FR2892981A1 - Exhaust device for e.g. spark ignition engine, has exhaust gas treating assembly arranged between cylinder head and turbine whose inlet is connected to outlet of assembly, where assembly has gas post-treatment system and particle filter - Google Patents

Abstract

The device has a cylinder head (3), a turbine of a turbocharger (5) and an exhaust gas treating assembly (4). The assembly is arranged between the cylinder head and the turbine whose inlet (13) is connected to an outlet of the assembly. The assembly has a gas post-treatment system and a particle filter (9). A high pressure turbine is interposed between outlet of the cylinder head and the inlet of the treating assembly.

Description

Engine exhaust system and engine The present invention

  the field of diesel engine or spark ignition internal combustion engine exhaust systems and such engines. The invention relates more particularly turbocharged turbocharged engines equipped with a system for post-treatment of pollutant emissions including soot emissions and the supply of the turbine burnt gas.

  In order to comply with international environmental standards, the control of emissions of hydrocarbon compounds, carbon monoxide, nitrogen oxides and particles is essential. The treatment of particles from diesel engines is possible by introducing into the exhaust line of these engines a particulate filter designed to trap the soot particles contained in the exhaust gases during their flow into the engine. the exhaust line. Particle filters require a particle combustion phase, also known as the regeneration phase, to prevent fouling that is harmful to the engine and to the operation of the vehicle and produces progressive clogging. It has been envisaged to add an organometallic compound in the fuel to reduce the combustion temperature of the particles and promote the combustion phenomenon in the soot bed due to the presence of this additive in the composition of each particle formed in the combustion chamber. To adapt this concept to the temperature conditions encountered on lean burn engines, particularly on diesel engines, the fuel additivation must be coupled with a strategy of post-fuel injection into the cylinders to create an exothermic process upstream. of the particulate filter through the addition of an oxidation catalyst. The presence of the organometallic additive in the structure of the soot and additives present in the lubricating oil of the engine leads to a production of ash resulting in regular maintenance and overconsumption of fuel due to the post-injection to reach the combustion conditions of the soot particles. It has also been envisaged an electric heating of the particulate filter by introduction of electrical resistances inside the filter. This causes additional power consumption and therefore also additional fuel consumption. It is also possible to impregnate the walls of the particulate filter with an oxidation catalyst which makes it possible to lower the soot combustion temperature and to ensure cleaning of the walls of the filter continuously. However, it turns out that the regeneration of the filter is only partial because of the difficulty to propagate the combustion within the soot bed. It is also necessary to heat the gases to cause combustion before reaching a soot mass limit harmful to the filter system and the engine.

  Document US 2004/55287 (Isuzu Motors) describes a system for purifying the exhaust gases of an internal combustion engine equipped with a particulate filter disposed downstream of a turbocharger turbine. A continuously regenerating particulate filter system is provided by means of a catalyst disposed in the filter.

  Thus, the particulate filter and the catalytic converter are placed downstream of the turbine and therefore do not benefit from conditions at temperatures sufficient to ensure regeneration in a continuous manner. It is then necessary to use additional fuel injection phases to burn the particles in the particulate filter, which is expensive in terms of engine consumption. In addition, the strong releases of energy released during the phases where the fuel is injected into the particulate filter and the catalytic converter cause strong temperature gradients that can damage the structure of the particulate filter and adversely affect its reliability. US 4,641,496 (Ford Motors) discloses a particle filter provided with a continuous rotary regeneration system. Such a system equipped with motor and gears is bulky, expensive and subject to breakdowns. EP-A-0 997 616 (Minnesota Mining and Manufacturing Company) discloses a method of filter regeneration by means of a heating element arranged upstream of the particulate filter to increase the temperature of the gases and ensure a continuous regeneration. In addition, an additive is incorporated in the fuel, the intake gas or the exhaust gas. The electric heating causes an overconsumption of energy from the engine by means of an electric generator.

  Document FR 2 855 218 (Renault) describes a management system for the regeneration of a particulate filter comprising a means of distributing fuel between a first fuel injection and a main fuel injection as a function of the combustion temperature of the fuel. particle filter particles or temperature upstream of a turbine. However, the need has appeared to further reduce fuel consumption and simplify regeneration management. The invention aims to remedy the disadvantages mentioned above. The invention proposes a particularly compact, economical engine exhaust device which ensures a continuous or almost continuous regeneration of the particulate filter and this in a reliable manner.

