gidra gidng nhau Nguyen nhdn lara xudt hien
xu hirdng nay la do ty le CO2 cd trong nhign lieu
Biogas da lara gidm he sd nap va can trd tdc do lan
nay da chi ra rang gdc danh lua sdra cua ddng ca cdn
phai dugc dieu chinh theo hdm lugng CO2 cd trong
nhign ligu
Hinh 6 trinh bay ket qua nghien ciiu ve dnh hudng
tdi uu ddi vdi hai trugng hgp la khdi lugng nhien hgu cdp khdng ddi (Gni = const) va ? = 1 d cirag dilu kien
Id n = 1400 vdng/phut va IT = MBT Tir cdc kdt qud thu dugc cd thg thdy rang gdc ddnh lira sdra tdi uu cua ca hai trudng hgp gidng nhu hara sd tuygn tinh thay doi theo hara lugng CO2 trong nhign lieu, gia tri tuyet ddi ciia gdc danh lua sdra tang khi ham luong CO2 tang Chinh xac han la phdi dieu chinh gdc danh trong nhien heu tang Xet vdi trudng hgp Gni = const, cac ket qua rao phdng da chi ra rang khi hdra lugng CO2 trong nhign lieu tucmg iing Id 0%i, 3%i, 10%i vd 22% thi gdc danh Ida sdra tdi uu ldn lugt la IT = 16, ldm xuat hien xu hudng nay Id do su xuat hien cua CO2 cd trong nhign lieu da Idra can trd qua trinh dot hgp (Gni = const), gdc danh lira sdra cdn phdi dieu chinh sdm hon so vdi trudng hgp ^ = 1 bdi vi nhiet tri thdp vd ndng lugng lap trung cua nhien lieu d ben trong xylanh ddng ca da bi giara rat nhanh khi hara lugng CO2 cd trong nhign tang den 22%, Tir cac ket qua thu dugc d trgn cd thg thdy rang dnh hudng cua ham lugng CO2 cd trong nhign lieu dgn dac tinh lara viec cua ddng co la raf ro rdng, tuy nhien cdn phai xem xet vd phdn tich anh hudng cua hdm lugng CO2 den dac dnh khi thdi cua ddng ca
Hinh 5 Anh hudng cua %C02 den md raen va hie sudt cua ddng co
M i l F i i U t i i : B l o g »
W O T
= 1^,00 r p m
' s C O ; IroDg DbliB Iftu
Trang 5Hinh 6 Anh hudng cua hdm lugng CO2 den
danh Ida
5
0
N h i a EiftL B l o g u
/ -»-C02 = 3W
-m-coi=wn
^dc
§
^/JS
^
Nlilcn Ilea' Bkigas
I T : MBT
00 1200 1
^
00^ w o o 1800
1
- l - C 0 Z = 3 «
" i , - C 0 2 = M ' *
j ^ C 0 2 = 2 I * t
looo 2200 2
1000 1200 1400 160O 1800 2000 2200
TMdgaoB|cir,ii(v-oQ&'pliiO
Hinh 7 Phdt thai CO theo tdc do ddng ca
•> CO m n g nC
Hinh 8 Phdt thai NOx vd HC dieo ty le CO2
Hinh 9 Phdt thai NOx theo tdc do ddng ca
Hinh 10 Anh hudng cua tdc do din phdt thai H C
3.2 Anh hie(9ng cua % CO2 din phdt thai cua dong
Cff
Quan sat cac k i t qua thu dugc tir Hinh 7 cd the nhan thdy rdng dnh hudng cua CO2 trong nhien lieu din phat thai CO tai d i l u kien rad phdng A = 1 la phat thai CO cd xu hudng tang ddn ddi vdi tdt cd cdc
ty le CO2 trong nhign lieu Trudng hgp nhien lieu Biogas cd hara lugng CO2 trong nhien Ueu thap hon hdm lugng nay ldn hon 3% thi phdt thai CO tang rat hudng ldn cua CO2 cd trong nhign lieu den phat thai
CO la rdt ldn, hara lugng CO2 trong nhien heu vd phdt thdi CO nhu Id mdt hara ddng bign Khi so sanh giira nhien lieu Biogas cd CO2 = 22%i vd nhien lieu Biogas cd CO2 = 0%) thi hara lugng phdt thai CO tang gap khoang 25 ldn Nguyen nhdn chd yeu lam cho
CO tang la do ham Iugng CO2 trong nhien lieu da lam giam kha nang chay cua hdn hgp d bgn trong xylanh thai NOx vd H-C se co su thay doi khac nhau, Hinh 8 thg hien lugng phdt thai N O , vd H-C ldn nhat theo sir gia tang cua ham lugng CO2 cd trong nhien lieu tai digu kien A = 1 Theo chilu tang cua CO2 trong nhien heu, phdt thai NO^ ed xu hudng gidra Nguygn nhan Id do su gia tang thanh phdn CO2 chdy cua dgng ca Nguoc !ai ddi v<Ti phdt Uiai H-C, khi tang ham lugng CO2 cd trong nhien lieu, se lam thdi H-C cd xu hudng tang len Dg ldm rd hon anh hudng cua CO2 d i n phdt thdi N O , vd H-C, cdn phdi xem xet d dieu kien tdc do ddng co thay ddi Hrah 9 the hien su anh hudng ciia thanh phdn CO2 CO trong nhien heu din phdt thai NOx tai dilu trgn hinh ve cd the thdy rang theo chilu tdng cua t i c
