ITTO990156A1 - DEVICE AND METHOD OF DECOMPOSITION OF PARTICLES PRESENT IN THE EXHAUST GASES. - Google Patents

Description

DESCRIPTION

of the patent for industrial invention

The present invention relates to a device and a method for decomposition of particles present in the exhaust gases.

In particular, the present invention finds an advantageous, but not exclusive, application for the decomposition of particles present in the exhaust gases produced by any type of internal combustion engine, be it diesel or Otto cycle, installed on vehicles or in fixed systems, as well as in the treatment of exhaust gases produced by thermal boilers used in industrial and civil systems.

As is known, numerous harmful substances are present in the exhaust gases produced by internal combustion engines, in particular by diesel engines, such as, for example, particulate matter, unburnt hydrocarbons, nitrogen and carbon oxides, etc.

There are numerous systems and devices designed to reduce atmospheric pollution due to exhaust gases produced by internal combustion engines.

Generally, they are of the type comprising a hollow casing provided, at its ends, with an inlet for the exhaust gases to be purified and an outlet for the purified exhaust gases, and purification means interposed between the entrance and exit mouth.

For the reduction of particulate matter, the use of ceramic trap devices is known, for example, which retain the particulate present in the exhaust gas and then burn it by means of suitable heating bolts fed by a suitable combustor.

However, these devices have not found widespread use due to the excessively high cost and low operating reliability consequent to their tendency to clog, which causes an excessive increase in the back pressure to the engine which affects its regular operation.

The object of the present invention is to provide a device and a method for decomposition of particles present in the exhaust gases different from those known.

According to the present invention, a decomposition device for particles present in the exhaust gases is provided, comprising a casing provided with an inlet for the exhaust gases to be purified and an outlet for the purified exhaust gases, and means of discharge decomposition housed in said casing and interposed between said inlet and said outlet, characterized in that said decomposition means comprise magnetic field generating means generating a magnetic field crossed, in use, by the exhaust gases advanced transversely to lines of force of the magnetic field itself.

According to the present invention, a method of decomposition of particles present in the exhaust gases is also provided, characterized in that it comprises the steps of generating a magnetic field and advancing said exhaust gases within said magnetic field transversely to lines of force. of the magnetic field itself.

For a better understanding of the present invention, two preferred embodiments are now described, purely by way of non-limiting example and with reference to the attached drawings, in which:

Figure 1 is an axial section of a decomposition device according to a first embodiment of the present invention;

Figure 2 is a front view of the decomposition device of Figure 1;

Figure 3 is an enlarged scale view of a detail of the decomposition device of Figure 1;

- figure 4a schematically illustrates a first sequence of polar expansions and the direction of lines of force of the magnetic field obtained with this sequence;

Figure 4b shows the time course of the intensity of the magnetic field obtained with the sequence of polar expansions of Figure 4a;

Figure 5 schematically illustrates a second sequence of polar expansions and the direction of lines of force of the magnetic field obtained with this sequence; and - figure 6 is a longitudinal section of a decomposition device according to a second embodiment of the present invention.

Figures 1-3 show a particle decomposition device according to a first embodiment of the present invention.

The decomposition device, indicated as a whole with 1, comprises a hollow casing 2 with an elongated shape along an axis A and provided, at its opposite axial ends, with an inlet 4 for the exhaust gases to be purified and with a mouth outlet 6 for the purified exhaust gases, both having a circular section and having diameters substantially equal to each other so as to delimit the passage sections of the exhaust gases which are substantially identical to each other.

The casing 2 is made of ferromagnetic material, preferably ferritic stainless steel or iron, and comprises two half-shells 10, 12 having an approximately funnel-like shape axially coupled to each other at the ends with a larger section.

In particular, the first half-shell 10 comprises a first substantially cylindrical shaped portion 10a defining the inlet port 4; a second portion 10b having a substantially frusto-conical shape extending integrally from the first portion 10a and having an increasing diameter starting from the first portion 10a itself; and a third portion 10c of substantially cylindrical shape extending integrally from the second portion 10b and having a diameter greater than the maximum diameter of the second portion 10c itself.

