"LIQUID FUEL COMBUSTION DEVICE FOR DOMESTIC HEATING, LIQUID FUEL STOVE COMPRISING SAID COMBUSTION DEVICE AND RELATIVE COMBUSTION METHOD OF THE LIQUID FUEL"

FIELD OF THE INVENTION

The present invention concerns a combustion device for domestic heating and a stove comprising this combustion device, to produce thermal energy by means of the combustion of a liquid fuel, in particular, but not restrictively, ethyl alcohol. The combustion device according to the present invention can be used both in stoves, and in free flame heating apparatuses, also called fireplace appliances.

In particular, the present invention is applicable to medium-small housing units, such as apartments and mini-apartments.

The present invention also concerns the relative combustion method of the liquid fuel for use in domestic heating.

BACKGROUND OF THE INVENTION

It is known to manufacture liquid fuel stoves for the cooking of food and for heating, which are of the transportable type, for example for boats or campers. The liquid fuel generally used is ethyl alcohol, or a suitable hydrocarbon such as kerosene, or other suitable liquid fuels.

Alcohol is a particularly advantageous liquid fuel for such stoves, thanks to its low risk of explosion, its stability during transport and in storage, its absence of suffocating fumes and in general its low danger level in the event of fuel leaks. Alcohol is also relatively economical and easily available. One disadvantage of the stoves in question is connected to the difficulty of obtaining a good and efficient combustion of the liquid fuel. The traditional solution to this difficulty is to vaporize the liquid fuel and mix the vaporized fuel with air to generate an optimum combustion mixture.

In particular, the alcohol is vaporized by heating it to its boiling temperature of about 78-79°C.

However, the vaporization of the fuel presents a serious problem in cold starts, since it is necessary to provide an auxiliary source of heat, as for example the use of a flammable gas to burn initially, or other sources of heat, to vaporize the

liquid fuel.

This disadvantage lengthens the time in which the known stove takes to become effectively operative in heating.

Furthermore, the need to boil the alcohol also represents a serious risk to safety, above all in the event that the known stove is used for domestic heating.

Another disadvantage not to be overlooked is connected to the energy consumed in order to heat the liquid fuel and bring it to vapor condition.

Another solution known in the state of the art is to provide the tank of liquid fuel with a pump to put the alcohol under pressure, and with suitable injectors in the combustion chamber. The pressure is needed to create an appropriate feed and vaporization of the alcohol to the burner.

However, even this type of solution does not allow an optimum combustion, because of the difficulty of forming a correct mixture of the combustion air and the vaporized fuel and the limited time available for the formation of the mixture, due to the high pressure and speed with which the fuel is injected. Moreover, with this technique, the size of the vaporized fuel particles is in any case too high, not allowing a complete and optimum combustion.

Furthermore, disadvantages common to the solutions of stoves known in the state of the art in question, in particular those that use alcohol, are connected to the instability and fluctuation of the flame, the scarce possibility of regulating the heat generated, and the limited maximum heating capacity of the flame.

One purpose of the present invention is to manufacture a liquid fuel combustion device, particularly using alcohol, for domestic heating, and a stove comprising said combustion device, which allows an optimum combustion, which is both easy to manufacture, safe, therefore without needing to boil the liquid fuel and/or use pressure containers for the injection under pressure of the liquid fuel, and reliable.

Another purpose is to perfect a method for the combustion of a liquid fuel in a liquid fuel combustion device which is efficient, safe and reliable. The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, a liquid fuel combustion device for domestic heating according to the present invention comprises:

- a container able to contain the liquid fuel and having inside it a mixing chamber in which the mixing of the liquid fuel with air is able to take place,

- adduction means associated with the container in order to introduce, inside the mixing chamber, a stream of combustion air able to mix with the fuel; - conveyor means, mounted on the container and able to convey the fuel mixed with the air stream from the mixing chamber toward a combustion zone.

According to a characteristic feature of the present invention, the container comprises pre-heating means, able to pre-heat the liquid fuel present in the mixing chamber to a pre-determined temperature, less than the boiling temperature of the liquid fuel.

According to the present invention, a nebulization means of the ultrasound type is also provided, able to nebulize the fuel.

The ultrasound nebulization means is normally at least partly immersed in the fuel, or in any case in contact, directly or indirectly, with the surface, and determines a desired agitation of the fuel in order to nebulize it.

