Note: Descriptions are shown in the official language in which they were submitted.
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FLOW COUPLED ARC DISCHARGE IGNITION IN AN IC ENGINE
FIELD OF THE INVENTION
This invention relates to spark ignition internal combustion (IC) engines and
to the
improved ignition and combustion of air-fuel mixtures in IC engines through
the faster and more
vigorous combustion ofthe air-fuel mixture brought about by high air-flows of
both the directed
bulk flow type and of the more random turbulent flow type produced in a highly
compact
combustion zone ofthe combustion chamber. In particular, the invention relates
to combustion
systems which can simultaneously produce high directed bulk flow at the spark
plug site at the
time of ignition and more random and intense turbulent flow inside a compact
combustion
chamber during the time of ignition and combustion to speed-up the burn. In
particular, the
invention relates to a system which involves the design and control of high
flows, high energy
ignition spark discharges, and resulting intense flame kernels, all three of
which interact among
themselves in ways that produce a very rapid and controlled burn in a comp act
combustion zone
for low NOx emissions and high engine efficiency through lean and high EGR
(exhaust gas
recirculation) combustion at a high engine expansion ratio.
BACKGROUND OF THE INVENTION AND PRIOR ART
High flows are used in IC engines to improve engine efficiency and emissions
through
rapid combustion of lean and high EGR air-fuel mixtures. These flows are
either swirl- tumble
(vertical vortex), or squish. The predominant type of flow used is swirl,
especially for the purpose
of generating mixture stratification at the spark plug site to allow for
ignirion of lean mixtures.
Numerous examples of these exist, especially with Japanese manufacturers such
as Toyota,
Mazda, and others. To a lesser extent tumble flow is used, as in the
Mitsubishi Vertical V ortex
(MW) engine now in production. Squish is rarely used for ef~nciency and
emissions
improvement. It is used principally in racing and performance for speeding up
the combustion of
high speed engines. Moreover, such squish flow is not used in conjunction with
the spark except
in my U.S. patent No. 5,517,961, where it is used in conjunction with a high
energy. fiow-
resistant spark to help spread the spark and speed up the burn.
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2
SUMI~~iARY OF THE II~TVENTION
In this patent application is disclosed an ignition and combustion system
based on the
interaction of two generic types of flows which can be generated in an engine
cylinder. One is
bulk flow which can be produced at the spark plug site at the time of ignition
to interact /couple
to the spark discharge to direct and spread the spark, along arc runners if
practical; the other is
turbulent flow which can be produced by impinging squish flows directed
towards each other as
colliding flows reinforced by the piston compression of swirl or tumble flow,
into which the spark
discharges and resulting initial flame kernels can move in the form of flow-
coupled-spark-
discharges ofthe type disclosed in my U. S. patent No. 5,517,961. Preferably
the more random
turbulent flows (colliding flows or piston converted swirl or tumble) occur in
ahighly confined
region or zone ofthe engine combustion chamber defined bythe piston or other
movable element
nearing top center (TC) and the walls of the combustion volume, made up, for
example, of the
engine cylinder wall and cylinderhead in a conventional piston engine.
Preferably, ~e combustion
zone is located partly or mostly underthe exhaust valve, or in some other high
temperature zone
of the combustion chamber, with the bulk flow occurring at one or more edges
of the turbulent
zone to move and direct one or more high energy flow-resistant spark
discharges into the mixture
turbul~ce to produce a rapid and complete combustion of an air-fuel mixture
without engine knock
or other deleterious effect. In this way, very lean and high EGR mixtures can
be burnt rapidly to
produce high engine efficiencies and low emissions, especially low NOx
emissions whose
formation depends on both temperature and time, both of which are reduced.
With the use of one spark plug and two valves, the spark plug is preferably
located
between the valves disposed preferably along or near a center diameter line of
the engine cylinder
if bulk flow is present at the spark plug site, e. g. ifthe combustion chamber
is under the exhaust
valve; or the spark plug may be placed offset of the valve center line at a
high bulk flow region
if the combustion chamber includes part or most of the region under both
valves, either in the
cytinderhead orinthe piston as has been disclosed in my U. S.
PatentNo.5,517,961. If two spark
plugs are used, with one or two intake and one exhaust valve, more options are
available for
achieving spark coupling to the bulk flow. The spark plugs can be disposed on
either side ofthe
exhaust valve under which is def ned the main combustion chamber and region
ofturbul~t flow,
with two inward moving bulk flows (BFs) occurring at the two spark plug sites
for two flow-
coupled-spark discharges (FCSD), producing a more elongated combustion zone
and even more
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rapid burning ofthe air-fuel mixture. Placing the combustion chamber under the
exhaust valve
improves the engine's lean burn capability and reduces its knock
susceptibility, especially ifthe
end-gas region ofthe combustion chamber is narrow and subject to cooling.
These are preferred
embodiments of the invention. Furthermore, in these preferred embodiments, the
piston is flat, or
slightly cupped under the combustion zone, with thermal barrier coatings used
to limit heat
transfer to the piston.
Near top center (TC), i.e. within 30° of TC, the bulk flow (BF) in the
spark gap is
produced by the piston which induces squish flows which move towards each
other and collide
to, in turn, produce an intense turbulence in the combustion zone (a colliding
turbulence
generating flow, or CTF). Advanced ofTC, the bulk flows in the spark gap are
produced by swirl
or tumble, or by a combination of these which are converted by the piston
motion near TC to
turbulent flows to produce a very rapid and vigorous burn. When squish flow
dominates this
process, it can be viewed as a colliding-flow-coupled-spark-discharge (CFCSD),
versus simply
an FCSD for swirl or tumble. Both are made up of high energy, flow-resistant,
flow-coupled-
spark-discharges which move into, and/or produce initial flame kernels which
move into the high
turbulence region (of small eddies),produced by colliding flows or piston
compression converted
bulk flow which help homogenize the mixture and help spread the flame.
