US00829.

1891B2

(12) United States Patent (10) Patent No.: US 8,291,891 B2

Alger,9 II et al. 45) Date of Patent: Oct. 23,9 2012

(54) EGR SYSTEM WITH DEDICATED EGR 3,805,752 A 4/1974 Cataldo ....................... 123,75. R.
CYLNDERS 3,924,576 A 12, 1975 Siewert ............................. 123, 1
3,941,113 A 3/1976 Baguelin ........ 123,179 R
4,108,114 A 8/1978 Kosaka et al. .................... 123,3
(75) Inventors: Terrence Francis Alger, II, San 4,131,095 A * 12/1978 Ouchi ............ ... 123,58.8
Antonio, TX (US); Barrett Wade 4,179,892 A * 12/1979 Heydrich ... 60.605.2
Mangold, Atascosa, TX (US); Jess 5,178,119 A 1/1993 Gale .................. ... 123,570
5,257,600 A 11/1993 Schechter et al. . 123,78B
Witman Gingrich, San Antonio, TX 5,456,240 A 10/1995 Kanesaka .......... ... 123,565
(US); Darius Mehta, San Antonio, TX 5,517,976 A 5/1996 Bachle et al. .. 213,569
(US) 5,894,726 A 4, 1999 Monnier ......................... 60,274
6,009,709 A 1, 2000 Bailey . . . . . . . . . . . . . . . . . . . . . . . . . 60.605.2

(73) Assignee: Southwest Research Institute, San 6,138,650 A 10/2000 Bailey ... . . 123,568. 12
Antonio, TX (US 6.286,489 B1* 9/2001 Bailey ...................... 123,568.11
intonio, TX (US) 6.425,381 B1 7/2002 Rammer .................. 123,568.12
- 6,484,702 B1 1 1/2002 Riley ....................... 123,568.11
(*) Notice: Subject to any disclaimer, the term of this (Continued)
patent is extended or adjusted under 35
U.S.C. 154(b) by 0 days. FOREIGN PATENT DOCUMENTS
(21) Appl. No.: 12/140,878 GB 2 110791 A1 11, 1982
(Continued)
(22) Filed: Jun. 17, 2008
OTHER PUBLICATIONS
(65) Prior Publication Data International Search Report with Written Opinion, PCT/US05/
US 2009/O3O807OA1 Dec. 17, 2009 40483, 12 pages. Oct. 2, 2006.
(51) Int. Cl. (Continued)
FO2B 47/08 (2006.01) Primary Examiner — Mahmoud Gimie
F02M 25/07 290) Assistant Examiner — David Hamaoui
(52) U.S. Cl. .................. 123/568.11:123/58.8:123/315; (74) Attorney, Agent, or Firm — Chowdhury & Georgakis
701/108; 60/278 PC: Ann C. Livingston
(58) Field of Classification Search ............. 123/568.11,
123/58.8, 315,568. 17: 701/108; 60/278, (57) ABSTRACT
60/280, 288,605.1, 605.2
See application file for complete search history. Improved exhaust gas recirculation system and methods that
use one or more of the engine's cylinders as dedicated EGR
(56) References Cited cvlinders.
y All of the exhaust from the dedicated EGR cvlin
y
ders is recirculated back to the engine intake. Thus, the EGR
U.S. PATENT DOCUMENTS rate is constant, but the EGR mass flow may be controlled by
3,156,162 A 11, 1964 Wallace et al. ................... 92/82 adjusting the air-fuel ratio of the dedicated EGR cylinders or
3,303,831 A 2, 1967 Sherman .......... ... 123f48 by using various variable valve timing techniques.
3,405,679 A 10, 1968 Norris et al. ...................... 118.2
3,405,697 A 10, 1968 Marchand ....................... 123,78 14 Claims, 4 Drawing Sheets
EGR
LOOP

