Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to pulse combustion
apparatus and to heaters of the pulse combustion type.
A pulse combustion apparatus conventionally
includes a combustion chamber and an exhaust pipe which
forms a resonant system with the combustion chamber. At
each cycle of the apparatus, a fuel charge is admitted
to the combustion chamber and is ignited. The charge
expands into the exhaust pipe causing a partial vacuum
transient in the combustion chamber which both assists in
drawing in a fresh charge, and causes high temperature gas
to be drawn back into the combustion chamber from the
exhaust pipe. The fresh fuel charge spontaneously ignites,
establishing the next cycle and the apparatus is self-
sustaining after initial ignition. In a heater of the
pulse combustion type, a fluid to be heated is brought
into heat exchange relationship with the exhaust pipe.
My United States Patent No. 3,267,985 discloses a
pulse-combustion-type heater in which the combustion
chamber has substantially the shape of two conical shells
joined together at their major diameters along a common
line of juncture. Five exhaust pipes are coupled to the
combustion chamber for heating and are disposed in a
chamber through which water is circulated. While this
form of combustion chamber and exhaust system has been
found to provide a very stable combustion cycle, the
present invention is aimed at providing further improve-
ments intended to enhance performance.
According to the invention there is provided a
pulse combustion heater including a housing, a combustion
chamber within the housing haYing an inlet and an outlet !
means for omitting successive fuel charges to the chamber
through said inlet, ignition means operable to initiate
combustion in the chamber, and an exhaust system. The ex-
haust system includes a primary exhaust pipe having first
and second ends and coupled to the combustion chamber at its
first end so as to extend generally tangentially from the
combustion chamber. The primary exhaust pipe is of a length
selected so that combustion of gases is substantially com-
plete before the gases leave the pipe. The system also in-
cludes a manifold having an inlet to which the second end
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of the primary exhaust is coupled, and a plurality of
outlets spaced around the manifold. A corresponding plur-
ality of heat exchange coils is provided. Each coil is in
the form of a hollow tube shaped to define a helix of sub-
stantially constant diameter extending about a longitudinalaxis and having an inlet coupled to one of the manifold
outlets, and an outlet. The coils are arranged around the
manifold with their longitudinal axes generally parallel to
one another. A heat exchange chamber is provided in the
housing and contains the heat exchange coils, the chamber
having an inlet and an outlet for fluid to be heated. An
exhaust chamber is also provided in the housing and communi-
ca~es with the outlets o~ the heat exchange coils and has an
outlet for exhaust gases.
1~ In order that the invention may be more clearly understood, reference will now be made ~o the accompanying
drawings which illustratP a number of preferred embodiments
of the invention by way of example, and in which:
Figure 1 is a vertical sectional view through a
pulse combustion heater according to the invention;
Figure 2 is a vertical sectional view through
the combustion chamber of the apparatus shown in Figure l;
Figure 3 is a transverse sectional view on line
III of Figure 2;
25- Figure 4 is a perspective view, partly in section
and partly exploded, showing the valve means of the
combustion chamber of Figures 2- and 3;
Figure 5 is a vertical sectional view of part
~f Figure 4;
Figure 6 is a perspective view of the exhaust
system of the apparatus of Figure l;
Figure 7 is a plan view corresponding to Figure
6;
Figure 8 is a diagrammatic illustration of the
gas flow pattern in the combustion chamber of the apparatus
shown in Figure l;
Figures 9 and 10 are views corresponding to
Figures ~ and 3 respectively showing modified combustion
chamber;
Figure 11 is a vertical sectional view partly
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exploded, of a pulse combustion heater according to a
further embodiment of the invention;
Figure 12 is a transverse sectional view on
line XII-XII of Figure 11;
Figure 13 is a perspective view of the gas
cushion chamber of the apparatus shown in Figures 11 and
12; and,
Figure 14 is an exploded perspective view of
the impeller assembly of the apparatus of Figures 11 and
12;
Referring first to Figure 1, a pulse combustion
-heater is generally indicated at 20 and includes a
combustion chamber 22, valve means 24 at the top of the
chamber for admitting fuel charges thereto, and an
exhaust system 26. The components of the apparatus are
disposed within a housing 28 which is designed to be self-
standing on a suitable support surface. Reference numeral
30 indicates a control box which is disposed at one side
of the housing and which houses suitable control e~uipment
~0 including an ignition transformer connected by a high
tension lead (not shown) to a spark plug in the combustion
chamber. The spark plug is used for starting only.
Housing 28 is divided internally as will be
described to define, from top to bottom, an air inlet
2S chamber 32, an air cushion chamber 34, a heat exchange
chamber 36, a muffler chamber 38 and an exhaust chamber
40. The housing is defined by inner and outer casings
denoted 42 and 44 respectively. The inner casing is made
of high strength concrete, while the outer casing is made
of steel. At the position of the air cusion chamber 34,
the inner casing is fitted with a liner 46 of galvanized
steel. The top o~ chamber 34 is defined by a plate 48
which separates the air cushion chamber 34 from the air
~ inlet chamber 32. Supporting structure above plate 4~
is generally indicated at 50 but will not be described in
detail. Also, it should be noted that suitable sound
insulating material is incorporated in the top of the
housing and in the inner casing, but has not been shown,
~- again because it forms no part of the invention.
