Title: Compound gas turbine engines and methods of operation thereof
Abstract: The engine (10) has a compressor (12) for compressing air, a plurality of combustion chambers (22a-f) in which fuel mixed with the compressed air combusts, and a turbine (16) which is driven by the products of combustion. Each combustion chamber operates in a cycle comprising the phases of: A. charging the combustion chamber with a charge of compressed air from the compressor while preventing air from escaping from the combustion chamber; B. then compounding by charging with a compounding charge of gas to form a compounded charge; C. then injecting fuel into the combustion chamber so that there is spontaneous ignition and combustion of the fuel with the compounded charge; and D. then exhausting the products of combustion to the turbine. The cycles of the combustion chambers are out of phase in a sequence, and part of the compounded charge (and/or the products of combustion thereof) in each combustion chamber during the combustion phase thereof is transferred to the next combustion chamber in the sequence to provide the compounding charge for that next combustion chamber.
Patent Number: 7,000,402 Issued on 02/21/2006 to Benians
| Inventors:
|
Benians; Hubert Michael (Bleak Cottage, White Horse Lane, Denmead, Waterlooville Hampshire PO7 6JP, GB)
|
| Appl. No.:
|
482604 |
| Filed:
|
July 1, 2002 |
| PCT Filed:
|
July 1, 2002
|
| PCT NO:
|
PCT/GB02/03018
|
| 371 Date:
|
December 26, 2003
|
| 102(e) Date:
|
December 26, 2003
|
| PCT PUB.NO.:
|
WO03/004846 |
| PCT PUB. Date:
|
January 16, 2003 |
Foreign Application Priority Data
| Current U.S. Class: |
60/776; 60/39.39; 60/39.76 |
| Current Intern'l Class: |
F02C 5/00 (20060101) |
| Field of Search: |
60/3938,393.9,394,397.6,397.8,776
|
References Cited [Referenced By]
U.S. Patent Documents
| 1903292 | Apr., 1933 | Holzwarth.
| |
| 2579321 | Dec., 1951 | Kadenacy.
| |
| 2705867 | Apr., 1955 | Lewis.
| |
| 2937498 | May., 1960 | Schmidt.
| |
| 4693075 | Sep., 1987 | Sabatiuk.
| |
| 5237811 | Aug., 1993 | Stockwell.
| |
| 5901550 | May., 1999 | Bussing.
| |
| Foreign Patent Documents |
| 383286 | Oct., 1923 | DE.
| |
| 515635 | Jan., 1931 | DE.
| |
| 1014794 | Aug., 1957 | DE.
| |
| 1131310 | Feb., 1957 | FR.
| |
| 296267 | Aug., 1928 | GB.
| |
| 646302 | Nov., 1950 | GB.
| |
| 710252 | Jun., 1954 | GB.
| |
| 892143 | Mar., 1962 | GB.
| |
Primary Examiner: Casaregola; Louis J.
Attorney, Agent or Firm: Stewart; John V.
Claims
The invention claimed is:
1. A method of operation of a gas turbine engine (
10) having a compressor
(
12) for compressing air, a plurality of combustion chambers (
22a-f)
in which fuel mixed with the compressed air combusts, and a turbine (
16)
which is driven by the products of combustion, wherein:
(i) each combustion chamber operates in a cycle comprising the phases of:
A. charging the combustion chamber with a charge of compressed air from the compressor
while preventing air from escaping from the combustion chamber;
B. then compounding by charging with a compounding charge of gas to form a compounded charge;
C. then commencing injection of fuel into the combustion chamber so that there
is spontaneous ignition and combustion of the fuel with the compounded charge at
generally constant pressure; and
D. then exhausting the products of combustion to the turbine;
(ii) the cycles of the combustion chambers are out of phase in a sequence; and
(iii) part of the compounded charge (and/or the products of combustion thereof)
in each combustion chamber during the combustion phase thereof is transferred before
the exhaust phase thereof to the next combustion chamber in the sequence to provide
the compounding charge for that next combustion chamber.
