WO2017092771A1

WO2017092771A1 - A diesel particulate filter regenerating device and a method of regenerating a diesel particulate filter

Info

Publication number: WO2017092771A1
Application number: PCT/DK2016/050409
Authority: WO
Inventors: Lars Frederiksen
Original assignee: Exilator Aps
Priority date: 2015-12-04
Filing date: 2016-12-02
Publication date: 2017-06-08

Abstract

The present invention relates to a diesel particulate filter regenerating device (1) for oxidation of particulate matter from a diesel engine exhaust, said filter device (1) comprises a filter substrate (2) and a heating unit (3) arranged for heating one or more selected sections (7) of the filter substrate (2) to a temperature which causes accumulated particulate matter in said sections to ignite. Once the combustion of particulate matter is initiated, a further exothermal reaction is generated which propagates along the filter substrate and ignites particulate matter in an area around the selected sections. The filter device according to the invention therefore provides a very economical and simple filter device, since the resulting thermal 'cascade' is sufficient to result in very high soot conversion rates.

Description

A diesel particulate filter regenerating device and a method of regenerating a diesel particulate filter.

The present invention relates to a diesel particulate filter regenerating device, a method of regenerating a diesel particulate filter, and the use of said filter device.

Over the last forty years increasingly stringent legislative limits have been introduced to regulate the emissions from both petrol (gasoline) and diesel internal combustion engines. This has led to the implementation of exhaust systems for addressing the emissions of CO, HC (DOC) and nitrogen oxides (NOx) . However, in addition to the gaseous components, the diesel exhaust stream also contains entrained solids, commonly referred to as particulate matter or soot. This carbon-based material is a by-product of incomplete combustion and arises due to heterogeneity of the air-fuel mixture within the cylinder and presents a unique and specific challenge with regards to its control and conversion into environmentally benign products.

In order to prevent the particulate matter from being emitted into the environment, diesel particulate filters (DPFs) are widely employed as a means to reduce the particulate matter in diesel exhaust.

Often these filters are comprised of an inert porous ceramic e.g. silicon carbide, cordierite etc. and achieves high filtration efficiency of particulate matter including nano- particles as a result of the physical filtration achieved by forcing the exhaust flow through the porous filter. However, over time this results in a build up of stored material, which results in an ever increasing back pressure penalty, arising from the work required to force the gas flow through an increasingly dense flow restriction. This flow restriction will eventually cause excessively high exhaust gas pressure drop in the filter, which would negatively affect the engine operation. Therefore, diesel particulate filter systems have to provide a way of reducing particulates from the filter to restore its soot collection capacity.

Many filter components around the world are considered broken due to insufficient regeneration resulting in clogged and broken filter components.

This reduction of particulate matter, known as the filter regeneration, can be performed either continuously, during regular operation of the filter, or periodically, after a predetermined quantity of particulate matter/soot has been accumulated. In either case, the regeneration of filter systems should be ' ' invisible " to the vehicle driver/operator and should be performed without his intervention.

Accordingly, thermal regeneration of diesel particulate filters is typically employed, where the collected particular matter is oxidized by oxygen and/or nitrogen dioxide to ashes and gaseous products, primarily to carbon dioxide. However, in order to ensure that the particular matter is oxidized at a sufficient rate, the filter must operate at the required conditions, e.g. temperature, in order to facilitate the oxidation of the particulate matter.

Naturally Diesel particulate matter combusts when temperatures above a combustion (oxidation) temperature such as 550°C - 600°C are attained, and it is therefore required to incorporate a heat source or other measures in the system in order for the desired regeneration to take place.

In some filter systems, the source of heat is the exhaust gas stream itself. In this type of filter system, referred to as a passive filter, the filter regenerates continuously during the regular operation of the engine. Passive filters usually incorporate some form of a catalyst, which lowers the particulate matter/soot oxidation temperature to a level that can be reached by exhaust gases during the operation of the vehicle. One problem with this approach is that when the engine of the vehicle is in idle mode, the desired temperature in the exhaust gas cannot be reached, and since the filter is still collecting particular matter, the filter will eventually be clogged . Another approach uses an outside energy source to raise the temperature of the filter or the exhaust gas to facilitate reliable regeneration, these filters are known as active filters . One strategy for increasing the temperature in such actives filters involves raising the exhaust gas temperature either by in-cylinder engine management methods, such as late cycle injection of additional fuel quantities, or injection and combustion of fuel in the exhaust gas.

In another approach the active filter is heated for example, by placing an electric heater or a burner upstream of the filter. Such devices are e.g. known from US2009/0113883 ; US2011/0000195; and US2013/0125534 in which an upstream filter heats the exhaust gas before entering the filter. Alternatively it is known to incorporate heaters around the filter, to use electrically conductive media (such as metal fleece) which can act as both the filter and the heater, and/or to heat the complete filter to the soot combustion temperature.

