2-stage turbo egr
TRANSCRIPT
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Ricardo – Josef Božek Research Center
2-Stage Turbocharged Engine EGR System Development
Masive exhaust gas recirculation (EGR) presents one a! for noada!s and soon co"ing e"ission
regulations satisf!ing like E#R$ % or &'ER 't significantl! helps to reduce so carefull! "onitored
*$x concentrations Re+uired EGR levels for previous e"ission regulations ere not so high, -ut for
these up co"ing regulations steepl! increase up to %./ in so"e operating points0 &his ork deals
ith finding and developing applica-le a!s of control strategies for such a high EGR percentage
rates 't uses to designed EGR routes – a short and a long one ith control ele"ents 1 co"parison
of different EGR strategies is descri-ed and the "ost suita-le one is chosen for co"plete engine "ap
co"puting
.234523 si"ulation codes are not appropriate tools for *$x concentrations "odelling even if the!
o-tain rough esti"ation "odels to do this &he feasi-ilit! of this si"ple "odels are li"ited to the
areas closed to "easured points here the "odel is cali-rated $ther ords said the! are useful
"ainl! for +ualitative esti"ation (trends predicting) &herefore e"ission regulations are "odelledindirectl! -! setting of re+uired EGR level that is fro" experience knon for these li"its "eeting –
see 6ig 5
&he co"plete engine "ap opti"isation (creation) follos right after successful tur-ocharger "atch 't
consists of developing of engine "anage"ent that is a-le to set re+uired EGR level at each engine
orking point inside co"plete engine "ap 2 6ig 5 &he control "anage"ent is applied on selected
actuators such as EGR valves and throttles that can increase the tur-ine upstrea" and co"pressor
outlet pressure difference if needed &he pressure difference ould not -e ala!s positive or high
enough to provide the target EGR flo 6or that reason throttling is used often
&he EGR "ap in 6ig 5 has to -e supple"ented -! 16R li"it values that prevents extensive engine
s"oking and satisf! fine fuel co"-ustion &he values of EGR and 16R ithin the "ap are
preli"inar! &he! could differ fro" engine to engine -ut the! are appropriate for the first
approxi"ation
5
Fig. 1: Expected EGR rates within complete engine map for Euro 4regulations meeting. (LDD Engines Ricardo data!ase" Re#uiredminimum $FR limits to pre%ent smo&ing.
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Boosting Strategy
6irst of all it is necessar! to develop a -oosting strateg! that orks ithin all engine operating range
't is developed firstl! without EGR and it contains a setting of -oosting actuator4actuators in
co"plete characteristic 6or that reason a boosting pressure controller as developed 't keeps (if
possi-le) the full load "axi"u" -oosting pressure using 78& -!2pass in this case &he -oth &C
speeds (78 and 98) is +uite high at all engine operations hich "eans that the highest possi-le
exhaust -ack pressure ensures the highest possi-le EGR flo ithout throttling 'n principle this is
so"e kind of "odel si"plification, -ecause the "odel (engine "anage"ent) orks auto"aticall!
controlled -! controller and does not need an! "anual ad:ust"ents during EGR sensitivit!
co"putations
EGR System
1s as said -efore the a"ount of recirculated "ass flo is pri"aril! dependent on pressure
difference -eteen tur-ine -ack pressure and co"pressor outlet pressure (for short route) 'f this
difference is positive, the exhaust fu"es go to the inlet "anifold #nfortunatel! this is not satisfied at
all engine operating points (engine speed, load) &he co"pressor outlet pressure is often loer than
tur-ine inlet one at lo engine speeds 'f the EGR valve is opened in this situation, the intake "ass
flo ould go directl! to the exhaust "anifold 2 this is not ena-led &here exist to si"ple a!s ho
to prevent this ;-ack< EGR flo &he first a! uses engine "anage"ent progra""ing that closes the
EGR valve in the not2alloed regions 7oever this solution could have trou-les during transient
regi"es here the EGR valve actuator is not ;+uick< enough to close the EGR valve to prevent the
EGR -ack flo &he second and here used variant is an usage of reed EGR valves that prevents -ack
flo auto"aticall! &he exhaust flo can go through the reeds e+uipped valve onl! -! one direction
&he spontaneous EGR "ass flo (defined -! pressure difference) is fre+uentl! not high enough to
=
Fig. ': hort and long EGR route with 4 regulation elements. 'stage tur!ochargedengine.