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Air inlet chamber 32 communicates with the
exterior of the housing by way of an air inlet 52 which
extends through the inner and outer casing. This allows
ambient air or air from a supply pipe to be drawn into
the housing for combustion as required. A fan unit
generally denoted 54 is suspended below plate 48 and has
an inlet 56 within chamber 32. The fan unit includes an
electric motor 58 driving fan blades 60 arran~ed within a
fan chamber 62 which discharges into the air cushion cham-
ber 34. This chamber provides a reservoir of combustionair. Air is drawn from chamber 3~ into the combustion
chamber ~2 as required under the control of the valve means
generally indicated at 24. Fan unit 54 is used only for
starting; after ignition, the combustion process is self-
aspirating.
Heat exchange chamber 36 is defined by a linerassembly generally denoted 64, which, in efect, forms a
boiler inside housing 28. Thus, it will be seen that the
liner assembly includes a cylindrical portion 65 and top
and bottom closures or "heads" 66 and 68 respectively at
opposite ends of the heat exchange cham~er and that the
chamber is provided with an inlet 70 and an outlet 72
which extend through housing 28. Each of these components
is in the form of a tubular sleeve which passes through
the housing 28 and communicates with an associated pipe
connection which mates with a corresponding opening in the
relevant closure member of liner assembly 64~ In Figure 1,
the pipe connection associated with inlet 70 is denoted 76
and the associated opening in the top closure 66 is
indicated at 78. The corresponding pipe connection for
outlet 72 is denoted 80 and the corresponding opening is
indicated at 82. The inlet and outlets are coupled to
external equipment (not shown) for circulating water
through a heat exchange chamber 36 for heating. The
combustion chamber 22 is mounted in an opening 74 in the
top closure 66 of the liner assembly 64 so that water
entering the heat exchange chamber 36 through inlet 70
will flow around the combustion chamber for transfer of
heat from the chamber to the water. Similarly, as the
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water flows down in chamber 36 towards outlet 72, it will
flow around the exhaust system 26 and receive heat there-
from.
Muffler chamber 38 is defined between the lower
S closure member 68 of liner assembly 64 and a plate 84
which extends transversely inside housing 28 at a spacing
below the bottom closure member 68. The exhaust system 26
discharges generally vertically downwards into chamber 38
as will be described and a heat shield 86 is attached to
the upper surfaces of plate 84. A muffler tube 88 extends
generally vertically through plate 84 at a position spaced
laterally from the position at which the exhaust system
discharges into chamber 38. Thus, exhaust gases entering
chamber 38 from the exhaust system 26 will pass into
exhaust chamber 40 by way of muffler pipe ~8. Chamber 40
has an exnaust outlet pipe 90 through which the exhaust
gases leave housing 28 and from which the gases may be
vented to atmosphere or otherwise disposed of as approp-
riate. A narrow condensate drain tube 92 is provide~ at
the bottom of chamber 40 and is inclined downwardly so
that any liquid which may collect in the chamber will
drain to the outside.
Reference will now be made to Figure 2 and 3 in
describing the combustion chamber 22 of the apparatus.
Combus~ion chamber 22 is in the form of a one-piece bron~e
casting, denoted 94, at the top of which the valve means
2~ is located. The combustion chamber has an internal
cavity 96 which is generally of flattened spherical shape.
Thus, cavity 96 extends about a median plane 98, on which
plane section III-III is taXen. The cavity is of a shape
which is circular in said plane, and which curves generally
inwardly from both sides of said plane around its entire
- periphery towards first ana second ends 100 and 102 of
said cavity. Casting 94 defines at inlet 104 at the first
end of the cavity through which successive fuel charges
can enter the combustion chamber cavity, while the second
end 102 of the cavity is closed and generally flat. An
exhaust outlet 106 is provided in the wall of the combus-
-- tion chamber and is located in median plane 98. An
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integral sleeve 108 extends from the combustion chamber
generally tangentially with respect to cavity 96 and a
pipe 110 of the exhaust system (see later) is coupled to
the sleeve.
The combustion chamber inlet 10~ is in the form
of a passageway which extends through casting 94 ~rom a
top flange 112 to cavity 96 and includes three portions
114, 116 and 118 of progressively reducing diameter con-
sidered in the direction of fuel charge flow. As will be
seen from Figure 4, the flange 112 and passageway portions
114, 116 and 118 are of circular shape in plan. The center
passageway portion 116 receives a flame trap 120 for
preventing blow-back of burning gases through the combus-
tion chamber inlet. Flame trap 120 is in the form of an
outer tubular retainer 122 and a core 124 formed of a
spiral of corrugated stainless steel strip; the corruga-
tions leave openings between the turns of the spiral
through which fuel charges can flow. A screw threaded
opening 125 adjacent inlet 104 raceives a spark plug (not
shown) for initiating the combustion process.
Referring now more particularly to Figures ~ and
5, valve means 24 includes a valve plate 126 mount~d on
the top surface of the flange 112 of casting 94. Plate
126 is provided with a number of sets of openings for
admitting fuel charges of air and natural gas to the
combustion chamber. In Figure 4, the sets of openings are
denoted by reference numeral 12~ and it will be seen that
five such sets are visible; in fact, plate 126 is provided
with seven sets of valve openings although two of the sets
do not appear in Figure 4. Each set of openings includes
a central opening 130 for admitting natural gas and a
plurality of openings 131 distributed around opening 130
~ and through which air is admitted to the combustion
chamber. Each central opening 130 is fitted with an inlet
tube 132 which extends vertically upwardly from plate 126.