WO94/21900 discloses a filter body partitioned into a number of filter segments, and wherein a heating unit is placed between the filter segments in order to provide a homogeneous heating of the filter segments thereby reducing thermal stress in the segments. However, the above configurations all have inherent problems. For example, if the filter is heated from the outside, this will result in non-uniform and incomplete soot combustion where the periphery of the filter is regenerated but the center retains some level of unburned soot. If a heater is placed upstream of the filter, an undesirable large amount of energy is required in order to heat the required considerable amount of exhaust gas enough for the regeneration to take place in the filter .

An excessive amount of energy is also required in situations where the whole filter is to be heated in order for regeneration to take place, as is e.g. the situation with the filter device described in WO94/21900. This means that in only relatively small filters can be regenerated this way, as a complete heating of large filters will be practically impossible. Furthermore, such filters can only be regenerated when the engine/motor is not running. Exhaust gas passing though the filter will effectively cool the filter, and accordingly either require a further heating of the filter or prevent an effective regeneration of the filter. Moreover, filters which are to be heated completely, will unavoidably be subjected to large thermal stresses over a prolonged period of time, thereby reducing the filter's efficiency and shorten the filter's lifetime.

If exhaust gas combustion is used for raising the temperature of the gas, additional fuel is required, and this extra fuel or "fuel penalty" reduces the fuel economy advantage of the diesel engine.

Furthermore, if the regeneration process is incomplete, this can result in uncontrolled soot combustion, i.e. thermal runaway. This can cause the filter to crack and/or melt, and in extreme circumstances, the filter itself will burn, whereby extreme temperature from the filter and/or from unburned fuel, in the worst case, can lead to vehicle fires and/or explosions .

Accordingly, heating the complete filter and/or the exhaust gas using an external energy source, will not only result in use of an excess amount of energy from either heating the exhaust gas or heating the complete filter substrate, but must also be carefully controlled, in order to obtain the desired regeneration .

Accordingly, there remains a demand for improved filters and/or methods for the control and conversion of particulate matter in a diesel particular filter whilst offering both a reduction in fuel penalty for regeneration and decreased complexity with regards to initiation and control of the regeneration cycle.

It is therefore a first aspect of the present invention to provide a filter device arranged for being regenerated in a fast and effective manner, using much less energy for the regeneration compared to the traditional diesel particulate filters .

It is a second aspect of the present invention to provide a filter device having a low fuel penalty for the user and a compact structure, thereby reducing both costs and space.

It is a third aspect according to the present invention to provide a filter device having decreased complexity with regards to initiation and control of a regeneration cycle.

It is a fourth aspect of the present invention to provide a filter device in which neither the exhaust gas nor the complete filter is heated in order for the regeneration to be effected. It is a fifth aspect according to the present invention to provide a filter device having a high mechanical strength as well as capability of treating a large quantity of exhaust gas containing particular matter both with a high efficiency and with a small initial pressure drop. It is a sixth aspect according to the present invention to provide a method for regeneration of the filter, using less energy than hitherto known.

It is a seventh aspect according to the present invention to provide a combination of the filter device and a catalyst in order to lower the necessary temperature to initiate the regeneration .

These and further aspect are achieved according to the present invention due to the fact that the particulate filter regenerating device according to the invention comprises a filter substrate and a longitudinal heating unit arranged for heating one or more selected sections of the filter substrate to a temperature which causes accumulated particulate matter in said sections to ignite, and wherein said longitudinal heating unit is placed in the filter substrate along a longitudinal axis of said filter substrate.

The heat provided by the heating unit to the selected sections has to be sufficient such that the temperature of the particulate matter in the selected sections, will reach a point of ignition (light-off) and thus start regeneration. Then once the combustion of particulate matter is initiated, a further exotherm is generated which propagates through/along the filter substrate and ignites soot in an area around the heated selected sections. The regeneration process obtained with the filter device according to the invention is therefore both precise, fast and efficient.

In the present application the terms "ignition temperature", "oxidation temperature" and "combustion temperature" all refer to the temperature in which the particulate matter is ignited and combusted.

As the heating unit is placed internally in the filter substrate, heat from the heating unit is distributed to the parts of the filter substrate which is in proximity to and/or adjacent to said heating unit, and the areas/sections of the filter substrate which is heated to the soot ignition temperature (oxidation temperature) defines the one or more selected sections. As the heating unit is elongated, heat can be delivered to the filter substrate along the entire length of the heating unit as well as along the periphery of said heating unit, after which the exotherm cascade can travel along/through the remaining filter, providing a very effective regeneration process.

In order to ensure a fast and effective regeneration process, the longitudinal heating unit will preferably extend in at least 80% of the longitudinal length of the filter substrate, and preferably at least 90%. In one embodiment the heating unit extend in the complete length of the filter substrate, and in another it extend beyond the boundaries of the filter substrate, at one or both ends of said substrate. Since the particulate matter/soot only are to be ignited in the selected zones (ignition zones) for the exotherm cascade to be initiated/activated, only a very small amount of energy is required for the filter regeneration to be effectuated, whereby the filter substrate can be regenerated in a fast, simple and economical manner.

