Note: Descriptions are shown in the official language in which they were submitted.
~O~V751
The present invention is directed to heat conser-
vation in a Stirling engine.
To employ a Stirling engine power plant in an
automotive vehicle application, one noticeable change over
conventional internal combustion engines becomes apparent.
The engine cooling water, employed to extract heat from the
closed gas working system, must be regulated to a
considerably lower temperature than that in today's internal
combustion engine. Accordingly, the size and effectiveness
of the radiator must be considerably increased to effect -
such lower water temperature regulation. In addition,
because of the continuous external combustion cycle of the
Stirling engine, a large quantity of thermal units will be
rejected to ambient conditions by the exhaust gases.
Because of diminishing fuel supplies, and the need to reduce
the size of the Stirling engine when employed as an automo-
tive power plant, the conservation of energy in the cooling
circuit as well as in the external combustion circuit of the
Stirling engine must be achieved.
If a vehicle passenger compartment were to be -~
heated by heater core connected to the normal water cooling
circuit, in those instances where the controls for the
heater core of the passenger compartment is not calling for
heat, the heat normally in such cooling circuit will be
radiated by the main radiator. This requires the main
radiator to be sized considerably greater than needed in
the situations where heat is called for in conditioning the
air for the passenger compartment.
For purposes of heat conservation, it would be
most beneficial if the high heat content rejected to
atmosphere by the exhaust gases could be sequestered and
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put to use for purposes of heating a passeng~r compartment
heating core in those instances where it is needed. One of
the problems related to utilizing exhaust gas heat is the
problem of efficiently promoting heat transfer between a
heated gas and an enclosed fluid, such as air flow about a
water tube. If the temperature of the heated gas is at an
undesirably high temperature level, the efficiency of -
imparting thermal units to the interior cooling water is
retarded. Since the temperature of the exhaust gas is to
some degree directly controlled by engine operation as
opposed to separate operation, the ability to achieve a
precise temperature at the gas-to-water heat exchange is
difficult.
In accordance with the present invention, there ~
is provided in a vehicle having a passenger compartment -
and a Stirling engine for powering the vehicle, the engine
having a closed fluid system for transferring heat to
promote engine work, the fluid system having a zone in which
heat is extracted, a heat conservation assembly, comprising:
(a) a heat rejecting means for cooling the fluid system
zone, the heat rejecting means having a fluid circuit, the
fluid in the fluid circuit immediately downstream of the
system zone being at an average temperature of 165F or
less; (b) first and second radiators interposed in parallel
in the fluid circuit, the first radiator being arranged to
reject heat to-ambient conditions and the second radiator
being arranged to reject heat to the passenger compartment;
(cl an open external heating circuit for imparting heat to
the closed fluid system, the external heating circuit having
an air intake passage and an exhaust passage with at least
one portion of the exhaust passage divided into parallel paths;
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(d) a heat regenerator disposed in the exhaust passage to
transfer heat from gases in the exhaust passage to gases in
the intake passage, the gas in the exhaust passage downstream
of the heat regenerator being regulated to have a temperature
in the range of 200 to 800F; ~e) a heat absorption means
in the fluid circuit associated with the second radiator,
the absorption means being disposed in one of the divided
paths for transferring heat from the exhaust gases to the
fluid circuit; and (f) control means effective to continu-
ously sequester a portion of the exhaust gases subjected to ~ -
the heat regenerator during engine operation and effective
to continuously inject the exhaust gas portion into the one ~ .
path so as to be subjected to the heat absorption means. ~:
By utilizing the heat conservation assembly of : ~
this invention, the heat content of the exhaust gases is ~-
sequestered in a regulated manner to control gas temperature
surrounding a gas/water heat exchanger unit.
The invention is described further, by way of
illustration, with reference to the accompanying drawings,
wherein: . :
Figure 1 is a schematic diagram of prior art
showing the conventional fluid cooling circuit for an internal :
combustion engine, the circuit being deployed both for
purposes of passenger compartment heating as well as rejection
of the heat to ambient conditions by way of a radiator;
Figure 2 is a schematic layout for a heat extraction
system for a Stirling-type engine employed in an automotive
vehicle; a portion of the exhaust heat is deployed to assist
heating the water directed to the passenger compartment
heater core, the exhaust gas to cooling water heat exchange : .-.
taking place subsequent to heat extraction for regeneration;
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Figure 3 is a schematic layout of a heat extraction
system like Figures 1 or 2 showing a further improvement in
the system wherein a control for modulating temperature of
the sequestered exhaust gas used to add heat units to the
fluid flowing to the heater core; and
Figure 4 is a circuit diagram for the external
heating circuit of a Stirling-type engine, showing still -
another mode whereby oert~in heat units of the exhaust gas may be
deployed for purposes of heating a fluid cooling circuit.