In another preferred embodiment, the inlet air flow is used to reinforce the
combustion
process. Such an inlet flow can be a vertical vortex flow which reinforces one
or more of the
squish induced flows, especially at advanced ignition timings when squish is
low. Alternatively,
the combustion chamber and inlet valve, one or two inlet valves, and intake
runners may be
designed to produce swirl flow to reinforce the squish flows.
For the ignition, preferably triangular distribution spark with a peak
amplitude above 200
milliamps (ma) is used, say 300 to 800 ma, operating in part in the flow-
resistant arc discharge
mode (versus glow discharge) which can sustain flow velocities of20 meters/sec
(m/s) or greater
without spark segmentation, as disclosed in my U. S. PatentNo. 5,517,961, to
produce a very fast
ignition and combustion of the mixture.
In another preferred embodiment, the spark may be fired to the piston given
the ability
to operate the engine with ignition near top center, between 5 ° and
30° before top center (BTC),
with special electrode tips acting as arc runners which improve coupling of
the spark to the
flowing mixture. Special design halo-disc spark plugs of my U. S. Patent No.
5,577,471 can be
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used, or similar plugs with large thin discs at their ends to define a runner
along which the spark
can move under the influence of the flow. Preferably, erosion resistant
material such as tungsten-
nickel-iron is used for the spark plug electrode material.
In another preferred embodiment, the valve timing is selected to make best use
of
CFCSD. This includes setting the intake valve opening preferably near TC (a
few degrees before
TC) for the cases with no combustion volume under the intake valve. The
exhaust valve closing
is preferably set at or before TC (BTC), e.g. 0° to 30° BTC to
trap the last part ofthe exhaust for
both high internal exhaust gas residual fraction to eliminate or minimize the
need for EGR as well
as minimize hydrocarbon (HC) emissions since the last part of the burnt
mixture to be exhausted
contains proportionallymore unbumtHC. Havingthe combustion chamber under the
exhaust valve
can help the process oftrapping die (last) part ofthe exhaust coming from the
ring clearances and
other chamber crevices which have the most unburnt HC emissions, to be burnt
in the subsequent
ignition and combustion firing cycle.
In another preferred embodiment using preferably a high energy, high
efficiency, flow
resistant ignition spark, an improved combustion chamber ofthe squish type is
used which has
the combustion chamber in the cylinder head under both the intake and exhaust
valves which are
centrally located and made as small as practical to allow for large squish
flows, especially in a
direction transverse to the line joining the two valves, with one or two spark
plugs located in the
squish zone. Preferably, the intake valve is recessed so that in its fully
open condition it clears the
top of the piston when positioned at top center (TC), and likewise for the
exhaust valve which is
preferably even further recessed. This represents a free-wheeling system which
will not damage
the engine should the timing belt break (in the preferred overhead cam
configuration). In such a
design several advantages result, including thorough mixing of the air-fuel
mixture due to the
squish induced colliding flows, rapid burning of the air-fuel mixture,
especially of high dilution,
2 5 high exhaust gas recirculation (EGR) and high air-fuel ratio (AFR)
mixtures which produce high
efficiency and low emissions, and high internally retained exhaust gas,
especially that located at
the fiuther regions ofthe combustion chamber, e. g. in the ring crevices where
most of die unbumt
hydrocarbons are formed which can be re-burned in the subsequent ignition
firing cycle.
Preferably, a squish land exists around the entire periphery of the piston so
that the end gas can
be cooled and therefore allow for higher compression ratio operation.
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More ideally, the disclosed ignition/combustion/flow systems are used in
aMiller Cycle
engine or variable-valve-timing engine with high expansion ratios of 10 to 12
to one or higher and
delayed intake valve closing (for effective lower compression ratio). If
practical, the systems
disclosed are used in the virtual 3-stroke engine disclosed in my U. S. patent
SN 5,454,352 where
in FIG. 7 ofthat patent is shown apreferred embodiment ofthe virtual 3-stroke
engine in the form
of an opposed piston with two valves and two spark plugs. Preferably, the
valves are smaller
which is more practical with the use of a turbocharger to create a more
compact combustion
chamber in the cylinder head and higher squish at the spark plug sites. The
low compressive
friction makes this engine easy to start and ideal for the forthcoming dual
rail 14/42 volt battery
systems with integrated starter/generator (ISG). It also makes it very
efficient and of very low
emissions. NOx emissions are low due to the low adiabatic heating of the
intake air on
compression and low overall temperatures due to the long expansion stroke
(preferably of 12 to
one or higher expansion ratio). Because ofthe inherently high efficiency
(BSFC, or brake specific
fuel consumption), especially at part load, combustion can be somewhat
delayed, as in the diesel
engine, to limit peak combustion temperatures below the level where
significant NOx emissions
are formed. This engine can be operated either premixed, i. e. indirect inj
ection or carbureted, or
direct in-cylinder injection, either moderate pressure injection as in the GDI
engine, or higher
pressure injection as in the diesel engine.
Other improvements of the ignition-engine system include improved forms of
dual
ignition, especially of the low inductance type, high energy, high efficiency
inductive ignition,
which use capacitance type plugs, if practical, with erosion resistance
electrode materials. Also,
such low inductance type coils can be improved by having magnetically
uncoupled secondary high
voltage windings to aid in reducing an over-voltage coil end effect associated
with low resistance
high e~ciency coil windings.
