ES2759498A1 - DIESEL ENGINE PARTICLE FILTER USING CARBIDE BIOMORPHIC SILICON (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Use of biomorphic silicon carbide as a substrate in wall flow filters in diesel engines. The present invention relates to a filter for particulates released after combustion in diesel engines comprising a biomorphic silicon carbide wall flow filter. The result is a new ceramic filter whose hierarchical microstructure depends on the selection of an optimal plant precursor. Following the usual design and geometry of wall flow filters, an improvement in the technical specifications for efficiency and pressure drop is favored. The present invention is applicable to the automotive and industrial sector, in particular to the removal of particles and purification of residual gases in combustion processes. (Machine-translation by Google Translate, not legally binding)

Description

FILTER FOR PARTICLES OF DIESEL ENGINES USING BIOMORPHIC SILICON CARBIDE

The present invention relates to a filter for particulates released after combustion in diesel engines comprising a biomorphic silicon carbide wall flow filter. The result is a new ceramic filter whose hierarchical microstructure depends on the selection of an optimal plant precursor. Following the usual design and geometry of wall flow filters, an improvement in the technical specifications for efficiency and pressure drop is favored. The present invention is applicable to the automotive and industrial sector, in particular to the removal of particles and purification of residual gases in combustion processes.

BACKGROUND OF THE INVENTION

European regulations establish emission limits for all diesel vehicles, said emission limit in the number of particles is 6 * 1011 particles / km and where said particles have a limit of 4.5 mg / km in their mass. Advances in the design of engines contribute to reducing their production of particles but they are not enough to satisfy these thresholds, so it is necessary to also use post-treatment systems.

Currently, the most widely used aftertreatment system for controlling particulate emissions in automotive diesel engines is wall-flow filters (in its English terminology wall-flow filters). Wall-mounted flow filters are the longest running particle filters on the market given their renowned filtration efficiency, capable of meeting not only current standards but also coping with future regulatory hardening. The main problem with wall flow filters is the loss of charge they introduce into the exhaust and the difficulties associated with the on-board regeneration process. Said regeneration process is prevented by the high back pressure in the engine exhaust, which in turn increases the losses associated with the engine pumping loop and with it increases fuel consumption and CO2 emissions to the medium. Therefore, reducing and / or controlling the pressure drop of the filters is nowadays a recurring objective in many of the research works carried out in the field of diesel particulate filters. By On the other hand, the rapid saturation of the filter and the difficulties of regenerating these filters are additional challenges that present filters present.

The behavior of a wall flow filter in terms of efficiency and pressure drop is determined macroscopically by its geometry (length, section, cell density, wall thickness) and microscopically by the properties of the material used as substrate (permeability , porosity, pore size, tortuosity). Given a certain geometry, the microstructural properties of the substrate are what determine the pressure drop and the filtration efficiency of the filter. The problem is that head loss and filtration efficiency generally go hand in hand; an increase in the first generally leads to an increase in the second and vice versa. One of the main challenges today is to design substrates that reduce filter pressure drop without compromising filter efficiency.

On the other hand, the filters must have a good behavior in the regeneration processes. A slow regeneration of the filter (low rate of combustion of accumulated particles) would be safer for the filter, but would mean a greater penalty to the fuel consumption of the engine. Typically, you regenerate using the drop-to-idle process. This process consists of rapidly reducing the gas flow just after regeneration has started, so that a temperature spike occurs and soot combustion is accelerated. The problem is that this process generates a high cyclical thermal stress on the material that, under certain conditions, can cause its fracture and its consequent collapse. A possible solution to this problem is the use of a different porous material that, while maintaining the same particle capture efficiency and low pressure drop for longer, is also more sensitive to regeneration, and capable of causing soot combustion. at lower temperature.

The main requirements that the materials considered as materials for particle filters must meet are that said material has a high filtration efficiency, low pressure drop, high thermal and chemical stability, and high capacities to resist the various heating cycles that will occur. in the subsequent filter regeneration cycles. In this sense, currently, the most used materials as a particle filter are Cordierite (2MgO'2Al2O3'5SiO2), Silicon Carbide (SiC), Mullite (ACM, Al2SiO5), Aluminum Titanate (AT, Al2TiO5), and Alloy Foams (AF).

Depending on the combination of porosity, pore size and microstructural arrangement, the resulting filter will have characteristics in terms of filtration efficiency, pressure drop and regeneration behavior. The development of new particle filters combining new substrate materials and geometries with a combination of optimized properties will improve performance compared to existing filter systems

DESCRIPTION OF THE INVENTION

The present invention relates to a filter for particles released after combustion in diesel engines using biomorphic silicon carbide, of certain characteristics, in wall flow filters for said particles emitted by diesel engines. Biomorphic Silicon Carbide (bioSiC) is a particular type of silicon carbide that is obtained from pyrolysis of wood and its subsequent infiltration with silicon. The bioSiC is characterized by having a porous microstructure that replicates the biological cellular microstructure of the woody precursor used in its manufacture. One of its main advantages with respect to current commercial materials is the possibility it offers to manipulate its microstructural properties through the proper selection of the precursor.