102 -> EXHAUST

NTAKE
MANFOLD 103
EXHAUS
MANFOLD

100
 US 8,291,891 B2
Page 2

U.S. PATENT DOCUMENTS 2005/00224.50 A1 2/2005 Tan et al. ..................... 48,198.3

ck
6,536,392 B2 3/2003 Widener .................. 123,179.19 39.83 A. 299; E. al. et......al. .........
oozenboom . . 123,568.11
60/612
6,655,324 B2* 12/2003 Cohn et al. .. ... 123/1 A 2009,01998.25 A1* 8, 2009 Piper
Oer et
et all
al. ............... 123,568.21
6,742,507 B2* 6/2004 Keefer et al. ... 123,585 2011/0041495 A1* 2/2011 Yager 60.605.2
6,789,531 B1* 9/2004 Remmels ... 123,568.11 -v vy -- - - - - , , , tes, r.
6,820.415 B2 * 1 1/2004 Abet et al. .. ... 60,286 FOREIGN PATENT DOCUMENTS
6,871,642 B1* 3/2005 Osterwald ... ... 123,568.11
6,877,492 B1 * 4/2005 Osterwald ... 123,568.11 JP 11-247665 A 9, 1999
7,290,504 B2 * 1 1/2007 Lange ........................... 123, 1 A
7,389,770 B2 * 6/2008 Bertilsson et al. ....... 123/568. 17 OTHER PUBLICATIONS
7,721,541 B2* 5/2010 Roberts et al. . ... 60.605.2
7,945,376 B2 * 5/2011 Geyer et al. ... ... 701 108 International Preliminary Report on Patentability PCT/US2005/
2002/0189598 A1 12/2002 Remmels et al. 123,568.11 04.0483, 8 pages. May 18, 2007.
2003/0121484 A1* 7/2003 Wang ......................... 123.90.16
2004.0099256 A1 5/2004 Stewart .................... 123,568.11 * cited by examiner
U.S. Patent Oct. 23, 2012 Sheet 1 of 4 US 8,291,891 B2

EGR
LOOP

102 -> EXHAUST

INTAKE
MANFOLD 103
EXHAUST
MANFOLD
U.S. Patent Oct. 23, 2012 Sheet 2 of 4 US 8,291,891 B2

340

330

BSFC
g/kWh)

