Fuel bath volume compensator for stored chemical energy power propulsion system

An ullage compensator is disclosed for a stored chemical energy power propulsion system. With the invention, at least one movable wall (16) is provided within a reactor having a chamber (10) which is movable between a first position at which the chamber has a maximum reaction volume to a second position at which the reaction chamber has a minimum volume. A force is applied to the movable wall by a bellows to cause the wall to project into the chamber in response to the force when a reaction is occurring within the chamber. The invention eliminates damage to the interior surface of the chamber and the inlet port(s) for introducing an oxidant into the chamber which sustains the reaction caused by direct contact with a gaseous oxidant which causes the reaction.

TECHNICAL FIELD 
The present invention relates to stored chemical energy exothermic reaction 
systems having a reactor chamber in which a molten metallic fuel is 
reacted with gaseous oxidant gas to create heat used in steam generation. 
More particularly, the present invention relates to stored chemical energy 
exothermic reaction systems of the foregoing type used in vehicular 
propulsion systems which have a controlled ullage in the reactor chamber. 
BACKGROUND ART 
U.S. Pat. No. 4,714,051, assigned to the assignee of the present invention, 
discloses a stored chemical energy power propulsion system having a 
reactor having a closed chamber in which lithium in the form of a body of 
lithium metal shot encapsulated in a thin layer of predominantly fluorine 
substituted polyolefin based polymeric material is reacted within the 
chamber with a gaseous oxidant such as SF.sub.6. An exothermic reaction is 
initiated when the aforementioned lithium shot is melted in the presence 
of gaseous SF.sub.6 which is introduced into the closed chamber via an 
inlet port. An initiator supplies sufficient thermal energy to the 
metallic lithium within the chamber to melt the encapsulated lithium which 
reacts initially with the polymeric material and thereafter in a highly 
exothermic manner to generate heat upon reaction with the SF.sub.6. A heat 
exchanger, which is part of the chamber walls, converts water which is 
pumped to an inlet of the heat exchanger into superheated steam which is 
used for supplying propulsive power to a vehicle such as a torpedo. This 
system has approximately 75-80% of the volume of the chamber initially 
charged with the encapsulated lithium. The remainder of the volume 
contains the initiator and ullage to allow for temporary expansion of the 
fuel at the start of the reaction. The reaction has short pressure peak 
above ambient pressure followed by a highly exothermic reaction having 
pressures within the chamber below the ambient pressure. As the reaction 
is ongoing, the ullage within the chamber is occupied by a low pressure 
fuel vapor with solid reaction products being contained within the liquid 
metal. 
While the foregoing system produces a high power output useful for the 
propelling of a vehicle such as a torpedo, the chemical reaction can cause 
damage or failure in the chamber walls when the attitude of the chamber 
rapidly changes consequent from vehicular motion or is varied 
substantially from a horizontal plane. Rapid changes in attitude or 
altitudes substantially varied from the horizontal plane cause the gaseous 
oxidant inside the chamber to move about the chamber and directly contact 
the chamber wall(s) and end plate including inlet port(s) for introducing 
the gaseous oxidant which is introduced into the reactor chamber at a 
metered rate to sustain the exothermic chemical reaction. When the 
interior of the chamber is directly exposed to the gaseous oxidant, an 
increase in the pressure occurs within the chamber and further the direct 
contact of the gaseous oxidant can corrode the interior wall(s) thereof or 
the inlet port(s) because the gaseous oxidant does not react sufficiently 
with the liquid lithium. The effects of these two occurrences can cause 
the chamber to rupture and fail. 