In the present invention, the same is understood by "wall flow filter" as by "disk assembly".

Said bioSiC is characterized by presenting a hierarchical microstructure that replicates the microstructure of the original plant pattern. The bioSiC can have permeabilities of between 10 "11 m2 and 10 ~ 12 m2 and thermal conductivities in the range of 4 Wm" 1K "1 to 88 Wm" 1K "1. Furthermore, the bioSiC manufacturing process differs considerably from that of others granular ceramic materials.

The advantages of using bioSiC as a substrate in wall flow filters, compared to its application to wall flow filters for internal combustion engines, compared to the use of commercial granular SiC substrates are:

- Firstly, the bioSiC has a lower coefficient of thermal expansion (in its CTE) than SiC, which gives it greater resistance to thermal shock (TSR). At 200 ° C, the CTE of the bioSiC is around 210-6 K-1; while the CTE of the p-SiC can be 3,510-6 K-1. At 800 ° C, the CTE of the bioSiC is around 310-6 K-1; while the CTE of the p-SiC can be 510-6 K-1. And since the TSR is inversely proportional to the CTE, since the TSR of the bioSiC can exceed that of the p-SiC. Thanks to its greater resistance to thermal shock, it is foreseeable that bioSiC will better resist regeneration processes and present greater durability. In addition, it is likely to reduce the need to manufacture SiC filters in a segmented manner as is customary to limit the thermal expansion that would occur from being manufactured in one piece.

- Secondly, the wide spectrum of different microstructures that the bioSiC offers depending on the selected precursor, widens the originally close relationship between filtration efficiency and head loss. That is, in granular substrates, the greater the filtration efficiency, the greater the pressure drop and vice versa. And although the size and shape of the grains can be manipulated a little, the relationship between the two variables is close and does not allow one to be improved without harming the other. BioSiC, on the other hand, offers greater independence between filtration efficiency and head loss.

In a first aspect, the present invention relates to the diesel engine particulate filter characterized in that it comprises the following elements

(i) a set of discs (1) having a total length of between 0.12m and 0.25m, where each disc is composed of biomorphic silicon carbide that

• has a hierarchical pore microstructure

or with a first pore size between 2 pm and 60 pm; and

or a second pore size between 30 pm and 440 pm; and

• it has a porosity percentage of between 45% and 75%;

• it has a diameter of between 0.14 m and 0.18 m and a thickness of between 0.005 m and 0.010 m; and

• presents a conformation of longitudinal channels along the thickness of the disc, where said channels are between 50 cells per square centimeter (cpsc) and 60 cells per square centimeter (cpsc),

where the channels of each disc are aligned with the channels of the previous disc and later,

and where the set of discs comprises a first input disc and a second output disc,

and where half of the channels of the first inlet disc and the second outlet disc of the set of discs are configured to block the passage of the flow of gases and combustion residues, and where half of the channels of the first disc of inlet and second outlet disk, are configured to allow the flow of flow; where the channels configured to block the flow of gases and combustion residues from the first inlet disk correspond to the channels configured to allow the flow of gases and combustion residues from the second exit disk, and vice versa;

where the discs are joined together by an adhesive;

so that the flow of gases and combustion debris from the diesel engine containing particles and debris between 1 nm and 100 pm are retained in the walls of the disc set channels and the flow of combustion gases the diesel engine continues its way to the exhaust pipe; (ii) an insulating coating (2), wrapping the set of discs (1), which maintains the filter's working temperature stable;

(iii) a post-injection system (3) to increase the fuel input to the main engine (4) when there is excessive overpressure in the exhaust, and induce combustion and elimination of accumulated particles in the filter;

(iv) a differential pressure sensor (5) for the flow of gases and combustion residues of the diesel engine, which has two connected probes, a first probe located at the entrance of the disk assembly by the first entrance disk and a second one probe located at the outlet of the disk assembly by the second outlet disk, and which measures the pressure difference in the flow of gases and residues of combustion of the diesel engine before entering the filter and the flow of exhaust gases of the filter, and sends said collected data to the electronic monitoring and control system (7);

(v) at least two temperature sensors (6), one in the filter inlet section and the other in the filter outlet section, which record the temperature of the gas flow at both points and send the collected data to the electronic system monitoring and control (7); and

(vi) an electronic monitoring and control system (7) that collects the data from the differential pressure sensor (5) and the temperature sensors (6), monitors the particle retention process in the set of discs (1) , and activates the post-injection (3) when the overpressure in the exhaust given by the differential pressure sensor (5) reaches a certain level.