Referring back to Figure 1 the tubes 132 communicate with
a gas cushion chamber defined by a casing 134 which in this
case is made of sheet brass. The gas cushion chamber is of
~` generally cylindrical shape with domed ends ~although the
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particular shape is not critical) and is fitted at one end
with a corrugated fuel inlet tube 136 which extends through
housing 28 and communicates outside the housing with a
source of natural gas (not shown). Thus, the gas cushion
chamber 134 will provide the combustion chamber with what
is, in effect, a reservoir of gas at source pressure for
admission to the chamber through the fuel inlet tubes 132.
Air cushion chamber 34 provides a similar reservoir of
combustion air. A pressure sensing tube 138 is shown
ad~acent the air cushion chamber 134 in Figure 1 and can
be connected to switch in control box 30 for indicating
when combustion has been estabIished. Means (not shown)
may also be provided for maintaining a substantially
constant air/fuel ratio as described by my United States
Patent No. 3,267,985.
Referring back to Figures 4 and 5, the sets 128
of openings in plate 126 are controlled by individual
valves, each of which includes a light and freely movable
valve disc such as those shown in exploded positions at
140 in Figure 4. In this particular embodiment, the discs
are made of Dacron tT.M.) fabric coated with polychloro-
trifluorethylene sold under the trade mark Xel-F by M. W.
Kellog Co. Each disc 140 is retained below the associated
set of openings by a support plate 142 suspended from
valve plate 126. Each support plate 142 is of circular
shape and is formed with a set of openin~s corresponding
generally to the openings in plate 126. Three integral
lugs 144 project upwardly from plate 142 for suspending
the plate. The luys extend through opening in plate 126
and are bent over and sealed by silver brazing as can
best be seen in Figure 5. Thus, it will be appreciated
that each valve disc 140 is supported by the associated
- plate 142 and is trapped against lateral movember by lugs
144. The openings in plate 142 permit pressure waves
from the combustion chamber to force the valve disc 140
upwardly to close off the associated openings in valve
plate 126. When the pressure decreases, the discs will
move down and admit fuel to ~he combustion chamber.
- Figures 6 and 7 show the exhaust system of the
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heater and will now be more particularly described. The
system includes a single primary e~haust pipe 110 part of
which is visible in Figures 3 and 4. This primary
exhaust pipe has an inlet end coupled to the combustion
chamber so as to extend outwardly from the chamber
tangentially with respect to its circular configuration.
Pipe 110 is of relatively substantial length (see later)
and is shaped to define a generally circular loop portion
which extends around the combustion chamber (see Figure
1), and an end porti~n which is bent downwardly and
connected to a manifold 146. Manifold 146 has a single
central inlet to which the primary exhaust pipe 110 is
coupled. In this embodiment the inlet is defined by a
sleeve 148 which projects upwardly ~rom a main body
portion 150 of the manifold and which is angled to corres-
pond with the inclination of outlet end portion of the
primary exhaust pipe 110. Pipe 110 is received in and
welded to sleeve 148. The body portion 150 of the mani-
fold 146 is generally cylindrical in shape and is formed
with a plurality of outlets in the form of openings in
its outer surface which communicate with the single
central inlet. The outlet openings are arranged in pairs
in equally spaced relationship around the body portion
150 of manifold 146 with the outlets in each pair spaced
vertically from one another and staggered laterally to a
slight extent as can clearly-be seen in Figure 6 in the
case of one pair of outlet openings ~deno~ed 152a and
152b). A plurality of heat exchan~e coils generally
denoted 154 are provided for connecting manifold 146 with
the muffler chamber 38 ~Figure 1). Each coil is in the
form of a hollow tube shaped to define a helix of sub-
stantially constant diameter extending about a long-
~ itudinal axis and having an inlet coupled to one of said
manifold outlets, and an outlet which communicates with
the muffler chamber 38 of the heater. The heat exchangecoils are arranged in pairs around manifold 146 and each
pair comprises one left hand wound coil and one right hand
would coil of identical shape and size. Referring to
Figure 6, reference numeral 154L denotes the left hand
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coil of a pair while 154R denotes the corresponding right
hand coil. The corresponding pair of coils are similarly
designated in Figure 7. Five such pairs of coils are
provided around manifold 146.
It will be apparent from Figures 6 and 7 that,
by virtue of the verticall~ staggered arrangement of the
- manifold outlets 152a and 152b the coils in each pair can
"mesh" with or be interleaved with one another so that the
turns of one coil fit between the turns of the corres-
ponding coil. Similarly, adjacent coils of different
pairs can be meshed or interleaved with one another. This
provides for a very compact heat exchange unit having
large capacity. A further advantage of this arrangement is
that it can be readily fabricated using conventional coil
winding equipment and with minimum bending of the pipes.
Thus, successive coiled sections can be taken directly from
a coil winding machine and fitted into the manifold without
the need for special fabrication techniques.
A still further advantage of this heat exchanger
construction is that heat exchangers having even more coils
can be readily fabricated by enlarging the manifold and
adding coils around the periphery of the existing coils
are indicated in chain dotted line at 154' in Figure 7.
These additional coils may be arranged in pairs of left
and right hand coils interleaved with one another in the
same fashion as the center coils. The inlet ends of the
coils would be extended inwardly as shown in Figure 7 and
connected into the larger manifold in a second row of
staggered manifold outlets above the outlets shown in
Figure 6.
