IT201900014304A1 - EXHAUST GAS AFTER-TREATMENT SYSTEM FOR A DIESEL CYCLE INTERNAL COMBUSTION ENGINE - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

"EXHAUST GAS AFTER-TREATMENT SYSTEM FOR A DIESEL CYCLE INTERNAL COMBUSTION ENGINE"

Field of the invention

The present invention relates to an exhaust gas after-treatment system for a diesel cycle internal combustion engine.

Description of the prior art

As is known, an After Treatment System (ATS) receives the exhaust gas from an internal combustion engine and, according to the cycle implemented in that engine, for example a petrol or diesel cycle, it comprises a a certain number of devices to reduce / eliminate pollutants contained in the exhaust gas, such as NOx, HC, particulate matter, etc.

In particular, EGR is a strategy consisting in recirculating the exhaust gas in order to limit the production of NOx.

At the same time, in the field of diesel cycle engines, the ATS is usually equipped with a filter, for example a Diesel Particulate Filter (DPF, Diesel Particulate Filter), in order to trap and collect the particulate contained in the exhaust gas. . Particulate matter mainly includes soot, which are particles resulting from the incomplete combustion of hydrocarbons. Soot filters are usually regenerated in order to automatically convert the accumulated soot. Regeneration is performed passively (at normal operating temperatures from NO2, e.g. 200-550 ° C) or actively (generating additional heat under predetermined operating conditions, so as to achieve relatively high temperatures, e.g. 550-650 ° C). During regeneration, the collected soot is burned in the filter, by oxidation by O2. Filters are usually combined with a catalytic coating, in order to lower the activation temperature of this oxidation and therefore favor regeneration.

In addition, NOx filters and catalysts can be implemented together with EGR lines.

In this field, there is a need to provide timely NOx oxidation and timely soot filtering along the ATS exhaust line, particularly to improve regeneration capacity and to protect a possible downstream EGR line from soot particulate matter, in order to avoid corrosion and engine wear due to engine intake due to this EGR line.

There is a further need to provide filters with a small size, in order to use the ATS after-treatment system for so-called "small" engines, but without compromising the high level of efficiency required during the treatment of particulate matter.

An object of the present invention is to satisfy the aforementioned needs.

Summary of the invention

The aforementioned purpose is achieved by an exhaust gas after-treatment system for a diesel cycle internal combustion engine, as defined in the attached set of claims.

The basic principle of the invention is to provide an after-treatment system in which the particulate filtering function in the after-treatment system is divided into two filters, i.e. a first filter defined by a soot filter and a second filter arranged downstream of the first filter and defined by an ash collection filter, in which this second filter can be subjected to maintenance so as to periodically remove the collected ash.

Preferably, the after-treatment system is associated with a single-stage or two-stage supercharging system to compress the air fed into the internal combustion engine, in which the first soot filter is arranged upstream of a turbine of this system. of supercharging, so as to operate at higher pressures and at higher temperatures and the second filter is arranged downstream of the turbine, or turbines, of the supercharged system.

Brief description of the drawings

For a better understanding of the present invention, a preferred embodiment is described below, by way of non-limiting example and with reference to the attached drawing, which is indicated as Figure 1 and schematically shows an exhaust gas aftertreatment system for a diesel cycle internal combustion engine according to the present invention.

Detailed description of the preferred embodiment

In Figure 1, the acronym ATS indicates, as a whole, an exhaust gas after-treatment system, for an E-cycle internal combustion engine, preferably a four-stroke type engine.

The engine E comprises a plurality of cylinders C, which are in communication with an intake line IP through the respective intake valves (not shown) to receive a flow of air, in particular a flow of compressed air. The air drawn in by, or compressed into, cylinders C is mixed with diesel fuel, metered into these cylinders C by respective injectors (not shown). At the same time, cylinders C are in communication with the ATS system through their respective exhaust valves (not shown).