Accordingly the required energy for regeneration of the filter device according to the invention is much less than for the known filter devices where either the heating unit is placed upstream of the filter substrate, e.g. in US2009/0113883; US2011/0000195; US2013/0125534 or where the entire filter substrate has to be heated to the soot combustion temperature as e.g. in WO94/21900.

In a preferred embodiment the heating unit and the filter substrate is coaxially arranged, wherein the filter substrate will surround the heating unit, defining a core-sheath like structure, i.e. the heating unit is the core and the filter substrate is the sheath. It is preferred that the heating unit has a substantially tubelike form, preferably having an annual, circular or a square- formed cross-sectional shape, however other cross-sectional shapes, e.g. a polygon shape, are also contemplated within the scope of the present invention,

The heating unit can in one embodiment continuously heat the selected sections, i.e. the heating unit will constantly be active and apply sufficient heat to the selected sections in order to continuously ignite the particulate matter in said sections.

By constantly applying energy to the selected sections, the required maintenance energy for keeping the sections at the desired temperature will be very low, providing a very simple and inexpensive device according to the invention. Since the selected sections accordingly does not have to be heated excessively when the regeneration process are to be initiated, the requirement for at intervals providing large amounts of energy for raising the temperature in the selected sections is eliminated. Furthermore, the filter device will be automatically regenerated when the concentration of particulate matter (soot) reaches a concentration that sets off the exotherm cascade, thereby ensuring that small delays in the offset of said process, in order to allow the selected sections to reach the oxidation temperature, will not occur. However, the heating unit can also be activated at predetermined intervals, or on demand, allowing the regeneration process to be initiated at any desirable time. The filter device according to the invention thereby provides a wide range of possibilities for its use.

Within the context of the present invention the term "vehicle" means any kind of equipment where diesel engines are used, such as heavy industrial equipment, ships, locomotive equipment, commercial transport vehicles, passenger vehicles, generators, farm equipment, mining equipment, and the like. It is however preferred that the vehicle is a "large" vehicle, i.e. a vehicle arranged for industrial application, such as containerships , cruise ships and freight trains.

The filter device according to the invention is unique by only heating one or more selected sections of the filter device, whereby only a small amount of energy is required to initiate the regeneration process, e.g. by maintaining the temperature of the selected section. The filter device according to the invention therefore provides a very economical and simple filter device, since the resulting thermal 'cascade' is sufficient to result in very high, efficient and fast soot conversion rates.

Independently of whether or not the selected sections are heated continuously or at intervals, the required energy for the regeneration process can in a preferred embodiment be provided by the vehicles diesel engine. Since it is neither the complete filter substrate nor the exhaust gas which is heated to the oxidation temperature, as in the conventional regeneration filter devices, the unique construction of the filter device according to the invention will therefore effectively reduce the required energy for the regeneration process to 5 - 10% compared to the energy conventionally required for regenerating the above known filter devices. Due to the lower required energy, the vehicles diesel engine can provide said energy independently of the engines operations mode, i.e. the energy can be provided from the engine to the heating unit both when the engine is in the idle mode, the propulsion mode etc.

Furthermore, since it is the particulate matter (soot) that is ignited by the heating unit in the filter device, very high oxidation rates are provided ensuring a uniform and complete soot combustion throughout the filter substrate.

Heat from the heating unit is only transferred to the selected sections, i.e. one or more minor section(s) of the filter substrate, and even though the temperature in the filter substrate can be high during the exotherm cascade, this high temperature will only affect the filter for a limited duration, i.e. during the oxidation. When the soot is combusted or the level of soot is so low that the exotherm cascade can no longer continue, the regeneration process is halted/stopped by itself, quickly reducing the temperature in the filter substrate. In this way it is ensured that the filter substrate is only exposed to high temperatures for a limited time. This is an advantage compared to the known device in WO94/21900, in which the whole filter substrate has to be heated homogenously for the regeneration process to be effectuated and wherein said filter substrate accordingly will be subjected to large thermal stresses for a long period.

Furthermore, since the particulate matter (soot) is effectively removed from the filter substrate the filter device according to the invention will reduce the risk of incomplete regeneration, and accordingly thermal runaway, explosions etc.

Naturally diesel particulate matter combusts when temperatures above a combustion temperature such as 550°C to 600°C are attained, and in one preferred embodiment the temperature of the selected sections of the filter substrate is raised to approximately 600°C or higher where the carbon-rich particulate matter (soot) readily oxidizes.

In a preferred embodiment the filter substrate comprises at least one catalyst arranged for lowering the oxidation temperature of the soot, i.e. the temperature needed for initiation of the desired exotherm cascade/reaction can be reduced to a temperature between 300°C and 400°C, depending on the used catalyst.