Turning first to Figure l, there is shown a prior
- art heat rejection system for an internal combustion engine
utilized in a typical vehicle. The internal combustion
circuit ll for the engine lO, inducts a specific quantity
of air from the surrounding ambient and to which appropriate
fuel is added at 9 and internally combusted, the resulting
gases are exhausted through passage 8.
The cooling system 13 for the engine head and
block circulates water from pump 21 through passages 22 in -
the engine and thence through two different parallel paths
of the circuit, path 14 having therein a heater core 15
across which air is delivered by way of fan 16 to the
passenger compartment of the vehicle. Path 17 delivers a
larger quantity of water to a radiator 18 exposed to ram
air at the front end of the vehicle or supplementary air
driven by fan l9. The amount of cooling water circulated
through either one of the branches 14 and 17 is regulated
by thermostat 7 which can effect a shunt of cooling water
- across passage 20 to by-pass the radiator 18 or heater core
15. Thermal units are lost in the rejection of exhaust
gases; thermal units lost through the cooling system are
tolerable due to the higher temperature of the coolant at
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which it is regulated. However, the engine still remains
deficient because the known apparatus required to carry out .:
the engine and vehicle thermal activities do not assist
each other conserve heat units and provide weight savings.
In Figure 2, an elementary mode of conserving
heat units according to this invention is illustrated with
reference to a
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1 Stirling engine automotive application. An external heating
2 circuit 25 is employed having an intake passage 26 delivering
3 fresh air through a preheater wheel 27 to a burner unit 28
4 having a nozzle 29 for admitting fuel to support combustion.
Combusted gases are carried from the heating chamber 30 through
6 wheel 27 into an exhaust passage 31 having a portion thereof
7 split into parallel paths 32 and 33. The T,~heel 27 rotates so
8 that the same sector may be exposed to the exhaust gases passing
9 from the engine and to the fresh intake air.
The heat extraction system ~ for the engine has a
11 primary circuit 35 into which fluid is forced under power from
12 pump 36; fluid is carried to the cooling zone 37 of the engine
13 through a suitable heat absorbing matrix 38. The circuit 35 con-
14 tinues along two separate and independent parallel paths 39 and
40; the path 40 comprises a fluid passage 41, a heat exchange
16 matrix 42, and a passage 43 leading to a heat rejecting core 44
17 disposed adjacent the vehicle passenger compartment. The parallel
18 path 40 is completed by a passage 45 connecting to the return
19 passage 46 by-passing radiator 47. The other path 39 comprises
a passage 48 connected to radiator 47 (heat rejecting means
21 exposed to ambient temperature conditions) and returns back to the
22 pump 36 by return passage 46. Heat from the gases in exhaust
23 passage leg 32 is picked up by the fluid in the heat absorbing
24 matrix 42; the increased temperature of the fluid carried to
heater core 44 is capable of radiating a greater amount of heat
26 for greater air comfort control.
27 Although the system of Figure 2 is capable of providing
28 heat conservation by utilizing exhaust gas heat units to heat
29 the passenger compartment, it is difficult to maintain a high
efficiency for the system because the exhaust gases are exposed
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1 to the matrix 42 after having gone through the regenerator wheel
2 27 and thus are usually at a typically low temperature about
3 336F. This temperature level is not sufficientl~ hi~h enough
4 to create an optimum temperature differential across the thick-
ness of tubing walls of matrix 42; one side of the tube wall
6 is exposed to a gas at 336F and the other side is ex~osed to
7 water at a temperature of about 165F or less.
8 It is possible to control the gas temperature to some
9 degree traversing the heat absorption matrix 42 b~ emplo~ing
a by-pass valve assembly (see Figure 3) which directs ap~rox-
11 imately 28% at most of flow through both of the parallel passages
12 51 or 52 and thereby approximates a temperature control condition
13 to maintain the gas temperature in passage 53 sufficiently high
14 to promote optimum heat exchange characteristics.
The preferred embodiment of Figure 3 has external heating
16 circuit 54 for the Stirling engine is comprised of an intake
17 passage 55 receiving air from an air blower (not shown), such
18 intake air being delivered through one sector of a preheating
19 or regenerating wheel 56 at zone 57. The air passing through
the regenerator is warmed or heated so that upon mixture with -
21 fuel and passage into the burner unit 58, it has increased
22 combustibility. Upon combustion, the gases of external circuit
23 pass from heating chamber 59 through a different sector 60 of
24 the regenerator 56 and thence either into exhaust passage 52
or shunt passage 51. The exhaust passage 52 splits into paraliel
26 branches 61 and 53; the branches re~oin again at a main outlet
27 passage 62. Thus there is 3 possible exhaust routes, one through
28 shunt passage 51 and branch 53, another through passage 52 and
29 branch 53 and still another through passage 52 and branch 61.
