This invention relates to the field of alcohol-burning fires and, in particular, to a design of burner compartment that generates heat and flame through the combustion of ethanol for use in such fires.

With a rising demand for environmentally-friendly living, the market for alternative fuel sources has grown rapidly in recent years. Ethanol is particularly attractive as a fuel in that its combustion products are carbon dioxide and water, which cause no damage to the environment. A fireplace that bums ethanol provides the aesthetics of a real flame without the requirement for a chimney or flue, which represents a significant source of heat loss in gas and solid fuel fires. In addition, the absence of a flue means that an ethanol fire can be installed in any room and in any part of that room, even centrally or inset to a wall. An ethanol-fuelled fire therefore is environmentally-friendly, efficient and versatile, which has led to its increasing popularity for home, commercial and garden use.

Whereas traditionally ethanol has been sourced from petrochemical feed stocks, it is now increasingly being derived from the fermentation of the sugar and starch components of plant materials such as sugarcane and com as well as more sustainable non-food stocks such as tree trimmings, wheat straw and fast-growing grasses. The term “bioethanol” is used to indicate the more sustainable origin of biologically-derived ethanol as opposed to that of its chemically-synthesised equivalent. Fireplaces based on ethanol combustion are now almost universally sold as bioethanol fires, to be run on bioethanol fuel, maximising its environmentally-friendly credentials.

Although in theory bioethanol will combust to produce only carbon dioxide and water, complete combustion is, in practice, difficult to ensure. Insufficient residence and reaction time in the ethanol burner allows combustion products escape the burner boundaries before their reaction is complete. Various hydrocarbon products, which are identifiable by their strong, unpleasant small, are therefore also emitted. If present in the environment for any length of time, such hydrocarbon by-products tend to cause headaches and discomfort. The problem of incomplete combustion is exacerbated by the fact that bioethanol fuel quality varies. Commercially available bioethanol fuels tend to have an ethanol component in the range of 85 - 97%. Some impurities are deliberately added to prevent consumption; others are a by-product of the biological production process. Regardless, their presence affects combustion efficiency, the heat output and level of hydrocarbon emissions.

EP 3 211 304 describes a bioethanol stove in which bioethanol is stored in a reservoir and transferred, as needed, to a separate burner bed. A controller adjusts the feed rate of the fuel in order to maintain its level during the combustion process. Having a limited quantity of fuel present in the burner bed increases the likelihood of complete combustion. This document however acknowledges that the design can be improved and complete combustion is further encouraged by including a carburettor in the pipe system in order to atomise and aerate the bioethanol after it is drawn from the reservoir and before it is sprayed onto the burner bed. A carburettor though increases the complexity of the system as well as its cost. Moreover, the carburettor itself has been found to be insufficiently reliable to guarantee consistency through the combustion process and its safety has been questioned.

Despite the fact that combustion occurs in the burner bed, surprisingly little research has been done into the effects of bed design and most known prior art bioethanol fires use a simple rectangular tray. EP 3 211 304 describes a tray with outwardly sloping sides as well as one with a V- shaped profile that rests in a broader trough that not only holds it in position but also catches any spills. BE 1018106 also discloses a burner with a V- shaped profile and describes how the oblique walls enable the edges of the burner to remain clear of the flames so they do not inhibit the combustion process. That is, this shape encourages complete combustion. Moreover, less fuel is needed to be stored in the V-shape profile to achieve the same level of flame, making this type of burner safer. Finally, the angle of the V- shape influences the oxygen that is fed into the combustion process, which in turn affects the size of the flame. Nonetheless, despite these advances, it is apparent that incomplete combustion can too easily occur, causing odour, discomfort and headaches.

There is therefore a perceived need for an alternative design of alcohol- burning fire system, which avoids the complexity of the prior art whilst maintaining aeration of the flame to encourage complete combustion.

According to a first aspect, the present invention provides a burner for the combustion of a liquid alcohol fuel, the burner comprising a longitudinally extending burner tray with a lower region and upper region, wherein: the lower region includes lower side walls that form a V-shaped cross-section; and the upper region includes upper side walls that extend upwardly and outwardly away from the lower side walls.

