The invention relates to a device for sucking a gas or a gas mixture and for mixing it with a liquid fuel flowing in a flow duct provided with walls, the device comprising: an intake duct and an outlet duct for the liquid, the ducts having first flow cross-sectional areas; a throttle section between the intake and outlet ducts, the throttle section comprising at least one elongate throttle duct for the flowing liquid fuel; and at least one gas duct, transverse to the center line of the throttle duct, which opens as a gas supply orifice to the throttle duct, the said throttle duct forming for the flow a second flow cross-sectional area, which is substantially smaller than the said first flow cross-sectional area, and extending with a substantially unchanging flow cross-sectional area from the said gas supply orifice to a downstream distance on the downstream side of the liquid flow.

Publications EP-0 417 776 and EP-0 607 166 describe devices which include in the flow-through duct for the flowing medium a plug which considerably reduces the flow cross-sectional area, whereby, as is known, the flow velocity is increased and underpressure is produced at the point of the rapid flow. The plug is hollow, and its wall has, at a distance from the narrowest point of the gap between the plug and the flow-through duct on the downstream side of the flow, a small orifice, whereby a supply passage is created for the additive via the hollow interior of the plug and the small orifice. The above-mentioned underpressure at the point of the rapid flow sucks the additive via the small orifice into the flowing medium. The purpose is to enable an additive to be introduced also into a medium having a high viscosity, such as a gel, and to enable an additive to be introduced into a flow of a medium having a high discharge resistance. It is possible that the device described in the publications works in some manner in the conditions mentioned above, but when the flowing medium is a fuel in liquid state, such as diesel oil, fuel oil, kerosene, or the like, the flow rate of which varies within a wide range and may additionally change suddenly, and the additive supplied is a gas, such as air or oxygen, considerable problems are encountered. First, if the device according to the publications is calibrated to supply a correct gas amount into a small liquid flow, the device will not suck a sufficient amount of gas into the liquid at a high liquid flow rate. Although the increasing of the liquid flow rate does somewhat increase the underpressure, and thus the amount of gas sucked in, the gas amount does not increase to a sufficient degree. As the liquid flow increases and its velocity increases, another problem is encountered, namely, the foaming of the liquid, for which liquid fuels have a tendency and which appears when the underpressure drops sufficiently low at the point of the small cross-sectional area, regardless of whether or not there is a sufficient amount of gas entering the liquid flow. Publication EP-0 607 166 additionally describes in the additive duct a valve the purpose of which is to control the amount of additive. This is, however, a one-way valve equipped with a straight valve disc, and the valve cannot serve to control the amount, since it has only two positions, open and shut. In a structure such as this, a disturbance in the steady flow of medium, such as its sudden decrease, which is usual or regular when the device is used in a liquid fuel flow, leads to a situation in which the medium flows backward into the additive duct and all the way to the one-way valve. The result is the blocking of the additive duct and/or the one-way valve.

Publications WO-96/15848 and DE-295 14973 U1 describe arrangements corresponding to that described above for introducing an additive, such as air, into diesel oil or fuel oil. In these publications, the structure of the device in the area of the liquid duct is precisely of the type discussed in the preceding paragraph, but they additionally have a device for drying the feed air in order to decrease the relative humidity of the air. Decreasing the humidity of the air does not in the least help to solve the problems described in the preceding paragraph.

Publication WO-93/12385 describes a device arranged in the fuel supply of a heating boiler in order to inject air into a liquid fuel so that a large, number of small bubbles are formed in it. For this purpose the device includes an air bubble device, of which there are presented as embodiments a jet pump (diffusion pump), a Venturi tube, and a flow duct provided with throttling. In the throttled flow duct the intake cross-sectional area is approximately equal to the outlet cross-sectional area, and the flow-through cross-sectional area between them is much smaller than the intake/outlet cross-sectional areas, and the smallest cross-sectional area is constant within a certain distance, which is a multiple of the corresponding diameter. It is seen from the figures that the air duct comes directly to the throttle duct, and that the apparatus does not include a one-way valve opening under a certain pressure. The purpose of the air bubbles is to improve gasification of the fuel in the oil burner. Such air bubbles may indeed work in the manner intended in the publication when used in a heating boiler oil burner, in which the burner nozzle supplies fuel into a furnace under atmospheric pressure or slight underpressure. In this case the fuel pump is required to produce only a relatively low pressure, in which case the air bubbles present in the liquid fuel will perhaps not badly disturb the operation of the pump. Furthermore, in the said use the liquid fuel flow is always constant during combustion, i.e. in heating boilers the control is always so-called two-point control, i.e. the burner either operates at full power—in which case the fuel flow is always of a constant magnitude—or the burner is not at all in operation—in which case there is no fuel flow. When a combustion engine, such as a diesel engine, is concerned, it is necessary to supply fuel for very short moments, at a varying fuel flow rate and under a very high pressure, in which case the air bubbles, being compressible, cause uncontrolled changes in the fuel supply and spoil the operation of the engine. Furthermore, in a combustion engine a strongly varying flow tends to cause a back flow of fuel and, because of capillary effect, into the air ducts, where the fuel will block the small ducts, preventing further operation of the device, since the underpressure caused by the flow in the throttle is not, owing to the capillary forces, sufficient to remove the liquid fuel from the gas ducts. This problem is not solved by the construction according to the publication.

