U.S. patent application number 16/866256 was filed with the patent office on 2021-11-04 for passive pre-chamber ignition with varying nozzle sizes for internal combustion engine.
The applicant listed for this patent is Southwest Research Institute. Invention is credited to Zainal Abidin, Kevin L. Hoag, Matthew M. Hoffmeyer, Bansal Shah.
Application Number | 20210340899 16/866256 |
Document ID | / |
Family ID | 1000004857952 |
Filed Date | 2021-11-04 |
United States Patent
Application |
20210340899 |
Kind Code |
A1 |
Hoag; Kevin L. ; et
al. |
November 4, 2021 |
Passive Pre-Chamber Ignition with Varying Nozzle Sizes for Internal
Combustion Engine
Abstract
A passive ignition pre-chamber for an internal combustion
engine. The pre-chamber is typically implemented as a cap on the
electrode end of a spark plug, and encloses a pre-chamber volume in
which fuel is mixed with air to form a consistently ignitable
mixture. The pre-chamber is passive in the sense that gas exchange
with the engine's main combustion chamber is realized by local flow
fields near nozzles into the main chamber and by pressure
differences between the pre-chamber and the main chamber. The
nozzles are sized such that at least one of the nozzles has a
larger diameter than the remaining nozzles, as optimized using flow
field and pre-chamber turbulence analysis.
Inventors: |
Hoag; Kevin L.; (San
Antonio, TX) ; Hoffmeyer; Matthew M.; (San Antonio,
TX) ; Shah; Bansal; (San Antonio, TX) ;
Abidin; Zainal; (San Antonio, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Southwest Research Institute |
San Antonio |
TX |
US |
|
|
Family ID: |
1000004857952 |
Appl. No.: |
16/866256 |
Filed: |
May 4, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02B 19/18 20130101;
F02B 19/12 20130101 |
International
Class: |
F02B 19/12 20060101
F02B019/12; F02B 19/18 20060101 F02B019/18 |
Claims
1. An ignition pre-chamber for an internal combustion engine, the
engine having cylinders each with a spark plug with an electrode
end and a combustion chamber, the engine being equipped for exhaust
gas recirculation (EGR), comprising: a pre-chamber housing that
encloses a volume between the electrode end of the spark plug and
the combustion chamber; a bottom wall of the pre-chamber housing
having a number of nozzles that provide flow between the
pre-chamber housing and the combustion chamber; and wherein the
number, size(s), and arrangement of the nozzles is manufactured by
the following process: modeling the ignition pre-chamber at a
desired engine operating point. the pre-chamber having a candidate
configuration of nozzles, the configuration having a specific
number of nozzles, size of each nozzle, and location of each
nozzle, mapping. the EGR residual content during a compression
stroke of the engine as a function of crank angles of the engine,
repeating the modeling and mapping steps for a number of candidate
configurations, and selecting a candidate configuration on the
basis of EGR residual content.
2. The pre-chamber of claim 1, wherein the pre-chamber housing is
implemented as a cap at the electrode end of the spark plug.
3. The pre-chamber of claim 1, wherein the spark plug has a center
electrode and wherein a nozzle under the center electrode end has a
larger diameter than the remaining nozzles.
4. The pre-chamber of claim 1, wherein the spark plug generates a
tumble flow field when activated, and wherein one or more nozzles
aligned with the tumble flow field have a larger diameter than the
remaining nozzles.
5. The pre-chamber of claim 1, wherein the spark plug generates a
tumble flow field when activated, and wherein one or more nozzles
orthogonal to the tumble flow field have a larger diameter than the
remaining nozzles.
6. (canceled)
7. (canceled)
8. The pre-chamber of claim 1, wherein the spark plug has a J''
electrode that extends under the center electrode.
9. A method of manufacturing an ignition pre-chamber for an
internal combustion engine, the engine having cylinders each with a
spark plug with an electrode end and a combustion chamber,
comprising: modeling a pre-chamber having a housing that encloses a
volume between the electrode end of the spark plug and the
combustion chamber; a bottom wall of the pre-chamber housing having
a number of nozzles that provide flow between the pre-chamber
housing and the combustion chamber; using computational fluid
dynamics modeling to evaluate the pre-chamber with nozzles having
varying nozzle diameters; and selecting nozzle diameters based on
the step of using computational fluid dynamics modeling.
10. The method of claim 9, wherein the pre-chamber housing is
modeled as a cap at the electrode end of the spark plug.
11. The method of claim 9, wherein the spark plug has a center
electrode and wherein a nozzle under the center electrode end has a
larger diameter than the remaining nozzles.
12. The method of claim 9, wherein the spark plug generates a
tumble flow field when activated, and wherein one or more nozzles
aligned with the tumble flow field have a larger diameter than the
remaining nozzles.
13. The method of claim 9, wherein the computational fluid dynamics
modeling models residual gasses in the pre-chamber during a late
portion of a compression stroke of the cylinder.