  The supercharged engine exhaust system includes a cylinder head, a turbocharger turbine, and an exhaust gas treatment assembly. The treatment unit is disposed between the cylinder head and the turbine. The inlet of the turbine is connected to the output of the treatment unit.

  Thus, the treatment unit, in particular a particulate filter, receives the hot gases coming directly from the cylinder head. The treatment unit is thus subjected almost permanently to a high temperature sufficient to ensure the combustion of soot. As the soot is burned almost continuously, their accumulation in the treatment unit is very small and the size of the treatment assembly, including its size, can be reduced. The regeneration is generally considered as continuous from temperatures of between 550 and 600 C. The temperature level and the proportion of oxygen present in the exhaust gases are then sufficient to ensure the combustion of soot particles trapped in the reactor. treatment set. The invention allows even higher temperature conditions at engine load levels and lower engine speeds, resulting in near-continuous regeneration of the processing unit over a very large number of engine operating points. . This continuous regeneration of the treatment unit avoids all or part of the use of heating devices such as electric heating or by fuel injections, both penalizing the consumption of the engine. Due to the almost continuous regeneration of the treatment unit, the pressure drop generated by said treatment unit during the soot loading phases is eliminated, which improves the engine performance and decreases the thermal stresses at high speed and at full load due to improved engine performance. It is no longer necessary to inject fuel to regenerate a set of treatment, where in any case, much smaller amounts can be injected. The risk of cracking of the particulate filter and / or the oxidation catalyst due to the high thermal gradients during the post-fuel injection phases is considerably reduced by reducing the number of post-injections carried out and away from lower temperature between post-injection and normal operation of the filter. The particulate filter and the oxidation catalyst can be made from materials that are less resistant to thermal shock and therefore less expensive.

  The high temperature conditions allow an excellent catalyst priming especially during the cold start phases of the engine. This results in a better operation of the catalyst and a better depollution at startup. The operating conditions at a higher temperature, especially compared to a conventional architecture with particulate filter and oxidation catalyst mounted downstream of the turbine allows a reduction in the loading of the oxidation catalyst into precious metals, for example platinum, palladium , rhodium ... necessary for the oxidation of carbon monoxide, unburned hydrocarbons and nitric oxide. The very high temperature operating conditions improve the efficiency of the conversion of nitric oxide to nitrogen dioxide. Nitrogen dioxide is then the main oxidant of soot particles between 300 and 400 C. The invention promotes this process for low temperatures and thus facilitates continuous regeneration. Although separated from the cylinder head by the treatment unit, the turbine is supplied with exhaust gas under favorable conditions for transient operation and for low-end torque because of the small size of the particulate filter and the possible absence of exhaust manifold. The particle filter and the oxidation catalyst arranged upstream of the turbine do not generate back pressure usually encountered on this type of engine. This is favorable for the operation of the turbocharger and for the operation of the engine at full load and at high speed, for example about 4000 revolutions per minute for a diesel engine. The compactness of the particulate filter which allows a mounting close to the cylinder head and the turbine allows a reduction of the pressure losses at the exhaust, thus losses by pumping of the engine and consequently a reduction of the specific consumption of the engine with strong load and high speed. Regeneration is continuous, it is no longer necessary to have regeneration management systems, expensive, complex to develop and difficult to control by the engine control system. Due to the total or partial removal of the exhaust manifold, the entire exhaust gain compactness and can be more easily implanted in the engine compartment of a vehicle. Advantageously, the treatment unit comprises an exhaust gas after-treatment system, for example a catalytic converter and a particulate filter. In one embodiment, the input of the processing set has a biconical form. In another embodiment, the input of the processing assembly has a conical shape. The conical shape may be divergent in the flow direction of the exhaust gas. In one embodiment, the input of the processing unit is connected to the output of the cylinder head. This prevents the pressure losses between the treatment unit and the cylinder head. In one embodiment, a high pressure turbine and a low pressure turbine are mounted downstream of the treatment assembly.

  In another embodiment, a high pressure turbine is interposed between the output of the cylinder head and the inlet of the treatment unit. A convergent may be mounted between the output of the treatment assembly and the inlet of a low pressure turbine. In one embodiment, the cylinder head is provided with ducts meeting upstream of the exhaust manifold. In another embodiment, the yoke is provided with separate conduits. The duct or ducts of the cylinder head open into the treatment unit.