Publication EP-0 814 254 A1 discloses a mixing device for introducing air into fuel oil. The device does have an intake duct and throttle, and an air intake duct opening into it, but immediately on the downstream side there is specifically an expansion connected with the throttle, without any unchanging portion. The optimum value of the cross-sectional area of the throttle is defined as 2.5-3.8 mm

2

, and the optimum value of the cross-sectional area of the air ducts is defined as 0.013-0.025 mm

2

. The magnitude of the throttle in proportion to the intake/outlet duct, i.e. the desired underpressure, is not defined in the publication. The aim in the publication is specifically the foaming of the fuel oil which is arrived at by arranging the ratio of the cross-sectional area of the throttle to the cross-sectional area of the air ducts to be 100:1-290:1. The said expansion of the downstream side increases this foaming. The duct expansion is always open, and the air is introduced, in the case of one air duct, into the throttle directly from the same side on which it is taken from the outside. The publication also discloses embodiments having a plurality of air ducts, but in them air is supplied into the throttle from all of its sides. The objects of the publication, and the foam-like liquid fuel obtained thereby, do not work in a combustion engine, for the same reasons as stated above with respect to publication WO-93/12385.

One object of the present invention is thus to provide a device for sucking a gas or a gas mixture and for mixing it with a liquid fuel flowing in a flow duct provided with walls, in such a manner as to obtain in the liquid fuel, with practicable precision, the same gas content desired in the given case, regardless of the flow-through rate of the liquid fuel, at least when the flow-through rates are substantially variable. Another object of the invention is to provide a device of this type which would not produce foam in the liquid fuel flowing therein, or at least this foaming tendency would be minimal. A third object of the invention is to provide a device of this type, wherein the gas introduced into the liquid fuel within the throttle section would not have the tendency later to separate from the liquid fuel or this separation tendency would at least be minimal. A fourth object of the invention is to provide a device of this type, wherein the flow of liquid fuel into supply ducts for a gas or a gas mixture would be minimal in all operating situations in connecting with engines or burners or other devices using a liquid fuel. A further object of the invention is a device of this type, which would be simple and the operation of which would not require a control power source separate from the liquid fuel flow.

The disadvantages described above can be eliminated and the objects defined above can be implemented by means of the device according to the invention.

The following facts can be mentioned as advantages of the device according to the invention. Foam does not tend to be formed in the liquid fuel flowing through the device, and thereby disturbances in the supply of liquid fuel into its combustion chamber are avoided. Furthermore, in the device there is not a tendency for the liquid fuel to flow in a non-intended manner into the supply ducts for the gas or the gas mixture, and thereby disturbances in the flow of the gas/gas mixture are avoided, since the ducts intended for the gas/gas mixture remain cleaner of liquid fuel than in prior-known devices. With the help of the device of the invention, the specific amount of gas or gas mixture introduced into the liquid fuel will remain in it and will not tend to separate from the liquid fuel, wherein there is, of course, the restricting factor of the solubility of the gas/gas mixture in the liquid fuel. In prior-known devices, separation of the gas/gas mixture tends to occur even if the amount supplied ought to dissolve in the liquid fuel. By means of the device of the invention, air can thus be caused to dissolve in a liquid fuel, which thus remains a liquid and will not in any case turn into foam or gas. The device according to the invention can easily be supplemented and calibrated in accordance with the invention so that the amount of the gas/gas mixture supplied corresponds quite precisely to the desired concentration in the liquid fuel also at considerably different flow rates of the fuel, varying during operation. Furthermore, the device has the advantage that the device operates with merely the liquid fuel flow, in which case no control means driven electrically or with other pneumatics or other hydraulics are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in detail, with reference to the accompanying drawings.

FIG. 1

depicts one embodiment of the device according to the invention in its entirety in a longitudinal section through plane I-I in FIG.

2

.

