FR2948412A1 - Exhaust line for diesel engine of motor vehicle, has fuel introducing device comprising fuel vaporizer equipped with vaporizing chamber, and heating unit partially located inside vaporizing chamber to vaporize liquid fuel - Google Patents

Abstract

The exhaust line (5) has an exhaust manifold (19) provided with exhaust gas inlets (21). A fuel introducing device (29) introduces liquid fuel i.e. diesel, inside the manifold. The fuel introducing device has a fuel vaporizer (47) equipped with a vaporizing chamber (55). The vaporizing chamber has a liquid fuel inlet (57) and a vapor outlet (59) emerging inside the manifold. A heating unit i.e. spark plug (61), is partially located inside the vaporizing chamber to vaporize the liquid fuel.

Description

The invention relates generally to the exhaust system of a motor vehicle, in particular for vehicles equipped with diesel engines.

More specifically, the invention relates in a first aspect to a motor vehicle exhaust line, of the type comprising: an exhaust manifold having a plurality of exhaust gas inlets designed to collect gas streams; exhaust from the combustion chamber of a combustion engine of the motor vehicle; an oxidation catalyst, inserted downstream of the exhaust manifold; a device for introducing a fuel into the exhaust manifold. Such an exhaust line is known from US 2009/0064668, which describes that it comprises liquid fuel injection device inside the collector. This device comprises an injection chamber and an injector provided for injecting liquid fuel into the injection chamber. The injection chamber communicates with the interior of the exhaust manifold, and is arranged so that the exhaust gases circulate inside the chamber with a sufficient residence time so that the liquid fuel injected is totally vaporised. When the vehicle engine runs at low load, for example in the city or in traffic jams, the exhaust gas temperature at the engine output is insufficient to vaporize all the liquid fuel injected. Furthermore, the vaporization chamber has a significant size that adds to that of the exhaust manifold. The implementation of such a set is difficult, given the large number of equipment to be housed inside the engine compartment. Moreover, when the control system issues the order to inject fuel, for example in order to regenerate the particle filter placed downstream in the exhaust line, the residence time of the gases in the chamber causes a delay. . The start of the regeneration is time-shifted significantly relative to the instant at which the injection order was started.

In this context the invention aims to provide an exhaust line whose device for introducing the fuel into the collector is more compact and more efficient. To this end, the invention relates to an exhaust line of the aforementioned type, characterized in that the device for introducing a fuel comprises a vaporizer of said fuel, provided with a vaporization chamber having a liquid fuel inlet and an outlet steam opening into the exhaust manifold, and a heating member at least partially located within the vaporization chamber and provided for vaporizing the liquid fuel. The exhaust line may also have one or more of the following characteristics, considered individually or in any technically possible combination (s): - the heating element operates by Joule effect; the heating member is a candle; the exhaust line comprises a turbo compressor interposed between the exhaust manifold and the oxidation catalyst; the turbo compressor comprises a turbine provided with a gas inlet connected to an exhaust gas outlet of the exhaust manifold, a gas outlet connected to the oxidation catalyst, and a rotor provided for be rotated by the exhaust gas flowing from the gas inlet to the gas outlet; the vaporizer is mounted on the manifold with the vaporization chamber at least partially located inside the exhaust manifold; - the fuel is diesel fuel; the exhaust line comprises a particle filter interposed downstream of the oxidation catalyst, and a control member of the fuel introduction device with estimation means for estimating whether the particulate filter needs be regenerated, and means for controlling the introduction of fuel into the exhaust manifold when the estimating means estimates that the particulate filter needs to be regenerated.

According to a second aspect, the invention relates to an exhaust assembly with a diesel engine having combustion chambers, and an exhaust line having the above characteristics, the exhaust gas inlets of the manifold being connected to exhaust gas outlets of said combustion chambers. Other features and advantages of the invention will emerge from the detailed description given below, by way of indication and in no way limiting, with reference to the appended figure showing an exhaust assembly according to the invention.

In the following description, the upstream and downstream agree relative to the direction of flow of the exhaust gas. The exhaust assembly shown in the attached figure comprises: a heat engine 1 provided with combustion chambers 3; an exhaust line intended to capture and treat the exhaust gases leaving the combustion chambers 3 of the engine; an air intake line 7 intended to supply the combustion chambers 3 of the engine with fresh air taken from the atmosphere. The engine 1 is a heat engine, typically a diesel type engine.

