U.S. patent number 3,874,166 [Application Number 05/419,275] was granted by the patent office on 1975-04-01 for method of and apparatus for reducing harmful emissions from internal combustion engines.
This patent grant is currently assigned to BBC Brown Boveri & Company Limited. Invention is credited to Hubert Kirchhofer, Josef Perevuznik, Alfred Wunsch.
United States Patent |
3,874,166 |
Kirchhofer , et al. |
April 1, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Method of and apparatus for reducing harmful emissions from
internal combustion engines
Abstract
Combustion air for an internal combustion engine is compressed
in a dynamic pressure-wave machine by utilization of heat remaining
in the engine exhaust gases. A reduction in harmful emissions from
the engine is effected within the rotor of the pressure-wave
machine due to a primary recirculation of the exhaust gas into the
air at the interface between the exhaust gas and the air, the
amount of the recirculation being at its lowest value at full load
on the engine and being increased sharply with decreasing load. The
change in the amount of exhaust gas being recirculated is made more
uniform over the whole load range by means of a secondary
recirculation, increasing at full load, and which is brought about
by introducing exhaust gas directly into the machine in at least
one place at which the cells of the rotor are filled with air by
means of a crossover pipe.
Inventors: |
Kirchhofer; Hubert (Nussbaumen,
CH), Perevuznik; Josef (Baden, CH), Wunsch;
Alfred (Baden, CH) |
Assignee: |
BBC Brown Boveri & Company
Limited (Baden, CH)
|
Family
ID: |
4424938 |
Appl.
No.: |
05/419,275 |
Filed: |
November 27, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Nov 29, 1972 [CH] |
|
|
17373/72 |
|
Current U.S.
Class: |
60/772; 60/39.45;
123/559.2; 60/39.52; 417/64 |
Current CPC
Class: |
F02B
33/42 (20130101); F02M 26/40 (20160201); F02M
26/02 (20160201); F04F 13/00 (20130101); F02B
1/04 (20130101) |
Current International
Class: |
F04F
11/02 (20060101); F04F 11/00 (20060101); F02B
1/00 (20060101); F02B 1/04 (20060101); F02b
001/06 () |
Field of
Search: |
;60/598,599,600,604,605,611,614,616,621,623,39.02,39.45,39.52
;123/119C ;417/64 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Freeh; William L.
Assistant Examiner: Olsen; Warren
Attorney, Agent or Firm: Pierce, Scheffler & Parker
Claims
We claim:
1. In the method of providing combustion air for an internal
combustion engine by compressing the air in a gas-dynamic
pressure-wave machine by utilization of heat still contained in the
engine exhaust gases and wherein harmful emissions from the engine
are reduced as a result of a primary recirculation of exhaust gas
into the air at the interface between the exhaust gas and the air
in the celled rotor of the machine, the amount of the exhaust-gas
recirculation being at its lowest value at full load and increasing
sharply with decreasing load, the improvement which comprises the
step of introducing exhaust gas directly into the machine in at
least one place at which the cells of the rotor are filled with air
thereby effecting a secondary recirculation of the exhaust gas
which increases at full load and which serves to render
recirculation of the exhaust gas more uniform over the whole load
range.
2. Apparatus for providing combustion air for an internal
combustion engine comprising a gas-dynamic pressure-wave machine in
which the air is compressed by utilization of heat still contained
in the exhaust gases from the engine, harmful emissions from the
engine being reduced as a result of primary recirculation of
exhaust gas into the air at the interface between the exhaust gas
and the air in the celled rotor of the machine, said gas
recirculation being at its lowest value at full load and increasing
sharply with decreasing load, and means for rendering said
recirculation of exhaust gas more uniform over the whole load range
of the engine comprising a crossover duct for effecting secondary
exhaust-gas recirculation extending from a space filled with
exhaust gas to an opening facing air filled cells in the rotor in
one side of the machine.
3. Apparatus as defined in claim 2 and which further includes a
cooling device located in said crossover duct.
4. Apparatus as defined in claim 2 wherein said crossover duct is
constituted by a return-flow pipe, the inlet opening of which as
viewed in the rotational direction of the rotor lies within the
first half of the low-pressure gas outlet port from the rotor and
the outlet opening of which lies within the second half of the
low-pressure air inlet port to the rotor.