  The internal combustion engine comprises a cylinder head, a treatment assembly and a turbocharger turbine arranged in the direction of flow of the exhaust gas. The input of the processing unit is connected to the output of the cylinder head.

  Depending on the arrangement of the cylinders, the engine may comprise one or more heads associated with one or more particulate filters and one or more turbines each driving a compressor. The invention is applicable to supercharged diesel engines or still to direct injection gasoline engines operating in lean mixture and provided with a particulate filter. The turbocharger can be of the turbine type with fixed or variable geometry, compressor with fixed or variable geometry, electrically assisted, etc. In the case of multi-stage turbocharging, the turbines can be placed in series or in parallel. In order to further reduce the thermal inertia of the particulate filter, the outer casing of the particulate filter and the aftertreatment system may be made of a poorly heat-conducting, ceramic-like material, or heat-insulated material. using thermally insulating material or disposed in an outer envelope trapping a layer of dry air between two walls, resulting in a reduction in thermal losses by conduction and radiation. In the case of a multi-stage supercharging engine, the pollution control system comprising the particulate filter and optionally an oxidation catalyst may be placed between the first and second turbines. Such an architecture is very favorable for increasing the energy at the inlet of the high-pressure turbine, thanks to the reduction of thermal losses at the exhaust and to obtaining very high pulsation levels at the inlet of the turbine. turbine, which is particularly favorable for the operation of the engine at low speed and in transient. The invention applies to engines provided with one or more exhaust valves per cylinder.

  The present invention will be better understood on reading the detailed description of some embodiments taken as non-limiting examples and illustrated by the appended drawings in which: FIG. 1 is a schematic view of an engine according to a first embodiment; Fig. 2 is a cross-sectional view of the bolt outlet; Fig. 3 is a schematic view of an engine according to another embodiment; - Figure 4 is a schematic view of an engine according to another embodiment; FIG. 5 is a cross-sectional view of the outlet of the cylinder head of FIG. 4; Figure 6 is a general schematic view of another embodiment of the invention; Figure 7 is a cross-sectional view of the outlet of the cylinder head of Figure 6; Figure 8 is a side view of the exhaust device of Figure 6; FIG. 9 is a general schematic view of an engine according to another embodiment; Figure 10 is a general schematic view of an engine according to another embodiment of the invention; Figure 11 is a pressure curve versus engine speed; and - Figure 12 is a torque versus time curve. As can be seen in Figure 1, a motor referenced 1 as a whole comprises a plurality of cylinders 2, here four in number, arranged along parallel axes, a cylinder head 3, a gas treatment unit 4 and a turbocharger 5. Each cylinder 2 comprises two exhaust valves 6 opening into lines 7 of the cylinder head 3. The cylinder head 3 comprises pipes 7 so that each exhaust valve 6 is connected to a pipe 7. Two associated pipes 7 at the same cylinder 2 meet opposite the cylinder 2 in a common portion 8. The treatment unit 4 comprises a particle filter 9 and an oxidation catalyst 10 mounted downstream of the particulate filter 9 in the direction Exhaust gas flow. The assembly 4 is also provided with an inlet 11 connected to the common portions 8 of the pipes 7. The treatment unit 4 is surrounded by a wall 12 thermally insulating. The turbocharger 5 comprises a turbine 13 driving a compressor 14 in rotation. The turbine 13 receives the exhaust gas at the outlet of the treatment unit 4 via a pipe 15. A pipe 15 ensures the flow exhaust gas at the outlet of the turbine 13 and can be connected downstream to a silencer not shown. The compressor 14 is associated with a fresh air intake pipe 17 and an outlet pipe 18 of compressed air. The operation of the engine 1 is as follows. The exhaust leaving the inside of the cylinders 2 passes through the exhaust valves 6, the pipes 7 and the common portions 8 and then into the inlet 11 of the treatment unit. Due to the small distance between the cylinders 2 and the treatment unit 4, the exhaust gases enter the treatment unit 4 at a very high temperature of several hundred degrees, for example greater than 550 ° C. immense majority of the operating points of the engine. The particulate filter 9 ensures the retention of soot particles present in the exhaust gas. The soot particles arrested by the particulate filter 9 are oxidized in contact with the oxygen and nitrogen dioxide present in the exhaust gas. The oxidation with nitrogen dioxide is particularly effective at temperatures of the order of 300 to 400 C. The soot particles are therefore oxidized relatively quickly and have a time of presence in the particulate filter 9 particularly low. What is known as a continuous or quasi-continuous regeneration is obtained from which the small size of the particulate filter 9 does not need to store a large quantity of soot. The exhaust gases freed of soot then pass into the oxidation catalyst in which the unburnt hydrocarbons and carbon monoxide are oxidized, in particular by reducing nitrogen dioxide to nitrogen. The purified exhaust passes through line 15 and then passes through turbine 13 at a still very high temperature sufficient to satisfactorily drive the turbocharger as a whole. In the embodiment illustrated in FIG. 1, the inlet 11 of the treatment unit 4 has a convergent biconical shape and then a divergent shape in the direction of flow of the exhaust gases. In the embodiment illustrated in FIG. 3, the inlet 11 of the treatment unit 4 has a reduced axial length with a general shape of a simple cone converging towards the particulate filter 9, in other words in the direction Exhaust gas flow. The reduced length of the inlet 11 of the treatment unit 4 makes it possible to reduce the pressure losses at the flow of the exhaust gases and a reduction of the thermal losses by conduction or radiation. As can be seen in Figure 2 which shows the cross-section of the output of the cylinder head of the engine shown in Figure 1 and also the engine shown in Figure 3, the common portions 8 of the pipes 7 are aligned and substantially coplanar. This results in a relatively elongated cylinder head outlet transversely. In the embodiment illustrated in FIG. 4, the inlet 11 of the treatment assembly has a generally conical and divergent shape towards the particulate filter 9. The common portions 8 of the pipes 7 of the cylinder head 3 are uniformly distributed in the output plane of the bolt visible in Figure 5. The cylinder head 3 has a circular section output. The pipes 7 may be symmetrical with respect to a plane separating the rolls in groups of 2. This particular architecture makes it possible to better distribute the pipes 7 in the cylinder head 3 and to have a particulate filter of even smaller size, which is favorable to reduce the thermal inertia of the treatment unit 4 and overall thermal inert devices upstream of the air turbine. In the embodiment illustrated in FIG. 6, the common portions of the pipes 7 of the central cylinders meet in a common section 19. The output of the cylinder head 3 has a circular shape and contains the common section 19 and two common portions 8. The dimensions of the output of the cylinder head can be further reduced and the pipes 7 have an excellent spatial distribution. The thermal inertia of the exhaust is further reduced, which is advantageous for the efficiency of the engine. In Figure 8, is shown an example of implementation of the processing assembly substantially parallel to the axis of the cylinder block.