A still further advantage of the heat exchange
structure shown in the drawings derives from the fact that
~ curved pipes are used. Thus, in a heat exchanger having
straight pipes, the boundary layer effect produces, in
effect, an insulating layer of stagnant air which tends to
inhibit heat transfer from the pipes and reduces the
efficiency of the heat exchanger. In the present applic-
ation in which high velocity gas flows are encountered,-the
use of curved pipes minimized the boundary layer effect
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and increases the efficiency of the heat exchange~ compared
with a conventional unit having straight pipes. Curved
pipes also have th~ advantage that they are capable of
accommodating thermal expansion and contraction without
the need for specia,l precautions in the construction o~
the heat exchanger.
Referring back to Figure 6, it will be seen that
the outlet end portion of each of the heat exchange tubes
is shaped to define an axially parallel end portion 154a
which extends through the bottom boiler head 68 of the
heat exchange liner assembly 64 (see Figure 1).
The operation of the heater will now be described
initially with reference to Figure 1 of the drawings. As
indicated previously, the apparatus is designed to be self-
sustaining after initial starting. Thus, a supply of fueland air is delivered to the combustion chamber from the gas
cushion chamber 134 and from the fan 54 respectively and
is ignited by the spark plug in`the combus~ion chamber.
The pressure rise which occurs in the chamber upon ignition
causes the valve discs 140 (Figure 4) to be propelled up-
wardly and close off the air and gas inlet openings in the
valve plate 126. The combustion gases expand and enter
the primary exhaust pipe 110, causing a vacuum transient
in the combustion chamber itself. This allows the valve
discs 140 to move downwardly under the effect'of the
pressurized air and fuel acting on the discs from above
so that a fresh fuel charge enters the combustion chamber.
The ~acuum transient also has the effect o~ causing
combustion gases in the exhaust system to return to the
combustion chamber.
The combustion chamber has been designed so that
this returning pressure wave of c~mbustion gases entering
~ the combustion cXamber is caused to flow in a double
toroidal flow pattern as indicated diagrammatically in
Figure 8. In that view, the wall of the combustion chamber
cavity is indicated by a chain dottea outline denoted 96
and a tangential portion of the primary exhaust pipe is
indicated at 110. By virtue of the tangential arrangement
of this pipe and its position on the median plane of the
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_ 11
combustion chamber cavity, the returning gases ~eet the
combustion chamber wall generally in the region of the
median plane. Since the wall curves inwardly at both
sides of that plane, the gas~s are caused to ~low inwardly
both above and below the median plane in addition to being
caused to follow the curvature of the wall around the
circumference of the cavity. This generates the double
toroidal flow pattern. Next the succeeding fuel charge
enters the combustion chamber from inlet 104 generally
centrally of the chamher and thus enters the center of
the toroidal flow pattern of the combustion gases. In
Figure 8, the flow path of the fuel charge is indicated
generally at 158.
It has been found that the flame in the combus-
tion chambex is not extinguished at any time during the
cycle of the apparatus. During the low pressure part of
the cycle (that is during the vacuum transient - generally
about one third to one half of the cycle time depending
on cycle strength) the gases in the combustion chamber
are relatively stagnant and a number of flame fronts
persist throughout the mixture. This low pressure draws
the next fuel charge into the center of the combustion
chamber with very little turbulance. The combustion gases
returning to the combustion chamber through the primary
exhaust pipe 110 are delayed due to the length~of the pipe,
but enter the combustion chamber at a very high velocity.
These gases may be well balow ignition temperature (since
the exhaust system is water cooled); however, while the
temperature will have an effect on the operating frequency
of the apparatus, it has not been found to cause instab-
ility in the combustion cycle. In any event, as these
returning gases enter the combustion cham~er the residual
~ gases containing the flame fronts are rapidly mixed with
the fresh charge due to the double toroidal flow pattern
described above. There is a rapid increase of temperature
and pressure and gases again start to flow out of the
combustion chamber through the exhaust pipe. Complete
ignition and pressure rise has been found to occur within
approximately one tenth of the cycle time. This double
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toroidal turbulance pattern in the combustion chamber is
very consistent with virtually no stray tails of flame
which could cause pre-ignition of the charge and produce
a pressure rise at the wrong time in the cycle. Thus,
it will be understood that ignition of the incoming charge
should be kept to a minimum until the high velocity comb-
ustion gases return to the combustion chamber. Ignition
will then take place at a rate which is related to the gas
velocity and the turbulance pattern.
An additional advantage derived from the combus-
tion chamber design shown in the drawings is that the out-
side dimension of the combustion chamber can be minimized
for a given volume, substantially reducing the space
required to accommodate the combustion chamber. Another
- 15 advantage is that the ratio of surface area to volume of
the combustion chamber is at a minimum so as to reduce any
quenching effect on the burning gases in the combustion
chamber due to the presence of cooling water in the heat
exchange chamber 36.