It comprises for each combustion chamber 3 a fresh air intake 9, and an exhaust gas outlet 11. The air intake line 7 comprises an intake manifold 13 and an intake duct 15. fresh air connecting the collector 13 to the atmosphere. The manifold 13 has a plurality of mouths 17, each connected to the air inlet 9 of one of the combustion chambers 3. The exhaust line 5 comprises: an exhaust manifold 19, having a plurality of exhaust gas inlets 21, each connected to the exhaust gas outlet 11 of one of the combustion chambers of the engine, and designed to capture the exhaust gases emitted by said outlet; a turbo-compressor 23 interposed in the exhaust line downstream of the exhaust manifold 19; an oxidation catalyst 25, interposed in the exhaust line downstream of the turbo-compressor 23; an exhaust gas purification assembly 27, interposed in the exhaust line downstream of the oxidation catalyst 25; a device 29 for introducing a fuel inside the exhaust manifold 19; a member 31 for controlling the device for introducing fuel 29. The exhaust manifold 19 has at least one outlet 33 connected to a gas inlet 34 of the turbine 35 of the turbo-compressor 23.

The turbine 35 also has a gas outlet 36 connected downstream to the oxidation catalyst 25, and a rotor 37 designed to be rotated by the exhaust gas flowing from the inlet 34 to the outlet 36 of the the turbine. Furthermore, the turbo-compressor 23 comprises a compressor 38 placed in the intake duct 15, whose rotor 39 is mechanically coupled by the shaft 40 to the rotor 37 of the turbine 35. The compressor 38 compresses the fresh air sucked in the atmosphere and sends it to the intake manifold 13. The oxidation catalyst 25 is provided for oxidizing the carbon monoxide CO (CO) contained in the exhaust gases discharged from the heat engine 1. This reaction of oxidation is strongly exothermic. The oxidation device 25 comprises a casing (not shown) having an inlet connected to the outlet 36 of the turbine 35 and an outlet connected to the purification assembly 27, and a monolithic substrate placed inside the casing . The envelope defines an exhaust gas passage conduit forcing them to cross the monolithic substrate. The monolithic substrate is of a type known per se. It comprises a matrix, for example cordierite, and a catalyst suitable for the oxidation of hydrocarbons and COR. The catalyst is for example a coating of Pt / Pd, transition metals, oxides, etc. The oxidation catalyst may also be of the type described in WO 2005/064131.

The exhaust gas purification assembly 27 typically comprises a NOx trap 41 and a particulate filter 43. The NOx trap 41 is connected upstream to the oxidation catalyst 25, and downstream to the filter The particulate filter 43 is connected downstream to the cannula 45 through which the purified exhaust gas is released into the atmosphere. Other equipment, for example silencers, can be interposed between the particulate filter 43 and the cannula 45. A selective reduction catalyst (SCR) can alternatively replace the NOx trap 41. The NOx trap 41 and the filter particles 43 are of known type and will not be described here in detail. The device 29 for introducing the fuel comprises a vaporizer 47, a capacity 49 for storing a liquid fuel reserve, a line 51 connecting the reserve 49 to the vaporizer 47, and a metering member 53 interposed on the line 51.

The liquid fuel is typically diesel. Alternatively, the liquid fuel may be gasoline, provided for the supply of a gasoline engine engine operating according to the Otto cycle. The reserve 49 may be the diesel storage tank intended for supplying the engine of the vehicle. Alternatively, the reservoir 49 may be a reservoir dedicated to the vaporizer. The metering device 53 is for example a metering pump, driven by the computer 31. Alternatively, the metering member 53 may be a valve controlled by the control member 31. In this case, the liquid fuel circulates through gravity flow from the reservoir 49 to the vaporizer 47. The vaporizer 47 is for example of the type described in FR0851716 or FR0758505. The vaporizer comprises a vaporization chamber 55 having a liquid fuel inlet 57 and a steam outlet 59 opening inside the exhaust manifold 19, and a heating member 61 at least partially located inside the chamber vaporization 55 and intended to vaporize the liquid fuel.

More specifically, the vaporizer comprises: - a hollow envelope 63, internally defining the vaporization chamber 55, and in which is formed the liquid fuel inlet 57 and the steam outlet 59; a candle 61, acting as a heating member; an electric generator 65 for supplying the spark plug 61, electrically connected to the spark plug 61 and controlled by the piloting member 31; - means not shown for fixing the casing 63 to the wall of the exhaust manifold 19.