Such catalysts are known in the art and will accordingly not be discussed in details in the present application. However, within the scope of the present invention the catalyst can be both of the kind which involves catalytic oxidation of carbon by oxygen and/or involves catalytic oxidation of NO to N0₂, followed by the oxidation of carbon by N0₂.

The catalyst are preferably placed directly on the filter substrate surface e.g. as a coating, as this will provide a very simple and inexpensive system, however in addition, or as an alternative, to placing the catalyst directly on the surface of the filter substrate, the catalyst can also be added to the fuel as an additive. The only requirement being that the catalyst lowers the temperature needed for combustion of the soot, i.e. the temperature required for regeneration of the filter device according to the invention.

Within the context of the present invention the term "selected section" is the part of the filter substrate which is raised to a temperature that causes accumulated particulate matter in said sections to ignite, i.e. the selected sections can be seen as an ignition area or "hot zone" of the device.

It is preferred that the selected sections of the filter substrate is the part of the filter substrate in immediate proximity to the heating unit, i.e. the selected section is defined as the part of the filter substrate that is heated to the combustion temperature for the particulate matter, and said selected section (s) is accordingly the part of the filter substrate which is either in direct contact with the heating unit and/or the part of the filter substrate which is closest to the heating unit. Preferably the selected sections further comprises a small part of the filter substrate which is extending away (in all possible directions) from said heating unit .

The dimensions/size of the selected section (s) will depend on the specific construction of the filter device, and a person skilled in the art will understand that the dimension of the selected section(s) will depend on a number of factors, e.g. whether or not the filter substrate is coated with a catalyst for lowering the oxidation temperature.

It is however, preferred that the selected sections, i.e. the sections which is heated above the oxidation temperature of the particulate matter (soot) accumulated in the filter substrate by the heating unit, constitute less than 25 vol-% of the filter substrate, preferably including the interface between the heating unit and the filter substrate. '

When the filter substrate comprises a catalytic coating, the selected sections, can be lower and can preferably constitute less than 10 vol-% of the filter substrate, even more preferred less than 5 vol-%.

It will be understood for at person skilled in the art that the selected sections are not limited areas, and that heat from the heating unit in some situation can (will) extend beyond the "boundaries" of said sections. It is however intended that "only" the selected sections are heated to the relevant soot ignition temperature, in order to save energy. This will not only ensure that the particulate matter is heated to the oxidizing temperature in the selected sections, but also that the required energy for initiating the regeneration process is very low, since only a small part of the filter substrate is raised to the desired soot oxidation temperature.

A person skilled in the art will understand that a temperature gradient develops in the filter substrate during propagation of heat from the selected sections, i.e. the ignition areas (hot zones), however, it is preferred that only the selected sections is raised to the oxidation temperature (combustion temperature) of the particulate matter, and not the complete filter substrate, as this both will reduce the amount of energy required for initiating the regeneration process but also that the thermal runaway is substantially eliminated.

A person skilled in the art will based on the disclose of the present invention, understand that the area of the selected section (s) can be adjusted among others by adjusting the size of the heating unit, the material of said heating unit and/or the amount of heat provided by said unit.

In order to ensure a quick and a constant regeneration process it is preferred that the selected sections are continuously heated to the respective oxidation temperature. This ensures that when the filter substrate has accumulated sufficient particulate matter to initiate the exotherm reaction, the regeneration process is automatically started. The relevant oxidation temperature in the filter device will depend on whether or not a catalyst for lowering the oxidation temperature is used. However, said temperature is typically 550-600°C for filter substrates without a catalyst, and 300- 400°C for filter substrates with a catalyst coating. In an alternative embodiment the heating unit is activated at desirable intervals, and it is preferred that the selected sections is heated to the oxidation temperature as quickly as possible, preferably in less than 10 seconds, preferably in less than 5 seconds, and even more preferred in less than 2 seconds .

Since rapid regeneration according to the present invention will provide relatively high temperatures in the filter substrate during the regeneration process, it is preferred that the filter substrate is of a kind which can withstand these temperatures and thermal gradients. Thermal shock resistance, heat resistance and low reactivity at high temperatures of the filter substrate are therefore required. It is accordingly preferred that the filter substrate is not made of metal or similar materials.

Filter substrates made of or comprising silicone carbide (SiC) and/or re-crystallised silicone carbide (r-SiC) are accordingly preferred. Such filters are known in the art, see e.g. EP0336883, EP1741685, US2007032370 , and W02007003428 , all of which can be used in the present invention. One preferred filter substrate is disclosed in WO2013076045 which describes a porous SiC-containing filter with a high porosity, a good mechanical stability and a definable pore structure. Filter substrates made of SiC or r-SiC are normally made of segments, which are bonded together after the final sintering process with a special ceramic cement. This cement usually contains ceramic fibers with a high Youngs modulus which makes the cement able to withstand high mechanical stress including thermal gradients. EP2477716 describes a cement that has the same or even a higher thermal conductivity than the filter substrate and a similar or lower thermal weight, making said cement one of the preferred for binding ceramic filter substrate segments together in the present invention. Filter substrates made of SiC or r-SiC are not only capable of trapping particulate matter on the nano-order with a very low pressure loss, but they also has a high coefficient of thermal conductivity. This feature is especially important in the present invention, because when trapped particulate matter (soot) is ignited in the selected sections the heat is efficiently diffused to an area that surrounds said sections, ensuring that the production of local high temperature sections in the filter substrate can be avoided and maximum temperature inside the filter substrate can be reduced thereby improving the durability of the filter device.