It has also been found that the design of the
exhaust system has a significant impact on the operation
of the apparatus. Thus, it will be noted that the system
includes a primary exhaust pipe ~ ) which is of relative-
ly large diameter and is of a significant length. These
characteristics are selected with the aim of insuring that
combustion is completed in the primary exhaust pipe 110
and is not carried through into the heat exchange portion
of the exhaust system. Thus, it has been found that, even
with the improved combustion chamber design provided by
the invention, some combustion occurs in the exhaust
system. The high velocity of the gases entering the
exhaust system results in a high rate of heat transfer to
- the surrounding water which, with the temperature drop
which occurs due to expansion, results in some carbon
monoxide in the gases. By providing an exhaust system in
which substantially all of the combustion takes place up-
stream from the heat exchange coils this cooling effect on
the gases and hence the high carbon monoxide content of the
exhaust is minimized, while at the same time achieving
~1~2~ii 1l3
efficient heat exchange to the water in the heat exchange
chamber 36 through the medium of the heat exchange coils
154~ A thin layer of an insulating material may even be
applied to the primary exhaust pipe llO in an effort to
maintain the temperature of the combustion gases in the
pipe and thereby to reduce the carbon monoxide content of
the gases. In practice, it has been found that an increase in s~face
tempera~re of even 100F will make a significant difference to the
perrentage of carbon m~noxide in the exhaust.
A further expedient which may be adopted in the
interest of minimizing carbon monoxide emission is to
provide a restricter or nozzle (not shown) in the exhaust
pipe at its connection to the combustion chamber. Thus,
since the combustion cycle is dependent upon the high
velocity of the gases returning to the combustion chamber
during the low pressure part of the cycle for providing
fast ignition, a restricter or nozzle provides for a
larger volume for secondary combustion and at the same time
gives the returning pressure wave a high velocity as it
enters the combustion chamber (for rapid ignition). In
practice, it has been found that, ~or optimum results,
the inside diameter of the combustion chamber cavity in
the median plane should be equal to or less than three
times its height. Also, it has been found that the inside
diameter of the primary exhaust pipe should be at least
about 3/4 of an inch and that the pipe should be not less
than ten inches in length. `
It has been found that a single pipe is suitable
fQr an apparatus having a relati~ely small heat output
rating and that, for a larger apparatus the number of pipes
may be multiplied `in proportion to the increase in output
rating. For example, in practical tests, an apparatus
xated at lO0,000 B.t.u. per hour required a single pipe
of l" internal diameter and a 400,000 B.t.u. apparatus
required for such pipes. In a multiple pipe installation
they will be equally spaced around the combustion chamber
and will each be disposed tangentially thereto. A more
complex manifold (as manifold 146) is obviously required
in such cases.
Reference will finally be made to Figures g and
lO which illustrate a modified form of combustion chamber
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which may be advantageous in certain applications. Primed
reference numerals have been used in Figures 9 and 10 to
illustrate parts which correspond with Figures 2 and 3.
The combustion chamber shown in Figures 9 and 10 has, in
S fact, been designed primarily for use in a pulse combus-
tion apparatus in which the combustion chamber is air
cooled; that is, where the apparatus is either an air
cooled engine or is being used for heating air. For this
reason, the combustion chamber is shown as having external
~ins denoted 160 for promoting heat transfer from the
combustion chamber to the surrounding air. However, it
should be noted that this is only one example of an appli-
cation o~ this form of combustion chamber and that, in
other applications, the fins might well be omitted.
The primary difference between the combustion
chamber of Figures 9 and 10 and that shown in the previous
views is that the inner wall of the combùstion chamber is
contoured to define an inwardly protuberant surface portion
around the inner periphery of the combustion chamber in its
median plane 98'. The èffect of this protuberant portion
is to positively separate the returning combustion gases
which enter the chamber cavity into two distinct flow
paths. Thus, the flow pattern in the chamber of Figures 9
and 10 is essentially the same as that which occurs in the
case of the combustion chamber of Figures 2 and 3, but is
somewhat more discrete. This form of flow pattern may be
desirable in some situations although it should be empha-
si~ed that, in practice, it has not generally been found
essential to provide for physical separation of the
returning gases in this fashion in order to achieve satis-
factory combustion.
Reference will now be made to Figures 11 to 1
in describing a pulse combustion heater according to a
further embodiment of the invention.
In principle, the heater shown in these views is
similar to the heater described above with reference to
Figures 1 to 7. Thus, the heater includes a housing,
~ generally indicated at 200, which defines internally, an
air inlet chamber 202, an air cushion chamber 204, a heat
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_ 15 -
exchange chamber 206, a muffler chamber 208 and an exhaust
chamber 210. A fan unit 212 is positioned between the air
inlet chamber 202 and the air cushion chamber 2 4 although
the unit is shown in a partly exploded position in Figure
11. A gas cushion chamber Z14 is disposed within the air
cushion chamber 204 and a gas supply pipe 216 is coupled
to chamber 214. The chamber forms part of a sub-assembly
which is illustrated in detail in Figure 13, and which
includes valve means of the same form as that described
previously in connection with Figure 4.
A combustion chamber 218 is disposed in the heat
exchange chamber 206 and supports the gas cushion chamber
sub-assembly as will be described. An exhaust system 220
is associated ~ith combustion chamber 218 and discharges
into the muffler chamber 208. The combustion chamber and
exhaust system are of the same form as the combustion
chamber 22 and exhaust system 26 described with reference
to the previous views.
A primary difference between the heater being
described and the heater of Figures 1 to 7 resides in the
construction of the housing 200. As in the first embodi-
ment, housing 200 includes inner and outer casings, denoted
222 and 224 respectively. The outer casing 224 is in the
form of a one piece steel shell of cylindrical ~orm and
the inner casing 222, while also of generally cylindrical
~orm, is an assembly of three generally cylindrical casing
sections r namely an air cushion chamber section 226, a
boiler section 228, and an exhaust chamber section 230.