As can be seen in the Figure, the vaporization chamber 55 is located inside the exhaust manifold 19. More precisely, the vaporization chamber is delimited by a distal end 67 of the hollow envelope, this distal end being located at the inside of the exhaust manifold 19. The proximal end 69 of the casing is located outside the exhaust manifold 19. Thus, the exhaust manifold 19 has an orifice 71 for mounting the vaporizer, the envelope 63 being engaged in this orifice 71 and sealingly connected to the peripheral edge of the orifice 71. For example, the envelope 63 is screwed to the wall of the exhaust manifold 19, or welded by a sealed weld. If necessary, a seal is interposed between the casing 63 and the wall of the manifold 19. The heating element, as indicated above, is a spark plug, for example of the type described in FR0758505. The heating element operates by Joule effect. The heating member 61 comprises for example a threaded portion 75 intended to cooperate with a tapping carried by the casing 63, and an active heating portion 77. The tapping is formed at the proximal end of the casing 63. threaded thread 75 is screwed tightly into said tapping, with if necessary interposition of a seal. The active heating portion 77 is disposed inside the vaporization chamber 55. It comprises, for example, a heating resistor, not shown, electrically connected to the electric generator 65 through the threaded portion 75. The liquid fuel inlet 57 is connected to the conduit 51.

The control member 31 comprises estimation means for estimating whether the particulate filter 43 and / or the NOx trap 41 need to be regenerated, and means for controlling the introduction of fuel into the collector. exhaust by the device 29 provided for this purpose, when the estimation means estimate that the particulate filter and / or the NOx trap need to be regenerated. The estimation means may comprise, for example, pressure probes making it possible to determine the pressure drop at the level of the particulate filter 43. They may also comprise a calculator, or a calculator part, making the estimation of the regeneration requirements in function of data relating to the life of the vehicle and in particular to the operation of the heat engine. These data are found for example in the computer control of the engine. These data can be for example the number of kilometers traveled since the previous regeneration, data related to the instantaneous load of the engine, the temperatures of the exhaust gases at the given moment, data concerning the engine operating history. , etc .. The control member 31 is provided to control the tripping or stopping of the power supply 65, and to control the operation of the metering member 53. The control member 31 is also intended to determining the amount of liquid fuel to be introduced for the regeneration of the NOx trap 41 and / or the particulate filter 43. The control member determines said quantity according to data in the control computer of the engine, for example the operating time and the load of the heat engine since the previous regeneration. The operation of the exhaust line described above will now be detailed. When the heat engine is in operation, the exhaust gases exit the combustion chambers 3 through the outlets 11 and are sensed by the inputs 21 of the exhaust manifold. The exhaust gases exit the manifold 19 through the outlet 33, drive the turbine 35 and successively pass through the oxidation catalyst 25, the NOx trap 41 and the particulate filter 43. They are released into the atmosphere by the intermediate of the cannula 45. In the oxidation catalyst, the HC are oxidized to CO2 and H2O. COs are oxidized to CO2.

In the NOx trap, the NOx contained in the exhaust gas is fixed during an accumulation phase. During a regeneration phase of the NOx trap, the NOx fixed by the trap 41 are converted to N2 and released into the atmosphere. In the particulate filter, the soot particles from the engine are blocked during an accumulation phase. During a regeneration phase, the soot particles are burned at high temperature and released into the atmosphere. The control member 31 periodically estimates whether the particulate filter and / or the NOx trap need to be regenerated. For example, when the vehicle has traveled a predetermined number of kilometers since the previous regeneration, the computer triggers the regeneration of the NOx trap and the particulate filter. To do this, the control member triggers the power supply of the heating member 61, by activating the power supply 65. After a possible latency time for preheating the heating member 61, the control member triggers the supply of the vaporizer 47 with liquid fuel, by activating the metering member 53. The liquid fuel from the reservoir 49 enters the vaporization chamber 55 through the inlet 57. Under the effect of the heat generated by the heating member 61, the liquid fuel is vaporized in its entirety. The heating member 61 is sized to heat the vaporization chamber 55 to a temperature above the vaporization temperature of all the hydrocarbons contained in the liquid fuel. Under the vaporization of the liquid fuel, the pressure in the vaporization chamber is higher than the pressure in the exhaust manifold. Under the effect of this difference in pressure, the fuel vapors leave the combustion chamber via the steam outlet 59 and enter the manifold 19. They mix with the exhaust gas and leave the manifold via the outlet 33.

The fuel vapors mixed with the exhaust gas then pass through the turbine 35 of the turbo compressor. While crossing the turbine, they are intimately mixed with the exhaust gases. The fuel vapors then reach the oxidation catalyst 25.

