FR3087835A1 - INJECTOR FOR INJECTING A GAS REDUCING AGENT INTO THE EXHAUST GAS FLOW OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The injector includes at least one injection nozzle (34), a metering system for providing a metered flow of the gaseous reducing agent to the or each injection nozzle (34), and an injection line ( 38) connecting the metering system to the or each injection nozzle (34). The injection line (38) comprises at least one buffer chamber (50), an upstream pipe (52) connecting the buffer chamber (50) to the metering system (36), and a downstream pipe (54) connecting the buffer chamber (50) to a respective injection nozzle (34). The buffer chamber (50) has an enlarged flow section with respect to the upstream pipe (52).

Description

DESCRIPTION TITLE: Injector for injecting a gaseous reducing agent into the flow of exhaust gas of an internal combustion engine The present invention relates to an injector for injecting a gaseous reducing agent into the flow of exhaust gas of an internal combustion engine internal, the injector tu being of the type comprising at least one injection nozzle, a metering system for providing a metered flow of the gaseous reducing agent to the nozzle or to each injection nozzle, and an injection line connecting the dosing system to the nozzle or to each injection nozzle.

The invention further relates to an exhaust pipe for an internal combustion engine comprising such an injector, and a motor vehicle comprising such an exhaust pipe.

The gaseous reducing agent comprises, for example, ammonia, a mixture of air and ammonia, or a mixture of ammonia and neutral gas such as helium.

Automotive internal combustion engines are known to produce nitrogen oxides also referred to as "NOx".

These can be a significant source of air pollution since they contribute to the formation of fog and acid rain, and affect ground-level ozone.

It is therefore desirable to eliminate the NOx contained in the exhaust gas of these engines.

To this end, a process known as "selective catalytic reduction" (SCR) has been developed, in which ammonia is used to reduce NOx to harmless nitrogen.

The most common way to carry out this process consists in injecting into the exhaust pipe an agent based on liquid urea which will be mixed with the exhaust gas and subjected to thermal hydrolysis to turn into ammonia, before that the mixture of exhaust gas and ammonia passes through an SCR catalyst in which the ammonia reduces NOx to nitrogen.

However, this method is not very efficient.

It has been found that it is much more efficient to inject ammonia directly into the exhaust line, upstream of the SCR catalyst, rather than the aforementioned liquid urea agent.

In this way; the aforementioned first step is eliminated.

2 This observation has led to the development of injectors of the aforementioned type, which are known, for example, from document FR 2 994 455.

These injectors are commonly used as a replacement for liquid urea agent injectors.

Nevertheless; these known injectors are not entirely satisfactory.

Indeed; it has been found that, when the ambient temperature is low, after stopping the engine; the injection nozzles of these injectors are generally clogged with ammoniacal salts formed by a chemical reaction between water, carbon dioxide and the reducing agent. It is therefore impossible to inject ammonia into the mixer, and the treatment of Nex is inefficient. tu When the injection nozzle is partially clogged, it takes several hours before the injection nozzle is unclogged and the injector can operate.

During this time; ! The exhaust gas cannot be decontaminated.

An objective of the invention is therefore to prevent or at least reduce the obstruction of the injection nozzle by salts formed by the reaction between the reducing agent, water and carbon dioxide, in order to allow the injector of the aforementioned type to be operational when necessary after starting the engine.

To this end, the invention deals with an injector of the aforementioned type, in which the injection line comprises at least one buffer chamber, an upstream pipe connecting the buffer chamber to the metering system, and a downstream pipe connecting the buffer chamber. buffer chamber 20 at a respective injection nozzle; the buffer chamber having an enlarged flow section with respect to the upstream pipe.

