Patent Description:
From the state of the art, an air-gas mixture burning appliance having a burning unit, a flame detector, an air-gas mixing unit, and a gas valve is known. More specifically, known air-gas mixture burning appliances usually mix air and gas directly before the burning unit. During the ignition phase, the combustible air-gas mixture enters the burning unit where it is ignited. However, internal leakage, which is sometimes also referred to as "let-by", of a closed gas valve can lead to a hazardous accumulation of gas within the air-gas mixture burning appliance. While gas valves typically have redundancy through the use of two independent actuators acting in series in the gas train, safety engineering standards require a third layer of protection. Moreover, conventional air-gas mixture burning appliances are usually equipped with a small number of sensors that can be used for safety functions. In the gas combustion system, the only signals available to the safety controls are usually the fan speed and the flame signal which indicates the strength of any flame in the burning unit. Addition sensors in the burning unit may be costly in terms of complexity and materials.

The document <CIT> shows an appliance having the features specified in the preamble of claim <NUM>.

Documents <CIT>, <CIT>, <CIT> and <CIT> disclose other related burning appliances.

In the remainder of this description, the term "gas" refers to any fuel in gaseous form that, when mixed with air, forms a combustible air-gas mixture. Examples for such a gas include hydrogen, propane, butane, methane, liquefied petroleum gas, etc. Moreover, the term "air" refers to any suitable oxidizer that may be mixed with a fuel gas to form a combustible air-gas mixture.

The present invention relates to an air-gas mixture burning appliance, comprising a burning unit for burning a combustible air-gas mixture, a flame detector for sensing a presence of a flame in the burning unit, an air-gas mixing unit that is arranged upstream of the burning unit and is adapted for mixing of air and gas to form the combustible air-gas mixture, a gas valve that is arranged upstream of the air-gas mixing unit and is adapted for regulating a flow of the gas to the air-gas mixing unit, and a controller that is adapted for determining an earliest flame appearance time for an ignition phase of the burning unit by selecting from at least two different durations of time, wherein the controller determines the earliest flame appearance time as an anticipated minimum duration of time that elapses between an opening of the gas valve and the flame detector sensing the presence of a flame in the burning unit.

Accordingly, the inventive air-gas mixture burning appliance may be able to predict the time that elapses before a flame is established in the burning unit.

Optionally, not in accordance with the invention, the air-gas mixture burning appliance further comprises a secured gas pathway that is arranged between the gas valve and the air-gas mixing unit and is adapted for providing the gas from the gas valve to the air-gas mixing unit, and wherein the controller determines the earliest flame appearance time based on an inferred concentration of the gas in the secured gas pathway.

Thus, the controller can select the earliest flame appearance time based on whether the secured gas pathway is already filled with a gas or whether the secured gas pathway is filled with air at the beginning of the ignition phase.

According to the invention, the air-gas mixture burning appliance further comprises a gas valve leak detector that is adapted for detecting a leak of the gas valve during the ignition phase of the burning unit based on measuring a measured duration of time between the opening of the gas valve and the flame detector sensing the presence of a flame in the burning unit, and checking that the measured duration of time is shorter than the determined earliest flame appearance time.

Accordingly, the air-gas mixture burning appliance may be able to detect a leaky gas valve without using an additional sensing device.

According to one aspect of the invention, the air-gas mixture burning appliance further comprises
a gas valve leak handling device that, in response to the gas valve leak detector detecting a current leak of the gas valve, is adapted for signalling the current leak of the gas valve and for putting the air-gas mixture burning appliance in at least one of a safe state, a non-operational state, or a restricted performance state.

Thus, the air-gas mixture burning appliance can react to a leaky gas valve and ensure a safe operation.

According to another aspect of the invention, the gas valve is shut off periodically for a predetermined period of time to provide the gas valve leak detector an opportunity for detecting a leak of the gas valve.

Accordingly, a leaky gas valve may be detected early.

Optionally, not in accordance with the invention, the controller determines the earliest flame appearance time based at least on the type of the gas.

Thus, the inventive air-gas mixture burning appliance may be operated with different gas types.

Optionally, not in accordance with the invention, the controller determines the earliest flame appearance time based at least on an elapsed time since the flame detector previously sensed a flame in the burning unit.