The ATS system releases the exhaust gas into the external environment and is designed to reduce the pollutants contained in the exhaust gas.

Preferably, the air flow in the IP intake line is compressed by means of a supercharging system, in particular a two-stage supercharging system TC. The TC system includes two compressors C1 and C2 arranged in series along the suction line IP to compress the air fed into cylinders C and two turbines T1 and T2 arranged along an EP discharge line of the ATS system and coupled respectively to the compressors C1 and C2, for example by means of respective shafts, to operate such compressors C1 and C2. According to figure 1, the compressor C1 is arranged downstream of the compressor C2, considering the direction of air flow in the suction line IP; and the turbine T1 is arranged upstream of the turbine T2, considering the direction of the exhaust gas in the exhaust line EP.

According to a variant, not shown, a single-stage supercharging system is provided, ie with a single compressor arranged along the suction line IP and a single turbine arranged along the exhaust line EP.

According to another variant, at least one of the turbines T1 and T2 drives an electric generator, so as to feed electricity to an engine which, in turn, is controlled to drive the corresponding compressor.

As shown in Figure 1, the suction line IP comprises a portion P1, which is connected to an outlet orifice of the compressor C1 to direct the flow of compressed air to the suction valves and is, therefore, at a high pressure. An intermediate cooler or an AC air cooler is preferably provided along the portion P1. The suction line IP also comprises a portion P2, which connects an outlet orifice of the compressor C2 to an inlet orifice of the compressor C1 and, therefore, is at an intermediate pressure; and a portion P3, which is connected to an inlet of the compressor C2 and receives air from the external environment.

At the same time, the discharge line EP comprises: a portion P4, which is connected to an inlet orifice of the turbine T1 and is therefore at high pressure and temperature; a portion P5, which connects an outlet orifice of the turbine T1 to an inlet orifice of the turbine T2 and, therefore, is at an intermediate pressure and temperature; and a portion P6, which is connected to an outlet of the turbine T2 and channels the exhaust gas from the turbine T2 to an exhaust pipe TP, which discharges the exhaust gas into the external environment.

The EP exhaust line preferably also comprises a muffler, not shown.

Preferably, an EGR system is provided so as to recirculate a part of the exhaust gas from the exhaust line EP into the intake line IP, for example under the control of the valves and / or devices which are not shown and are generally known in the technique. Preferably, the EGR system comprises an EGR1 recirculation line which connects the portion P5 to the P2 portion and an EGR2 recirculation line which connects the P6 portion to the P3 portion, to withdraw respective flows of the exhaust gas from the exhaust line EP. According to a variant, not shown, only one of the recirculation lines EGR1 and EGR2 is provided. More preferably, the EGR system also includes an additional EGR3 recirculation line that connects the P4 portion (or the turbine inlet T1) to the P2 portion, to draw an additional flow of exhaust gas from the EP exhaust line.

The EGR system can optionally include one or more coolers (not shown) to cool the flow or flows of exhaust gases taken from the EP exhaust line, before mixing these flows with the air in the IP suction line.

According to an aspect of the present invention, the ATS system comprises a filter F1 configured to trap and collect soot from the exhaust gas flowing along the exhaust line EP and to let the ash flow downstream of the filter F1. In other words, the porosity and / or pore size in the F1 filter is sufficient to trap most of the soot, but it is too high to trap and collect all fine particles, such as ash and / or PM10 particles.

Preferably, the filter F1 is arranged upstream of at least one of the turbines T1 and T2 (considering the direction of the exhaust gas), so as to be relatively close to the engine E. In other words, the filter F1 operates at higher pressures and at higher temperatures, for more efficient regeneration (in fact, higher temperatures and pressure improve the passive regeneration capacity). Therefore, the materials for the filter walls of filter F1 are to be chosen on the basis of these temperatures and pressures.