In the present invention, “biomorphic silicon carbide or bioSiC” is understood to be any porous silicon carbide (ceramic material) obtained from pyrolysis and silicon infiltration of a plant precursor, resulting in a material with the same thermal resistance and mechanical than silicon carbide obtained by conventional sintering methods, but with a hierarchical porous cellular microstructure that favors the preservation of low pressure drop over long periods of time. This hierarchical porous microstructure replicates the original pattern microstructure, which has its origin cellulosic or is a cellulosic material. To characterize the porosity of said bioSiC, as well as the percentage of pores, the mercury porosimetry method is used. Mercury porosimetry is based on the effect of capillary depression. When a solid absorbent it is immersed in a liquid that does not wet, as in the case of mercury, the liquid penis It enters your pores only by the action of external pressure. The pore radius is inversely proportional to the applied pressure, at low pressures large pores fill and each increase in pressure causes mercury to penetrate pores of smaller and smaller radii. Characteristic textural parameters such as pore size, pore volume distribution and total porosity of the sample can be obtained from the mercury intrusion into a sample.

In the present invention, “material of cellulosic origin or cellulosic material” is understood to mean any block material that comes from the different plant species selected from the list: pine in axial section, ayous in axial section, iroko in axial section, oak in axial section, medium density fiberboard, pine in radial section, ayous in radial section, iroko in radial section and oak in radial section, and on which the size of the first pore range and the second pore range depends, as well as the density, permeability, porosity and specific surface area of biomorphic silicon carbide.

In the present invention, “hierarchical structure or hierarchical microporous structure” is understood to mean the characteristic structure of plant tissues in which pores of different dimensions are combined by grouping and are distributed according to a specific order in response to genetic and / or climatic causes from the smallest levels, the nanopores and mesopores, to the micropores and macropores of greater size, and which give rise to the different structures of the woods selected in the present invention.

In the present invention, the term "filter working temperature" is understood to be the one in which the wall flow filter of the present invention is found most of the time during its operation on board the vehicle as a consequence of the thermal conditions of input of the gas stream from the engine, and which results from a value between 300 ° C and 400 ° C

In the present invention, “insulating coating” is understood to mean any low conductivity material that, placed on the outer surface of the set of disks as a wraparound jacket, prevents heat exchange with the casing and the environment. The material used in the insulating coating must be easy to handle and install, while providing a high insulation density. In the present invention the insulating coatings are: glass wool, rock wool, rubber foam, or aluminum coils.

In the present invention, a "post-injection system" is understood to mean the injection of fuel into diesel engines which is carried out with delay with respect to the top dead center of the piston. This injection provides a fuel that cannot be burned inside the cylinder due to lack of time and oxygen nearby. The fuel burns during the exhaust phase, considerably raising the temperature of these gases during their release into the atmosphere. This type of injection is used to raise the temperature of the gases as they pass through the wall flow filter and cause combustion of the particles retained therein, that is, their regeneration.

In the present invention, a “differential pressure sensor” is understood to be one that is in charge of measuring the pressure difference in the exhaust gases, between the inlet and the outlet of the particulate filter, and therefore, the one that is It is in charge of indirectly measuring the level of particle saturation in the porous filter substrate. The differential pressure sensor must necessarily have two pressure taps. The two pressure taps converge on an electrical output, using a logic of comparison between both pressure ports, so we will have a positive voltage value depending on the pressure increase or negative, depending on the pressure decrease, from one intake to the other. The sensor used can be of any type: a capacitive transducer, a piezo-electric sensor, or a membrane sensor.

In the present invention, “granular silicon carbide” is understood to be any silicon carbide manufactured by sintering from powdered silicon carbide, resulting in a porous material with microstructure in the form of grains, with a final porosity of between 40% and 50% and pore size between 10 pm and 20 pm, both depending on the size of the powder particles and the type of binder.

The advantages associated with the particle filter described in the first aspect are

- a filtration of the particles and residues contained in the gas flow and combustion residues of the diesel engine throughout the particle size range: from the largest particles that are retained in the porous substrate mainly by interception, to the smallest ones that adhere to its walls mainly due to diffusion phenomena. due to the complex path they follow along the hierarchical microporous structure of the bioSiC.

- greater filtration efficiency in the initial state (clean) compared to conventional filters and on the market,

- a manageable and reducible pressure drop depending on the choice of the plant precursor with which the bioSiC is manufactured,

- a release of particles in the exhaust less than that of conventional filters and on the market, and much lower than the limit established by the regulations.

In a preferred embodiment of the diesel engine particulate filter, where the channels of each disc that make up the set of discs are square in the direction perpendicular to the length of the channel.

In another preferred embodiment of the diesel engine particulate filter, where the square channel shape is a honeycomb shape and where the squares have a side size of between 0.8mm and 1mm, and a wall thickness of between 0.3 mm and 0.4 mm;

In another preferred embodiment of the diesel engine particulate filter, where all the disks are equal to each other and have the same number of channels.

In another preferred embodiment of the diesel engine particulate filter, where the set of discs are joined by an adhesive resistant to temperatures between 15 ° C and 1000 ° C, such as Nural 30® (Pattex).