Accordingly, the inventive air-gas mixture burning appliance may reliably predict the concentration of the gas in the secured gas pathway at the beginning of the ignition phase.

Optionally, not in accordance with the invention, the controller determines the earliest flame appearance time by selecting from a continuous range of values, wherein all values in the continuous range of values are greater than a predetermined minimum earliest flame appearance time.

Thus, the controller may fine-tune the earliest flame appearance time and react to the combination of multiple parameters that may have an influence on the earliest flame appearance time.

Accordingly, the invention allows for the detection of leaks from the gas valve into the secured gas way without the need for a gas sensor.

Exemplary embodiments of the present invention are described in detail hereinafter with reference to the attached drawings. In these attached drawings, identical or identically functioning components and elements are labelled with identical reference signs and they are generally only described once in the following description.

<FIG> shows an exemplary air-gas mixture burning appliance <NUM> with a burning unit <NUM> for burning a combustible air-gas mixture <NUM>, an air-gas mixing unit <NUM>, a gas valve <NUM>, a flame detector <NUM>, and a controller <NUM>. By way of example, the air-gas mixture burning appliance <NUM> may be used in a boiler or, more generally, in a building heating system.

The air-gas mixing unit <NUM> is arranged upstream of the burning unit <NUM> and is adapted for mixing of air <NUM> and gas <NUM> to form the combustible air-gas mixture <NUM>. Preferentially, the combustible air-gas mixture <NUM> is a homogenous mixture of the air <NUM> and the gas <NUM>.

The air-gas mixing unit <NUM> includes an air supply unit and a gas supply unit. Illustratively, the air supply unit includes a fan <NUM> that may be operated with an adaptable fan speed and/or within predetermined ranges of fan speeds to draw and/or push air <NUM> into the air-gas mixing unit <NUM>.

The gas supply unit includes the gas valve <NUM>. The gas valve <NUM> is arranged upstream of the air-gas mixing unit <NUM> and is adapted for regulating a flow of the gas <NUM> to the air-gas mixing unit <NUM>. A secured gas pathway <NUM> is arranged between the gas valve <NUM> and the air-gas mixing unit <NUM> and is adapted for providing the gas <NUM> from the gas valve <NUM> to the air-gas mixing unit <NUM>.

The air supply unit and the gas supply unit are interconnected via a mixer <NUM> which forms a corresponding discrete point of mixing. Preferably, the combustible air-gas mixture <NUM> is formed at the discrete point of mixing and guided via the mixer <NUM> and the combustible air-gas pathway <NUM> to the burning unit <NUM>.

Illustratively, the burning unit <NUM> is provided with a burner surface <NUM> that is arranged downstream of the air-gas mixing unit <NUM> such that the combustible air-gas mixture <NUM> flows towards the burner surface <NUM>. The combustible air-gas mixture <NUM> is burned by the burning unit <NUM> and, more specifically, at the burner surface <NUM>.

During an ignition phase of the air-gas mixture burning applance <NUM>, the combustible air-gas mixture <NUM> from the air-gas mixing unit <NUM> is ignited in the burning unit <NUM> at the burner surface <NUM>. The resulting flame <NUM> is illustratively stabilised against the burner surface <NUM>.

The flame detector <NUM> is provided for sensing presence of a flame <NUM> in the burning unit <NUM>. Thus, the flame detector <NUM> is suitable for determining whether a flame <NUM> is present at the burner surface <NUM> in the burning unit <NUM>. However, it should be noted that suitable flame detection techniques that may be used with the flame detector <NUM> are well-known to the person skilled in the art and are, therefore, not described in more detail, for brevity and conciseness. For instance, the flame detector <NUM> may use any suitable sensing element for sensing presence of the flame <NUM> in the burning unit <NUM>.

The flame detector <NUM> is connected to the controller <NUM>. The flame detector <NUM> generates and/or provides a flame detection signal <NUM> to the controller <NUM> based on whether the flame detector <NUM> senses the presence of a flame <NUM> in the burning unit <NUM> or fails to sense the presence of a flame <NUM> in the burning unit <NUM>.

