Note: Descriptions are shown in the official language in which they were submitted.
CA 02366120 2001-09-14 pCT/SE00/00526
WO 00/55542
A METHOD AND DEVICE FOR SUPERVISION AND CONTROL OF A HEAT GENERATOR WITH
PULSATING
COMBUSTION
Technical Field
The present invention relates to a method and device
for supervision and control. of a heat generator with pulsa-
ting combustion.
Background of the Invention
A heat generator of this type can be constructed in
different ways, but in an exemplary commercially available
variation it comprises a Helmholtz resonator with a reso-
pant chamber arranged as a combustion chamber, a pulse tube
connected to the combustion chamber at one of its ends, a
decoupler with an exhaust pipe being connected to its other
end, an inlet chamber with an initiation blower, a valve
controlled by the pulse pressure in the combustion chamber
for regulating the connection between the inlet chamber and
the combustion chamber, a device for injecting fuel in the
combustion chamber, and an ignition device for igniting the
fuel in the combustion chamber.
V~lhen this heat generator is to be started or initia-
ted, the initiation blower is started, which sucks in air
in the inlet chamber and creates a certain overpressure,
whereupon an ignition device (a spark plug) is activated,
at the same time as fuel is injected, so that the fuel is
ignited and herewith a rythmic movement of the valve can
commence. When this has happened, however, the initiation
blower and the ignition device shall be shut down, which of
course should occur automatically by means of a suitable
control system.
A heat generator of the type mentioned above must
have a completely dependable supervision system, which
determines whether it is operative or not. In a conventio-
nal furnace with an open fire this can occur by means of a
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photocell or the like, but in a pulsating heat generator
supervision may be difficult to attain.
Through SE-B-462 661 it is known to utilize the
frequency of the pressure variations for this purpose. In
this case the pressure variations in the inlet chamber are
sensed, and their frequency is compared with a predeter-
mined frequency, so that the ignition device and the initi-
ation blower can be shut down, when the frequency of the
pressure variations shows a requisite conformity with the
predetermined frequency.
Certain problems and drawbacks are associated with
such a frequency measurement. A furnace or heat generator
has a certain resonant frequency for physical reasons, and
this frequency is dependent on the construction and tempe-
rature of the furnace, type and quality of the fuel and air
surplus, and so on. The frequency does not give a clear
indication of the function of the heat generator; it would
be advantageous to have a better signal of the generator
function. It has also in practice appeared that the method
with frequence measurement caused great problems in that an
initiation which should have been approved has not actually
been approved.
The Invention
A better way of supervising and controlling a heat
generator or furnace of this kind is according to the
invention attained in that the amplitude of the sound gene-
rated during the operation of the heat generator and/or the
gas pressure is sensed and that the initiation means or
electrical operative system of the heat generator is shut
down, when the amplitude reaches a predetermined value or
falls outside a predetermined area, respectively.
The shut down should here occur with a certain delay,
so that for example singular pressure increases and explo-
sions in the furnace are not taken as an indication of
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approved operation or do not lead to the shut down of the
furnace .
In a practical embodiment of a heat generator of the
mentioned kind the amplitude in the inlet chamber is sensed
and the ignition device and the initiation blower are shut
down, when the amplitude reaches a predetermined value.
A supervising and controlling device for carrying out
the method according to the invention has an electronic
circuit device for emitting a signal for shutting down the
initiation means or a signal for shutting down the electri-
cal operative system of the heat generator at the receipt
from a sensor of an amplitude signal over a predetermined
value or outside a predetermined area.
This circuit device is preferably supplemented with a
delay circuit.
In order to allow connection to a so called fire con-
troller for the furnace, the electronic circuit device can
be supplemented with an adaptation unit. The circuit device
can in such a case be phantom fed with current from the
fire controller.
In the practical embodiment described above the sen-
sor can be arranged in the inlet chamber, and the initia-
tion means can comprise the ignition device and the initia-
tion blower.
The pressure connection of the sensor can here be
provided with a snorkel, which extends down to the bottom
of the inlet chamber. Oil or water which possibly leaks in
will hereby lead to a shut down of the furnace, as the mea-
sured amplitude hereby decreases.