FIG. 2

depicts a cross-section of those parts of the device of

FIG. 1

which are in direct contact with the liquid fuel flow, in the area of one gas duct system and through plane II-II in FIG.

1

.

FIG. 3

depicts a cross-section of those parts of the device of

FIG. 1

which are in direct contact with the liquid fuel flow, in the area of another gas duct system and through plane III-III in FIG.

1

.

FIG. 4

depicts those parts of another embodiment of the invention which are in direct contact with the liquid fuel flow, in a longitudinal section through plane IV-IV in FIG.

5

.

FIG. 5

depicts a cross-section of the device parts of

FIG. 4

, in the area of the gas ducts and through plane V-V in FIG.

4

.

FIG. 6

depicts those parts of a third embodiment of the invention which are in direct contact with the liquid fuel flow, in a longitudinal section through plane VI-VI in FIG.

7

.

FIG. 7

depicts a cross-section of the device parts of

FIG. 6

, as seen from the upstream end of the throttle ducts and through plane VII-VII in FIG.

6

.

FIG. 8

depicts those parts of a fourth embodiment of the invention which are in direct contact with the liquid fuel flow, in a longitudinal section through plane VIII-VIII in FIG.

9

.

FIG. 9

depicts a cross-section of the device parts of

FIG. 8

, through plane IX-IX in the figure.

FIG. 10

depicts those parts of a fifth embodiment of the invention which are in direct contact with the liquid fuel flow, in a longitudinal section through plane X-X in FIG.

11

.

FIG. 11

depicts a cross-section of the device parts of

FIG. 10

, through plane XI-XI in the figure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1

shows generally a device for the sucking of a gas, such as oxygen, or of a gas mixture, such as air, and for mixing it with a liquid fuel F, such as combustible oil, which flows in a flow duct provided with walls and which is burned in a burner, not shown in the figures, or an engine, not shown in the figures. The liquid fuel is here a fuel which, at least at this point of fuel feed, is definitely liquid, and the flow of liquid fuel is indicated by F*. The combustible oil may be, for example, heating oil, heavy fuel oil, diesel oil, kerosene, gasoline, etc. The invention is thus not relate to the introduction of a gas or a gas mixture into, for example, dust-like, i.e. in principle solid, fuel and not to the introduction into a gaseous fuel. It is a different matter that in the case of the device according to the invention the liquid fuel F later gasifies or is gasified for combustion. The object of the invention is specifically to obtain a liquid fuel containing oxygen or air dissolved therein so that this oxygen-enriched fuel can further be treated in a closed duct. The gas or gas mixture G dissolved in the liquid fuel F must not separate from the liquid during any further transfers of the liquid. Thus the invention in no way relates to the gasification of fuel, which is carried out substantially later and for the actual combustion process. Also, the invention does not relate to the introduction of a gas or a gas mixture into a liquid which is stationary and/or has an open surface relative to the surroundings. The invention thus relates to those situations which concern, for example, a combustible liquid F which is flowing, for example, to a burner or an engine or other targeted use and which must be as well as possible insulated/separate from the surroundings, such as engine parts causing a risk of ignition, and which must not even otherwise leak into the environment. The fuel F must thus flow in a duct, such as a pipe or a hose, tightly closed relative to the environment.

For this purpose the device has as basic parts a frame part

31

and therein a liquid fuel F intake duct

3

and outlet duct

4

, which have first flow cross-sectional areas A

1

a

and respectively A

1

b

. The intake duct

3

is connected to a liquid fuel container, not shown in the figures, which may be of any known or old type. The outlet duct, for its part, is connected to a burner, an engine, or a corresponding drive device. Inside the frame part

31

there is between the intake duct

3

and the outlet duct

4

a throttle section

1

, which forms for the flow F* of the liquid fuel F a second flow cross-sectional area A

2

, which is substantially smaller than the said first cross-sectional areas A

1

a

and A

1

b

. The first cross-sectional areas A

1

a

and A

1

b

are in general equal or approximately equal in size, but they may deviate from each other considerably, which, according to the knowledge at present, has hardly any significance in terms of the invention. The throttle section

1

has, opening into it, at least one gas supply orifice

21

, via which oxygen or air G is supplied as a gas flow G* into the liquid fuel flow F*. It is most expedient to use as the oxygen source

20

ambient air G, i.e. the atmosphere, in which case air G is sucked through an air filter

40

and further in a closed pipe or hose as a flow G* into the mixing device according to the invention.