DISCLOSURE OF THE INVENTION 
The present invention solves the foregoing problem by minimizing the ullage 
within the chamber during the aforementioned exothermic reaction to 
prevent substantial direct exposure of the interior walls and end plate 
including inlet port(s) to the gaseous oxidant which is introduced into 
the chamber in metered quantities to sustain the exothermic reaction. The 
present invention continually reduces the ullage within the chamber as the 
reaction is ongoing to minimize direct exposure of the interior wall(s) 
and inlet port(s) to the gaseous oxidant. One or more movable walls 
continually decrease the interior volume of the chamber as the exothermic 
reaction proceeds toward completion when the fuel within the chamber is in 
a liquid phase to minimize the ullage to prevent the aforementioned direct 
exposure of the interior wall(s) and inlet port(s) of the chamber to the 
gaseous oxidant. The continual movement of the one or more movable walls 
during the reaction decreases the volume of the reactor chamber while 
sustaining an operating pressure within the chamber below a pressure at 
which the chamber would rupture and further reduces the ullage to a point 
where very little surface area of the interior wall(s) of the chamber or 
inlet port(s) can be exposed to the gaseous oxidant introduced into the 
chamber during rapid changes in attitude or altitudes varied substantially 
from the horizontal plane. Furthermore, the present invention promotes 
maximum heat transfer between the exothermic reaction occurring within the 
chamber and the heat exchanger within the chamber wall(s) by maintaining 
substantially complete surface contact of the liquid metal within the 
chamber during the reaction with the interior wall(s) of the chamber to 
efficiently transfer heat to the heat exchanger within the walls of the 
chamber. The maximized transfer of the thermal energy occurs to a fluid 
being circulated through the heat exchanger which is used to power a 
turbine driving a vehicle such as a torpedo. 
A thermal energy generator in which first and second substances are reacted 
to produce an exothermic reaction in accordance with the invention 
comprises a closed chamber in which the substances are reacted to produce 
reaction products contained within the closed chamber with the first 
substance being disposed within the chamber prior to initiation of the 
reaction; at least one inlet port for permitting the second of the 
substances to be introduced into the chamber to sustain the reaction; an 
initiator disposed within the chamber for initiating the reaction within 
the chamber; and a mechanim for decreasing the reaction volume of the 
chamber after the reaction is initiated to minimize the ullage within the 
chamber to minimize direct contact of the second substance with the at 
least one inlet port and interior surface of the chamber. The variation in 
volume is preferably a controlled decreasing in volume as the reaction 
proceeds to completion. The mechanism for decreasing the volume of the 
chamber comprises at least one movable wall which projects into the closed 
chamber upon movement from a first position to a second position. A spring 
applies a force to the at least one movable wall within the chamber toward 
an interior part of the chamber. The first substance is solidified in the 
chamber prior to initiation of the reaction in contact with the at least 
one movable wall to hold the at least one movable wall in a first position 
at which the chamber has a maximum reaction volume, and upon commencement 
of the reaction causing the one substance in contact with the at least one 
movable wall to melt, the at least one movable wall is free to move from 
the first position to a second position at which the chamber has a minimum 
reaction volume. After an initial pressure peak, the force causes the 
reaction volume to continually decrease as the reaction is ongoing to 
minimize the ullage of the chamber during the reaction to preclude 
substantial direct exposure of the inlet port(s) or interior surfaces of 
the chamber to the second substance introduced into the chamber. 
Furthermore, a heat exchanger is within the chamber wall(s) for conducting 
heat created by the exothermic reaction away from the chamber by a fluid 
circulated through the heat exchanger. Furthermore, a connecting wall 
connects the at least one movable wall to the chamber with each connecting 
wall containing a bellows which expands from a first compressed dimension 
to a second dimension when the movable wall moves from the first position 
to the second position. Preferably, the spring in each of the connecting 
walls is the bellows. During the reaction, each bellows causes the movable 
wall to move from the first position toward the second position to a 
position where gas pressure within the chamber is balanced with ambient 
gas pressure outside the chamber and the spring bias to minimize the 
ullage within the chamber to preclude substantial direct exposure of the 
inlet port(s) or interior surfaces of the chamber to the substance 
introduced into the chamber. 