It must be stressed that even though it is preferred that the filter substrate is made completely or partly of SiC or R-SiC, the filter substance can in other embodiments be made of other kinds of suitable materials, e.g. materials having properties similar to SiC and/or R-SiC. But other filter substrate materials e.g. cordierite are also contemplated within the scope of the invention. Cordierite is a ceramic material that provide excellent filtration efficiency, are relatively inexpensive, and have thermal properties that make packaging them for installation in a vehicle exhaust system simple. The major drawback is that cordierite has a relatively low softening, melting and/or cracking point (about 1200-1500 °C) and cordierite substrates have therefore been known to melt or otherwise being destroyed during filter regeneration. Accordingly, cordierite substrates is preferably for use in the present invention only when a catalyst for lowering the temperature needed for combustion of the soot, is used simultaneously and the regeneration takes place very often or continually .

The filter substrate according to the invention can be both an open and closed filter substrate. However, since the filtration power of closed systems is significantly higher and removes up to 99.9% of the particulate matter from the gas, a closed system construction is preferred in the filter device according to the invention. Closed systems are also called wall-flow filters. The exhaust gas is guided through the porous walls of the filter substrate and are thereby cleaned of soot particles. Open and closed systems are known in the art and will not be discussed in further details in the present invention .

The heating unit can preferably be incorporated/embedded in the filter substrate using any suitable means, e.g. using the special cement disclosed in EP2477716 for bonding segments of filter substrates made of SiC or r-SiC together. When such an embedding means is used, said means is considered to be part of the heating unit .

In some situations it is preferred to have more than one heating unit in the filter device, e.g. in order to ensure that the desired ignition temperature is reached faster and/or if several heating units can provide a synergistic effect, thereby e.g. reducing the required energy for continually heating the selected section (s) to the ignition temperature of the particulate matter. Furthermore, if the filter substrate is large or if the particulate matter is build up in separate zones of the filter, such that the exotherm reaction cannot travel from one zone to the next, it can also be preferred to have one or more heating unit(s) in each zone in order to ensure a complete regeneration process.

It is preferred that the heating unit is arranged for connection to a power source. Said power source can e.g. be an power source outside the vehicle, e.g. an electrical plug, but in a preferred embodiment said power source is an internal power source, i.e. the power/energy for activating the heating unit is provided by the vehicle on which the filter device is placed, preferably from a generator or a battery loaded through the power of the vehicles diesel engine. The heating unit can be connected to such power device in any suitable and appropriate way, as long as said heating unit obtains the energy sufficient for allowing said unit to heat the selected sections to the relevant oxidation temperature.

In order to protect the components used for providing the heating unit with power, e.g. electrodes, electric wires etc. it is preferred that said components are physically separated from the selected zones of the filter device, and that they in addition hereto, or as an alternative, is insulated, such that the large temperatures which will be generated during heating of the selected sections and during the exotherm cascade/reaction, cannot cause any damage to the respective components .

The heating unit used in the filter device according to the invention can within the scope of the present invention be any kind of heating unit capable of either providing a continued, or a rapid, increase in temperature in the selected sections of the filter substrate. The heating unit can in a preferred embodiment be selected from one or more of an electrical heating element, a heating wire, a spark igniter, resistive heating coils, and/or using a unit emitting microwaves, etc.

In order to prevent degradation of the heating unit during operation, i.e. when the heating unit is active, it is preferred that the heating unit has a very high coefficient of thermal conductivity, a high heat resistance and low reactivity at high temperatures. Thus, in one preferred embodiment the heating unit is an electric heating element made of silicone carbide (SiC) and/or re-crystallised silicone carbide (r-SiC) , i.e. the electric heating element can be made of the same substrate as the filter substrate. Alternatively, a section of the filter substrate might function as a heating unit.

Thus, when power is applied to the heating units, either constantly or at intervals, the selected sections and/or the soot accumulated in said sections of the filter substrate is heated to the relevant oxidation temperature (depending on whether or not a catalyst is used) whereby the regeneration process is initiated. More specifically, soot in sections of the filter substrate is heated to a point of ignition, defining the selected sections. The ignition of the soot creates an exotherm that propagates along/through the filter substrate and heats soot in the sections extending e.g. radially away from the selected sections, thereby effectively burning the accumulated particulate matter (soot) in the complete filter.

