WO2022268881A1

WO2022268881A1 - Burner assembly for a domestic fireplace

Info

Publication number: WO2022268881A1
Application number: PCT/EP2022/067014
Authority: WO
Inventors: Adriaan Cornelis Christiaan Hund
Original assignee: Kal-Fire Beheer B.V.
Priority date: 2021-06-25
Filing date: 2022-06-22
Publication date: 2022-12-29
Also published as: EP4359705A1; NL2028541B1; AU2022299382A1

Abstract

The present invention relates to a burner assembly for a domestic fireplace, configured to burn a mixture of a first combustible fuel and a second combustible fuel, comprising a combustible long chain hydrocarbon fuel, the assembly comprising at least one burner and a mixing device, the mixing device comprising: a housing, defining a mixing interior, at least one discharge opening in the housing, connected to the at least one burner and configured to provide access from the mixing interior towards the burner, a first fuel supply, projecting into the mixing interior and configured to supply the first fuel into the mixing interior, and a second fuel supply, projecting into the mixing interior and configured to supply the second fuel into the mixing interior, characterized in that, the mixing device further comprises: a heating element, e.g. a second heating element, arranged at least partially in the mixing interior and configured to heat the second fuel to a mixing temperature, wherein the mixing device is configured to mix the first fuel with the heated second fuel to form the fuel mixture, and wherein the at least one burner is configured to combust the fuel mixture.

Description

Title: Burner assembly for a domestic fireplace

Field of the invention

The present invention relates to a burner assembly for a domestic fireplace. The present invention further relates to a mixing device of a burner assembly and to a method of creating a fire by means of a burner assembly.

State of the art

At present, various types of domestic fireplaces are known. Such fireplaces are typically installed in domestic places, such as houses or offices. Generally, these fireplaces have the purpose of displaying flames to contribute to the ambiance in the rooms. Several types of fuels are often used in such domestic fireplaces.

Originally, domestic fireplaces mainly relied on wooden logs as fuel, which logs are burnt directly. Alternatively, gas hearths were developed, which are configured to burn a gas, such as natural gas. In an aim to reduce emissions, ethanol fireplaces have been developed, which burn alcohols instead of hydrocarbons. Such alcohols, like ethanol, burn cleaner than wood or natural gas, but have the drawback that the flames resulting from the combusting of alcohols do not have properties that are desired, i.e. to mimic wood-burning fireplaces. The flames in ethanol fireplaces are typically too vivid, i.e. move too fast, and are coloured relatively bright and transparent, whereas wood flames are more orange.

It was found by the present inventors that a mixture of two fuels could achieve both a reduction in emissions, whilst still offering appealing characteristics for the flames. However, the existing burner assemblies of domestic fireplaces are not able to burn such a fuel mixture in a hybrid domestic fireplace.

Object of the invention

It is therefore an object of the invention to provide a burner assembly for a hybrid domestic fireplace that is configured to burn a fuel mixture, or at least an alternative burner assembly.

Detailed description

The present invention provides a burner assembly for a domestic fireplace, configured to burn a mixture of a first combustible fuel and a second combustible fuel, comprising a combustible long chain hydrocarbon fuel, the assembly comprising at least one burner and a mixing device, the mixing device comprising: a housing, defining a mixing interior, at least one discharge opening in the housing, connected to the at least one burner and configured to provide access from the mixing interior towards the burner, a first fuel supply, projecting into the mixing interior and configured to supply the first fuel into the mixing interior, and a second fuel supply, projecting into the mixing interior and configured to supply the second fuel into the mixing interior, characterized in that, the mixing device further comprises: a heating element, e.g. a second heating element, arranged at least partially in the mixing interior and configured to heat the second fuel to a mixing temperature, wherein the mixing device is configured to mix the first fuel with the heated second fuel to form the fuel mixture, and wherein the at least one burner is configured to combust the fuel mixture.

The present burner assembly is intended for use in a hybrid domestic fireplace, which means that it is configured to burn a mixture of a first fuel and a second fuel. This forms a first difference with existing burner assemblies, which generally relied on a single fuel, such as natural gas or ethanol.

The burner assembly comprises a mixing device, in which the first fuel and the second fuel are mixed, and a burner, in which the obtained fuel mixture from the mixing device is combusted, so that flames can be visible in the fireplace. The burner may thereto comprise dedicated ignition means to ignite the fuel mixture supplied to it from the mixing device.

The mixing device is configured to mix the first fuel and the second fuel to obtain the fuel mixture. This mixing may involve the mixing of a gaseous first fuel with a gaseous second fuel, of a gaseous first fuel with a liquid second fuel, of a liquid first fuel with a gaseous second fuel or of a liquid first fuel with a liquid second fuel.

The first fuel may be any type of fuel that is combustible and that can be mixed with the second fuel. Preferably, the first fuel comprises an alcohol with a relatively short chain of carbon atoms, for example less than 6 carbon atoms. Alternatively, however, the first fuel may comprise non-hydrocarbons fuels, such as molecular hydrogen.

The first fuel may be a liquid at ambient conditions, e.g. at room temperature, but may be heated by the mixing device. Upon heating of the first fuel in the mixing device to a vaporizing temperature, the first fuel is vaporized to end up in a gaseous state. In the gaseous state, the mixing of the first fuel with the heated second fuel, i.e. that is vaporized and/or nebulized, may be improved to obtain a more homogeneous fuel mixture. Furthermore, the fuel mixture may effectively become a vapor, so that it can flow towards the burner more easily, as compared to when it were in a liquid state. The mixture that is to be combusted by the burner assembly further comprises the second fuel, which is configured to be mixed with the first fuel. The second fuel comprises a long-chain hydrocarbon fuel, which means that the second fuel comprises, but not necessarily exclusively consists of the long-chain hydrocarbon fuel. Hence, the second fuel may be a mixture of the long-chain hydrocarbon fuel and, for example, a short-chain hydrocarbon fuel. In an embodiment, however, the second fuel may substantially consist of the long-chain hydrocarbon fuel, possibly only having a slight fraction of impurities.

The long-chain hydrocarbon fuel in the second fuel is defined as a hydrocarbon material of which the hydrocarbon chains have a length of between 16 and 32 carbon atoms. This may include hydrocarbons with elongate, e.g. substantially straight, carbon chains, or possibly entangled, cyclic and/or curved carbon chains.

The fractions of the first fuel and the second fuel in the fuel mixture may vary. For example, the ratio between the first fuel and the second fuel may be 50wt% for each of them. Alternatively, for example where the first fuel is in a liquid state at room temperature, such as in particular a first fuel comprising ethanol, and where the second fuel is in a solid state at room temperature, such as in particular a second fuel comprising paraffin or stearin, the ratio may be in between 98wt% - 75wt% of first fuel and 2wt% - 25wt% of second fuel, for example 95wt% of ethanol and 5wt% of paraffin or 70wt% of ethanol and 30wt% of paraffin.

The mixing device of the burner assembly comprises a housing, in which the mixing of the first fuel and the second fuel is configured to take place. The housing thereto defines a mixing interior that may be substantially enclosed, for example being substantially surrounded by a housing wall. The enclosed mixing interior may contribute in obtaining a more homogenous fuel mixture, as compared to when the mixing interior were not to be enclosed.

The at least one discharge opening of the mixing device, which may be embodied as a single discharge opening, is provided to connect the mixing device to the burner. A burner channel may be provided at the discharge opening, to allow for a fluid connection between the mixing device and the burner.

The first fuel supply and the second fuel supply project into the mixing interior of the mixing device, in order to respectively feed the first fuel and the second fuel into the mixing device. The mixing interior comprises an enclosed volume in which the fuels are discharged.

The first fuel supply may comprise a first fuel line that may project, e.g. indirectly, into the mixing device. This indirect projection may be affected by means of a first nozzle, which is in fluid contact with the first fuel line and which may be able to withstand the heat in the mixing device better than the first fuel line itself would.

Similarly, the second fuel supply may comprise a second fuel line that may project, e.g. indirectly, into the mixing device. This indirect projection may be affected by means of a second nozzle, which is in fluid contact with the second fuel line and which may be able to withstand the heat in the mixing device better than the second fuel line itself would.

The mixing device is, in addition to the mixing, configured to heat the second fuel. To effect this heating, the heating element is provided. This heating element for heating the second fuel can be referred to with the term second heating element, since mixing devices according to other embodiments of the invention may comprise another heating element, i.e. a first heating element, to heat the first fuel.

The second heating element is arranged in the mixing interior, i.e. to be in contact with the second fuel that is supplied therein by the second fuel supply. In particular, the second heating element may be associated with the second fuel supply, so that it can be configured to only heat the second fuel, without heating the first fuel, i.e. before the first fuel and the second fuel become mixed to form the fuel mixture.

This heating of the second fuel by the second heating element may take place to a mixing temperature, which may be chosen such that the mixing of the fuels is optimized. Instead of mixing the second fuel in the state supplied by the second fuel supply, the mixing device is now configured to mix the first fuel with the heated second fuel to form the fuel mixture.