In particular, the filter F1 is arranged along the portion P5, ie between the turbines T1 and T2. More preferably, the EGR1 line starts from a point which is arranged downstream of the filter F1, so that the exhaust gas taken and recirculated by the EGR1 and EGR2 lines is already filtered by the soot, in order to protect the engine.

Preferably, the filter F1 is regenerated only passively, i.e. the active regeneration of the soot is not provided in the ATS system and in the E engine.

In particular, the F1 filter is associated with a catalyst to promote the oxidation of NOx and, therefore, to lower the activation temperature of the regeneration in the F1 filter. This arrangement also allows for a timely oxidation of NOx along the ATS system.

More particularly, this catalyst can be defined by the catalytic material directly in the filter F1, for example the filter walls of the filter F1 are produced in such a way as to include this catalytic material. By way of example, filter F1 is defined by a so-called catalyzed soot filter (CSF, Catalyzed Soot Filter).

In combination or as an alternative, the catalyst can be defined by a dedicated catalytic converter, for example a so-called Diesel Oxidation Catalyst (DOC), arranged upstream of the F1 filter. The DOC has the task of subjecting the hydrocarbons to oxidation and generating NO2, both for the reduction of NOx (rapid reaction) and for the oxidation of passive soot in the filter. In this approach, the main purpose may be the filtering of the exhaust gas for EGR. Therefore, a DOC / filter combination may be preferred.

In any case, any type of anti-soot filter can be chosen as the F1 filter, among those available on the market.

To date, soot filters (bare or catalyzed) usually have an average pore size between 15 and 20 microns and wall thicknesses of approximately 10 milli-inches. By way of example, the substrate materials are SiC or Cordierite. Cell densities are between 300 and 400 cpsi (cells per square inch) and are preferably partially asymmetrical to increase ash capacity.

Advantageously, the filter F1 could be designed in a dedicated way, so as to subject the soot and HC to oxidation in order not to pollute the engine intake system and not to cause wear of the cylinder, to back pressure losses and regeneration needs of minimal soot. This allows for some ash migration downstream, relatively low pressure losses and relatively high filtration efficiency.

According to another aspect of the present invention, the ATS system further comprises a filter F2, which is arranged downstream of the filter F1 (considering the direction of the exhaust gas) and is configured to trap and collect the ash. In other words, the porosity and / or pore size in the F2 filter is small enough to trap and collect ash and ultrafine particles, for example particles classified as PM10. At the same time, the F2 filter is configured to be serviced, in order to allow the maintenance personnel to periodically remove the ash collected by the ATS system. By way of example, the filter F2 is temporarily removed from the discharge line EP by such personnel and is treated in a known way so as to discharge and eliminate the ash.

This type of filter can also be chosen from those commonly available on the market.

Advantageously, this F2 downstream filter could be designed in a dedicated way, to better comply with the requirements on ash retention (and the ash cleaning service) and on the reduction of fine particulate emissions, to fulfill the requirements up to 10 nm. .

In other words, the F2 filter allows to reach an arrangement that achieves a very high filtration efficiency, so as to reduce PN (the number of particles) even for particle size in the range between 5 and 23 nm (and not only greater than 23 nm).

As shown in Figure 1, the filter F2 is arranged downstream of the turbines T1 and T2, ie along the portion P6, in which the temperatures and pressures are relatively low.

Preferably, the ATS system further comprises at least one SCR device arranged along the portion P6, for adding a urea-based liquid or an ammonia-based liquid to the exhaust gas in order to perform a selective catalytic reduction process and, therefore, convert NOx. In particular, the ATS system comprises two SCR devices arranged in series, ie a SCR1 device arranged upstream of the filter F2 and a SCR2 device arranged downstream of the filter F2. The SCR1 device favors the conversion of any part of soot that has passed through the filter F1, without being trapped and burned. On the other hand, the SCR2 device is controlled in order to achieve certain emission / pollutant targets at the TP exhaust pipe, if the SCR1 device is not sufficient to achieve these objectives.