2. A method as claimed in claim 1, wherein the cycle of each combustion chamber
also includes a phase E, between its exhaust phase D and its charging phase A,
of permitting scavenge/cooling air to flow through the combustion chamber from
the compressor to the turbine.
3. A method as claimed in claim 2, wherein, following the end of the scavenging/cooling
phase, the duration of the charging phase is such that the pressure of the fresh
air charge in the combustion chamber is increased and preferably maximised by a
"ram" effect.
4. A method as claimed in claim 1, wherein each combustion chamber is elongate.
5. A method as claimed in claim 4, wherein:
the charging with air takes place at or adjacent one end of each combustion chamber; and
the exhausting of the products of combustion takes place at or adjacent the opposite
end of each combustion chamber.
6. A method as claimed in claim 4, wherein:
the transfer of the compounding charge takes place at or adjacent one end of
each combustion chamber; and
the injection of fuel takes place at or adjacent the other end of each combustion chamber.
7. A gas turbine engine (
10) comprising:
a compressor (
12) for compressing air;
a plurality of combustion chambers (
22a-f) each having at least
one fuel injector (
42a-f) and in which fuel mixed with the compressed
air can combust; and
a turbine (
16) which is driven by the products of combustion;
wherein:
each combustion chamber is connected to the compressor via a respective inlet
port (
24) having a respective inlet valve (
28a-f);
each combustion chamber is connected to the turbine via a respective exhaust
port (
32) having a respective exhaust valve (
38a-f);
the combustion chambers are arranged as at least one series and in the, or each,
series are operable sequentially;
each combustion chamber is connected to the next combustion chamber in the, or
the respective, series via a respective transfer port (
44) having a respective
transfer valve (
46ab,
46,
bc,
46cd,
46de,
46ef,
46fa); and
the engine further comprises means (
30) for operating the valves so that
the engine operates such that: each combustion chamber operates in a cycle comprising
the phases of:
charging the combustion chamber with a charge of compressed air from the compressor
while preventing air from escaping from the combustion chamber; then compounding
by charging with a compounding charge of gas to form a compounded charge;
then commencing injection of fuel into the combustion chamber so that there is
spontaneous ignition and combustion of the fuel with the compounded charge at generally
constant pressure; and
then exhausting the products of combustion to the turbine;
the cycles of the combustion chambers are out of phase in a sequence; and
part of the compounded charge (and/or the products of combustion thereof) in
each combustion chamber during the combustion phase thereof is transferred before
the exhaust phase thereof to the next combustion chamber in the sequence to provide
the compounding charge for that next combustion chamber.
8. An engine as claimed in claim 7, wherein the valve operating means is operable
so that, during the charging phase for each combustion chamber, the inlet valve
for that chamber is open and the exhaust valve for that chamber is closed.
9. An engine as claimed in claim 7, wherein the valve operating means is operable
so that the cycle of each combustion chamber also includes a phase, between its
exhaust phase and its charging phase, of permitting scavenge/cooling air to flow
through the combustion chamber from the compressor to the turbine, and during the
scavenge/cooling phase for each combustion chamber, the inlet valve and the exhaust
valve for that chamber are both open.
10. An engine as claimed in claim 7, wherein the compressor and the turbine each
have housings that are fixed relative to the combustion chambers.
11. An engine as claimed in claim 7, wherein each inlet valve, exhaust valve
and/or transfer valve comprises a respective poppet valve, piston-operated valve,
rotary valve or sleeve valve.
12. An engine as claimed in claim 7, wherein the valve operating means is mechanically
driven by the turbine via at least one gearbox.
13. An engine as claimed in claim 7, wherein the compressor is mechanically driven
by the turbine via at least one gearbox.
14. An engine as claimed in claim 7, wherein each combustion chamber is elongate.
15. An engine as claimed in claim 14, wherein:
each inlet port is disposed at or adjacent one end of the respective combustion
chamber; and
each exhaust port is disposed at or adjacent the opposite end of the respective
combustion chamber.
16. An engine as claimed in claim 14, wherein:
each transfer port is disposed at or adjacent one end of the respective combustion
chambers; and
each fuel injector is disposed at or adjacent the opposite end of the respective
combustion chamber.