14. The method of claim 9, wherein the spark plug has a J''
electrode that extends under the center electrode.
15. A method of operating an internal combustion engine, the engine
having cylinders each with a spark plug with an electrode end and a
combustion chamber, comprising: placing a pre-chamber housing at
the electrode end of the spark plug, such that the pre-chamber
encloses a volume between the electrode end of the spark plug and
the combustion chamber; wherein the bottom wall of the pre-chamber
housing has a number of nozzles that provide flow between the
pre-chamber housing and the combustion chamber; and sizing the
diameter of the nozzles to have varying diameters based on
computational fluid dynamics modeling of residual gasses in the
pre-chamber during activation of the spark plug.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to internal combustion engines, and
more particularly to using passive pre-chamber ignition with such
engines.
BACKGROUND OF THE INVENTION
[0002] The pre-chamber ignition concept is used with spark-ignition
engines to enable lean or diluted engine operation while having a
suitable combustion process. The basic function of a pre-chamber is
to provide a small space where fuel can be combined with air to
form a mixture consistently ignitable by a spark plug. When
ignited, this mixture provides the required energy to combust a
lean or dilute mixture within the cylinder's main combustion
chamber at the optimum time for efficiency and/or pollution
control.
[0003] Various types of pre-chamber configurations exist, which can
be classified into active and passive configurations. An active
pre-chamber system is equipped with additional fuel and/or air
injection inside the prechamber. A passive pre-chamber realizes its
gas exchange by local flow fields near orifices into the main
chamber and by pressure differences between the pre-chamber and
main-chamber.
[0004] A passive pre-chamber spark plug is composed of an ordinary
spark plug with electrodes, on which a cap with orifices is put.
The encapsulated volume is the pre-chamber and is connected to the
main combustion chamber by the orifices.
[0005] In addition to lean-burn natural gas engines, passive
pre-chambers are attractive to improve the robustness of combustion
in dilute mixture (high EGR) gasoline engines, as well as for
increased burning rate in stoichiometric and rich gasoline
engines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
[0007] FIG. 1 illustrates an engine cylinder equipped with a
pre-chamber spark plug.
[0008] FIG. 2 illustrates a pre-chamber spark plug.
[0009] FIG. 3 is a cross-sectional view of the pre-chamber of the
spark plug of FIG. 2.
[0010] FIG. 4 is an inside view of a conventional pre-chamber.
[0011] FIG. 5 is an inside view of a pre-chamber having an enlarged
center nozzle.
[0012] FIGS. 6 and 7 are inside views of a pre-chamber having
enlarged side and center nozzles.
[0013] FIG. 8 illustrates how various nozzle configurations may be
evaluated using computational fluid dynamics modeling.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The following description is directed to passive
pre-chambers for spark-ignited engines. The pre-chamber's nozzles
(orifices) are varied in size, rather than being all the same size.
This improves scavenging while maintaining the original objectives
of pre-chamber ignition.
[0015] FIGS. 1-3 illustrate the general concept of pre-chamber
ignition. In the example of FIGS. 1-3, the pre-chamber 100 is
implemented as a cap at the end of a spark plug 11. However, as
explained below, a pre-chamber may be any housing that encapsulates
a small volume between the spark plug electrodes and the main
chamber, with orifices for fluid flow.
[0016] FIG. 1 illustrates an engine cylinder 10 equipped with a
pre-chamber spark plug 11. FIG. 2 illustrates spark plug 11, and
FIG. 3 is a cross-sectional view of the pre-chamber portion of
spark plug 11.
[0017] The pre-chamber 100 is a bowl-shaped housing that surrounds
the electrode end of sparkplug 11. The pre-chamber 100 is installed
such that it communicates with the main chamber 10 of the
combustion cylinder via orifices (herein referred to as "nozzles")
22 and 23. The pre-chamber housing is made from a metal or other
material that will withstand engine conditions, and is permanently
attached to the end of spark plug 11 to form a sealed pre-chamber
compartment.
[0018] During the engine's intake stroke, the pre-chamber nozzles
22 and 23 scavenge the residual in the main chamber 10 with fresh
mixture from the intake flow. During compression, fresh mixture
from the larger main chamber volume is forced through the nozzles
22 and 23 into the pre-chamber. When the sparkplug 11 ignites this
mixture, burning jets expand through each nozzle 22 and 23, back
into the main chamber. The result is multiple ignition points in
the main chamber, providing a faster and more robust combustion
event.
[0019] A feature of the invention is the recognition of engine
conditions at which it is difficult to maintain reasonable
performance of the passive pre-chamber concept. Under high load
conditions, passive pre-chambers have been found to work very well.
The mixture in the pre-chamber is easily ignited, and a burning jet
exiting each nozzle provides multiple ignition sources in the main
combustion chamber. The 10-90 burn duration (time or crank angle
increment during which the tenth percentile to the ninetieth
percentile of fuel is burned) is reduced to nearly half the
duration seen under the same conditions in an open chamber
engine.
