The invention relates to a method and a device for monitoring and controlling a pulse combustion heating generator.

This type of heating generator comprises a Helmholtz resonator having a resonant chamber arranged as a burning chamber, a pulse tube connected in one

10 end thereof to the burning chamber, a decoupler connected to the other end of said pulse tube and having an exhaust pipe, an inlet chamber having an initiation blower, a valve controlled by the pulse pressure of the burning chamber for regulating the

₁₅ connection between said inlet chamber and said burning chamber, a device for injecting gaseous, floating or fluidized fuel in said burning chamber, and an ignition device for the ignition of the fuel injected in said burning chamber.

2 _Q When the heating generator is started an initiation blower is initiated, the initiation blower taking in air into said inlet chamber and producing there some positive pressure, and an ignition device (spark plug) , are activated simultaneously with the

25 injection of fuel for ignition of the fuel and thereby initiating a rythmical movement to the valve. However, when this has happened the initiation blower and the ignition device should be turned off, naturally automatically by means of a suitable control system.

Generally, all combustion systems must be

30 provided with a 100% reliable monitoring system determining whether the combustion system is functioning or not. In conventional cumbustion systems having an open flame this is generally accomplished by

„ _c means of a photocell or a ionization detector, but in

a pulse combustion heating generator it is difficult and also expensive to apply this type of monitoring.

To monitor and control the pulse combustion heating generator in this respect there has previously been performed a registration of the positive pressure existing in the burning chamber during operation and in a pressure chamber on the downstream side of the valve, the pressure chamber communicating with said burning chamber. The pressure can be transferred mechanically, pneumatically or hydraulically to a control unit placed outside of the heating generator. However, this arrangement has turned out to be unreliable and there has been a problem with a leakage of soot and oil at the pressure tap on the heating generator resulting in a destruction of the control unit.

In another previously known method for monitoring and controlling the heating generator there has been utilized a photocell in the burning chamber, the photocell being responsive to the radiation generated during combustion. The drawback of this arrangement is first of all that the photocell is easily obstructed by soot and also generating false signals as a result of being responsive to radiation other than the radiation emanating from the flame in the burning chamber. The photocell can also disturb the atomizing and/or dispersion of the injected fuel. The optical sensor or a sensor comprising a magnet and a Hall element, has also been utilized to derive the movement of the valve. However, such an arrangement is not appropriate because the valve could come into vibration at a single explosion in the heating generator during start up which leads to a false indication of the sensor followed by a turn-off of the initiation blower and the ignition device before the

heating generator has reached normal mode of operation. Furthermore, the placing of the sensor in the vicinity of an active part of the heating generator makes the mounting thereof more complicated.

An object of the invention is to eliminate the difficulties and drawbacks mention above, and to accomplish a realiable indication of normal operation of a pulse combustion heating generator by utilizing a control system which in relation to previously known control systems is more simple and more reliable. Thus, the invention is based on the fact that said type of heating generator operates at an essentially constant and well defined pulse frequency, normally at about 60-100 Hz. To achieve the specified object the invention relates to a method for controlling a pulse combustion heating generator which has been given the characteristics of claim 1, and to a control apparatus in accordance with claim 8 for carrying out said method.

The invention will be described in more detail with reference to the figures, of which:

FIG. 1 is a diagrammatic vertical sectional view of a pulse combustion heating generator,

FIG. 2 is an enlarged vertical sectional view of the inlet and burning chambers disclosing details of the embodiment, and

FIG. 3 is a block diagram on the electronic part of the control apparatus according to the invention.

The heating generator of the present type is shown in FIG. 1 and 2, has a pulse combustion operation according to previously known technique, and is disposed in a water tank 10 having a water inlet 11 and outlet 12, the water being circulated in a water based heating pipework. The heating generator

comprises a Helmholtz resonator having a resonant ^' chamber 13 and a pulse tube 14 one end thereof being connected to the resonant chamber. The resonant chamber forms the burning chamber of the heating generator and is provided with a nozzle 15 for supplying a gaseous, floating or fluidized fuel through a solenoid valve 16 and a spark plug 17, connected to an inition transformer 17A. An inlet chamber 18 is connected to the burning chamber through 0 and air inlet 19 controlled by a valve 20. The valve is arranged to operate in an automatic fashion to alternately close at positive pressure in the burning chamber and to open at negative pressure therein in a rythmical movement. The inlet chamber communicates 5 with the external air through a silencer and/or a filter and an inlet 21 provided with an inition blower 22.