17. An engine as claimed in claim 7, further including a nozzle ring (
36)
between the exhaust ports and the turbine, the nozzle ring having a plurality of
segments (
34a-f) each corresponding to a respective one of the combustion chambers.
Description
This invention relates to engines and to methods of operation thereof.
The invention is applicable to engines of the type having a compressor for compressing
air, a plurality of combustion chambers each having at least one fuel injector
and in which fuel mixed with the compressed air combusts, and a turbine which is
driven by the products of combustion. Such an arrangement forms the basis of a
conventional gas turbine engine. Such engines are typically used to produce mechanical
power via a power take-off and/or to produce thrust, and the turbine is typically
used to drive the compressor.
The thermal efficiency of a conventional gas turbine engine is relatively poor
when compared with that of a turbo-charged diesel engine or, more particularly,
a compound diesel engine. The reason for the lower thermal efficiency of the gas
turbine engine is primarily due to the comparatively low temperature and pressure
at which combustion takes place, and these parameters are limited by the pressure
ratio of the compressor.
The present invention, or at least specific embodiments of it, is concerned with
improving the performance of the gas turbine engine by enabling the temperature
and pressure at which combustion takes place to be increased substantially.
In accordance with a first aspect of the present invention, there is provided
a method of operation of a gas turbine engine, wherein each combustion chamber
operates in a cycle comprising the phases of: charging the combustion chamber with
a charge of compressed air from the compressor while preventing air from escaping
from the combustion chamber; then compounding by charging with a compounding charge
of gas to form a compounded charge; then injecting fuel into the combustion chamber
so that there is spontaneous ignition and combustion of the fuel with the compounded
charge; and then exhausting the products of combustion to the turbine. The cycles
of the combustion chambers are out of phase in a sequence, and part of the compounded
charge (and/or the products of combustion thereof) in each combustion chamber during
the combustion phase thereof is transferred to the next combustion chamber in the
sequence to provide the compounding charge for that next combustion chamber. It
will be appreciated that this transfer of a compounding charge from one combustion
chamber to the next increases the temperature and pressure by compression of the
air in the latter combustion chamber. The ensuing combustion in the latter combustion
chamber therefore takes place at an elevated temperature and pressure, thus improving
the thermal efficiency of the engine and/or enabling lower grade and/or higher
flashpoint fuel to be used.
Patent document GB-A-892143 describes a method of operation of a combustion
gas generator that has some similarities to the present invention. However, in
the method of GB-A-892143, the charging phase acts solely as a scavenging phase
so that the pressure in the combustion chamber at the end of the charging/scavenging
phase is somewhere between the compressor outlet pressure and either the turbine
back-pressure or atmospheric pressure and is thus comparatively low so that the
overall efficiency of the engine is thereby compromised. Furthermore, the method
of GB-A-892143 relies on spark-ignition of the air/fuel mixture and is therefore
prone to excessively high peak temperatures and pressures before the exhaust phase
commences. Moreover, there is a risk of pre-ignition and/or detonation of the air/fuel
charge in one combustion chamber by a carry-over flame from the previous combustion
chamber during the compounding phase. By contrast, the method of the present invention
employs spontaneous ignition, whereby the ensuing combustion can readily be controlled
to provide progressive and prolonged fuel burning at generally constant pressure.
Preferably, the cycle of each combustion chamber also includes a phase,
between its exhaust phase and its charging phase, of permitting scavenge/cooling
air to flow through the combustion chamber from the compressor to the turbine.
This serves to scavenge the combustion chamber and also to cool the combustion
chamber, any exhaust valves, and the turbine. Preferably, following the end of
the scavenging/cooling phase, the duration of the charging phase is such that the
pressure of the fresh air charge in the combustion chamber is increased and preferably
maximised by a "ram" effect.
Preferably, each combustion chamber is elongate, ie has a length substantially
greater than its diameter or its cross-sectional dimensions. In this case, preferably
the charging with air takes place at or adjacent one end of each combustion chamber,
and the exhausting of the products of combustion takes place at or adjacent the
opposite end of each combustion chamber. This serves to encourage stratification
along the combustion chamber.
