U.S. patent application number 16/998539 was filed with the patent office on 2022-02-24 for method and system for extending dilution limit of a prechamber spark ignition engine.
This patent application is currently assigned to ARAMCO SERVICES COMPANY. The applicant listed for this patent is ARAMCO SERVICES COMPANY. Invention is credited to Nayan Engineer, Alexander Voice, Xin Yu.
Application Number | 20220056835 16/998539 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-24 |
United States Patent
Application |
20220056835 |
Kind Code |
A1 |
Voice; Alexander ; et
al. |
February 24, 2022 |
METHOD AND SYSTEM FOR EXTENDING DILUTION LIMIT OF A PRECHAMBER
SPARK IGNITION ENGINE
Abstract
A system includes an engine having a main combustion chamber and
a prechamber containing a spark plug. The prechamber is in fluid
communication with the main combustion chamber through at least one
orifice. An engine intake line provides intake air to the engine.
An engine exhaust line receives exhaust gases from the engine. An
exhaust gas recirculation line transports a portion of the exhaust
gases from the engine exhaust line to the engine intake line,
forming an exhaust gas recirculation loop through the engine. The
system includes a reformer having a reactor containing a
catalyst-coated substrate. The reformer generates a gaseous
reformate from a fuel. The system includes a prechamber feed line
to transport a stream of the gaseous reformate from the reformer to
the prechamber.
Inventors: |
Voice; Alexander; (Detroit,
MI) ; Engineer; Nayan; (Canton, MI) ; Yu;
Xin; (New Hudson, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ARAMCO SERVICES COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
ARAMCO SERVICES COMPANY
Houston
TX
|
Appl. No.: |
16/998539 |
Filed: |
August 20, 2020 |
International
Class: |
F02B 19/12 20060101
F02B019/12; F02B 19/10 20060101 F02B019/10 |
Claims
1. A system, comprising: an engine comprising: a main combustion
chamber; and a prechamber containing a spark plug, the prechamber
disposed at least partially within the main combustion chamber and
in fluid communication with the main combustion chamber through at
least one orifice; an engine intake line having an inlet end in
communication with an ambient environment and an outlet end in
communication with the engine, the engine intake line to provide
intake air to the engine; an engine exhaust line having an inlet
end in communication with the engine and an outlet end in
communication with the ambient environment, the engine exhaust line
to receive exhaust gases from the engine; an exhaust gas
recirculation line in communication with the engine intake line and
the engine exhaust line, the exhaust gas recirculation line to
selectively transport a portion of the exhaust gases from the
engine exhaust line to the engine intake line and thereby form an
exhaust gas recirculation loop through the engine; a reformer
comprising a reactor containing a catalyst-coated substrate, the
reformer to generate a gaseous reformate from a fuel; a prechamber
feed line in fluid communication with the reformer and the
prechamber, the prechamber feed line to transport a stream of the
gaseous reformate from the reformer to the prechamber; and an
exhaust feed line in fluid communication with the engine exhaust
line and the reactor, the exhaust feed line to transport a stream
of the exhaust gases from the engine exhaust line to the reactor,
wherein the exhaust feed line includes a mixing section in which
the fuel contacts the stream of the exhaust gases; and wherein the
exhaust feed line includes the mixing section in which a supply of
air contacts the stream of the exhaust gases.
2. The system of claim 1, wherein the prechamber feed line includes
the mixing section in which a supply of air contacts the stream of
the gaseous reformate.
3. The system of claim 2, wherein the prechamber feed line is
connected to an intake port of the prechamber, and further
comprising a valve disposed in the intake port to selectively
permit flow from the prechamber feed line into the prechamber.
4. (canceled)
5. (canceled)
6. (canceled)
7. The system of claim 1, further comprising an exhaust vent line
in fluid communication with the engine exhaust line and a portion
of an environment containing the reformer, the exhaust vent line to
transport the stream of the exhaust gases from the engine exhaust
line to the portion of the environment containing the reformer, the
stream of the exhaust gases transported by the exhaust vent line to
provide heating to the reformer.
8. The system of claim 1, wherein the reformer further comprises a
vaporizer in fluid communication with the reactor, the vaporizer
arranged to receive the fuel and output a vaporized fuel to the
reactor for generation of the gaseous reformate.
9. The system of claim 1, further comprising a valve disposed in
the exhaust gas recirculation line to control flow of the exhaust
gases from the engine exhaust line to the engine intake line.
10. The system of claim 9, further comprising a cooling device
disposed in the exhaust gas recirculation line and operable to
remove heat from the exhaust gases flowing from the exhaust gas
recirculation line into the engine intake line.
11. The system of claim 10, further comprising: a compressor
disposed in the engine intake line and operable to compress flow in
the engine intake line; and a turbine disposed in the engine
exhaust line and driven by the exhaust gases flowing through the
engine intake line, the turbine operatively coupled to the
compressor.
12. A method for operating an engine, comprising: generating a
stream of hydrogen-rich gaseous reformate in a reformer located
outside of an engine cylinder, the generating comprising contacting
a fuel with a catalyst-coated substrate in a reactor of the
reformer; for each of a plurality of operating cycles of the
engine, providing a first combustible mixture comprising a portion
of the hydrogen-rich gaseous reformate in a prechamber of the
engine; providing a second combustible mixture in a main combustion
chamber of the engine; spark igniting the first combustible mixture
in the prechamber to generate a plurality of flame jets; ejecting
the plurality of flame jets from the prechamber into the main
combustion chamber, whereby the flame jets ignite the second
combustible mixture in the main combustion chamber; ejecting
exhaust gases generated from igniting the second combustible
mixture out of the main combustion chamber; directing at least a
portion of the exhaust gases ejected out of the main combustion
chamber to the reformer; and diluting the second combustible
mixture for a subsequent operation cycle with at least one of air
and a portion of the exhaust gases ejected out of the main
combustion chamber in a previous operation cycle.
13. The method of claim 12, wherein generating a stream of
hydrogen-rich gaseous reformate in a reformer located outside of an
engine cylinder comprises generating hydrogen-rich gaseous
reformate comprising hydrogen and carbon monoxide.