The other end of the pulse tube is connected to a decoupler 23 having an exhaust pipe 24 connected to a _Q chimney or other flue.

When the heating generator is in normal mode of operation the fuel injected in the burning chamber 13 is ignited when entering the hot burning chamber, and will be burnt up in combination with the oxygen present in the burning chamber which results in a positive pressure and a closing of the valve 20 as an effect of said positive pressure. When a subsequent negative pressure is created the valve 20 is reopened to allow an inflow of air in the burning chamber from the inlet chamber 18, followed by another ingnition and combustion of fuel. Thus, combustion pulses having a regular frequency are generated in the burning chamber.

The heating generator is run intermittently in dependence on the temperature of the water in the tank

10 in a conventional way; when a predetermined increased temperature of the water is reached the heating generator is turned off and then restarted when the temperature is decreased to a predetermined lower temperature. At a restart of the heating generator after a stand period the fuel must be ignited externally by means of the spark plug 17 and aior must be forced into the inlet chamber 18 by means of the inition blower 22. Thus, the ignition device and the initiation blower are turned on at start up, but must be turned off when the heating generator is in normal operation, such a function defined here as a self-ignition of the fuel and the air being injected by a negative pressure in the burning chamber. During normal operation of the heating generator pressure varations are created in the communicating system extending between the air inlet 21 and the exhaust outlet 24 and as the frequency of said pressure variations falls within a very well defined frequency interval the pressure variations are utilized when the invention is applied in controlling the heating generator. For said object a sensor 25 in the disclosed embodiment is disposed in the inlet chamber 18 to sense the pressure variations appearing in the inlet chamber during normal operation of the heating generator. Preferably, the sensor comprises a piezoelectric-crystal element because of the reliability thereof but another type of sensor can also be used when applying the invention. The sensor may for instance comprise a diaphragm responsive to the pressure variations, the movements of the diaphragm generated by said pressure variations being registered by an optical sensor. However, this arrangement is more expensive than the piezoeletric sensor and also more complicated and yet not as

reliable. It is also possible to sense the movements of the diaphragm by means of a strain gauge but such an arrangement is even more expensive. Anohter possible arrangement is offerred by inductive sensors which have a tendency of natural resonance at low frequencies, possibly interfering with the control function. Finally, there is a possibility of utilizing a microphone, preferably a carbon microphone, as a sensor. However, such a sensor is disadvantageous because it intercepts ambient sounds leading to a false indication in the control system.

The electric signal received from the sensor 25 is supplied to an electronic system shown as a block diagram in FIG. 3. As the signal in normal operation of the heating generator has a frequency in the interval 60-100 Hz the signal from the sensor is first passed through a filter 26 transmitting frequencies between 30 and 200 Hz whereby noice emanating from turbulence in the heating generator, ambient sounds an sounds from the initiation blower is cut off from the signal. When the filtered signal has been amplified in a signal amplifier 27 a frequency is measured in a circuit 28. The measured value is compared with a prescribed frequency in a comparator 29 .and the outcome is registered by a control device 30 controlling the supply of fuel, the ingition and the initiation blower. When normal operation has been registered by the control device, i.e. when there is a sufficient conformity with the prescribed frequency, the supply of fuel is maintained by the solenoid valve 16 while the ignition device 17, 17A and the intiation blower 22 are turned off after some delay. The control device 30 prepared to start the ignition device and initiation blower immediately, if the signal to the turn off device would drop off, for instance due to

functional trouble.

Preferably, the sensor 25 is mounted in the inlet chamber because the environment therein is "good" but other locations are possible. Thus, the sensor could instead be disposed in the pressure chamber arranged on the downstream side of the valve 20 and having a reference number 31 in FIG. 2, the environment in the pressure chamber also being suitable but where the disposal adjacent to the valve and the inlet nozzle can make the mounting complicated and can also make the sensor less available for inspection and exchange. The sensor can also be disposed in the burning chamber 13, in the decoupler 23 or in the exhaust pipe 24 but said locations are less favourable considering the environment present there. Thus, the placing of an piezoelectric sensor shown is the embodiment which at present for several reasons is the preferred one.

To accomplish the described function the electronic system can be implemented with other components than those utilized in the disclosed embodiment.