Preferably, the combustion phase for each combustion chamber includes
injecting fuel into that combustion chamber. In this case, preferably the transfer
of the compounding charge takes place at or adjacent one end of each combustion
chamber, and the injection of fuel takes place at or adjacent the other end of
each combustion chamber. Accordingly, there is a tendency for the compounding charge
to be air, rather than products of combustion.
In accordance with a second aspect of the present invention, there is provided
a gas turbine engine, wherein: each combustion chamber is connected to the compressor
via a respective inlet port having a respective inlet valve; each combustion chamber
is connected to the turbine via a respective exhaust port having a respective exhaust
valve; the combustion chambers are arranged as at least one series and in the,
or each, series are operable sequentially; each combustion chamber is connected
to the next combustion chamber in the, or the respective, series via a respective
transfer port having a respective transfer valve; and the engine further comprises
means for operating the valves so that the engine operates according to the method
of the first aspect of the invention.
Preferably, the valve operating means is operable so that, during the
charging phase for each combustion chamber, the inlet valve for that chamber is
open and the exhaust valve for that chamber is closed, so as to provide the ram
effect mentioned above.
Preferably, the valve operating means is operable to provide a scavenge/cooling
phase for each combustion chamber, in which the inlet valve and the exhaust valve
for that chamber are both open.
In the arrangement of GB-A-892143, the combustion chambers are arranged as a
rotating
drum sliding between two stationary ported valve plates. With such an arrangement,
it is envisaged that satisfactory sealing of the ports and/or the provision of
adequate air or liquid cooling for the combustion chambers in such a rotating assembly
would be impracticable. By contrast, in the present invention, each inlet valve,
exhaust valve and/or transfer valve preferably comprises a respective poppet valve,
piston-operated valve, rotary valve or sleeve valve. Furthermore, the compressor
and the turbine preferably each have housings that are fixed relative to the combustion
chambers. Designed to contain high combustion pressures, these chambers can therefore
form an integral part of the overall engine structure.
In the arrangement of GB-A-892143, the rotating drum of combustion chambers is
driven by the turbine shaft so that the porting operates at turbine speed. Accordingly,
each sector of turbine blading may always experience the same part of the working
cycle, so that some sectors of the turbine blading may be hotter others. This may
lead to difficulties with differential heating, carbon build-up and so on. By contrast,
in the present invention, the valve operating means is preferably mechanically
driven by the turbine via at least one gearbox. Accordingly, it can be arranged
that the turbine blading precesses relative to the engine cycle.
Preferably, the compressor is mechanically driven by the turbine via
at least one gearbox. This may be particularly advantageous in the case of a centrifugal
compressor and an axial turbine.
In the case where each combustion chamber is elongate, preferably each inlet
port
is disposed at or adjacent one end of the respective combustion chamber, and each
exhaust port is disposed at or adjacent the opposite end of the respective combustion chamber.
The engine preferably further includes, for each combustion chamber, at least
one respective fuel injector. In this case, preferably each transfer port is disposed
at or adjacent one end of the respective combustion chambers, and each fuel injector
is disposed at or adjacent the opposite end of the respective combustion chamber.
Each inlet valve, exhaust valve and/or transfer valve preferably comprises a
respective poppet valve, piston-operated valve, rotary valve or sleeve valve.
Preferably, the engine further includes a nozzle ring between the exhaust
ports and the turbine, the nozzle ring having a plurality of segments each corresponding
to a respective one of the combustion chambers. Such segmentation reduces interference
between neighbouring turbine inlet nozzle segments and adjacent combustion chambers
due to fluctuating pressures.