The filter device according to the invention can in a preferred embodiment comprise a control module arrange for determine when the filter substrate requires regeneration. Said control module preferably controls both the diesel engine of the vehicle and the filter regeneration based on various sensed information. More specifically, the control module can be arranged for estimating soot loading of the filter device, when the estimated loading is at a predetermined level and/or when the exhaust flow rate is within a desired range. The control module is further arranged for turning the heating unit on, e.g. via a power source thereby initiating the regeneration process. The duration of the regeneration process may vary based upon the estimated amount of particulate matter within the filter substrate, the size of the filter etc. In this way the device according to the invention is arranged for ensuring that the regeneration process can be effectuated independently of the operation mode of the vehicle, i.e. it does not matter if the engine is running in idle mode or propels the vehicle. The determination of whether or not to initiate the regeneration process can in one embodiment be based on soot levels within the filter substrate. Alternately, regeneration can be performed constantly, periodically or on an event basis. The control module may estimate when the entire filter needs regeneration or when zones within the filter need regeneration.

The filter can in one embodiment be divided into zones, wherein each zone can be controlled individually by the control module. When the control module determines that the filter needs regeneration, the control module can e.g. sequentially activates one or more of the heating units at a time to initiate regeneration of the respective zones of the filter. After the zone or zones are regenerated, one or more other zones are activated while the others are deactivated. This approach continues until all of the zones have been activated and regenerated. When the control module determines that one of the zones needs regeneration, the control module activates the zone corresponding to the associated zone of the filter needing regeneration. In this way, it is ensured that only the zones that requires regeneration is exposed to a regeneration process, thereby further reducing the energy needed to complete the regeneration of the filter substrate. The present invention also relates to a method for regeneration a particulate filter said method comprises:

providing a particulate filter regenerating device according to the present invention, and

heating one or more selected sections of the filter substrate to an ignition temperature of the particulate matter accumulated in said filter substrate, thereby creating an exotherm reaction thereby oxidising/burning the particulate matter in the filter substrate. Since the heat generated in the selected sections of the filter causes the soot to reach a point of ignition the regeneration is started by using a smaller amount of energy, independently or whether the selected sections is heated continuously or at intervals. Thereafter the exotherm cascade will propagate from the selected sections (ignition sections), igniting the particulate matter in the rest of the filter substrate thereby regenerating the filter in a fast and effective manner.

The filter device according to the invention is preferably incorporated in a system arranged for installation in an exhaust passage of a diesel engine, e.g. an exhaust silencer, a diesel particulate filter, a diesel catalyst and similar systems .

It is preferred that said system also comprises one or more units arranged for reducing other components of the exhaust gas, e.g. for reducing the emissions of CO, HC (DOC) and nitrogen oxides (NOx) . Such units are well known in the art and will not be discussed in further details in this application. The invention will be explained in greater detail below, describing only exemplary embodiments of the filter device with reference to the drawing, in which

Fig. 1 shows a first embodiment of a diesel particulate filter regenerating device according to the present invention, fig. 2 is a graph showing measured temperatures inside a filter substrate, and fig. 3 is an exhaust system incorporating a silencer, a particulate filter regenerating device according to the invention and a catalyst.

The invention will be described below with the assumption that the filter substrate is made of r-SiC or SiC without a catalytic coating for lowering the oxidation temperature of the particulate matter (soot) . It is further assumed that the filter device is arranged for being placed in an exhaust system of an industrial ship. However, these assumptions are not to be construed as limiting. For example, the filter substrate can be made of another suitable material, and/or comprise a suitable coating for lowering the oxidation temperature, and the filter device can be placed in a different kind of system arranged for being placed in an exhaust passage of a diesel engine. Fig. 1 shows a first embodiment of a particulate filter regenerating device 1 according to the invention. Said device has the form of a cylinder and basically consist of a filter substrate 2 and a longitudinal heating unit 3. The filter substrate is divided into a number of segments 4, bonded together with a ceramic cement 5.

In the embodiment shown the heating unit 3 is placed along a longitudinal center axis of the filter substrate 2, and is embedded in the filter substrate by means of cylinder formed center section 6, made of the ceramic cement 5 that is also used to connect the segments 4.

A selected section 7, illustrated in dotted line, defined by the part of the filter substrate which is heated by the heating unit 3 to the oxidation temperature of the particulate matter (soot), extend radially away from the outer surface of the heating unit. The volume of the section 7 is below 25% of the total volume of the filter substrate, i.e. to the volume of the shown cylinder shaped filter substrate.

For the sake of the present disclosure the centre section 6 is considered to be part of the heating unit 3. In the present embodiment the heat from the heating unit 3 will first be transferred to the center section 6, which as described above is part of the heating unit, and then to the selected section 7 of the filter substrate 2. It is therefore preferred that the center section 6 has a dimension which ensure that the heating unit is securely placed in the center, without substantially affecting the function of the device. It is therefore preferred that the ceramic cement 5 of at least the center section 6 has the same or even a higher thermal conductivity than the filter substrate 2.