According to specific embodiments of the invention, the injector further exhibits one or more of the characteristics mentioned below, considered independently or together in any technically possible combination - the downstream pipe has a length of less than 15 cm. ; - the buffer chamber is fluidly interposed between the upstream and downstream pipes; - the buffer chamber is configured to cool faster than the pipes 30 upstream and downstream when the internal combustion engine is stopped - the buffer chamber has an enlarged flow section with respect to the downstream pipe; - The injector comprises a cooling means configured to increase the heat exchange surface between the buffer chamber and an ambient fluid; - the cooling means comprises cooling fins extending outwardly from the body of a housing of the buffer chamber; 3 - the buffer chamber is defined inside a housing, said housing consisting of a corrugated tube; the injector includes a thermal bridge to conduct heat between the upstream and downstream pipes while thermally bypassing the buffer chamber; - the two pipes upstream and downstream extend through a bottom of the buffer chamber and open into the buffer chamber through an opening which is at a certain distance from said bottom; - The injector comprises a heating means for the accelerated heating of the buffer chamber when the internal combustion engine is started; ii - the heating means comprises a supply line opening into the buffer chamber to collect exhaust gas and supplying the collected exhaust gas to the buffer chamber, and a control valve mounted on said gas line. feed to selectively open and close the feed line; - the injector comprises a single buffer chamber, the volume of which is between 10 cm3 and 100 cm3, for example, 50 cm3, or the injector comprises a plurality of buffer chambers, the total volume of which is between 10 cm3 and 100 cm3; for example, 50 cm3.

The invention also relates to an exhaust pipe for an internal combustion engine comprising a mixer configured to be traversed by an exhaust gas produced by the internal combustion engine and an injector as defined above for injecting the gas. gaseous reducing agent in said mixer.

The invention further relates to a motor vehicle comprising an exhaust pipe as defined above.

Other characteristics and advantages of the invention will be evident from a detailed description which is provided below by way of indication and in no case of limitation, with reference to the appended figures, in which: [Fig 1 ] Figure 1 is a general diagram of an exhaust pipe according to the invention; [Fig 2] Figure 2 is a sectional view of a section of the exhaust pipe of Figure 1, according to a first embodiment of the invention, [Fig 3] Figure 3 is a side view. sectional view of a section of the exhaust pipe of Figure 1, according to a second embodiment of the invention, 4 [Fig4] Figure 4 is a sectional view of a section of the exhaust pipe of Figure 1, according to a third embodiment of the invention, [Hg 5] Figure 5 is a sectional view of a section of the exhaust pipe of Figure 1, according to a fourth embodiment of the The invention, [Fig 6] Figure 6 is a sectional view of a section of the exhaust duct of Figure 1, according to a fifth embodiment of the invention, and [Fig 7] Figure 7 is a sectional view of a section of the exhaust duct of Figure 1, according to a sixth embodiment of the invention.

The exhaust pipe 10 shown in Figure 1 is part of a motor vehicle (not shown).

This exhaust line 10 carries a flow of exhaust gas generated by an engine 12 of the motor vehicle through various upstream exhaust components 14 to reduce emission and control noise in a known manner.

The various upstream exhaust components 14 may include one or more of the following: pipes, filters, valves, catalysts, mufflers etc.

In the exemplary configuration, the exhaust line 10 comprises a diesel oxidation catalyst (CCD) 16 having an inlet 18 and an outlet 20 positioned downstream of the upstream exhaust components '14, so that these Upstream exhaust components 14 direct engine exhaust gases into COD 16.

In the example shown, the exhaust pipe 10 further comprises a diesel particulate filter (FPD) 21 positioned downstream of the CCD 16.

This FPD is able to remove contaminants from the exhaust gas in the known manner.

The exhaust line 10 also includes a selective catalytic reduction (SCR) catalyst 22 having an inlet 24 and an outlet 26, and downstream exhaust components 28 positioned downstream of the RCS catalyst 22.

This RCS 30 22 catalyst is here positioned downstream of the CCD 16 and of the optional FPD 21.

The RCS catalyst 22 may optionally include a catalyst which is configured to perform a selective catalytic reduction function and a particulate filter function.

