Compound regenerative engine

An Ericsson-Stirling type engine is disclosed having a semi-open regenerative working fluid system employing intermittent internal combustion. The regenerator is modified to act also as a catalytic combustor and is located at the terminal end of the unswept clearance volume most adjacent the high temperature chamber or hot swept space. The clearance volume is reduced and engine efficiency increased by (a) elimination of any leak path around the regenerator (b) positive exhaust purging, and (c) lower peak combustion temperature.

BACKGROUND OF THE INVENTION 
The Stirling cycle engine utilizes contraction and expansion of heated and 
cooled inter-communicating gas volumes in timed relation to the extraction 
of working energy. Engines utilizing this cycle can be either of the 
external combustion type or of the internal combustion type. Typically 
those of the external combustion type should be referred to as a true 
Stirling type engine commensurate with the first embodiments of Rev. 
Stirling back in the early 1800's. When operating an internal combustion 
circuit, it is convenient to refer to such engine as an Ericsson type 
Stirling engine wherein the flow of working fluid is controlled by valves 
as opposed to the use of the volume changes to control flow. More simply, 
the regenerative thermodynamic cycle is closed in the true Stirling cycle 
machine and is open in the Ericsson-Stirling cycle machine. This invention 
is primarily concerned with an Ericsson-Stirling cycle machine. 
External heating of a chamber, as required in a true Stirling engine, 
inherently requires substantial start-up time and necessitates the use of 
significant quantities of costly and limited high temperature metals, for 
example, nickel based alloys. Improved efficiency of heat transfer from 
such external heating circuit to the closed working fluid is obtained by 
use of a working fluid having low density and high thermal conductivity, 
such as hydrogen or helium. However, no convenient mass distribution means 
is currently available for vehicular users of these types of gases; such 
gases must be separately stored in the vehicle, thereby introducing 
additional cost factors. 
SUMMARY OF THE INVENTION 
The primary object of this invention is to provide a Stirling engine which 
will operate with intermittent combustion thereby eliminating the need for 
exotic high temperature materials, and at the same time have improved 
regeneration. 
Another object of this invention is to provide an Ericsson-Stirling engine 
of the type that will operate on an open regenerative thermodynamic cycle 
requiring intermittent combustion, said intermittent combustion being 
improved. 
Yet still another object of this invention is to provide an 
Ericsson-Stirling engine which has increased efficiency. 
Features pursuant to the above objects comprise: (a) with respect to 
increasing efficiency, the use of a reduced clearance volume in the open 
circuit of said working fluid, provision for predetermined integral 
exhaust gas recirculation, provision of a positive displacement means 
effective to purge the low temperature spaces of the combusted working 
fluid when a reverse flow clearance volume is employed, or to use a 
plurality of commonly connected displacer means for timed regulation of 
intake and exhaust of the working fluid synchronized with intermittent 
combustion when a non-reversable working fluid path is employed; (b) with 
respect to improvement of regeneration in an Ericsson-Stirling cycle 
engine, the regenerator is immersed in the hot volume space of the working 
fluid path, constituting a part of the clearance volume, and located at 
the extreme end of said clearance volume; (c) with respect to improvement 
of combustion, the regenerator is constructed to act as both a regenerator 
and a catalyst to support chemical combustion within the hot volume space 
of the Ericsson-Stirling system.

DETAILED DESCRIPTION 
Systems and methods in accordance with the invention provide a novel 
Ericsson-Stirling cycle engine using a low thermal conductivity working 
fluid, such as air, in which combustion may be internally supported in an 
intermittent manner. The internal hot gas volume may be closely controlled 
and held at a high pressure (about 1200 psi) with the air fuel proportion 
nonetheless being very high if desired. A unique heat regenerator (serving 
also as a catalytic combustor) is employed within the hot gas volume of 
the system and is arranged so that the zone into which fuel is injected is 
separated from the principal zone of expansion for extracting work from 
the engine. Thus, high efficiency and a compact, light weight construction 
is achieved concurrently. 
