SE1350008A1 - Method for dimensioning a particle filter intended for an exhaust system of an internal combustion engine - Google Patents

Abstract

SUMMARY The present invention relates to a method for dimensioning a particulate filter intended for an exhaust system of an internal combustion engine. The particulate filter comprises a porous body of silica fibers. The method comprises the steps of determining the maximum exhaust flow of the exhaust system and then selecting the surface area of the porous body so that the following conditions are met: FV = Qmax / A 1 m / s; vani FV = flow per surface area - Qmax = maximum exhaust flow in the exhaust system (m3 / s); and A = the surface area (m2) of the porous body (m2) through which the exhaust stream passes. The process further comprises the step of selecting the amount of silica fibers so that the ratio fiber mass / maximum exhaust flow in the porous body is: mf / Qmax 500g / 1 m3 / s; vani mf = fiber mass Finally, the porosity of the porous body is adjusted so that it is less than or equal to 99.3%. With the method according to the invention it is possible to dimension a silica fiber filter so that a filtration degree of at least 99 (:) / 0 is obtained.

Description

Application: Scania CV AB Method for dimensioning a particulate filter intended for an exhaust system of an internal combustion engine FIELD OF THE INVENTION The present invention relates to a method for dimensioning a particulate filter intended for an exhaust system of an internal combustion engine. The invention also relates to a particle filter which has been dimensioned according to the method as well as an exhaust line which comprises the particle filter.

BACKGROUND OF THE INVENTION AND KNOWLEDGE TECHNOLOGY Diesel engines are equipped with exhaust gas purification devices in order to reduce particulate emissions and harmful gases present in the exhaust gases of the diesel engine. In order to regulate emissions from engines, for example in vehicles, there are various standards and legal requirements that regulate levels for permitted exhaust emissions.

Internal combustion engines can be included in several different applications, for example in heavy vehicles, such as trucks or buses. The vehicle can alternatively be a car. Also motor boats, ships, ferries or ships, industrial engines and / or motorized industrial robots, power plants, such as e.g. an electric power plant that includes a diesel generator, locomotive or other application may include an internal combustion engine.

Particle emissions from internal combustion engines, especially in diesel-powered heavy vehicles, can be reduced with the help of a particulate filter. A particulate filter comprises a body of material of a porous material. The porous material can, for example, consist of a mineral-based material such as cordierite or ceramic or sintered material. With these filter materials it is possible to obtain a high degree of filtration of particles from an exhaust stream, and it is common to obtain a degree of filtration of Over 99 (:) / 0. Ceramic filters are also effective in depositing fine particles which are preferably carbon particles with a diameter of less than 100 nanometers (nm). Filters of this type can typically be regenerated spontaneously during the operation of the engine by allowing accumulated particles, mainly soot, to be combusted so that the filter is kept clean and thereby can continuously fulfill its filtering function. However, the disadvantage of these mineral-based, keranic or sintered materials is that they have a relatively large tern mass. They must also be cleaned of ash at appropriate intervals so as not to lose their function, as the material in the particles that will not burn off in the long run loses to passages in the material. Furthermore, these materials are not malleable in a simple manner and they are suitable for adapting to tight spaces.

As an alternative to the materials above, fibrous materials have also been used in particulate filters. SE 535454 C2 discloses a particulate filter comprising ceramic or sintered material in combination with silica fibers. Furthermore, EP1624165 discloses a particulate filter with silica fibers coated with iridium in combination with platinum and / or palladium.

However, fibrous material has not been used to a large extent in the particulate filter of an internal combustion engine, since it has been black to dimension the filter so that a sufficient degree of filtration, for example 99 (:) / 0, is achieved.

SUMMARY OF THE INVENTION Therefore, there is still a need to further develop particulate filters. In particular, there is a great need to be able to dimension a particle filter which comprises a porous body of a fibrous material, so that a degree of filtration of at least 99 (:) / 0 can be achieved. Since the fibrous material is malleable, it is relatively easy to design a filter with a laid back pressure and which can be adapted to narrow outlets, for example piles in a muffler. Therefore, it is undesirable to be able to use fibrous material even in a particulate filter in diesel-powered motor vehicles, but so far it has not been possible to ensure that a sufficient degree of filtration is achieved.

There is therefore a need to be able to ensure that a degree of filtration of at least 99% can be achieved with a particle filter which comprises a porous body of fibrous material. By using fibrous materials, the need for space can be reduced, while at the same time a sufficient degree of filtration for exhaust emissions can be achieved.

Silica fibers have been found to be very suitable for use as a fibrous material in a particulate filter as a material for the porous body.