The various downstream exhaust components 28 include, for example, one or more of the following: pipes, filters, valves, catalysts, mufflers, etc.

The upstream 14 and downstream 28 components can be mounted in various configurations and combinations depending on the vehicle application and the available packaging space.

The exhaust pipe 10 further comprises, upstream of the inlet 24 of the RCS catalyst 22, a mixer 30 configured to be traversed by the flow of exhaust gas before it enters the RCS catalyst 22.

This mixer 30 is here positioned downstream of the outlet 20 of the COD 16 and of the optional FPD 21.

Mixer 30 is preferably configured to generate swirling or rotary motion of the exhaust gas stream.

Alternatively, mixer 30 consists of a single pipe.

The exhaust line 10 also includes an injector 32 for injecting a gaseous reducing agent into the exhaust gas stream in the mixer 30 so that the mixer 30 can thoroughly mix the reducing agent and the exhaust gas.

The gaseous reducing agent here comprises ammonia.

Alternatively, the reducing agent comprises a mixture of ammonia with, or a mixture of ammonia with an inert gas such as helium.

Injector 32 includes an injection nozzle 34 positioned inside mixer 30 to direct the injected reducing agent into mixer 30 to mix it with engine exhaust gas, a metering system 36 to provide a metered flow of reducing agent to the injection nozzle 34, and an injection line 38 connecting the metering system 34 to the injection nozzle 32.

Metering system 36 includes a source of reducing agent 40, a metering valve 42 for metering the amount of reducing agent supplied to injection nozzle 34, and a control unit 44 for controlling metering valve 32. so as to control the dosage of the reducing agent in a known manner.

The source of reducing agent 40 here consists of a source of ammonia.

This source usually includes a reservoir (not shown) in which ammonia gas is stored under pressure.

Alternatively, the source comprises urea or strontium chloride (SrC12) salts believed to be heated to generate ammonia.

Looking at Figures 2 to 7, the injection line 38 comprises a buffer chamber 50, an upstream pipe 52 connecting the buffer chamber 50 to the metering system 36, and a downstream pipe 54 connecting the buffer chamber 50 to the injection nozzle 34.

Preferably, the downstream pipe 54 has substantially the same flow section 35 as the nozzle 34.

Buffer chamber 50 is outside of mixer 30, 6 Buffer chamber 50 is defined inside of housing 56.

The buffer chamber 50 has an enlarged flow section with respect to the upstream pipe 52.

In other words, the flow section of the buffer chamber 50 is larger than the flow section of the upstream pipe 52.

In the examples, the upstream pipe 52 and the buffer chamber 50 have a tubular shape with a circular section.

The buffer chamber 50 then has an enlarged diameter with respect to the upstream pipe 52.

In other words, the diameter of the buffer chamber 50 is larger than the diameter of the upstream pipe 52.

The ratio between the flow area of the buffer chamber 50 and the flow area r0 of the upstream pipe 52 is preferably between 2 and 200, more preferably between 10 and 150, for example, 100.

Thanks to this change in flow section between the buffer chamber 50 and the upstream pipe 52, it has surprisingly been discovered that, when stopping the internal combustion engine 12, the buffer chamber 50 cools faster than the internal combustion engine 12. upstream pipe 52.

Therefore, the buffer chamber 50 is a preferential area for storing potential crystallized salts, thus preventing the obstruction of the injector 32.

The buffer chamber 50 is fluidly interposed between the upstream and downstream pipes 52, 54.

In other words, the buffer chamber 50 and the upstream and downstream pipes 52, 54 are connected in such a way that the flow from one of the pipes 52, 54 must flow through the buffer chamber 50. before reaching the other pipe 52, 54.

In the examples shown, the buffer chamber 50 is spaced from the mixer 30.

The downstream pipe 54 therefore comprises an external part 57 extending outside the mixer 30, said external part 57 preferably having a length of less than 15 cm.