During heating, the second fuel may undergo a transformation, such as a phase transformation, e.g. vaporizing from a liquid state to an at least partial gaseous state, i.e. into a vapor. Such a vaporized second fuel may consist of gaseous second fuel or may comprise only a fraction of gaseous second fuel.

Alternatively or additionally, the second fuel may be nebulized at least partially by the heating, which implies that small droplets of the second fuel become airborne to form a mist of the second fuel in the mixing device. Since the droplets in the mist remain in the liquid phase, no phase transformation will take place. The external surface areas of all droplets combined is significantly larger as compared to when no nebulizing would take place, which increased surface also increases the reactivity of the second fuel.

The mist of second fuel in the mixing device may also be generated when at least part of the vaporized second fuel condenses from the gas phase into the liquid phase, giving rise to a mist of small liquid second fuel droplets.

The heating of the second fuel in the mixing device may offer a way to improve the flames that are to be generated by the burner assembly. Hence, in the prior art, it was only foreseen to combust fuels that were at ambient temperature, e.g. room temperature. However, at room temperature, not all fuels can be mixed to obtain a substantially homogeneous fuel mixture. By heating the second fuel in the mixing device, the mixing of the fuels can be improved, e.g. irrespective of the condition where the fuels are in at room temperature. In an embodiment of the burner assembly, the first fuel is in a liquid state at room temperature and/or the second fuel is in a solid state at room temperature.

With the first fuel being provided as a liquid, it may either be heated in the mixing device, i.e. prior to the mixing with the heated second fuel, or may be mixed with the heated second fuel in the liquid state, for example where the second fuel is heated such, that it becomes a liquid inside the mixing device.

The heating of the second fuel may furthermore effect that the second fuel, i.e. at the mixing temperature, is no longer a solid after leaving the mixing device. It is noted that a fireplace, i.e. in which the burner assembly is provided, may be configured to preheat the second fuel, so that it is fed into the mixing device as a liquid. Alternatively, however, the second fuel may be supplied into the mixing device as a solid. After heating in the mixing device, the second fuel may be in a liquid, e.g. nebulized, or gaseous state, so that its combustibility is improved, compared to when it were to be in a solid state.

In an additional or alternative embodiment of the burner assembly, the first fuel supply is configured to supply the first fuel to the mixing device in a gaseous state. This embodiment of the burner assembly may lack a heating element for the first fuel, i.e. a first heating element, since the first fuel is already supplied to the mixing device in the gaseous state, which means that no further heating in the mixing device is needed for the first fuel.

According to this embodiment, the burner assembly, or a fireplace in which this burner assembly is provided, may comprise a fuel pre-heating element, separate from the mixing device, which is configured to pre-heat the first fuel towards the gaseous state at a location remote from the mixing device.

In an embodiment of the burner assembly, the mixing device further comprises an air supply, projecting into the mixing interior and configured to supply a flow of air into the housing to provide a flow of air through the mixing interior along a flow path, e.g. between the air supply and the at least one discharge opening.

The flow path of the flow of air may be defined as the path that the flow of air is configured to travel through the mixing interior of the mixing device, i.e. after being supplied therein from the air supply. This path extends from the air supply, in particular from the point where the air is actually introduced into the mixing interior, towards the discharge opening, i.e. where the flow air, being mixed with the fuel mixture, departs the mixing interior towards the burner.

The flow of air through the mixing device may act as a carrier for the first fuel and/or the heated second fuel, so that these fuels are drawn through the mixing device by the air, instead of having to be pumped at high pressures by the first fuel supply and the second fuel supply. The flow of air induced by the air supply may flow along the first fuel supply and the second fuel supply to pick up the first fuel and the second fuel directly. Preferably, the flow of air is guided along the second heating element, to pick up heated, e.g. vaporized and/or nebulized, second fuel.

The flow of air in the mixing device may further give rise to turbulences in the mixing device, which turbulences may contribute to the mixing of the first fuel and the second fuel, i.e. with each other and with the air in the flow of air, in order to provide for a more homogeneous fuel mixture.

Furthermore, with the air being mixed with the fuel mixture, primary combustion air may already be present in the mixture that is fed from the mixing device towards the burner. This primary combustion air may contribute in reducing the formation of CO and carbon, e.g. soot, upon combusting the fuel mixture.

In a further embodiment of the burner assembly, the air supply forms part of the first fuel supply, configured to supply a gas mixture to the mixing device, which gas mixture comprises the flow of air and the gaseous first fuel.

According to this embodiment, the functionalities of the first fuel supply and of the air supply are combined. The gaseous first fuel is thereby mixed with the flow of air before entering the mixing device. The mixing device may thereto lack a first heating element for heating the first fuel, but may, instead, comprise only a single second heating element for heating the second fuel. The gas mixture, containing the flow of air and the first fuel, may be supplied into the mixing device at a location at or near the second fuel supply and/or the second heating element.

In an embodiment of the burner assembly, the first fuel supply is configured to supply the first fuel to the mixing device in a liquid state and the mixing device further comprises a first heating element, arranged at least partially in the mixing interior and configured to heat the first fuel to a vaporizing temperature to vaporize the first fuel inside the mixing interior.

The mixing device according to this embodiment is, in addition to the heating of the second fuel and the mixing, also configured to heat the first fuel. To effect this heating, another heating element is provided, i.e. to which is referred with the term first heating element.

The first heating element is also arranged in the mixing interior, i.e. to be in contact with the first fuel that is supplied therein by the first fuel supply. In particular, both heating elements may be associated with their respective fuel supplies, so that they are each configured to heat the respective fuels independently, i.e. before the first fuel and the second fuel become mixed to form the fuel mixture.

The first fuel may thereby be a liquid at ambient conditions, e.g. at room temperature, but may be heated by the mixing device as well. Upon heating of the first fuel in the mixing device to the vaporizing temperature, the first fuel is vaporized to end up in a gaseous state. In the gaseous state, the mixing of the first fuel with the heated second fuel, i.e. that is vaporized and/or nebulized, may be improved to obtain a more homogeneous fuel mixture. Furthermore, the fuel mixture may effectively become a vapor, so that it can flow towards the burner more easily, as compared to when it were in a liquid state.

The heating of the first fuel may thereby effect that the first fuel, i.e. at the vaporizing temperature, is no longer a liquid after leaving the mixing device. Instead, the first fuel may be in a gaseous state, so that its combustibility is improved, compared to when it were to be in a liquid state.

In a further embodiment of the burner assembly, the first heating element is a resistive heating element, projecting at least partially into the mixing interior. The resistive first heating element may, under influence of electrical resistance induced by an electric current through it, be configured to undergo an increase in temperature, thereby heating the first fuel in the mixing interior. In particular, an outer surface of the resistive first heating element may be subject to an increased temperature, so that the first fuel may be heated by conductive heat transfer and/or convective heat transfer.

In an embodiment, the burner assembly further comprises a control unit, configured to control the mixing device. The control unit may thereto be configured to control one or more parameters of the mixing device. The control unit may thereto comprise a proportional- integral-derivative controller (PID-controller).

The control unit may be configured to control the first heating element of the mixing device, in order to set the vaporizing temperature. This vaporizing temperature is preferably set indirectly by setting a temperature of the first heating element, which will, in turn, determine the vaporizing temperature. The control unit may comprise a first PID-controller for controlling the first heating element.

Alternatively or additionally, the control unit may be configured to control the second heating element of the mixing device, in order to set the mixing temperature. This mixing temperature is preferably set indirectly by setting a temperature of the second heating element, which will, in turn, determine the mixing temperature. The control unit may comprise a second PID-controller for controlling the second heating element. The control unit may comprise a first PID-controller and a distinct second PID-controller. Alternatively, however, their functionalities may as well be combined in a single PID- controller, for controlling both the first heating element and the second heating element.

In a further embodiment of the burner assembly, the mixing device further comprises: a first temperature sensor located in the mixing interior, configured to emit a first temperature sensor signal representative for the temperature inside the mixing interior, a control unit, configured to control the first heating element on the basis of the first temperature sensor signal to set the vaporizing temperature.

According to this embodiment, the mixing device is controlled on the basis of the temperature in the mixing interior, as measured by the first temperature sensor. The control unit may be configured to operate in a feedback manner, for which a temperature difference between a desired temperature and the measured temperature forms the basis for a new set temperature for the first heating element.

The first temperature sensor is preferably associated with the first fuel supply and/or the first heating element, which is configured to emit a first temperature sensor signal representing the temperature at which the first fuel is heated, for example representing the temperature of the first heating element. The control unit may be configured to control the first heating element on the basis of the first temperature sensor signal.

The first temperature sensor may be located inside the first heating element, to improve the accuracy of the first temperature sensor signal and to avoid disturbances of a flow of air and/or first fuel around the first temperature sensor.

In a further embodiment of the burner assembly the first temperature sensor is a thermocouple. This thermocouple may be associated with the first heating element, so that the first temperature sensor signal is representative for the temperature of the first heating element.

