The present patent application relates to a method for operating a gas burner.
According to
In other words, according to the prior art the mixing ratio of the gas/air mixture is kept constant over the entire fan speed range of the fan, either to provide a 1:1 gas-air control having a ratio between the gas pressure and the air pressure of 1:1 over the entire modulation range of the gas burner or to provide a 1:N (N>1) gas-air control having a ratio between the gas pressure and the air pressure of 1:N over the entire modulation range of the gas burner. In both cases a so-called λ-value is usually greater than 1.
Against this background, a novel method for operating a gas burner is provided.
The method for operating a gas burner is defined in the claim 1.
The novel method for operating a gas burner provides over the entire modulation range of the gas burner an optimized mixing ratio of the gas/air mixture. At relative low fan speeds and therefore at the lower end of the modulation range a gas/air mixture is provided having a mixing ratio of gas and air which provides a stable combustion, especially a stable ignition, of the gas/air mixture.
For fan speeds being smaller than the lower thresholds a gas/air mixture is provided being preferably leaner or alternatively richer than the gas/air mixture which is provided for fan speeds being larger than the upper threshold. It is also possible that for fan speeds being smaller than the lower thresholds a gas/air mixture is provided having the same mixing ratio of gas and air as the gas/air mixture which is provided for fan speeds being larger than the upper threshold.
A leaner gas/air mixture has a gas amount being reduced compared to a richer gas/air mixture.
Preferred developments of the invention are provided by the dependent claims and the description which follows. Exemplary embodiments are explained in more detail on the basis of the drawing, in which:
The gas/air mixture is provided to the burner chamber 11 of the gas burner 10 by mixing an air flow with a gas flow. A fan 14 sucks in air flowing through an air duct 15 and gas flowing though a gas duct 16. A gas valve 17 for adjusting the gas flow through the gas duct 16 and a safety valve 18 are assigned to the gas duct 16. The position of the gas valve 17 is adjusted by a pressure regulator 19.
The gas/air mixture having a defined mixing ratio of gas and air is provided to the burner chamber 11 of the gas burner 10. The gas/air mixture is provided by mixing the air flow provided by an air duct 15 with a gas flow provided by a gas duct 16. The air flow and the gas flow become preferably mixed by a mixing device. Such a mixing device can be designed as a Venturi nozzle (not shown).
The quantity of the air flow and thereby the quantity of the gas/air mixture flow is adjusted by the fan 14, namely by the speed of the fan 14. The fan speed can be adjusted by an actuator 22 of the fan 14.
The defined mixing ratio of the gas/air mixture is controlled by a controller 20 on basis of a signal provided by an electrical or electronic sensor 23. In the shown embodiment, the electrical or electronic sensor 23 is coupled to the gas duct 16 and to a reference point 24. The electrical or electronic sensor 23 is preferably designed as a flow-meter.
An actual value corresponding to a pressure ratio between the gas pressure in the gas duct 16 and the air pressure at the reference point 24 is provided by the electrical or electronic sensor 23. This actual value is compared by the controller 20 with a nominal value stored in the controller 20.
The controller 20 generates a control variable for the gas valve 17, namely for an actuator 21 of the gas valve 17, on basis of the control deviation between the actual value provided by the electrical or electronic sensor 23 and the nominal value stored in the controller 20.
The gas valve position of the gas valve 17 is adjusted by the actuator 21 of the same on basis of this control variable in order to provide the defined mixing ratio of gas and air in the gas/air mixture.
According to
Exhaust gas resulting from the combustion of the gas/air mixture can exit from the burner chamber 11 though an exhaust pipe 28. An exhaust gas sensor 27 assigned to the exhaust pipe 28 can be used to analyze the emissions of the exhaust gas, especially NOx emissions of the same. The exhaust gas sensor 27 is a component of the gas burner 10.
The mixing ratio of gas and air of the gas/air mixture provided to the burner chamber 11 is not kept constant over the modulation range of the gas burner.
The mixing ratio of gas and air of the gas/air mixture provided to the burner chamber 11 is changed as a function on the speed of the fan 14.