Specific embodiments of the present invention will now be described, purely
by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a side view of a gas turbine engine with an enclosure of its combustion
stage shown in phantom line;
FIG. 2 is a sectioned end view of the engine of FIG. 1, taken along the section
line 2—2 shown in FIG. 1, and on a larger scale;
FIG. 3 is a schematic developed view of the engine of FIGS. 1 and 2, taken along
the development line 3—3 shown in FIG. 2;
FIG. 4 is a phase diagram to illustrate one mode of operation of the engine
of FIGS. 1 to 3;
FIG. 5 is a more detailed phase diagram to illustrate the operation of one of
the combustion chambers of the engine of FIGS. 1 to 3;
FIG. 6 is similar to FIG. 3, but for a different configuration of engine;
FIG. 7 is a phase diagram to illustrate the operation of the combustion chambers
of the engine of FIG. 6;
FIG. 8 is a schematic developed view taken on the line 8—8
in FIG. 6; and
FIG. 9 is a schematic developed view taken on the line 9—9
in FIG. 6.
Referring to the drawings, a gas turbine engine
10 has a compressor
12, combustion stage
14 and turbine
16. The compressor
12
and turbine
16 may be of generally conventional design/construction, and
each may be a multi-stage unit. The turbine
16 is typically connected to
and drives the compressor
12 through shaft
18. A second co-axial
shaft
19 is provided for the operation and synchronisation of the auxiliary
equipment, including the valves, the fuel injection system, the governor and the
lubrication system. Shaft
18 and the co-axial shaft
19 are preferably
connected by means of gearing or, in the case of stationary applications, the co-axial
shaft
19 may be driven by external means, in which case, the governor must
be driven by the shaft
18 in order to control the output speed. The engine
10 may have a mechanical power take-off, for instance in stationary or marine
applications, or it may be used as a turboprop engine or as a turbojet or in any
other configuration of thrust producing engine. The novelty of the engine
10
lies primarily in the method of compounding in the combustion stage
14.
In the configuration of FIGS. 1 to 3, the combustion stage
14 has an enclosure
20, which houses a circular array of six elongate combustion chambers
22a-f,
or pressure vessels, with their longitudinal axes generally parallel to and arranged
around the shafts
18 and
19.
One end of each combustion chamber
22a-f is connected via a respective
inlet port
24 to a manifold
26 at the outlet of the compressor
12.
Each inlet port
24 contains a respective inlet valve
28a-f which
is operated by an inlet and transfer valve actuator mechanism
30 which may
in turn be driven by the co-axial shaft
19. Each inlet valve
28a-f
may be a poppet valve which is forced open by the actuator mechanism
30,
preferably by means of a cam and which is closed by a spring and which is assisted
in remaining closed by the pressure in the respective combustion chamber
22a-f.
Alternatively, other types of inlet valve may be employed including piston, rotary
or sleeve operated valves. The other end of each combustion chamber
22a-f
is connected via a respective exhaust port
32 to a respective segment
34a-f of a nozzle ring
36 at the inlet to the turbine
16.
Each exhaust port contains a respective exhaust valve
38a-f which
is operated by an exhaust valve mechanism
40 which may in turn be driven
by the co-axial shaft
19. Each exhaust valve
38a-f may be
a piston operated valve which is operated by the actuator mechanism
40,
preferably by means of an eccentric or short stroke crank. Alternatively, other
types of exhaust valve may be employed including poppet valves, rotary or sleeve
operated valves.
Adjacent the exhaust end of each combustion chamber
22a-f,
a respective fuel injection nozzle
42a-f is provided. The fuel injection
nozzles are operated sequentially to inject diesel fuel into the respective combustion
chambers
22a-f and their timing is controlled by a fuel injection
pump
43 driven by (and shown diagrammatically adjacent to) co-axial shaft
19. More than one fuel injection nozzle
42a-f may be provided
to serve each combustion chamber
22a-f. Where the shafts
18,
19
are mechanically linked, the fuel injection pump
43 may be an in-line fuel
pump fitted with an integral governor, or a rotary distribution fuel pump, again
with an integral governor. Alternatively, each chamber
22a-f may
be supplied with fuel using individual combined fuel pump/injector/nozzle units
which in turn may be actuated by co-axial shaft
19, although such an arrangement
would require a separate linked governor unit driven by shaft
18 in order
to control the output speed.