Preferably, the thermocouple is located inside the first heating element, in order to provide for a first temperature sensor signal representative for the actual temperature inside the first heating element, without being disturbed by possible temperature variations at the interface between the first fuel and the first heating element, e.g. at an outer surface of the first heating element.

In an embodiment of the burner assembly, the mixing device further comprises: a second temperature sensor located in the mixing interior, configured to emit a second temperature sensor signal representative for the temperature inside the mixing interior, and the control unit, further configured to control the second heating element on the basis of the second temperature sensor signal to set the mixing temperature.

According to this embodiment, the mixing device is additionally or alternatively controlled on the basis of the temperature in the mixing interior, as measured by the second temperature sensor.

The second temperature sensor is preferably associated with the second fuel supply and/or the second heating element, which is configured to emit a second temperature sensor signal representing the temperature at which the second fuel is heated, for example representing the temperature of the second heating element. The control unit may be configured to control the second heating element on the basis of the second temperature sensor signal.

In a further embodiment of the burner assembly, the second temperature sensor is a thermocouple. This thermocouple may be associated with the second heating element, so that the second temperature sensor signal is representative for the temperature of the second heating element.

Preferably, the thermocouple is located inside the second heating element, in order to provide for a second temperature sensor signal representative for the actual temperature inside the second heating element, without being disturbed by possible temperature variations at the interface between the second fuel and the second heating element, e.g. at an outer surface of the second heating element.

In an additional or alternative embodiment of the burner assembly, the second heating element is a resistive heating element or a radiant heating element, for example an infrared heating element, projecting at least partially into the mixing interior. The second heating element may be subjected to an electric current through it.

Where the second heating element is a resistive heating element, electrical resistance in the second temperature sensor is configured to result in an increase in temperature, thereby heating the second fuel in the mixing interior. In particular, an outer surface of the resistive second heating element may be subject to an increased temperature, so that the second fuel may be heated by conductive heat transfer and/or convective heat transfer.

Where the second heating element is a radiant heating element, the electric current may induce electromagnetic radiation, in particular in the infrared regime, which is emitted towards the second fuel. The radiant second heating element may comprise a coil with which the radiation is to be emitted. Accordingly, radiant transfer of this radiation onto the second fuel is configured to heat the second fuel. In an embodiment of the burner assembly, the mixing device further comprises a plurality of obstructions, which are located in the mixing interior and configured to promote mixing of the fuel mixture.

During use of the burner assembly, the first fuel and the second fuel, in particular when nebulized, may collide with the obstructions, which may result in an improved interaction between the first fuel and the second fuel, to promote the mixing thereof. Furthermore, the obstructions in the mixing interior may give rise to turbulences in the mixing device, which turbulences may further contribute to the mixing of the first fuel and the second fuel, i.e. with each other and with the air in the flow of air, in order to provide for a more homogeneous fuel mixture.

With the obstructions, the amount of surface area responsible for mixing and turbulences inside the mixing interior may be improved, possibly resulting in further improved mixing of the first fuel and the second fuel.

In an embodiment of the burner assembly, the mixing interior comprises a first interior section and a second interior section, e.g. a second interior section substantially separate, for example remote from, the first interior section, wherein the first fuel supply projects into the first interior section, and wherein the second fuel supply projects into the second interior section.

According to this embodiment, the mixing interior is subdivided into two interior sections. These interior sections may, but not necessarily need to, be physically separated from each other. Hence, a mixing interior may comprise a first zone, for example at a first side thereof, and a second zone, for example at an opposed second side, which may be located remote from each other.

The benefit of having a first interior section and a substantially separate second interior section is that the first fuel may be supplied into the mixing interior at a location remote from where the second fuel is supplied. As such, the first fuel and second fuel may not necessarily become mixed with each other directly after being supplied into the mixing interior, but may instead be given time to be heated, prior to the mixing, as a result of having to travel for a certain distance to encounter each other.

In a further embodiment of the burner assembly, the first heating element and/or the first temperature sensor is arranged at least partially in the first interior section. According to this embodiment, in addition to the first fuel being supplied in the first interior section, the heating of the first fuel may also take place in the first interior section, i.e. separate from where the second fuel is supplied into the mixing interior, e.g. separate from where the second fuel is heated. With the first heating element being arranged in the first interior section, it may be safeguarded that substantially only the first fuel will be heated by the first heating element and that no substantial amount of heat from the first heating element may reach the second fuel in the second interior section, to ensure independent heating of both fuels.

Additionally or alternatively, the provision of the first temperature sensor in the first interior section may provide that the measured temperature in the mixing interior, i.e. in the first interior section, by the first temperature sensor may not be disturbed significantly by the heating of the second fuel in the second interior section. This may result in an improved first temperature sensor signal, more accurately representing the actual temperature at or near the first heating element, thus resulting in improved controlling of the first heating element by the control unit.

In an additional or alternative embodiment of the burner assembly, the second heating element and/or the second temperature sensor is arranged at least partially in the second interior section. According to this embodiment, in addition to the second fuel being supplied in the second interior section, the heating of the second fuel may also take place in the second interior section, i.e. separate from where the first fuel is supplied into the mixing interior, e.g. separate from where the first fuel is heated.

Wth the second heating element being arranged in the second interior section, it may be safeguarded that substantially only the second fuel will be heated by the second heating element and that no substantial amount of heat from the second heating element may reach the first fuel in the first interior section, to ensure independent heating of both fuels and to prevent either one of the fuels to be heated to a temperature level that is too low or too high as a result of the other one of the fuels.

Additionally or alternatively, the provision of the second temperature sensor in the second interior section may provide that the measured temperature in the mixing interior, i.e. in the second interior section, by the second temperature sensor may not be disturbed significantly by the heating of the first fuel in the first interior section. This may result in an improved second temperature sensor signal, more accurately representing the actual temperature at or near the second heating element, thus resulting in improved controlling of the second heating element by the control unit.

In an embodiment of the burner assembly, the housing of the mixing device comprises: a first chamber, of which an interior forms the first interior section, and a second chamber, separate from the first chamber, of which an interior forms the second interior section, wherein the first chamber and the second chamber are fluidly connected in series along a flow path.

According to this embodiment, the first interior section is formed by an interior of the first chamber and the second interior section is formed by an interior of the second chamber. Accordingly, the first interior section and the second interior section are now substantially physically separated from each other, only being connected by a fluid connection in between them. This fluid connection may be a channel or opening between the chambers that has a size, e.g. cross-section, that is relatively narrow compared to a size, e.g. a length or cross- section, of the first chamber and of the second chamber.

By having the mixing interior subdivided in a first chamber and a second chamber, the first fuel is supplied in a chamber that is separate from the chamber in which the second fuel is supplied. In particular, the heating of the fuels may take place in separate chambers as well, e.g. where the first heating element is provided in the first chamber and where the second heating element is provided in the second chamber. This may further contribute in avoiding the supplying and/or heating of the first fuel from influencing the supplying and/or heating of the second fuel and vice versa.

In a further embodiment of the burner assembly, the first chamber is an elongate first chamber, comprising a first end and an opposed second end, and wherein the flow path through the first chamber extends between its first end and its second end, the second chamber is an elongate second chamber, comprising a first end and an opposed second end, and wherein the flow path through the second chamber extends from its first end to its second end, and the first chamber and the second chamber are arranged next to each other, so that the flow path through the first chamber is parallel or anti-parallel to the flow path through the second chamber.

According to this embodiment, each of the chambers is substantially elongate, for example each extending in a respective longitudinal direction, wherein the longitudinal direction of the first chamber is parallel to the longitudinal direction of the second chamber. The first chamber and the second chamber may have a circular cross-section, seen in a plane perpendicular to the longitudinal direction.

The length of the first chamber, i.e. parallel to the longitudinal direction, may be substantially the same as the length of the second chamber. Alternatively, the length of the first chamber may be larger than the length of the second chamber, or vice versa.

The width, e.g. diameter, of the first chamber, i.e. in a plane perpendicular to the longitudinal direction, may be substantially the same as the width of the second chamber. Alternatively, the width of the first chamber may be larger than the width of the second chamber, or vice versa. The second end of the first chamber is located opposite to its first end, seen along the longitudinal direction. Similarly, seen along the longitudinal direction, is the second end of the second chamber located opposite to its first end. The flow path through the first chamber and the flow path through the second chamber thereby extends parallel to longitudinal direction. Accordingly, the flow path in the first chamber may extend parallel to the flow path in the second chamber, i.e. both extending from the first end to the second end.

Alternatively, however, the flow path in the first chamber may extend from the second end to the first end, whereas the flow path in the second chamber may extend from the first end to the second end, or vice versa. According to this variant, the flow paths in the first chamber and the second chamber are in opposite directions, i.e. being anti-parallel to each other.

In a further embodiment of the burner assembly, the first end of the first chamber is located adjacent to the first end of the second chamber, the second end of the first chamber is located adjacent to the second end of the second chamber, and the flow path through the first chamber extends from its second end to its first end, so that the flow path through the first chamber is substantially anti-parallel to the flow path through the second chamber.