According to the present invention, a control unit is provided to control the functioning at least of the pre-heating means and the ultrasound nebulization means.

The pre-heating means is set to heat the liquid fuel to a suitable temperature, or temperature range, well distant from the boiling temperature.

In the case of alcohol, the pre-heating occurs advantageously to a temperature comprised between about 35°C and 50°C, preferably between about 38°C and 46°C, and therefore well distant from the boiling temperature of alcohol which is about 78°C - 79°C. The pre-heating means is, for example, a resistance of the thermo-regulated type, with a pre-determined maximum heating temperature, beyond which it deactivates, which temperature advantageously coincides with the upper limit of the temperature range of required pre-heating.

Advantageously, the pre-heating of the liquid fuel both promotes the nebulization by the ultrasound and the convective motion of the combustion mixture from below to above, and also maintains the liquid fuel at a temperature which allows the ignition of the mixture of liquid fuel and combustion air. This prevents the liquid fuel from cooling below a determinate temperature value, an eventuality which, particularly in the case of alcohol, would cause the flame to go out and therefore the combustion device not to function.

Advantageously, since the volumes of liquid fuel involved are relatively low, comprised between about 200 ml and 800 ml, but even up to about 1 ,000 ml, the pre-heating step lasts approximately from 30 seconds to 5 - 8 minutes.

The present invention advantageously uses ethyl alcohol, denatured or not. However, according to needs, other suitable liquid fuels, such as hydrocarbons like kerosene can be used.

Alcohol has the advantage that, in optimum combustion conditions, it does not produce combustion by-products that are harmful or need to be discharged into the environment. The present invention therefore does not need, for installation in closed areas, the assembly of a chimney to discharge the combustion fumes, which signifies an undoubted advantage with regard to speed and economy of installation, even in housing units which would not easily allow the building of pipes to discharge the fumes.

Another advantage in using alcohol, compared to other hydrocarbons, is that it allows to obtain nebulized fuel particles of a much reduced size, with a nominal diameter of about 0.2 - 0.3 microns, which thus allow a complete and optimum combustion, increasing the thermal efficiency. The present invention has the advantage that it performs the nebulization by means of ultrasound, operating substantially at environmental pressure, without needing to bring the liquid fuel to the boil. In this way, we obtain both an adequate mixture of the nebulized fuel with the air, which ascends at a suitable speed along the mixing chamber, and also a clear energy saving, as no thermal energy is needed to vaporize the liquid fuel. A much greater efficiency of the combustion device is also obtained, above all during cold starts, since the limit in the state of the art of the thermal inertia necessary for the vaporization of the liquid fuel is overcome by using the pre-heating described above and the

subsequent ultrasound nebulization.

According to the present invention, the mixing chamber is operative substantially at environmental pressure, and also the liquid fuel is introduced into it at environmental pressure, without being atomized under pressure during introduction.

The mixture of nebulized liquid fuel and combustion air is carried out in an efficient way, thanks to the adequately slow ascent upwards by convection of the nebulized fuel, or by ventilation.

The present invention thus allows an optimum combustion, inasmuch as the combustion mixture which is obtained is made in the correct way. Unlike known stoves in which the fuel is injected under pressure, and therefore the time in which it mixes with the air is very short and can be insufficient to create a correct mixture, with the present invention there is all the time necessary, correlated to the ascent of the nebulized fuel by convection, for the nebulized fuel to mix with the combustion air in the desired proportions.

The present invention is also simple to produce, safe and reliable.

The optimum combustion mixture, advantageously with characteristics that are constant over time, or selectively adjustable by the user, allows a good stable flame and high heat yield of the liquid fuel used. Thanks to the innovative ultrasound nebulization, the present invention also keeps the advantages of atomization that are found in the traditional vaporization technique, hot and/or under pressure, used in liquid fuel stoves, but also overcomes the disadvantages of the state of the art as we said.

The air adduction means is advantageously calibrated, that is, with a holed portion to introduce the air with a pre-determined nominal diameter, for the passage of a determinate flow of combustion air, the quantity of which is directly correlated to the quantity of nebulized liquid fuel and the need to optimize the combustion mixture for optimum combustion.

A liquid fuel stove for domestic heating that comprises a combustion device as described above also comes within the spirit of the present invention.

It is clear however, that the combustion device according to the present invention can also be used in free-flame heating appliances, also called fireplace appliances.