Other means for producing CFCSD are possible, including in other types of
engines, such
as two-stroke, rotary, gas direct inj ection, and offers, the main inventive
principle disclosed herein
being the combination and interaction of flow coupled-spark-discharge,
especially ofhigh-energy
high-afficiency flow-resistant sparks with turbulence generating flows,
especially in a compact,
hot region of the combustion chamber of a spark ignition engine.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 a and 1 b are drawings of air-flow vectors and flow interactions in a
compact
engine combustion chamber (combustion zone) that characterize a key feature of
the invention.
FIGS. 2a and 2b are approximately to-scale drawings of the side and top view
of a
combustion chamber with a preferred embodiment ofthe invention with central
combustion zone
under a central exhaust valve, and two intake valves and spark plugs located
in the squish zones.
FIG. 3 is a top view similar to that of FIG. 2b but with one intake valve.
FIGS. 4ato 4c show various arc runners forthe spark to move alongunderthe
action of
bulk flow, such as squish flow.
FIG. 5 is an approximately to-scale side view drawing through a line
intersecting the two
spark plugs of FIGS. 2b and 3 with arc runner construction.
FIGS. 6a and 6b are two types of spark plug firing ends for ignition firing to
the piston.
FIG. 7 is a more idealized embodiment of FIG. 5 with special spark plugs
located on an
electrically insulating cylinder head, achievable in a two stroke engine or
other engine where
valves are absent from the cylinder head or highly confined in the head.
FIG. 8 is a preferred embodiment of a direct inj ection version of the
invention with the
fuel injector located at the edge of a combustion zone under the exhaust valve
across from a single
spark plug in the squish zone.
FIG. 8a is a possible side view of the embodiment of FIG. 8 during the intake
process.
FIG. 8b is a view of FIG. 8 without the fuel injector, with the piston near
top center.
FIGS. 9a and 9b is atop and side view drawing of a combustion chamber with two
intake
valves and one exhaust valve with the combustion zone under the exhaust valve
and a single spark
plug located at a more central point at the edge of the combustion zone.
FIGS.1 Oa and 1 Ob is a more conventional pent-roof chamber with combustion
zone both
in the head and piston under the single intake and exhaust valves and two
spark plugs at the edge
of the combustion zone in the squish zones,
FIGS. 1 l, 1 I a, l l b, l l c and 11 d are partial side views and a top view
of a combustion
chamber with one small intake and exhaust valve centrally located and with the
compact
combustion zone under the two valves, and with two spark plugs located ax two
opposite sides of
3 0 the combustion zone in regions of high squish flow, and a central fuel inj
ector shown as an option
in FIGS. 11 c and 11 d.
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FIGS. 12a,12b, 12c, and 12d are approximately to-scale partial top and side
views of
a combustion chamber ofFIGS. I l, I 1 a and I I b detailing and emphasizing
certain aspects of the
combustion chamber for improved operation.
FIG. 13 is a cam timing diagram showing a preferred valve timing for the
present
invention.
FIG.14 is a design of the ignition coil output structure for providing dual
ignition firing
to the piston ofthe present invention in which the return path for the
electrical current is entirely
though the spark plugs and not through the engine block.
FIG. 15a is a partial, not to scale, top view layout of two side-by-side
engine cylinders
in a mufti-cylinder engine, with FIG. l Sb depicting a preferred approximately
to-scale combustion
chamber with dual ignition ofthe present invention in which the valves are
lined up approximately
in the length axis of the engine.
FIG.16a is a partial, not to scale, top view layout of two side-by-side engine
cylinders
in a mufti-cylinder engine, with FIG.16b depicting a preferred approximately
to-scale combustion
chamber with dual ignition ofthe present invention in which the valves are
lined up transverse to
the length axis of the engine.
FIGS.17a, l 7b and 17c are partial top views oflow inductance, high energy
ignition coil
structures with open magnetic paths suitable for application where greater
than 12 volts power
is available and designed for having two high voltage towers suitable for dual
ignition.
FIG.18 is atop partial view of an open E-type low inductance, high energy
ignition coil
with open magnetic path with some lower turns loosely coupled secondary
windings constituting
a series of secondary circuit external leakage inductors, usable also in the
designs ofFIGS.17a
and 17b, for reducing the end effect voltage overshoot. FIG.18a is an
equivalent circuit of the
coil of FIG. 18 used in an inductive ignition circuit.
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DESCRIPTION OF PREFERRED EMBODIMENTS
FIGS. la and lb are drawings depicting, in schematic form. flow vectors and
flow
interactions that lead to the principles of this invention. Region 1 denotes
the region of the ignition
source which can be the gap bet<veen spark plug electrodes and the region
adjacent to the
electrodes into which the spark discharge moves by the action of the air-flow
indicated by flow
vectors 2, representing bulk flow, BF, to produce what has been described as a
flow-coupled-
spark-discharge, FCSD. Region 3; shown with small partially circular curves
with arrows 3c,
indicating tiny turbulent eddies. is the region of high turbulence generated
by the approximately
equal and oppositely directed colliding flows 3a and 3b, producing what has
been designated as
CT. The spark discharge region 1 preferably penetrates the turbulence region 3
at approximately
right angles to the direction of the colliding flow vectors 3a and 3b, as
shown. A second ignition
source region can be equally well placed at the right side of the turbulence
region 3, as is indicated
with reference to FIGS. 2a, 2b, and other figures.