In another preferred embodiment of the diesel engine particulate filter, which further comprises a block (8) comprising an oxidation catalyst selected from the following: M-Series DOC® (Nett Technologies), AZ Purifier® (CDTi), DOC standard® (Donaldson), Empro DOC® (BASF), as well as any other suitable for the oxidation process of the retained particles, and which is located adjacent to the set of disks so that the flow of gases and residues from the combustion of the Diesel engine enters first through it and then through the disk set.

In another preferred embodiment of the diesel engine particulate filter, which further comprises a casing (9) with conical sections of gas inlet and outlet for the diesel engine to encapsulate the filter, which encompasses all the elements of the wall flow filter.

In the present invention, “diesel oxidation catalyst or DOC” is understood to be any monolithic block with a honeycomb structure with open channels impregnated with catalyst that, placed upstream of the wall flow filter, contributes to reducing carbon monoxide (CO), hydrocarbons (CxHy) and partially oxidized hydrocarbons (CxHyO) and diesel particulate matter to inert and non-polluting substances for the environment. Catalysts that oxidize in the desired temperature range can be used in the present invention, whose catalyst element are elements such as platinum, palladium and cerium oxide, as well as any other that meets the established requirements, and which are selected from the following from M-Series DOC® (Nett Technologies), AZ Purifier® (CDTi), DOC Standard® (Donaldson), Empro DOC® (BASF).

In another preferred embodiment of the diesel engine particulate filter, where half of the channels configured to block the passage of the flow of gases and combustion residues, comprises a molded silicon carbide moldable paste filler.

In another preferred embodiment of the diesel engine particulate filter, where half of the channels configured to block the passage of the flow of gases and combustion residues, is obtained by machining.

Another aspect of the present invention is the set of discs characterized in that • they have a total length of between 0.12 m and 0.25 m;

formed by discs linked together,

where each disc is composed of biomorphic silicon carbide porous ceramic material that has a hierarchical pore microstructure

or with a first pore size between 2 pm and 60 pm; and

or a second pore size between 30 pm and 440 pm; and

• where said material has a porosity percentage of between 45% and 75%;

• it has a diameter of between 0.14 m and 0.18 m and a thickness of between 0.005 m and 0.010 m; and

• presents a conformation of longitudinal channels along the thickness of the disc,

• where these channels are between 50 cells per square centimeter (cpsc) and 60 cells per square centimeter (cpsc),

• where the channels of each disc are aligned with the channels of the anterior and posterior disc,

where the set of discs comprises a first input disc and a second output disc;

where half of the channels of the first inlet disc and the second outlet disc of the set of discs are configured to block the passage of the flow of gases and combustion residues, and where half of the channels of the first inlet disc and second outlet disc, are configured to allow flow flow;

where the channels configured to block the flow of gases and combustion residues from the first inlet disk correspond to the channels configured to allow the flow of gases and combustion residues from the second exit disk, and vice versa;

A preferred embodiment of the disc assembly, where said discs are joined by a temperature resistant adhesive, between 15 ° C and 1000 ° C, such as Nural 30® (Pattex).

Another preferred embodiment of the disk assembly, where the channels are square in the direction perpendicular to the length of the channel.

Another preferred embodiment of the disk set, where all the disks are the same and have the same number of channels.

Another preferred embodiment of the disk assembly, where the conformation of square and longitudinal channels is a honeycomb conformation and where the squares have a side size of between 0.8 mm and 0.1 mm, and a wall thickness of between 0.3 mm and 0.4 mm.

In the present invention, the procedure for obtaining the bioSiC disc set described above is defined by the following steps:

a) performing a pyrolysis of a dry, precut block of cellulosic material by heating to a temperature between 900 ° C and 1050 ° C in the absence of oxygen;

b) carry out a grooved transverse machining of the pyrolyzed parts of step (a), a perimeter milling and a facing of the upper and lower surfaces;

c) coating the machined parts obtained in the transversal machining stage (b) with silicon powder in an amount of between 350% and 400% by mass of the carbon of the part obtained in stage (b) and heating in vacuum up to a temperature above the silicon melting temperature; d) removing the residual silicon from the pieces obtained in the coating step (c) by capillarity and evaporation by heating under vacuum above the evaporation temperature of the silicon;

e) cleaning the parts obtained in the silicon removal stage (d) from the residual silicon dust that may remain inside the channels;

f) polishing the upper and lower surfaces of the pieces obtained in the cleaning stage (e);

g) joining the pieces obtained in the polishing step (f) with a high-temperature resistant sealing adhesive; and

h) Manually blocking the alternating channels of the initial and final parts of the joined parts obtained after the joining step (g) with moldable silicon carbide paste in a configuration such that the set of discs comprises a first input disc and a second output disk;

where half of the channels of the first inlet disc and the second outlet disc of the set of discs are configured to block the passage of the flow of gases and combustion residues, and where half of the channels of the first inlet disc and second outlet disc, are configured to allow flow flow;

where the channels configured to block the flow of gases and combustion waste from the first inlet disc correspond to the channels configured to allow the flow of gases and combustion waste from the second outlet disc, and vice versa.