The throttle section

1

according to the invention comprises, first, at least one elongate throttle duct

6

, as in the embodiment of

FIGS. 4-5

, or two throttle ducts

6

a

and

6

b

, as in the embodiment of

FIGS. 1-3

, or more throttle ducts

6

a

,

6

b

,

6

c

, for the flowing liquid fuel. The two or more throttle ducts

6

a

,

6

b

, etc., are coupled in parallel relative to the liquid flow F*. Each throttle duct

6

,

6

a

,

6

b

,

6

c

, or the combination thereof, forms the said second flow cross-sectional area A

2

; A

2

a

, A

2

b

, A

2

c

in such a manner that the sum of these second flow cross-sectional areas is substantially smaller than the first flow cross-sectional area, i.e. A

2

<<A

1

a

and A

1

b

, and &Sgr;(A

2

a

+A

2

b

+A

2

c

+ . . . )<<A

1

a

and A

1

b

. Into each throttle duct there opens at least one gas duct

2

via at least one gas supply orifice

21

. In particular the throttle ducts

6

,

6

a

,

6

b

,

6

c

extend, with a substantially unchanging flow cross-sectional area, from the point of the gas supply orifice

21

in the direction of the liquid flow F* on the downstream side to the distance of downstream length L

2

, which is at least equal to the mean diameter of the throttled flow cross-sectional area A

2

; A

2

a

, A

2

b

, A

2

c

. The downstream length L

2

is measured from the gas supply orifice

21

closest to the downstream end

16

b

of the throttle duct when the throttle duct concerned has several gas supply orifices. Preferably the said second flow cross-sectional area A

2

; A

2

a

, A

2

b

, A

2

c

of the throttle duct extends with substantially the same flow cross-sectional area to the distance of a downstream length L

1

which is at least twice, and typically five times, the mean diameter of the throttled flow cross-sectional area. It is known that the throttling of a flow accelerates the flow and lowers the pressure at the throttle point This lowered pressure, i.e. underpressure P

&Dgr;

, in the throttle duct

6

,

6

a

,

6

b

,

6

c

causes the suction of air or other gas or gas mixture G from the gas/gas mixture source

20

, such as the atmosphere, via gas ducts

2

and connecting ducts

7

, to be described below, and further via the gas supply orifice

21

into the liquid fuel F flowing at a high rate in the throttle duct. By means of this unchanging cross-sectional area of the throttle ducts over a sufficient downstream length L

2

, the air G or the like sucked into the liquid fuel is caused to remain in the liquid fuel so that it will not even later tend to separate from the liquid. In this manner at least almost that amount of gas G which can theoretically dissolve in the liquid fuel concerned at the temperature concerned can be caused to dissolve in the liquid fuel F. By a substantially unchanging flow cross-sectional area is meant here that the cross-sectional area A

2

; A

2

a

, A

2

b

, A

2

c

of the throttle duct changes over the downstream length L

2

at maximum 30%, preferably at maximum 20%, and typically at maximum 10%, from the point of the gas supply orifice

21

in the direction of the liquid flow F* to the end of the downstream length L

2

on the downstream a side. Typically the cross-sectional area of the throttle duct remains, within the limits of the precision of normal machining, such as the drilling of a bore, the same over this downstream length L

2

.

Furthermore, the throttle section

1

according to the invention comprises at least one gas duct

2

, transverse to the center line

8

of each throttle duct, the gas duct opening as a gas supply orifice

21

into the throttle duct

6

;

6

a

,

6

b

,

6

c

at least in the main on the first side of a plane T; T

1

, T

2

, T

3

running through its center line. The gas duct

2

continues as a connecting duct

7

outside the throttle duct

6

;

6

a

,

6

b

,

6

c

to the opposite side of the said plane T; T

1

, T

2

, T

3

, and further to the source

20

of the gas/gas mixture. This thus means that the combinations of the gas duct or gas ducts

2

and the connecting duct or connecting ducts

7

make a curve outside the throttle duct or around it so that on the first side of the curve the gas duct

2

points on one side of the plane running through the center line

8

of the throttle duct towards the throttle duct and opens into it through a supply orifice

21

, and on the other side of the curve the connecting duct

7

extends to the opposite side of this plane, in which case it may in principle point in the same direction as the supply orifice

21

on the said first side of the curve. If the throttle section

1

has several throttle ducts

6

;

6

a

,

6

b

,

6

c

, the planes T; T

1

, T

2

, T

3

, discussed above, running through their center lines are specifically parallel or at least in the main parallel. In this case the possible several connecting ducts

7

must extend to the other side of the planes disposed farthest from each other, i.e. in

FIGS. 6 and 7

to above plane T

3

, and in

FIGS. 1-3

to above plane T

2

. However, each gas duct

2

connected with a throttle duct needs to be only on the first side of its own plane, as can be seen clearly in FIG.