32O

31 O --
OO 1.05 110 1.15 120 1.25
CYLINDER #1)
FIG. 2

2O

O BSCO
16 O BSHC
A BSNO
{X COV imep
BS 12
EMISSIONS
g/kWh)
COV (%) 8

1.OO 105 11 0 1 15 120 125

CYLINDER #1)
FIG. 3
U.S. Patent Oct. 23, 2012 Sheet 3 of 4
U.S. Patent Oct. 23, 2012 Sheet 4 of 4 US 8,291,891 B2
 US 8,291,891 B2
1. 2
EGR SYSTEM WITH DEDICATED EGR tion engine system. One or more cylinders of the internal
CYLNDERS combustion engine is used to generate the exhaust gas that
will be recirculated and used as a diluent for the intake charge
TECHNICAL FIELD OF THE INVENTION of the entire engine. The use of one or more cylinders to
generate its entire output of exhaust for recirculation is
This invention relates to internal combustion engines, and referred to herein as use of “dedicated EGR cylinder(s)'.
more particularly to an improved exhaust gas recirculation FIG.1 illustrates an internal combustion engine 100 having
system for Such engines. four cylinders 101 (referenced as cylinders 1-4). One of the
cylinders 101 is a dedicated EGR cylinder, that is, 100% of its
BACKGROUND OF THE INVENTION 10 exhaust is recirculated back to the intake manifold. The
exhaust of the other three cylinders 101 is directed to an
For control of internal combustion engines, three important exhaust system. In this example, the engine is said to have
control parameters are spark timing (or fuel injection timing “25% dedicated EGR because one of its four cylinders has
in a diesel engine), the exhaust gas recirculation (EGR) rate, 100% of its exhaust redirected to the intake manifold 102.
and the air/fuel ratio (AFR). Control of spark timing or injec- 15 Experiments have shown that if the exhaust from one or
tion timing affects the timing of the initiation of the combus more cylinders is redirected into the intake manifold, and that
tion process. Control of EGR and AFR affects the speed and cylinder is run at rich of stoichiometric A/F ratios (d. 1.0),
duration of the combustion process. the EGR tolerance of the engine increases while the overall
The AFR is often controlled by an exhaust oxygen sensor to fuel consumption decreases. Further research has shown that
produce a desired AFR in a closed loop system. EGR is 20 if the dedicated EGR cylinder is run rich of stoichiometric, a
generally controlled by a combination of different parameters significant amount of H2 and CO are formed, both of which
Such as exhaust backpressure, engine coolant temperature, can promote increased EGR tolerance by increasing burn
engine speed, throttle position or manifold pressure and has rates, increasing the dilution limits of the mixture and reduc
proven difficult to control accurately. Spark or injection tim ing quench distances.
ing is generally determined from a stored table indexed by 25 Although not explicitly illustrated in FIG. 1, it is assumed
engine speed and load parameters which may build in retard that engine 100 has a turbocharger, which is located after the
in response to a knock, MAP or throttle movement detector. exhaust manifold 102 and before the intake manifold 103.
To implement EGR, a fraction of the exhaust gases are FIG. 2 illustrates, for an engine with 25% dedicated EGR,
recycled through a control valve from the exhaust to the such as engine 100, fuel consumption results at 2000 rpm/2
engine intake system. The recycled exhaust gas is usually 30 barbmep (brake mean effective pressure). At low loads, as the
mixed with the fresh fuel-air mixture. EGR can be imple equivalence ratio of the dedicated cylinder (cylinder #1)
mented in internal and external configurations. External con increases, more hydrogen (H2) gas is produced, the engine's
figurations can be implemented as either a high pressure or stability improves, and fuel consumption decreases. Fuel
loop pressure loop, depending on whether the recirculated consumption is plotted as values of brake specific fuel con
exhaust is introduced to the intake post compressor (high 35 sumption (BSFC).
pressure loop) or pre-compressor (low pressure loop). FIG. 3 illustrates emissions results for an engine having
EGR has a long history of use in both diesel and spark 25% dedicated EGR, also at 2000 rpm/2 barbmep. The addi
ignited engines for reduction of NOx emissions. It affects tional H2 promotes more rapid and complete combustion,
combustion in several ways. The combustion is cooled by the which results in lower CO and HC emissions from the non
presence of exhaust gas, that is, the recirculated exhaust gas 0 dedicated cylinders (cylinders #2-4). The “CoV imep', an
absorbs heat. The dilution of the oxygen present in the com engine operation parameter referring to the coefficient of
bustion chamber reduces the production of NOX. Also, if variation of indicated mean effective pressure, is also
exhaust gas is being recirculated, less air is breathed by the reduced. It is assumed that the non-dedicated cylinders run at
engine, so reducing the amount of exhaust gas produced. d=1.0 and are connected to a 3-way emissions reduction
As a relatively simple and low cost technology, EGR can be 45 catalyst. The NO emissions from these cylinders increase
expected to be widely used on all types of engines. Of par slightly, due to improved combustion and the hotter tempera
ticular interest is that EGR can reduce the need for fuel tures it brings, but the increased amount was much less than
enrichment at high loads in turbocharged engines and thereby for an engine without EGR.
improve fuel economy. In addition, engine 100 also performed better at knock
50 limited conditions, improving low speed, peak torque results,
BRIEF DESCRIPTION OF THE DRAWINGS due to increased EGR tolerance and the knock resistance
provided by H2 and CO.
FIG. 1 illustrates an example of an internal combustion In the case of the example engine of FIG. 1, the estimated