Adjacent the inlet end of each combustion chamber (e.g. chamber
22b),
the combustion chamber is connected to the two adjacent combustion chambers (e.g.
chambers
22a,
22c) by respective transfer ports
44.
Each transfer port
44 contains a respective transfer valve
46ab,
46bc,
46cd,
46de,
46ef,
46fa which is operated by the inlet and transfer valve actuator mechanism
30. Each transfer valve
46ab,
46bc,
46cd,
46de,
46ef
46fa may be a piston valve which is operated by the actuator
mechanism
30, preferably by means of an eccentric or short stroke crank.
Alternatively, other types of transfer valve may be employed, including rotary
or sleeve operated valves.
The inlet and transfer valve actuator mechanism
30 has been considered
above and shown schematically as a single unit operated by the co-axial shaft
19,
but in practice separate units or mechanisms may be provided for actuating the
inlet valves
28a-f and for actuating the transfer valves
46ab,
46bc,
46cd,
46de,
46ef,
46fa.
Whilst it has been stated earlier that the co-axial shaft
19 may either
be driven through gearing by the shaft
18 or alternatively driven by external
means, it is foreseen that provision would also be made for small variations in
the respective valve timings and/or the respective fuel injection timings to meet
different operating conditions, whilst still maintaining overall synchronisation
of the auxiliary functions. It is also foreseen that the gear ratio between shaft
18 and the auxiliary co-axial drive shaft
19 must be chosen such
that the sequence of functions taking place in the combustion chambers will be
out of synchronisation with, or multiples of, turbine rotational speed. This will
ensure, for example, that the exhaust pulses will be constantly precessing in relation
to the rotation, or multiples of revolutions, of the turbine blading, irrespective
of the relative speeds or directions of shaft rotation, with a view to minimizing
differential heat stresses.
The operation of the engine in the steady state of the six chamber configuration
depicted in FIGS. 1 to 3 is now described assuming the starting point where, say,
- the inlet valve 28c of combustion chamber 22c
is open, its exhaust valve 38c is on the verge of closing, and
scavenging/cooling is about to cease; its transfer valve 46cd to
the next combustion chamber 22d is closed, its transfer valve 46bc
from the previous combustion chamber 22b is closed, no fuel is
being injected at nozzle 42c;
- combustion chamber 22b leads combustion chamber 22c
by one sixth of a cycle; and
- combustion chamber 22d lags behind combustion chamber
22c by one sixth of a cycle.
From the starting point, the operational phases A to E of the engine and the
transitions between them, AB, BC, CD, DE, EA, insofar as the combustion chamber
22c is concerned, are as follows:
Transition E-A: The exhaust valve 38c closes to end the scavenging/cooling phase.
Phase A: Charge. Air continues to flow from the compressor outlet manifold
26 through the open inlet valve 28c into the combustion chamber
22c until the pressure therein approaches that of the compressor
outlet manifold.
Transition A-B: As the pressure in the combustion chamber 22c
generally reaches the compressor outlet manifold pressure, the inlet valve
28c closes and the transfer valve 46bc connecting with
the previous combustion chamber 22b opens.
Phase B: Compound. High pressure air and/or products of combustion flow
from the previous combustion chamber 22b (under approximately constant
pressure conditions, maintained by fuel injection into combustion chamber 22b),
highly compressing the air in combustion chamber 22c and thereby
substantially raising the temperature and pressure of the air charge in combustion
chamber 22c, in anticipation of fuel injection.
Transition B-C. The transfer valve 46bc connecting with the
previous combustion chamber 22b closes. Fuel injection through nozzle
42c into combustion chamber 22c is initiated as the
transfer valve 46cd connecting with the next combustion chamber 22d opens.
Phase C: Combustion. Spontaneous ignition and combustion of the fuel/air
takes place due to the existing high temperature and pressure in the combustion
chamber 22c. During combustion, high pressure air and/or products
of combustion flow from the combustion chamber 22c at approximately
constant pressure into the next combustion chamber 22d thereby providing
the compounding pulse phase B for the next combustion chamber 22d.