Another procedure for obtaining the set of bioSiC discs described above is defined by the following steps:

a) performing a pyrolysis of a dry, precut block of cellulosic material by heating to a temperature between 900 ° C and 1050 ° C in the absence of oxygen;

b) carry out a grooved transverse machining of the pyrolyzed parts of step (a), a perimeter milling and a facing of the upper and lower surfaces;

c) carry out additional machining, preferably facing, of at least two of the pieces obtained after the machining step (b) to block the alternating channels in the initial and final pieces of the filter;

d) coating the machined parts obtained in machining steps (b) and (c) with powdered silicon in an amount of between 350% and 400% by mass of the carbon of the part obtained in step (b) and (c) and heating in vacuo to a temperature above the silicon melting temperature; e) removing residual silicon from the pieces obtained in the coating step (d) by capillarity and evaporation by heating under vacuum above the evaporation temperature of the silicon;

f) cleaning the parts obtained in the step of removing silicon (e) from dust residual silicon that may remain inside the channels;

g) polishing the upper and lower surfaces of the pieces obtained in the cleaning stage (f);

h) joining the pieces obtained in the polishing step (f) with high temperature resistant sealing adhesive, in such a configuration that the set of discs comprises a first inlet disc and a second outlet disc; where half of the channels of the first inlet disc and the second outlet disc of the set of discs are configured to block the passage of the flow of gases and combustion residues, and where half of the channels of the first inlet disc and second outlet disc, are configured to allow flow flow;

where the channels configured to block the flow of gases and combustion waste from the first inlet disc correspond to the channels configured to allow the flow of gases and combustion waste from the second outlet disc, and vice versa.

The result of these procedures is the obtaining of a filter with geometry and channels with a microstructure that replicates that of the original plant precursor (Figure 2). Among the main advantages of said bioSiC obtaining procedure it is worth highlighting:

- It is possible to obtain a wide range of filter materials with designable physico-chemical-microstructural properties, such as their total porosity, pore size distribution, by selecting the starting plant precursor from among the different available plant precursors, previously described.

- The final material preserves the cellular microstructure of the starting wood precursor, thus giving it optimal filtering properties, low pressure loss during its use as a filter, and adequate mechanical properties due to its directionally interconnected pore morphology and hierarchical microstructure which is the result of millions of years of evolution and are difficult to replicate artificially.

- Use of natural and renewable resources, both wood of natural origin, and recycled wood products (medium density boards) in the which raw materials are waste products from the manufacture of other wood products, giving less impact on the environment and on environmental pollution.

- No need to add sintering additives.

- Possibility of manufacturing ceramic materials with complex shapes from the previous machining of the carbon preform obtained from the pyrolysis of the wood, thus allowing the pieces to be given the honeycomb structure with channels of square section used in conventional wall flow filters.

The procedure for obtaining the particulate filter for diesel engines also includes the following steps in addition to those already described for obtaining the set of discs:

i) placing the set of discs in the casing (9) after the block (8) that includes an oxidation catalyst, and closing it ensuring a correct placement of the insulating coating;

j) coupling of the assembly obtained in step (i) in the vehicle's exhaust pipe;

k) connection of the ends of the differential pressure sensor (5), and of the two temperature sensors (6) to the conical inlet and outlet sections of the housing of the block assembly comprising an oxidation catalyst and the filter of the present invention.

l) placement of the electronic monitoring and control system (7); and

m) connection of the differential pressure sensor (5) and the temperature sensors (6) to the electronic monitoring and control system (7); and from this, in turn, to the engine's post injection system.

Another aspect of the present invention is the use of the disc assembly of the present invention, as a particulate filter for diesel engines.

A preferred embodiment of using the disc assembly of the present invention is as a diesel engine wall flow filter to retain particulates contained in the gas stream and combustion debris of a diesel engine.

Throughout the description and claims, the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages, and features of the invention will emerge in part from the description and in part from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 Micrograph of a bioSiC disc from DM boards. In this case the microstructure is fibrous since the DM is a processed wood made up of pressed wood chips.

FIG. 2 A single bioSiC disc after the numerical control machining process where square channels have been made, forming a general honeycomb structure typical of wall-flow type particle filters.

FIG. 3 Finished prototype of the wall flow filter or set of bioSiC discs, where in said set of discs the configuration of the first inlet disc is seen to block the flow of gases and waste from combustion with moldable carbide paste. granulated silicon, and with half the channels of the first inlet disk in configuration to allow the flow.

FIG.4 Diagram of a filter for particles in the exhaust of a diesel engine.

EXAMPLES

The invention will now be illustrated by tests carried out by the inventors, which shows the effectiveness of the product of the invention.

Example 1. Procedure for obtaining the set of biomorphic silicon carbide discs or wall flow filter, for diesel particles using medium density boards (DM) as precursor.

The manufacturing procedure in that case would consist of the following stages: A first stage of cutting the MDF boards into 40cm x 40cm plates and drying them in an oven at a temperature of 70 ° C for 24 hours to remove the moisture present.