7

. This gas flow circulation described above from one side of the throttle ducts to the other side prevents liquid fuel from flowing in a non-intended direction, and the ducts, i.e. at least the connecting duct(s)

7

, will remain clean of liquid fuel F even when the device is not in operation, i.e. when there is no flow F*. Without this design of the invention, the liquid fuel could flow in the connecting ducts and block them or any components therein.

As a mechanical structure the device described above may, for example, include in the frame part

31

a recess

50

provided with inside threading

49

, in which case the throttle section

1

comprises corresponding outside threading

49

. The throttle section

1

may be made, according to one implementation principle of the invention, of a dense and strong material, such as a suitable plastic or metal. In this case the throttle ducts

6

;

6

a

,

6

b

,

6

c

are bores machined either to be parallel to the threads

49

, as in

FIGS. 1-3

and

6

-

7

, or possibly at a slant. However, the throttle ducts

6

;

6

a

,

6

b

,

6

c

must extend through the throttle section

1

so that the upstream ends

16

a

of the throttle ducts communicate with the intake duct

3

and the downstream ends

16

b

communicate with the outlet duct

4

. In addition, a throttle section such as this has a groove or grooves, parallel to the circumference, extending around the entire throttle section and forming an annular connecting duct

7

or, respectively, a plurality of annular connecting ducts

7

. In the area of this annular connecting duct

7

there are formed, for example, by machining one or more gas ducts

2

transverse to the length L

1

of the throttle ducts, the gas ducts typically connecting one throttle duct and one connecting duct on one side of the above-described plane T, T

1

, T

2

or T

3

of this throttle duct, as can be clearly seen in

FIGS. 1-3

and

FIGS. 6-7

. A throttle section such as this can be easily screwed in place in the frame part and to the correct depth, whereupon the annular connecting ducts

7

settle in their correct positions in alignment with the connecting duct

7

extensions

17

, transverse to the throttle ducts, in the frame part

31

. At this point it is to be noted that for each annular connecting duct

7

and its extension

17

there is one or more gas ducts

2

extending to one throttle duct

6

;

6

a

,

6

b

,

6

c

, as shown in

FIGS. 1-3

and

6

-

7

, or a plurality of gas ducts, as shown in

FIGS. 8-9

. In terms of manufacturing technology, the option described above is simple. The connecting duct

7

may also be shaped as an annular duct in the frame part

31

. In the embodiment of

FIGS. 10-11

, wherein the throttle piece in its entirety is of a porous material

36

, there is shown a structure such as this, wherein the connecting duct extends to that portion of the throttle section

1

circumference which is located on the above-described one side of a plane T running through the center line

8

of the throttle duct

6

. If the throttle piece is not of a porous material but, instead, of the above-mentioned dense material and has gas ducts

2

formed therein in the manner defined above, even in this option the connecting duct can be extended over the entire circumference.

The embodiment of

FIGS. 4-5

does not have a separate, i.e. separately made, throttle piece, but the throttle piece

1

is made up of a portion of the frame part

31

. In this case also the throttle duct

6

or throttle ducts has/have been machined directly in the throttle piece

1

constituting a structural part of the frame part, as are the gas ducts

2

and the connecting ducts

7

. The connecting ducts

7

and the gas ducts

2

, for example, are drilled into the frame part from the outside in such a manner that they intersect each other and the gas duct(s) so that it/they extends/extend all the way to the throttle duct

6

or the throttle ducts. The open ends of the apertures on the surface of the frame part are closed with plugs

19

or the like. In other respects the throttle ducts, gas ducts and connecting ducts of even this option are placed and calibrated as defined earlier in this text.

According to the invention, the gas ducts

2

, whether they are mechanically cut/machined in the throttle section or are made up of rows of pores in a porous material

36

, can be oriented towards the throttle duct or ducts

6

,

6

a

,

6

b

,

6

c

either radially or in parallel, or as combinations or intermediate forms thereof, or as an incidental combination of pores. In one embodiment of the invention, the gas supply orifices

21

of the gas ducts

2

open into the throttle ducts

6

;

6

a

,

6

b

,

6

c

entirely on the first side of a plane T; T

1

, T

2

, T

3

running through its center line, and these gas supply orifices are open into the throttle ducts within the sector the sides of which form, in relation to the said plane T; T

1

, T

2

, T

3

, an angle K

1

, K

2

, which is at least 10° or at least 30°. In another option of the invention, wherein the plurality of gas ducts is made up of rows of open pores in a porous material,