Alternatively (not shown), buffer chamber 50 is placed alongside mixer 30.

The downstream pipe 54 therefore extends only into the mixer 30; In other words, the outer part 57 of the downstream pipe 54 has a length equal to zero.

In the embodiment of Figure 2, the buffer chamber 50 has a flow section which is substantially equal to the flow section of the downstream pipe 54.

In this embodiment, the downstream pipe 54 and the buffer chamber 50 have a tubular shape with a circular section.

The buffer chamber 50 therefore has a diameter substantially equal to that of the downstream pipe 54.

In the embodiments of Figures 3 to 7, the buffer chamber 50 is configured to cool faster than both the upstream and downstream pipes 52, 54 when the internal combustion engine 12 is stopped.

It was found that this feature allowed buffer chamber 50 to be a preferred area for salt crystallization, preventing clogging of downstream pipe 54.

To this end, the buffer chamber 50 has, in these embodiments, an enlarged flow section with respect to the downstream pipe 54.

In other words, the flow section of the buffer chamber 50 is greater than the flow section of the downstream pipe 54.

In these examples, the downstream pipe 54 and the buffer chamber are tubular in shape with a circular section.

The buffer chamber 50 therefore has an enlarged diameter with respect to the downstream pipe 54.

In other words, the diameter of the buffer chamber tu 50 is larger than the diameter of the downstream pipe 54.

The ratio between the flow area of the buffer chamber 50 and the flow area of the downstream pipe 54 is preferably between 2 and 200, more preferably between 10 and 150, for example, 100.

For example, the ratio between the flow section of the buffer chamber 50 and the flow section of the downstream pipe 54 is similar to the ratio between the flow section of the buffer chamber 50 and the flow section of the pipe. upstream 52.

In the embodiment of FIG. 3, the injection pipe 38 comprises two buffer chambers 50, and an intermediate pipe 58 connecting these buffer chambers 50.

In this embodiment 50, the flow section of the two buffer chambers 50 is also larger than the flow section of the intermediate pipe 58.

The flow section of the buffer chambers 50 is therefore larger than the flow section of the upstream pipe 52 and / or the downstream pipe 54 and / or the intermediate pipe 58.

Preferably, the upstream pipe 52, the downstream pipe 54 and the intermediate pipe 58 have the same flow section.

The ratio between the flow section of each buffer chamber 50 and the flow section of the upstream pipe 52 and / or the downstream pipe 54 andd'or the intermediate pipe 58 is between 20 and 80, for example 50.

In other variants (not shown), the injection pipe 38 may comprise more than two buffer chambers 50, these chambers therefore being connected to each other by intermediate pipes similar to the intermediate pipe 58.

Preferably, the volume of each buffer chamber 50 depends on the number of buffer chambers 50 of the injector 32.

Therefore, a plurality of buffer chambers 50 with a reduced volume allows to have the same technical advantage as a single buffer chamber 50 with a large volume.

8 The volume of the buffer chamber 50 when the injector 32 comprises a single buffer chamber 50, or the total volume of the buffer chambers 50, when the injector 32 comprises a plurality of buffer chambers 52, is preferably between 10 cm3 and 100 cm3, for example, 50 cm3.

The use of several buffer chambers 52 with a reduced volume compared to a large buffer chamber 52 makes it possible to have a compact injector 32 with the same efficiency.

In the embodiments of Figures 4 to 7, the injection line 38 includes a single buffer chamber 50. In the embodiments of Figures 4 to 6, the buffer chamber 50 is configured to have accelerated cooling at the same time. stopping the internal combustion engine 12, with respect to the cooling of the upstream and downstream pipes 52, 54.

It has been found that such accelerated cooling has further contributed to preferably achieve crystallization of the salts in the buffer chamber 50.

To this end, the housing 56 comprises, in the embodiment of FIG. 4, a cooling means 60 configured to increase the heat exchange surface between the buffer chamber 50 and an ambient fluid, this ambient fluid being of ordinary room air.