Transition C-D: As fuel injection from nozzle 42c into combustion
chamber 22c satisfies the power requirement, and transfer to the
next chamber is completed, the transfer valve 46cd connecting with
combustion chamber 22d closes. The exhaust valve 38c opens.
Phase D: Exhaust. The high pressure residual products of combustion exhaust
from the combustion chamber 22c via the nozzle segment 34c
to the turbine 16, and the pressure in the combustion chamber 22c drops.
Transition D-E: The inlet valve 28c opens.
Phase E: Scavenge. Air flows from the compressor outlet manifold 26
through the inlet valve 28c, through the combustion chamber 22c
and the exhaust valve 38c thereby providing uniflow scavenge
of the combustion chamber 22c as well as providing cooling of the
combustion chamber 22c, the exhaust valve 38c, the
turbine nozzle segment 34c and the turbine 16.
Transition E-A: This is a repeat of the transition E-A described at the
beginning of section.
These phases for all six of the combustion chambers
22a-f are
shown in FIG. 4. The relative lengths of the phases A to E are shown in FIG. 4
as: A—90°; B—60°; C—60°; D—60°; and
E—90°. Nevertheless, the relative phases of A, D and E may vary considerably
from those shown in FIG. 4 although the compounding phase B and the combustion/transfer
stage C are equal and limited to a maximum of 60° for the six combustion chamber configuration.
FIG. 5 is a more detailed cycle diagram for any one of the combustion chambers
22. Again it shows that the compounding phase B and the combustion/transfer
phase C are equal and limited to 60°. Fuel injection is shown diagrammatically
to commence with the start of transfer and the rate of fuel injection is intended
to maintain approximately constant pressure throughout the combustion and transfer
phase. Normally, fuel injection will be completed before the end of the transfer
phase, leaving sufficient tolerance for the governor to maintain the required speed/power
output to match the engine load. It will be appreciated, however, that the configuration
lends itself to a wide range of predetermined rates of fuel injection and timing
such that under certain operating conditions injection may commence marginally
before the start of transfer or it may end marginally after the end of transfer.
As mentioned previously, each combustion chamber
22a-f is elongate,
ie its length between its inlet ports
24 and its exhaust ports
32
is substantially greater than its diameter or cross-sectional dimensions. Furthermore,
the fuel injectors
42a-f and the transfer ports
44 are located
at opposite ends of each combustion chamber in order to provide optimum stratification
between charge air and the residual products of combustion. When fuel is injected
during the combustion phase C, combustion will tend to be concentrated at the same
end as the injection nozzle whereas the charge air will be concentrated at the
transfer port end of the chamber. Therefore, the air/gas which is transferred to
the next combustion chamber in the sequence will have a high concentration of unburned
air. For the six-combustion chamber single cycle engine shown in FIGS. 1,
2,
3,
4 and
5 the transfer ports are located adjacent the inlet
ports and the injection nozzles are located adjacent the exhaust ports. Although
this is the preferred arrangement, it will be appreciated that stratification can
also be achieved if the injection nozzles are adjacent the inlet valves and the
transfer ports are adjacent the exhaust valves. This is the subject of an alternative
double cycle or duplex engine described later with reference to FIGS. 6 to 9.
The engine
10 described above is preferably used at near constant speed
and/or with near constant power output. It requires additional equipment for starting,
such as a means of cranking it up to operating speed and may require the introduction
or injection of a volatile fuel with synchronised spark ignition, until the compression
ignition cycle can be sustained.
In the engine
10 described above, the enclosure
20 may serve to
collect used lubricating oil, for example on a dry sump basis, and to carry additional
cooling air bled from the compressor and exhausted into a late turbine stage. This
bleed air may be used for additional external cooling for the combustion chambers
and, particularly for the transfer ports and their respective valves. The enclosure
20 may also be used to contain and vent any gas leaks which may occur, for
example at the inlet poppet valve stems or past the piston rings of the transfer
and exhaust valves. The external surfaces of the combustion chambers
22a-f
may be provided with radial, longitudinal or spiral finning to assist in cooling
and/or the combustion chambers
22a-f may be provided with liquid
cooling. In the case where longitudinal finning is employed, the combustion chambers
may be formed by extrusion.