5. Apparatus as defined in claim 4 wherein the inlet opening of
said return-flow pipe is located immediately after the front edge
of said low-pressure gas outlet port, and wherein the outlet
opening of said return-flow pipe is located immediately in front of
the rear edge of said low-pressure air inlet port.
6. Apparatus as defined in claim 2 wherein said crossover duct is
constituted by a return-flow pipe which branches off the
high-pressure gas inlet pipe and which as viewed in the rotational
direction of the rotor emerges in a web located before the
high-pressure air outlet port.
7. Apparatus as defined in claim 2 wherein said pressure-wave
machine includes a compression pocket located adjacent one end of
the rotor and wherein said crossover duct is constituted by a
return-flow pipe which branches off the high-pressure gas inlet
duct and emerges in said compression pocket.
8. Apparatus as defined in claim 2 wherein said crossover duct is
constituted by a connecting pipe which branches off the
high-pressure gas inlet duct and which as viewed in the rotational
direction of the rotor emerges from a web located before the
high-pressure gas inlet port.
9. Apparatus as defined in claim 8 wherein said connecting pipe
terminates in at least one nozzle.
10. Apparatus as defined in claim 2 and which further includes a
throttling device in said crossover duct provided for the secondary
exhaust-gas recirculation.
11. Apparatus as defined in claim 10 and wherein the flow
cross-section of said throttling device is adjustable.
Description
The present invention concerns a method of reducing harmful
emissions from internal combustion engines the combustion air for
which is compressed in a gas-dynamic pressure-wave machine by
utilising energy still contained in the engine exhaust gases, a
primary recirculation of exhaust gas into the air taking place in
the rotor of the pressure-wave machine at the interface between the
exhaust gas and the air, and further concerns apparatus for
effecting this method.
Viewed from the overall economic standpoint there is at present no
real alternative to the diesel engine for road vehicles. If, as to
the future, the diesel engine is to continue to fulfil its
objective, namely increased output with the highest possible
power/weight ratio and lowest possible specific fuel consumption,
then particular attention must be paid to the exhaust-gas behaviour
of the diesel engine owing to the worldwide interest in
environmental pollution.
It is known that the recirculation of exhaust gases into the
combustion air of an internal combustion engine reduces the
emission of harmful substances such as nitrous oxides and
hydrocarbons. This recirculation, which with the diesel engine has
proved especially effective for reducing nitrous oxide emission,
consists in returning exhaust gas into the intake air, or in the
case of a pressure-charged engine into the charge air.
Exhaust gas recirculation lowers the oxygen content of the
combustion air and hence the effective excess air of the intake
gases. By way of the O.sub.2 concentration of the cylinder
contents, therefore, influence is exerted on the kinetics of the
combustion reaction, which in turn influences the combustion
procedure and the exhaust-gas composition. Reducing the O.sub.2
concentration by means of exhaust-gas recirculation means slower
combustion, under certain circumstances also accompanied by a
lowering of the maximum combustion temperature, on which the speed
of reaction in the formation of nitrous oxide to a large degree
depends. For this reason, reducing the maximum temperature of
combustion is the most appropriate way of decreasing nitrous oxides
in the exhaust gases. For the same reason, as regards nitrous oxide
emission it is more effective to recirculate cooled exhaust
gas.
Another very important aspect of exhaust-gas recirculation is the
reduction of the ignition lag, i.e. the time from the commencement
of fuel injection until the commencement of combustion. It is due
to the higher final compression temperature resulting from the
higher fresh gas inlet temperature. Apart from other advantages,
e.g. reduction of ignition noise, shortening the ignition lag has
the effect of improving combustion, which in turn reduces harmful
emissions.
With a diesel engine, because load is regulated in terms of the
calorific value of the mixture, the excess air coefficient rises as
load decreases. At small loads, therefore, more exhaust gas can be
recirculated without immediately causing an air deficiency because
the combustion-air excess is then very large. Thus in the range of
low and medium loads, nitrous oxide emission can be reduced
particularly effectively by recirculating exhaust gas into the
intake air. In the region of full load, on the other hand, heavy
recirculation of exhaust gases would lower the attainable power
output of the engine. But it is desirable to recirculate more
exhaust gas at partial load than at full load not only from the
standpoint of the engine, but also in view of legal emission
requirements, which take into account practical operation of the
vehicle. The optimum quantity of exhaust gas to be recirculated is
thus not constant: it depends on the duty point of the engine when
in service.