  In the embodiment illustrated in FIG. 9, the engine 1 comprises two turbochargers, a high pressure turbocharger and a low pressure turbocharger. The high pressure turbocharger is arranged as in the previous embodiments. The low-pressure turbocharger 20 comprises a turbine 21 connected at the inlet to the outlet pipe 17 of the high-pressure turbine 13 and a high-pressure compressor connected as input to the outlet pipe 18 of the high-pressure compressor 14. A gas outlet pipe 23 is mounted at the outlet of the low-pressure turbine 21. The cylinder head may be of the type analogous to that illustrated in FIG. 6. In the embodiment illustrated in FIG. 10, the engine 1 comprises a high-pressure turbocharger 24. comprising a turbine 25 and a compressor 26. The high-pressure turbine 25 is mounted between the outlet of the cylinder head 3 and the treatment unit 4. The engine 1 also comprises a low-pressure turbocharger 27 provided with a low-pressure turbine 28 and a low-pressure compressor 29. The low-pressure turbine 28 is mounted downstream of the treatment unit 4. The low-pressure compressor 29 is connected to the outlet pipe 17 e of the high pressure compressor 26.

  More specifically, the turbine 25 is provided with an inlet 30 in direct contact with the outlet of the cylinder head 3. The cylinder head 3 can be of the type illustrated in FIG. 6. The high-pressure turbine 25 is mounted in the immediate vicinity of the outlet. 3. The output of the high-pressure turbine 25 opens into the inlet 11 of the treatment unit 4 of generally conical type diverge downstream. The treatment unit 4 also comprises an outlet 31 of generally conical shape convergent downstream and connected directly to the low pressure turbine 28.