36

, the plurality of gas supply orifices

21

of the plurality of gas ducts

2

opening into each throttle duct

6

;

6

a

,

6

b

,

6

c

are located within the partial area A

6

of the throttle-duct length L

1

and the circumference, and the plurality of gas intake apertures

22

of these gas ducts for their part communicate with either one or more connecting ducts

7

. The throttle section

1

surrounding the throttle duct or throttle ducts

6

;

6

a

,

6

b

,

6

c

may be made up entirely or in part of the said porous material

36

. At least in case the throttle section in its entirety is made up of, i.e. the throttle duct/throttle ducts are surrounded on all sides by, a porous material

36

which is relatively soft or resilient, the connecting duct(s)

7

is/are disposed in the manner described above in the frame part

31

surrounding this throttle section

1

. Otherwise the connecting ducts

7

may be disposed according to need and to the manufacturing technique in the frame part

31

and/or the throttle section

1

. In the connecting duct the gas intake apertures

22

, i.e. to that end of the gas ducts or gas duct combinations produced by rows formed by pores, have an open portion of those ends which point away from the throttle duct, only on the said first side of the plane T; T

1

, T

2

, T

3

running through the center line of the throttle duct. The said partial area A

6

of the circumference ends at a distance of at least L

2

from the downstream ends

16

b

of the throttle ducts and likewise, when the throttle section is in its entirety made of a porous material, the connecting duct

7

, forming part of the circumference, ends at a distance of at least L

2

from the downstream ends

16

b

of the throttle ducts. The connecting duct/connecting ducts

7

surround the porous material

36

substantially on the said first side of the plane (T; T

1

, T

2

, T

3

) running through the center line of the throttle ducts. Thereby the general principles of the invention, described earlier in this text, can be implemented, even though, owing to the structure of the material, the path of a single gas duct cannot be known precisely. In the event that the said porous material

36

forms only part of the wall of the throttle duct or ducts

6

,

6

a

,

6

b

,

6

c

, according to the invention it is possible to use a piece which is located between the throttle duct

6

;

6

a

,

6

b

,

6

c

and the connecting duct and only on the said first side of the plane T; T

1

, T

2

, T

3

running through the center line

8

of the throttle duct. This porous material may be a metal, a metal alloy or a ceramic material or a suitable plastic, as long it is of a type which withstands chemically the fuel F and the operating temperature of the device of the invention without losing its properties which are essential in terms of the operation. Examples which can be mentioned of ceramic materials are porous glass, and of plastics, porous polytetrafluorethylene. The pores are open pores, i.e. they are open towards each other and outward, in which case a gas such as air can be sucked through it into the fuel, so that the pores form both the gas ducts

2

and the gas supply orifices

21

according to the invention; there being in this case large numbers of both of them. When necessary, that surface of such porous material forming the gas supply orifices which faces the inlet duct

3

can be protected with an end plate

41

a

, which prevents the entering fuel from penetrating the porous material

36

, as indicated by a dotted line in FIG.

10

. The porous material

36

may also be placed between two end plates

41

a

,

41

b

, for example to prevent a bypass flow between it and the frame part

31

, especially if the porous material cannot be attached to the frame part by means of a compression joint or threading.

According to one preferred embodiment principle of the invention, there open into each throttle duct

6

;

6

a

,

6

b

,

6

c

at least two gas ducts

2

at a distance L

3

parallel to the downstream length L

2

of the throttle duct and/or at a distance C parallel to the throttle duct circumference from one another. These several gas ducts communicate with one or, preferably, several connecting ducts

7

. In the case of several connecting ducts

7

there is, in one embodiment of the invention, between the gas supply orifice/orifices

21

and the source

20

for the gas/gas mixture G one valve assembly

30

;

30

a

,

30

b

,

30

c

for each connecting duct

7

, the valve assembly being made up either of only a control valve

29

or of a combination of a one-way valve

28

and a control valve

29

. According to another embodiment of the invention, two or more connecting ducts

7

, whether they are connected with one or more throttle ducts, may be connected to each other for the purpose of sucking gas/gas mixture G, in which case they are thus together coupled to one valve assembly common to them. In the device of the invention there may be one or more of these. The one-way valves

28

are coupled in such an orientation that they let the gas/gas mixture G to flow G* from its source

20

towards the throttle ducts. In another embodiment of the invention, into each separate throttle duct

6

there opens one or more gas ducts

2

at a distance L

3

parallel to the downstream length L

2

of the throttle duct from one another and/or at a distance C parallel to the circumference of the throttle duct from each other, but all of the gas ducts leading to one of the throttle ducts