The heat provided by the heating unit 3 to the selected section 7 has to be sufficient such that the temperature of the particulate matter in the selected section 7, will reach the point of ignition (light-off) i.e. the temperature is preferably just above 600°C, whereby the regeneration process is started. Then once the combustion of particulate matter is initiated, a further exotherm is generated which propagates along the filter substrate 2 from the selected section 7 to the periphery 9 of the cylinder formed device, thereby igniting soot in the remaining filter substrate 2.

It should be noted, that if the filter device 1 is combined with a catalyst or catalytic coating the ignition temperature might be lower than 550-600 °C .

In order to ensure that the heating unit 3 can withstand the high temperatures that will be generated inside the filter device during operation, i.e. when the heating unit is active, it is preferred that the heating unit 3 is an electric heating element made of silicone carbide (SiC) and/or re-crystallised silicone carbide (r-SiC) , thereby ensuring that the heating unit has a high coefficient of thermal conductivity, a high heat resistance and low reactivity at high temperatures.

In the embodiment shown in fig. 1 the heating unit 3 comprises two electrodes 10 which via electric wires 11 are connected to an external power source such as a generator or a battery (not shown) for operation in a conventionally manner. In order to prevent the electrodes and wires from being subjected to direct heat in the filter substrate, the heating unit 3, extends beyond the filter substrate, i.e. the electrodes 10 are placed at a distance and thermal isolated from the filter substrate, thereby ensuring that the generated heat from the exotherm reaction in the filter substrate cannot negatively influence the respective electronic components. It is further preferred that both electrodes and wires are arranged for operating at high temperatures, e.g. by using sufficient insulation. By placing the heating unit 3 co-axilally with the filter substrate, i.e. in the center of the filter substrate, the selected section 7 of the filter substrate, i.e. the ignition zones of the particulate matter, is also placed near or at the center axis of the filter substrate, thereby ensuring that when the particulate matter/soot is ignited the exotherm is quickly diffused in all directions from the selected section (ignition zone), such that the filter substrate 2 in a fast and simple manner can be regenerated using only a very small amount of energy for heating the selected filter section and the accumulated particulate matter.

That a very fast soot conversion rate is obtained in the filter device according to the invention is e.g. clear from the measured temperatures inside a filter substrate. In fig. 2 the temperature inside the filter substrate is plotted against the oxidation time, and it is evident that at low temperatures i.e. temperatures below 600°C there is no substantial fluctuations in the temperature, meaning that oxidation rates are very slow and the regeneration of the filter is incomplete. The temperatures inside the filter substrate are equal to the temperature of the exhaust gas when regeneration does not take place .

However, when temperatures around 600°C are reached, a further exotherm is generated which propagates along the filter substrate and ignites soot in an area around the heated selected sections quickly raising the temperature of the filter substrate in a short period of time. This is clearly depicted by the two peaks in fig. 2. These peaks illustrate that particulate matter (soot) is oxidized quickly and completely, and that the oxidation rate changes with the amount of soot accumulated in the filter substrate.

Fast oxidation rates are observed when the temperature in the selected sections exceeds 550-600°C (i.e., the two steep up going curves in fig. 2) . As the mass of soot in the sample decreases, so does its oxidation rate (i.e., steep down going curves in fig. 2) .

Thus, when the soot is combusted or the level of soot is so low that the exotherm cascade can no longer continue, the regeneration process is halted by itself, quickly reducing the temperature in the filter substrate 2. The heating unit is preferably constantly active, whereby a further regeneration process is self-initiated when the level of soot in the filter substrate is so high that the exotherm reaction is allowed to run .

Thus, fig. 2 shows that by only heating one small part of the filter substrate 2, a small amount of energy is sufficient to initiate the regeneration process. The inventor of the present invention has shown that the required energy can be reduced to 5-10% of the energy conventionally required to regenerate the conventional filters. The filter device according to the invention therefore provides a very economical and simple filter device, since the resulting thermal 'cascade' is sufficient to result in very high soot conversion rates in the complete filter substrate. Furthermore, the regeneration process can be initiated independently of the operation state of the engine. Fig. 3 shows an exhaust system 12 arranged for installation in an exhaust passage of a diesel engine. Said exhaust system has an inlet 13, an outlet 14, and comprises a filter device 1 according to the invention and an additional unit 15 downstream of the filter device 1. Said unit is arranged for reducing the emission of one or more additional undesirable component in the diesel exhaust gas, e.g. NOx . The system 12 can be considered as a silencer system. The construction of exhaust systems are known for a person skilled in the art, and can accordingly be constructed in the conventional way, the only difference being that the particulate filter regenerating device 1 according to the invention is used instead of a conventional Diesel Particulate Filter in said exhaust system.

The filter device according to the invention provides a very effective means for regenerating the filter substrate independently of the temperature of the exhaust gas. Said filter can be deployed in a wide range of applications, and will accordingly play an active and sustainable role in protecting the environment and people's health. What's more, said filter ensures that diesel-powered vehicles and machines comply with all statutory emissions requirements, while also improving their economic performance.