14. The method of claim 12, wherein directing the at least a
portion of the exhaust gases to the reformer comprises providing
the at least a portion of the exhaust gases as a stream of exhaust
gases and feeding the stream of exhaust gases into the reactor.
15. The method of claim 14, further comprising at least one of
injecting the fuel into the stream of exhaust gases that is fed
into the reactor and injecting air into the stream of exhaust gases
that is fed into the reactor.
16. The method of claim 14, wherein directing the at least a
portion of the exhaust gases to the reformer comprises heating the
reformer by contacting the reformer with the at least a portion of
the exhaust gases.
17. The method of claim 12, wherein contacting a fuel with a
catalyst-coated substrate in a reactor of the reformer comprises
providing gasoline or methanol as the fuel.
18. The method of claim 17, further comprising vaporizing the fuel
prior to contacting the fuel with the catalyst-coated
substrate.
19. (canceled)
20. The method of claim 12, further comprising cooling the portion
of the exhaust gases prior to diluting the second combustion
mixture with the portion of the exhaust gases, wherein a dilution
level of the second combustible mixture with at least one of the
air and the portion of the exhaust gases is up to 50%.
21. A method for operating an engine, comprising: generating a
stream of hydrogen-rich gaseous reformate in a reformer located
outside of an engine cylinder, the generating comprising contacting
a fuel with a catalyst-coated substrate in a reactor of the
reformer; for each of a plurality of operating cycles of the
engine, providing a first combustible mixture comprising a portion
of the hydrogen-rich gaseous reformate in a prechamber of the
engine; providing a second combustible mixture in a main combustion
chamber of the engine; spark igniting the first combustible mixture
in the prechamber to generate a plurality of flame jets; ejecting
the plurality of flame jets from the prechamber into the main
combustion chamber, whereby the flame jets ignite the second
combustible mixture in the main combustion chamber; ejecting
exhaust gases generated from igniting the second combustible
mixture out of the main combustion chamber; and directing at least
a portion of the exhaust gases ejected out of the main combustion
chamber to the reformer; diluting the second combustible mixture
for a subsequent operation cycle with at least one of air and a
portion of the exhaust gases ejected out of the main combustion
chamber in a previous operation cycle; and cooling the portion of
the exhaust gases prior to diluting the second combustion mixture
with the portion of the exhaust gases, wherein a dilution level of
the second combustible mixture with at least one of the air and the
portion of the exhaust gases is up to 50%.
Description
FIELD
[0001] The disclosure relates generally to spark ignition (SI)
engines and more particularly to a method and system of extending
an operating limit of a prechamber SI engine.
BACKGROUND
[0002] One opportunity for improving engine efficiency and reducing
transport related emissions, such as CO.sub.2 emissions and other
pollutants, without significantly increasing transportation costs
is a concept known as turbulent jet ignition (TJI). TJI uses a
prechamber to combust a small quantity of fuel. As a result of the
combustion, high energy flame jets are ejected from the prechamber
into a main combustion chamber, where they ignite compressed
fuel-air mixture in the main combustion chamber. The high energy
flame jets provide distributed ignition sites that enable fast
combustion and high burn rates of the fuel-air mixture in the main
combustion chamber. TJI enables efficient combustion of very lean
or dilute mixtures. However, TJI technology suffers from challenges
with operation at low load and cold start and with emissions when
operating lean. In particular, dilution tolerance with recycled
inert exhaust gases is usually poor, and dilution with excess air
is limited by ignitability of the gases in the prechamber.
Furthermore, operation of the main combustion chamber under lean
conditions generates nitrogen oxide (NO)) emissions, requiring
expensive aftertreatment technology.
SUMMARY
[0003] In a first summary example, a system includes an engine
having a main combustion chamber and a prechamber containing a
spark plug. The prechamber is disposed at least partially within
the main combustion chamber and is in communication with the main
combustion chamber through at least one orifice. The system
includes an engine intake line having an inlet end in communication
with an ambient environment and an outlet end in communication with
the engine. The engine intake line provides intake air to the
engine. The system includes an engine exhaust line having an inlet
end in communication with the engine and an outlet end in
communication with the ambient environment. The engine exhaust line
receives exhaust gases from the engine. The system includes an
exhaust gas recirculation (EGR) line in communication with the
engine intake line and the engine exhaust line. The EGR line
selectively transports a portion of the exhaust gases from the
engine exhaust line to the engine intake line and thereby forms an
EGR loop through the engine. The system includes a reformer having
a reactor containing a catalyst-coated substrate. The reformer
generates a gaseous reformate from a fuel. The system includes a
prechamber feed line in fluid communication with the reformer and
the prechamber. The prechamber feed line transports a stream of the
gaseous reformate from the reformer to the prechamber.
[0004] The prechamber feed line may include a mixing section in
which a supply of air contacts the stream of the gaseous reformate.
The prechamber feed line may be connected to an intake port of the
prechamber. The system may include a valve disposed in the intake
port to selectively permit flow from the prechamber feed line into
the prechamber.
[0005] The system may include an exhaust feed line in fluid
communication with the engine exhaust line and the reactor. The
exhaust feed line transports a stream of the exhaust gases from the
engine exhaust line to the reactor. The exhaust feed line may
include a mixing section in which a supply of air contacts the
stream of the exhaust gases.
[0006] The system may include an exhaust vent line in fluid
communication with the engine exhaust line and a portion of an
environment containing the reformer. The exhaust vent line may
transport a stream of the exhaust gases from the engine exhaust
line to the portion of the environment containing the reformer. The
stream of the exhaust gases transported by the exhaust vent line
may provide heating to the reformer.
[0007] The reformer may include a vaporizer in fluid communication
with the reactor. The vaporizer may be arranged to receive the fuel
and output a vaporized fuel to the reactor for generation of the
gaseous reformate.