6

;

6

a

,

6

b

,

6

c

are linked to a common connecting duct

7

. Even in this case there is, between the gas supply orifice/orifices

21

and the gas/gas mixture G source

20

, a separate valve assembly

30

a

,

30

b

, which is made up of a combination of a one-way valve

28

and a control valve

29

. The valve assemblies are arranged to open each under a predetermined underpressure P

&Dgr;

, usually different from those of the others, at the downstream end

16

b

of the throttle duct, as is described in greater detail below. Above there was thus noted the embodiment of the invention wherein, into one or several continuously open throttle ducts there open several gas ducts

2

, which each in turn will begin to supply gas into the fuel F when a certain underpressure P

&Dgr;

value is exceeded. When the drive device, such as a burner or an engine, is in operation, but at low power, in which case the flow F* is small for example, the gas supply orifice

21

of only one gas duct is supplying gas under the effect of suction. When the power of the drive device is increased, as the flow F* accelerates and thereby the underpressure P

&Dgr;

increases, the gas supply orifices

21

of the subsequent gas ducts, one at a time, under the effect of suction will supply more gas into the flow of fuel F. In this option all of the throttle ducts are continuously open, and the amount of the gas G supplied under suction increases as the flow F* accelerates, whereupon the amount of gas supplied per one volume unit of liquid fuel increases somewhat. It is to be understood that, as the power of the drive device decreases, also the underpressure P

&Dgr;

decreases, and the amount of gas/gas mixture G supplied will decrease gradually. This is a reverse process as compared with the increasing of the power of the drive device.

In a further alternative and preferred embodiment of the invention, which has at least two throttle ducts

6

a

,

6

b

,

6

c

, one throttle duct

6

b

is continuously open, but the other throttle duct

6

a

and any further throttle duct

6

c

comprises at the upstream end

16

a

and/or downstream end

16

b

of the liquid flow F* a one-way valve

35

a

and/or

35

b

in such a manner that the one-way valves

35

a

,

35

b

of the various throttle ducts

6

a

and

6

c

are arranged to open under an underpressure P

&Dgr;

substantially deviating from those of the others, i.e. the various other valve assemblies, at the downstream end

16

b

of the throttle ducts. The one-way valves

35

a

,

35

b

are coupled in such an orientation that they allow the liquid fuel F to flow from the fuel container towards the drive device in direction F*. Here has thus been stated that embodiment of the invention wherein the throttle ducts will open and begin each in turn to let liquid fuel F through when a certain value of underpressure P

&Dgr;

is exceeded. When the drive device, such as a burner or an engine, is in operation, but with low power, in which case the flow F* is small, for example, the gas supply orifice

21

of only one gas duct of the throttle duct will, under the effect of suction, supply gas/gas mixture G into the liquid fuel of this throttle duct. When the power of the drive device is increased, as the flow F* accelerates and thus the underpressure P

&Dgr;

increases, the subsequent throttle ducts, one at a time, will begin to open and, under the effect of the underpressure P

&Dgr;

now produced in them as a result of this, the gas supply orifices

21

of these throttle ducts will begin, under the effect of suction, to supply more gas into the flow of liquid fuel F. In this option the throttle ducts are thus open or closed, depending on the strength of the flow F*, and the amount of the gas G supplied under suction increases as the total amount of the flow F* increases, but since the number of open throttle ducts, i.e. their total cross-sectional area &Sgr;A

2

a,b,c

increases, the amount of gas supplied per volume unit of liquid fuel will remain approximately the same. Since the throttle ducts open step by step, and their number is limited, the amount of gas/gas mixture G supplied per volume unit of liquid fuel F is, of course, theoretically not continuously precisely the same but varies within certain limits. However, in practice the variation can be regarded as being so slight that, when the values of the pressure differences opening the one-way valves

35

a

,

35

b

, etc., are suitably selected, the amount of gas/gas mixture per volume unit of liquid fuel can be set at a value very close to the optimum value. This optimum value is the gas concentration which will remain dissolved in the liquid fuel concerned. It is to be understood that, when the power of the drive device decreases, also the underpressure P

&Dgr;

decreases, whereupon the one-way valves

35

a

,

35

b

, etc., will close step by step and the amount of gas/gas mixture G supplied will decrease step by step. This is a reverse process compared with the increasing of the power of the drive device.