Alternatively, the controller <NUM> may determine whether a flame <NUM> is present in the burning unit <NUM> by comparing the detected flame signal <NUM> with a predetermined flame detection threshold.

As shown in <FIG>, the controller <NUM> is connected to the gas valve <NUM>. Illustratively, the controller <NUM> may receive a control signal <NUM> from the gas valve <NUM>. By way of example, the control signal <NUM> may be indicative of the status of the gas valve <NUM>. For example, the controller signal <NUM> may indicate whether the gas valve <NUM> is open or closed.

The controller <NUM> sends an actuator signal <NUM> to the gas valve <NUM>. If desired, the actuator signal <NUM> may direct the gas valve <NUM> to open and/or to close. At the beginning of an ignition phase, the controller <NUM> directs the gas valve <NUM> to open.

During the ignition phase, the controller <NUM> tracks the duration of time between the opening of the gas valve <NUM> and the detection of a flame signal <NUM> at the burning unit <NUM>. To avoid a delayed ignition, which refers to igniting a hazardous accumulation of the combustible air-gas mixture <NUM> and which usually leads to an explosion that may damage internal components of the air-gas mixture burning appliance <NUM> and endanger the surrounding environment, the maximum allowed opening time of the gas valve <NUM> without a flame <NUM> being detected is limited to a short period of time, which is sometimes also referred to as the ignition safety time.

In contrast thereto, the gas valve <NUM> needs to be open for a minimum opening time. The minimum opening time is defined as the time that is required for the gas <NUM> to flow from the gas valve <NUM> through the secured gas pathway <NUM> to the air-gas mixing unit <NUM> and from there, as a combustible air-gas mixture <NUM> to the burner surface <NUM>, where a sufficient quantity of the combustible air-gas mixture <NUM> is required to accumulate such that a reliable ignition of the flame <NUM> is ensured.

However, the time between the opening of the gas valve <NUM> and the accumulation of a quantity of the combustible air-gas mixture <NUM> in the burning unit <NUM> that is sufficient for a sustained ignition may depend on the concentration of the gas <NUM> in the secured gas pathway <NUM> at the opening of the gas valve <NUM>. If the air-gas mixture burning appliance <NUM> were to stop burning gas <NUM>, but after a short period of time be re-lit, then the secured gas pathway <NUM> would still be filled with gas <NUM>, and the combustible air-gas pathway <NUM> would still be filled with the combustible air-gas mixture <NUM>, and, as a result, a flame <NUM> could be established comparatively quickly at the burner surface <NUM>.

In between periods of operation, the concentration of the gas <NUM> in the secured gas pathway <NUM> and in the combustible air-gas pathway <NUM> decays over time. Thus, if the air-gas mixture burning appliance <NUM> is re-lit after a sufficient period of time, the secured gas pathway <NUM> and the combustible air-gas pathway <NUM> is nominally filled with air and contains a negligible concentration of the gas <NUM> at the start of the ignition sequence. In this case, the nominally air that is present in the secured gas pathway <NUM> and in the combustible air-gas pathway <NUM> must be displaced by gas <NUM> that is streaming through the opened gas valve <NUM>.

This process of re-priming the secured gas pathway <NUM> and the combustible air-gas pathway <NUM> takes some time, which may depend, for example, on the flow rate of nominally air and the volume of the consecutive pathways <NUM>, <NUM>.

Consequently, a flame <NUM> appears at the burner surface <NUM> only after this priming process has sufficiently progressed, which takes more time in comparison to the ignition attempt made shortly after an end of a previous burn that was described in the previous example.

Thus, the controller <NUM> is adapted for determining an earliest flame appearance time for an ignition phase of the burning unit <NUM> by selecting from at least two different durations of time. Thereby, the controller <NUM> determines the earliest flame appearance time as an anticipated minimum duration of time that elapses between an opening of the gas valve <NUM> and the flame detector <NUM> sensing a flame <NUM> in the burning unit <NUM>.

Since the decay of the concentration of the gas <NUM> in the secured gas pathway <NUM> over time is driven by a diffusion process that is relatively repeatable and predictable, the controller <NUM> may determine the earliest flame appearance time based on an inferred concentration of the gas <NUM> in the secured gas pathway <NUM>.