[0020] However, at light loads and high dilution ratios, it is
difficult to achieve ignition, much less complete combustion. The
difficulty is explained by the inability to sufficiently evacuate
the pre-chamber of the burned mixture from the previous cycle and
low turbulence. A high percentage of the mass in the pre-chamber at
the time of the spark event is burned exhaust gas. This dilutes the
fresh mixture to the point that it will not ignite, or if it
ignites the flame front is not sustained. Low turbulence slows down
the flame propagation within the pre-chamber.
[0021] FIG. 4 is a bottom view of a conventional pre-chamber 100,
having seven equally sized nozzles in its bottom wall. That is, all
nozzles have the same size diameter.
[0022] In this embodiment, the pre-chamber 100 has a round
bowl-shaped bottom wall, such as the end cap of a spark plug as
described above. However, other configurations are possible. For
example, the "cap" could be cylindrical with nozzles on both a
bottom wall and side walls.
[0023] The view of FIG. 4 is from the sparkplug 11, looking into
the pre-chamber 100 toward the main chamber 10. The side electrode
32 of the sparkplug 11 is shown. In the example of FIG. 4, and in
the embodiments of this description, the "J electrode" 32 extends
under the center electrode 31, but other electrode configurations
are possible.
[0024] Referring to both FIGS. 3 and 4, a "center" nozzle 23 is the
nozzle in the bottom wall directly under the spark plug's center
electrode 31. "Side" nozzles 22 are placed around the sides of the
pre-chamber, here around the circumference of the bottom wall of
the pre-chamber 100.
[0025] FIGS. 5-7 illustrate various embodiments of a pre-chamber
100 in accordance with the invention. Only the bottom wall of the
pre-chamber is shown. Although pre-chamber 100 is of the type
described above, suitable as a cap for a spark plug, other
configurations are possible. Pre-chamber 100 may be any housing
that provides an enclosure between the electrode end of the spark
plug and the top of the combustion chamber, and has a bottom wall
that separates the pre-chamber from the main combustion chamber.
The significance of the invention is the configuration of nozzles
22 and 23 within the pre-chamber end wall.
[0026] Based on bulk flow field and pre-chamber turbulence
analyses, one or more of the nozzles between the pre-chamber and
main chamber is made larger. This facilitates removal of residual
from the pre-chamber while still creating a flame jet at each
nozzle.
[0027] In the embodiment of FIG. 5, the center nozzle 53 is
enlarged relative to the side nozzles 52. The side nozzles 52 are
smaller, and here are all of the same diameter.
[0028] In the embodiments of FIGS. 6 and 7, the center nozzles 63
and 73 are enlarged relative to a portion of the side nozzles 62
and 72. However, another portion of the side nozzles, here two, are
enlarged relative to the other side nozzles. These two enlarged
side nozzles 64 and 74 are spaced 180 degrees apart from each
other.
[0029] In the embodiment of FIG. 6, the enlarged side nozzles 64
are crossways from the bulk tumble flow field within pre-chamber
100. In the embodiment of FIG. 7, the enlarged side nozzles 74 are
aligned with the bulk tumble flow field within pre-chamber 100. In
general, the "bulk tumble flow field" is a flow field that runs
orthogonal to the side electrode 32 when the spark plug is
activated.
[0030] Each of the configurations shown in FIGS. 5-7 are examples
of the general notion that by using more than one nozzle diameter,
and hence more than one nozzle flow area, pre-chamber evacuation
and turbulence can be optimized to the needs of a particular
engine. Various combinations of an enlarged center nozzle and one
or more enlarged side nozzles may be implemented.
[0031] FIG. 8 illustrates how various nozzle configurations may be
evaluated using computational fluid dynamics modeling. A
pre-chamber with a nozzle configuration of interest is modeled at a
desired engine operating point. Here the engine operating points is
a light-load (two bar BMEP) operating point with 22 percent exhaust
gas recirculation (EGR).
[0032] The residual percentage in the pre-chamber is plotted during
the late portion of the compression stroke. The dropping residual
percentage is an indication of the burned gas being evacuated from
the pre-chamber and replaced with fresh air-fuel mixture. For the
case shown, complete evacuation would take the EGR percentage to
31% which is equal to the total (external+internal) EGR percentage
inside the main chamber.
[0033] The top two plots are of two different pre-chambers having
seven nozzles of the same diameter. The bottom two plots are of two
pre-chambers with differently sized nozzles, such as those of FIGS.
5-7. Pre-chamber spark timing is typically in the range of 55 to 35
degrees before TDC, making the reduced residual content at that
Crank Angle Degree (CAD) range especially important.
[0034] For the configurations of FIGS. 5-7, it was also important
to assure that the varying nozzle diameters did not adversely
impact full load performance. Full-load conditions were evaluated,
and it was confirmed that the desired performance was achieved.
* * * * *