A second pyrolysis stage under the inert atmosphere of the cut blocks, from which the thermal decomposition of organic matter, evaporation of water and volatile substances occurs, resulting in a carbon matrix that preserves the fibrous microstructure of the DM board. Specifically, an anoxic atmosphere was used, heating rates of 0.5 ° C per minute up to 500 ° C and 1 ° C per minute up to 900 ° C, which is maintained for 30 minutes and the subsequent cooling to room temperature.

A third stage of machining sections of carbon preforms obtained in stage two, with optimal geometry of channels that will later be joined to form the wall flow filter. Machining of discs with a diameter of 14.2 cm and 1 cm thick, with a honeycomb structure, with square channels (58 cpsc) and 0.38 mm wall thickness. The shape can be shaped by robotic numerical control means.

A fourth stage of infiltration of the mechanized pieces of coal obtained in the fourth stage with silicon. Weighing the optimal amount of monocrystalline silicon powder based on the density and porosity of the carbon. An additional 15-25% of the stoichiometrically necessary amount of silicon (1: 1) will be added for the formation of SiC to guarantee the complete reaction of the carbon preform. The infiltration process will be carried out in non-reactive crucibles painted with boron nitride, placing the silicon powder on top of the carbon preforms. The heating process will be carried out at a heating rate up to a final temperature of 1550 ° C, a temperature higher than the silicon melting point and where complete infiltration of the samples will occur by capillarity.

A fifth stage of elimination of the excess residual silicon present in the pores of the ceramic samples, from a process by capillarity and evaporation at high temperature. Placing the pieces obtained in the fourth stage with excess silicon between porous carbon blocks and the heating the assembly under vacuum above the evaporation temperature of the silicon (1800 ° C), thus obtaining samples with high porosity.

6. A sixth stage of cleaning the pieces obtained in the fifth stage;

Elimination of residual silicon dust that may remain inside the channels and that may cause their blockage.

7. A seventh stage of facing the upper and lower surfaces of the grooved transverse pieces obtained in the sixth stage, in such a way that they are plane-parallel and as polished as possible, facilitating their connection to the adjacent parts in later stages.

8. An eighth stage of joining the different sections obtained in the seventh stage with a high-temperature resistant sealing adhesive in such a way that the adhesive allows the sections to join without blocking the longitudinal channels, obtaining complex parts with mechanical resistance similar to commercial filters.

9. A ninth stage of blocking alternate channels in the initial and final parts of the filter with moldable silicon carbide paste to obtain the set of discs with the usual structure for use in a wall flow filter.

Example 2. Technical characteristics of the bioSiC depending on the plant species (cellulosic material) selected as a precursor.

Table 1: Measured characteristic parameters of various samples tested from bioSiC

The samples of radial ayous, radial pine, radial iroko and radial oak are the ones with the highest efficiency, understood as particle retention capacity. Among the axial samples, pine presents an efficiency comparable to that of radial samples. In axial ayous and axial iroko, on the other hand, given the presence of macropores arranged in the same direction of flow, they show the least efficiency. The bioSiC manufactured from DM boards has a filtering behavior in terms of efficiency and permeability similar to that of axial samples when tested in the compression direction of the fibers, that is, when the gas is flowed perpendicular to the pressing plane. that contains the fibers. It has been found that the permeability of bioSiC from MDF boards when tested in the direction perpendicular to that of compression can have a permeability of 1 to 2 orders of magnitude lower.

From the point of view of the application in question, that is, with a view to the manufacture of a wall flow filter for diesel vehicles, it is considered that a suitable precursor for the manufacture of the substrate can be the axial pine given its good balance between high filtration efficiency and pressure drop.

Example 3. Use of the diesel particulate disc flow filter or wall assembly with a soot generator.

Small prototypes of the set of discs of the present invention, manufactured from DM boards, have been tested at the laboratory level, to check their filtering efficiency and pressure drop, with the help of a soot generator. These were sets of discs with a square section of 9.2 x 9.2 mm2 and 31 mm in length, with a total of 45 channels, 21 inlet and 24 outlet, which implies a cell density of 370 pcsi (58 cells per centimeter). square), and a wall thickness of 0.3 mm. The prototypes were found to have an initial state (clean) filtration efficiency of 77% and a pressure drop of 2.3 kPa. After two hours of operation, subjected to a gas stream of 5 LPM of argon, at atmospheric temperature, with a mass flow of carbon particles of 4 mg / h and a particle size distribution characterized by having an average diameter of 140 pm, the prototypes achieved efficiencies of the order of 100% and pressure drops of 25 kPa.

Example 4. Behavior of the disc assembly or wall flow filter of example 1, in a diesel particulate filter under real operating conditions of diesel engines .