Methods herein, in accordance with the invention, maintain a confined high 
pressure gas volume in a selected high temperature range 
(1000.degree.-1700.degree. F) and cycle the gas between separate chambers 
while extracting work energy in the fashion of the Stirling cycle. A 
portion of the working fluid, in its initial state, is continuously 
substituted for the gas mixture that is concurrently withdrawn at 
pressures compatible with the interior gas volume pressure. A high 
air-to-fuel ratio can be maintained and the temperature is kept in the 
range favorable to catalytic combustion, but below that favorable to the 
formation of oxides of nitrogen and below that which is consistently used 
in a closed cycle Stirling type engine. In its broad aspects (see FIG. 1), 
the apparatus of this invention comprises means A defining at least a 
relatively hot and a relatively cool gas chamber for confining a working 
fluid having a combustible constituent. Means B is associated with said 
chambers for shifting a major part of the working fluid between said 
chambers while extracting work from the thermal energy content thereof; 
means B is effective to intermittently release thermal energy directly 
thereinto as a result of combustion of a portion of said working fluid. 
Means B includes a catalytic combustor B-1 facilitating said combustion 
and serving as a heat regenerator to the working fluid passing reversibly 
therethrough. Third means C is coupled to said chambers for substituting 
new working fluid for existing or combusted working. 
Turning to FIGS. 1-4, most of the principal elements of the engine 
conforming to the present invention are shown. The elements comprise a 
housing 10 that serves to contain the internal working fluid system of the 
engine. Walls in the housing and fluid passages outside of the housing 
combine to define an integral heating and working fluid circuit 11. Said 
walls provide a principal cylindrical volume 12, auxiliary cylindrical 
volume 13, and a cylindrical pumping volume 14. Reciprocating elements 15, 
16 and 17 are disposed respectively in each of said cylindrical volumes 
13, 12 and 14, define respective variable volume spaces 18, 19 and 20. The 
minimum variable volume space within each of said cylindrical volumes, 
when combined with the volume of the intercommunicating passage 21 between 
said volumes, constitutes the unswept clearance volume for the engine. 
This clearance volume is not interrupted by movement of the positive 
displacement means or reciprocating elements. 
The reciprocating elements comprise either a piston or displacer head. Head 
16 is mounted for axial movement within the cylindrical volume 12, the 
axis of such movement being generally in a vertical direction. The piston 
or displacer head 16 has an upper working surface 16a subject to the 
pressure of the working fluid or gas in space 19. Mechanical linkage 22 
connects the displacer head 16 with a crank 23 extending from a crankshaft 
24; the linkage converts the reciprocating movement of the displacer into 
rotary motion. 
A second piston or expander head 15 is located within volume 13 and is 
adapted for axial movement in phase with head 16; suitable linkage 25 
connects the reciprocating head with a crank 26 which in turn connects to 
shaft 24. If reciprocating elements 15 and 16 are to be pistons, suitable 
piston rings should be used about each head; a displacing head permits 
some leakage of fluid along the sides of the head whereas a piston head 
should not. The displacer-head-wall clearance is typically very small and 
permits operation without sealing means while still achieving satisfactory 
Stirling cycle operation. 
Reciprocating head 17 is disposed in volume 14 and acts as a compressor; 
suitable sealing means 27 are mounted on the head. The head is connected 
to shaft 24 by linkage 28 and crank 29 so as to operate in timed phase 
relation with heads 15 and 16. 
The integral heating and working fluid containment system 11 thus provides 
two separate variable volume portions or chambers 18 and 19 for effecting 
Stirling cycle operation. Although shown as separate portions within 
separate cylinders, they may be employed as portions of a single cylinder. 
In any event, they are herein referred to as individual chambers or 
containment volumes. One volume 18 is that existing between the upper end 
13a of cylinder 13 and the upwardly facing side 15a of the head 15. This 
is termed a relatively low temperature chamber (compression volume) or 
slightly higher than ambient. The space existing between the upper end 12a 
of the cylinder 12 and the upper face 16a of the head 16 is herein termed 
a hot volume chamber or space which is maintained at a relatively high 
temperature. The higher temperatures in space 19 is maintained by 
injection of energy thereinto, and ambient temperature in space 20 is 
maintained by drawing in a fresh supply of ambient air which is at a 
relatively cooler temperature. Thermodynamic cycling in the fashion of a 
Stirling engine is obtained by having the working fluid (air and fuel) 
undergo ideally the following sequence: constant pressure expansion (FIG. 
1), constant volume cooling (FIG. 2), constant pressure compression (FIG. 
3), and constant volume heating (FIG. 4). 