The invention is based on the principle that the sen-
sor senses the amplitude for the sound generated at the
combustion. The sensor therefore needs not be placed in the
inlet chamber of the furnace - even if this is the prefer-
red position - but may for example alternatively be posi-
tinned in the combustion chamber itself, between the fur-
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pace body and the outer shell of the furnace or even com-
pletely outside the furnace.
At the initiation procedure for a furnace, which is
presently preferred, currency is concurrently supplied to
the ignition device in the form of an electrode and to an
oil pump with an initiation blower on the same shaft, an
oil valve being opened at the same time. When an approved
initiation has occured, the blower continues to operate,
whereas the electrode is shut off. A two stage oil pump can
be utilized with a lower oil pressure during the initiation
procedure and a higher pressure at operation. Variations of
blower systems can be envisaged for meeting different
demands. This is also true for the ignition device. For gas
furnaces there is no need for a fuel pump, but here there
are safety valves and so forth.
When the furnace is shut off, the currency supply to
the oil pump and the oil valve is shut off. In certain
cases post-ventilation with a blower can occur.
The supervision and control of the pulsating genera-
for need not only cover the initiation, but it can be equ-
ally essential to shut off the electric operative system of
the generator, when the sensed amplitude falls outside a
predetermined area, which indicates that the operation of
the furnace is defective.
The invention is equally applicable to all types of
pulsating heat generators and is not limited to use at the
embodiment chosen as an example.
There are reasons to believe that the control of
pulsating heat generators will be computerized, and the
3o invention is applicable also in such cases.
Brief Description of the Drawings
The invention shall be described in more detail below
under reference to the enclosed drawings, in which Fig 1 is
a very diagrammatic vertical sectional view of a heat gene-
rator with pulsating combustion and Figs 2 and 3 are block
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diagrams of two embodiments of supervising and controlling
devices according to the invention.
Detailed Description of Preferred Embodiments
The heat generator of the present type shown in Fig
1, which works with pulse combustion according to a previ-
ously known technique, is disposed in a water tank 10 with
an inlet 11 and an outlet 12 for the water, which in a
known way shall be circulated in a water based heating
system. The heat generator comprises a Helmholtz resonator
with a resonant chamber 13 and a pulse tube 14, which is
connected to the resonant chamber at one of its ends. The
resonant chamber forms the combustion chamber of the heat
generator and is provided with a nozzle 15 for the supply
of gaseous, liquid or fluidized fuel via a magnet valve 16
and with a spark plug 17, connected to an initiation trans-
former 17A. An inlet chamber 18 is connected to the combus-
tion chamber through an air inlet 19, which is controlled
by a valve 20. The valve is arranged to operate in an auto-
matic fashion for alternately closing at a supra-atmosphe-
ric pressure in the combustion chamber and opening at a
sub-atmospheric pressure therein in a rythmical movement.
The inlet chamber communicates with the external air
through an inlet 21, which is provided with an initiation
blower 22, via a silencer and/or a filter.
The other end of the pulse tube is connected to a
decoupler 23 having an exhaust pipe 24 connected to a chim-
ney or other flue.
When the heat generator is in a normal mode of opera-
tion, the fuel injected in the combustion chamber 13 is
ignited when entering the hot combustion chamber and will
be burnt up in combination with the oxygen present in the
combustion chamber, which results in a supra-atmospheric
pressure and a closing of the valve 20 as a result of said
supra-atmospheric pressure. When a subsequent sub-atmosphe-
ric pressure is created, the valve 20 is reopened to allow
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an inflow of air in the combustion chamber from the inlet
chamber 18, followed by another ignition and combustion of
fuel. Thus, combustion pulses having a regular frequency
are generated in the combustion chamber.
The heat generator is run intermittently in depen-
dence of the temperature of the water in the tank 10 in a
conventional way; when a predetermined increased tempera-
ture of the water is reached, the heat generator is turned
off and then restarted, when the temperature is decreased
to a predetermined lower temperature. At a restart of the
heat generator after a stand period the fuel must be igni-
ted externally by means of the spark plug 17 and air must
be forced into the inlet chamber by means of the initiation
blower 22. Thus, the ignition device and the initiation
blower are turned on at start up, but must be turned off
when the heat generator is in normal operation, such a
function being defined as a self-ignition of the fuel and
the air being injected by a sub-atmospheric pressure in the
heat combustion chamber.