FIGS. 2a and 2b depict in partially schematic, approximately to-scale
drawings, side and
top views of a combustion zone 4 of a conventional piston engine contained
within a larger
combustion chamber volume defined by a piston 5; cylinder head 6, and cylinder
sleeve 7. The
term "combustion zone" 4 shall be used to indicate the region where the major
and first part of the
combustion. or burning, occurs as distinguished from "combustion chamber"
which indicates the
entire volume as already defined. In this preferred embodiment, the combustion
zone 4 is shown
located in a central part of the combustion chamber under an approximately
centrally located
exhaust valve 8 with exhaust tube 8a. with two intake valves 9a. 9b shown at
one side of the
combustion chamber with intake tubes 9c and 9d (allowing for the more central
exhaust valve 8
and combustion zone 4 under the exhaust valve 8). In this preferred embodiment
is shown two
high voltage spark plug electrodes l0a and lOb disposed symmetrically at
opposite ends of the
elongated combustion zone 4 with ground electrodes lla and llb defined by
small rises on the
piston for producing spark discharges between the tips l Oc and l Od of
electrodes l0a and l Ob and
the piston surface regions l la and l lb, i.e. ignition firing to the piston
versus to conventional "J"
ground electrodes. Spark firing tips lOc; lOd, 1 la, and 1 lb are made of
erosion resistant material.
For ease of visualization in FIG. 2a are shown. around the gap of the left-
most electrodes
lOc/lla, bull: flow vectors 2, and around the right-most electrodes lOd/1lb
spark discharges 1
being directed by the bulk flow vectors into the turbulence region 3,
understanding that both the
bulk flow (2 and 2a of FIG. 2b) and spark discharges (1 and la of FIG. 2b) are
present around
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both spark gaps. In this preferred embodiment, a central combustion zone is
provided with high
bulk flow at the plug sites and high turbulence inside the combustion zone.
When used with a high
energy ignition system with flow resistant sparks {direct current arc
discharge mode) of long
duration, i.e. of order of magnitude one millisecond, one can achieve a very
rapid bum of a dilute
air-fi~el mixture, dilute with excess air (lean mixture) and/or with retained
exhaust gas (high
exhaust residual or EGR), for very high efficiency and low emissions.
Preferably, a high and
optimum compression ratio (CR) is used, e.g. between IO: I CR and 15:I CR, for
best e~ciency,
which depends on several factors including fuel type used and heat transfer to
the combustion
chamber surfaces which increases with compression ratio (and can be reduced
with thermal barrier
coatings). More ideally, a Miller type cycle is used with late intake valve
closing of 60° a$er
bottom center (ABC) or greater, and a high expansion ratio (ER) of 12 to one
or higher.
FIG. 3 is an approximately to-scale, partially schematic top view of a spark
ignition piston
engine representing a preferred embodiment of CFCSD of the type of FIGS. 2a
and 2b except that
it has one intake valve 9 instead of two. Like numerals represent like parts
with respect to the
earlier figures. In this preferred embodiment, the spark plugs 12a and 12b are
shown (instead of
the electrodes), understanding that the spark plugs can be located at an angle
to the vertical as is
depicted in FIG. 5, versus vertical as shown in FIGS. 2a, 2b. This design is
especially usefiil for
use with a centrally located side overhead cam 13, as depicted, with the two
spark plugs located
with an angle to the vertical to help clear the cam as well as to better
position their tips in the
combustion chamber. Another embodiment is to have two smaller intake vale es,
one at the present
location and the other at the opposite side, I $0 degrees away.
For better coupling of the spark discharge to the liow, an electrode geometry
that acts in
part as an arc runner may be practical. FIGS. 4a to 4c show a pair of
electrodes IO and I 1 with
firing tips 13 and 14, the electrodes subtending progressively smaller
irncluded angles from FIG.
4a to 4c. Flow vectors 2 are shown emanating from the spark gaps 15 as are
spark discharges 1
which move along the runners 10111. It can be appreciated that the smaller the
included angle
between the electrodes, say from 30° to 90°, the more directed
is the flow and the less stretching
there is of the spark discharge as it moves along ~e nuu~ers l oll 1 per unit
motion, making FIG.
4c the more preferred embodiment for electrode geometry which can produce
greater motion of the
spark discharges 1 and hence greater penetration of the spark into the
turbulence region 3. FIG.
S shows an embodiment of the spark plug electrodes of FTGS. 2b and 3 to
produce better spark
penetration aral size.
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FIG. 5 is a partially schematic, approximately to-scale side view drawing
through a line
intersecting the two spark plugs of FIGS. 2b and 3, representing a preferred
embodiment of
CFCSD. Like numerals represent like parts with respect to the earlier figures.
In this embodiment
are shown spark plugs 12a and 12b, preferably 18 mm, with large diameter,
thin, erosion resistant
5 electrodes lOc, lOd disposed at right angles to the plug axis forming a
small included angle
(approximately 45°) with the piston top (shown close to TC) to produce
a preferred arc runner of
FIG. 4c (versus FIG. 2a which represents arc runners of FIG. 4b). As in FIG.
Za, the flow vectors
2 are shown on the le$ and the spark discharges 1 on the right for ease of
visualization, both
moving into the turbulence region 3. The spark gaps 15 are made with small
rises 1 la and l lb on
10 the piston surface, which represents the second arc rurn~er crnnbination 11
of FIGS. 4a to 4c.
Systems involving firing to the piston have been disclosed in several of my
prior patents, including
U.S. patents Nos. 4,774,914 and 4,841,925 among others. Also, many electrode
types have been
disclosed, two of several possible types being depicted in FIGS. 6a and 6b.