It is envisaged that the ideal application for this engine, to take full advantage
of the improved efficiency, would be for electrical generation, particularly standby
generation and for marine propulsion and the associated marine auxiliary engines,
in each case using a geared mechanical power take-off. The engine may also be developed
for aircraft propulsion, in turboprop, turbojet and other configurations, where
the improved efficiency can be shown to offset any increase in weight and where
the engine would provide improved safety by using high flashpoint, low grade diesel fuels.
Many modifications and developments may be made to the embodiment of the invention
described above. For instance, six combustion chambers
22a-f have
been shown merely by way of example, and other numbers of combustion chambers may
be provided. As previously stated the auxiliary functions including the valves
and fuel injection equipment may be operated by the co-axial gear driven shaft
19 or, in stationary installations, the co-axial shaft
19 may be
driven by external means such as an electric motor so that the speed of operation
of the valves and injection equipment can be controlled more easily independently
of the speed of the gas turbine shaft
18. The speed of such a motor may
be controlled so as to provide precession between the working cycles of the combustion
chambers and the turbine. In either case, the governor must be linked to the shaft
18 in order to control the output speed. Whether the shaft
19 is
linked mechanically through gearing to shaft
18, or driven by external means,
it is foreseen that the absolute and/or the relative timing of the auxiliaries
may be varied, for example by providing automatic or manually-operable advance/retard
mechanisms or systems, to fine tune the engine performance in respect of variations
in load/speed.
In the embodiment described above, the combustion chambers are operated in a
single
cycle, and it will be appreciated that this produces an unbalanced axial load on
the turbine. Alternatively, the combustion chambers may be operated in a double
cycle where an engine has say ten combustion chambers such that diametrically opposite
chambers are synchronized by using double lobe cams to actuate opposing valves,
instead of eccentrics or short stroke cranks. Accordingly, it will be appreciated
that, at any time when one of the combustion chambers is in its exhaust phase,
the diametrically opposite combustion chamber will also be in its exhaust phase
such that the axial loads on the turbine are balanced. However, it will also be
appreciated that the effective combustion and transfer phases are being shortened
with the increase in number of chambers, in this case being limited to a maximum
of 36°, so an alternative layout is proposed below and this is shown in FIGS.
6 to 9.
FIGS. 6 to 9 show that a balanced arrangement can be achieved by providing
say ten combustion chambers in a double series of five interposed chambers. In
this example, alternate chambers are linked for transfer and this configuration
allows a maximum of 72° for each combustion/transfer phase and also allows
the use of eccentrics or short stroke cranks for the control of the transfer and
exhaust valves. Odd numbered chambers
22o are connected to each other
by transfer ports
44o and even numbered chambers
22e are
connected by transfer ports
44e. The valve and injection timing is
arranged such that diametrically opposite chambers are always performing the same
operation and thereby preserve the axial balance. Other features of the engine
of FIGS. 6 to 9 are referenced with the same reference numerals as those used above
in relation to FIGS. 1 to 5.
It has been stated that the shaft
18 may provide a direct drive between
the turbine and the compressor, whilst gearing between concentric shafts
18,
19
ensures that the engine combustion cycles precess in relation to the turbine rotation.
Alternatively, in order to match the characteristics of the compressor accurately
with those of the turbine, for example where a centrifugal compressor and axial
compressor are used, gearing may be included at each end of the shaft
19,
in which case there is no need for the shaft
18. Such an arrangement is
preferred to allow for the pre-selection of optimum speed ratios between the compressor,
the auxiliaries and the turbine. It also permits the use of short stroke cranks
along the shaft
19 for the operation of the piston valves via connecting rods.
Although the turbine has been described above as a single unit, alternatively
two turbines may be employed, one to drive the compressor and the auxiliaries,
and the other to provide a mechanical output.
It should be noted that the embodiments of the invention have been described
above
purely by way of example and that many other modifications and developments may
be made thereto within the scope of the present invention.
*