Here, this cooling means 60 comprises cooling fins 62 extending outwardly from a cylindrical body 64 of the housing 56 within which the buffer chamber 50 is defined.

These cooling fins 62 are, in the example shown, disc-shaped and extend around the buffer chamber 50.

Alternatively (not shown), the cooling fins 62 consist of ridges extending parallel to a main axis of the buffer chamber 50.

The cooling fins 62 are preferably formed integrally with the housing 56.

Alternatively, the cooling fins 62 are added to the housing 56 and / or made of a material different from the material of the housing 56.

In the embodiment of FIG. 5, the accelerated cooling of the buffer chamber 50 is obtained with the housing 56 consisting of a corrugated tube.

More particularly, the corrugated tube comprises a succession of outwardly parallel ridges and inwardly grooves.

The ridges form an internal cavity in which the potential salts formed with the reducing agent can crystallize and be stored.

In addition, the ridges include an optimum heat exchange surface with the ambient air.

In the embodiment of Figure 6, accelerated cooling of the buffer chamber 50 is achieved with the injector 32 including a thermal bridge 66 to conduct heat between the upstream and downstream pipes 254 while thermally bypassing it. the buffer chamber 50.

In the example shown, the thermal bridge 66 consists of a metal part welded between the upstream pipe 52 and the downstream pipe 54.

As a variant (not shown), the thermal bridge 66 is formed by the welded contact between the upstream pipe 52 and the downstream pipe 54.

Preferably, the hermetic conductivity of the thermal bridge 66 is greater than 20 Wel.K-1.

Another feature of the embodiment of Figure 6 is that both the upstream and downstream pipes 52, 54 extend through a lower bottom 68 of the buffer chamber 50 and open into the buffer chamber. 50 through an opening 70 which is at a distance from said lower bottom 68.

In this way, potential formed salts can be stored on both sides of the upstream and downstream pipes 52, 54 without obstruction of said upstream and downstream pipes 52, 54.

In another variant, the upstream pipe 52 and the downstream pipe 54 are concentric.

The upstream pipe 52 surrounds the downstream pipe 54.

In other words, the downstream pipe 54 is internal.

In the embodiment of Figure 7, the injector 32 includes heating means 72 for the accelerated heating of the buffer chamber 50 upon starting of the internal combustion engine 12.

It has been found that such accelerated heating helps to break down potential salts formed in injection line 38 and helps to remove them quickly.

Here, the heating means 72 comprises a supply line 74 opening into the buffer chamber 50 to collect the exhaust gas upstream of the mixer 30 and supply the collected exhaust gas to the buffer chamber 50; a control valve 76 mounted on said supply line 74 for fully opening and closing the supply line 74, and a control unit 78.

Control unit 78 is configured to control control valve 76 so that control valve 76 opens when engine 12 is started and closes before the first supply of reducing agent from metering system 36.

In the example shown of this embodiment, the injection pipe 38 also comprises a non-return valve 80 mounted on the upstream pipe 52, said non-return valve 80 being configured so as to allow the circulation of fluid from the metering system 36 to buffer chamber 50, and preventing fluid from flowing from buffer chamber 50 to metering system 36.

This check valve 80 is preferably close to the buffer chamber 50, that is, at a distance from the buffer chamber 50 of less than 10 cm.

By virtue of the aforementioned invention, the obstruction of the injection nozzle 34 is prevented or at least significantly reduced.

In addition, in the event of a partial obstruction, the injector 32 can be unclogged quickly on start-up and thus, is quickly effective.

Consequently, the downtime of the injector 32 at the start of the gaseous reducing agent metering phase is reduced.

Although the features of the invention have been disclosed in several embodiments, it should be understood that these embodiments can also be combined with each other, and that the invention also extends to these combinations.