The biomorphic silicon carbide disk assembly of Example 1, used in a wall flow filter with the configuration described in the present invention, has been simulated under real operating conditions, in a real diesel vehicle, and following a driving cycle standard (NEDC) according to European regulations. The numerical model used to carry out the simulation was initially validated based on the experimental results with the small-scale prototype. As a result of such simulation, the inventors have calculated that the wall flow filter of Example 1 has an initial (clean) filtration efficiency of 98% and a pressure drop of 3.5 kPa.

This filtration efficiency translates into a maximum release of particles in the engine of 8.75-108 particles / km and 0.129 mg / km, which is considerably below the limits established by the regulations. The results of this filter have been compared with a series of commercial filters found in the literature, obtaining the following results:

Table 2. Initial Filtration Efficiency of a Diesel Particulate Wall Flow Filter Made from DM Boards Compared to Other Equivalent Commercial Filters

[1] P. Tandon, A. Heibel, J. Whitmore, N. Kekre, and K. Chithapragada, “Measurement and prediction of filtration efficiency evolution of soot loaded diesel particulate filters,” Chem. Eng. Sci., Vol. 65, pp. 4751-4760, 2010.

[2] T. Mizutani et al., “Filtration Behavior of Diesel Particulate Filters (2),” SAE Tech.

Pap. 2007 World Congr. ( SAE Tech. Pap. 2007), 2007.

[3] T. Wolff, H. Friedrich, L. Johannesen, and S. Hajizera, “A New Approach to Design High Porosity Silicon Carbide Substrates,” SAE Tech. Pap., Vol. 2010 01-05, pp. 1-11,2010.

[4] T. Bollerhoff, I. Markomanolakis, and G. Koltsakis, “Filtration and regeneration modeling for particulate filters with inhomogeneous wall structure,” Catal. Today, vol. 188, no. 1, pp. 24-31,2012.

[5] K. Tsuneyoshi, O. Takagi, and K. Yamamoto, “Effects of Washcoat on Initial PM Filtration Efficiency and Pressure Drop in SiC DPF,” SAE Tech. Pap. Ser., Vol. 1, no. 817, pp. 1-10, 2011.

[6] RH Dabhoiwala, JH Johnson, and JD Naber, "Experimental Study Comparing Particle Size and Mass Concentration Data for a Cracked and Un-Cracked Diesel Particulate Filter," SAE Tech. Pap. Ser., Vol. 2009-01-06, pp. 1 12, 2009.

Table 3. Initial pressure drop of a diesel particulate wall flow filter made from DM boards compared to other equivalent commercial filters.

[2] T. Mizutani et al., "Filtration Behavior of Diesel Particulate Filters (2)," SAE Tech.

Pap. 2007 World Congr. ( SAE Tech. Pap. 2007), 2007.

[3] T. Wolff, H. Friedrich, L. Johannesen, and S. Hajizera, "A New Approach to Design High Porosity Silicon Carbide Substrates," SAE Tech. Pap., Vol. 2010 01-05, pp. 1- 11,2010.

[5] K. Tsuneyoshi, O. Takagi, and K. Yamamoto, "Effects of Washcoat on Initial PM Filtration Efficiency and Pressure Drop in SiC DPF,” SAE Tech. Pap. Ser., Vol. 1, no. 817, pp . 1-10, 2011.

[7] RH Dabhoiwala, JH Johnson, JD Naber, and ST Bagley, "A Methodology to Estimate the Mass of Particulate Matter Retained in a Catalyzed Particulate Filter as Applied to Active Regeneration and On-Board Diagnostics to Detect Filter Failures," SAE Tech Pap. Ser., Vol. 2008-01-07, pp. 1-23, 2008.

The filtration efficiency of the biomorphic substrate wall flow filter is, in all cases, higher than that of the commercial filter used as a reference. The head loss in general superior but inferior in two of the cases.

Considering that the filter is made of DM boards, and that this was one of the precursors with lower permeability, it is inferred that the use of other more permeable precursors could significantly reduce the pressure drop. Axial pine, for example, has an efficiency similar to that of DM but with greater permeability, then its use could further improve the performance of the filter.

Claims (16)