The object of the present invention is thus to provide a method for dimensioning a particle filter which comprises a porous body of silica fibers, and which has a degree of filtration of at least 99%. At the same time, the filter and the porous body are malleable and space-saving and have a low thermal mass.

It is a further object of the invention to provide a particulate filter having a porous body of silica fibers having dimensions to withstand the degree of filtration of at least 99%.

The above objects are achieved by the initially mentioned method for dimensioning a particle filter which comprises a porous body of silica fibers which can be characterized by what is stated in claim 1.

The method comprises the steps of: a) determining the maximum exhaust gas flow Qmax of the exhaust system; 4 b) select the surface area of the porous body so that the following conditions are met: FV = Qmax / A 1 m / s; vani FV = flow per surface area - Qm „= maximum exhaust flow in the exhaust system (m3 / s); and A = the surface area (m2) of the porous body, through which the exhaust gas flow passes to select the amount of silica fibers so that the ratio fiber mass / maximum exhaust gas flow in the porous body is: mf / Qm „500g / 1 m3 / s; vani mf = fiber mass to adjust that the porosity of the porous body is less than or equal to 99.3%.

The process also comprises the step of selecting that the average diameter of the silica fibers is preferably between 5-20 .mu.m, whereby a large contact area between the fibers and the particles of the exhaust river is obtained.

The porous body suitably has a thickness of at least 15 mm. With this thickness of the porous body together with the surface area and the porosity according to the criteria above, it is ensured that the exhaust gas does not compress the porous body at the high river.

The method further preferably comprises the step of: selecting the volume of the porous body such that: SV = Qm „/ V 150000; vani SV = space velocity, flow per volume Qm „= nmaximal exhaust flow in the exhaust system m3 / s; and V = the volume m3 of the porous body, through which the exhaust gas flow passes.

The porosity of the porous body is preferably adjusted to be between 95-99%. In this way, the dimensions of the filter are optimized so that the porous body is not too hard or loosely packed.

The invention also relates to a particle filter which comprises a porous body and the porous body is dimensioned according to the method according to the invention.

The invention also relates to an exhaust line for an internal combustion engine, for example in a vehicle, which comprises a particle filter with a porous body which is dimensioned according to the method according to the invention.

Additional features and advantages of the invention will become apparent from the following detailed description and examples.

DETAILED DESCRIPTION Definitions Particulate filter is a device that includes a porous body for the accumulation of particles Than an exhaust flood.

Fiber material is a material that consists of fibers. The fibers are elongated, flexible material elements with relatively small cross-dimensions.

The porous body has a porosity, which defines how much air or tonnage the porous body contains. The porosity can be determined with the aid of the solidity of the porous body, a. Porosity = 1- a. The solidity is the volume of the fibers / total porous body volume. The mass of the fibers can be defined on the basis of the density of the raw material of the fibers. The density of the silica fibers can be e.g. 2200 kginn3.

The porous body has a surface area A, which corresponds to the projected surface area and is the surface through which the exhaust stream flows.

The porous body has a fiber mass mf sonn corresponds to the weight of the porous body.

Filtration rate, FE, is a measure of the proportion of the number of particles that are filtered out with the help of the filter. The degree of filtration is calculated using the ratio between the number of particles in the exhaust gas stream after each pre-filtration according to the following formula: FE (%) = 100 (1fore, '-PNefter / PNdar PN = number of particles Detailed description of embodiments The porous body comprises silica fibers ( SiO2) as a fibrous material and preferably the porous body consists essentially only of silica fibers.Silica dioxide is amorphous (non-crystalline) and is obtained from quartz or manufactured synthetically.The silica fibers preferably consist of substantially pure silica.

Silica has a high melting point, about 1700 ° C, and is excellent for use in a particulate filter in an internal combustion engine, where the exhaust gas temperature can reach about 1200 ° C. Silica fibers are resistant to high temperatures, temperature shocks and many chemicals, among others. a strong acids, which can be found in the exhaust river.

The fibers preferably have an average diameter of 5-20 μm. The thinner the fibers of the porous body, the larger the shape it has to receive 7 particles from the exhaust stream. Fiber materials of this type are supplied, for example, by the company Saint Gobain Quartz, for example under the product sheet Quartzel® Wool.

To form a porous body, the fibers supplied, for example, in the form of a fiber mat where the fibers are randomly distributed, can be packed or compressed. The gasket can be made by mechanical gasket, for example by compression molding. The fibers in the formed body are randomly tangled and form a net and soot particles may have a sticky surface, thereby both sticking to the surface of the silica fibers and becoming trapped in the formed fiber net. The porous body of silica fibers is malleable and can assume almost any shape and can thereby be adapted to different applications.