The sections are bolted together as will be described to
form the inner casing 222 and are designed to provide a
gas-tight assembly in which there can be no leakage of
gases between the exhaust or muffler chambers of the heater
- and the air cushion chamber. This form of inner casing
also has the advantage that the heater can be manufactured
as three sub-assemblies ~an air cushion chamber sub-assembly,
a boiler sub-assembly, and an exhaust cham~er s ~ assembly) which can
be easily bolted together in asse~bling the heater.
~ he air cushion chamber section 226 and exhaust
chamber section 230 of the inner casing 222 are cast in
concrete. The castings may be manufactured by any appro-
priate concrete casting techni~ue, e.g. by rotational
moulding. In this particular embodiment, the sections are
designed to be made by a technique in which a steel shell
is employed for forming the outer surface of each section
and remains associated with the concrete casting after
the casting operation has been completed. Thus, as shown
in Figure 11, steel sh~lls 226a and 230a remain around the
respective castings 226 and 230 of the inner casing. The
casting which makes up the air cushion chamber section 226
is of generally cylindrical shape but is formed within its
ends with upper and lower recesses 232 and 234 of annular
form. The space between the recesses defines the air
cushion chamber 204 of the apparatus. Recess 232 is of
significant depth compared with recess 234 and is dimen-
sioned to define the air inlet chamber 202. Recess 232
has an annular face 236 which is disposed normal to the
longitudinal axis of section 226 and which forms a support
for the fan unit 212 of the apparatus. A cast concrete
lid 238 is provided for fitting over the open upper end of
section 226 and is held in place by four screw threaded
studs, two of which are indicated at 240 which are cast
into section 226 so as to extend upwardly from the top end
face of the section. The lid 238 is formed with openings
to correspond with the three studs so that the lid can be
fitted over the studs and secured in place by nuts and
washers such as those indicated at 244. Four similar studs
2~2 are provided at the lower end of the section.
A steel air inlet tube 248 is fitted into an
opening which'extends through casting 226 at a position
above the end face 236 of recess 232. Tube 48 is secur~d
in place by a suitable epoxy adhesive. Casting 226 is also
formed with suitable openings for the gas supply pipe 216
and for other necessary external connections ~see later).
All of these openings are air-tightly sealed with respect
to ambient air~
The exhaust chamber casting 230 is also of
generally cylindrical shape but includes an integral wall
250 at its lower end. At its upper end, section 23~ is
~lZZ~
- 17 -
formed with a recess 252`generally similar to and of the
same diameter as the recess 234 at the lower end o the
air cushion chamber section 226. Four eq~ally spaced
screw-threaded studs, two of which are visible at 254 and
256 are cast into section 230 so as to extend vertically
upwardly from the top edge of the section. Internally,
section 230 is shaped to define a narrow annular shoulder
258 which supports a metal muffler plate 260. Plate 260
is secured in-place using a suitable silicon sealer and
divides the interior of section 230 into the muffler
chamber 208 and the exhaust chamber 210. Plate 260 is
made of steel and is fitted with a heat shield 262 and a
muffler tube 264 generally similar to the structure des-
cribed in connection with the first embodiment. An
exhaust outlet pipe 266 extends through the wall of casting
230 below plate 260 and is secured in place by an epoxy
adhesive. A condensate drain outlet 268 is similarly
secured in an opening in the casting but below pipe 266
The boiler section 228 of the inner casing of
the heater is in the form of a cylindrical steel shell
having an external diameter selected so that the shell can
be fitted between the upper and lower casing sections 226
and 228 respectively with the respective ends of the shell
received`in the recesses 234 and 252 of the other two
sections as shown. Be~ds of a suitable silicon sealer are
introduced into the recesses before assembly to ensure gas-
tlght sealing. The casing sections are then assembled and
clamped together in gas-tight fashion by means of the
screw-threaded studs 242 and 254 which respectively project
30 downwardly from section 226 and upwardly from section 230.
Angle section brackets such as that indicated at 272 are
welded to the external surface of shell 270 in positions
- to correspond with the positions of the studs 242 and 254.
Each bracket has a limb, as limb 272a-, which projects out-
wardly from the external surface of shell 270 and which is
formed with an opening for receiving the relevant stud.
Thus, the studs 242 and 254 project through the openings
in the brac~ets and are fitted with suitable nuts and
washers for clamping the shell 270 between the casing
:
~225~3
- 18
sections 226 and 230. A suitable silicon sealer is used to
coat the bottom faces of the recess 234 and 252 to ensure
gas-tight sealing.
Shell 270 forms part of a bo}ler sub-assembly of
the heater and is provided at its upper and lower ends with
respective boiler heads 274 and 276 which are welded inside
the ends of the shell in accordance with conventional
boiler manufacturing practice. Head 274 is formed with an
opening 278 and the combustion chamber 218 is bolted to
head 274~-so as to protrude upwardly through opening 278.
Thus, it will be noted that the combustion chamber includes
an integral flange 218a which fits against the under sur-
face of head 274 and by which the combustion chamber is
bolted to the head. The exhaust system 220 of the heater
will not be described in detail since it is essentially the
same as the exhaust system praviously described with ref-
erence to the first embodiment. For present purposes, it
is sufficient to note that the exhaust system is disposed
inside shell 270 and extends from the combustion chamber
218 to the bottom head 276. Suitable openings are provided
in head 276 for receiving the lower end portions of the
heat exchange coils of the exhaust system.