The gas-dynamic pressure-wave machine is very well suited to
pressure-charging internal combustion engines, and particularly
vehicle diesel engines, for which rapid response of the charging
device and high charging in the lower and middle speed range are
desired. Since in the pressure-wave machine exhaust gas and intake
air are in direct contact, a certain degree of mixing takes place
at the interface between these two gases.
At full load the passage of exhaust gas into the air, in the
following termed primary recirculation, can be largely prevented by
ensuring in the design of the pressure-wave machine that the
gas/air interface does not reach the high-pressure air outlet. A
buffer zone of air then prevents the exhaust gas from passing into
the combustion air. In addition, at full load the low-pressure
section is greatly over-scavenged, i.e. the pressure-wave machine
draws in more air than it compresses and feeds to the engine on the
high-pressure side. This extra scavenging air is used to flush the
mixing zone. However, it is not possible to maintain this
over-scavenging of the pressure-wave machine at operating points in
the region of partial engine loads. As load falls, it decreases
progressively until finally, at low partial loads, it becomes
under-scavenging, i.e. the pressure-wave machine draws in less air
than it supplies compressed gas to the engine being charged.
These features of the pressure-wave machine thus already meet the
requirements made of an exhaust-gas recirculation system for
internal combustion engines with the purpose of reducing harmful
emissions, in that gas recirculation increases as engine load
falls. It is sufficient for certain engines which, in order to
satisfy the California 13-point test, require exhaust-gas
recirculation only at partial load.
Thus with the usual design of the pressure-wave machine for
pressure-charging purposes, the quality of the engine exhaust gas
is scarcely affected at full load because then practically no gas
is recirculated. It is quite possible to increase gas recirculation
over the whole operating range of the pressure-wave machine, but it
is difficult to influence parts of the range. If gas recirculation
is increased at full load, the engine soon begins to smoke as load
decreases, and there is a danger that at the bottom of the load
range it receives too much exhaust gas and stops. Recirculating
very hot exhaust gas direct into the combustion air at full load
would also be less effective because it is known that hot exhaust
gas does not reduce the harmful components so greatly. Also, by
diminishing the combustion air ratio, hot exhaust gas in the
combustion air would cause a reduction in engine output.
The object of the present invention is to reduce emissions of
harmful substances from an internal combustion engine
pressured-charged by a gas-dynamic pressure-wave machine,
particularly in the full-load region, to values below those
resulting from primary exhaust-gas recirculation, without thus
disturbing operation of the engine and as far as possible without
forfeiting engine power.
This object is achieved in that primary exhaust-gas recirculation,
which is least at full load and increases sharply with decreasing
load, is made more uniform over the whole load range by secondary
recirculation, which increases at full load, by introducing exhaust
gas direct into the pressure-wave process in at least one place at
which the cells of the rotor are filled with air.
Apparatus for effecting this method comprises at least one
crossover duct for secondary recirculation from a space filled with
exhaust gas to an opening, facing the cells, in one side of the
pressure-wave machine.
An improvement can be achieved by means of a cooling device in the
crossover duct for secondary exhaust-gas recirculation.
In another version of the invention the crossover duct is in the
form of a return-flow pipe, the inlet opening of which, viewed in
the direction of rotation of the rotor, lies within the first half,
preferably immediately after the front edge of the low-pressure gas
outlet port, and its outlet opening lies within the second half,
preferably immediately before the rear edge of the low-pressure air
inlet port.
Another version employs a return-flow pipe as the crossover duct
which branches off the high-pressure gas inlet and, viewed in the
direction of rotation of the rotor, emerges in the web before the
high-pressure air outlet port.
If the pressure-wave machine incorporates a compression pocket, the
crossover duct can be a return-flow pipe which branches off the
high-pressure gas inlet and emerges in the compression pocket.
A further possibility comprises a connecting pipe as the crossover
duct which branches off the high-pressure gas inlet and, viewed in
the direction of rotation of the rotor, emerges in the web before
the high-pressure gas inlet port.
An improvement is then achieved if the termination of the
connecting pipe comprises at least one nozzle.
Such devices can easily be adapted to the motor in question by
means of a throttle device in the crossover duct for secondary gas
recirculation, and this can be further improved if the flow
cross-section of the throttle is adjustable.