According to this embodiment, both first ends are located next to each other and both second ends are located next to each other as well. The overall flow path through the mixing interior is thus from the second end of the first chamber to the first end of the first chamber, to the first end of the second chamber, e.g. via a connection channel, and eventually to the second end of the second chamber, where the discharge opening may be provided to guide the flow towards the burner.

In a further embodiment of the burner assembly, the second chamber comprises a head section at its first end, which is substantially separated from the second interior section by a transverse wall, the first chamber projects into the head section of the second chamber, the transverse wall comprises a plurality of apertures that provide a fluid connection between the head section and the second interior section, and the second heating element and/or the second temperature sensor extends into the second interior section through the head section and one of the apertures in the transverse wall.

According to this embodiment, the second chamber defines the second interior section, i.e. in which the second fuel is supplied, and additionally comprises the head section. Seen along the flow path, the head section is provided in between the first chamber and the second interior section of the second chamber. The first chamber thereby projects into the head section, for example via the connection channel, so that a flow of first fuel first enters the head section, before entering the second interior section, i.e. in which the second fuel is supplied and heated.

The head section is physically separated from the second interior section by the transverse wall in the second chamber, which may be provided in a plane perpendicular to the longitudinal direction of the second chamber. As such, the separation may be provided over substantially the entire cross-section of the second chamber. Nonetheless, the transverse wall comprises multiple apertures, preferably spread over the entire cross-section of the second chamber, to allow for the passage of the first fuel into the second interior section.

The benefit of having these apertures is that the entrance of the first fuel into the second interior section is spread over multiple locations, i.e. multiple apertures, instead of only at a single location. This spread supply of first fuel in the second interior section may provide for improved dispersion of the first fuel amongst the second fuel that is supplied in the second interior section, and may thus provide for improved mixing between the first fuel and the second fuel.

The second heating element is configured to heat the second fuel in the second interior section, and not in the head section. Hence, the transverse wall in the second chamber may provide for thermal insulation between the second interior section and the head section. To heat the second fuel, the second heating element thus extends entirely through head section, not being configured to apply heat in the head section, and projects into the second interior section. The second heating element thereto extends through one of the apertures in the transverse wall to reach the second interior section from the head section.

The same applies for the second temperature sensor, which is configured to measure the temperature in the second interior section and not in the head section. To this effect, the second temperature sensor projects into the second interior section through an aperture in the transverse wall, for example through the same aperture as through which the second heating element extends.

The transverse wall may, as a result of its thermal insulation, provide a further advantage in that the temperature in the head section can be lower than the temperature in the second interior section, i.e. where the mixing temperature, to which the second fuel is heated, is higher than the vaporizing temperature, to which the first fuel is heated. As such, the vaporized first fuel, i.e. at the low vaporizing temperature, may, upon entering the head section, be configured to cool down components of the first fuel supply and of the first heating element and the first temperature sensor, such as connections thereof.

In an embodiment of the burner assembly, the first fuel supply and the first heating element project into the first chamber at the first end thereof, the second fuel supply and the second heating element project into the second chamber at the first end thereof, and the at least one discharge opening is provided at the second end of the second chamber.

According to this embodiment, the first fuel supply and the first heating element thus enter the first chamber at the first end. However, both the first fuel supply, for example the first nozzle thereof, and the first heating element may extend through the first chamber along the longitudinal direction over a substantial part of the length of the first chamber. As such, the first fuel may be supplied into the first chamber at multiple locations spread over the length of the first chamber, for example from multiple discharge openings of the first fuel supply, i.e. spread over the length of the first nozzle. Accordingly, the first fuel may be heated over at least part of the length of the first chamber, instead of only at a certain discrete point.

Furthermore, the second fuel supply and the second heating element enter the second chamber at the first end as well. Both the second fuel supply, for example the second nozzle thereof, and the second heating element may extend through the second chamber along the longitudinal direction over a substantial part of the length of the second chamber. As such, the second fuel may be supplied into the second chamber at multiple locations spread over the length of the second chamber, for example from multiple discharge openings of the second fuel supply, i.e. spread over the length of the second nozzle. Accordingly, the second fuel may be heated over at least part of the length of the second chamber, instead of only at a certain discrete point.

In an embodiment of the burner assembly, the air supply projects into the first chamber at the second end thereof and is configured to provide the flow of air along the flow path through the first chamber and the second chamber.

The flow of air thereby acts as a carrier for the first fuel, e.g. upon vaporizing thereof, as it passes along the first nozzle of the first fuel supply. The flow of air, and thus of the first fuel in the first chamber, is directed from the second end of the first chamber to the first end of the first chamber. Next, the flow of air, e.g. with the first fuel, is guided towards the head section of the second chamber. From the head section, the flow of air is fed into the second interior section of the second chamber, i.e. through the apertures.

In the second interior section, the flow of air is guided from the first end to the second end, i.e. to the discharge opening and towards the burner. In the second interior section, the flow of air and first fuel is passed along the second nozzle where the second fuel is supplied. Upon heating of the second fuel by the second heating element, the heated second fuel may be mixed with the flow of air, containing the first fuel, to obtain the fuel mixture of the first fuel and the second fuel. In an embodiment of the burner assembly, the housing is made of a ceramic material, for example a low thermal expansion coefficient ceramic material. The ceramic material is able to resist the temperatures that may occur in the mixing device, in particular during the heating the first fuel and/or the second fuel.

The low thermal expansion coefficient ceramic material may have a further advantage in that the dimensions of the mixing device may remain more constant during the service life of the burner assembly, i.e. irrespective of whether fuel is heated in the mixing device or not.

In an embodiment of the burner assembly, the burner has an outer shape that corresponds to the outer shape of a wooden log. Such a burner may offer a more realistic impression for a user, i.e. to more accurately mimic a wood-burning fireplace, in particular in an embodiment of a fireplace in which only the burner is visible for a user, e.g. behind a front opening of the fireplace, and in which the mixing device is concealed in an interior of the fireplace, e.g. not being visible for a user.

In particular, the burner according to this embodiment may be embodied as the burner disclosed in NL2005264, of which the contents are incorporated herein in their entirety. The present inventors have surprisingly found that this wooden log burner is also suitable for combusting the present fuel mixture, instead of only combusting the natural gas disclosed in NL2005264.

In an embodiment of the burner assembly, the vaporizing temperature is in the range between 50°C and 130°C, preferably between 70°C and 110°C, for example 90°C. It was found by the applicant that, for certain first fuels, vaporizing temperatures in these ranges may effectively result in vaporizing of the first fuel.

It is noted here that the above-mentioned temperature ranges represent the temperatures to which the first fuel is subjected in the mixing device. To obtain these temperatures, the mixing device may comprise one or more first heating elements that are at a higher temperature by themselves, for example at a temperature in the range between 100°C and 400°C, preferably between 200°C and 300°C, for example 250°C.

In an embodiment of the burner assembly, the mixing temperature is in the range between 250°C and 350°C, preferably between 275°C and 325°C, for example 300°C. It was found by the applicant that, for certain second fuels, mixing temperatures in these ranges may effectively result in vaporizing and/or nebulizing of the second fuel.

Also here, it is noted here that the above-mentioned temperature ranges represent the temperatures to which the second fuel is subjected in the mixing device. To obtain these temperatures, the mixing device may comprise one or more second heating elements that are at a higher temperature by themselves, for example at a temperature in the range between 400°C and 800°C, preferably between 500°C and 700°C, for example 600°C.

In an embodiment of the burner assembly, the first fuel is in a liquid state at room temperature, comprising an alcohol, such as ethanol, or a spirit, for example comprising alcohol and up to 50wt% of water.

According to this embodiment, the first fuel comprises an alcohol, which means that the first fuel comprises, but not necessarily exclusively consists of the alcohol. Hence, the first fuel may be a mixture of the alcohol and, for example, water.

The alcohol in the first fuel may be defined as an alcohol with a relatively short chain of carbon atoms, for example less than 6 carbon atoms, such as methanol, ethanol, propanol or butanol.

An example of a mixture comprising alcohol is a spirit, which may typically contain ethanol with about 15wt% water in it. The water may have a positive contribution in the vaporizing of the first fuel in the mixing device and in the combusting of the fuel mixture in the burner, for example contributing to flames that more accurately mimic flames in wood-burning fireplaces. In other examples, the amount of water in the first fuel may be up to 50wt%.

In another example, the first fuel may substantially consist of the alcohol, possibly only having a slight fraction of impurities. An example thereof would be bioethanol, which mainly consists of ethanol.

Alternatively, however, the first fuel may comprise non-hydrocarbons fuels, such as molecular hydrogen.

In an embodiment of the burner assembly, the second fuel is in a solid state at room temperature, comprising a wax, such as paraffine, stearin and/or candle wax.

The second fuel comprises a long-chain hydrocarbon fuel, which is defined as a hydrocarbon material of which the hydrocarbon chains have a length of between 16 and 32 carbon atoms. This may include hydrocarbons with elongate, e.g. substantially straight, carbon chains, or possibly entangled, cyclic and/or curved carbon chains.