The second half-shell 12 comprises a first substantially cylindrical shaped portion 12a defining the outlet mouth 6; and a second portion 12b of substantially frusto-conical shape extending integrally from the first portion 12a, having an increasing diameter starting from the first portion 12a itself and provided at the end with an annular flange 14 projecting towards the outside of the second half-shell 12 and bearing, in correspondence of its own radially external perimeter portion, a cylindrical fixing collar 15 extending transversely to the flange itself and to which an end of the third portion 10c of the first half-shell 10 is in use fixed.

A first guide body 16 having a substantially bell shape and comprising a first portion 16a having a substantially conical shape internally facing the second frusto-conical portion 10b of the first half-shell 10 is coaxially mounted inside the first half-shell 10 by means of lamellar spacers 17; and a second portion 16b of substantially cylindrical shape extending integrally from the first portion 16a, having a diameter smaller than the maximum diameter of the first portion 16a itself and facing the third portion 10c of the first half-shell 10.

The second frusto-conical portion 10b of the first half-shell 10 and the first conical portion 16a of the first guide body 16 define a first annular section cavity with a circular profile, communicating with the inlet 4 and defining a gas inlet duct 18 drain to be purified.

In particular, the second portion 10b and the first portion 16a converge towards the third portion 10c of the first half-shell 10 in such a way that the exhaust gas passage section, normal to the direction of advance of the exhaust gases, is substantially constant for the entire length of the inlet duct 18 and substantially equal to the section of passage of the exhaust gases defined by the inlet port 4 so as not to cause pressure losses and not to generate significant back pressures to the engine.

Preferably, the annular section for the passage of the exhaust gases defined by the portions 10b, 16a is comprised between 80% and 120% of the passage section defined by the inlet port 4.

The lamellar spacers 17 interposed between the first half-shell 10 and the first guide body 16 are angularly equidistant from each other inside the inlet duct 18 and conveniently have a helical vane shape so as to define flow orienting elements having the purpose of imparting a helical movement to the exhaust gases flowing through the intake duct 18.

Inside the second half-shell 12 is mounted coaxially, by means of lamellar spacers 19, a second guide body 20 having a substantially bell-shaped shape, internally facing the second truncated-conical portion 12b of the second half-shell 12 and provided at the end with a protruding annular flange 22 towards the inside of the second guide body 20 and carrying, in correspondence with its own radially internal perimeter portion, a cylindrical fixing collar 24 extending transversely to the flange 22 itself and to which an end of the second cylindrical portion 16b is in use fixed of the first guide body 16.

The second frusto-conical portion 12b of the second half-shell 12 and the first conical portion 20a of the second guide body 20 define a second annular section cavity with a circular profile, communicating with the outlet 6 and defining a gas emission duct 26 purified exhaust pipe substantially equal to the intake duct 13.

In particular, the second portion 12b and the first portion 20a converge towards each other towards the flange 22 in such a way that the section of passage of the exhaust gases, normal to the direction of advancement of the exhaust gases themselves, is substantially constant throughout the length of the emission duct 26 and substantially equal to the section of passage of the exhaust gases defined by the outlet mouth 6 (in turn equal to the section of passage of the exhaust gases defined by the inlet port 4) so as not to cause leaks load and not to generate significant back pressures to the engine.

Preferably, the annular section of passage of the exhaust gases is comprised between 80% and 120% of the passage section defined by the outlet mouth 6.

The third cylindrical portion 10c of the first half-shell 10 and the second portion 16b of the first guide body 16 define, together with the flanges 14 and 22 of the second half-shell 12 and the second guide body 20, a chamber 28 with an annular section communicating with the inlet conduit 18 and with the emission conduit 26 and inside which a magnetic field generator device 30 of the two-stage type is arranged.