In the enclosed figures, the particulate filter regenerating device according to the invention has been depicted as a cylinder with the heating unit placed in the middle/centre. However this design in not to be construed as limiting. The filter device can equally well be made up of a single segment or segments having different shapes and profiles, e.g. quadratic, triangular or plate like. The only requirement being, that the heating unit is placed such that only a minor portion of the filter substrate is heated above the oxidation temperature of the particulate matter (soot) accumulated in the filter substrate, thereby defining selected section (s) .

Modifications and combinations of the above principles and designs are foreseen within the scope of the present invention.

Claims

A particulate filter regenerating device (1) arranged for oxidation of particulate matter from a diesel exhaust, said filter device (1) comprises a filter substrate (2) and a longitudinal heating unit (3) arranged for heating one or more selected sections (7) of the filter substrate (2) to an oxidation temperature which causes accumulated particulate matter in said sections to ignite, said longitudinal heating unit is placed inside the filter substrate along a longitudinal axis of said filter substrate .

A particulate filter regenerating device (1) according to claim 1, wherein the longitudinal heating unit (3) is placed near or at a longitudinal center axis of the filter substrate ( 2 ) .

A particulate filter regenerating device (1) according to claim 1 or 2, wherein the heating unit (3) and the filter substrate (2) is coaxially arranged, and wherein the filter substrate surround the heating unit defining a core-sheath like structure.

A particulate filter regenerating device (1) according to claim 1, 2 or 3, wherein the filter substrate (2) comprises at least one catalyst arranged for lowering the oxidation temperature of the particulate matter.

A particulate filter regenerating device (1) according to claim 4, wherein the catalyst preferably are coated on the surface of the filter substrate (2) .

A particulate filter regenerating device (1) according to

any of the preceding claims, wherein the one or more selected sections (7) at least comprises the interface between the heating unit (3) and the filter substrate (2) and wherein the one or more selected sections (7) constitutes less than 25 vol% of the total filter substrate of the device.

A particulate filter regenerating device (1) according to any of the claims 4 to 6, wherein the one or more selected sections (7) at least comprises the interface between the heating unit (3) and the filter substrate (2) and wherein the one or more selected sections (7) constitutes less than 10 vol% of the total filter substrate of the device, preferably less than 5 vol% of the total filter substrate of the device.

A particulate filter regenerating device (1) according to any of the preceding claims, wherein the filter substrate (2) is made of or comprises silicone carbide (SiC) and/or re-crystallised silicone carbide (r-SiC) and/or a material with thermal properties similar to SiC and/or r-SiC.

A particulate filter regenerating device (1) according to any of the preceding claims, wherein the heating unit (3) is selected from one or more of an electrical heating element, a heating wire, a spark igniter, resistive heating coils, a unit arranged for emitting microwaves and similar heating devices.

A particulate filter regenerating device (1) according to any of the preceding claims, wherein the heating unit (3) is an electric heating element made of silicone carbide (SiC) and/or re-crystallised silicone carbide (r-SiC) .

A particulate filter regenerating device (1) according to claim 10, wherein the heating element is a part of the filter substrate (2) .

12. A particulate filter regenerating device (1) according to any of the preceding claims, wherein the filter device (1) is arranged for activating the regeneration process independently of the operation mode of the vehicle.

13. A particulate filter regenerating device (1) according to any of the preceding claims, wherein the heating unit is arranged for being activated at predetermined intervals, and/or on demand.

14. A particulate filter regenerating device (1) according to any of the preceding claims, wherein the heating unit is arranged for continuously heating the selected sections.

A particulate filter regenerating device (1) according to claim 12 or 13, wherein the filter device (1) comprise a control module arranged for determining when the filter substrate (2) requires regeneration and activating the regeneration process if the filter substrate requires regeneration .

A method for regenerating a particulate filter:

providing a particulate filter regenerating device according any of the claims 1 - 15, and

heating one or more selected sections (7) of the filter substrate (2) to an ignition temperature of the particulate matter accumulated in said filter substrate .

17. A method according to claim 16, wherein the heating unit continually will heat the selected sections to the relevant ignition temperature.

18. method according to claim 16, wherein the heating unit

11 heat the selected sections to the relevant ignition temperature at predetermined intervals or in response to one or more parameters of the filter substrate.

A system (12) comprising a particulate filter regenerating device (1) according to any of the claims 1 - 15, said system is arranged for installation in an exhaust passage of a diesel engine.

An exhaust system (12) wherein the diesel particulate filter has been replaced with a particulate filter regenerating device (1) according to any of the claims 1 - 15.

An industrial vehicle comprising an exhaust system according to claim 20, said industrial vehicle is selected from heavy industrial equipment, ships, locomotive equipment, commercial transport vehicles, passenger vehicles, generators, farm equipment, mining equipment, and the like.