Examples of such a long-chain hydrocarbon fuel are paraffine, stearin, candle wax or other types of synthetic or natural waxes, which are in a solid state at room temperature. Hereinafter, wax is used to refer to all these materials.

The second fuel comprises, but not necessarily exclusively consists of a wax that is solid at room temperature. Hence, the second fuel may be a mixture of the wax and, for example, a short-chain hydrocarbon fuel. In an embodiment, however, the second fuel may substantially consist of the wax, possibly only having a slight fraction of impurities, like it is the case with tealight, e.g. remains thereof, or other candles. The second fuel cannot be mixed in the mixing chamber when it is a solid at room temperature. However, by heating the second fuel in the mixing device and/or by preheating the second fuel outside the mixing device, the mixing of the fuels can be facilitated.

In an alternative embodiment of the burner assembly, the second fuel is in a liquid state at room temperature, for example comprising lamp oil and/or paraffine oil.

Also in this embodiment, the second fuel comprises a long-chain hydrocarbon fuel, such as paraffine, stearin or other types of synthetic or natural hydrocarbons. The second fuel further comprises other ingredients, such as liquid hydrocarbon fuels, which are mixed with the long-chain hydrocarbon fuel, e.g. the solid ingredient. This mixture is liquid at room temperature, which implies that no storage heating device may be needed in the second fuel storage and/or that no line heating device may be needed in the second fuel line, because the liquid second fuel can already be pumped at room temperature.

An example of a liquid second fuel is lamp oil or paraffine oil, which may be a mixture of paraffine or stearin and a liquid hydrocarbon, such as kerosene.

According to a second aspect, the present invention provides a mixing device of a burner assembly according to the present invention. The mixing device according to the second aspect may comprise one or more of the features and/or benefits disclosed herein in relation to the burner assembly according to the present invention, in particular one or more of the features disclosed in the claims.

According to a third aspect, the present invention provides a hybrid domestic fireplace, configured to burn a fuel mixture of a first combustible fuel and a second combustible fuel, comprising a combustible long chain hydrocarbon fuel, the fireplace comprising: the burner assembly according to the present invention, a combustion chamber, in which the burner is accommodated, and a flue gas discharge, configured to discharge flue gasses out of the combustion chamber.

The fireplace according to the third aspect may comprise one or more of the features and/or benefits disclosed herein in relation to the burner assembly according to the present invention and/or the mixing device according to the present invention, in particular one or more of the features disclosed in the claims.

The burner of the burner assembly is thereby configured to combust the fuel mixture inside the combustion chamber, to generate the fire. Upon burning the fuel mixture, flue gasses may be produced, which need to be discharged out of the combustion chamber. In conventional fireplaces, the combustion chamber would be connected to a chimney in order to discharge the flue gasses. Chimneys are normally subject to a pressure difference. The pressure difference may result in draft through the chimney, to contribute in obtaining an air flow along the burner, to provide secondary combustion air to the fire.

The present fireplace may operate in the absence of a chimney, since the flue gasses may be less toxic, compared to the emissions of wood-burning fires or gas fires. The flue gas discharge of the present environment is configured to provide the air flow along the burner in the absence of a chimney, so that the burner may be provided with sufficient secondary combustion air. Optionally, the flue gas discharge may comprise a fan, e.g. a high- temperature fan, for example located at an upper section of the combustion chamber. The fan may be configured to upwardly withdraw the flue gasses out of the combustion chamber, meanwhile withdrawing secondary combustion air in to the combustion chamber from below.

According to a further aspect, the present invention provides a method of creating a fire by means of a burner assembly, comprising the steps of: supplying a first combustible fuel to a mixing interior of a mixing device of the burner assembly, supplying a second combustible fuel, comprising a second combustible long chain hydrocarbon fuel, to the mixing interior, heating, inside the mixing interior, the second fuel to a mixing temperature, mixing, in the mixing device, the first fuel with the heated second fuel to form a fuel mixture, and combusting the fuel mixture with a burner of the burner assembly to create the fire.

The present method according to the present invention relies on the combusting of a mixture of a first fuel and a second fuel. This forms a first difference with existing methods, which generally relied on a single fuel, such as wood, natural gas or ethanol.

The present method is carried out in a burner assembly that comprises a mixing device, in which the first fuel and the second fuel are mixed into a fuel mixture. After mixing, the fuel mixture is fed towards a burner, in which the obtained fuel mixture from the mixing device is combusted, so that flames can be visible.

The method may, but not necessarily needs to, be carried out in a burner assembly according to the present invention, as disclosed herein. In particular, the burner assembly used in the present method may comprise one or more of the features and/or benefits disclosed herein in relation to the burner assembly according to the present invention, in particular one or more of the features disclosed in the claims.

The first fuel may be a liquid at ambient conditions, e.g. at room temperature, but may be heated by the mixing device. Upon heating of the first fuel in the mixing device to a vaporizing temperature, the first fuel is vaporized to end up in a gaseous state. In the gaseous state, the mixing of the first fuel with the heated second fuel, i.e. that is vaporized and/or nebulized, may be improved to obtain a more homogeneous fuel mixture. Furthermore, the fuel mixture may effectively become a vapor, so that it can flow towards the burner more easily, as compared to when it were in a liquid state.

The mixture that is to be combusted by the burner assembly further comprises the second fuel, which comprises a long-chain hydrocarbon fuel, which means that the second fuel comprises, but not necessarily exclusively consists of the long-chain hydrocarbon fuel. Hence, the second fuel may be a mixture of the long-chain hydrocarbon fuel and, for example, a short-chain hydrocarbon fuel. In an embodiment, however, the second fuel may substantially consist of the long-chain hydrocarbon fuel, possibly only having a slight fraction of impurities.

The mixing device defines a mixing interior that may be substantially enclosed, for example being substantially surrounded by a housing wall. The enclosed mixing interior may contribute in obtaining a more homogenous fuel mixture, as compared to when the mixing interior were not to be enclosed.

The mixing device may comprise at least one discharge opening of the mixing device, which may be embodied as a single discharge opening, to connect the mixing device to the burner. A burner channel may be provided at the discharge opening, to allow for a fluid connection between the mixing device and the burner.

When the method is carried out, the mixing device, in addition to the mixing, heats the second fuel. To effect this heating, a heating element may be provided, which may be in contact with the second fuel that is supplied therein by the second fuel supply.

This heating of the second fuel may take place to a mixing temperature, which may be chosen such that the mixing of the fuels is optimized. Instead of mixing the second fuel in the state supplied by the second fuel supply, the mixing device now mixes the first fuel with the heated second fuel to form the fuel mixture.

The heating of the second fuel in the mixing device may offer a way to improve the flames that are to be generated by the burner assembly. Hence, in the prior art, it was only foreseen to combust fuels that were at ambient temperature, e.g. room temperature. However, at room temperature, not all fuels can be mixed to obtain a substantially homogeneous fuel mixture. By heating the second fuel in the mixing device, the mixing of the fuels can be improved, e.g. irrespective of the condition where the fuels are in at room temperature.

In an embodiment, the method further comprises the step of: heating, inside the mixing interior, the first fuel to a vaporizing temperature to vaporize the first fuel inside the mixing interior. According to this embodiment, the first fuel may be heated by the mixing device as well. Upon heating of the first fuel in the mixing device to the vaporizing temperature, the first fuel is vaporized to end up in a gaseous state. In the gaseous state, the mixing of the first fuel with the heated second fuel, i.e. that is vaporized and/or nebulized, may be improved to obtain a more homogeneous fuel mixture. Furthermore, the fuel mixture may effectively become a vapor, so that it can flow towards the burner more easily, as compared to when it were in a liquid state.

In a further embodiment, the method further comprises the steps of: measuring, with a first temperature sensor located in the mixing interior, the temperature inside the mixing interior, e.g. in a first interior section thereof, and controlling, with a control unit, the heating of the first fuel on the basis of the measured temperature to set the vaporizing temperature.

According to this embodiment, the heating of the first fuel by the mixing device is controlled on the basis of the temperature in the mixing device, as measured by the first temperature sensor, in particular on the basis of the temperature in the first interior section of the mixing interior, i.e. in which the first fuel supply and the first temperature sensor may be provided.

The control unit may be configured to operate in a feedback manner, for which a temperature difference between a desired temperature and the measured temperature forms the basis for a new set temperature for the mixing device. The first temperature sensor is thereto preferably associated with a first fuel supply and/or a first heating element, which emits a first temperature sensor signal representing the temperature at which the first fuel is heated. The control unit may be configured to control the heating, e.g. with the first heating element, on the basis of the first temperature sensor signal.

In an embodiment, the method further comprises the steps of: measuring, with a second temperature sensor located in the mixing interior, the temperature inside the mixing interior, e.g. in a second interior section thereof, and controlling, with the control unit, the heating of the second fuel on the basis of the measured temperature to set the mixing temperature.