The silica fibers can be coated with a catalytic material, such as platinum, to increase the ability to oxidize, for example, NO at low temperatures. With such a coating, soot can be burned at a relatively low temperature. The fibers can be coated by spraying or impregnating the porous body of silica fibers with the catalytic coating material. Other methods can also be used.

Face velocity, FV, which is also called flow per surface area, is a parameter used in the filtration technique to describe the velocity of an exhaust stream flowing into the filter. Face velocity is determined according to the following formula: FV = Qmax / A, vani Qmax = maximum exhaust flow (m3 / s): A = surface area of the porous body (m2) By surface area is meant the projected surface area of the porous body. The maximum value for FV according to the present invention must be less than 8 or equal to 1 m / s. In the first step of the dimensioning of the particle filter, or the porous body in the filter, the maximum exhaust flow Qmax of the exhaust system must be determined. This exhaust flow corresponds to the engine's maximum exhaust flow and the porous body is thus defined from the engine's maximum exhaust flow.

Once the exhaust flow has been observed, it is possible to define which surface area the porous body must have at least. The maximum surface area of the porous body is determined by the construction of the particle filter. By dimensioning the surface area of the porous body as a function of the maximum exhaust flow in the exhaust system and saying that the FV is less than or equal to 1 m / s, it can be ensured that the porous body has such a large surface area that the velocity of the flow through the filter is sufficiently low. for the porous body to be able to process the maximum exhaust flow.

In a next step of the dimensioning process, the fibrous mass of the porous body is selected. In accordance with the present invention, it has been found that with a specific proportion of fiber mass to maximum flow in the exhaust system, it can be ensured, together with the other dimensioning parameters, that a filter having a sufficiently large capacity to achieve a filtration degree of at least 99% can be obtained. According to the present invention, the ratio of fiber mass to maximum flow in the exhaust system must be at least 1.5 kg of fibers for an exhaust flow of 3600 m3 / h or 1 m3 / s.

Therefore, the weight of the fibers in the porous body of the filter can be dimensioned by the following formula: 1500g / 1 m3 / s mf / Qmax, vani rnf = fiber mass Since Qmax has already been determined in the first step of the process, it can be further developed that rinf500g * Qmax / 1 rin3 / s Based on the values for minimum surface area A and minimum fiber mass, etc., a value is obtained for the basis weight g / m2 required for the porous body to meet the conditions in the dimensioning process.

In a next step of the dimensioning process, the porosity of the porous body is adjusted.

The porosity can be controlled, for example, by varying the degree of packing of the porous body. The more the fibers are packed, the higher the solidity and thus the lower porosity the porous body gets. According to the present invention, the porosity should be less than or equal to 99.3%, so that the porous body can withstand the pressure of the exhaust gas flow during operation, and in this way the risk of the porous body being compressed by the exhaust gas flow is avoided. With a porosity above 99.3%, there is a risk of such compression. The fibers should also not be packed too hard and therefore the porosity is preferably between about 9 (:) / 0 and 99%. If the porosity is less than 95 (:) / 0, there is a risk that the back pressure in the exhaust system will be too high and thereby, for example, engine performance may be impaired. Also the risk of the fibers being damaged increases.

In order to further ensure that a high degree of filtration can be achieved with the aid of the dimensions of the porous body, the "Space Velocity" (SV) of the porous body, or flow rate per volume, can also be determined.

With the help of SV, the residence time of the exhaust gases in the filter can be controlled. SV is the inverse of the gas residence time in the filter, and is determined according to the following formula: SV = QmaxN, vani Qmax = maximum exhaust gas flow (m3 / s): V = volume of the porous body (m3) 9 The maximum value of SV according to the present invention should be less than or equal to 150,000 1 / s. The residence time should therefore suitably be 6.7 ps - 10 ps, and is preferably about 7 ps.

It has also been found that the porous body of a particulate filter should preferably have a thickness of at least 15 mm of practical shells. Even thinner filters can be used if the filter is folded, for example.

The dimensions of the porous body of a particulate fiber filter according to the present invention ensure that a degree of filtration of at least 99% is achieved.

Dimensioning examples Below are some examples of dimensions for a particle filter which comprises a body of a pot according to the invention.

A first example illustrates an application where the space for the porous body in the particle filter is limited and the porous body can have a thickness of at most 25 mm. The maximum exhaust flow in the system is 3600 m3 / h (= 1m3 / s). It can then be deduced that the area for the porous body must be at least 1m2. The volume will then be 0.025 m3. The fiber mass must be at least 1.5 kg (1.5 kg * 1 (m3 / s)). The density of silica is 2200 kg / m3 and the porous body is packed to the volume 0.025 m3 whereby the porosity can be traced by 100% - (100 * 1.5 kg / (2200 kg / m3 * 0.025 m3)%) = 97.3% .