With the method described it is possible, by influencing the
pressure-wave process, to alter the characteristic of primary
exhaust-gas recirculation in a gas-dynamic pressure-wave machine
with the aid of secondary gas recirculation in such a way that it
is approximately optimum at all duty points of the engine.
Comparable methods which operate with exhaust-gas turbochargers
require a separate control system for this purpose.
Recirculated exhaust gas, especially when cooled, is particularly
effective where it is most needed within the operating range of the
internal combustion engine to reduce severe harmful emission,
namely at high loads and high speeds. Cooling the recirculated gas
improves the reduction of harmful substances in the ranges of
engine operation with the greatest emission of such substances, and
decreases the unavoidable drop in engine output which is caused by
the lowering of the combustion air density but can be reduced by
suitable cooling.
When an engine is charged with a pressure-wave machine, it is easy
in this way to improve the quality of the exhaust gas by
recirculating exhaust gas into the combustion air to be
compressed.
The method described is also superior to comparable methods
operating with exhaust-gas tubochargers in that the gas-dynamic
pressure-wave machine, which even in its known form exhibits
considerable exhaust-gas recirculation, is to a large extent
insensitive to contamination. The quantity of soot entrained into
the pressure-wave machine with the secondary recirculated gas does
not therefore impair the performance of the machine, whereas with a
turbocompressor the consequences can be very serious. It is
practically impossible to operate a turbocompressor for any length
of time while introducing exhaust gases containing solid matter on
the intake side. With the method described, the contamination
problem is restricted to the cooler, but this can be so designed
that it can easily be cleaned periodically.
Several examples of the invention are shown schematically in the
drawings, in which:
FIG. 1 shows a gas-dynamic pressure-wave machine in longitudinal
section;
FIG. 2 is a side section of the housing at line II - II of FIG. 1
and viewed in the direction of the arrows;
FIG. 3 is the other side section of the housing at line III--III in
FIG. 1 and viewed in the direction of the arrows;
FIG. 4 is a cross-section of the rotor at line IV--IV in FIG. 1 and
viewed in the direction of the arrows;
FIG. 5 is part of a developed projection of a cylindrical section
at half the cell height through the rotor and through the adjacent
portions of the side sections of the housing with a gas
recirculation system according to the invention;
FIG. 6 is a diagram showing the effect achieved by the invention;
and
FIG. 7 and 8 are alternative versions to FIG. 5;
In all the drawings, the same parts are identified by the same
reference symbols.
FIG. 1 to 4 show a known construction of a gas-dynamic
pressure-wave machine. The rotor 1 turns between fixed side
sections of the housing, namely air housing 2 and gas housing 3,
which are joined by the middle portion 4 of the housing, which
encloses the rotor in the manner of a jacket. The high-energy,
high-pressure gas, here the exhaust gas of an internal combustion
engine, enters gas housing 3 at 5 and flows through inlet ports 9
into rotor 1, where it surrenders part of its energy to the air in
the pressure-wave process. It leaves the rotor again as
low-pressure gas through outlet ports 10 in gas housing 3, and
flows out of the gas housing at 6, e.g. towards the exhaust pipe.
Air normally at atmospheric pressure, termed low-pressure air,
enters the air housing 2 at 7 and flows through inlet ports 11 into
the rotor, where it is compressed. It leaves the rotor again as
high-pressure air through the outlet ports 12 in air housing 2 and
flows out of the air housing. This cannot be seen in these drawings
because in the present case the direction of the outlet flow is
perpendicular to the plane of the drawing.
A compression pocket 13, for pre-compressing the air, can be
provided in the side of the air housing 2 facing the rotor before
the high-pressure air outlet port 12, when viewed in the direction
of rotation of the rotor.
The rotor 1 is overhung in air housing 2, is driven at 8 and in
that portion in which the pressure-wave process takes place
comprises hub 14 and shroud 15 between which cell walls 16 extend
radially, enclosing cells 17 which are open in the directions of
the air housing and gas housing. Since there are two inlet and
outlet ports each in the air housing and gas housing, as can be
seen in FIGS. 2 and 3, the rotor passes through the gas-dynamic
cycle twice per revolution.