1. A diesel engine particulate filter characterized by comprising the following elements: (i) a set of discs (1) having a total length of between 0.12m and 0.25m, where each disc is composed of biomorphic silicon carbide that • has a hierarchical pore microstructure or with a first pore size between 2 pm and 60 pm; and or a second pore size between 30 pm and 440 pm; and • it has a porosity percentage of between 45% and 75%; • it has a diameter of between 0.14 m and 0.18 m and a thickness of between 0.005 m and 0.010 m; and • presents a conformation of longitudinal channels along the thickness of the disc, where said channels are between 50 cells per square centimeter and 60 cells per square centimeter, where the channels of each disc are aligned with the channels of the anterior and posterior disc, and where the set of discs comprises a first input disc and a second output disc, and where half of the channels of the first inlet disc and the second outlet disc of the set of discs are configured to block the passage of the flow of gases and combustion residues, and where half of the channels of the first disc of inlet and second outlet disk, are configured to allow the flow of flow; where the channels configured to block the flow of gases and combustion residues from the first inlet disk correspond to the channels configured to allow the flow of gases and combustion residues from the second exit disk, and vice versa; where the discs are joined together by an adhesive; so that the flow of gases and combustion debris from the diesel engine containing particles and debris between 1 nm and 100 pm are retained in the walls of the disc set channels and the flow of combustion gases the diesel engine continues its way to the exhaust pipe; (ii) an insulating coating (2), wrapping the set of discs (1), which maintains the filter's working temperature stable; (iii) a post-injection system (3) to increase the fuel input to the engine main (4) when there is excessive overpressure in the exhaust, and induce combustion and elimination of accumulated particles in the filter; (iv) a differential pressure sensor (5) for the flow of gases and combustion residues of the diesel engine, which has two connected probes, a first probe located at the entrance of the disk assembly by the first entrance disk and a second one probe located at the outlet of the set of disks by the second outlet disk, and which measures the pressure difference of the gas flow and combustion residues of the diesel engine before entering the filter and the flow of exhaust gases from the filter, and sends said collected data to the electronic monitoring and control system (7); and (v) at least two temperature sensors (6), one in the filter inlet section and the other in the filter outlet section, which record the temperature of the gas flow at both points and send the collected data to the electronic system monitoring and control (7); (vi) an electronic monitoring and control system (7) that collects the data from the differential pressure sensor (5) and the temperature sensors (6), monitors the particle retention process in the set of discs (1) , and activates the post-injection system (3) when the overpressure in the exhaust given by the differential pressure sensor (4) reaches a certain level. 2. The diesel engine particulate filter according to claim 1, wherein the channels of each disc that make up the set of discs are square in the direction perpendicular to the length of the channel. The diesel engine particulate filter according to either of claims 1 or 2, wherein the channel shape of the disk assembly (1) is a honeycomb shape and where the squares have a side size of between 0, 8mm and 0.1mm, and a channel spacing of between 0.3mm and 0.4mm. 4. The diesel engine particulate filter according to any of claims 1 to 3, where all the disks are equal to each other and have the same number of channels. 5. The diesel engine particulate filter according to any of claims 1 to 4, wherein the set of discs are joined by an adhesive resistant to temperatures between 15 ° C and 1000 ° C. 6. The diesel engine particulate filter according to any of claims 1 to 5, further comprising a block (8) comprising an oxidation catalyst and located adjacent to the disk assembly so that the flow of gases and debris The diesel engine's combustion enters first through it and then through the disk assembly. The diesel engine particulate filter according to any of claims 1 to 6, which further comprises a housing (9) with conical sections of gas inlet and outlet of the diesel engine for encapsulation of the filter, which includes all the elements of the wall flow filter. The diesel engine particulate filter according to any of claims 1 to 7, wherein half of the channels configured to block the passage of the flow of gases and combustion residues, comprises a moldable filling of silicon carbide paste granulated. The diesel engine particulate filter according to any of claims 1 to 7, where half of the channels configured to block the passage of the flow of gases and combustion residues, is obtained by machining. 10. A set of discs characterized by the fact that • it has a total length of between 0.12 m and 0.25 m; formed by discs linked together, where each disc is composed of biomorphic silicon carbide that has a hierarchical pore microstructure or with a first pore size between 2 pm and 60 pm; and or a second pore size between 30 pm and 440 pm; and • where said material has a porosity percentage of between 45% and 75%; • it has a diameter of between 0.14 m and 0.18 m and a thickness of between 0.005 m and 0.010 m; and • presents a conformation of longitudinal channels along the thickness of the disc, • where said channels are between 50 cells per square centimeter and 60 cells per square centimeter, • where the channels of each disc are aligned with the channels of the disc anterior and posterior, where the set of discs comprises a first input disc and a second output disc; where half of the channels of the first inlet disc and the second outlet disc of the set of discs are configured to block the passage of the flow of gases and combustion residues, and where half of the channels of the first inlet disc and second outlet disc, are configured to allow flow flow; where the channels configured to block the flow of gases and combustion residues from the first inlet disk correspond to the channels configured to allow the flow of gases and combustion residues from the second exit disk, and vice versa; The set of discs according to claim 10, wherein said discs are joined by a temperature resistant adhesive, between 15 ° C and 1000 ° C. 12. The disk assembly according to any of claims 10 or 11, wherein the channels are square in the direction perpendicular to the length of the channel. 13. The set of discs according to any of claims 10 or 11, wherein all the discs are the same and have the same number of channels. 14. The disk assembly according to any one of claims 10 to 13, wherein the conformation of square and longitudinal channels is a honeycomb conformation and where the squares have a side size of between 0.8 mm and 0.1 mm , and a wall thickness of between 0.3 mm and 0.4 mm; 15. Use of the disc assembly according to any of claims 10 to 14, as a particulate filter for diesel engines. 16. Use of the disk assembly according to claim 15, as a diesel engine wall flow filter to retain the particles contained in the gas flow and combustion residues of a diesel engine.