Means C comprises peripheral apertures (30-33) in the cylinders to provide 
ingress and egress of fluid; passage 21 interconnects the spaces 18 and 19 
and openings 31 and 32; a passage 36 fluidly connects spaces 19 and 20 and 
openings 30 and 34; an air intake passage 37 connects space 20 through 
opening 35 with ambient conditions and exhaust passage 38 connects space 
18 through opening 33 with ambient conditions. There is no heat 
regenerator maintained in such peripheral flow passages and flow through 
said passages is controlled by suitable poppet valves which are sequenced 
in their opening and closing position in conformity with the rotary action 
of the rotary driven means, such as by conventional rocker arm actuation 
(not shown) operating against valve springs 40. 
Means C provides for a fresh combustible mixture and provides extraction of 
the combusted mixture in controlled relation to the operation of the 
system and at pressure levels consistent with internal pressures. The 
compressor cylinder 14 receives the compressor head or piston 17 in 
reciprocating relation, the compressor head being controlled by the 
connecting rod 28 coupled to the crank arm 29. Ambient air is supplied to 
the compressor cylinder through a compressor intake valve 43, the air 
being derived from an intake conduit having a throttle 44 therein. 
Compressed air is injected into passage 36 by way of compressor outlet 
valve 45 and introduced to the top of cylinder 12 via hot chamber inlet 
valve 46. 
Positive exhaust flow is established by the expander head 15 which forces 
gases out into exhaust passage 38 via exhaust valve 49. 
Stirling cycle gas transfer takes place between cylinders 12 and 13; power 
head 16 operating to force expanded hot gases back out through regenerator 
B-1 into passage 31 via valve 47 and introduced into the ambient chamber 
18 by way of valve 48. Head 15 operates to force the same gas back through 
passage 31 into the hot chamber. 
Means B comprises principally said displacer or piston heads synchronously 
coupled to driven element for shifting a major part of the working fluid 
while extracting work energy, fuel injection element 41 and sparking 
element 42 to intermittently release thermal energy the working fluid as a 
result of combustion, and catalytic combustor-regenerator by which 
facilitates combustion and heat storage. The sparking element 42 may be a 
spark plug or other conventional ignition device powered by voltage supply 
and controlled by a switch mounted adjacent the voltage supply. The fuel 
injection element 41 may use a combustible fuel comprised of lead free 
gasoline, supplied to the high temperature chamber 19 through a fuel 
injector via a carburetor (having a fuel controller) receiving fuel from a 
supply (not shown) and air from a compressor. The fuel is not critical 
because superior burning conditions are provided; diesel fuel and propane, 
for example, can also be successfully utilized. 
The use of a regenerator is vital to the attainment of thermodynamic 
cycling of a Stirling type engine. The regenerator in this invention is 
located uniquely within the hot chamber 19 in such a manner that (a) the 
fuel injector element 42 is separated from the working face 16a of the 
head 16 by such regenerator, (b) the regenerator spans across the lateral 
dimension of the cylinder 12 so that fluid flow reversibly passing through 
or into the cylinder must pass entirely through the regenerator, (c) the 
regenerator is immersed in the extreme end of the clearance volume leading 
to the hot chamber 19. The regenerator, so located, can function to more 
efficiently store heat from combusted gases passing out of the hot chamber 
and release such heat to the incoming combustible mixture for preheating; 
in addition, the location permits the regenerator to function as a 
catalytic combustor which supports combustion without the necessity for 
continued spark. 
A regenerator-catalyst meeting the above needs may be constructed as a 
honeycomb ceramic matrix having an overall disc configuration. The ceramic 
matrix may also be coated with a solid oxidation catalyst although the 
ceramic substrate may inherently operate as an oxidation catalyst 
depending on selection. The catalytically active component of the catalyst 
is generally metal either in the elemental state or in the combined state 
such as an oxide in the ceramic matrix. These metals usually include the 
heavy metals of the refractory type such as zirconium, vanadium, chromium, 
manganese, copper, platinum, palladium, iridium, rhodium, ruthenium, 
cerium, cobalt, nickel and iron. 
A useful method of making the regenerator may be to form a plastic solid 
slurry of a ceramic consisting of lithium aluminum silicate and impregnate 
paper with this slurry. The impregnated paper is then formed to 
alternating flat and corrugated layers to define the matrix. 