A thermal energy generator in which first and second substances are reacted 
to produce an exothermic reaction in accordance with the invention 
comprises a closed chamber in which the substances are reacted to produce 
reaction products contained within the closed chamber; at least one 
movable wall contained within the closed chamber which is movable between 
first and second positions with the first position providing a maximum 
reaction volume in the chamber, movement from the first position to the 
second position decreasing the reaction volume of the chamber and the 
second position of the at least one wall providing a minimum reaction 
volume in the chamber; a spring applies a force to the at least one 
movable wall toward an interior part of the chamber; an inlet port for 
permitting the second substance to be introduced into the chamber; the 
first substance being solidified in the chamber prior to initiation of the 
reaction in contact with the at least one movable wall to hold the at 
least one movable wall in the first position and upon commencement of the 
reaction causing the first substance in contact with the at least one 
movable wall to melt, the at least one movable wall is free to move 
between the first and second positions to control the ullage within the 
chamber during the reaction to minimize direct exposure of the at least 
the inlet port or an interior surface of the chamber to the second 
substance; and an initiator disposed in the chamber for initiating the 
reaction within the chamber. The spring causes the reaction volume of the 
chamber to continually decrease as the reaction proceeds to completion to 
minimize ullage within the chamber to minimize direct contact of the 
second substance with at least one inlet port and an interior surface of 
the chamber. Furthermore, the invention includes a heat exchanger in 
thermal contact with the chamber for conducting heat created by the 
exothermic reaction away from the chamber by a fluid circulated through 
the heat exchanger. A connecting wall connects each of the at least one 
movable walls to the chamber, each connecting wall containing a bellows 
which increases from a first compressed dimension to a second expanded 
dimension when the movable wall moves from the first position to the 
second position. The spring is preferably the bellows. Each bellows causes 
a connected movable wall to move from the first position toward the second 
position to a position where gas pressure within the chamber is balanced 
with ambient gas pressure outside the chamber and the spring bias to 
minimize ullage within the chamber to minimize direct exposure of the at 
least one inlet port or the interior surface of the chamber to the second 
substance introduced into the chamber.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 illustrates a thermal energy generation system in accordance with 
the present invention prior to and during an exothermic reaction within an 
annular reactor having a chamber 10. Prior to initiation of the exothermic 
reaction, the chamber 10 contains pellets of encapsulated metallic fuel 30 
such as those disclosed in U.S. Pat. No. 4,714,051 with an ullage 11 of 
typically 20%. It should be understood that the ullage 11 would actually 
extend across the chamber prior to initiation of the reaction with the 
portion of the chamber 10 to the left of line 15, as illustrated, being 
the chamber prior to reaction and the portion of the chamber to the right 
of line 15 being the chamber during the reaction. The interior of the 
chamber is the reaction volume. Furthermore, during the reaction, the 
ullage 11' is minimized as much as possible to cause the liquid reactants 
to be in complete surface contact with all interior surfaces of the 
annular chamber to minimize direct contact of the gaseous oxidant with the 
interior surfaces or with the inlet ports 14 for introducing the gaseous 
oxidant into the chamber. 
During the exothermic reaction, the metallic fuel is in a liquid state as 
identified by reference numeral 13. During the ongoing reaction, the 
pressure within the chamber 10 in the ullage 11' is low as a consequence 
of the nature of the exothermic reaction in which the reaction products 
are contained within the liquid metal 13 with the volume of the reaction 
products and unconsumed liquid metal continually shrinking as the reaction 
proceeds to completion at which point all of the metal has been reacted. 
The minimal ullage 11' eliminates the prior art problem of substantial 
direct contact of the interior surface of the reaction chamber or inlet 
port(s) with gaseous oxidant during rapid changes in attitude consequent 
from vehicular motion or orientations tipped substantially from the 
horizontal plane. The closed chamber 10 defines a reaction volume in which 
pelletized metallic fuel 30 is liquified and reacted with gaseous oxidant 
which is stored in an oxidant tank 12 that is introduced into the chamber 
10 through inlet ports 14. It should be understood that any number of 
inlet ports 14 may be provided in the annular end walls 16 and 18. Valves 
20 are disposed in conduits 22 which connect the oxidant tank 12 to the 
inlet ports 14. It should be understood that flexible sections in the 
conduits 22 have been omitted but should be included where necessary to 
accommodate movement of the wall 16. The supply of the gaseous oxidant 
from the oxidant tank 12 to the inlet ports 14 may be implemented in any 
suitable manner such as disclosed in the aforementioned U.S. Pat. No. 
4,714,051 and do not form part of the present invention. 
