2-Stage Turbo EGR

8/10/2019 2-Stage Turbo EGR

http://slidepdf.com/reader/full/2-stage-turbo-egr 1/9

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.




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.




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




&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.




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.




&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.




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.




Fig. 3: Resulting E* maps of control actuators ensuring a proper !oosting pressure (0 !+pass" and EGRle%el (rest ones".




&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

2-Stage Turbo EGR

Documents