For example, the buffer chamber 50 may have a flow section which is substantially equal to the flow section of the downstream pipe 54, while being configured to have accelerated cooling on shutdown of the internal combustion engine 12 by. with respect to the cooling of the upstream and downstream pipes 52, 54.

Thus, the buffer chamber 50 can be configured to cool faster than both the upstream and downstream pipes 52, 54 even without the buffer chamber 50 having an enlarged flow section relative to the downstream pipe 54.

Further, although the injector 32 described herein comprises a single injection nozzle 34, the invention is not limited to this single embodiment.

In variants (not shown) of the invention, the injector 32 comprises several injection nozzles 34,

Claims (15)

CLAIMS 1.- Injector (32) for injecting a gaseous reducing agent into the exhaust gas flow of an internal combustion engine (12), the injector (32) comprising at least one injection nozzle (34), a metering system (36) for providing a metered flow of the gaseous reducing agent to the or each injection nozzle (34), and an injection line (38) connecting the metering system (36) to the or to each injection nozzle (34), characterized in that the injection pipe (38) comprises at least one buffer chamber (50), an upstream pipe (52) connecting the buffer chamber (50) to the system of metering (36), and a downstream pipe (54) connecting the buffer chamber (50) to a respective injection nozzle (34), the buffer chamber (50) having an enlarged flow section with respect to the upstream pipe (52). 2. An injector (32) according to claim 1, wherein the downstream pipe (54) has a length of less than 15 cm. 3. An injector (32) according to claim 1 or 2, wherein the buffer chamber (50) is fluidly interposed between the upstream and downstream pipes (52, 54). 4. An injector (32) according to any preceding claim, wherein the buffer chamber (50) is configured to cool faster than the upstream and downstream pipes (52, 54) when the engine is stopped. internal combustion (12). 5. An injector (32) according to claim 4, wherein the buffer chamber (50) has an enlarged flow section with respect to the downstream pipe (54). 6. An injector (32) according to claim 4 or 5, comprising cooling means (60) configured to increase the heat exchange surface between the buffer chamber (50) and an ambient fluid. 7. An injector (32) according to claim 6, wherein the cooling means (60) comprises cooling fins (62) extending outwardly from the body (64) of a housing (56) of the. buffer chamber (50). 8.- An injector (32) according to any one of claims 4 to 7, wherein the buffer chamber (50) is defined inside a housing (56), said housing (56) consisting of a tube. corrugated. 9. An injector (32) according to any one of claims 4 to 8, comprising a thermal bridge (66) for conducting heat between the upstream and downstream pipes (52, 54) while thermally bypassing the buffer chamber ( 50). 10. An injector (32) according to any preceding claim, wherein the upstream and downstream pipes (52, 54) extend through a bottom (68) of the buffer chamber (50) and s 'open into the buffer chamber (50) through an opening (70) which is at a distance from said bottom (68). 11. An injector (32) according to any one of the preceding claims, comprising heating means (72) for the accelerated heating of the buffer chamber (50) on starting of the internal combustion engine (12). 12. An injector (32) according to claim 11, wherein the heating means (72) comprises a supply line (74) opening into the buffer chamber (50) to collect the exhaust gas and supply the gas. exhaust gas collected at the buffer chamber (50), and a control valve (76) mounted on said supply line (74) for selectively opening and closing the supply line (74). 13.- Injector (32) according to any one of the preceding claims, comprising a single buffer chamber (50), the volume of which is between 10 cm3 and 100 cm3, for example, 50 cm3, or the injector (32 ) comprises a plurality of buffer chambers (52), the total volume of which is between 10 cm3 and 100 cm3, for example, 15 50 cm3. 14.- Exhaust pipe (10) for an internal combustion engine (12) comprising a mixer (30) configured to be traversed by a flow of exhaust gas produced by the internal combustion engine (12) and the An injector (32) according to any preceding claim for injecting the gaseous reducing agent 20 into said exhaust gas stream. 15. A motor vehicle comprising the exhaust pipe (10) according to claim 14.