The chamber 10 contains a heat exchanger within the inner cylindrical wall 
21 and the outer cylindrical wall 23. The heat exchanger comprises a 
central helical fluid conducting coil 24 which is connected to a water 
source 26 that supplies water which is pumped into the heat exchanger and 
converted to steam to carry away the heat generated by the exothermic 
reaction occurring within the reaction chamber 10, concentric exterior 
coil 26, and connecting crossover pipe 28. Each of the turns of the 
central helical coil 24 are welded together to form a fluid tight seal 
with the inner cylindrical wall 21 of the reaction chamber 10. The central 
helical coil 24 may be made from any metallic material having the 
requisite chemical inertness to withstand the reaction products of the 
exothermic reaction and to further withstand the high thermal energy 
generated within the reaction chamber 10. The central helical coil 24 is 
connected to the concentric exterior helical coil 26 by means of the 
crossover pipe 28 as illustrated in FIG. 3. The crossover pipe 28 contains 
an adaptor 29 which changes from the smaller interior diameter of the 
central helical coil 24 to the larger inner diameter of the exterior 
helical coil 26. The increase in diameter provided by the adaptor 29 is 
utilized to permit the requisite flow of superheated steam through the 
exterior helical coil 26 to permit sufficient thermal transfer from the 
reaction chamber 10 to superheated steam flowing in the exterior helical 
coil. The water pumped into the heat exchanger from water source 26 
changes to superheated steam at approximately the end of the central 
helical coil 24 just before crossover to the exterior coil 26 by means of 
the crossover pipe 28. Each of the turns of the exterior coil 26 are 
welded together to form the fluid tight exterior wall 23 to contain the 
reaction products. As illustrated, the encapsulated metal 11 prior to 
initiation of the reaction fills approximately 75-80% of the volume of the 
chamber with initiator 32 displacing some of the remaining volume and the 
remainder being ullage 11 as illustrated to the left of line 15. Initiator 
32, may be any known initiator which provides sufficient thermal energy to 
change the encapsulated solid metal pellets to a liquid state indicated as 
13 at which the chemical reaction between the gaseous oxidant and the 
liquid metal takes place. The initiator 32 may be detonated by a signal 
from a controller (not illustrated) which is applied by means of wire 34. 
Similarly, the valves 20 are controlled by the controller by means of 
signals applied on wires 36. 
Control of the ullage 11' during the reaction within the chamber 10 is 
produced by one or more movable walls 16 which are movable from a first 
position at which the reaction volume of the chamber is a maximum to a 
second position at which the reaction volume of the chamber is a minimum. 
As illustrated, the left-hand end wall 16 is within a recess defined by a 
closed connecting wall 37. It should be further understood that the 
present invention may be equally implemented by a number of smaller 
movable walls located in different portions of the chamber 10, for 
example, while not being limited thereto, as illustrated in FIG. 4 
described below. The closed connecting wall 37 contains a bellows which 
may be fabricated from any suitable metallic material having the inertness 
to withstand the reaction products and heat generated within the chamber 
and further which functions as a compressed spring at the temperature of 
the reaction and has a spring rate which minimizes the ullage 11' within 
the chamber when the encapsulated lithium 30 within the chamber is 
converted to the liquid state 13 to minimize direct exposure of the 
interior walls of the reaction chamber 10 or inlet ports 14 to the gaseous 
oxidant during rapid changes in attitude or orientations tipped 
substantially from the horizontal. It should be further understood that 
the spring function of the bellows of the present invention further 
maximizes heat transfer from the reaction chamber 10 to the central coil 
24 and exterior coil 26 of the heat exchanger as a consequence of 
maximizing direct surface area exposure of the walls of the chamber 10 to 
the liquid metal 13 during the reaction by minimizing the ullage 11'. The 
bellows may be made of the same materials from which the end plate 18 and 
the continuous wall 36 are made. 
Operation of the present invention to control ullage 11' within the 
reaction chamber 10 to minimize direct exposure of the interior walls of 
the chamber and the inlet port(s) 14 to gaseous oxidants, such as 
SF.sub.6, during rapid attitude changes or orientations tipped 
substantially from the horizontal and to maximize heat transfer to the 
fluid (water and superheated steam) flowing in the central helical coil 24 
and exterior helical coil 26 of the heat exchanger is as follows. 