In particular, the magnetic field generating device 30 comprises a first and a second magnetic field generating stage 32, 34 of substantially tubular shape, arranged in the chamber 28 coaxially one inside the other with radial clearance and delimiting between them an annular section cavity with circular profile, defining a treatment duct 36 interposed between, and communicating with, the inlet duct 18 and the emission duct 26 and inside which it is carried out, in the manner described in detail below , the decomposition of exhaust gases.

In the direction of advancement from the inlet 4 to the outlet 6, the exhaust gases then travel through an annular section duct comprising an initial portion consisting of the inlet duct 18, delimited by the frusto-conical portion 10b and by the conical portion 16a, in which the section of passage of the exhaust gases is substantially constant and equal to the section of passage defined by the inlet port 4 and has an increasing average radius, measured with respect to axis A; an intermediate section consisting of the treatment duct 36, delimited by the magnetic field generating stages 32, 34, in which the exhaust gas passage section is substantially constant and equal to the passage section defined by the portions 10b, 16a and has a substantially constant mean radius and substantially equal to the maximum mean radius of the inlet duct 18; and a final section consisting of the emission duct 26, delimited by the truncated conical portion 12b and by the conical portion 20a, in which the exhaust gas passage section is substantially constant and equal to the passage section defined by the outlet mouth 6 and has a mean radius, measured with respect to axis A, decreasing.

A tubular diaphragm 40 acting as an exhaust gas separator is coaxially mounted inside the treatment duct 36, which is arranged in a radially median position between the magnetic field generating stages 32, 34, and is fixed to the casing 2 by means of fins. 42 projecting axially (shown in broken line), is made of ferromagnetic material and may or may not be provided with radial through holes.

The first and second magnetic field generating stages 32, 34 are each formed by a plurality of annular coils 44 axially adjacent to each other and mutually separated by discoidal elements 46 defining pole pieces of the magnetic field generating stages 32, 34.

The coils 44 and the disc-shaped elements 46 are tightly packed together inside the chamber 28 and their number is chosen according to the decomposition effect to be obtained on the particles present in the exhaust gases and the application to which the decomposition device 1 is intended, as better described below.

The coils 44 can be made of drawn wire or strips of conductive material, for example copper, NiCr alloys or stainless steel, while the disc-shaped elements 46 are made of ferromagnetic material.

The coils 44 of each magnetic field generator stage 32, 34 can be powered both in direct current and in alternating current and can be connected in series, in series-parallel or in parallel with each other (i.e. within the same stage) and with those of the other magnetic field generator stage 32, 34.

The supply leads of the coils 44 can then be either both available outside the decomposition device 1 or one of the two can be internally connected to the casing 2 (ground connection) while the other can protrude from the casing 2 itself for be connected to a source of electrical energy.

Whatever the type of power supply and the connection of the coils 44 may be, they must in any case be wound in such a way that along the treatment duct 36 there is a variable magnetic field, in particular mainly discontinuous, orthogonal to the direction of advance of the exhaust gases.

Figure 4a schematically illustrates a sequence of NORTH pole pieces and SOUTH pole pieces along the treatment duct 36 of the N-S-N-S-N type and the theoretical direction of lines of force of the magnetic field generated by the coils 44 inside the treatment duct 36.

According to what is illustrated in Figure 4a, each discoidal element 46 defines two theoretical polar expansions of opposite sign side by side. Furthermore, in each of the magnetic field generating stages 32, 34 facing and successive polar expansions defined by two successive discoidal elements 46 in the direction of advance of the exhaust gases have opposite magnetic polarity, as well as each of the two defined polar expansions from a discoidal element 46 of the magnetic field generating stage 34 has magnetic polarity opposite to that of the polar expansion corresponding to it and facing it defined by the corresponding discoidal element 46 of the magnetic field generating stage 32 (i.e. of the discoidal element 46 of the generating stage of magnetic field 32 placed inside the discoidal element 46 of the magnetic field generating stage 34).