For fan speeds of the fan 14 being smaller than a lower threshold a gas/air mixture is provided having a mixing ratio of gas and air adapted to provide a stable combustion, especially a stable and secure ignition, of the gas/air mixture. Preferably, for fan speeds being smaller than the lower threshold a gas/air mixture having a mixing ratio of gas and air is provided resulting in a combustion with an almost constant output of the flame ionization sensor 13 or alternatively with an almost constant output of the exhaust gas sensor 27.
For fan speeds of the fan 14 being larger than an upper threshold a gas/air mixture is provided having a mixing ratio of gas and air adapted to provide a combustion with reduced emissions. For fan speeds being larger than the upper threshold a gas/air mixture having a mixing ratio of gas and air is provided resulting in a combustion with an output of the exhaust gas sensor 27 being smaller that an emission threshold.
For fan speeds being larger than the lower thresholds, especially for fan speeds being larger than the lower thresholds and lower than the upper threshold, the mixing ratio of gas and air of the gas/air mixture is freely adjustable as a function of the fan speed of the fan 14. It is possible to use intermediate thresholds between the upper threshold and the lower threshold in order divide this fan speed range into sub-ranges.
According to the invention, for fan speeds of the fan 14 being larger than the lower thresholds and lower than the upper threshold a gas/air mixture is provided being leaner than the gas/air mixture which is provided for fan speeds of the fan 14 being larger than the upper threshold. Further on, for fan speeds of the fan 14 being larger than the lower thresholds and lower than the upper threshold a gas/air mixture is provided being leaner than the gas/air mixture which is provided for fan speeds of the fan 14 being smaller than the lower threshold.
For fan speeds of the fan 14 being smaller than the lower thresholds a gas/air mixture is provided being preferably leaner than the gas/air mixture of the fan 14 which is provided for fan speeds being larger than the upper threshold. Alternatively, for fan speeds of the fan 14 being smaller than the lower thresholds a gas/air mixture is provided being richer than the gas/air mixture of the fan 14 which is provided for fan speeds being larger than the upper threshold. It is also possible that for fan speeds being smaller than the lower thresholds a gas/air mixture is provided having the same mixing ratio of gas and air as the gas/air mixture which is provided for fan speeds being larger than the upper threshold.
According to a preferred embodiment, in a first section of the modulation range of the gas burner, namely for fan speeds being larger than the upper threshold, a 1:1 gas-air control having a ratio between the gas pressure and the air pressure of 1:1 is provided. In a second section of the modulation range of the gas burner, namely for fan speeds of the fan 14 being larger than the lower thresholds and lower than the upper threshold, a 1:N (N>1) gas-air control having a ratio between the gas pressure and the air pressure of 1:N is provided. In a third section of the modulation range of the gas burner, namely for fan speeds being smaller than the lower thresholds, a 1:M (N>M>1 or N>M=1 or N>1 >M) gas-air control having a ratio between the gas pressure and the air pressure of 1:M is provided. The second section of the modulation range can be divided into subsections by e.g. intermediate thresholds.
As a function of on the fan speed of the fan 14 the controller 20 generates an offset value which becomes added to the nominal value for the signal provided by the electrical or electronic sensor 23. Alternatively, as a function on the fan speed of the fan 14 the controller 20 generates an offset value which becomes added to control variable for a gas valve 17.
The respective offset value which is a function of the fan speed and which is stored in the controller 20 is freely programmable as a function of the fan speed.
The above variation of the mixing ratio of the gas/air mixture provided to the burner chamber 11 as a function of the speed of the fan 14 is preferably allowed only at defined operating conditions of the gas burner 10.
If the defined operating conditions of the gas burner 10 are not fulfilled, the controller 20 preferably blocks the above variation of the mixing ratio of the gas/air mixture as a function of the speed of the fan 14.
According to a first preferred aspect, the variation of the mixing ratio of the gas/air mixture is only allowed if the heat exchanger temperature measured by the temperature sensor 26 is greater than a temperature threshold. If the temperature of the heat exchanger 25 is below the temperature threshold, the defined mixing ratio of gas and air of the gas/air mixture is kept constant over the entire modulation range of the gas burner 10 and thereby over the entire fan speed range of the fan 14. However, if the temperature of the heat exchanger 25 is above the temperature threshold, the defined mixing ratio of gas and air of the gas/air mixture is not kept constant over the modulation range of the gas burner 10. In this case the mixing ratio of gas and air of the gas/air mixture is variable as a function of the fan speed as discussed above.