[0008] The system may include a valve disposed in the EGR line to
control flow of the exhaust gases from the engine exhaust line to
the engine intake line. The system may include a cooling device
disposed in the EGR line and operable to move heat from the exhaust
gases flowing through the EGR line into the engine intake line. The
system may include a compressor disposed in the engine intake line
and operable to compress flow in the engine intake line. The system
may include a turbine disposed in the engine exhaust line and
driven by the exhaust gases flowing through the engine intake line.
The turbine may be operatively coupled to the compressor.
[0009] The system may include an exhaust emission control device.
The reformer may be constructed concentrically inside the exhaust
emission control device. Alternatively, the system may include a
vaporizer that is constructed concentrically inside the exhaust
emission control device and in communication with the reformer.
[0010] In a second summary example, a method for operating an
engine includes generating a stream of hydrogen-rich gaseous
reformate in a reformer located outside of an engine cylinder. The
act of generating a stream of hydrogen-rich gaseous reformate in a
reformer located outside of an engine cylinder includes contacting
a fuel with a catalyst-coated substrate in a reactor of the
reformer. The method includes, for each of a plurality of operating
cycles of the engine, providing a first combustible mixture
including a portion of the hydrogen-rich gaseous reformate in a
prechamber of the engine; providing a second combustible mixture in
a main combustion chamber of the engine; spark igniting the first
combustible mixture in the prechamber to generate a plurality of
flame jets; ejecting the plurality of flame jets from the
prechamber into the main combustion chamber, whereby the flame jets
ignite the second combustible mixture in the main combustion
chamber; ejecting exhaust gases generated from igniting the second
combustible mixture out of the main combustion chamber; and
directing at least a portion of the exhaust gases ejected out of
the main combustion chamber to the reformer.
[0011] The act of generating a stream of hydrogen-rich gaseous
reformate in a reformer located outside of an engine cylinder may
include generating a hydrogen-rich gaseous reformate comprising
hydrogen and carbon monoxide.
[0012] The act of directing at least a portion of the exhaust gases
to the reformer may include providing the at least a portion of the
exhaust gases as a stream of exhaust gases and feeding the stream
of exhaust gases into the reactor. The method may include injecting
the fuel into the stream of exhaust gases that is fed into the
reactor. The method may include injecting air into the stream of
exhaust gases that is fed into the reactor. The method may include
spraying the fuel directly onto the catalyst-coated substrate. The
act of directing at least a portion of the exhaust gases to the
reformer may include heating the reformer by contacting the
reformer with the at least a portion of the exhaust gases.
[0013] The act of contacting a fuel with a catalyst-coated
substrate in a reactor of the reformer may include providing
gasoline or methanol as the fuel. The method may include vaporizing
the fuel prior to contacting the fuel with the catalyst-coated
substrate.
[0014] The method may include diluting the second combustible
mixture for a subsequent operation cycle with at least one of air
and a portion of the exhaust gases ejected out of the main
combustion chamber in a previous operation cycle. The portion of
the exhaust gases may be cooled prior to diluting the second
combustion mixture with the portion of the exhaust gases. A
dilution level of the second combustible mixture with at least one
of the air and the portion of the exhaust gases may be up to 40% or
50%.
[0015] The foregoing general description and the following detailed
description are exemplary of the invention and are intended to
provide an overview or framework for understanding the nature of
the invention as it is claimed. The accompanying drawings are
included to provide further understanding of the invention and are
incorporated in and constitute a part of the specification. The
drawings illustrate various embodiments of the invention and
together with the description serve to explain the principles and
operation of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0016] The following is a description of the figures in the
accompanying drawings. In the drawings, identical reference numbers
identify similar elements or acts. The sizes and relative positions
of elements in the drawings are not necessarily drawn to scale. For
example, the shapes of various elements and angles are not
necessarily drawn to scale, and some of these elements may be
arbitrarily enlarged and positioned to improve drawing legibility.
Further, the particular shapes of the elements as drawn are not
necessarily intended to convey any information regarding the actual
shape of the particular elements and have been solely selected for
ease of recognition in the drawing.
[0017] FIG. 1 is a schematic diagram of a reformer for generating a
gaseous reformate onboard according to one illustrative
implementation.
[0018] FIG. 2 is a modification of FIG. 1 showing nozzles arranged
to spray fuel onto a catalyst-coated substrate in a reactor.
[0019] FIG. 3 is a schematic diagram of a reformer for generating a
gaseous reformate onboard according to another illustrative
implementation.
[0020] FIG. 4 is a schematic diagram showing the reformer of FIG. 1
operatively coupled to a spark ignition (SI) engine according to
one illustrative implementation.
[0021] FIG. 5 is a modification of FIG. 4 showing independent
feeding of a gaseous reformate and air into a prechamber.
[0022] FIG. 6 is a modification of FIG. 4 showing feeding of a
gaseous reformate, air, and a liquid fuel into a prechamber.
[0023] FIG. 7 is a modification of FIG. 6 showing a high pressure
exhaust gas recirculation (EGR) loop.
[0024] FIG. 8 is a schematic diagram showing the reformer of FIG. 3
operatively coupled to an SI engine according to another
illustrative implementation.
DETAILED DESCRIPTION
[0025] In the following detailed description, certain specific
details are set forth in order to provide a thorough understanding
of various disclosed implementations and embodiments. However, one
skilled in the relevant art will recognize that implementations and
embodiments may be practiced without one or more of these specific
details, or with other methods, components, materials, and so
forth. In other instances, well known features or processes
associated with internal combustion engine systems have not been
shown or described in detail to avoid unnecessarily obscuring
descriptions of the implementations and embodiments. For the sake
of continuity, and in the interest of conciseness, same or similar
reference characters may be used for same or similar objects in
multiple figures.