According to a variant, the present invention is provided with a plurality of safety measures, which are able to prevent a backfire from the combustion zone toward the mixing chamber. In particular, the conveyor means has vertical conveyor pipes with ends shaped diagonally, which in the determinate range of the nominal diameter of the pipes used in the stove according to the invention, prevent the flame from propagating.

The conveyor means also has an ascent space where there is an element sensitive to temperature, for example of the electromechanical type, such as a bimetallic blade, which in the event of a propagation of the flame into said space, is deformed as a consequence of the increase in temperature, for example above 7O ⁰ C; this deformation activates a switch that stops the electric feed which makes the stove function, and makes everything safe.

Furthermore, immediately upstream of the combustion zone and downstream of the conveyor means, there are metal grids and metal fiber elements, which function as fire barriers.

Advantageously, the metal fiber elements also function as homogenizers to homogenize the mixture of nebulized liquid fuel and combustion air, determining a uniform formation of the flame.

The provision of a temperature sensor member in the container of the liquid fuel also allows, in the case of a backfire directly in the mixing chamber, the corresponding considerable increase in temperature to be detected and supplies a signal to interrupt the functioning of the stove.

Furthermore, the means to introduce the combustion air, being advantageously calibrated, determines a limited passage of the air which, in the event of a backfire in the mixing chamber, in any case prevents the liquid fuel from igniting, since the resulting atmosphere would be poor in oxygen.

According to another feature of the present invention, a combustion method for a liquid fuel in a combustion device for domestic heating comprises the following steps: - a first step in which a determinate quantity of liquid fuel is introduced into a mixing chamber, by means of introduction means; this introduction can be done for example by pump means, in the case where the tank for the liquid fuel is located on the level of or below the container of the mixing chamber, or by free

fall possibly regulated by an electro valve in the case where the tank for the liquid fuel is located above the mixing chamber;

- a second step in which the liquid fuel is pre-heated to a temperature comprised in a determinate range, below the boiling point of the liquid fuel, by means of pre-heating means, advantageously, in the case of alcohol, to a temperature comprised between about 35°C and 50 ⁰ C, preferably between about 38°C and 45°C;

- a third step in which, once the pre-determined pre-heating temperature of the fuel is reached, the fuel is nebulized in the mixing chamber by means of ultrasound nebulization means;

- a fourth step in which the nebulized fuel is mixed in the mixing chamber with a determinate stream of air, introduced by means of adduction means;

- a fifth step in which the nebulized fuel mixed with the stream of air is made to pass from the mixing chamber to a combustion chamber, through conveyor means, in order to carry out combustion;

- a sixth step in which, in the combustion chamber and by means of ignition heating means, the fuel - nebulized and mixed with the stream of air - is ignited.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is a lateral schematic view of a stove according to the present invention;

- fig. 2 is a schematic section of part of the stove in fig. 1 ;

- fig. 3 is a section of an enlarged detail of fig. 2; - fig. 4 is a lateral view of an embodiment of a combustion device according to the present invention;

- fig. 4ais a section of an enlarged detail of fig. 4;

- fig. 5 is a front view of fig. 4;

- fig. 6 is a plane view from above of fig. 4; - fig. 7 is a partly sectioned view of the combustion device in fig. 4;

- fig. 8 is a schematic representation of one embodiment of the combustion device according to the present invention;

- fig. 9 is a schematic representation of a variant embodiment of the combustion

device according to the present invention.

DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF

EMBODIMENT

With reference to fig. 1, an alcohol stove 10 for domestic heating according to the present invention comprises a supporting frame 13 in which a combustion device 11 is housed. The combustion device 11 is able to burn alcohol, in a combustion chamber 19, for domestic heating.

An intake 15 for the entering air, taken in by suction means, in this case a suction fan 31, allows the ambient air to enter the stove 10. The air is pre-heated in a heat exchanger 21 in contact with the combustion chamber 19 and heated by the hot combustion air exiting from the combustion chamber 19. In particular, the hot combustion air, at about 250 ⁰ C, arrows G, and the pre-heated air, at about 50 ⁰ C, arrow F, mix together and exit at about 80 ⁰ C, due to convective motion, from an outlet 17, in order to heat the room. The combustion chamber 19 is separated from the outlet zone E of the hot air by a wall 25 on which a Venturi effect suction device 27 is installed, which determines a narrowing in the section where the hot air passes, arriving from the combustion chamber 19, and hence an acceleration of said air and suction toward the top and outside the stove 10. This determines, advantageously in cooperation with the suction fan 31 , a stream of air from the bottom toward the top even in the first seconds or minutes when the stove 10 starts functioning, where the effect of natural convection may not be very relevant for the ascent of the hot air.