According to this embodiment, the heating of the second fuel by the mixing device is also controlled on the basis of the temperature in the mixing device, but then as measured by the second temperature sensor, in particular on the basis of the temperature in the second interior section of the mixing interior, i.e. in which the second fuel supply and the second temperature sensor may be provided. To enable controlling by the control unit, e.g. in a feedback manner, the second temperature sensor is preferably associated with a second fuel supply and/or a second heating element, which emits a second temperature sensor signal representing the temperature at which the second fuel is heated. The control unit may be configured to control the heating, e.g. with the second heating element, on the basis of the second temperature sensor signal.

In an embodiment of the method, the first fuel is in a liquid state at room temperature, for example comprising an alcohol, such as ethanol, or a spirit, for example comprising alcohol and up to 50wt% of water.

In an embodiment of the method, the second fuel is in a solid state at room temperature, for example comprising a wax, such as paraffine, stearin and/or candle wax.

Examples of such a long-chain hydrocarbon fuel are paraffine, stearin, candle wax or other types of synthetic or natural waxes, which are in a solid state at room temperature. Hereinafter, wax is used to refer to all these materials. The second fuel comprises, but not necessarily exclusively consists of a wax that is solid at room temperature. Hence, the second fuel may be a mixture of the wax and, for example, a short-chain hydrocarbon fuel. In an embodiment, however, the second fuel may substantially consist of the wax, possibly only having a slight fraction of impurities, like it is the case with tealight, e.g. remains thereof, or other candles.

The second fuel cannot be mixed in the mixing chamber when it is a solid at room temperature. However, by heating the second fuel in the mixing device and/or by preheating the second fuel outside the mixing device, the mixing of the fuels can be facilitated.

In an alternative embodiment of the method, the second fuel is in a liquid state at room temperature, for example comprising lamp oil and/or paraffine oil.

In an embodiment, the method comprises a preheating cycle for preheating the burner to a predetermined preheating temperature, the preheating cycle comprising the steps of: supplying the first combustible fuel to the burner, via the mixing device, combusting the first fuel with the burner of the fireplace to create the fire, and heating the burner by means of the fire, wherein the preheating cycle is terminated and the second combustible fuel is supplied to the mixing device and mixed with the first fuel after a temperature of the burner exceeds the predetermined preheating temperature.

This embodiment of the method may improve working of the burner assembly, since the second fuel is only supplied towards the mixing device and the burner after the burner has reached the predetermined preheating temperature. Especially where the burner is located at a distance from the mixing device, the fuel mixture may condense or even solidify partly in the trajectory between the mixing device, i.e. where the fuels can be vaporized, which may cause pollution of the burner. In case of solidification of the fuel mixture, the burner may even get blocked, possibly resulting in malfunction of the fireplace. According to the present embodiment, the fire is first obtained by burning the first fuel only. This fuel is relatively light and may have a relatively low vaporizing temperature, so that the first fuel will not tend to condense, let alone solidify in the trajectory between the mixing device and the burner, nor in the burner itself. The fire created with the first fuel will heat up the burner, from the ambient temperature to an elevated operating temperature, for example of about 200°C. At a certain moment, the burner may reach a temperature equal to the predetermined preheating temperature, which may be representative for a temperature level at which at least solidification, but preferably condensation of the fuel mixture may be substantially prevented.

After reaching the predetermined preheating temperature, the preheating cycle is ended and the second fuel may also be supplied towards the mixing device. This may effect that not only the first fuel is supplied towards the burner, but that the first fuel and the second fuel are mixed. The fire then burns the fuel mixture, since the risk of condensation and solidification thereof is minimized.

Brief description of drawings

Further characteristics of the invention will be explained below, with reference to embodiments, which are displayed in the appended drawings, in which:

Figure 1 schematically depicts a mixing device of an embodiment of the burner assembly according to the present invention,

Figure 2 schematically depicts a cross-section of the mixing device of figure 1,

Figure 3 schematically depicts the mixing device of figure 1 in an exploded-view representation,

Figure 4 depicts the entire burner assembly according to the embodiment of figure 1,

Figure 5 schematically depicts a cross-section of an alternative mixing device, and

Figure 6 schematically depicts the mixing device of figure 5 in an exploded-view representation.

Throughout the figures, the same reference numerals are used to refer to corresponding components or to components that have a corresponding function.

Detailed description of embodiments

Figure 1 schematically depicts a mixing device of an embodiment of the burner assembly according to the present invention, to which is referred with reference numeral 10. The mixing device 10 is configured to mix a first fuel F1 and a second fuel F2 to form a fuel mixture. The mixing device 10 comprises a housing 103, which is made of a low thermal expansion coefficient ceramic material. The ceramic material is able to resist the temperatures that may occur in the mixing device 10, in particular during the heating the first fuel F1 and/or the second fuel F2.

The first fuel F1 is in a liquid state at room temperature, comprising an alcohol. In particular, the first fuel F1 is a mixture comprising a spirit, which contains ethanol with about 15wt% water in it.

The second fuel F2 is in a solid state at room temperature, comprising a wax. In particular, the second fuel F2 contains paraffin or stearin.

Furthermore, burner assembly comprises a burner 40, as is best shown in figure 4, which has a shape that corresponds to the outer shape of a wooden log. The burner 40 is fluidly connected to a discharge opening 42 of the mixing device 10 by means of a burner channel 41 to guide a flow of the fuel mixture from the mixing device 10 towards the burner 40. The burner 40 is, in turn, configured to combust the fuel mixture, so that flames are visible at the outer surface thereof, i.e. of the log.

The mixing device 10 is configured to heat the first fuel F1 by means of a first heating element 11, which is embodied as an infrared heating element. The mixing device 10 is configured to heat the first fuel F1 to a vaporizing temperature to vaporize the first fuel F1 in the mixing device 10. In the present embodiment, the vaporizing temperature is set at 90°C. To obtain this temperature, the first heating element 11 itself is controlled to reach a temperature of 250°C.

The mixing device 10 comprises a first temperature sensor 13, which is arranged adjacent the first heating element 11. The first temperature sensor 13 is configured to emit a first temperature sensor signal representing the temperature at which the first fuel F1 is heated, e.g. representing the temperature of the first heating element 11.

The mixing device 10 is further configured to heat the second fuel F2 by means of a second heating element 12, which is, in the embodiment shown in figures 1 - 4 embodied as a resistive heating element. The mixing device 10 is configured to heat the second fuel F2 to a mixing temperature to heat the second fuel F2 in the mixing device 10, to vaporize and/or to nebulize the second fuel F2. In the embodiment shown in figures 1 - 4, the mixing temperature is set at 300°C. To obtain this temperature, the second heating element 12 itself is controlled to reach a temperature of 600°C.

The mixing device 10 further comprises a second temperature sensor 14, which is arranged adjacent the second heating element 12. The second temperature sensor 14 is configured to emit a second temperature sensor signal representing the temperature at which the second fuel F2 is heated, e.g. representing the temperature of the second heating element 12. The burner assembly further comprises a control unit (not visible in the figures), which is embodied as a proportional-integral-derivative (PID) controller and which is configured to control the mixing device 10 and to operate in a feedback manner. The control unit is electrically connected to the first heating element 11 and to the second heating element 12, for providing electricity towards the respective heating elements 11, 12, and is electrically connected to the first temperature sensor 13 and to the second temperature sensor 14, for transmitting the sensor signals from the respective temperature sensors 13, 14 to the control unit.

The control unit is configured to control the first heating element 11 on the basis of the first temperature sensor signal, in order to set the vaporizing temperature, and is configured to control the second heating element 12 on the basis of the second temperature sensor signal, in order to set the mixing temperature.

The mixing device 10 comprises a first fuel supply, which is configured to feed the first fuel F1 into the mixing device 10. The first fuel supply comprises a first fuel line that projects into the mixing device 10 indirectly, by means of a first nozzle 27.

The mixing device 10 further comprises a second fuel supply, which is configured to feed the second fuel F2 into the mixing device 10. The second fuel supply comprises a second fuel line that projects into the mixing device 10 indirectly, by means of a second nozzle 37.

Figure 2 shows a cross-sectional view on the mixing device 10 of figure 1, seen from the top in a vertically downward direction. It is shown in figure 2 that the mixing device 10 comprises a first chamber 15 and a second chamber 16, which respectively form a first interior section and a second interior section 16a. The first chamber 15 and the second chamber 16 are substantially physically separated from each other by an intermediate wall 104 of the housing 103, only being connected by a fluid connection in between them, which is embodied as an opening 19’ between the chambers 15,16.

The first chamber 15 is substantially elongate along a longitudinal direction L and comprises a first end 151 and a second end 152. A flow path in the first chamber 15, indicated by means of arrows, extends from the second end 152 to the first end 151.

Similarly, the second chamber 16 is elongate along the longitudinal direction L as well, extending parallel to the first chamber 15, and also comprises a first end 161 and a second end 162. A flow path in the second chamber 16, indicated by means of arrows, extends from the first end 161 to the second end 161.