Shell 270 is also provided with internally screw-
threaded water inlet and outlet couplings ~80 and 282
which are located in openings in the shell and are welded
in place. These couplings will xeceive external pipe work
to be connected to the interior of the "boiler" represent-
ated by shell 270 and heads 274 and 276 for circulation of
water around the combustion chamber and exhaust system. A
third, similar coupling ~84 is provided adjacent the lower
end of shell 270 and is fitted with a plug 286 for clean
out purposes.
It will be appreciated that the inner casing
construction as described above has a significant advantage
in that the air cushion chamber section 226 and the exhaust
chamber section 230 are essentially isolated from one an-
other by a sealed boiler section 228. As a result, there
is virtually no risk of leakage of exhaust gases from the
muffler chamber 208 or the exhaust chamber 210 to the air
. ~:
.
,.. -: ~-. :,: . :
5il 3
-- 19 --
cushion chamber 204. Additionally, this form of construc-
tion has the advantage that the heater can be constructed
as three sub-assemblies which can be assembled individually
and then bolted together as described. The assembly is
then fitted into the outer casing 22~ and the space between
the two casings is filled with fiberglass insulation.
Figure 13 illustrates the gas cushion sub-
assembly of the heater, which is generally designated 288.
This assembly includes cushion chamber 214 itself and the
valve means associated with the combustion chamber 218.
The valve means is essentially the same as that previously
described with reference primarily to Figures 4 and 5 and
will not therefore be described again in detail. It is
sufficient to note that the valve means includes a valve
plate 290 which is coupled to the gas cushion chamber 214
by a series of gas inlet tubes 2g2. The tubes 292 commun-
icate with the interior of the gas cushion chamber 214 and
with gas inlet openings in plate 290. At its lower end,
each tube is surrounded by a series of air openings in
plate 290 which allow air from the air cushion chamber 204
to enter the combustion chamber. Also associated with each
series of openings is a valve comprising a valve retainer
plate 294 and a valve disc (not shown) all as previously
described with refer~nce to Figures 4 and 5.
A pressure sensing tube 296 also extends upwardly
from plate 290 and is fitted with coupling 298 at its outer
end. Tube 296 communicates a~ its lower end with an
opening in plate 290 which provides communication with the
interior of the combustion cham~er 21~ when the gas cushion
chamber sub-assembly is in place on the combustion chamber.
Thus, by means of tube 296 a signal can be obtained as an
indication of the pressùre in the combustion chamber. This
signal is used as an indication of whether or not combus-
tion has been satisfactorily established in chamber 218
When the gas cushion chamber sub-assembly is
fitted to the combustion chamber, valve plate 290 is
disposed on top of the chamber and is held in place by a
clamping ring 300 which extends around the-gas inlet tubes
292 above plate 290. Ring 300 is formed with four e~ually
L3
_ 2~ _
spaced openings 302 which match both with corresponding
openings 304 in plate 290 and with four externally screw-
threated studs 306 which pro~ect upwardly from the top of
combustion chamber 218. Thus, sub-assembly 2a8 is mounted
on the combustion chamber by fitting the valve plate 290
and the clamping right 300 over the studs 306 and fitting
suitable nuts and washers to the studs. One of these nuts
is indicated at 306 in Figure 11 and the nuts associated
with all four studs are similarly designated in Figure 12.
In order to provide for ease of access to the nuts 305 for
fitting of sub-assembly 288 to the combustion chamber (and
subsequent removal thereof if necessary) gas cushion
chamber 214 is specially designed to provide recessed areas
308 in its external surface. Referring back to Figure 13,
the gas cushion chamber 214 is assembled from two sub-
stantially identical shell sections 310 and 312 which meet
in a horizontal median plane of the chamber. Both sections
are of oval shape in said plane and ha~e side walls which
are progressively shaped in moving away from said plane to
define arcuate section troughs which foxm the recesses 308
referred to above. As a result, the top wall of each shell
has the general appearance of an oval which has been in-
wardly constricted at both sides of a center section. The
upper shell 312 is formed around its lower margin with an
outwardly stepped portion 312a which defines a recess
receiving the upper^marginal portion of the lower shell
section 310.
The gas cushion chamber sub-assembly 288 has
been designed so that its component parts can be assembled
or stacked together generally in the positions in which
they are shown in Figure 13 and passed through a furnace
brazing oven for brazing of the parts to one another. In
this connection, it will be recalled that the valve disc
retaining plates of the valve arrangement (as plates 29~)
are designed to be secured in place by brazing. The
design of the gas cushion chamber sub-assembly also has the
advantage that it can be bolted onto the combustion chamber
of the heater as a unit. The design of the gas cushion
chamber also allows ready access to the mounting studs 306
,
l~Z~i~3
- 21 _
(Figure 11) using a socket wrench as discussed previously.
Referring back to Figures 11 and 12, it will be
remembered that gas is delivered to the gas cushion chamber
214 through a gas supply pipe 2~6 which extends through the
wall of the air cushion chamber section 226 of the inner
casing. Externally of both the inner and outer casing,
pipe 266 is fitted with a gas pressure regulator 314 which
has a control port 316 for receiving an air pressure signal
by which the regulator 314 is biassed to vary the gas
pressure delivered to the gas cushion chamber 214 according
to the air pressure in chambe~ 226. This signal is
provided by way of a pressure sensing tube 318 which ex-
tends from port 316 through the inner and outer casings 222
and 224 and which is secured in place by a suitable adhe-
sive. Regulator 314 is designed to control the prèssureof the gas supplied to chamber 214 in accorda~ce with the
air pressure in air cushion chamber 204 so as -to maintain a
substantially constant/gas ratio. This has been found to
be advantageous from the viewpoint of improving reliability
of the heater.