The combustion device 11 comprises a container 12, of the box-like type made with lateral and bottom walls of stainless steel with a thickness of about 4 mm, or of plastic heat-resistant material, having inside it a chamber 14 to mix the alcohol

16, for example with a capacity of about 200-700 ml, or even about 1000 ml (fig.

T). Above the container 12, and in fluid communication therewith, an anti explosion collector 38 is provided, along which the combustion mixture is conveyed toward an ignition zone D, in the combustion chamber 19, which will be described in more detail hereafter. Here combustion is selectively triggered by an ignition heating element, for example an ignition resistance 56 or a piezoelectric element, in order to generate a heating flame 58.

As shown schematically by a continuous line in fig. 1, and shown in detail in

fig. 8, the alcohol 16 is introduced inside the chamber 14 by means of a pump 18, which could be of the vane type or impulse metering type, which is connected on one side by means of a suction pipe 22 to a tank 20 for the alcohol, underneath the container 12, for example with a capacity of about 5 liters, and on the other side is connected by means of a delivery pipe 24 to the chamber 14.

According to a variant, shown schematically by a line of dashes in fig. 1 and shown in detail in fig. 9, instead of the tank 20 underneath, it is possible to make the tank above the container 12, so that the alcohol descends through gravity or free fall inside the mixing chamber 14. An electro valve 121 controls the flow of alcohol from the top downward.

As shown in detail in the following description, the alcohol 16 in the mixing chamber 14 is pre-heated by a resistance 28 and nebulized by an ultrasound nebulizer 26 (figs. 1 and 2) or several ultrasound nebulizers (figs. 4 to 9). In the variant shown in figs. 1 and 2, the ultrasound nebulizer 26 is completely immersed in the alcohol 16. In the variant shown in figs. 4-9, the two ultrasound nebulizers 26 are mounted on the bottom of the chamber 14, and protrude inside it only with an upper surface, which causes the agitation and vibration of the fuel. In this way, by embedding the two ultrasound nebulizers 26 in the bottom of the chamber 14, and therefore reducing their height inside it, it is possible to reduce the minimum operating level of the fuel, and therefore operate with minimum operating levels, for example, of as little as about 200 ml.

The nebulized alcohol is mixed with a stream of air A entering into the chamber 14, to form an aerosol combustion mixture 34 that ascends toward the combustion chamber 19 where it is ignited. The combustion device 11 thus operates batch- wise, in the sense that, during combustion, it uses pre-determined quantities of alcohol 16 introduced on each occasion into the mixing chamber 14. The pump 18, or in the same way the opening of the electro valve 121, provides for the first load of alcohol 16, and also for subsequent refills. The alcohol 16 in fact, which is gradually used up during use, is fed into the chamber 14 until it reaches a pre-determined maximum operating level L _max inside the chamber 14.

A level sensor 36 detects the level of the alcohol 16 in the chamber and sends

a relative signal to a control unit 60, connected to the pump 18. The sensor 36 operates between two levels, L _min and L _max which are close to each other, so as to have a great sensitivity in detecting the level. For example, the difference in volume between the volume at level L _max and at level L _mm is about 40-60 ml. This means that, once this quantity has been burnt, the sensor 36 detects an insufficient level, sends a relative signal to the unit 60 which commands the alcohol 16 to be topped up.

The control unit 60, according to the level signal received from the sensor 36, automatically commands alcohol to be fed or topped up, so as to fill or keep the chamber 14 at the desired value L. The feed of alcohol is stopped when the desired level L _max is reached. The pump 18 or the electro valve 121 will again be activated when the level of alcohol 16 is lower than a determinate minimum operative level L _1111n . For example, with the quantities indicated above, it is possible to fill up the alcohol 16 about every 10 - 20 minutes of standard functioning.

If the sensor 36 detects a level insufficient for a time of longer than a predetermined value, for example about 1 - 2 minutes, it sends a signal that is interpreted as a safety alarm by the control unit 60.