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satisf! the 6ig 5 re+uire"ents &hus so"e "anner for EGR increasing has to -e found &he intake
"anifold throttling offers an eas! applica-le a! for pressure difference changing 1lternative a! is
a usage of long EGR route together ith co"pressor inlet throttling
>ince there is no infor"ation a-out the reacha-le EGR rates the investigation is undertaken in detail
for -oth short and long EGR route ith to throttling ele"ents separatel! and together – see 6ig =
Short route is -asicall! a direct connection -eteen exhaust and intake "anifold 't is controlled -!
EGR valve place upstrea" the EGR intercooler *otice? the -!2passing of EGR intercooler as not
taken into account in this ork &he intake "anifold throttle is a-le to increase the EGR rate even if
the EGR valve is full! opened or if the negative pressure difference is indicated
Long route presents a connection of tur-ine outlet and co"pressor inlet &he pressure difference is
increased -! co"pressor inlet throttle and allos EGR increasing &he trou-le ith long route ould
-e the exhaust fu"es co"ing to the co"pressor that is not usuall! developed for soot etc &his trou-le
could -e solved -! several i"prove"ents like so"e kind of filter or route connection after catal!st a
386 -ut this as not solved here
&hus there are @ actuators designed for proper EGR flo setting &he logical step is to find out a
algorith" of opening and closing all or onl! several of the" &he ai" is to "eet EGR levels ith the
loest B>6C
6ig illustrates ;reacha-le< spontaneous EGR levels ithin co"plete engine "ap (no throttling)
&his shos hat EGR percentages could the s!ste" provide naturall! ith full! opened EGR valve
ith onl! short route, long route and combination of -oth of the" &his gives a -asic idea a-outho high and ere in the co"plete engine "aps the particular EGR percentages appears &here is no
EGR applied at full load in all shoed cases &he "aps are co"puted for 5../ (no EGR), A%/, %./,
=%/, %/ load ith widely opened EGR valves and no throttling
&here ere to controllers used for the "aps creating &he 5 st – -oost pressure one sets the "axi"u"
(full load) -oosting pressure and the =nd sets re+uired BME8 at selected engine speed (eg
%./load=..."in25) &he 16R li"iting is not taken into account in these "aps, -ecause the! are
designed for the rough EGR level exploring onl!
&he iso2lines of specific fuel consu"ption are shon in each picture &he differences are not
significantl! visi-le at the first sight &he! "oves around several percent at lo EGR rates, at higher
ones the differences increase "ore significantl! &he real fuel consu"ption differences ill -e higher
co"pared to the realit! 't is caused -! co"-ustion profile that is onl! speed dependent and does not
respect the load and EGR changes &he general presu"ption is that co"-ustion ill -e longer ith
EGR increase and load decrease
&he results shon in 6ig predicts higher EGR levels for short route co"pared to long one (no
throttling) &heir co"-ination gives the highest EGR though, -ut the 6ig 5 re+uest is not reached that
is h! the throttling ill have to -e used to increase the EGR additionall! &he highest EGR levels
(no throttling) are sensed at the area ith high engine speed and lo load, -ut this is unfortunatel! an
area here so high EGR is not needed &his area is not so often traded on -! engine
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&he contour of B>6C is not full! ho"ogeneous in the last "ap 't is caused -! ver! high EGR "ass
flo that increases the engine perfor"ance so cruell! that the BME8 controller is not a-le to set eg
=%/load at @%..rp" &his is :ust the area here the engine operates rarel! and here an! EGR is not
re+uired >o e do not have to orr! a-out this situation
Throttling lgorithm Development
&he throttles in the intake "anifold and upstrea" the co"pressor are proposed to do an increasing ofEGR levels to the desired values ithin co"plete engine "ap &hus it is necessar! to find a proper
algorith" for their opening and closing &he fuel consu"ption defines the "ain decision2"aking
criteria &he reference operating point as chosen for all possi-le cases testing &his regi"e is shon
in 6ig @ (orange point) – %./ load at =... "in25 &his is the point here the re+uired level should -e
significantl! higher that the one availa-le ithout an! throttling
6ig @ shos also li"iting 16R nu"-ers that should ensure no2s"oking operation 't is clear that
engine ill pro-a-l! operate at these li"its – especiall! hen ver! high EGR levels are re+uired But
in those regi"es here the re+uired EGR level is not so high or none ill the 16R -e "uch higher
than presented li"its Cross "arked points illustrates the points here not EGR ill -e applied
1s as alread! said, the s!ste" has to throttles that ill -e used for additional EGR increase &hree
@
Fig. ): Reacha!le EGR le%els: *omparison of particular EGR routes with widel+ opened %al%es withoutthrottling for short, long and !oth together EGR routes.
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possi-le controlling variants ere tested?