As can be seen, with a configuration such as the one illustrated, lines of force emerge from the NORTH polar expansion which reach, through the diaphragm 40, on a SOUTH polar expansion defined by an adjacent discoidal element 46. From the SOUTH polar expansion, these lines of force then close again on the NORTH polar expansion from which they emerged through the third portion 10c of the first half-shell 10 (not shown in Figure 4a).

Furthermore, the magnetic field lines of force cross the exhaust gases present in the space between each magnetic field generating stage 32, 34 and the diaphragm 40 along a direction which is predominantly orthogonal to the direction of advance of the exhaust gases, indicated by the letter B.

In a configuration of the type described above, a generic particle of the exhaust gases originating from the incomplete combustion of hydrocarbons passes through the treatment duct 36 along a direction of advance substantially orthogonal to the lines of force of the magnetic field present inside the treatment duct 36 itself, for example a particulate particle, indicated in the figure with the letter "P", is comparable to a coil that cuts a magnetic flux orthogonal to the coil itself or, alternatively, to a coil crossed by an alternating magnetic flux having a certain frequency .

Due to the Newman-Lenz effect, the variable magnetic field present inside the treatment duct 36 induces an electromotive force in the particle which, thanks to the electroconductive characteristics of the particle itself, induces in the molecular structure of the particle itself a current which is all the greater how much greater are the magnetic flux, the variation of flux in the unit of time produced by the alternation of polar expansions, the speed of movement of the particle and the conductivity of the particle itself.

Due to the Joule effect, the current induced in the particle therefore produces heat, which raises the temperature of the particle up to over 500 ° C, thus causing its decomposition and its subsequent possible oxidation up to the transformation into carbon dioxide and water.

However, not all particles have the same conductivity and if the conductivity of some particles is not high enough to ensure that the surface current induced in them is sufficient to cause their transformation into carbon dioxide and water, they will simply be divided or fragmented by effect. evaporation.

As previously mentioned, the oxidizing effect possessed by the present decomposition device 1 also depends, among other things, on the speed of movement of the particle, and therefore on the time in which the particle remains in contact with the magnetic field.

Therefore, the number of coils 44 or of permanent magnets present in each magnetic field generating stage 32, 34 will be determined according to the application for which the decomposition device is intended and to the oxidizing effect to be obtained. Furthermore, it is useful to underline the fact that the helical motion of the exhaust gases also contributes to increasing the time in which the particle remains in contact with the magnetic field before reaching the inside of the treatment duct and produced by the vanes arranged at the 'inside the intake duct 18.

Figure 4b illustrates the theoretical trend of the intensity of the magnetic field "seen" by a particle in the treatment duct 36 in the case in which the sequence of polar expansions illustrated in Figure 4a is adopted.

As can be seen, the particle P "sees" a magnetic field having a substantially alternating discontinuous type trend given by the sum of two components: a basic sinusoidal component (represented in dashed line) having a very small amplitude and an alternating component superimposed on the component base (shown in solid line) having a greater amplitude.

Figure 5 instead schematically illustrates a sequence of NORTH polar expansions and SOUTH polar expansions along the treatment duct 36 of the N-S-S-N-N-S-S-N type and the theoretical direction of lines of force of the magnetic field generated by the coils 44 in the vicinity of the treatment duct 36 in presents of such a sequence.

Unlike what is illustrated in Figure 4a, in this solution each discoidal element 46 defines a single polar expansion. Furthermore, in each of the magnetic field generating stages 32, 34 the two pole pieces defined by two successive discoidal elements 46 have opposite signs, just as each pole piece defined by a discoidal element 46 of the magnetic field generating stage 34 has an opposite sign with respect to that of the corresponding polar expansion defined by the discoidal element 46 of the magnetic field generating stage 32.

The exhaust gases purified from the part deriving from carbon and coming out from the outlet 6 of the decomposition device 1 can be introduced directly into the atmosphere or the decomposition device 1 according to the present invention can be associated with a traditional catalyst in order to complete the decomposition of other gaseous emissions present in the exhaust gases.