FIGS. 6a and 6b are approximately to-scale, partial side view drawings of two
spark plug
ends firing to the piston 5. Like numerals represent like parts with respect
to the earlier figures.
In FIG. 6a the center conductor 16 is preferably copper extending axially into
the combustion
chamber near the piston surface at the TC point with a coating 10
(representing the arc rurnier) of
erosion resistant material, such as tungsten-nickel-iron. The runner geometry
conforms to that of
FIG. 4b (90° included angle). In FIG. 6b the arc runner is erosion
resistant disc 17 at right angles
to the plug axis shown located slightly away from the end surface of insulator
18 (versus on the
surface of the insulator, as in FIG. 5). These piston firing embodiments
produce better spark
penetration towards the corner of the combustion zone.
FIG. 7 is a more idealized embodiment of FIG. 5 which can be attained in a two-
stroke
engine where valves are absent from the cylinder head or rotary type valves
are used (with a four
2S stroke engine also). The engine cylinder is a partially schematic,
approximately to-scale side-view
drawing representing another preferred embodiment of CFCSD. Like numerals
represent like parts
with respect to the earlier figures. In this preferred embodiment, the
cylinder head is shown made
of insulating thermal barrier material (as in an adiabatic engine), with a
central triangular cross-
section combustion zone 4, on the two angled surfaces of which are placed
large, flat, thin
electrodes 17a, 17b connected to high voltage terminal 16a and 16b
respectively. In this
embodimer~, extremely effective and large arc rurmers between 17a and 17b and
the piston surface
are achievable for extensive penetration of the arc discharge imo the
turbulence region 3 of the
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combustion zone 4. However, to accomplish this a high energy ignition with
long duration flow-
resistant sparks of the types I have disclosed elsewhere is preferred. Also,
special treatment of the
piston surface is required, e.g. such as coating with erosion resistant
material which can also be
a relatively poor thermal conductor.
In many applications arc runners are not practical, so more conventional spark
gaps with
proper oriented electrodes may be used (that do not interfere with the flow),
or circularly symmetric
spark gaps may be used. In such a case, the high energy-flow coupled-spark-
discharge (FCSD) acts
as a stationary extended spark (a plume) through which the mixture flows under
the action of bulk
flow to produce flame kernels which move and grow as they enter the turbulence
region 3 of the
combustion zone 4. FIG.8 depicts such an embodiment.
In FIG. 8 is shown a partially schematic, approximately to-scale top view of a
piston IC
engine representing a preferred embodiment of CFCSD with a single spark plug
12 and single
intake valve 9, with the valves and spark plug placed collinear in an
approximately central cylinder
7 diameter line with the spark plug in the center between the valves.Like
numerals represent like
parts with respect to the earlier figures. In this embodiment, the combustion
zone 4 is located
mainly under the exhaust valve with small piston clearance for the intake
valve to allow for squish
bulk flow 2 at the spark plug site. The use of a rotary intake valve would
obviate any concern
associated with the preferred small clearances between the valve and piston.
Shown also in the figure is a fuel injector nozzle 18 preferentially located
across from the
spark plug, representing a gas-direct-injection (GDI) version of the present
invention allowing for
the use of various fuels. The injector injects the fuel spray 19 into the
turbulence region where it
becomes rapidly mixed and homogenized for clean burning and prevention of
spark plug fouling
(a problem with spark ignition diesels).
A partially schematic, side view, approximately to-scale drawing of a cylinder
of the
engine of FIG. 8 with the piston near the end of the intake stroke is shown in
FIG. 8a. The intake
air 20 is shown entering in a vertical circular form representative of tumble
flow which can
reinforce the flow 2 at the spark gap 21 of FIG. 8b, which represents the
engine of FIG. 8a with
the piston at the end of the compression stroke near TC. Like numerals for
both FIGS. 8a and 8b
represent like parts with respect to the earlier figures. In FIG. 8a is shown
the alternative possible
fuel nozzle 18 (not shown in FIG. 8b representing the more conventional
engine).
FIG. 9a shows a partially schematic. approximately to-scale top view of a
piston IC engine
representing a preferred embodiment of CFCSD with a single spark plug 12 and
two intake valves
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I2
9a and 9b, with the exhaust valve 8 and spark plug 12 placed collinear in an
approximately central
cylinder 7 diameter line. Like numerals represent like pans with respect to
the earlier figures. The
shaded portion shown indicates the sloping region of the combustion zone from
its peak just under
the exhaust valve 8.
FIG. 9b is a partially schematic side-view drawing of the engine cylinder of
FIG. 9a, with
like numerals representing like parts with respect to the earlier figures. As
in most of the drawings,
the piston is shown near TC in the compression ignition firing stage. In this
embodiment, the
combustion chamber zone 4 is under the exhaust valve 8 and the spark gap is in
a high squish zone
as required.
FIG. l0a and lOb indicates the combustion chamber of a more conventional type
pent-roof
engine with the combustion zone shared between the cylinder head 6 and the
piston 5, but mostly
in the piston. Two spark plugs I2a and 12b are shown as one of several options
(one spark plug
being the more conventional option). The spark plug tips may be more
conventional or similar to
those of FIGS. 5 and 6b which can act as arc runners as already discussed.
Like numerals represent
I 5 like parts with respect to the earlier figures.