According to a variant, not shown, the SCR2 device is not provided.

From the above description it is clear that the filtering function of the ATS system is divided into the two filters F1 and F2. Thanks to this feature, it is possible to achieve high efficiency in conversation and in the removal of particulate matter, using a solution having a relatively small size and resulting in a relatively low pressure loss along the ATS system.

At the same time, only the filter F2 needs to be serviced, for removal and / or cleaning from ash. Therefore, the proposed solution is relatively inexpensive.

Furthermore, if an EGR system is provided, the E engine is more effectively protected against corrosion and wear, as the main part of the soot is converted by the F1 filter, upstream of the EGR1 and EGR2 line, so that these lines I recirculate the gas having a reduced quantity of particulate matter.

A minor part of the soot may still be present in the exhaust gas flowing into the P6 portion, i.e. towards the F2 filter, but this part is trapped by the F2 filter itself, together with the ash and is converted by the selective catalytic reduction process performed by the device SCR1. At the same time, the efficiency of the SCR devices is greater thanks to the timely oxidation of NOx performed by the catalyst that is associated with the F1 filter.

From the foregoing it should be clear that changes can be made to the ATS system described above, without departing from the scope of protection defined by the attached claims.

In particular, as mentioned above, any type of anti-soot filter can be chosen as filter F1 and any type of anti-ash filter can be chosen as filter F2.

Claims (1)

CLAIMS 1.- Exhaust gas after-treatment system (ATS) for a diesel-cycle internal combustion engine (E), the after-treatment system comprising: - an exhaust line (EP) for channeling the exhaust gas from said engine (E) to an external environment; - a first anti-particulate filter (F1) and a second anti-particulate filter (F2) arranged in series along said exhaust line (EP); where the first particulate filter (F1) is configured to trap and collect the soot and allow the ash to pass through the first particulate filter (F1) and where the second particulate filter (F2) is configured to trap and collect the ash , is arranged downstream of said first anti-particulate filter (F1), considering the direction of the exhaust gas in said exhaust line (EP) and is configured to be subjected to maintenance, so as to allow the removal of the collected ash. 2.- Post-treatment system according to Claim 1, characterized in that said first anti-particulate filter (F1) is associated with a catalyst. 3.- Post-treatment system according to claim 2, characterized in that said catalyst comprises catalytic material in said first anti-particulate filter (F1). 4.- Post-treatment system according to Claim 2 or 3, characterized in that said catalyst comprises a catalytic converter (DOC) arranged upstream of said first anti-particulate filter (F1). 5.- Post-treatment system according to any one of the preceding claims, characterized in that said first anti-particulate filter (F1) is a passive regeneration filter. 6.- Post-treatment system according to any one of the preceding claims, characterized in that it comprises at least one turbine (T1, T2) suitable for operating, directly or indirectly, an air compressor and arranged along said discharge line (EP ) downstream of said first anti-particulate filter (F1); said second anti-particulate filter (F2) being arranged downstream of said turbine (T1, T2). 7.- Post-treatment system according to any one of the preceding claims, characterized in that it comprises at least one EGR line (EGR1, EGR2) to recirculate a part of the exhaust gas in an intake line (IP) for said internal combustion engine (E); said EGR line (EGR1, EGR2) starting from a point of the exhaust line (EP) downstream of said first anti-particulate filter (F1). 8.- Post-treatment system according to any one of the preceding claims, characterized in that it comprises at least one SCR device (SCR1) arranged along said exhaust line (EP) between said first anti-particulate filter (F1) and said second filter particulate matter (F2). 9.- Post-treatment system according to Claim 8, characterized in that it comprises a further SCR device (SCR2) arranged along said discharge line (EP) downstream of said second particulate filter (F2). 10.- Group comprising: - a diesel cycle internal combustion engine e - an exhaust gas after-treatment system according to any one of the preceding claims.