Alternatively, magnesium aluminum silicate may be formed as slurry and 
pressed into extruded sheets having ribs. Extrusion is carried out by 
using a ribbed die to form sheets of the material with closely spaced 
projecting ribs or fins. The sheets are cut to size and interleaved with 
the edges of the ribs fused to the back of the next adjacent sheet. In 
this manner a foraminous matrix is formed having suitable gas channels 
with suitable mass to act as a heat storage element. The matrix may then 
be dipped to obtain a uniform coating of platinumsilver or other suitable 
combustion catalyst. 
Still another mode may be to corrugate strips of a refractory metal 
(operative as heat sink-regenerator and operative as catalyst) and 
sandwich the corrugated strips between vaporizable separation sheets; roll 
the sandwich into a spiral and vaporize the separations. The resulting 
structure will be somewhat brittle, but this is unimportant to a 
non-stressed application as herein envisioned. 
In operation, the air/fuel mixture in proper ratio (can be in the lean 
range of 100:1-250:1, if desired) is fed continuously in while the 
ignition switch is closed to fire the spark element 42. When the high 
temperature chamber is up to a desired operating temperature, only fuel is 
thereafter injected by operation of the fuel control, the air supply being 
separately controlled from the same source to maintain desired proportion. 
A pressure-temperature relationship that is supportive of combustion as 
well as consistant with efficient Stirling cycle operation is maintained 
in the hot chamber portion of the system. The internal gas is cycled 
between the high temperature chamber and the ambient temperature chamber 
in known Stirling cycle fashion, but comprises a semi-closed system, 
inasmuch as a portion of the working fluid, which comprises not only air 
but the products of combustion, is constantly replinished with fresh air. 
The internal working fluid is maintained at an elevated pressure as well 
as temperature by the action of the compressor head 17 which supplies 
increments of fresh air in cyclic fashion while the expander head 16 is 
concurrently operating to remove increments of working fluid from the 
internal volume. In a very general sense, the crankshaft derives energy 
from the head 16 as well as some from the action of the head 15. Heads 16, 
17 and 15 reciprocate approximately 90-135.degree. out of phase with each 
other to displace the working fluid therebetween. Energy to drive the 
heads is extracted from the heat supplied by the combustion in the high 
temperature chamber 19. 
In FIG. 1, the heads are shown in an approximate position representing 
completion of the expansion phase ideally at constant pressure. During 
this phase all valves are closed except that fresh air is inducted via 
open valve 43. Working fluid in chamber 10 has previously had fuel added 
thereto and the mixture burned during this phase to promote expansion of 
the volume in space 19, and thereby moving head 16 to extract work. 
Burning was initiated and sustained by the catalytic regenerator B-1 
during the downstroke of head 16. The catalyst ingredient operates at a 
temperature approximating the theoretical adiabatic flame temperature of 
the fuel/air admixture charged to the combustion zone. Note that crank 29 
is 90.degree. out of phase with crank 23, and crank 24 is about 
135.degree. out of phase with crank 23. 
In FIG. 2, the heads are shown at the completion of constant volume 
transfer of working fluid from the hot chamber 19 through catalyst 
regenerator B-1 (absorbing heat from the flow) to the ambient chamber 18. 
Valves 47 and 48 must be open to permit flow through passage 21. 
Additional fresh air induction may be permitted through valve 43. Flow in 
this phase is ideally at constant volume. The catalyst regenerator B-1 
acts also on the upstroke of the head 16, much in the fashion of a 
catalytic converter, to chemically convert unburned ingredients of the 
combusted gases passing therethrough. Thus, the catalyst-regenerator may 
serve both as a combustor and a converter. 
In FIG. 3, the heads are shown at the completion of the compression phase 
ideally at constant pressure in the hot chamber 19; all valves are closed. 
Fresh air is being compressed in space 20 by head 17. 
In FIG. 4, the heads are shown at the completion of gas transfer from the 
compression chamber 20 to the hot chamber 19 while being preheated by 
absorption of heat units from regenerator B-1; this phase takes place 
ideally at constant pressure. Valves 45 and 46 are open to permit transfer 
of gas through passage 36; valves 47 and 48 are closed permitting no 
transfer through passage 21. 