An interesting and relevant variation of the combustion chamber of FIGS. i Oa
and l Ob
is that of Jim Feuling most recently reported in the February 1999 issue of
Hot Rod magazine in
an article entitled "Lean, Mean, and Clean, Part One". The combustion chamber
is a Figure 8
combustion chamber in the cylinder head under the intake and exhaust valves
with the spark plug
in the middle. This design creates high turbulence in the combustion chamber
except that the
volume is larger (combustion wne is under both valves). Moreover, since the
spark plug is in the
middle and not at the edges of the combustion zone, as in FIGS. l0a and 1 Ob,
oral does not use a
high energy, flow resistant spark, it is not subject to bulk flow, as is
disclosed in the present
invention, to spread the spark discharge and create a rapid initial bum
In the preferred embodiments of this invention, the ignition and combustion
stage is so fast
that ignition can occur near TC, even for dilute mixtures (which permits
piston firing as one
alternative for generating and locating the spark, al~ough it is not require).
Preferably, ignition
occurs as close to I O° BTC as practical since the inward directed
squish flog- (bulk flow) is at its
maximum near that ignition timing. Under such conditions, the very powerful
and rapid ignition
and burn means that highly dilute mixt~es can be burnt effectively for low
exhaust emissions and
high fiiel economy. Preferably mixture dilution is produced internally (versus
EGR) by valve
timing, i.e. by advancing the exhaust valve closure, although it may be
supplemented with EGR
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13
and with excess air (lean mixtures). The very fast bum of dilute mixtures
results in very low NOx
emissions due to both the faster burn (less time for NOx to form) and lower
peak combustion
temperatures, while the higher trapped exhaust results in lower HC emissions.
Also the bulk flow
and colliding flow turbulence generation produces very good air-fuel mixing
for a more homogen-
eous mixture for lower HC emissions and higher engine efficiency. Rapid burn
also allows for
higher compression ratio and higher engine efficiency.
FIGS. 11,11 a, l l b, l l c and 11 d depict various partial views of an engine
combustion
chamber in which the compact combustion zone 110 is contained in the cylinder
head under both
the intake and exhaust valve of preferably small size and with two spark plugs
in the combustion
I O chamber located in the region of high flow. FIG.11 depicts a top part of a
spark plug 118 with
a preferred capacitive sp ark plug boot I 17, which may also be built into the
spark plug to provide
a typical capacitance of 30 to 60 picofarads.
The combustion chamber zone 110 disclosed has preferably intake valve 121 a
and
exhaust valve 12I b disposed parallel to the flat top ofthe piston 119b and
are made as small as
practical to provide squish zones 122a and 122b at the far edges as shown. The
valves are
located in line as close as is practical to each over, as shown in the top
view ofFIG. l l a, where
like numerals represent like parts with respect to FIG. l l . The combustion
chamber zone 110 is
in the head in an elongated region defined by a volume under each valve and
open in the central
region 123 between the two valves. Preferably, the larger volume is under the
exhaust valve 121 b,
which is more recessed than the intake valve 121 a, which is preferably
recessed to just to miss
the piston at its TC position when the intake valve is fully open (which can
occur if the timing belt
breaks for an overhead cam engine design).
With further reference to FIG.11 a, the design shown provides large squish
areas 124a and
124b, as is also shown in FIGS. 1 lb, l lc, l l d which are side-views
disposed 90° from that of
2 5 FIG.1 i . In FIGS.11 b, l l c, l l d like numerals represent like parts
with respect to FIG.11. In both
FIGS. 11 a , 1 lb,11 c, I 1 d are shown the possibility for inclusion of two,
instead of just one,
symmetrically placed spark plugs 118 and 118a, making preferably about
30° with the vertical
and placed at the inner edge of the large squish zones 124a and 124b so that
the spark gaps 125 a
and 125b are subjected to high squish flow near TC during ignition. In a
preferred design, the
squish lands 124a and 124b have a transverse length "1" approximately equal to
or greater than
the transverse radial dimea~sion "r" ofthe compact combustion chamber, as is
shown to produce
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high squish at the spark plug site and high colliding flows in the compact
combustion chamber
zone110. This helps vaporize, by the radial intense flow prior to TC, any fuel
that may have
collected on the piston lands, and produces rapid mixing of the air-fuel
mixture in the combustion
chamber zone 110 due to the turbulent colliding flows, even at low speeds
where combustion is
normally poor. The piston to head clearance in the land
areas122a,122b,124a,124b is typically
0.04" to 0.1"to create adequate squish without undue heat losses for atypical
engine with a bore
and stroke in the 3" to 4" range. The clearance is scaled appropriately for
larger engines. The
engine cylinder views of FIGS.11,11 a, l l b, l l c are approximately 2/3 of
full scale of a typical
IC engine cylinder. In FIGS.11 c and 11 d, where FIG. 11 d is an exploded view
of the central part
of FIG. 11 c, are shown a centrally located fuel injector 130, operable at
moderate pressure as in
a GDI engine, or at high pressure as in a diesel engine, located betweenthe
two valves and spark
plugs with central fuel spray cone 131 covering the central combustion region
123. By spraying
the fuel in the central region 123, it does not directly impinge on the spark
plug electrodes but
locates close to them for a better mixed state for ignition. In FIG.11 d, the
squish flow vectors 2
are shown on the left side at the tip of spark plug 118 (representing the
piston near TC) which help
prevent fuel from settling on the spark plug end and clean the end; the fuel
spray is shown on the
right side (representing the piston position prior to ignition), being
directed by the slight cup 133
in the piston up and to the right as a curved spray 132 moving towards the
spark gap 125 b to be
ignited. This combination of flow, fuel spray, and ignition location and
intensity (high energy),
make for a practical system.