In particular, in the part of the chamber indicated by the letter B, the part normally filled with alcohol 16, below the level L, the ultrasound nebulizer device 26, of a known type, is provided, which is immersed in the alcohol 16 and, when functioning, nebulizes it or atomizes it, generating the cloud of aerosol 34. The power of agitation and excitation of the alcohol 16 by the ultrasound device 26 can be selectively regulated and the regulation is made by the control unit 60. It is clear that, according to requirements, two or more ultrasound devices 26 could be installed.

The aerosol 34 ascends upward in the part of the chamber 14 indicated by the letter C, where it mixes thoroughly with the stream of air A arriving from outside the chamber 14, in particular through a pipe 30. A valve 32 is provided in the pipe 30, of the open/close type, with the function, determined by the control unit 60, of allowing or preventing the stream of air A into the chamber 14. Downstream of the valve 32 a calibrated hole 33 is provided, which opens into the mixing chamber 14 and which allows the passage of a flow of combustion air

with a value pre-determined a priori during the design phase, according to the combustion characteristics to be given to the stove 10.

The part C of the mixing chamber 14 has sizes in height and plane designed so that the time taken for the nebulized alcohol to ascend is such as to allow an optimum formation, in the desired proportions, of the combustion mixture with the stream of air A.

In particular, the pre-heating resistance 28, of the thermo-regulated type to a maximum heating temperature for example of about 50 ⁰ C, is immersed in the alcohol 16, in part B of the chamber 14, disposed between the nebulizer device 26 and the minimum operating level L _min of the alcohol 16.

The resistance 28 serves to pre-heat the alcohol 16 so as to assist the nebulization and formation of the aerosol 34, the convective motion from the bottom upward and subsequent combustion, advantageously at a temperature comprised between about 35°C and 50 ⁰ C, preferably between about 38°C and 45°C. The resistance 28 has a propedeutic function with regard to the subsequent combustion, allowing the combustion mixture to have a temperature sufficient for an effective combustion.

By regulating the pre-heating temperature the thermal yield of the stove 10 is also regulated and optimized, that is, substantially, the temperature of the air exiting from the outlet aperture 17.

The temperature of the alcohol 16 and the functioning of the resistance 28 are controlled by a temperature probe 29 mounted in the chamber 14, connected to the control unit 60 so as to render the management of the heating automatic, also as a function of the level of alcohol 16. The functioning of the temperature probe 29 is synchronized with the level sensor 36, so as to avoid a situation in which the resistance 28 is not completely immersed in the alcohol, and thus prevent overheating and damage to the stove 10.

The aerosol 34 thus formed, mixed with the combustion air A, then ascends due to convection and/or the Venturi effect of the suction device 27, through the collector 38, in particular by means of a series of conveyor pipes 40 disposed on three rows, which convey the aerosol 34 upward, from the chamber 14 toward the ignition resistance 56. The pipes 40 develop vertically inside the collector 38 in a

suitable conveyor zone 46 (figs. 2 and 3).

The collector 38 is connected to the container 12 by means of a plate 42, which functions as a cover for the chamber 14. The plate 42 is suitably shaped so that the pipes 40 can be assembled vertically. Immediately after the conveyor zone 46, the collector 38 provides an ascent zone 48 which takes the aerosol 34 mixed with air A toward the ignition resistance 56.

The ascent zone 48 is provided with a sensor with a bimetallic blade 43 (fig. 2). If there is a backfire and a violent increase in temperature in the zone 48 or the upper part C, the sensor 43 deforms correspondingly, and mechanically closes a feed circuit which stops the electric feed to the stove 10, for safety reasons.

The conveyor zone 46 and the ascent zone 48 are made as two box-like bodies, adjacent and offset upward, open one toward the other, so that the upper ends 44 of the pipes 40 are at about half-way up the height of the ascent zone 48 and the combustion mixture can pass from one zone 46 to the other zone 48 (fig. 3).

In particular, the ends 44 of the pipes 40 are cut diagonally and open precisely toward the ascent zone 48. The shaped profile reduces the risks of a backfire.

Furthermore, the cross section and length of the pipes 40 is calibrated in a desired manner. This geometric disposition of the zones 46 and 48, and also the particular geometry and calibration of the pipes 40 and their shape at the end 44, are all strategies that allow to convey the aerosol 34 mixed with the combustion air A in such a manner as to prevent backfires toward the mixing chamber 14.

Before reaching the resistance 56 in the combustion zone D, the aerosol 34 mixed with air A and arriving from zone 48 passes through a separator made of metal fiber 50, of the steel wool type, supported by a lower sealing grid 52 and an upper sealing grid 54. The grids 52 and 54 advantageously have a fire barrier function.