In comparison with the prior art, this design of tray is found to be advantageous in promoting complete combustion of a liquid alcohol fuel. In use, liquid fuel is contained in the V-shaped lower region. In comparison with a tray of rectangular cross-section, the shape of this region allows the volume of fuel to be accurately controlled: a small change in fuel volume is observable as a relatively large rise or fall in its surface level. The surface area of a liquid fuel determines its rate of evaporation and consumption. Accordingly, this can be controlled by maintaining the height of the liquid in the tray. Combustion occurs above the level of the liquid i.e. once the alcohol is heated and in its gaseous phase. It is advantageous therefore to maximise the volume of the upper region in order to reduce the likelihood of gaseous products escaping the burner before their reaction is complete. In brief, the lower region of the tray allows accurate control of the rate of fuel consumption, the upper region increases residency time in the burner, allowing time for the combustion reaction to run to completion.

The lower and upper side walls may meet at a smooth transition zone, or they may be discontinuous, separated by a horizontal, vertical or sloping surface. In preferred embodiments, the lower side walls of the lower region form an angle at the V-shaped cross section that is within a range of 25° to 35°, preferably 27° to 33° and, most preferably, around 30°. It is also preferred that the upper side walls of the upper region are inclined such that extensions of the side walls would intersect at an angle within a range of 80° to 120°, preferably within a range 90° to 110° and, most preferably, around 100°.

The burner may include a fuel level sensor, the sensor extending into the burner tray, and preferably the lower region of the burner tray, and is configured to provide a signal dependent on whether the sensor is in contact with air or liquid. The sensor may be in communication with a microprocessor, the microprocessor arranged to stop or start action of a pump configured to deliver fuel to the burner tray in response to a signal received from the sensor. This provides an accurate mechanism by which to maintain liquid level in the burner tray and so control the rate of combustion. The sensor may comprise a pair of electrodes separated by a gap, the electrodes preferably being spark electrodes.

The burner tray may further include at least one inlet that is in fluid communication with a fuel reservoir, the at least one inlet being located towards a base of the lower region. This provides an access point for fuel being pumped into the burner tray. It may also include a respective splash cap extending across the lower region above the at least one inlet. This helps prevent flammable liquid splashing out of the tray and presenting a fire-risk.

A burner preferably includes a burner sump of rectangular cross section in which the burner tray is mounted on a series of mounting brackets.

The burner may include a ceramic heater, which is preferably in the form of a glow plug, in contact with the burner tray. This provides a reliable low- voltage mechanism with which to ignite the alcohol in the tray.

The tray preferably includes a series of slots arranged along the side walls to allow for its expansion and contraction. In the absence of these slots, or other such precaution, the burner tray is found to buckle under thermal stress as the temperature changes.

In a second aspect, the present invention provides an alcohol-burning fire including: a burner as described above a reservoir for storing liquid alcohol; and a pump arranged to pump alcohol from the reservoir through a pipe network to the burner tray.

In a further aspect, the present invention provides an alcohol-burning fire including: a burner as described above a microprocessor; a reservoir for storing liquid fuel; and a pump arranged to pump fuel from the reservoir through a pipe network to the burner tray; wherein the microprocessor is arranged to control activation of the pump in response to the signal from the fuel-level sensor. This provides an alcohol-burning fire that enables complete combustion of its liquid-alcohol fuel. The shape of the burner tray combined with a sensitive mechanism for controlling the level of liquid fluid within together give control of combustion and improved residency time in the burner tray.

The microprocessor may be arranged to switch off the pump in response to a signal from the sensor indicating that fuel in the burner tray has reached the sensor. It may alternatively be arranged to switch on the pump in response to a signal from the sensor indicating that the sensor is clear of ethanol. In either case, the pump may be switched for a set period of time.

The invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is an exploded view of an alcohol-burning fire in accordance with the present invention;

Figure 2 is an exploded view of the burner component of the fire shown in Figure 1 ;

Figure 3 is an exploded view of the burner tray, showing the pumping system used to set and maintain fuel levels;

Figure 4 is a cross-sectional view of the assembled burner component; and

Figure 5 is a perspective view of the assembled alcohol-burning fire.