Upstream of the gas pressure regulator 314, the
gas supply line includes a solenoid operatea gas valve for
controlling delivery of gas to combustion chamber. The
valve is a conventional on/o~f valve and has not been shown
in detail.
The fan unit 212 of the heater is shown in an
exploded position in Figure 11. The unit includes an
electric motor 320 and a shrouded impeller enclosed within
a housing indicated at -322 in Figure 11. The housing
includes a peripheral flange 324 which rests on the bottom
face 236 of the recess 232 in the air cushion chamber
section 226 when the fan unit is in its installed position.
- A foam rubber gasket 326 is secured to flange 324 by
adhesive for sealing with face 236. The impeller casing
322 includes an upwardly extending, central air inlet 328
and a helical compression spring 330 extends around inlet
328 and is dimensioned to fit between the portion of the
impeller casing around tne inlet and the underside of the
lid 238 of the inner casing. Thus, when the fan unit is
~2~3
- 22 -
in its installed position, flange 324 rests on the end
face 236 in recess 232 and the lid 238 is bolted onto the
top of the air cushion chamber section 226. In this
condition, spring 230 is under slight compressive loading
and serves to urge the impeller casing 322 against face
236.
Figure 14 is an exploded view of the impeller and
housing. Housing 3~2 made in two parts, comprising an
upper housing part 322a and a lower housing part 322b.
The two parts have flattened peripheral portions which co-
operate to define flange 324. Housing part 3~2a has the
general shape o~ a shallow dome with a generally cylind-
rical upward extension a~ its center which defines air
inlet 328. The lower housing part 322b is generally dish-
shapèd and includes-a recessed central region 332 of
circular shape surrounded by an annular wall 334. Wall 334
is formed with a series of circular air outlet openings
336. An impeller 338 is shown positioned between the two
parts of the housing in Figure 14. The impeller includes
a disc-shaped main portion 340 surrounding a central boss
342 and having on its upper surface a plurality of arcuate
shaped vanes 344 which radiate outwardly from boss 342.
Boss 342 has a central bore which receives the drive shaft
of motor 320 (not shown) and the boss is clamped to the
drive shaft by a set screw (not shown).
A thin alwminum shroud 346 of slightly disced
circular shape is fitted to the tops of the vanes 344 so
that open ended air passageways are defined between the
vanes. At their outer ends, the vanes extend above the
main portion of 340 of the impeller so that the passage-
ways are open at their outer ends. At their inner ends,
the vanes 344 are cut away to define an air inlet region
- around boss 342. Shroud 346 is heid in place by a number
of relatively fine pins or studs which are formed on
certain of the vanes which project through holes in the
shroud and are peened over to hold the shroud in place.
The main portion 3~0 of the impeller is dimen-
sioned to be accommodated within the recessed central
portion 332 of lower housing part 322b so that the open
; ~
~L~ Z~13
-- 23 --
outer ends of the air passageways defined between the vanes
344 discharge generally in the direction of the air outlet
openings 336.
The form of impeller shown in Figure 14 has been
found to provide increased pressure output compared with a
conventional impeller of comparable size. By way of exam-
ple, a shrouded eight inch diameter impeller has been found
eminently satisfactory for a heater of 100,000 B.t.u. output.
A relatively high impeller output pressure has been found
particularly desirable for ensuring reliable combustion
cycle initiation where hot return water is present in the
heat exchange chamber.
It should be noted that the preceding description
relates to specific embodiments of the invention only and
that many modifications are possible within the broad scope
of the claims. For example, the specific materials
referred to herein are not to be considered as essential,
but rather as indicating materials which have been found
satisfactory in practice. Also, it should be noted that
the apparatus described has been designed primarily for
burning gaseous fuels such as natural gas or propane
- although the principles of the invention are applicable to
an apparatus for burning other fuels, for example, fuel oil
or coal dust. For this reason, the term "fuel charge" has
been used to denote any appropriate combustion medium and
is intended to include a gas-air mi~ture. Of course, where
different fuels are used, diferent expedients would undou-
btedly be required for delivering the fuel charge to the
combustion chamber. Fuel delivery may be effected in the
manner disclosed in my United States patent aforesaid.
With reference to the valve means specifically
disclosed in this application, it is to be understood that
the number of valves will vary according to the size of
the apparatus. Seven valves have been found appropriate
to a 100,000 B.t.u. unit, but a larger number would be
required for a larger apparatus.
Also, while the preceding description relates
specifically to a heater, it is to be noted that the in-
vention is not limited in this regard. For example r a
2~3
2~ -
pulse combustion apparatus of the form provided by the
invention could be used as an engine for the recovery of
mechanical or electrical energy.
With reference to the exhaust system of the
apparatus, it should be noted that the primary exhaust
pipe could be omitted in some applications and heat
exchange coil(s) connected directly to the combustion
chamber (without a manifold). Of course the heat exchange
pipes are also exhaust pipes whether or not a primary
exhaust pipe (jet pipe) is present.
The primary exhaust pipe and/or the heat exchange
coils may be internally coated with lead for corrosion
protection and long life. The lead coating may be applied
by conventional techniques to a suitable thickness. A
small percentage of tin or other material may be included
with the lead for improved adhesion.