FIG. 5 shows a developed projection of approximately half the rotor
and of the adjacent parts of the side sections of the housing. The
high-pressure gas entering at 5 only partially fills the cells 17,
the direction of movement of which is indicated by the arrow 20,
since a residue of air remains in the cells. The hatched area 21 is
the space filled with engine exhaust gas, and the ideal interface
between gas and air is denoted 22. 18 designates the high-pressure
air outlet. The pressure-wave process taking place in the rotor is
indicated by the sequence of lines 23.
The circumstances illustrated in FIG. 5 relate to full engine load.
If the mixing zone of gas and air, as occurs in practice, is
separated from the high-pressure air outlet port 12 by a
sufficiently wide air buffer zone, exhaust gas cannot leave
together with the compressed air. The buffer zone containing gas is
completely scavenged in the low-pressure section so that in the
following cycle impurities cannot be carried into the engine with
the charge air. It can be seen that the interface 22 leaves the
cells well before the end of the low-pressure gas outlet port 10.
The cells are then purged with fresh air. This configuration of the
pressure-wave machine is necessary in order to avoid excessive
under-scavenging at very low engine load. When over-scavenging at
full load is 30 percent, under-scavenging at no-load is of the same
order of magnitude. Since at low loads the pressure differences
betweeen low-pressure air and low-pressure gas become very small,
and consequently the pressure-wave effect in the low-pressure
section is very weak, at low loads the interface 22 does not leave
the rotor 1 before the end of the low-pressure pressure gas outlet
port 10. The proportion of primary recirculated exhaust gas over
the whole load range is determined by selecting one point. If the
design chosen is such that at full load 5 to 10 per cent by volume
of exhaust gas is recirculated, the quantity recirculated at
no-load can become so great that the engine no longer runs
stably.
Curve A of FIG. 6, for example, shows the quantity of primary
recirculated exhaust gas at rated engine speed with a pressure-wave
machine of the usual construction, plotted as degree of
recirculation R.sub.z in per cent volume against mean effective
piston pressure p.sub.me, where 100 p.sub.me corresponds to the
piston pressure at full load. It can been seen from this diagram
that at full load the quantity of recirculated exhaust gas is very
small, but rises sharply with decreasing load, corresponding to
decreasing p.sub.me. However, a flatter recirculation
characteristic is desirable, and therefore to be aimed at: at full
engine load the quantity of exhaust gas recirculated in the
pressure-wave machine should be up to 10 per cent by volume, while
at low partial loads it should not be greater than with a machine
of the usual construction.
This is the purpose of the invention. A crossover duct which joins
a space filled with engine exhaust gas to an opening facing the
cells in one of the two end sections of the pressure-wave machine,
is used to introduce a secondary flow of exhaust gas direct into
the pressure-wave process at a place where the cells of the rotor
are filled with air.
In FIG. 5 the crossover duct comprises return-flow pipe 24. It
begins in the low-pressure gas outlet port 10 immediately after its
leading edge 27 when viewed in the direction of rotation of the
rotor, its inlet 25 faces the cells of the rotor and it ends in the
low-pressure air inlet port 11 immediately before its rear edge 28,
the outlet 26 of the return-flow pipe also facing the cells. At
some arbitrary point along the return-flow pipe 24 is a throttle
valve 29, and before it, viewed in the flow direction, is the
exhaust-gas cooler 30.
The scavenging process ends as soon as the cells reach the end of
the low-pressure gas outlet port 10. The gas flowing out of the
return-flow pipe 24 into the rotor has no opportunity to flow
straight out again through outlet port 10, but takes part in the
next pressure-wave cycle, whereupon it is compressed together with
the air flowing in through low-pressure air inlet port 11, is
expelled through the next high-pressure air outlet port 12 and
passed to the engine.
This secondary recirculation of exhaust gas is not simply
superimposed on the primary recirculation, but has the effect of
influencing and changing the whole pressure-wave process in such a
way that the sum of primary and secondary recirculated gas flows
corresponds to curve B in FIG. 6. The degree of recirculation can
be raised to 10 percent by volume at full load, without causing a
corresponding increase at partial load as well. Curve B is flatter
than curve A over the whole load range, and in this example even
shows smaller values at low partial loads than does curve A, which
represents primary recirculation alone.