[0026] Efficiency improvements in a spark ignition (SI) engine is
realized through generation of H.sub.2-rich gaseous reformate
outside of the engine cylinders and use of the H.sub.2-rich gaseous
reformate in fueling a prechamber containing a spark plug, where
the prechamber acts as a main ignition source for a main combustion
chamber. For an engine operating under stoichiometric conditions,
the prechamber fueled with H.sub.2-rich gaseous reformate extends
the dilution limit of the combustion with cooled exhaust gas
recirculation (EGR). The H.sub.2-rich gaseous reformate is
generated through catalytic reforming. In a preferred example, the
H.sub.2-rich gaseous reformate contains H.sub.2 and CO and may
contain other diluents such as N.sub.2. In a more preferred
example, the H.sub.2-rich gaseous reformate is pure syngas
consisting of H.sub.2 and CO. The prechamber fueled with
H.sub.2-rich gaseous reformate is capable of igniting combustible
mixtures that have been significantly diluted with excess air or
exhaust gases. Tests show combustion stability with dilution level
in the engine of 40% EGR or greater for H.sub.2-rich gaseous
reformate containing H.sub.2, CO, and N.sub.2 while operating the
engine under stoichiometric conditions. Dilution with exhaust gases
reduces NO.sub.x emissions out of the engine and avoids the need
for expensive aftertreatment systems.
[0027] FIG. 1 shows one illustrative implementation of a reformer
100 that may used to generate a gaseous reformate during steady
state operation of an engine, i.e., after engine startup. The term
"reformate" refers to the product of the reformer. Reformer 100
includes a reactor 104 containing a catalyst-coated substrate 108.
The substrate may be, for example, cordierite or other ceramic
material. The catalyst coating may include one or more catalysts
selected from platinum (Pt), palladium (Pd), rhodium (Rh), and
other precious metal catalysts or platinum group metals. The
selected catalyst(s) are carried by a washcoat, which may include
one or more refractory inorganic materials, such as alumina,
silica, and ceria. In one particular example, the catalyst coating
contains Rh in an amount of approximately 1 percent by weight. In
another particular example, the catalyst coating contains Rh and
Pt, each in an amount ranging from approximately 0.01 to 5 percent
by weight. For these examples, the remainder of the catalyst
coating may be the materials of the washcoat.
[0028] Reformer 100 outputs a stream of gaseous reformate 112 into
an output line 114, which may be connected to a feed line of a
prechamber (not shown). Reformer 100 converts a fuel 116 into
gaseous reformate 112 in the presence of catalyst(s). The reforming
process may include steam reforming or partial oxidation reforming
or both steam reforming and partial oxidation reforming. In one
implementation, exhaust gases 120 provide steam and/or CO.sub.2 for
reforming reactions. A stream of exhaust gases 120 is fed into
reactor 104 through a feed line 124, which may be in communication
with an exhaust line of an engine (not shown). An exhaust control
valve 126 may mediate flow of exhaust gases from the exhaust line
into feed line 124. Fuel 116 can be injected into a stream of
exhaust gases 120 passing through feed line 124 into reactor 104.
An alternative to injecting fuel 116 into the stream of exhaust
gases 120 in feed line 124 is to spray fuel 116 directly onto
catalyst-coated substrate 108. For illustrative purposes, FIG. 2
shows nozzles 140 arranged to spray fuel 116 onto catalyst-coated
substrate 108. It is also possible to both spray fuel 116 onto
catalyst-coated substrate 108 (as illustrated in FIG. 2) and inject
fuel 116 into the stream of exhaust gases 120 in feed line 124 (as
illustrated in FIG. 1). Air 128 may be optionally added to the
stream of exhaust gases 120 in feed line 124, e.g., during startup
of reformer 100. Air 128 can be heated by the stream of exhaust
gases 120 and can enable fast warmup of reformer 100. A control
valve 130 may be used to selectively permit addition of air 128 to
the stream of exhaust gases 120 in feed line 124.
[0029] Referring to FIGS. 1 and 2, some reforming reactions inside
reactor 104 may be endothermic reactions. To promote these
reactions, heat may be applied to reformer 100 during the reforming
process. In one implementation, a stream of exhaust gases 132
provides heat to reformer 100 through a vent line 136. The heating
may be provided by bringing exhaust gases 132 into contact with
surfaces of reformer 100. When reformer 100 is operatively coupled
to an engine, vent line 136 can be fluidly connected to an exhaust
line of the engine (not shown). This means that exhaust gases 132
for heating and exhaust gases 120 for reforming reactions can come
from the same source. However, the stream of exhaust gases 132 will
generally be on a different flow path compared to the stream of
exhaust gases 120. Exhaust gases 132 may be fed in and around and
in contact with surfaces of reformer 100 through branches 136a,
136b of vent line 136. Vent line branch 136b passing through
reformer 100 may be isolated from reactor 104 so that exhaust gases
132 for heating do not mix with exhaust gases 120 fed into reactor
104 for reforming reactions. A control valve 138 may control flow
of exhaust gases 132 into vent line 136.
[0030] In one implementation, fuel 116 is gasoline or a gasoline
blend. If reformer 100 is operatively coupled to a gasoline engine,
then reformer 100 and the engine can share the same supply of fuel.
In the example where fuel 116 is gasoline, fuel 116 is partially
converted into H.sub.2 and CO inside reactor 104 via the following
reactions:
C x .times. H y .times. O z + x - z 2 .times. O 2 .fwdarw. x
.times. CO + y 2 .times. H 2 ( 1 ) C x .times. H y .times. O z + (
x - z ) .times. H 2 .times. O .fwdarw. x .times. C0 + ( y 2 + x - z
) .times. H 2 ( 2 ) C x .times. H y .times. O z + ( 2 .times. x - z
) .times. H 2 .times. O .fwdarw. xCO 2 + ( y 2 + 2 .times. x - z )
.times. H 2 ( 3 ) C x .times. H y .times. O z + ( x + y 4 - z 2 )
.times. O 2 .fwdarw. xCO 2 + y 2 .times. H 2 .times. O ( 4 ) C x
.times. H y .times. O z + ( x - z ) .times. CO 2 .fwdarw. ( 2
.times. x - z ) .times. CO + y 2 .times. H 2 ( 5 ) CO + H 2 .times.
O CO 2 + H 2 ( 6 ) ##EQU00001##
[0031] Reactions (1), (4), and (6) are exothermic processes.