Initiation of the reaction is caused by activation of the initiator 32 
which changes enough of the encapsulated metal 30 within the chamber 10 to 
melt so that introduction of gaseous oxidant from the oxidant tank 12 
through the inlet ports 14 sustains the reaction. As soon as the reaction 
is commenced, the metallic pellets 30 change to liquid 13. The controller 
(not illustrated) controls the valves 36 and other controls not 
illustrated to meter the introduction of the gaseous oxidant into the 
interior of the chamber 10 at a rate to produce the desired quantity of 
thermal energy. As the reaction is ongoing, the resultant liquid metal 
fuel and combustion products continually decrease in volume from the 
volume of the initial charge of lithium pellets 30 within the chamber and 
furthermore the gas pressure within the chamber is sufficiently low that 
the compressed spring characteristic of the one or more bellows which are 
part of the one or more movable walls 16 move from their maximum 
compressed state at which the interior reaction volume of the chamber is 
maximized by the metal pellets 30 holding the bellows in the first 
position toward the second position at which the chamber 10 has a minimum 
volume as illustrated in FIG. 2. It should be understood that like 
reference numerals identify like parts in FIGS. 1 and 2 with FIG. 2 having 
been simplified to merely illustrate the second position of the end wall 
16 at which the reaction volume of the chamber 10 is minimized without 
illustrating the structures exterior to the chamber or the end reaction 
products within the chamber. During the reaction, the bellows within wall 
37 continually expands such that the pressure of the interior of the 
chamber 10 balances the force applied by the spring function of bellows 
and the ambient atmospheric pressure. The spring rate is chosen to achieve 
the desired minimal ullage 11' within the reaction chamber 10 during the 
reaction with consideration being given to the lessening of spring rate of 
metals as a function of increased temperature for the material used for 
fabricating the bellows. When the reaction is completed, as illustrated in 
FIG. 2, the metallic charge is reacted with reaction products (not 
illustrated) being contained within the closed chamber 10 having its 
minimum volume. During the reaction, the rate of energy transfer from the 
exothermic reaction occurring within the reaction chamber 10 is regulated 
by the amount of water which is pumped from the water source 26 of FIG. 1. 
The water typically changes to steam at the end of the central helical 
coil 24 in proximity to the crossover 28. Superheated steam flows through 
the exterior helical coil 26 to discharge port 40 which is connected to a 
turbine (not illustrated) for providing propulsive power to a vehicle such 
as a torpedo. It should be understood that during movement of the end wall 
16 from its first position at which the reaction chamber 10 has a maximum 
reaction volume to its second position, as illustrated in FIG. 2, at which 
the chamber has a minimum reaction volume, the ullage 11' within the 
chamber is minimized so that the chamber is sufficiently full of the 
liquid metal 13 during the reaction to prevent the substantial direct 
exposure of the interior walls and inlet ports 14 to the gaseous oxidant 
which can cause damage or destroy the chamber and inlet ports as in the 
prior art. Accordingly, during the ongoing reaction at which the reaction 
volume of the chamber 10 is continually decreasing under the spring bias 
applied by the bellows within wall 37, rapid changes in attitude from the 
horizontal caused by vehicular motion or attitudes tipped substantially 
from the horizontal will not substantially expose the inlet ports 14 or 
the interior walls of the chamber directly to the highly reactive oxidant 
gas. 
It should be understood that the spring rate which is chosen for the 
bellows within wall 37 controls the force applied to the movable wall 16 
against liquid metal and ullage 11' within the chamber 10 during the 
reaction. The higher the spring rate, the smaller the ullage 11'. 
FIG. 4 illustrates an end view of another embodiment of the present 
invention which has a plurality of movable walls 50 located within a fixed 
end plate 52 in place of the single movable wall 16 of the embodiment 
illustrated in FIGS. 1-3. Like parts identify like parts in FIGS. 1-4. 
Each of the movable walls 50 may be biased to move within a cylindrical 
recess extending into the reaction chamber 10 upon initiation of the 
reaction from the fixed end plate 52 by a bellows like the bellows 
described above within wall 37. The embodiment of the invention in FIG. 4 
is not limited to the configuration as illustrated with the position, 
shape and area of the movable walls being variable. Furthermore, the 
movable walls 50 may be located in any portion of the chamber 10 to 
project into the chamber to decrease ullage 11'. 
While the present invention has been described in terms of its preferred 
embodiment, it should be understood that numerous modifications may be 
made thereto without departing from the spirit and scope of the present 
invention. While the preferred shape of the chamber 10 is annular, it 
should be understood that other shapes may be utilized within the scope of 
the present invention with one or more movable walls being provided within 
reactors having chambers of differing shape to decrease the volume of the 
chamber during the reaction to control the ullage 11' and minimize 
exposure of the inlet ports 14 and walls of the chamber to the gaseous 
oxidants. 
Furthermore, while the preferred reactive system is based upon the reaction 
of lithium with SF.sub.6, it should be understood that other exothermic 
reaction systems may be utilized in practicing the present invention in 
which the reaction is produced within a closed chamber with the reaction 
products being contained within the chamber under conditions that the 
volume of the reaction products and unspent fuel within the chamber is 
continually shrinking during the reaction.