The shape of curve B is by its nature subject to certain
variations, depending on the point at which the secondary
recirculated exhaust gas is introduced into the pressure-wave
process (see the examples described below) and how the process is
arranged. A criterion, however, is that the exhaust gas is
introduced at a point where the cells of the rotor are filled with
air. The configuration shown in FIG. 5, for example, can be varied
in that the inlet 25 of the return-flow pipe 24 is located within
the first half of the low-pressure gas outlet port 10 and its
outlet 26 lies within the second half of the low-pressure air inlet
port 11.
The dimensions of return-flow pipe 24 depends on the required
degree of recirculation, while account must also be taken of the
available pressure drop. A simplification is achieved by fitting a
throttle device so that the pipe cross-section does not have to be
matched to each individual case. By providing the throttle with a
variable flow cross-section, better optimisation is possible and
fine adjustment of the secondary recirculated gas flow is made
easier. It is of course also possible to regulate the flow
cross-section in relation to duty point, for example, in which case
curve B of FIG. 6 could be made even more uniform, if this is
desired.
The recirculated exhaust gas is cooled in cooler 30 before being
introduced into the pressure-wave process. In this way excessive
density loss of the compressed air due to heating of the
low-pressure air intake is avoided, and the flow rate of this
secondary recirculated gas can be influenced. Cooling the
recirculated gas, however, also further reduces the emission of
nitrous oxides, as has already been mentioned. But the exhaust-gas
cooler 30 cannot replace cooling of the entire high-pressure air on
its way to the engine. This cooling is well known in connection
with turbo-charging, and is particularly effective when
pressure-charging with a pressure-wave machine.
An example with recirculation of high-pressure gas is shown in FIG.
7. Exhaust gas coming from the engine is bled off supply duct 32
and fed to the air housing 2 by way of return-flow pipe 31. The
return-flow pipe ends in the compression pocket 13, from where the
gas is introduced into the pressure-wave process. The compression
pocket is incorporated in the web 33 before the high-pressure air
outlet port 12, when viewed in the direction of rotation of the
rotor. The throttling device consists of an interchangeable holed
diaphragm 34 located in the return-flow pipe at its junction with
the supply duct 32.
The action of the compression pocket is dependent on speed. At high
speeds the pocket has no influence on the pressure-wave process,
while at low speeds it has the effect of pre-compressing the
ingested fresh air. Throughout the whole speed range, however, the
pressure relationships are such that at full load the pressure drop
from the high-pressure gas supply duct 32 to the compression pocket
is greater than at partial load so that a correspondingly larger
quantity of exhaust gas is recirculated at full load.
A similar configuration is possible even when there is no
compression pocket. The return-flow pipe 31 then terminates in web
33, with its opening facing the cells of the rotor.
The curves of the degree of recirculation resulting from primary
and secondary recirculation are in both cases similar to curve B in
FIG. 6.
An example of high-pressure gas recirculation with the inlet flow
on the gas side is shown in FIG. 8. The connecting pipe 35
contained within gas housing 3 branches from the high-pressure gas
supply duct 32 and terminated in web 36 before the high-pressure
gas inlet port 9, when viewed in the direction of rotation of the
rotor, i.e. once again at a point where the cells of the rotor are
filled with air. This advance inlet flow not only influences the
pressure-wave process, but at the same time also displaces the
mixing zone further towards the air side. The result is that
principally at full load, and especially at high speeds, part of
the mixing zone discharges with the compressed air into the
high-pressure air outlet port 12. The effect can be intensified in
the termination of the connecting pipe 35 is fitted with a nozzle
37, which also replaces the throttle.
This version is of great advantage because no external piping is
required. Incorporating a cooler would necessarily be difficult,
and it would therefore be more convenient to cool the recirculated
exhaust together with the compressed on its way to the engine.
In all the examples the crossover duct is so arranged that a
pressure difference exists between its inlet and outlet. It is also
possible in principle to include a means of propelling the gas in
order to raise the flow velocity of the recirculating gas if the
pressure difference is small, or even to overcome a negative
pressure difference, but this would make the whole apparatus more
complicated and, moreover, requires additional energy.
Also included in the invention is the possibility of providing in a
given case a number of crossover ducts in parallel, or one or more
for each pressure-wave cycle. Furthermore, the various
possibilities can be combined.
It should also be noted that the method described for reducing
harmful emissions from internal combustion engines is equally
applicable to diesel and Otto-cycle engines.
* * * * *