With reference to Figure 1 , an alcohol-burning fire 10 in accordance with this disclosure includes a longitudinally extending burner compartment 12 and a fuel tank 14 for storing liquid alcohol fuel that, together, fit within a housing 16. In the following specific embodiments of the invention, the liquid alcohol fuel is assumed to be bioethanol, as it is with this fuel that the market for alcohol-burning fires is largest. It will however be apparent to one skilled in the art that the burner and fire in which it is contained are capable of combusting any liquid fuel, although they are particularly adapted to small chain alcohols, such as ethanol. The reference to bioethanol reflects only a preference for a more environmentally-friendly method of operation.

The burner compartment 12 provides a trough in which bioethanol is held as it combusts and rests on supports 18 to one side of the housing 16. The combusting ethanol heats the environment as well as providing an aesthetically-pleasing flame that extends along the length of the burner compartment. The fuel tank 14 is located towards the base of the housing 16 and on an opposite side from the burner compartment 12, maximising the distance between the stored bioethanol and the heat and flame of combustion. The tank 14 is fully enclosed and can be filled via a covered aperture 20 in its upper surface. A window 22 is also provided in order to allow a user to check the fill level. A pump 24 is arranged to extract bioethanol from the tank 14 by means of a connecting pipe 26 that exits from its upper surface. The pump 24 links to a network of burner pipes 28 that provide a feed to the burner compartment. In the embodiment shown, there are three inlets 30a, 30b, 30c from the pipe network distributed in a lower region along the length of the burner compartment 12. A power control assembly 32 is also fitted within the housing 16 and includes a printed circuit board (PCB). A microprocessor (not shown) and processing electronics for sensors and user inputs are mounted on the PCB, enabling microprocessor control of operation of the various components of the burner in response to sensor signals and user inputs. A safety switch 34 is configured to trigger on removal of a top plate from the housing 16 and to send a signal to the microprocessor. On receipt of this signal, the microprocessor is arranged to shut down power to the pump 24 and switch off the fire. This safety feature prevents a user from adding any fuel to the tank 14 while there are naked flames in the burner. With reference now to Figures 2 and 3, the burner compartment 12 comprises a burner tray 38 that is supported by a series of mounting brackets 40 that connect the tray to a floor of a burner sump 42. The burner sump 42 is substantially rectangular in cross section, which provides stability to the compartment 12. It is also wider than the burner tray 38, allowing it to safely catch any bioethanol that may spill from the tray, for example if the fire is knocked or moved. The burner tray 38 comprises a lower region 44 with a V-shaped cross section and an upper region 46 with sides that extend outwards and upwards from the V-shaped lower region 44 but at a shallower angle than the sides of the lower region. A transition zone 48 delineates the position at which the slope changes between the two 44, 46 regions. With reference specifically to Figure 3, it can be seen that each mounting bracket 40 has a V-shaped notch 40a in its upper edge in order to accommodate the V-profile of the lower region of the burner tray 38.

This shape of burner tray 38 is found to be particularly advantageous in encouraging the complete combustion of fuel, ideally bioethanol, contained within. First, it is noted that it is important to control the level of fuel in the burner tray 38. This not only dictates the height I intensity of the flames but also affects the efficiency of combustion. The combustion reaction occurs with bioethanol in its gaseous phase i.e. in a region above the liquid bioethanol. The surface area of the liquid in the burner tray 38 determines the rate of its evaporation I consumption. In a V-shaped burner tray 38, the surface area is clearly linked to the level of liquid. Next, the volume above the liquid has to be sufficient for the combustion reaction to run to completion, before any partially-reacted products can escape the burner. This is also affected by the level of bioethanol. In the V-shaped lower region 44, the sharp basal angle and steeply-sloping sides mean that displacement of a relatively small amount of liquid will lead to an observable change in liquid height. This makes maintaining liquid height a sensitive mechanism with which to control combustion. In addition, the volume of bioethanol below the surface and that will replace fuel as it combusts, is minimised, reducing the degree of damage should the flammable substance catch fire unintentionally. In contrast, the shape of the upper region 46 is such that the volume increase is much larger for a small rise in height. This provides a larger volume within the burner in which combustion can take place (in comparison with a fully V-shaped burner), giving a longer residency time for the reactants in the burner. This increases the likelihood of the reaction running to completion. Moreover, the sides of the upper region 46 move away rapidly from the combusting product, reducing the likelihood of interference with the flames, which may hinder combustion.