The function of the metal fiber separator 50 is both to homogenize the combustion mixture ascending from the collector 38, so as to have a uniform flame generation, and also as a fire barrier, creating conditions that discourage the propagation of a backfire toward the mixing chamber 14.

Immediately above the upper sealing grid 54, in correspondence with its external surface, the ignition resistance 56 is provided, operating at about 480°C,

or a piezoelectric element, where the aerosol 34 is ignited.

The functioning of the stove 10 is very efficient since, for example, with about 5 liters of ethyl alcohol, denatured or not, it gives about 24 hours of heating, that is, about 4-5 hours per liter of alcohol. The generation of the flame 58 can be interrupted at any moment by acting on the valve 32 to interrupt the stream of air A.

To summarize, the stove 10 advantageously provides a plurality of safety measures to prevent backfire in the mixing chamber 14, which are:

- shape of the profile 44 of the pipes 40; - sensor with bimetallic blade 43;

- metal grids 52 and 54;

- metal fiber separator 50.

Moreover, as an additional safety measure apart from the heat regulation of the resistance 28, which pre-heats to a determinate temperature value, the temperature probe 29 detects any possible anomalous increases in temperature, for example due to a backfire, in the mixing chamber 14, possibly sending a suitable signal to the control unit 60, which stops the functioning of the stove 10.

Further safety is given by the calibrated hole 33, which introduces air only in determinate conditions of the combustion mixture, defined during the design phase. A backfire or other functioning anomalies in any case would not cause the alcohol to ignite, since there would not be a quantity of oxygen sufficient for the anomalous conditions.

Furthermore, the volume of alcohol 16 in the container 12 is relatively low and if it were ignited, even if there were a sufficient quantity of oxygen, it would possibly cause it to burn until it were finished, without any danger for the environment outside the stove 10.

The stove 10 in general functions on electricity; there is a general on/off switch provided, accessible to the user, which starts or ends the functioning of the whole. The control unit 60 is advantageously of the multifunctional type, in the sense that it controls switching on, level, ultrasound device 26, the suction fan 31 , the pre-heating resistance 28 and ignition resistance 56, the temperature probe 29, the safe functioning and the automatic switching on and off of the whole, depending

on possible alarms or malfunctions.

With particular reference to figs. 4-9, in which the same reference numbers are used for the same parts as in figs. 1 and 2, the combustion device 11 mainly provides an anti-explosion collector 38 of a smaller size than in figs. 1 and 2. In fact, in this embodiment, above the mixing chamber 14, as a safety measure, the anti-explosion collector 38 has a passage zone 70 for the aerosol 34 that has a longitudinal slit 72 of an oblong shape (fig. 4), with a width of a few millimeters, through which the aerosol 34 is obliged to pass. The passage zone 70 is more easily visible in fig. 4a, defined by two steel sheets which are part of the collector 38, with two walls, first convergent and then parallel, that delimit the slit 72. The parallel parts of the sheet extend upward for example by about 15 mm and are separated by about 3 mm. In this solution, upstream of the slit 72 with respect to the ascending stream of aerosol 34, grids or holed sheets 52, 54 are in any case provided, made of steel, of which one is lower and planar and one is upper and shaped like an upside-down V. In the compartment created between the grids 52 and 54, a separator 50, made of metal fiber such as wire wool, is provided. This variant, in short, is lighter and less cumbersome, but in any case is equally safe, as far as backfires are concerned.

In fact, apart from the action of the grids 52, 54 and the separator 50, the slit 72 determines a narrowing or restriction of the passage for the stream of aerosol 34 upward, which causes a great acceleration of the aerosol 34. In this way, since the speed of passage of the aerosol 34 is much higher, any backfire is prevented. Furthermore, since the space is very narrow, the environment along the slit 72 is saturated with nebulized fuel, and has substantially no, or in any case little, oxygen, thus discouraging possible ignitions and backfires.

The combustion device 11 shown in figs. 4-9 also comprises aeraulic blower means, in this case a blower fan or ventilator 132, installed in a lower position, upstream of the air adduction pipe 30, by means of which the stream of air A is introduced into the pipe 30 and from here into the zone of the mixing chamber 14 along which the aerosol 14 ascends. The thrust of air determined by the blower fan 132 facilitates the ascent thereof, with the advantages we discussed before.