If the application of the decomposition device is such that it does not require high oxidizing effects or the engine to which it is applied has intrinsically low polluting emissions, the decomposition device can be simplified as illustrated in Figure 5.

In particular, according to what is illustrated in this figure, the decomposition device, indicated with 1 ', is substantially similar to the decomposition device 1 and differs from this in that the magnetic field generating device, indicated with 30', is of the single-stage type, i.e. it includes only the magnetic field generator stage 32.

In this configuration, the diaphragm 40 and the relative fastening fins 42 are no longer present, and its function is performed directly by the third portion, indicated here with 10c ', of the first half-shell, indicated here 10'.

In fact, according to this embodiment, the third portion 10c 'of the first half-shell 10' has a diameter equal to the maximum diameter of the second portion 10b of the first half-shell 10 'itself and faces the magnetic field generator stage 32 to perform the same functions as the diaphragm 40, while the second half-shell, indicated here with 12 ', no longer has the flange 14 but the fixing collar 15 is carried directly by the second portion 12b.

In this configuration, therefore, the treatment channel, indicated here with 36 ', is identical to the treatment channel 36 and is defined on one side by the free surfaces of the coils 44 and of the discoidal elements 46 of the magnetic field generator stage 30' and on the other hand by the third portion 10c 'of the first half-shell 10'.

According to a further variant, not illustrated, of the decomposition device 1, the magnetic field generating device could also be of the n-stage type, with n greater than two, and this configuration is particularly useful in all cases in which a high oxidizing effect is required. or the engine to which it is applied has high polluting emissions.

From an examination of the characteristics of the decomposition devices 1, 1 'made according to the present invention, the advantages that it allows to be obtained are evident.

In particular, the main characteristic of the decomposition devices 1, 1 'is that, by operating with a mixed electromagnetic and thermomechanical technique, they are able to decompose particles originating from unburnt hydrocarbons even when the temperature of the exhaust gases is above below the catalysis temperature, i.e. below the temperature at which the catalysis of the exhaust gases begins to take place in traditional catalysts.

This important feature ensures that the decomposition devices 1, 1 'according to the present invention have no limits of use and can therefore find application in all sectors in which a reduction of polluting emissions is required, especially in those in which there are significant quantities of polluting emissions or in those where the ceramic-based filtering technology has not been decisive in terms of operational reliability.

Furthermore, the decomposition devices 1, 1 'according to the present invention can find advantageous application also in all those countries where there are strict regulations on polluting substances that are not satisfied by the technology available up to now or in all those countries particularly attentive to the control of polluting emissions of goods handling vehicles operating in closed work environments.

Furthermore, the decomposition devices 1, 1 'can without any problem be associated with a traditional catalyst and the removal of the particles deriving from the carbon carried out by them, and in general of all the particles having electroconductive characteristics, significantly increases the duration of the catalysts. traditional, thus avoiding the formation of occlusions of the exhaust duct of the engines.

Finally, it is clear that modifications and variations can be made to the decomposition devices 1 and i 'described and illustrated here without thereby departing from the protective scope of the present invention.

For example, the magnetic field present inside the treatment ducts 36, 36 'could also be constant for the entire length of the treatment ducts 36, 36' themselves. In this case, in order for the decomposition effect of the particles to be identical to that obtainable with a variable magnetic field, the length of the treatment ducts 36, 36 'should be greater than that used with a variable magnetic field.

Furthermore, the coils 44 could be replaced with ferrite magnets or materials having Curie temperatures of the order of 350-450 ° C, all of what has been said regarding the coils 44 remains valid for them.

Furthermore, the lamellar spacers 17 interposed between the first half-shell 10 and the first guide body 16 could have a rectilinear shape instead of a helical one or could be replaced with cylindrical spacers and in this case the exhaust gases passing through the intake duct 18 would have a mainly straight motion.