An advantage of the high energy ignition as used in this engine design is that
it can
sustain flows as high as 20 meters/second (m/s) without spark break-up and can
deliver about 100
mJ of spark energy, which allows for very rapid ignition and rapid early flame
propagation (which
occurs in large part due to the high speed squish and turbulent colliding
flows). This allows for
ignition timing near TC even for lean and high EGR (or high internal exhaust
residual) mixtures,
which has several advantages including lower burn temperature and less time
available for NOx
formation, to minimize NOx emissions. Also, the more recessed exhaust valve
121 b allows for
more of the partially burnt gas formed at the piston ring regions 126 to be
trapped in the
combustion volume under the valves than to be exhausted because of the long
travel path,
allowing this partially burnt mixture to be reburned which minimizes
hydrocarbon (HC)
emissions. Also, the combination of rapid burn, the larger combustion volume
under the exhaust
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valve 121 h, and the large squish zones where the end gas (last part of the
mixture to burn) is
located and subjected to cooling by the reverse squish flow after TC, means
that higher
compression ratios can be used without engine knock forhigher e~ciency.
Moreover, the flat or
slightly cupped piston can be more readily coated with thermal barrier
coatings ~TBC) to
5 minimize heat transfer, reduce HC, and increase engine efficiency.
FIGS.12a,12b,12c, and I2d are approximately to-scale partial top and side
views of
a combustion chamber of FIGS. I 1, i 1 a and i 1 b detailing and emphasizing
certain aspects of the
combustion chamber for improved operation. Ldce numerals represent like parts
with respect to
the earlier figures.
10 FIG. i2a is a partial top view of the combustion chamber similar to FIG. I
Ia. However,
in this case the combustion zone 110 wraps tightly around the outer edges of
the valves l2la and
l2lb to have a flight fit with the edge of the combustion zone, defining the
tight fit regions I4la
and I4lh, also shown in partial side view FIGS. 12c and 12d. This allows far
larger squish zones
I22a and 122b on the smaller squish lands which are important in this case not
for IIow-coupIir~g
15 (produced by the large squish lands 124a and 124b) but for coating of the
end gas to permit higher
compression ratio operation of 10 to 12 to one compression ratio without
krrock. The spark plugs
118 and I I8a are shown located more towards the larger combustion volume 110a
under the
exhaust valve versus in-line with the cerm-al region i 23 in between the two
valves, for shorter
flame travel and faster burn.
FIGS. I2b and 12c are partial side views of the combustion chamber 12a, with
FIG. 12b
showing conventional type spark plugs 118 and l I8a with squish bulk flow
(vectors 2) induced
by the piston il9b near TC. The side view of FIG. i2c shows views of the two
combustion
volumes I IOa and 1 IOb, approximately scaled to each other, under the exhaust
and intake valves
respectively. The piston shows an optional combustion zone region 142
conforming to the
combustion zone in the cylinder head which would result in smaller volumes in
the cylinder head.
FiG. 12d is a partial view of FIG. 12c showing the intake valve 121a at its
approximately
fihly open position with intake flow vectors 143a emerging from the intake 143
with larger flow
(vectors) directed towards the center and right-most region of the combustion
chamber which can
generate tumble flow, useful for flow coupling to the spark gaps at more
advanced ignition firing
times (shown also with reference to FIGS. 8a and 8b). Likewise, exhaust flow
vectors 144a are
shown leaving the combustion chamber into the exhaust runner 144, with
partially open exhaust
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valve 121b, with minimum flow (small flow vectors 144a) along the far edge
141b nearest to the
piston ring crevice where unburnt hydrocarbons are foamed, to help trap them
as part of the
exhaust residual, as already discussed, with the major exhaust coming from the
central region of
the combustion zone I 1 (large flow vectors 144x). The net result is that more
unburnt hydrocar-
bops are trapped and higher compression ratios can be used because of the
squish land et the entire
far edge of the combustion chamber (where preferably the clearance at TC is
approximately 0.04"
as is known to those versed in the art).
FIG. 13 is a valve timing diagram depicting a preferred exhaust vah~e closing
(EC) at TC
for trapping more exhaust residual, and late intake closing (70° ABC)
for higher part-load
efficiency and higher, high engine speed output power (higher high shed
volumetric efficiency).
Intake opening (IO) and exhaust opening (EO) are shown 30° BTC and
30° BBC respectively.
FIG.14 is a design of ~e ignition coil output structure for providing dual
ignition firing
to the piston ofthe present invention in which the return path for the
electrical current is entirely
though the spark plugs and not through the engine block Like numerals repres
ent like parts with
respect to the earlier figures.
In this preferred embodiment, the coil secondary winding 146 (primary 147) has
two
floating high voltage outputs connected to spark plug el~trodes l0a and lOb
which fire to the
surface of the piston 5 at tips I 1 a and 1 lb respectively, as already
disclosed . The advantage in this
design is that current flows from one electrode (say 10a shown as positive) to
the piston surface
l la and back again to the other electrode lOb at piston surface point l lb,
so that the spark current,
which produces two sparks to the piston surface, does not have to find a
return path along the
pistonlcyiinder interface 148 or through other parts connected to the piston.
Preferably, one spark
gap I49a is smaller than the other (149b) to reduce the required spark firing
voltage, or the two
plugs have differing capaeitances to divide unevenly the output voltage, as is
known to those
versed in the art.