By varying the power supplied to the blower fan 32, advantageously automatically, or manually, by means of the control unit 60, it will thus be

possible to consequently vary the flow rate of air inside the mixing chamber 14, in this way interrupting at any moment the flame 58, simply by stopping the blower fan 132.

The blower fan 132 can therefore advantageously replace the valve 32 as above.

Furthermore, the blower fan 132 can also be provided simultaneously with the suction fan 31, to have an efficient and great stream of air ascending.

In this case, the combustion device in figs. 4-9 comprises two ultrasound nebulizer devices 26, to nebulize the alcohol 16, located on the bottom of the mixing chamber 14.

Furthermore, in this solution the air adduction pipe 30 has a plurality of calibrated holes 33, made with a defined inter-axis, to obtain an increased and uniform introduction of air into the mixing chamber 14 and a consequent optimum mixture of the ascending aerosol 34. The holes 33 are sized to introduce a desired quantity of air, for safety reasons.

The combustion device 1 1 and the relative stove 10 according to the present invention function as follows.

First of all, the container 12 is filled with alcohol 16 by means of the pump 18 or the selective opening of the electro valve 121, until the maximum operating level L _max is reached, signaled by the level sensor 36. When this level is reached, the control unit 60 commands the alcohol feed to stop.

After the functioning of the stove 10 has been started by means of the switch described above, the control unit 60 controls the level of alcohol 16 in the mixing chamber 14, and if necessary commands a fill-up. Afterwards, the control unit 60 commands the resistance 28 to start pre-heating, to take the alcohol 16 to about

38-45°C; this step can take for example 6-8 minutes.

Simultaneously, the ignition resistance 56 is activated, to heat up to the desired ignition temperature of about 480 ⁰ C. If a piezoelectric element is used, instead, the need to heat the resistance before ignition, and the relative wait, is obviated. Once the alcohol 16 is at the desired temperature, the control unit 60 commands the valve 32 to open, or the blower fan 132 to activate, and a determinate stream of air A is started, that enters into the mixing chamber 14, through the calibrated hole 33, or several calibrated holes 33, according to the

solution shown in figs. 4-9.

Furthermore, the control unit 60 activates the suction fan 31 which takes in ambient air to be heated from the intake 15 to the outlet 17 and/or the blower fan

132 can be activated, to introduce the desired stream of air A. A stream of air is created in outlet, initially cold, promoted both by the Venturi effect of the device

27, and also by the suction fan 31 and/or the blower fan 132.

At this point, the control unit 60 activates the nebulization of the alcohol 16, which now has the desired pre-heating temperature, by means of the ultrasound device 26. The aerosol 34 which is thus formed begins to ascend along the pipes 40 of the collector 38, until it reaches the combustion zone D, where the ignition resistance 56, already suitably heated, determines the ignition and combustion begins.

In the combustion chamber 19 a temperature probe 39 is mounted which, if the temperature in the combustion chamber 19 exceeds a determinate value, for example about 150 ⁰ C, sends a relative signal to the control unit 60, indicating the presence of a flame and hence that combustion has started. After a determinate time interval for stabilization, for example about 1 minute, the control unit 60 can then switch off the ignition resistance 56, preventing early wear.

If the temperature goes below the determinate value, the probe 29 sends a different signal to the control unit 60, which causes a malfunctioning signal of the stove 10 and it is deactivated for safety reasons.

The hot air that ascends, due to the Venturi effect and then also due to convection, gradually heats the combustion chamber 19, so as to obtain the desired heat exchange with the stream of ambient air F entering the heat exchanger 21.

In this way the desired heat balance is achieved between the streams of entering air, exiting air and combustion air.

The temperature and quantity of air generated the stove 10 can be regulated by acting on the pre-heating temperature of the alcohol 16. For example, the resistance 28, being thermo-regulated, can pre-heat the alcohol to three or more different temperature values, so as to define a relative and desired temperature profile for the heating. This regulation can be determined by the user, acting by means of a display interface and push button panel associated with the control

unit 60. It is clear that the temperature profile can be programmed automatically, to define desired temperatures over a determinate period of time.

It is clear that modifications and/or additions of parts and/or steps may be made to the liquid fuel combustion device 11 for domestic heating, the stove 10 comprising said combustion device 11 and the relative combustion method for liquid fuel as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of liquid fuel combustion device for domestic heating, the stove comprising said combustion device and the relative combustion method for liquid fuel, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.