The structural options described in these two preceding paragraphs can be used, arranged in a suitable manner, even in one and the same device according to the invention. If the upstream end

16

a

and the downstream end

16

b

of any throttle duct

6

or

6

a

or

6

b

or

6

c

has one-way valves

35

a

and

35

b

, and gas/gas mixture G is supplied into the said throttle duct by only one connecting duct

7

, it is advantageously sufficient that the connecting duct has only a control valve

29

, which will be described later in this text. If a throttle duct has at the upstream end

16

a

and the downstream end

16

b

one-way valves

35

a

and

35

b

, but gas/gas mixture G is supplied into the said throttle duct by only two or by several connecting ducts

7

, one of the connecting ducts is typically equipped with only a control valve but the other connecting ducts are equipped with valve assemblies

30

a

,

30

b

made up of a combination of a control valve

29

and a one-way valve

28

. The underpressures P

&Dgr;

by which the one-way valves of these valve assemblies are opened must be greater than the underpressure P

&Dgr;

by which the one-way valves of the throttle duct are opened, and also preferably mutually of different magnitudes in a manner which will be described in the next two paragraphs. If the throttle duct

6

or

6

a

or

6

b

or

6

c

does not have one-way valves, then preferably all of the connecting ducts

7

supplying gas/gas mixture G into it have their own valve assemblies

30

a

,

30

b

made up of a combination of a control valve

29

and a one-way valve

28

. In this case also, the valve assemblies must be such that their one-way valves open/close under underpressures P

&Dgr;

, which are described in the next two paragraphs. Thus, according to the most preferred embodiment of the invention, either the throttle duct has at its ends one-way valves, or the connecting duct

7

communicating with the throttle duct has a valve composition, but always one or the other.

In practical devices the cross-sectional area A

3

of the gas supply orifices

21

of the gas ducts

2

is at maximum 0.2 mm

2

, or preferably at maximum 0.07 mm

2

. The above values concern gas ducts formed by mechanical machining, such as drilling, in which case orifices smaller than 0.005-0.015 mm

2

are difficult to achieve. By laser beam machining it may be possible to obtain smaller orifices. By using a porous material

36

, considerably smaller gas ducts are obtained, in which case the pore size, i.e. the diameter of the cross-sectional area A

3

of the gas supply orifices, is in general on average at minimum 1 &mgr;m, but typically at minimum 3 &mgr;m, and in general on average at maximum 1000 &mgr;m, but typically at maximum 500 &mgr;m, or at maximum 200 &mgr;m. On the basis of experiments it seems that porous pieces having pores with diameters in the order of 5-35 &mgr;m (=nominal pore size, in an individual piece the pore size has some size distribution) work excellently. It is thus clear that gas ducts of different diameters are obtained by different manufacturing techniques. The flow cross-sectional area A

2

of the throttle duct

6

, the total flow cross-sectional area &Sgr;A

2

a,b,c

of the open throttle ducts, and the total flow cross-sectional area &Sgr;A

2

a,b,c

of both the open throttle ducts and the throttle ducts possibly opening as the fuel flow increases are calibrated so that at the downstream ends

16

b

of the throttle ducts

6

,

6

a

,

6

b

,

6

c

there will be during operation an underpressure P

&Dgr;

which is at least −0.1 bar (minimum value) and at most −0.6 bar, or preferably at most −0.5 bar (maximum value). With a smaller underpressure than −0.1 bar it is difficult to achieve substantial suction of gas/gas mixture G and effective dissolving of the gas in the liquid fuel F. On the other hand, under a greater underpressure than −0.6 bar the fuel F tends to foam, which causes a great deal of problems. These values are suitable for liquid fuels such as diesel oil and fuel oil. For kerosene and gasoline it is possible to use a slightly lower minimum value of underpressure P

&Dgr;

, such as −0.07 bar. For heavy fuel oil it is possible to use higher minimum values and maximum values of underpressure P

&Dgr;

, but it is to be noted that it is affected by the temperature and viscosity of the fuel oil. The values described above are based on the knowledge of today, and thus they are not to be regarded as limiting the invention. Furthermore, it is to be understood that various additives in the fuel may affect its flow properties and foaming tendency, thus changing the above-mentioned minimum and maximum values of underpressure P

&Dgr;

. The minimum and maximum values of underpressure P

&Dgr;

are indeed to be determined in advance separately for each fuel type according to need, and the second flow cross-sectional areas A

2

, A

2

a

, A

2

b

, A

2

c

of the throttle ducts and their ratios to the first flow cross-sectional areas A

1

a

, A

1

b

of the intake duct/outlet duct

3

,

4

are to be calibrated correspondingly.

One throttle duct of the device according to the invention is preferably arranged by means of either one-way valves

35

a

,

35

b

of the throttle duct or a one-way valve of the valve assembly

30

;

30