Reactions (2), (3), and (5) are endothermic processes. In general,
reactions (2) and (5) are preferred, and reactions (1) and (4) only
occur if optional air is used in reactor 104 (either as excess air
from combustion or auxiliary air supply). In an ideal case, all of
the fuel and exhaust species flowing into reactor 104 are converted
to H.sub.2 and CO, resulting in H.sub.2-rich gaseous reformate 112
with a composition of roughly 50% N.sub.2, 25% H.sub.2, and 25% CO.
The exact composition of H.sub.2-rich gaseous reformate 112 will
depend on the composition of the gasoline used as fuel 116, the
extent of conversion of the fuel, and the relative rates of various
competing reactions. For real systems, some amount of CH.sub.4,
small (C2-C4) hydrocarbons, and unconverted gasoline fuel are
expected. Table 1 shows an example gasoline composition fed to an
engine and a gaseous reformate produced by feeding the same
gasoline composition and exhaust gases from the engine to the
reformer.
TABLE-US-00001 TABLE 1 Theoretical Optimal Theoretical Engine
Engine Reformer Optimal Measured Inlet Exhaust Inlet Reformer
reformate Compo- Compo- Compo- Outlet compo- sition sition sition
Compo- sition (mol %) (mol %).sup.1 (mol %).sup.1 sition.sup.1 (mol
%) O.sub.2 20.58 0.00 0.00 0.00 0.00 N.sub.2 77.43 73.68 70.93
47.88 48.78 CO.sub.2 0.00 13.26 12.76 0.00 0.87 H.sub.2O 0.00 13.06
12.57 0.00 1.32 H.sub.2 0.00 0.00 0.00 25.86 23.47 CO 0.00 0.00
0.00 26.26 22.46 CH.sub.4 0.00 0.00 0.00 0.00 0.29 C.sub.2H.sub.4
0.00 0.00 0.00 0.00 0.04 C.sub.3H.sub.6 0.00 0.00 0.00 0.00 0.03
Gasoline 1.99 0.00 3.73 0.00 0.30.sup.2 .sup.1Calculated assuming
gasoline with average carbon number of 7, H/C ratio of 1.97, and
O/C ratio of 0.0305. For theoretical numbers, carbon is assumed to
be converted to CO.sub.2 in the engine and CO in the reformer. All
hydrogen is assumed to be converted to H.sub.2O in the engine and
H.sub.2 in the reformer.
[0032] In general, reformer 100 may use exhaust gases only, exhaust
gases and one or both of steam and air, air only, air and steam, or
steam only to generate gaseous reformate from fuel. The efficiency
and complexity of the reforming system will depend on the type of
oxidant used and the sensible heat requirements (i.e., the heat
required to warm the reactants, which is the difference between the
inlet and outlet temperatures of the reformer). Steam reforming is
preferred from a thermodynamic standpoint, but the temperature must
be sufficiently high for conversion to occur. Water that may be
converted to steam is present in exhaust gases. For example, a
typical spark ignition exhaust contains approximately 12 to 13% mol
water. Additional water for producing steam can be scavenged from
exhaust as the exhaust travels to the tailpipe of the vehicle and
cools down. Energy can be recovered via thermochemical recuperation
of exhaust heat and used to heat air or water for the reformer.
Endothermic steam reforming and dry reforming reactions, such as
reactions (2), (3), and (5) convert exhaust heat into chemical
potential energy.
[0033] FIG. 3 shows a reformer 100' that is a modification of
reformer 100. Reformer 100' includes a vaporizer 144 that is in
communication with reactor 104. Fuel 116' is fed into vaporizer
144, e.g., through a nozzle 146. In one implementation, fuel 116'
is an alcohol fuel or other alternative fuel carrying oxygen. Fuel
116' carrying its own oxygen does not require exhaust gases for
reforming reactions. In one example, fuel 116' is methanol, which
does not require an oxidant and can be reformed at low temperature.
In one example, fuel 116' as methanol is vaporized in vaporizer 144
and then dissociated into H.sub.2 and CO in reactor 104 as
follows:
CH.sub.3OH(l).fwdarw.CH.sub.3OH(g) (7)
CH.sub.3OH(g).fwdarw.CO(g)+2H.sub.2(g) (8)
[0034] The vaporization and dissociation of methanol are
endothermic processes. Heating for the vaporization of methanol may
be provided by exhaust gases 148 through feed line 152. Heating for
the dissociation of methanol may be provided by exhaust gases 132
flowing through vent lines 136, 136a, 136b. If only vaporized
methanol is fed to reactor 104, i.e., if exhaust gases are not fed
into reactor 104, then reformer 100' will produce substantially
pure syngas (67 mol % H.sub.2 and 33 mol % CO) as gaseous reformate
112. This higher content of H.sub.2 and CO in the gaseous reformate
has advantages in terms of ignition energy in the prechamber. As
shown in reaction (8), reforming reactions occur in the gas phase.
Vaporizing methanol allows methanol to be in a phase where
reforming reactions occur. However, it is possible to reform
methanol using the previously described reformers (in FIGS. 1 and
2), i.e., methanol could be injected or sprayed into any
combination of exhaust gases, air, and steam to enable reforming
reactions in the reactor.
[0035] FIG. 4 shows a system 200 including reformer 100 and an
engine 202. Engine 202 includes an engine cylinder 204 formed
within an engine body or engine block (not shown separately). For
ease of illustration, engine 202 is shown with a single cylinder
204. However, engine 202 is not limited to a single cylinder and
may have multiple cylinders. A piston 208 is arranged to move back
and forth inside cylinder 204. Piston 208 is connected to a
crankshaft (not shown), which converts the reciprocating motion of
piston 208 into rotary motion, as is well known in the art of
reciprocating engines. Main combustion chamber 212 is defined
within cylinder 204. The volume of main combustion chamber 212
depends on the position of piston 208 within cylinder 204. The head
of cylinder 204 includes an intake port 216 and an exhaust port
220. Intake port 216 is in fluid communication with an intake line
224 through an inlet line 228. Intake line 224 has an inlet end 232
to receive air 236 from the ambient environment. Intake line 224
may include a particulate filter 240 to remove particulate material
from the received air. Exhaust port 220 is in fluid communication
with an exhaust line 244 through an outlet line 248. Exhaust line
244 has an outlet end 248 to discharge exhaust gases 252 to the
ambient environment. Exhaust line 244 may include an exhaust
emission control device 256 (e.g., a catalytic converter) to reduce
toxic gases and pollutants in the exhaust gases discharged to the
ambient environment.