5 'ntake "anifold throttling (upstrea" the EGR intake "anifold inlet) short EGR valve full!
opened 9ong EGR route is closed
= Co"pressor upstrea" throttling long EGR valve idel! opened >hort EGR route valve
closed and no inlet "anifold throttling applied
Both EGR valves idel! opened co"pressor upstrea" throttling *o intake "anifold
throttling
&he co"parison of these three controlling possi-ilities is shon in 6ig % &he throttle angle is chosen
as an independent varia-le (x2axis) &he dependent varia-les are 16R (s"oke), fuel consu"ption and
EGR &he s"oke li"it for %./ =..."in25 e+uals approxi"atel! 16R of =. (see 6ig @)
&he first variant EGR co"es not even to the =./ ith the continuousl! highest fuel consu"ption
&he second one reaches =/ of EGR ith loer B>6C than the 5 st variant &he disadvantage of this
variant sta!s in a need of fast closing of short EGR route in those instants here it as full! opened
-efore (especiall! in transient operations) &he rd variant results look si"ilar as the =nd one &he
advantage of it follos fro" the eligi-le EGR routes opening se+uence and that is h! this variant
as chosen
%
Fig. 4: -ap of $FR limits. oints mar&ed !+ cross show the regimes, where there is no recirculation.
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&he chosen EGR control "anage"ent ( rd variant)?
The short EGR valve is gradually opened !or a slight EGR increase" !ter reaching o! its
ma#imum li!t the long EGR valve begins to open" $hen the !urther EGR increasing is need the
compressor inlet throttling is used up to the minimum %R" &hus the intake "anifold throttle is
not necessar! and could -e re"oved
&he variant nu"-er is used for re+uired EGR setting ithin hole engine "ap – see 6ig @ &he
78& -!2passing inter2stage cooling is used for -oosting control strateg! &his "eans that onl! one
actuator (78& -!2pass) sets the re+uired -oosting pressure 't is controlled -! a 83 controller
designed to keep the full load -oosting pressure ithin all engine loads at particular engine speed *ote that so"eti"es the full load -oosting pressure is not reached eg at lo loads even if the 78&
-!2pass is full! closed &he "ain engine control ele"ents (-oosting and EGR ones) are descri-ed in
the &a- 5
D
Fig. /: EGR additional increasing throttling strateg+. *omparison of three chosen %ariants using inta&emanifold throttle, compressor upstream throttle and their com!ination.
0a!. 1: 0he list of main engine control elements used in engine management (E*" for re#uired !oost pressureand EGR le%el.
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1 set of universal controller constants as found and the! are a-le to ork ithing co"plete engine
"ap correctl! &he EGR actuators opening as placed ithing "aps of engine speed and load
&he resulting EGR distri-ution ithin co"plete engine "ap is shon in 6ig D &he "axi"u"
reached EGR nu"-er is @%/ at the "iddle engine speed and load area 't "eans that the re+uired %./
EGR as not ac+uired – see 6ig 5 &he reason for that is the 16R li"it &he engine ould s"oke
significantl! ith "ore EGR $ther ords said it has not enough air "ass flo to provide this EGR
value &he further EGR increase ithin 16R li"it ould -e possi-le -! using of increased -oost
pressure 1nd this ould "ean a ne tur-ocharger "atching $n the other hand the %/ is not such an
extensive difference &he engine ould -e pro-a-l! a-le to "eet the E#R$ % regulations ith these
EGR levels &he *$x e"issions ould -e additionall! decreased -! other engine para"eters
ad:ust"ents such as start of in:ection retard, another fuel in:ectors, etc Besides the vehicle
trans"ission deter"ines hich engine operating points are used ithin e"ission c!cles &he
ad:ust"ents of particular gear could slightl! change the *$x resulting e"issions, as ell
&he "aps of control ele"ents used in EC# are presented in 6ig A &he first picture presents the
opening of 78& -!2pass as an engine speed and load dependence &he next actuators ensure
re+uired EGR level (6ig D) &he operating algorith" of those actuators as descri-ed a-ove
A
Fig. 2: EGR distri!ution within complete engine characteristic with $FR isolines.
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Fig. 3: Resulting E* maps of control actuators ensuring a proper !oosting pressure (0 !+pass" and EGRle%el (rest ones".
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&onclusions
&his ork descri-es a developing of co"plete engine "ap ith given EGR re+uire"ents using Fave
.234523 code 't co"pares different possi-ilities of EGR increasing &he "otst advantageous
variant is chosen and used for full characteristic co"puting &his is in principle the first step for
transient engine "odel developing that is currentl! on progress
c'nowledgement
&his ork has -een supported -! the Josef Božek Research Center, *o 9*..B.A &his help is
gratefull! appreciated