  Due to the absence of an exhaust manifold, the reduction of the system pressure drops and the direct supply of the high-pressure turbine 25 by the exhaust gases, the pulsations at the inlet of the high turbine pressure 25 are very high. The curve illustrated in FIG. 11 of the evolution of the average exhaust pressure as a function of the engine speed makes it possible to better understand the favorable effects of the treatment unit 4 mounted upstream of at least one turbocharger turbine. The operating points of the motor have been grouped into four zones. Zone A is close to the full load limit at high speed and corresponds to a zone of high temperature, greater than 550 ° C., where the regeneration of the continuous particle filter is possible. Zone B corresponds to a regeneration zone of the particulate filter possible by oxidation of soot by nitrogen dioxide for temperatures generally greater than 300 ° C. in an arrangement according to the prior art with the set of treatment arranged downstream. of the turbine or turbines. Zone C corresponds to the enlargement of zone B towards the low loads and the low speeds obtained thanks to the invention with a turbine mounted downstream of a treatment unit. Since the inlet temperatures of the treatment unit are much higher than in a conventional arrangement, the particulate filter regeneration limit by nitrogen dioxide is lowered to significantly lower charge and speed levels. Regeneration of the particulate filter is thus possible in much larger areas of engine operation, which makes regeneration of the particulate filter quasi continuous regardless of the operating conditions of the engine on a vehicle. For example, the zone D corresponds to idling while the zone C corresponds to a taxiing operation of the vehicle downhill or at a steady speed on flat ground in urban type driving. FIG. 12 illustrates the effect of the invention and in particular of the compact architecture with the exhaust ducts joining in the exhaust cylinder on the performance of the transient engine. The curves represent the evolution of the engine torque in the case where the driver suddenly depresses the accelerator pedal at t = 0. - The upstream FAP curve corresponds to a particulate filter architecture is located upstream of the turbine, but not benefiting from the architecture of the invention. The large volumes and exchange surfaces introduce a high thermal inertia of the system, penalizing from the point of view of the energy available at the inlet of the turbine. The response time (time to reach 90% of the maximum torque) is very much greater than 10s, which is not acceptable for the operation of the vehicle. the downstream FAP curve corresponds to a conventional situation where the particulate filter is situated downstream of the turbine. The energy recovered by the turbine is close to optimal and the response time of the motor is about 2s. On the other hand, the system is penalized for the regeneration as shown in FIG. 7. The invention curve corresponds to the proposed architecture with ducts joining in the cylinder head and particle filter upstream of the turbine (s). ). In this case, the system is penalized by a thermal inertia slightly higher than the downstream FAP situation, but the response time is very close to that of the downstream FAP curve. The performances are preserved, with a level of 15 20 25 30

Claims (12)

  1-Supercharged engine exhaust system (1), comprising a cylinder head (3), a turbocharger turbine (13) (5) and an exhaust gas treatment unit (4), characterized in that the treatment unit is disposed between the cylinder head (3) and the turbine (13), the inlet of the turbine (13) being connected to the outlet of the treatment unit (4).   2-Device according to claim 1, wherein the treatment unit (4) comprises an exhaust gas after-treatment system and a particulate filter (9).   3-Device according to any one of the preceding claims, wherein the inlet of the treatment unit (4) has a biconical shape.   4-Device according to claim 1 or 2, wherein the inlet 15 of the treatment assembly (4) has a conical shape.   5-Device according to claim 4, wherein the inlet of the treatment unit (4) has a divergent conical shape in the direction of flow of the exhaust gas.   6-Device according to any one of the preceding claims, wherein the input of the processing unit (4) is connected to the output of the yoke (3).   7-Device according to claim 6, wherein a high pressure turbine and a low pressure turbine are mounted downstream of the treatment unit (4). 25   8-Device according to any one of claims 1 to 5, wherein a high pressure turbine is interposed between the output of the yoke (3) and the input of the processing unit (4). 16   9-Device according to claim 8, wherein a convergent is mounted between the output of the processing assembly (4) and the inlet of a low pressure turbine.   10-Device according to any one of the preceding claims, wherein the yoke (3) is provided with ducts meeting upstream of the particulate filter.   11-Device according to any one of claims 1 to 9, wherein the yoke (3) is provided with separate conduits.   12-Internal combustion engine (1) characterized in that it comprises a cylinder head (3), a treatment assembly (4) and a turbine (13) turbocharger (5) arranged in the direction of gas flow exhaust system, the inlet of the treatment unit (4) being connected to the outlet of the cylinder head (3).