EP4083506A1 - Method and device for igniting a fuel / air mixture in a heating apparatus operable with different fuels - Google Patents

Abstract

The invention relates to a method and an arrangement for igniting a fuel-air mixture in a heating device (1) that can be operated with different fuels, having a premix burner (6) which supplies air (L) through an air supply (2) and fuel through a fuel supply (3). are supplied premixed in a mixing ratio (lambda), the mixing ratio (lambda) of fuel to air (L) being varied within a predeterminable time interval (Δt) for ignition to cover a predeterminable mixture range, specifically by varying the air supply (2). The fuel supply (3) is preferably kept constant in the time interval (Δt) for ignition or the air supply (2) is varied as much as possible and the fuel supply (3) varies only as much as is necessary to cover the entire mixture range. The present invention allows a heater (1) that can be operated with different fuels, in particular different combustible gases (G), to be reliably ignited without taking the risk of an undesirably high ignition load (Z) with possible consequential damage.

Description

The invention relates to a method and an arrangement for igniting a fuel-air mixture in a heater that can be operated with different fuels. In particular, so-called adaptive combustion systems, z. B. by means of an ionization controlled systems are able to burn a wide range of fuel gases. Natural gas from different sources or with admixtures of hydrogen can be used. It is not only a question of large systems, but also of wall-mounted units for heating water and, in general, heaters for heating buildings and/or providing hot water.

Combustion in such systems is generally performed in a closed-loop control system designed to maintain a desired fuel gas/air mixture (often characterized by a lambda value, which indicates the ratio of air to fuel gas relative to a stoichiometric ratio). Such a control circuit typically has a feedback loop in which the characteristics of a fuel are taken into account. In this way, the control circuit can recognize different fuels and react accordingly and burn them cleanly at the same time.

However, during the ignition of the fuel-air mixture, which is largely controlled and takes place without feedback, there is (still) information about the fuel gas supplied not before. However, since different combustible gases only ignite reliably with different lambda values, the lambda value is varied over a definable range (mixture range) during ignition within a time interval, within which ignition can be expected for all combustible gases that occur. According to the prior art, this is achieved by varying the supply of fuel gas with a constant supply of air. The supply of fuel gas can be changed very quickly, which is advantageous given the typically very short time intervals for ignition (e.g. 0.5 to 5 s [seconds]) and thus for varying the mixture.

One disadvantage, however, is that changing the fuel gas supply also changes the fuel energy (ignition load), which indicates how much energy is available and (suddenly) released during ignition. If more fuel is supplied, the energy that is released during ignition changes accordingly, which can lead to violent explosions or even damage to components in the case of a high ignition load and delayed ignition. Estimates show that the ignition load can increase (or decrease) by more than 30 % [percent] with typical variations in the fuel gas supply.

The object of the present invention is to at least partially solve the problems described with reference to the prior art. In particular, a method and an arrangement are to be created in which the ignition load does not change or changes only slightly despite a variation in the lambda value during a time interval for ignition.

A method and an arrangement as well as a computer program product according to the independent claims serve to solve this task. Advantageous configurations and developments of the invention are in the respective dependent claims stated. The description, in particular in connection with the drawing, illustrates the invention and specifies further exemplary embodiments.

A method for igniting a fuel-air mixture in a heating device that can be operated with different fuels, in particular with different combustible gases, contributes to this. This heater has a premixed burner to which air can be supplied premixed through an air supply and fuel through a fuel supply in a mixing ratio. In this case, the mixing ratio of fuel to air is varied within a predeterminable time interval for ignition in order to cover a predeterminable mixture range, specifically (solely) by varying the air supply.

The method can be used to ignite various fuel-air mixtures. The fuel can B. liquid (oil, etc.) and / or solid (pellets, etc.) and / or gaseous. The fuel is particularly preferably a combustible gas, so that this application is particularly emphasized here—without wanting to limit the use of the method.

The air supply is generally effected by a blower, which generates a volume flow dependent on its speed. The volume flow and thus the air supply can therefore be changed by varying the speed. This is a preferred way of varying the air supply, but this excludes other ways such as e.g. B. the change in the position of a throttle valve, aperture or the like.

The fuel supply is preferably kept constant in the time interval for ignition. This is always the easiest and preferred way when the possibilities sufficient to change the volume flow of air in order to pass through or cover the entire mixture range within the time interval.

In a special variant, the air supply is varied in the maximum possible way in the time interval and the fuel supply or fuel gas supply varies only as much as is required to cover the entire mixture range. This can be necessary in particular if a blower whose rotating parts cannot be accelerated or decelerated at any speed (the so-called speed dynamics are therefore not sufficient for a desired rapid change) alone is not sufficient for the necessary mixture change in the time interval. The supply of fuel or fuel gas is then also varied, but only to the smallest possible extent because of the described disadvantage of this procedure. For this purpose, the position of a fuel gas valve can preferably be changed, but other ways of changing the fuel gas supply are also possible here in principle.

In particular, the time interval and the mixture range are selected in such a way that a maximum ignition load is not exceeded by the end of the time interval, regardless of the type of fuel or combustible gas supplied. This ensures that even under the most unfavorable conditions with the fuel or fuel gas that generates the highest ignition load, there can be no violent (hard) ignitions, so that reliable ignition can be carried out successfully or the ignition process can be repeated.

To solve the problem is also an arrangement for igniting a fuel-air mixture in a operable with different fuels heater with a premix burner, the air through an air supply and fuel through a Fuel supply can be supplied premixed in a mixing ratio, with an ignition control being present which is set up to vary the air supply for covering a predeterminable mixture range during a time interval for igniting.