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lO~t~751
1 The heat extraction system has an appropriate water
2 mixture pumped by pump 63 through a principal passage ~ to the
3 cooling zone 65 of the Stirling engine; the cooling water after
4 having absorbed sufficient heat from the cooling zone is then
5 delivered by way of a passage 66 which spreads into two parallel
6 circuit portions, one circuit portion is comprised of a passage
7 67 communicating with a passage 68 through a heat absorbing
8 matrix 69. Passage 68 connects with a heater core or heat
9 rejection means 70 disposed in the air comfort system for
passenger compartment of the vehicle, air being driven across
11 such rejection means by a fan 71. The first circuit portion is
12 completed by a passage 72 connecting with return passage 73
13 slightly in advance of the pump 63.
14 The other circuit portion comprises a passage 74
communicating with a radiator 75 (the latter re~ecting heat to
16 ambient temperature conditions either by ram air or by auxiliary
17 air flow thereacross promoted by fan 76). The second circuit
18 portion is completed by said return passage 73. A temperature '`
19 responsive water by-pass valve 78 is employed to regulate the
water flowing through the second circuit portion. Valve 78 can
21 by-pass the radiator 75 by shunting water to passage 79 which
22 connects directly with return passage 73, or allow water to con-
~23 .tinue on through passage ~ to radiator 75.
24 The heat absorbing matrix or evaporator 69 is dis-
posed diagonally across branch 53. The temperature and volume
26 of exhaust gases flowing through branch 53 is controlled by a
27 pair of flow directional valves ~ and ~ forming part of
28 assembly 50. The valves may be linked together at 82 for
29 coordinated actuation between their full~y seated positions or
fully open positions and any intermediate position therebetween.
lO~V~51
1 Flow directional valve 81 controls exhaust gases which are
2 derived directly from the heating chamber without having passed
3 through the preheater wheel and therefore are of a considerably
4 higher temperature in the range of 1400-1900F. Flow directional
valve 80 controls exhaust gases having passed through the
6 preheating wheel and are at a temperature level lowered to the
7 range of 200-500F. An intermediate temperature condition can
8 be, of course, achieved by blending proportions of each gas flow
9 by positioning valves 80 and 81 at some intermediate position
to achieve an intermediate tem~erature preferably in the range
11 of 600F to 800F.
12 It has been proven that a cross flow heat exchanger
13 comprised of staggered flat tubes measuring 0.10 inches wide
14 by 0.737 inches long in cross section with a wall thickness
of 0.010 inch, and using a cooling fluid consisting of water
16 and glycol within said tubing, and surrounded b~ copper fins
17 f 0.004 inch thick spaced at 11.32 fins per inch can provide
18 the desired or optimum heat transfer. The entire heat exchanger
19 matrix 69 measures approximately 4 in. x 4 in. x 12 in. with the
exhaust gases flowing through the 4 x 4 opening and through the
21 12 inch length of multiple rows of staggered tubes. If the
22 gases enter the matrix at from 600F to 800F and the water enters
23 at about 165F, then the outgoing water temperature can be raised
24 to 190F foruse in the passenger compartment heater core.
Turning now to Figure 4, there is shown a modification
26 of the preferred embodiment wherein the external heat ng circuit
27 90 of the Stirling engine is comparably comprised of an intake
28 passage 91 leading to the fuel combusting section 92 thereof
29 and exhausted by way of a passage 93. A preheater or rotating
wheel 94 may be employed to exchange heat between the exhaust
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1 gases and the incoming air, Ihe incomin~ air being driven by a
2 blower 95; intake air being derived from an intake ~assage 96.
3 The exhaust gases are, of course, delivered from the preheater
4 wheel by passage 97 to ambient temperature conditions. An E~R
passage 98 may be employed to siphon a predetermined portion of
6 the exhaust gases and return it to blend with the incoming air
7 in passage 96.
8 Exhaust gases are deployed somewhat differently in this
9 embodiment; they are sequestered in advance of having entered
the preheater wheel by way of a passage 99, delivered to a heat
11 exchange coil 100, and returned to the exhaust gas passage 93
12 downstream of the preheater wheel 94. A suitable heat absorbing
13 matrix 101 forming part of the closed fluid cooling circuit 102
14 is employed. The degree of fluid flow permitted through the
matrix 101 being controlled by a temperature responsive valve
16 103 which has temperature sensed in the fluid cooling circuit;
17 similarly a temperature responsive valve 104 controls the volume
18 of flow through passage 99 and coil 100.
19 In this application, the temperature of the exhaust gas
passed through the heat exchange mechanism 100-101 will be of a
21 higher level than that of the embodiments of either Figure 2
22 or Figure 3. This may provide a disadvantage to some degree in
23 that at certain conditions of engine operation, the exposed
24 exhaust gas will have too high a temperature for optimum heat
transfer to the cooling fluid.