Moreover, the decay of the concentration of the gas <NUM> and/or the time to reprime the secured gas pathway <NUM> and the combustible air-gas pathway <NUM> may depend on the type of gas <NUM>. For example, the difference in density of hydrogen or any other fuel gas that is less dense than air may result in an exacerbated delay in the appearance of a flame <NUM> at the burner surface <NUM>. Therefore, the controller <NUM> may determine the earliest flame appearance time based at least on the type of the gas <NUM>.

Illustratively, the controller <NUM> may determine the earliest flame appearance time based at least on an elapsed time since the flame detector <NUM> previously sensed a flame <NUM> in the burning unit <NUM>.

By way of example, the controller <NUM> may determine the shortest duration of time after the opening of the gas valve <NUM> that a flame <NUM> appears in the burning unit <NUM> after the gas valve <NUM> has been opened. This shortest duration of time is sometimes also referred to as a predetermined minimum earliest flame appearance time.

Illustratively, the controller <NUM> may determine the earliest flame appearance time by selecting from a continuous range of values, wherein all values in the continuous range of values are greater than a predetermined minimum earliest flame appearance time.

For explaining the invention, consider the scenario in which the gas valve <NUM> has an internal leak. In this scenario, the concentration of the gas <NUM> in the secured gas pathway <NUM> is not decaying as predicted after the gas valve <NUM> is closed and the air-gas mixture burning appliance <NUM> is turned off. Instead, the concentration of the gas <NUM> remains high in the secured gas pathway <NUM>.

The diffusion of the gas <NUM> is a relatively slow process. Thus, a small leak of the gas valve <NUM> results in a high concentration of the gas <NUM> being sustained in the secured gas pathway <NUM>. Therefore, during an ignition attempt that occurs a comparatively long time after the end of the most recent detection of a flame <NUM> in the burning unit <NUM>, a new flame <NUM> will appear sooner than anticipated, and before the earliest anticipated time appearance time.

According to the invention, the air-gas mixture burning appliance <NUM> includes a gas valve leak detector <NUM> that is adapted for detecting a leak of the gas valve <NUM> during the ignition phase of the burning unit <NUM> based on measuring a measured duration of time between the opening of the gas valve <NUM> and the flame detector <NUM> sensing the presence of a flame <NUM> in the burning unit, and checking that the measured duration of time is shorter than the determined earliest flame appearance time.

If desired, the gas valve leak detector <NUM> may be adjusted such that the minimum detectable size of a leak of the gas valve <NUM> is lower than the minimum hazardous size of a leak. However, as internal leaks of the gas valve <NUM> are usually progressive in their development over a period of months, the leak of the gas valve <NUM> could be detected before a hazardous situation occurs.

According to an aspect of the invention, the air-gas mixture burning appliance <NUM> may include a gas valve leak handling device <NUM>. In response to the gas valve leak detector <NUM> detecting a current leak of the gas valve <NUM>, the gas valve leak handling device <NUM> may be adapted for signalling the current leak of the gas valve <NUM> and for putting the air-gas mixture burning appliance <NUM> in at least one of a safe state, a non-operational state, or a restricted performance state. Thereby, the gas valve leak handling device <NUM> may ensure that the current leak of the gas valve <NUM> is noticed and rectified.

If desired, the controller <NUM> may be adapted for signalling the current leak of the gas valve <NUM> and for putting the air-gas mixture burning appliance <NUM> in at least one of a safe state, a non-operational state, or a restricted performance state.

According to another aspect of the invention, the gas valve <NUM> is shut off periodically for a predetermined period of time to provide the gas valve leak detector <NUM> an opportunity for detecting a leak of the gas valve <NUM>. For example, the controller <NUM> may direct the gas valve <NUM> to shut off using actuator signal <NUM> and enforce a minimum period of standby. The minimum period of standby may be selected based on the type of gas, the dimensions of the secured gas pathway <NUM>, the dimensions of the combustible air-gas pathway <NUM>, etc. As an example, the minimum period of standby may be selected to last for approximately <NUM> to <NUM> minutes.

Advantageously, the gas valve <NUM> may be shut off during times of the day with typical low demand for the air-gas mixture burning appliance <NUM> to produce heat. For example, the controller may shut off the gas valve <NUM> for a short period of time during the night.