With this two-part design of burner tray, it is found that there is no requirement for additional aeration by means of apertures in the sides of the tray. In the prior art described in EP 3 211 304, such apertures that are intended to improve the supply of oxygen are in fact found to entrain excess air, which increases fuel consumption, and to cause turbulence, which reduces combustion efficiency. The effect of these apertures is therefore to increase emission of hydrocarbons and carbon monoxide.

In addition to the advantageous shape of burner tray 28, the present invention provides an improved ignition system in comparison with the bioethanol fire described in EP 3 211 304. For this purpose, a silicon ceramic heater 50 is provided. The heater 50 is similar to a glow plug and is fixed to a ledge 54 of the burner sump 42 extending inwards to contact the metal walls of the burner tray 38. For safety, that part of the heater that remains outside of the sump is fitted with a protective cover 56. During the ignition process, under control of the microprocessor, the heater 50 is energised and its tip heats up rapidly to a temperature of over 1000°C. The bioethanol rapidly ignites and the flame spreads to extend the length of the burner tray 38. Many prior art bioethanol fires require manual ignition and automatic ignition systems that have been incorporated in such fires tend to require a high voltage, have a less reliable sparking system and are more costly.

As noted above, for complete combustion to occur, it is important to maintain the level of bioethanol within the novel design of burner tray. Accordingly sensors 58 extend into the burner tray 38 through holes located at around the level of the transition zone 48. Data output from the sensors 58 is passed to the microprocessor. In this embodiment, the sensors 58 are a pair of spark electrodes, which are good metal conductors (tungsten alloy) protected by thermally insulating ceramic. The pair of electrodes 58 act as a capacitor, which will have a fixed capacitance value in air. The capacitance will change if the gap between the electrodes is filled with bioethanol. A voltage is therefore applied across the electrodes as the pump 24 is operated to supply bioethanol from the tank 14 to the burner tray 38. On detection of a change in capacitance, the pump 24 is stopped by the microprocessor. After a set period of burner operation, the pump 24 is restarted and voltage reapplied to the sensors 58 to repeat the top-up procedure. In this way, the level of bioethanol in the burner tray 38 can be precisely maintained.

With reference again to Figure 3, it is noted that a series of slots 62 are arranged at intervals along the sides of the upper region 46 of the burner tray 38. These slots 62 allow sufficient movement for the tray to accommodate expansion and contraction that will occur during use of the fire. The gaps within the slots are however narrow in order to prevent entrainment of oxygen, which is one of the problems of the prior art.

Figure 4 is a cross-sectional view of the burner compartment 12 when assembled. The V-shaped lower region 44 of the burner tray makes an angle a at its apex, whereas the sides of the upper region 46, if they were projected, would intersect at an angle p, p » a. It has been found that the angle a at the base of the lower region 44 should be in the range 25° - 35°, preferably 27° - 33° and, more preferably, around 30°. The projected intersection angle 0 of the sides of the upper region 46 should be in the range 80° - 120°, preferably 90° - 110° and, more preferably, around 100°.

The burner pipe 28 shown in this diagram connects to an inlet 30a near the base of the V-shaped lower region 44. A splash cap 64 extends across the width of the lower region just above and in the vicinity of the inlet 30a. This prevents the bioethanol splashing as it is fed into the burner tray 38. This reduces the risk of ethanol being agitated out of the burner, which would present an obvious safety risk. Moreover, it also reduces turbulence within the burner, which could lead to erratic combustion.

Figure 5 illustrates the housing 16 with burner compartment 12, bioethanol tank 14 and power control assembly 32 all fitted within. The bioethanol fire 10, as shown, is ready for incorporation in a decorative fireplace. The fireplace may include simulated fuel: imitation coal, logs and the like; or it may simply hide the fire, leaving the flames visible, depending on user taste.