According to a second preferred aspect, the variation of the mixing ratio of the gas/air mixture is only allowed if the gas burner 10 has been operated with a defined load for at least a defined time period, especially if the burner load has been greater than a burner load threshold for a time period being greater than a time threshold. If the burner load is below the burner load threshold and/or if the time period is below the time threshold, the defined mixing ratio of gas and air of the gas/air mixture is kept constant over the entire modulation range of the gas burner 10 and thereby over the entire fan speed range. However, if the burner load is above the burner load threshold and if the time period is above the time threshold the defined mixing ratio of gas and air of the gas/air mixture is not kept constant over the modulation range of the gas burner 10. In this case the mixing ratio of gas and air of the gas/air mixture is variable as a function of the fan speed as discussed above.
According to a third preferred aspect, the variation of the mixing ratio of the gas/air mixture is only allowed if the fan speed is stable, especially if the variation of the fan speed is lower than a variation threshold for a time period being greater than a time threshold. If the variation of the fan speed is above the variation threshold and/or if the time period is below the time threshold, the defined mixing ratio of gas and air of the gas/air mixture is kept constant over the entire modulation range of the gas burner 10 and thereby over the entire fan speed range. However, if the variation of the fan speed is below the variation threshold and if the time period is above the time threshold the defined mixing ratio of gas and air of the gas/air mixture is not kept constant over the modulation range of the gas burner 10. In this case the mixing ratio of gas and air of the gas/air mixture is variable as a function of the fan speed as discussed above.
It is possible to use two or all three of the above operating conditions in combination. In this case, the above variation of the mixing ratio of the gas/air mixture provided to the burner chamber 11 as a function of the speed of the fan 14 is allowed only if two of the operating conditions or all three of the operating conditions of the gas burner 10 are commonly fulfilled.
As described above, the controller 20 generates a control variable for the gas valve 17, namely for an actuator 21 of the gas valve 17. The actuator 21 of the gas valve 17 can be a stepper motor.
At certain times during burner-on phases, especially in fixed time intervals, the controller 20 preferably checks the function of the electrical or electronic sensor 23, especially the gain of the electrical or electronic sensor 23. In order to check the function of the electrical or electronic sensor 23, the controller 17 preferably generates an input variable for the actuator 21 by which the actuator 21 and thereby the gas valve 17 become adjusted by a defined degree or amount. If the actuator 21 is a stepper motor, the controller 20 generates an input variable for the stepper motor by which stepper motor is operated over a defined number of steps.
The output signal provided by electrical or electronic sensor 23 in response to this operation of the actuator 21 and thereby gas valve 17 is compared by the controller 20 with a nominal output signal expected in response to this operation of the actuator 21.
If a deviation between actual output signal of the electrical or electronic sensor 23 and the nominal output signal is greater than a threshold, the controller 20 determines an improper function of the electrical or electronic sensor 23, especially a non tolerable change of the sensor gain of the electrical or electronic sensor 23. If the deviation between actual output signal of the electrical or electronic sensor 23 and the nominal output signal is smaller than the threshold, the controller 20 determines a proper function of the electrical or electronic sensor 23, especially a tolerable change of the sensor gain of the electrical or electronic sensor 23 or no change of the sensor gain.
If the controller 20 determines an improper function of the electrical or electronic sensor 23, especially a non tolerable change of the sensor gain of the electrical or electronic sensor 23, the controller 20 preferably initiates at least one defined action.
One preferred action initiated by the controller 20 in case the same determines an improper function of the electrical or electronic sensor 23, especially a non tolerable change of the sensor gain, is that the controller 20 blocks the above variation of the mixing ratio of the gas/air mixture provided to the burner chamber 11 as a function of the speed of the fan 14. Only if the controller 20 determines a proper function of the electrical or electronic sensor 23, the controller 20 will allow the variation of the mixing ratio of the gas/air mixture as a function of the speed of the fan 14.
Other preferred actions initiated by the controller 20 in response to a detected improper function of the electrical or electronic sensor 23 are that the controller 20 generates a service signal indicating that the burner should be inspected by a service person, and/or that the controller 20 performs a calibration for the sensor gain of the electrical or electronic sensor 23, and/or that the controller 20 performs a compensation for the sensor gain shift by a defined offset value, and/or that the gas burner 10 is shut down.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.