engine having one dedicated EGR cylinder. level of H2 gas that can be generated is approximately 0.5%
FIG. 2 illustrates fuel consumption results for an engine 55 of the fuel mass at d=1.2. IN addition to improving perfor
having 25% dedicated EGR. mance, the dedicated EGR system is also beneficial in that the
FIG. 3 illustrates emissions and engine stability results for EGR level remains constant and is therefore much easier to
an engine having 25% dedicated EGR. control, eliminating the need for specialized sensors and con
FIG. 4 illustrates an EGR-equipped engine with 50% dedi trol algorithms.
cated EGR in a high pressure loop configuration. 60 An engine, as configured in FIG. 1 with 25% EGR, runs
FIG. 5 illustrates an EGR-equipped engine with 50% dedi well at low engine speeds. However, at Some conditions. Such
cated EGR in a low pressure loop configuration. an engine could benefit from higher EGR levels than 25%.
The increased EGR could be further enhanced if the addi
DETAILED DESCRIPTION OF THE INVENTION tional EGR were supplemented with H2.
65 FIGS. 4 and 5 illustrates engines having multiple dedicated
The following description is directed to various configura EGR cylinders. Both FIG. 4 and FIG.5 illustrate six-cylinder
tions of an EGR system implemented in an internal combus engines 40 and 50, respectively, with one bank of cylinders
 US 8,291,891 B2
3 4
(three cylinders) used to generate EGR for the opposite bank. Both engines 40 and 50 are furtherequipped with a mass air
In these engines, the nominal amount of EGR is 50%, which flow (MAF) sensor 45 and 55. Aftercoolers 46 and 56 cool the
is challenging for the engine to run. air from the compressor. The exhaust into the tailpipe 47 and
FIG. 4 illustrates a high-pressure loop (HPL) EGR system, 57 is stoichiometric, and may be treated with conventional
whereas FIG. 5 illustrates a low pressure loop (LPL) EGR exhaust aftertreatment devices, such as a three-way catalyst
system 50. In an HPL EGR-equipped engine 40, the exhaust (TWC) 48 and 58.
to be recirculated is extracted upstream of the turbine 41a and In Sum, an engine having dedicated EGR, as high as 50%,
routed to the engine intake downstream of the compressor can have its EGR tolerance improved by running dedicated
41b (post-compressor). In a LPL EGR-equipped engine 50. cylinders rich of stoichiometric to generate CO and H2 in
the exhaust to be recirculated is extracted downstream of the 10 either low-pressure loop or high-pressure loop configuration.
turbine 51a and introduced to the engine inlet upstream of the Running one or more dedicated EGR cylinders rich also
compressor 51b (pre-compressor). Both types of EGR sys improves fuel consumption and reduces emissions by
tems 40 and 50 may use a cooler, such as EGR coolers 42 and improving burn rates changing the composition of the EGR
52. The EGR cooler assists in operating the engine at appro gases and reducing pumping losses. Furthermore, running
priate temperatures and mass flow rates. 15 one or more dedicated EGR cylinders rich reduces the knock
In the case of both systems 40 and 50, for conditions at tendency through increased EGR tolerance and high octane
which the EGR tolerance is not high enough for the engine to additives (CO and H2), resulting in higher potential torque
remain stable with 50% EGR, the engine may be equipped output from the engine and better full load fuel consumption.
with either a cam phasing system or other type of variable As an alternative to running the dedicated EGR cylinder(s)
valve timing system to decrease the mass flow through the rich, the EGR rate of the engine may be controlled by running
EGR cylinders. While continuing to run the dedicated EGR some or all of the dedicated EGR cylinders lean of stoichio
cylinders rich, a system that decreases the cylinder's Volu metric (with excess air). The additional O2 in the EGR will
metric efficiency allows the engine to be calibrated for EGR serve to reduce the effective EGR rate. A sensor, such as an
levels between 30% and 50%. EGO sensor, may be installed on the EGR loop, to assist in
In the examples of FIGS. 4 and 5, engines 40 and 50 are 25 AFR control of the EGR loop.
equipped with dual camphasers 43 and 53 for each bank of Dedicated EGR cylinders simplify the EGR control of the
cylinders. For purposes of this description, “variable valve engine, reduce or eliminate the need for complicated control
timing (VVT) is used in a most general sense as a generic systems, and also reduce the sensor count on the engine.
term for any piston engine technology that allows the lift, Dedicated EGR cylinders improve transient response of
duration, timing, or phasing (some or all) of the intake or 30 engines running high levels of EGR by helping maintain EGR
exhaust valves (or both) to be controlled while the engine is in rates through transient events. The EGR rate of an engine with
operation. dedicated EGR cylinders can be controlled through a variable
In the case of the present invention, variable valve timing is valve system, such as by camphasing or variable lift/duration
used on the dedicated EGR cylinders to provide the capability systems, by reducing the volumetric efficiency of the dedi
of reducing the EGR mass flow by restricting flow through the 35 cated EGR cylinders when less EGR is required.
dedicated EGR cylinders. Although the VVT (in the form of The addition of a water-gas shift catalyst in the EGR circuit
cam phasing) is illustrated in FIGS. 4 and 5 as serving all of an engine with dedicated EGR cylinder running rich of
cylinders, in alternative embodiments, VVT could be imple Stoichiometric can increase the hydrogen (H2) content of the
mented for only the dedicated EGR cylinders. EGR gas.
In the case of a cam phasing system, the overlap between 40 Referring again to FIG. 1, the EGR system has a control