The first end 151 of the first chamber 15 is located adjacent to the first end 161 of the second chamber 16. The second end 152 of the first chamber 15 is located adjacent to the second end 162 of the second chamber 16, so that the flow path through the first chamber 15 is substantially anti-parallel, i.e. in opposite direction, to the flow path through the second chamber 16. The overall flow path through the mixing device 10 is thus from the second end 152 of the first chamber 15 to the first end 151 of the first chamber 15, to the first end 161 of the second chamber 16 , e.g. via the opening 19’, and eventually to the second end 162 of the second chamber 16, where the discharge opening 42 provided to guide the flow towards the burner 40.

Both the first chamber 15 and the second chamber 16 have a circular cross-section, seen in a plane perpendicular to the longitudinal direction L, and each have a diameter in this plane that is substantially equal to each other. Furthermore, the length of the first chamber 15, i.e. parallel to the longitudinal direction L, is substantially the same as the length of the second chamber 16.

Furthermore, the second chamber 16 comprises a head section 17 at its first end 161, which is substantially separated from a remainder of the second chamber 16, e.g. of the second interior section 16a, by a transverse wall 18. Seen along the flow path, the head section 17 is provided in between the first chamber 15 and the second interior section 16a of the second chamber 16. The first chamber 15 thereby projects into the head section 17, e.g. via the opening 19’, so that a flow from the first chamber 15 first enters the head section 17, before entering the second interior section 16a.

The transverse wall 18 in the second chamber 16 is provided in a plane perpendicular to the longitudinal direction L, so that it extends over substantially the entire cross-section of the second chamber 16. The transverse wall 18 comprises multiple apertures 19, as is best shown in figure 3, which are spread over the entire cross-section of the second chamber 16, to allow for the passage of a flow from the head section 17 into the second interior section 16a. The spread apertures 19 have the benefit that the entrance of the flow, e.g. comprising the first fuel F1, into the second interior section 16a is spread over multiple locations, i.e. multiple apertures 19, instead of only at a single location, to provide for improved dispersion of the first fuel F1 amongst the second fuel F2.

The mixing device 10 further comprises a plurality of obstructions, not visible in the figures, which are located in the second chamber 16, e.g. in the second interior section 16a thereof, and which are configured to promote mixing of the flow entering from the head section 17, e.g. to promote mixing of the first fuel F1 and the second fuel F2.

The first nozzle 27 projects into the first chamber 15 and the second nozzle 37 projects into the second chamber 16. The first fuel F1 is thus supplied into the first chamber 15 and the second fuel F2 is supplied in the second chamber 16.

The first nozzle 27 enters the first chamber 15 at the first end 151, but extends through the first chamber 15 along the longitudinal direction L over a substantial part, e.g. approximately two thirds of the length of the first chamber 15. As such, the first fuel F1 is configured to be supplied into the first chamber 15 from multiple discharge openings 28 of the first nozzle 27, spread over part of the length of the first chamber 15.

The second nozzle 37 enters the second chamber 16 at the first end 161 and extends through the entire head section 17. The second nozzle 37 is not configured to supply the second fuel F2 in the head section 17 and is, to this end, free of openings in the head section 17. The second nozzle 37 further extends through one of the apertures 19 in the transverse wall 18, to project into the second interior section 16a of the second chamber 16. The second nozzle 37 extends along the longitudinal direction L over a substantial part, e.g. approximately three quarters of the length of the second interior section 16a of the second chamber 16. As such, the second fuel F2 is configured to be supplied into the second chamber 16 from multiple discharge openings 38 of the second nozzle 37, spread over part of the length of the second chamber 16.

The first heating element 11 is embodied as a resistive heating element, which projects into the first chamber 15 at the first end 151 as well and comprises a thermocouple 13 as first temperature sensor. The first heating element 11 also extends through the first chamber 15 along the longitudinal direction L over a substantial part, e.g. approximately two thirds of the length of the first chamber 15, similar as the first nozzle 27. As such, the first fuel F1 is configured to be heated over part of the length of the first chamber 15, to improve the heating of the first fuel F1.

In the present embodiments, the first thermocouple 13 is integrated in the first heating element 11, in order to provide for a first temperature sensor signal representative for the actual temperature inside the first heating element 11, without being disturbed by possible temperature variations at an outer surface of the first heating element 11 with the first fuel F1.

In the embodiment shown in figures 1 - 4, the second heating element 12 is also embodied as a resistive heating element, which projects into the second chamber 16 at the first end 161 as well and comprises, in the embodiment shown in figures 1 - 4, a thermocouple 14 as second temperature sensor. Similar as the second nozzle 37, does the second heating element 12 extend through the entire head section 17. The second heating element 12 further extends through another one of the apertures 19 in the transverse wall 18, to project into the second interior section 16a of the second chamber 16. The second heating element 12 also extends through the second chamber 16 along the longitudinal direction L over a substantial part, e.g. approximately two thirds of the length of the second chamber 16. As such, the second fuel F2 is configured to be heated over part of the length of the second chamber 16, to improve the heating of the second fuel F2.

The second heating element 12 is configured to heat the second fuel F2 in the second interior section 16a, and not in the head section 17. Hence, the transverse wall 18 in the second chamber 16 provide for thermal insulation between the second interior section 16a and the head section 17.

The first heating element 11 and the first temperature sensor 12 are arranged at least partially in the first chamber 15 and the first fuel F1 is supplied in the first chamber 15 as well. As such, the heating of the first fuel F1 only takes place in the first chamber 15.

The second heating element 12 and the second temperature sensor 13 are arranged at least partially in the second chamber 16 and the second fuel F2 is supplied in the second chamber 16 as well. As such, the heating of the second fuel F2 only takes place in the second chamber 16.

The mixing device 10 further comprises an air supply, projecting into its interior and configured to provide a flow of air through the mixing device 10, to act as a carrier for the vaporized first fuel F1 and the heated second fuel F2. The mixing device 10 is further configured to mix the fuel mixture with the air supplied by the air supply. Inside the mixing device 10, the flow of air is guided along the first heating element 11, to pick up vaporized first fuel F1, and along the second heating element 12, to pick up heated second fuel F2.

The air supply comprises an air hose that projects into the mixing device 10 indirectly, by means of an air nozzle 67. The air nozzle 67 projects into the first chamber 15 and comprises an exit opening 68, through which the flow of air is introduced in the first chamber 15. The exit opening 68 of the air nozzle 67 is located at the second end 152 of the first chamber 15 and is configured to provide the flow of air along the flow path through the first chamber 15 and the second chamber 16. The flow of air thereby acts as a carrier for the first fuel F1 as it passes along the first nozzle 27 and the first heating element 11 , i.e. at which the first fuel F1 is vaporized.

The flow of air, thus comprising the first fuel F1, is directed from the second end 152 of the first chamber 15 to the first end 151 of the first chamber 15. Next, the flow of air, containing the first fuel F1, is guided towards the head section 17 of the second chamber 16. From the head section 17, the flow of air is fed into the second interior section 16a of the second chamber 16 through the apertures 19.

In the second interior section 16a, the flow of air is guided towards the discharge opening 42, located at the second end 162 of the second chamber 16, and towards the burner 40. In the second interior section 16a, the flow of air containing the first fuel F1 is passed along the second nozzle 37 where the second fuel F2 is supplied. Upon heating of the second fuel F2 by the second heating element 12, the heated second fuel F2 is mixed with the flow of air and the first fuel F1, to obtain the fuel mixture of the first fuel F1 and the second fuel F2.

The flow of air in the mixing device 10 may give rise to turbulences in the mixing device 10, which turbulences may contribute to the mixing of the first fuel F1 and the second fuel F2, i.e. with each other and with the air in the flow of air, in order to provide for a more homogeneous fuel mixture. Furthermore, with the air being mixed with the fuel mixture, primary combustion air may already be present in the mixture that is fed from the mixing device 10 towards the burner 40. This primary combustion air may contribute in reducing the formation of CO and carbon, e.g. soot, upon combusting the fuel mixture.

In figures 5 and 6, an alternative mixing device according to the invention is shown, to which is referred with reference numeral 10’. The mixing device 10’ in figures 5 and 6 is, to a large extent, similar to the mixing device 10 shown in figures 1 - 4. In particular, their first chambers 15, 15’, including the air nozzle, first nozzle, first heating element and first temperature are the same.

The housing 103’ of the mixing device 10’ in figures 5 and 6 is free of the transverse wall and the head section. Instead, the mixing device 10’ comprises a unitary second chamber 16’ that is fluidly connected to the first chamber 15 by means of the opening 19’. The second chamber 16’ comprises, at its first head end 16T, a removable head end wall 163. In figure 6, the head end wall 163 is shown removed from the second chamber 16’, thereby allowing access into the second chamber 16’. During normal use of the mixing device 10’, the head end wall 163 is installed in the second chamber 16’ to close off the interior of the second chamber 16’.

A further difference is provided by the second heating element 12’ of the mixing device 10’, which has a functionally combined with the second nozzle 37’. The second heating element 12’ is an infrared radiant heating element, which projects into the second chamber 16’ and which is configured to be subjected to an electric current through it, e.g. initiated by a control unit.