<FIG> shows a schematic view of an air-gas mixture burning appliance <NUM> having a fan <NUM> downstream of an air-gas mixer <NUM> and an air flow channel <NUM> to a reference pressure port <NUM> of a gas valve <NUM>. As shown in <FIG>, the air-gas mixture burning appliance <NUM> includes an air inlet for providing air <NUM>, a gas inlet <NUM> for providing gas <NUM>, and a flue outlet <NUM> for the evacuation of exhaust gas <NUM>. The air-gas mixture burning appliance <NUM> further includes an air-gas mixing unit <NUM>, a burning unit <NUM>, and a heat exchanger <NUM>.

The air-gas mixing unit <NUM> is adapted for mixing of air <NUM> and gas <NUM> to form a combustible air-gas mixture <NUM>. Preferably, the combustible air-gas mixture <NUM> is a homogenous mixture of the air <NUM> and the gas <NUM>.

Illustratively, the burning unit <NUM> is provided with a burner surface <NUM> that is arranged downstream of the air-gas mixing unit <NUM> such that the combustible air-gas mixture <NUM> flows towards the burner surface <NUM>. If desired, the fan <NUM> may drive the combustible air-gas mixture <NUM> through the combustible air-gas pathway <NUM> towards the burner surface <NUM>.

The combustible air-gas mixture <NUM> is burned by the burning unit <NUM> and, more specifically, at the burner surface <NUM>. The heat exchanger <NUM> may transfer the heat that is generated at the burner surface <NUM> to another medium. For example, the heat exchanger <NUM> may transfer the heat that is generated at the burner surface <NUM> to water in a water circuit. The flue outlet <NUM> may evacuate the exhaust gas <NUM> from the air-gas mixture burning appliance <NUM>.

The gas valve <NUM> may include a reference pressure port <NUM>. Preferably, the air flow channel <NUM> is adapted for providing the flow of the air <NUM> to the reference pressure port <NUM>, and the gas valve <NUM> is adapted for regulating the flow of the gas <NUM> based on the pressure of the flow of the air <NUM> at the reference pressure port <NUM>.

The controller <NUM> is adapted for determining an earliest flame appearance time for an ignition phase of the burning unit <NUM> by selecting from at least two different durations of time. Thereby, the controller <NUM> determines the earliest flame appearance time as an anticipated minimum duration of time that elapses between an opening of the gas valve <NUM> and the flame detector <NUM> sensing the presence of a flame <NUM> in the burning unit <NUM>.

The controller <NUM> sends an actuator signal <NUM> to the gas valve <NUM>. The actuator signal <NUM> directs the gas valve <NUM> to open and/or to close. At the beginning of an ignition phase, the controller <NUM> directs the gas valve <NUM> to open. As another example, the controller <NUM> may direct the gas valve <NUM> to close periodically using actuator signal <NUM> to provide the gas valve leak detector <NUM> an opportunity for detecting a leak of the gas valve <NUM>. Thus, actuator signal <NUM> may override the reference pressure port <NUM> of the gas valve <NUM>.

<FIG> shows a flowchart illustrating a method <NUM> of operating an air-gas mixture burning appliance. The air-gas mixture burning appliance comprises a burning unit for burning a combustible air-gas mixture, a flame detector for sensing a presence of a flame in the burning unit, an air-gas mixing unit that is arranged upstream of the burning unit and is adapted for mixing of air and gas to form the combustible air-gas mixture, and a gas valve that is arranged upstream of the air-gas mixing unit and is adapted for regulating a flow of the gas to the air-gas mixing unit.

The air-gas mixture burning appliance <NUM> of <FIG> or <FIG> comprises a burning unit <NUM> for burning a combustible air-gas mixture <NUM>, a flame detector <NUM> for sensing a presence of a flame <NUM> in the burning unit <NUM>, an air-gas mixing unit <NUM> that is arranged upstream of the burning unit <NUM> and is adapted for mixing of air <NUM> and gas <NUM> to form the combustible air-gas mixture <NUM>, and a gas valve <NUM> that is arranged upstream of the air-gas mixing unit <NUM> and is adapted for regulating a flow of the gas <NUM> to the air-gas mixing unit <NUM>.