Furthermore, the outlet portion of the decomposition devices 1, 1 'defined by the second half-shell 12, 12' and by the second guide body 20 placed inside it could be cylindrical in shape and define an emission duct 26 arranged on the extension of the ducts treatment ducts 36, 36 'so as to be able to connect the treatment ducts 36, 36' themselves directly to other exhaust gas treatment devices having annular exhaust gas passage sections.

Furthermore, the casing could have a different shape from that described and in particular it could have a generally flattened shape and in this case the treatment ducts 36, 36 'would have a flattened quadrangular or elliptical annular section. Alternatively, the treatment ducts 36, 36 'could also have a "full" quadrangular section, conveniently rectangular, in such a way that the exhaust gases are advanced within the magnetic field forming a plate-shaped flow with a thickness comparable to that of that of the treatment ducts 36, 36 'themselves.

Claims (1)

R I V E N D I C A Z I O N I 1.- Decomposition device (1; 1 ') of particles present in the exhaust gases, comprising a casing (2; 2') equipped with an inlet (4) for the exhaust gases to be purified and a outlet (6) for the purified exhaust gases, and decomposition means (30; 30 ') housed in said casing (2) and interposed between said inlet (4) and said outlet (6), characterized by the fact that said decomposition means comprise magnetic field generating means (30; 30 ') generates a magnetic field crossed, in use, by the exhaust gases advanced transversely to lines of force of the magnetic field itself. 2.- Device according to Claim 1, characterized in that said magnetic field is a variable magnetic field. 3. A device according to Claim 1 or 2, characterized in that said magnetic field is a mainly discontinuous magnetic field. 4.- Device according to any one of the preceding claims, characterized in that said exhaust gases are advanced inside said magnetic field in such a way as to form a flow with an annular section. 5. A device according to any one of claims 1 to 3, characterized in that said exhaust gases are advanced inside said magnetic field in such a way as to form a plate-shaped flow. 6.- Device according to any one of the preceding claims, characterized by the fact that said exhaust gases are advanced inside said magnetic field along a direction of advance (B) and by the fact that magnetic field generating means (30; 30 ' ) have, in said direction of advance (B), a succession of pole pieces having alternating polarity according to a predetermined sequence. 7.- Device according to Claim 6, characterized in that said magnetic field generating means (30 ') comprise at least one magnetic field generating stage (32) comprising in turn a plurality of magnetic field generating elements (44) between adjacent to them in said forward direction (B) and mutually separated by separator elements (46) defining said pole pieces. 8.- Device according to Claim 7, characterized in that said magnetic field generating elements (44) generate a magnetic field whose interaction with said separator elements (46) is such that each of said separator elements (46) defines two respective said pole pieces having opposite magnetic polarity. 9. A device according to Claim 8, characterized in that two successive pole pieces in said direction of advance (B) defined by two said separator elements (46) subsequent to each other have opposite magnetic polarity. 10.- Device according to Claim 7, characterized in that said magnetic field generating elements (44) generate a magnetic field whose interaction with said separator elements (46) is such that each of said separator elements (46) defines a respective called polar expansion. 11. A device according to Claim 10, characterized in that two separator elements (46) successive to each other in said direction of advancement (B) define respective pole pieces having opposite magnetic polarity. 12.- Device according to any one of claims 7 to 11, characterized in that said magnetic field generating stage (32) defines, together with said casing (2), a first treatment duct (36 ') communicating with said inlet mouth (4) and said outlet mouth (6), crossed in use by said exhaust gases and transversely intersected by lines of force of said magnetic field. 13.- Device according to Claim 12, characterized in that said first treatment duct (36 ') has an annular section. 14.- Device according to any one of claims 7 to 11, characterized in that said magnetic field generating means (30) comprise two said magnetic field generating stages (32, 34) arranged with play each inside the the other and delimiting each other a second treatment duct (36) communicating with said inlet (4) and said outlet (6), crossed in use by said exhaust gases and intersected transversely by lines of force of called magnetic field. 