[0036] Intake line 224 terminates in an intake manifold 260. Inlet
line 228 is connected between intake port 216 and intake manifold
260. The flow of air from intake manifold 260 into inlet line 228
may be controlled by a throttle valve 264. An intake valve 268 is
arranged at intake port 216 to control flow from inlet line 228
into main combustion chamber 212. In one example, a fuel injector
272 may be positioned to inject fuel into the air flowing into
intake port 216 from inlet line 228. The flowing air entrains the
fuel, delivering a fuel-air mixture to main combustion chamber 212.
Alternatively, a fuel injector may be positioned to inject fuel
directly into main combustion chamber 212, where the injected fuel
will mix with air received in main combustion chamber 212 through
intake port 216. Alternatively, both port injection and direct
injection of fuel into main combustion chamber 212 may be used.
Fuel injector 272 is connected to a fuel line 273 via an inlet line
274. Valve 275 may control flow of fuel to fuel injector 272. Fuel
line 273 is connected to a fuel supply 276. The details of fuel
supply 276 are not shown but are well known in the art. In general,
fuel supply 276 includes a fuel tank and a fuel pump to transfer
fuel from the fuel tank to fuel line 273. Exhaust line 244 begins
at exhaust manifold 276. Outlet line 248 from exhaust port 220 is
connected to exhaust manifold 276. An exhaust valve 280 is arranged
at exhaust port 220 to control flow from main combustion chamber
212 into outlet line 248. Opening and closing of valves 268, 275,
280 may be controlled by a computer (not shown) according to an
engine stroke cycle.
[0037] A prechamber 284 is formed within the engine body.
Prechamber 284 is arranged at the head of cylinder 204 such that at
least a portion of prechamber 284 is disposed inside main
combustion chamber 212. The portion of prechamber 284 disposed
inside main combustion chamber 212 includes one or more orifices
288 that allow fluid communication between prechamber 284 and main
combustion chamber 212. An intake port 292 is formed in a wall of
prechamber 284. Intake port 292 is connected to an inlet line 296,
which is in fluid communication with outlet line 114 of reformer
100. An intake valve 300 may be arranged in intake port 292 to
control flow of fluid from inlet line 296 into prechamber 284. In
one implementation, inlet line 296 has an inlet end 304 to receive
air 308 from the ambient environment. Inlet line 296 includes a
section 312 where air 308 is mixed with a stream of gaseous
reformate from outlet line 114 of reformer 100. Prechamber 284
receives the mixture of air and gaseous reformate through intake
port 292 when intake valve 300 is open. In this example, the
mixture of air and gaseous reformate form the scavenge gas for
prechamber 284, i.e., the gas that displaces or dilutes any
existing gas within the volume of prechamber 284. Prechamber 284
contains a spark plug 328, which delivers current to prechamber 284
to ignite the combustible mixture inside prechamber 284.
[0038] FIG. 5 shows an alternative implementation of feeding
prechamber 284. In FIG. 5, a gas injector 320 is installed in
prechamber 284. Outlet line 114 of reformer 110 is connected to gas
injector 320 via an inlet line 322, and gas injector 320 is used to
feed the gaseous reformate generated by reformer 100 into
prechamber 284. Valve 323 may control flow of the gaseous reformate
from inlet line 322 to gas injector 320. Inlet line 296 is used to
provide air to intake port 292 when valve 300 is open. In this
alternative implementation, air and gaseous reformate are fed
separately into prechamber 284. FIG. 6 shows another implementation
where a fuel injector 324 is installed in prechamber 284. Fuel
injector 324 is connected to fuel line 273 via inlet line 325.
Valve 326 may control flow of fuel from fuel line 273 to fuel
injector 324. A mixture of air and gaseous reformate is fed into
prechamber 284 through intake port 292. FIGS. 4-6 show that gaseous
reformate may be fed into prechamber 284 either directly, via gas
injector 320 (in FIG. 5), or indirectly, via first feeding the
gaseous reformate into air and then feeding the mixture of air and
gaseous reformate into prechamber 284 when valve 300 is open (in
FIGS. 4 and 6) in order to scavenge prechamber 284. In the example
where the gaseous reformate is added to prechamber 284 directly via
gas injector 320, the gaseous reformate is used as the sole fuel.
In the example were gaseous reformate premixed with air is added to
prechamber 284 via intake port 292, gaseous reformate can be used
as the sole fuel or as a supplemental fuel in prechamber 284.
[0039] Reformer 100 generates the gaseous reformate that is
supplied to prechamber 284. In one implementation, a stream of
exhaust gases from exhaust line 244 is fed into feed line 124 of
reformer 100. In one example, fuel 116 is injected into the stream
of exhaust gases passing through feed line 124 into reactor 104 of
reformer 100. Alternatively, fuel 116 may be sprayed directly onto
catalyst-coated substrate 108 (as shown in FIG. 2). Air 128 may be
optionally injected into the stream of exhaust gases passing
through feed line 124 into reactor 104. Fuel 116 contacts
catalyst-coated substrate 108 inside reactor 104 and is converted
into the gaseous reformate in the presence of catalyst(s) in the
catalyst-coated substrate 108. Exhaust gases from feed line 124
provide steam and/or CO.sub.2 for the reforming reactions. A stream
of gaseous reformate exits reformer 100 through outlet line 114.
Heat is provided to reformer 100 for reforming reactions through
vent line 136, which is connected to exhaust line 244. The
connection of vent line 136 may be before emissions control device
256. Valve 138 in vent line 136 may allow supply of exhaust gases
to reformer 100 for heating purposes to be bypassed under certain
conditions, e.g., during cold start of the engine. Exhaust that
indirectly contacts the reformer then travels to the three-way
catalyst in the emissions control device 256 and finally to the
tailpipe. In an alternative implementation, which is not shown, the
reformer may be located concentrically inside the three-way
catalyst of the emissions control device, in which case, the
exhaust is simultaneously providing heat to the reformer while
passing through the three-way catalyst.