The second heating element 12’ comprises a frame element 12T, which comprises a number of fins, and a coil 122’. The fins of the frame element 12T outwardly protrude away from each other and are together configured to guide the coil 122’. The electric current is adapted to be guided through the coil 122’, so that electromagnetic radiation, i.e. in the infrared regime, is emitted by the coil 122’. The infrared radiation is emitted towards the second fuel F2 in the second chamber 16’, in order to heat the second fuel F2 to the mixing temperature.

Claims

1. Burner assembly for a domestic fireplace, configured to burn a mixture of a first combustible fuel and a second combustible fuel, comprising a combustible long chain hydrocarbon fuel, the assembly comprising at least one burner and a mixing device, the mixing device comprising: a housing, defining a mixing interior, at least one discharge opening in the housing, connected to the at least one burner and configured to provide access from the mixing interior towards the burner, a first fuel supply, projecting into the mixing interior and configured to supply the first fuel into the mixing interior, and a second fuel supply, projecting into the mixing interior and configured to supply the second fuel into the mixing interior, characterized in that, the mixing device further comprises: a heating element, e.g. a second heating element, arranged at least partially in the mixing interior and configured to heat the second fuel to a mixing temperature, wherein the mixing device is configured to mix the first fuel with the heated second fuel to form the fuel mixture, and wherein the at least one burner is configured to combust the fuel mixture.

2. Burner assembly according to claim 1 , wherein the first fuel is in a liquid state at room temperature and/or wherein the second fuel is in a solid state at room temperature.

3. Burner assembly according to claim 1 or 2, wherein the first fuel supply is configured to supply the first fuel to the mixing device in a gaseous state.

4. Burner assembly according to any of the preceding claims, wherein the mixing device further comprises: an air supply, projecting into the mixing interior and configured to supply a flow of air into the housing to provide a flow of air through the mixing interior along a flow path, e.g. between the air supply and the at least one discharge opening.

5. Burner assembly according to claim 4 and claim 5, wherein the air supply forms part of the first fuel supply, configured to supply a gas mixture to the mixing device, which gas mixture comprises the flow of air and the gaseous first fuel.

6. Burner assembly according to any of the preceding claims, wherein the first fuel supply is configured to supply the first fuel to the mixing device in a liquid state and wherein the mixing device further comprises: a first heating element, arranged at least partially in the mixing interior and configured to heat the first fuel to a vaporizing temperature to vaporize the first fuel inside the mixing interior.

7. Burner assembly according to claim 6, wherein the first heating element is a resistive heating element, projecting at least partially into the mixing interior.

8. Burner assembly according to claim 7, wherein the mixing device further comprises: a first temperature sensor located in the mixing interior, configured to emit a first temperature sensor signal representative for the temperature inside the mixing interior, a control unit, configured to control the first heating element on the basis of the first temperature sensor signal to set the vaporizing temperature.

9. Burner assembly according to claim 8, wherein the first temperature sensor is a thermocouple.

10. Burner assembly according to any of the preceding claims, wherein the mixing device further comprises: a second temperature sensor located in the mixing interior, configured to emit a second temperature sensor signal representative for the temperature inside the mixing interior, and the control unit, further configured to control the second heating element on the basis of the second temperature sensor signal to set the mixing temperature.

11. Burner assembly according to claim 10, wherein the second temperature sensor is a thermocouple.

12. Burner assembly according to claim 10 or 11, wherein the second heating element is a resistive heating element or a radiant heating element, for example an infrared heating element, projecting at least partially into the mixing interior.

13. Burner assembly according to any of the preceding claims, wherein the mixing device further comprises a plurality of obstructions, which are located in the mixing interior and configured to promote mixing of the fuel mixture.

14. Burner assembly according to any of the preceding claims, wherein the mixing interior comprises a first interior section and a second interior section, e.g. a second interior section substantially separate, for example remote from, the first interior section, wherein the first fuel supply projects into the first interior section, and wherein the second fuel supply projects into the second interior section.

15. Burner assembly according to claim 6 and claim 14, wherein the first heating element and/or the first temperature sensor is arranged at least partially in the first interior section.

16. Burner assembly according to claim 14 and/or 15, wherein the second heating element and/or the second temperature sensor is arranged at least partially in the second interior section.

17. Burner assembly according to any of the claims 14 - 16, wherein the housing comprises: a first chamber, of which an interior forms the first interior section, and a second chamber, separate from the first chamber, of which an interior forms the second interior section, wherein the first chamber and the second chamber are fluidly connected in series along a flow path.

18. Burner assembly according to claim 17, wherein the first chamber is an elongate first chamber, comprising a first end and an opposed second end, and wherein the flow path through the first chamber extends between its first end and its second end, wherein the second chamber is an elongate second chamber, comprising a first end and an opposed second end, and wherein the flow path through the second chamber extends from its first end to its second end, and wherein the first chamber and the second chamber are arranged next to each other, so that the flow path through the first chamber is parallel or anti-parallel to the flow path through the second chamber.

19. Burner assembly according to claim 18, wherein the first end of the first chamber is located adjacent to the first end of the second chamber and wherein the second end of the first chamber is located adjacent to the second end of the second chamber, and wherein the flow path through the first chamber extends from its second end to its first end, so that the flow path through the first chamber is substantially anti-parallel to the flow path through the second chamber.

20. Burner assembly according to claim 19, wherein the second chamber comprises a head section at its first end, which is substantially separated from the second interior section by a transverse wall, wherein the first chamber projects into the head section of the second chamber, wherein the transverse wall comprises a plurality of apertures that provide a fluid connection between the head section and the second interior section, and wherein the second heating element and/or the second temperature sensor extends into the second interior section through the head section and one of the apertures in the transverse wall.

21. Burner assembly according to any of the claims 18 - 20, wherein the first fuel supply and the first heating element project into the first chamber at the first end thereof, wherein the second fuel supply and the second heating element project into the second chamber at the first end thereof, and wherein the at least one discharge opening is provided at the second end of the second chamber.

22. Burner assembly according to any of the claims 18 - 21 and claim 4, wherein the air supply projects into the first chamber at the second end thereof and is configured to provide the flow of air along the flow path through the first chamber and the second chamber.

23. Burner assembly according to any of the preceding claims, wherein the housing is made of a ceramic material, for example a low thermal expansion coefficient ceramic material.

24. Burner assembly according to any of the preceding claims, wherein the burner has an outer shape that corresponds to the outer shape of a wooden log.

25. Mixing device of a burner assembly according to any of the preceding claims.

26. Hybrid domestic fireplace, configured to burn a fuel mixture of a first combustible fuel and a second combustible fuel, comprising a combustible long chain hydrocarbon fuel, the fireplace comprising: the burner assembly according to any of the claims 1 - 24, a combustion chamber, in which the burner is accommodated, and a flue gas discharge, configured to discharge flue gasses out of the combustion chamber.

27. Method of creating a fire by means of a burner assembly, comprising the steps of: supplying a first combustible fuel to a mixing interior of a mixing device of the burner assembly, supplying a second combustible fuel, comprising a second combustible long chain hydrocarbon fuel, to the mixing interior, heating, inside the mixing interior, the second fuel to a mixing temperature, mixing, in the mixing device, the first fuel with the heated second fuel to form a fuel mixture, and combusting the fuel mixture with a burner of the burner assembly to create the fire.

28. Method according to claim 27, further comprising the step of: heating, inside the mixing interior, the first fuel to a vaporizing temperature to vaporize the first fuel inside the mixing interior.

29. Method according to claim 28, further comprising the steps of: measuring, with a first temperature sensor located in the mixing interior, the temperature inside the mixing interior, e.g. in a first interior section thereof, and controlling, with a control unit, the heating of the first fuel on the basis of the measured temperature to set the vaporizing temperature.

30. Method according to any of the claims 27 - 29, further comprising the steps of: measuring, with a second temperature sensor located in the mixing interior, the temperature inside the mixing interior, e.g. in a second interior section thereof, and controlling, with the control unit, the heating of the second fuel on the basis of the measured temperature to set the mixing temperature.

31. Method according to any of the claims 27 - 30, wherein the first fuel is in a liquid state at room temperature, for example comprising an alcohol, such as ethanol, or a spirit, for example comprising alcohol and up to 50wt% of water.

32. Method according to any of the claims 27 - 31 , wherein the second fuel is in a solid state at room temperature, for example comprising a wax, such as paraffine, stearin and/or candle wax.

33. Method according to any of the claims 27 - 32, wherein the second fuel is in a liquid state at room temperature, for example comprising lamp oil and/or paraffine oil.

34. Method according to any of the claims 27 - 33, comprising a preheating cycle for preheating the burner to a predetermined preheating temperature, the preheating cycle comprising the steps of: supplying the first combustible fuel to the burner, via the mixing device, combusting the first fuel with the burner of the fireplace to create the fire, and heating the burner by means of the fire, wherein the preheating cycle is terminated and the second combustible fuel is supplied to the mixing device and mixed with the first fuel after a temperature of the burner exceeds the predetermined preheating temperature.