FIG.15 a is a partial, not to-scale, top view layout of two side-by-side
engine cylinders
in a multi-cylinder engine with a preferred combustion chamber FIG.15b of the
present invention
in which the valves are lined up approximately in the length axis of the
engine and a single
overhead cam 150 (broken lines) is shown for actuating the valves (which can
also be actuated
3 0 by other means, i. e. push-rods and rockers, electronically, etc). Like
numerals represent like parts
with respect to the earlier figures. This embodiment is more suitable for
swirl generation as
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17
dictated by the intake runner 143 which is at the side of a combustion chamber
diameter line
which produces flow vectors 15 l and 152 (FIG 15b) at the spark plug sites
(two plugs indicated
although plug 118 is preferred if only one plug is used since it will move the
spark towards a more
central part of the combustion zone 110a.). The squish flow vectors are not
shown (but will be
approximately orthogonal to the swirl vectors). The exhaust runner may be
onthe opposite side
or same side as the intake runner, as indicated in FIG. 1 Sa, it being
understood that in an actual
engine one or the other would be used (the drawing showing two options, as is
also done in FIG.
16a, to conserve drawing space). The combustion zone is indicated as peas
shaped with larger
diameter zone 1 l0a under the exhaust valve.
FIG.16a is a partial, not to-scale top view layout of two side-by-side engine
cylinders
in a mufti-cylinder engine with a preferred combustion chamber FIG.16b of the
present invention
in which the valves are lined up transverse to the length axis of the engine.
Like numerals
represent like parts with respect to the earlier figures. This embodiment is
more suitable for tumble
flow generation as dictated by the intake runner which is along a combustion
chamber diameter
line. One ortwo intake valves (121aaand 121ab) areindicated. Two (double)
overhead cams 153
and 154 (broken lines) are indicated for separate operation of the intake and
exhaust valves, which
makes it easy to provide independent variable (intake and exhaust) valve
timing. In FIG.16b the
version with two intake valves 121aa and 121ab and two intake runners 143a and
143b are
shown, which can allow for swirl generation by deactivating one of the intake
runners, resulting
in flow vectors 155 and 156 if valve IN2 ( 121 ab) is deactivated. Squish
vectors 2 are also shown
in this figure.
FIGS.17a, l 7b and 17c are partial top views of low inductance, high energy
ignition coil
structures with open magnetic paths suitable for application where greater
than 12 volts power
is available and designed for having two high voltage towers 160a and 160b
suitable for dual
ignition. As disclosed elsewhere, this low inductance structure normally has a
concentric winding
structure with preferably a two layer primary winding 161 and secondary
winding 162 made up
of typically segmented bobbin winding. Each of the designs have two or more
open ends 163a,
163b (and 163c and 163d for FIG. 176) to provide a typical low primary winding
inductance Lp
of 0.3 milliHenry (mH) to 1.0 mH.
The coil of FIG. 17a features two side-by-side U-cores 164 and 165 of
approximately
equal area of each leg placed 180° to each other so that the secondary
winding 162 can have its two
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ends brought out at the two open ends at the high voltage towers for
compactness. The high
voltage towers I60a and 160b act to also place a clearance between the
magnetic fields 166a and
166b and arty external metallic surface where the fields might otherwise
couple. Likewise for FIG.
17b where two of the four open end magnetic field lines are shown (166a and
166b), FIG. 17c
S where one of the two open end magnetic field lines are shown. In FIG. 17a
preferably the core is
made of stacked U-laminations.
FIG. 17b features a center leg magnetic core 167 (preferably stacked
lamination) and outer
magnetic core 168 which can be a tube of wound insulated magnetic tape , e.g.
4 mil silicon iron
tape, or two stacked Iaminanons, or other material of different type or shape.
Three of four
mounting holes 169a, I69b, and 169c are shown.
FIG. 1?c is a two piece 170a,170b bobbin type magnetic core, preferably made
of stacked
laminati~s, disclosed elsewhere but here designed to have the two high voltage
outputs 160a,
164b at the two ends.
FIG.18 is atop partial view of an open E-type low inductance, high energy
ignition coil
with open magnetic pa'di with some lower toms loosely coupled secondary
windings constituting
a series of secondary circuit external leakage inductors, usable also in the
designs ofFIGS.17a
and 17b, for reducing the end effect voltage overshoot. FIG.18 a is an
equivalent circuit ofthe coil
of FIG.18 used in an inductive ignition circuit. Like numerals represent Iike
parts with respect to
the earlier figures.
in FIG.18, the secondary winding 162 is a segmented winding separated into
bays { 10
shown as shaded rectangles), withthe iastthree 162abeingthicmer and having
fewer toms as well
as extending beyond the inner concentric primary winding 161 and having looser
magnetic
coupling as indicated by the magnetic field lines 170 shown in the left half
of the drawing. This
is to reduce the bay-to-bay voltage immediately following breakdown ofthe
spark gap (gap 15
of FIG. 18a with gap capacitance 117a across it). The three windings are
chosen by way of
example only. In FIG.18a the Last three windings are shown as three external
inductors 171 of
total inductance Lend to which can be added an external inductor Lext, as
disclosed elsewhere,
to reduce the voltage overshoot end-effect imtneaiaDely following spark
breakdown That is, upon
spark breakdown, the high voltage terminal across ~e spark gap immediately
drops to zero volts,
and the voltages at the end of the various segments cannot drop as quickly, so
that an
anomalously high voltage can appear across the secondary bays.
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In the case where two spark plugs are shown per combustion chamber, a range of
options
exist for firing them. Under some conditions, e.g. wide-open-throttle (WOT),
only one plug may
be fired. In some conditions, the plug firing may not be simultaneous. In some
conditions, e.g. cold
start, the plugs may be mufti-fired.
Since certain changes may be made in the above combustion chamber designs, in
the
location and use of the ignition, and in the air-fuel mixture flows without
departing from the scope
of the invention herein disclosed, it is intended that all matter contained in
the above description,
or shown in the accompanying drawings, shall be interpreted in an illustrative
and not Iimiting
sense.