An example of a supervising and controlling device
for the heat generator as shown in Fig 1 is shown in Fig 2.
As shown in Fig 1, a sensor 25 is arranged in the wall of
the inlet chamber 18. The sensor 25 has the purpose of sen-
sing the amplitude of the sound and/or gas pressure in the
inlet chamber. The sensor 25 is preferably of a piezo elec-
tric type, but other types can also be used.
The sound is supplied to the sensor 25 through a con-
nection 25' in the inlet chamber 18. Memories 26 and 27, to
which the signals from the sensor 25 are supplied, memorize
the highest and the lowest acoustic pressure, respectively,
which recently has been measured, i a the highest and the
lowest signal, respectively, which has been supplied from
the sensor 25. If a lower signal than the highest one or a
higher signal than the lowest one is supplied to the memo-
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ries 26 and 27, the memorized values are successively
changed to the new input values.
Signals corresponding to the highest and lowest
pressures are supplied from the memories 26 and 27 to a
differentiator 28, where the lowest value of the signal is
subtracted from the highest value, so that a signal corres-
ponding to the signal amplitude is supplied to a further
differentiator 29. Herein the obtained amplitude signal is
compared with a predetermined minimum value for providing
an output clearing signal if the amplitude signal, i a the
amplitude to the sensor 25, is over the predetermined mini-
mum level.
A device of this kind can be called an amplitude con-
troller.
Fig 3 shows a version which is more developed in
relation to the amplitude controller according to Fig 2.
The description above of the device up to and including the
emitted signal from the differentiator 29 is the same. This
emitted signal is in this case supplied to a delay circuit
30, which has the function of only letting through other-
wise approved signals with a certain, predetermined dura-
tion. In this way singular pressure increases or explosions
in the heat generator will not be regarded as an approved
operation.
It is customary that the operation of an ordinary
heat generator is supervised by means of a so called fire
controller, which can make use of a photocell as sensor. It
can be suitable also for pulse furnaces of the kind descri-
bed above to utilize such a fire controller, which is
approved and cheap due to mass production. In order to be
able to connect the amplitude controller according to the
invention directly to such a fire controller it is required
that the output draws much current at an approved amplitude
and little current at a non-approved amplitude. This is
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carried out by a unit 31, which emits a signal 32 directly
to a photocell input of the fire controller (not shown).
The device can be supplemented with a so called phan-
tom feeder, which means that for example a sensor can have
its current supply through the same line as it emits its
signal. Hereby, the current which the fire controller nor-
mally emits for reading the otherwise connected photocell
be utilized as a driving current for all electronics in the
amplitude controller. A separate current supply is thus
obviated, which leads to a small amplitude controller cir-
cuit with a simple connection and a low cost. The device
also becomes independent of utilized net currency.
The pressure connection 25' of the sensor 25 can be
provided with a snorkel 33, which is arranged in the inlet
chamber 18 of the furnace and extends down to its bottom.
If liquid due to some defect leaks into the inlet chamber
18 and the liquid enters the snorkel 33, the measured amp-
litude decreases largely, which thanks to the function of
the amplitude controller results in a shut down of the fur-
pace, as an approved operation can not be indicated.
The amplitude controller according to the invention
is preferably mechanically constructed for mounting
together with the sensor at a suitable measurement posi-
tion. Hereby the mounting is simplified and the frequency
dependency is obviated that for example a connection hose
would give rise to.
The practical embodiment described above is connected
to a commercially available heat generator working with
pulsating combustion. Other such heat generators are like-
wise possible for the device according to the invention.
It is thus possible to use constructions with one or
more pulse tubes, exhaust chambers, exhaust tubes and/or
valves. Further, it is possible in certain cases to obviate
an initiation blower, and if the heat generator is equipped
with an initiation blower, it does possibly not need to be
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shut down after the initiation procedure. In the shown
embodiment the ignition device comprises a spark plug, but
alternatives such as glow means are possible. The device
for fuel injection can be a carburettor or a spreader
instead of an orifice. The decoupling chamber can lastly be
connected to a bubble chamber or the like instead of an
exhaust tube or a chimney.