15.- Device according to Claim 14, characterized in that said second treatment duct (36) has an annular section. 16.- Device according to Claim 14 or 15, characterized in that corresponding pole pieces defined by two discoidal elements (46) placed one inside the other have opposite magnetic polarity. 17. Device according to any one of claims 14 to 16, characterized in that it comprises a diaphragm (40) arranged inside said second treatment duct (36). 18. Device according to claim! 17, characterized in that said diaphragm (40) is arranged in a substantially median position inside said second treatment duct (36). 19.- Device according to any one of claims 7 to 18, characterized in that said magnetic field generating elements comprise coils (44). 20.- Device according to any one of claims 7 to 18, characterized in that said magnetic field generating elements comprise magnets (44). 21.- Device according to any one of claims 12 to 20, characterized in that it comprises an inlet duct (18) with an annular section interposed between said inlet (4) and said treatment duct (36; 36 ' ). 22.- Device according to claim 21, characterized in that said inlet duct (18) has transversal dimensions increasing towards said treatment duct (36; 36 '). 23.- Device according to claim 22, characterized in that said inlet pipe (18) has a substantially constant exhaust gas passage section. 24. Device according to claim 23, characterized in that the section of passage of the exhaust gases in said inlet duct (18) is substantially equal to the section of passage of the exhaust gases defined by said inlet mouth (4). 25.- Device according to any one of claims 22 to 24, characterized in that said inlet duct (18) is delimited by a pair of conical walls (10b, 16a) having an increasing diameter towards said treatment duct (36; 36) ') and converging to each other towards the treatment duct (36; 36') itself. 26.- Device according to any one of claims 21 to 25, characterized in that it comprises flow orienting means (17) arranged inside said inlet duct (18) to impart a substantially helical motion to said discharge gas. 27.- Device according to any one of claims 17 to 26, characterized in that it comprises an emission duct (26) with an annular section interposed between said outlet mouth (6) and said treatment duct (36; 36 ' ). 28.- Device according to claim 27, characterized in that said emission duct (26) has transversal dimensions increasing towards said treatment duct (36; 36 '). 29.- Device according to claim 28, characterized in that said emission duct (26) has a substantially constant exhaust gas passage section. 30.- Device according to claim: 29, characterized in that the exhaust gas passage section in said emission duct (26) is substantially equal to the exhaust gas passage section defined by said outlet mouth (6) . 31.- Device according to any one of claims 28 to 30, characterized in that said emission duct (26) is delimited by a pair of conical walls (12b, 20a) having an increasing diameter towards said treatment duct (36; 36 ') and converging to each other towards the treatment duct (36; 36') itself. 32.- Device according to any one of the preceding claims, characterized in that said inlet (4) and said outlet (6) define sections for the passage of exhaust gases substantially equal to each other. 33.- Method of decomposition of particles present in exhaust gas, characterized in that it comprises the steps of generating a magnetic field and of advancing said exhaust gases within said magnetic field transversely to lines of force of the magnetic field itself. 34.- Method according to claim 33, characterized in that said magnetic field is a variable magnetic field. 35. Method according to claim 33 or 34, characterized in that said magnetic field is a mainly discontinuous magnetic field. 36.- Method according to any one of claims 33 to 35, characterized in that said exhaust gases are advanced inside said magnetic field in such a way as to form a flow with an annular section. 37. A method according to any one of Claims 33 to 35, characterized in that said exhaust gases are advanced within said magnetic field in such a way as to form a plate-shaped flow. 38.- Method according to any one of claims 33 to 37, characterized in that said exhaust gases, inside said magnetic field, said exhaust gases pass through a succession of pole pieces having alternating polarity according to a predetermined sequence. 39.- Device for decomposition of particles present in the exhaust gases, substantially as described with reference to the attached drawings. 40.- Method of decomposition of particles present in the exhaust gas, substantially as described with reference to the attached drawings.