the intake and exhaust valves can be increased to raise the unit 105, which may be dedicated to EGR control or may be
level of in-cylinder residual and cut down on fresh airflow or part of a more comprehensive engine control unit. Control
the intake valve opening timing can be adjusted from its unit 105 may be implemented with conventional processing
optimum to limit the amount of fresh air inducted. and memory devices. For purposes of the various embodi
For an engine equipped with some other type of variable 45 ments described herein, control unit 105 may be programmed
valve timing system, the lift and/or duration of the intake to control the air-fuel ratio (AFR) as described above, such
valve events on the dedicated EGR engines can be adjusted to that the dedicated EGR cylinders may run rich or lean as
decrease the volumetric efficiency of the subject cylinders to desired for various engine operating conditions. Control unit
reduce the mass flow and lower the EGR percentage in the 105 may also be programmed to implement various VVT
engine. 50 schemes as described above. Thus, control unit 105 may be
Because the rich (d 1.0) cylinders also generate high lev used to control the composition and/or amount of recirculated
els of CO, there also exists the potential to installa water-gas exhaust by adjusting the AFR or by implementing various
shift (WGS) catalyst in the EGR system to further increase the VVT controls. EGR systems 40 and 50 may have similar
H2 level of the engine. Both engines 40 and 50 are equipped control units.
with a WGS catalyst 44 and 54, respectively, downstream 55
their EGR coolers. What is claimed is:
The WGS catalysts can be of several different composi 1. A method of operating an internal combustion engine,
tions, but their main use is to convert the CO in the EGR the engine having an intake manifold and having multiple
system to H2 through the WGS reaction: CO+H2O->H2+ cylinders, comprising:
CO2. Because the dedicated EGR cylinders are run rich of 60 operating at least one cylinder of the engine as a dedicated
stoichiometric, they will generate significant levels of CO, exhaust gas recirculation (EGR) cylinder, such that the
which is more favorable to the WGS reaction than typical, exhaust from the at least one dedicated EGR cylinder is
stoichiometric exhaust with low CO levels and high CO2 completely recirculated to the intake manifold, and Such
concentrations. Due to the limited ability of WGS catalysts to that none of the exhaust from the remaining cylinders is
function at high temperatures, the engine is equipped with a 65 recirculated to the intake manifold:
pre-catalyst EGR cooler to reduce the exhaust temperatures providing the engine with an exhaust gas recirculation loop
to the required, high-efficiency levels. in which recirculated exhaust flows from the at least one
 US 8,291,891 B2
5 6
dedicated EGR cylinder into the intake manifold with 4. The method of claim 1, wherein the variable valve timing
out fluid communication to the exhaust exiting the is implemented with variable valve lift or variable valve dura
engine; tion.
wherein the at least one dedicated EGR cylinder and the 5. The method of claim 1, wherein the exhaust is recircu
remaining cylinders share the same intake manifold, lated in a high pressure loop configuration.
such that the recirculated exhaustis combined with fresh 6. The method of claim 1, wherein the exhaust is recircu
air in the intake manifold; lated in a low pressure loop configuration.
using a water-gas shift catalyst in the loop to increase the 7. The method of claim 1, further comprising the step of
hydrogen level of the recirculated exhaust received into using an exhaust gas cooler in the exhaust gas recirculation
the intake manifold;
10 loop to cool the recirculated exhaust.
controlling the amount of the recirculated exhaust, at least 8. The method of claim 1, wherein the proportion of the
in part, by means of variable valve timing of the at least total exhaust from the engine that is recirculated is in the
one dedicated EGR cylinder; range of 30% to 50%.
9. The method of claim 1, further comprising treating the
operating the at least one dedicated EGR cylinder at a rich 15 exhaust from the engine with a three-way catalyst.
air-fuel ratio that is rich of stiochiometric; 10. The method of claim 1, wherein the step of controlling
operating the at least one non dedicated cylinder at a sto the composition is further performed to actively control the
ichiometric air-fuel ratio; and knock resistance of all cylinders.
controlling the composition of the recirculated exhaust by 11. The method of claim 1, wherein the step of controlling
controlling the rich air-fuel ratio provided to that cylin the composition is further performed to actively control the
der; combustion burn rates of all cylinders.
wherein the step of controlling the composition is per 12. The method of claim 1, wherein the step of controlling
formed to produce exhaust gas from the at least one the composition is further performed to actively control the
dedicated EGR cylinder having levels of hydrogen pre engine's transient response through transient events.
determined to provide a desired rate of fuel consumption 25 13. The method of claim 1, wherein the step of controlling
by all cylinders in accordance with a predetermined the composition is further performed to actively control the
relationship between the rich air-fuel ratio and fuel con octane content of the recirculated exhaust.
Sumption. 14. The method of claim 1, wherein the step of controlling
2. The method of claim 1, wherein half of the engine's the composition is performed to actively control the dilution
cylinders are dedicated EGR cylinders. 30 tolerance of all cylinders.
3. The method of claim 1, wherein the variable valve timing
is implemented with cam phasing. k k k k k