Trang 6luang CO2 cd trong nhien lieu Trong khoang n =
1000 vdng/phiit den n = 1200 vdng/phiit, lugng phat
thai NOx CO xu hudng tang va dat cue dai tai 1200
hon S\r khde biet cua NOx tai hai vung tdc do la do
bu6ng chay ciia ddng ca
Hinh 10 the hien su anh hudng cua thanh phdn
CO2 CO trong nhien heu tdi phat thai HC tai dilu kien
thi nghiem vdi A ^ I Ciing nhu phat thai N O , , khi
Sng tic dp dgng co, phdt thdi H-C cdng cd xu hudng
tang vd dat cue dai va giam d tdc dd ldn han Nhung
khi xet tai cung mot vi tri tdc do, khi tang thanh phdn
CO2 CO trong nhien lieu, phat thai H-C cd xu hudng
tang Nguygn nhdn chinh la do dnh hudng cua C02 cd
trong nhien lieu lam giam kha nang bat lua cua hdn
hop
4 Kit luan
Anh hudng cua hara luong CO2 d i n dac tinh
lam vi6c va khi thdi ddng co mgt xylanh hinh thanh
hon" hgp bgn ngoai dugc thuc hien d cac dieu kien
nhu; %= \, budra ga rad hoan toan (WOT), goc ddnh
Heu sinh hpc dugc sir dung vdi 4 ty le CO2 khac nhau
phan tich ket qua d tren cd thg nit ra cac ket luan sau:
Ham lugng CO2 cd trong nhien ligu anh hudng
rat Ion den cdng sudt, rad raen vd hieu suat nhiet cua
dgng CO
Xu hudng digu chmh gdc danh lira sdm theo
ham lugng CO2 va toe do ddng co la gidng nhau, tuy
nhien anh hudng cua hara lugng CO2 trong nhidn lieu
den gia tri gdc danh Ida la ldn hon
Anh hirdng cua hara lugng CO2 d i n thanh phdn
cac khi thdi la ldn hon so vdi tdc do ddng cg, ham
luong CO2 tang se Idra giara nhiet do ben trong budng
chay vi vay NOx dugc gidm ddng ke Tuy nhien, khi
thai H-C lai cd xu hudng tang nhanh la do kha nang bat chdy cda hdn hgp giam
Tai lieu t h a m khao [I] Shota Watanabe, Shuichi torii Development study of
a biomass fueled fiimace and impact of moisture Joumal of Advanced Transport Phenomena, Vol 01, No.Ol, December 2012, pp 1-5
[2], Muchin N.G, Wanjii S.M, Hinga P.K, Kahiu S N, A Review on biogas, its apphcation as a dual-fuel on Diesel engines for power generation, ISSN 2079-6226: Proceedings of the 2012 Mechanical engineering conference on Sustainable research and innovation Volume 4, 3rd-4th May 2012 [3] Tran Dang Qulc, Le Anh TuSn, Khlng Vu Quang, Tran Thi Thu Huong, Nguyen Due Khanh, Nghien cuu vl dgng co Stirling su dung nang lugng tai tao -Kha nang img dung a Viet Nam Tap chi Klioa hpc &
24, thang 10/2014, ISSN: 1859-3585, [4] Hoang Kim Giao, Cong nghe khi sinh hpc - Quy mo
hg gia dinh, Tai lieu diing de tap huan cho ky thuat vien ve khi sinh hpc, Ha Npi-2011
[5], Biii Van Ga, Truang Le Bich Tram, Truong Hoang Thien, Pham Duy Phuc, Dang HOu Thanh, JuHand keo may phat dien 2HP, Tap chi Khoa hpc va cong nghe, Bai hoc Da NSng, sl 03, 2007, trang 80 - 85 [6], Bnan Herringshaw, Thesis A study of biogas utilization efficiency highlighting intemal combustion electrical generator units College of Food, Agricultural, and Biological Engineering, the Ohio State University, 2009
[7] Mirko Barz, Nang luong fir smh khoi nong nghiep -Kmh nghiem va ylu td qujet dinh thinh cong, Dien 16/09/2013
[8] AVL Boost Theory, Version 2011