During a determining step <NUM>, the air-gas mixture burning appliance determines, not in accordance with the invention, with a controller, an earliest flame appearance time for an ignition phase of the burning unit by determining an anticipated minimum duration of time that elapses between an opening of the gas valve and the flame detector sensing the presence of a flame in the burning unit.

Not in accordance with the invention, air-gas mixture burning appliance <NUM> of <FIG> or <FIG> may use controller <NUM> to determine an earliest flame appearance time for an ignition phase of the burning unit <NUM> by determining an anticipated minimum duration of time that elapses between an opening of the gas valve <NUM> and the flame detector <NUM> sensing the presence of a flame <NUM> in the burning unit <NUM>.

If desired, the air-gas mixture burning appliance may further comprise a secured gas pathway that is arranged between the gas valve and the air-gas mixing unit.

For example, the air-gas mixture burning appliance <NUM> of <FIG> or <FIG> may comprise a secured gas pathway <NUM> that is arranged between the gas valve <NUM> and the air-gas mixing unit <NUM>.

In such an air-gas mixture burning appliance, the determining step <NUM> may further comprise the operation of determining, not in accordance with the invention, with the controller, the earliest flame appearance time based on an inferred concentration of the gas in the secured gas pathway.

Not in accordance with the invention, the controller <NUM> of the air-gas mixture burning appliance <NUM> of <FIG> or <FIG> may determine the earliest flame appearance time based on an inferred concentration of the gas <NUM> in the secured gas pathway <NUM>.

During a detecting step <NUM>, the air-gas mixture burning appliance detects, in accordance with the invention, with a gas valve leak detector, a leak of the gas valve during the ignition phase of the burning unit by measuring a measured duration of time between the opening of the gas valve and the flame detector sensing the presence of a flame in the burning unit, and checking that this measured duration of time is shorter than the determined earliest flame appearance time.

In accordance with the invention, the air-gas mixture burning appliance <NUM> of <FIG> or <FIG> detects, may with gas valve leak detector <NUM>, a leak of the gas valve <NUM> during the ignition phase of the burning unit <NUM> by measuring a measured duration of time between the opening of the gas valve <NUM> and the flame detector <NUM> sensing the presence of a flame <NUM> in the burning unit <NUM>, and checking that this measured duration of time is shorter than the determined earliest flame appearance time.

Preferably, the method may further include a handling step, comprising responding to the leak of the gas valve with a gas valve leak handling device by signalling the leak of the gas valve and accordingly putting the air-gas mixture burning appliance in one or more of a safe state, a non-operational state, or a restricted performance state.

Claim 1:
An air-gas mixture burning appliance (<NUM>), comprising:
a burning unit (<NUM>) for burning a combustible air-gas mixture (<NUM>);
a flame detector (<NUM>) for sensing a presence of a flame (<NUM>) in the burning unit (<NUM>);
an air-gas mixing unit (<NUM>) that is arranged upstream of the burning unit (<NUM>) and is adapted for mixing of air (<NUM>) and gas (<NUM>) to form the combustible air-gas mixture (<NUM>);
a gas valve (<NUM>) that is arranged upstream of the air-gas mixing unit (<NUM>) and is adapted for regulating a flow of the gas (<NUM>) to the air-gas mixing unit (<NUM>);
a controller (<NUM>) that is adapted for determining an earliest flame appearance time for an ignition phase of the burning unit (<NUM>) by selecting from at least two different durations of time; and
that is adapted to determine the earliest flame appearance time as an anticipated minimum duration of time that elapses between an opening of the gas valve (<NUM>) and the flame detector (<NUM>) sensing the presence of a flame (<NUM>) in the burning unit (<NUM>),
characterized in that it further comprises
a gas valve leak detector (<NUM>) that is adapted for detecting a leak of the gas valve (<NUM>) during the ignition phase of the burning unit (<NUM>) based on measuring a measured duration of time between the opening of the gas valve (<NUM>) and the flame detector (<NUM>) sensing the presence of a flame (<NUM>) in the burning unit, and checking that the measured duration of time is shorter than the determined earliest flame appearance time.