A second example illustrates an application where the space for the porous body in the particle filter is limited and the porous body can have a thickness of at most 25 mm. The maximum exhaust flow is 1800m3 / h. The area must then be at least 0.5 m2 and the volume is 0.0125 m3. The fiber mass must be at least 0.75 kg of fiber (1.5 kg * 0.5 (m3 / s)). The porosity is shaved as above and is 98.6%.

A further example illustrates an application where the space for the porous body in the particle filter is limited and the porous body can have a thickness of at most 50 mm. The area is chosen to be 1 m2 and the maximum exhaust flow is 1800 m3 / h. This gives a volume of 0.050 m3, and the weight of the porous body must be 0.75 kg of fiber (1.5 kg * 0.5 (m3 / s)). The porosity can be shaved as above and is 98.6%.

Examples of filtration degree feeds To ensure that a filtration degree of 99% is achieved, one can use a test cycle "World Harmonized Transient Cycle (WHTC)" (WHTC), which is defined in: "COMMISSION REGULATION (EU) No 582/2011", "Official Journal of the European Union ". A WHTC test cycle is 1800 seconds long and includes transient operation to feed emissions from vehicles.

The degree of filtration can then be defined by feeding the number of particles per unit volume of exhaust gases before and after the filter according to the formula: FE (%) = 100 * (1fore ,, -PNafter / PNdar PN = number of particles Example 1 A WHTC test cycle is arranged to illustrate truck operation To determine the level of particles both before and after the filter, use a food equipment, AVL Particle counter, which calculates the number of particles per unit volume of exhaust gases.The filtration rate is then calculated according to the above formula.12 In the test, the WHTC cycles were repeated until a stable level in the number of particles after the filter was reached.The amount of particles after 10 WHTC cycles is considered to be at a stable level.

Two filters were made, which ram consisted of a porous body of silica fibers of the brand Quartzel® Wool. Each of the filters had the shape of a thin steering wheel block and these filters were used in the degree of filtration. The filter in Example 1a is intended to illustrate a similar example, and has dimensions outside the paranneters of the invention. The filter of Example 1b is a filter sized according to the present invention. The conditions and the exhaust rivers were similar for the Dada examples. The density of the silica used in the example is 2200 kg / m3. 13 Example 1 Comparative example The dimensions for the filter are: Surface area: approx. 0.9 m2 Thickness: 25 mm Fiber mass: approx. 990 g, Porosity: 98%.

With this filter a filtration degree of 95-97% was achieved, which is lower than the desired filtration degree (99`) / 0). 14 Example lb The dimensions for the filter are: Surface area: approx. 0.9 m2 Thickness: 25 mm Fiber mass: approx. 1500 g, Porosity: 97%.

With this filter, a degree of filtration of about 99-99.5% was achieved already after two WHTC cycles, which is equal to or higher than the desired degree of filtration (99%).

The foregoing description of the preferred embodiments of the present invention has been provided for the purpose of illustrating and describing the invention. The described embodiments are not intended to be exhaustive or to limit the invention.

Claims (7)

A method for dimensioning a particulate filter intended for an exhaust system of an internal combustion engine, which particulate filter comprises a porous body of silica fibers, the method comprising the steps of: 1. determining the maximum exhaust flow Qmax of the exhaust system; 2. select the surface area of the porous body so that the following conditions are met: FV = Qmax / A 1 m / s; vani FV = flood per surface area 1. Qmax = maximum exhaust flow in the exhaust system (m3 / s); and 2. A = the surface area (m2) of the porOsa body through which the exhaust gas floc passes; c) selecting the amount of silica fibers so that the ratio of fiber mass / maximum exhaust flow in the porous body is: mf / Qmax 500g / 1 m3 / s; vani mf = fiber mass; d) adjusting the porosity of the porous body so that it is less than or equal to 99.3%. The method of claim 1, wherein the average diameter of the silica fibers is selected to be between 5-20 μm. The method of claim 1 or 2, wherein the method further comprises the step of shaping the porous body so as to have a thickness of at least 15 mm. A method according to any one of claims 1, 2 or 3, wherein the method further comprises the step of: e) selecting the volume of the porous body so that: 16 SV = Qm „I V 150000; vani SV = space velocity, flow per volume Qm „= maximum exhaust flow in the exhaust system m3 / s; and V = the volume m3 of the porous body through which the exhaust gas flow passes. A method according to any one of the preceding claims, wherein the porosity of the porous body is adjusted to between 95-99%. Particle filter comprising a porous body, characterized in that the porous body is dimensioned according to the method according to any one of claims 1-5. Exhaust line for an internal combustion engine, characterized in that it comprises a particulate filter according to claim 6.