[0040] The air (or air mixture) delivered to intake manifold 260
may be supercharged to increase the maximum power that the engine
can deliver. Supercharging involves compressing the air (or air
mixture). In one example, a compressor 332 is disposed in intake
line 224 to provide compressed air to intake manifold 260. A
cooling device 334 may be disposed in intake line 224, downstream
of compressor 332, to cool the compressed air that is delivered to
intake manifold 260. Cooling device 334 may be a chiller or other
suitable heat exchanger. Compressor 332 is driven by a turbine 336
that is disposed in exhaust line 244. Turbine 336 and compressor
332 are connected by a shaft 338. Turbine 336 is driven by exhaust
gases in exhaust line 244. Turbine 336 and compressor 332 on single
shaft 338 form a turbocharger. Other methods of supercharging
besides turbocharging may be used.
[0041] An EGR line 340 is in fluid communication with intake line
224 and exhaust line 244. EGR line 340 allows exhaust gases to be
transferred from exhaust line 244 to intake line 224. In one
implementation, an inlet end of EGR line 340 connects to exhaust
line 244 downstream of turbine 336, and an outlet end of EGR line
340 connects to intake line 224 upstream of compressor 332. In this
case, exhaust gases from EGR line 340 is mixed with ambient air
236, and the compressor 332 compresses the mixture of ambient air
and exhaust gases to produce the compressed air that is delivered
to intake manifold 260. An EGR loop is formed that includes EGR
line 340, the portion of intake line 224 running from EGR line 340
to engine 202, and the portion of exhaust line 244 running from
engine 202 to EGR line 340. The EGR loop including EGR line 340 is
a low pressure EGR loop. FIG. 7 illustrates a high pressure EGR
loop including EGR line 340'. In this example, inlet end of EGR
line 340' is connected to exhaust line 244 upstream of turbine 336,
and outlet end of EGR line 340' is connected to intake line 224
downstream of compressor 332. In this case, exhaust gases mix with
the compressed air (high pressure air) coming out of compressor
332. The high pressure EGR loop shown in FIG. 7 could be used with
any of the prechamber feeding examples shown in FIGS. 4 and 5 and
is not limited to the prechamber feeding example shown in FIG. 6.
In FIGS. 4-7, an EGR cooling device 344 is disposed in EGR line 340
(340') to cool the exhaust gases delivered to intake line 224. A
valve 348 may be disposed in EGR line 340 (340') to control flow of
exhaust gases from exhaust line 244 into EGR line 340.
[0042] FIG. 8 shows system 200' including alternative reformer 100'
(in FIG. 3) and engine 202. The main difference between system 200'
shown in FIG. 8 and system 200 shown in FIGS. 4-7 is in the routing
of exhaust gases from exhaust line 244 to the reformer. In the
system shown in FIG. 8, exhaust gases are not involved in the
reforming reactions. Therefore, exhaust gases are not fed to
reactor 104. Instead, a vent line 152 carries exhaust gases from
exhaust line 244 to vaporizer 144 in order to provide heat to
vaporizer 144. The exhaust gases carried to vaporizer 144 are
isolated from the inside of vaporizer where vaporizing of a fuel is
carried out. The fuel vaporized in vaporizer 144 and converted to a
gaseous reformate in reactor 104 may be an alcohol fuel such as
methanol or other fuel that carries oxygen. In this case, an
auxiliary fuel supply 352 can provide the fuel to vaporizer 144,
which then provides the vaporized fuel to reactor 104. The details
of fuel supply 352 are not shown, but fuel supply 352 may generally
include a fuel tank and a fuel pump to transfer fuel from the fuel
tank to an inlet line 356 and nozzle 146. The system of FIG. 8 uses
the prechamber feeding example shown in FIGS. 6 and 7. However, the
prechamber feeding example shown in FIG. 4 or FIG. 5 could be used
in other implementations of the system.
[0043] Referring to FIGS. 4-8, in one non-limiting example,
cylinder 204 may operate on a four-stroke cycle including an intake
stroke, a compression stroke, a power stroke, and an exhaust
stroke. During the intake stroke, intake valve 268 is open, exhaust
valve 280 is closed, and fuel and air are drawn into main
combustion chamber 212. Intake valve 300 of prechamber 284 is also
open, and gaseous reformate, air, and optionally a liquid fuel are
fed into prechamber 284. The fuel-air mixture in prechamber 284
fully purges (or completely fills or scavenges) the prechamber
volume. During compression stroke, valves 268, 300, 280 are closed,
and the fuel-air mixture in main combustion chamber 212 is
compressed by piston 208. This will push the fuel-air mixture in
main combustion chamber 212 against orifices 288 of prechamber 284.
At the end of compression stroke, the fuel-air mixture in
prechamber 284 is ignited by spark plug 328, resulting in high
temperature jets containing combustion products being ejected at
high velocity from prechamber 284 into main combustion chamber 212.
The high temperature jets rapidly burn the fuel-air mixture in main
combustion chamber 212. During the power stroke, the high-pressure
gases produced from combustion of the fuel-air mixture in main
combustion chamber 212 expand and push piston 208 down, generating
force on the crank and shaft and useful work. During the exhaust
stroke, valve 280 is open, and piston 208 pushes exhaust gases out
of main combustion chamber 212. The timing of opening and closing
of valves 268, 280, 300 and operation of injectors 272, 320, 324
during the various strokes may be controlled by a computer (not
shown).