The embodiment of FIGS. 1-4 stops loss in engine efficiency by eliminating 
any leak path for working fluid around the regenerator, permits the engine 
to burn the combustible mixture at a lower peak temperature by use of a 
catalytic-regenerator thereby improving emissions, and, most importantly, 
permits use of conventional engine, such as cast iron and aluminum, to 
reap cost savings over current closed cycle Stirling engines. Regeneration 
is improved by reducing the volume of the clearance volume and of the 
cycled volume for a given power output. The ambient temperature space is 
effectively purged of exhaust gases by use of uni-directional flow which 
receives a fresh supply of compressed air in phase with the Stirling 
cycle. 
It is important to note that the injection of fuel may not be in timed 
relation to the cycling of the engine, inasmuch as the basic consideration 
is that thermal energy be added to maintain the working temperature. 
Preferably, however, combustion takes place in this expansion space; such 
combustion increases the pressure level during expansion thereby 
increasing the work performed. Concurrently, the tendency of the gas to 
cool slightly during compression tends to decrease the pressure; this 
effect also contributes to the network output. 
Maximum pressures in the working volume may range from 100-300 atmospheres. 
Temperature in the high temperature chamber will be in the 
1000-1700.degree. F range. Preferably, the gas pressure is maintained at 
about 1200 p.s.i., taking the pressure at the low pressure point in the 
cycle at full throttle. In a general case, including engines for vehicular 
use, the low pressure cycle point at full throttle may be from 100-3000 
p.s.i. The compression ratio, typical in the range of 2:1 to 2.5:1 then 
determines the level at the high pressure point in the cycle. The maximum 
pressure of approximately 3000 p.s.i. is generally observed in a vehicular 
Stirling cycle engine. 
An alternative embodiment is illustrated in FIGS. 5-8. Housing means 50 
defines only two cylindrical volumes 51 and 52. A reciprocal head 53 
cooperates within volume 52 to define a variable volume ambient space or 
chamber 54. Reciprocal head 64 cooperates with cylinder 51 to define a 
variable volume hot space or chamber 55. The regenerator-catalyst 56 is 
again immersed totally within the terminal portion of the unswept clear 
volume most adjacent the hot space 55, the unswept volume consisting of 
the unswept portion of cylinders 51 and 52 and interconnecting passage 57. 
The Stirling cycle flow is reversed through passage 57. FIG. 5 shows the 
heads at the completion of the expansion phase ideally at constant 
pressure (combustion having taken place catalyzed by 56). Valves 58, 59 
are closed. Valve 60 is closed preventing leakage through exhaust passage 
63. Fresh air from blower 61 is prevented by the position of head 53 which 
closes off intake ports 62. 
In FIG. 6, the heads 64 and 53 are shown at the completion of gas transfer 
(ideally at constant volume) to the slightly higher than ambient chamber 
54 from hot chamber 55; valves 58 and 59 are open to permit flow in the 
direction of the arrow through passage 57. The transferred gas gives up 
heat units to the catalyst-regenerator 56 while also acting as a converter 
of emissions at a lower threshold temperature level than required for main 
combustion. Linkages 65 and 70 connected respectively to crank arms 66 and 
69, are in turn connected to shaft 68 at a predetermined angular 
difference to maintain proper phasing of heads 64 and 53. Ports 62 are now 
opened. In FIG. 7, two operations take place, (a) compression of the gas 
in hot space 55 (ideally at constant pressure) and (b) purge of exhaust 
gases by fresh air from blower 61 through ports 62 and out through passage 
63, valve 60 being open in FIG. 8, gas transfer from ambient chamber 54 to 
hot chamber 55 has taken place, ideally at constant volume. Valve 60 and 
ports 62 are closed; valves 58 and 59 are open to permit transfer through 
passage 57, the gas absorbing heat from catalyst-regenerator 56. 
In the embodiment of FIGS. 5-8, the regenerator is coated with catalytic 
material to facilitate combustion and here may be pentoxide. The 
conditions for effective catalytic combustion must be met in the working 
volume of this embodiment in accordance with the invention; there must be 
a high ratio of air/fuel, the pressure must be high, the temperature must 
be high, and there must be a large degree of contact between the fuel/air 
mixture and the catalytic surfaces. The use of reversed flow and purging 
ports provides for a predetermined degree of integral exhaust gas 
recirculation to the combustible mixture gas entering the hot chamber.