In a particular embodiment, the ignition controller is set up to vary a blower for air supply with maximum speed dynamics and also to vary the fuel supply if the speed dynamics are not sufficient to cover a mixture range within the time interval.

A further aspect also relates to a computer program product comprising instructions which cause the arrangement described to carry out the method described. Carrying out the ignition sequence described requires a program and data, both of which must be updated from time to time.

The explanations for the method can be used for a more detailed characterization of the arrangement, and vice versa. The arrangement can also be set up in such a way that the method is carried out with it.

Fig. 1:

ein Heizgerät mit einer Zündautomatik und

Fig. 2

Diagramme zur Veranschaulichung der Zündlast des hier vorgeschlagenen Verfahrens im Vergleich zum Stand der Technik.

A schematic embodiment of the invention, to which it is not limited, and the way the method works will now be explained in more detail with reference to the drawing. They represent:

Figure 1:

a heater with an automatic ignition and

2

Diagrams to illustrate the ignition load of the method proposed here compared to the prior art.

1 FIG. 1 shows schematically a heater 1 with an air supply 2 equipped with a fan 4 and conveying air to a burner 6. FIG. Combustion gas G is mixed with the air L via a fuel supply, here in the form of a fuel gas supply 3 with a fuel gas valve 5 . The combustible gas/air mixture produced is ignited and burned in a combustion chamber 7 by means of an ignition device 10 . Exhaust gases that are produced give off most of their heat to a heat exchanger 9 and are then discharged into the environment through an exhaust system 8 . An ignition controller 12, usually integrated into a control and regulation unit 11 of the heater 1, controls each start of the heater 1 and the actual ignition process that takes place. The ignition controller 12 controls the fan 4 and the fuel gas valve 5 via data or control lines 13. An ignition line 14 connects the ignition controller 12 to the ignition device 10, in most cases an ignition electrode for generating ignition sparks.

2 illustrates the invention using examples of the time sequences and the mixture ratios and ignition loads that occur. The upper diagram shows the state of the art and the ignition load Z (curve A) that occurs when the mixing ratio of air L and fuel gas G is changed by varying the fuel gas feed 3 . The ignition load Z increases in direct proportion to an increasing fuel gas supply 3, while the mixing ratio lambda (curve B) decreases. The time t is plotted on the x-axis (e.g. in seconds), the time interval Δt for the ignition being 10 s here. The ignition load Z is plotted on the left-hand Y-axis, and the mixing ratio lambda on the right-hand Y-axis.

In the middle diagram, the time t is again plotted on the x-axis, a mass flow of air L on the right-hand y-axis and a mass flow on on the left-hand y-axis Fuel gas G. According to the invention, the fuel gas supply 3 (curve C) is kept constant here, but the air supply 2 (curve D) is lowered in the time interval Δt.

The result can be seen from the lower diagram, in which the ignition load Z (curve E) remains constant while the mixture ratio lambda (curve F) changes (in the same way as in the upper diagram according to the prior art). The representation in the lower diagram corresponds to that in the upper one, and it can be seen that the ignition load Z is constant and therefore significantly lower than in the prior art when passing through the same mixing range. Here, too, the ignition load Z is practically proportional to the fuel gas supply 3 and this remains constant over the entire time interval Δt.

The present invention allows a heater 1, which can be operated with different fuel gases G, to be safely ignited without taking the risk of an undesirably high ignition load Z with possible consequential damage.

Reference List

1

heater

2

air supply

3

fuel gas supply

4

fan

5

fuel gas valve

6

(Premix) burner

7

combustion chamber

8th

exhaust system

9

heat exchanger

10

ignition device

11

control and regulation unit

12

ignition control

13

control lines

14

ignition wire

A

Ignition load curve according to the prior art

B

Mixture ratio (lambda) curve when changing the fuel gas supply

C

Fuel gas curve

D

curve air

E

Ignition load curve when changing the air supply

f

Mixture ratio (lambda) curve when changing the air supply

G

fuel gas

L

Air

Z

ignition load

t

time

Δt

(Delta t) time interval

Claims (7)

Method for igniting a fuel-air mixture in a heating device (1) that can be operated with different fuels, having a premix burner (6) which supplies air (L) through an air supply (2) and fuel through a fuel supply (3) in a mixing ratio (lambda ) are supplied premixed, with the mixing ratio (lambda) of fuel to air (L) being varied within a predeterminable time interval (Δt) for ignition to cover a predeterminable mixture range, specifically by varying the air supply (2). Method according to Claim 1, in which the fuel supply (3) is kept constant in the time interval (Δt) for ignition. Method according to Claim 1, in which, in the time interval (Δt), the air supply (2) varies as much as possible and the fuel supply (3) is varied only to the extent required to cover the entire mixture range. Method according to one of the preceding claims, wherein the time interval (Δt) and the mixture range are selected such that a maximum ignition load (Z) is not exceeded by the end of the time interval (Δt), regardless of the type of fuel supplied. Arrangement for igniting a fuel-air mixture in a heating device (1) that can be operated with different fuels and has a premix burner (6) to which air (L) can be supplied premixed by an air supply (2) and fuel by a fuel supply (3) in a mixing ratio (lambda), with an ignition control (12) being present which is set up during a time interval ( Δt) to vary the air supply (2) for ignition to cover a predeterminable mixture range. Arrangement according to claim 5, wherein the ignition control (12) is set up to vary a blower (4) of the air supply (2) with maximum speed dynamics and also to vary the fuel supply (3) if the speed dynamics are not for covering a mixture range within of the time interval (Δt) is sufficient. A computer program product comprising instructions which cause the arrangement according to any one of claims 5 or 6 to carry out the method according to any one of claims 1 to 4.

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