[0044] Prechamber 284 that is fueled with gaseous reformate from
reformer 100 (100') may provide various benefits. If the gaseous
reformate includes H.sub.2, the high flame speed of H.sub.2 will
allow combustion to proceed rapidly and easily when the spark plug
is fired in prechamber. CO in the gaseous reformate also helps
combustion in the prechamber. The gaseous reformate mixes readily
with air and residual gases, providing a more homogeneous mixture
for the prechamber, which translates to a more uniform distribution
of ignition sites for the main chamber. If the prechamber is fueled
only by a gaseous reformate, wetting of liquid on prechamber walls,
spark plug, and other components is avoided. If the prechamber is
fueled by a gaseous reformate and a liquid fuel, less of the liquid
fuel will be required, leading to less wetting of prechamber walls,
spark plug, and other components. The gaseous reformate can be
generated onboard, which would allow continued use of existing
liquid fuel infrastructure. The gaseous reformate, which is highly
flammable, results in ejection of high energy flame jets into main
combustion chamber 212 when prechamber 284 is ignited. These high
energy flame jets readily ignite fuel-air mixture in main
combustion chamber 212, even with fuel-air mixtures that have been
significantly diluted with excess air or exhaust gases, e.g.,
dilution levels up to 40% or higher (or up to 50% or higher), which
is well beyond what a typical spark plug is able to ignite.
[0045] By improving prechamber ignitability, dilution tolerance is
improved. The greater dilution tolerance allows the fuel-air
mixture in main combustion chamber 212 to be diluted with air or
with exhaust gas. Although dilution with air is preferable for
efficiency, dilution with exhaust gases reduces NO.sub.x emissions
and avoids the need for expensive aftertreatment systems. Dilution
with air can be achieved by simply opening the throttle valve (264
in FIGS. 4-8) to increase the intake air pressure or by operating a
turbo or supercharger device at high load. Dilution with exhaust
gases can be achieved via the EGR loop (340, 340' in FIGS. 4-8). At
low engine load, exhaust gases can be provided through phasing of
the intake and exhaust cams (the cams that control opening of the
intake and exhaust valves) to allow exhaust gases to flow back into
the intake or through an external EGR loop. In the case where
exhaust gases are allowed to flow back into the intake, at low
load, the intake port is at low pressure and the exhaust port is at
high pressure. Thus, if both intake and exhaust valves are open
(e.g., during the intake stroke), exhaust will flow from the
exhaust port back into the intake port. Thus, the "fresh" charge is
internally diluted with exhaust gas. At high engine load, only an
external EGR loop can be used. Low pressure EGR, where EGR is fed
after the turbine and before the compressor (as shown in FIGS. 4-6,
8) is preferred under high-load conditions. By improving prechamber
ignitability and including scavenge air, lean limits are extended,
reducing NO.sub.x emissions when air dilution is used in the main
chamber. A further benefit of air or exhaust dilution is the
reduction of knock propensity. Dilution reduces the peak end-gas
temperature and pressure reducing propensity of the mixture to
auto-ignite, which causes noise and engine damage. Less knock
allows an increase in compression ratio and more optimal combustion
phasing. Lower peak combustion temperatures reduce the need for
enrichment at high load and reduce NOx emission. Thus, by improving
prechamber ignitability and extending main-chamber dilution limits,
knock propensity is also reduced, allowing further efficiency
gains.
[0046] Five test fuels were prepared. The characteristics of each
fuel are shown in Table 2. The test fuels were fed to a prechamber
while operating the engine at 40% EGR, which is the percent of
total intake mixture that is recycled exhaust. N.sub.2 is a diluent
in all the fuels shown in Table 2. With the exception of
CO--N.sub.2 fuel, all the different test fuels used an equivalence
ratio of 0.92-0.93 in the main chamber. Equivalence ratio is the
ratio of the actual fuel/air ratio to the stoichiometric fuel/air
ratio. Combustion is stoichiometric if the equivalence ratio is 1,
lean with excess air if the equivalence ratio is less than 1, and
rich with incomplete combustion if the equivalence ratio is greater
than 1. For CO--N.sub.2, the equivalence ratio reduced below 0.92,
but only because this was needed to improve combustion stability.
Table 2 reports the coefficient of variation (COV) of indicated
mean effective pressure (IMEP), which is a measure of combustion
stability, for each test fuel. A lower value of COV in IMEP
indicates greater dilution tolerance. As shown,
H.sub.2--CO--N.sub.2 blend shows superior performance compared to
the other test fuels. Pure syngas, which does not have N.sub.2
diluent, is expected to have even better performance compared to
H.sub.2--CO--N.sub.2 blend.
TABLE-US-00002 TABLE 2 Gas EGR Equivalence COV Gas Name Composition
rate (%) Ratio IMEP (%) H.sub.2--N.sub.2 25% H.sub.2 in N.sub.2 40
0.922 1.1 H.sub.2--CO--N.sub.2 25% H.sub.2 and 40 0.927 0.81 25% CO
in N.sub.2 CH.sub.4--N.sub.2 25% CH.sub.4 in N.sub.2 40 0.925 2.47
CO--N.sub.2 25% CO in N.sub.2 40 0.847 1.09 C.sub.3H.sub.8--N.sub.2
25% C.sub.3H.sub.8 in N.sub.2 40 0.924 1.36
[0047] Table 3 shows additional parameters identified for optimal
performance of the prechamber for the test fuels identified in
Table 2.
TABLE-US-00003 TABLE 3 Prechamber Air flow Air valve Air valve Air
Prechamber fuel flow rate open duration pressure Fuel SOI
(scc/cycle) (SCFM) (bTDCF) (CAD) (psi) (bTDCF) H.sub.2--N.sub.2
2.41 0.393 160 30 30 95 H.sub.2--CO--N.sub.2 2.40 0.386 160 30 30
120 CH.sub.4--N.sub.2 2.28 0.56 160 30 45 95 CO--N.sub.2 2.18 0.185
170 30 15 115 C.sub.3H.sub.8--N.sub.2 0.73 0.67 160 30 45 95 scc =
standard cubic centimeter SCFM = standard cubic feet per minute
bTDCF = before top dead center (firing) CAD = crank angle
degree
[0048] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having the
benefit of this disclosure, will appreciate that other embodiments
can be devised that do not depart from the scope of the invention
as described herein. Accordingly, the scope of the invention should
be limited only by the accompanying claims.
* * * * *