In oxygen present, a portion of the fuel is oxidized in the oxidation catalyst 25, and is decomposed into various products (H2O, CO2, H2 ...). This oxidation is accompanied by a strong release of heat, which raises the temperature of the exhaust gas above the limit temperature to regenerate the particulate filter and the NOx trap. This limit temperature is for example 600 ° C. The exhaust gases, containing the fraction of the unoxidized fuel and the byproducts of the decomposition of the fuel in the oxidation catalyst, then pass through the NOx trap. Fuel and / or hydrogen at high temperature causes regeneration of the NOx trap, NOx being converted to nitrogen gas N2 and entrained with the exhaust gas. The exhaust gases then pass through the particulate filter, and regenerate this particulate filter. At high temperature and in the presence of oxygen, soot particles blocked by the particulate filter are converted to CO2 and are entrained with the exhaust gas.

The control member 31 interrupts the introduction of fuel into the exhaust manifold once the predetermined amount of fuel has been introduced. Alternatively, the control member can determine a regeneration time, and interrupt the introduction of fuel when the predetermined time has elapsed. Other modes of piloting the introduction device are possible. The exhaust line described above has many advantages. Because the fuel introduction device inside the exhaust manifold includes a fuel vaporizer, provided with a vaporization chamber having a liquid fuel inlet and a vapor outlet opening therein of the exhaust manifold, and a heating element at least partially located inside the vaporization chamber and provided for vaporizing the liquid fuel, the fuel introduced into the exhaust manifold is entirely in vapor form . Indeed, even if the engine runs at low load and if the temperature of the exhaust gas entering the exhaust manifold is less than 200 ° C for example, the liquid fuel will be fully vaporized inside the vaporizer. The degree of vaporization of the liquid fuel is therefore independent of the operating point of the engine. It is independent of the flow and temperature of the exhaust gas passing through the exhaust manifold. As a result, the exhaust gases leaving the manifold and entering the turbo compressor turbine do not contain any droplets of liquid fuel. The risk of such droplets damaging the rotor blades of the turbine is reduced to practically zero. Moreover, the introduction device is particularly compact, because it does not require the implantation of a vaporization chamber outside the collector. The vaporization chamber is located at least partially inside the exhaust manifold. Only a small portion of the vaporizer protrudes out of the collector casing. The fact of making the introduction of fuel at the exhaust manifold, that is to say upstream of the turbo compressor, makes it possible to obtain an excellent mixture of the fuel vapors in the exhaust gases, these vapors being mixed with the exhaust gas when passing through the turbine of the turbo compressor. Furthermore, the fuel vapors are oxidized downstream of the turbo compressor, and are not oxidized in the manifold or in the conduit connecting the manifold to the turbo compressor turbine. Thus, it does not occur heat release due to the oxidation of the fuel upstream of the turbo compressor. Such heat generation helps to increase the turbine load of the turbo compressor and thus increase the load of the compressor supplying air to the intake manifold. Such an increase in load must be imperceptible to the driver. Therefore, it is necessary to make corrections via the engine control computer, which makes the steering system more complex and more difficult to develop. Such corrections are unnecessary with the injection device of the invention. The exhaust line described above can have multiple variants.

The exhaust line does not necessarily include a turbo compressor interposed between the exhaust manifold and the oxidation catalyst. The heating member of the introduction device can be of any type. It is not necessary a candle. It does not necessarily work by Joule effect. The vaporization chamber could include an area with an exhaust gas inlet and an outlet for the vaporized fuel mixed with the exhaust gas.

The engine is not necessarily a diesel engine, but can be a gasoline engine running on an Otto cycle. The vaporization chamber is not necessarily located inside the exhaust manifold, but could be disposed outside. The piloting of the introduction device can be carried out according to different strategies in order to regenerate the particulate filter and / or the NOx trap. The exhaust line may not have a NOx trap and may only include a particulate filter. The vaporizer could be attached, not to the exhaust manifold, but to another structure of the exhaust line and / or the motor vehicle.

Claims (9)

REVENDICATIONS1. Motor vehicle exhaust line, the exhaust line (5) comprising: - an exhaust manifold (19), having a plurality of exhaust gas inlets (21) provided for collecting gas streams; exhaust outlet of combustion chambers (3) of a heat engine (1) of the motor vehicle; an oxidation catalyst (25) interposed downstream of the exhaust manifold (19); - a device (29) for introducing a fuel into the exhaust manifold (19); characterized in that the device for introducing a fuel (29) comprises a vaporizer (47) of said fuel, provided with a vaporization chamber (55) having an inlet (57) of liquid fuel and a steam outlet (59) opening within the exhaust manifold (19), and a heating member (61) at least partially located within the vaporization chamber (55) and provided for vaporizing the liquid fuel. 2. Exhaust line according to claim 1, characterized in that the heating member (61) operates by Joule effect. 3. Exhaust line according to claim 1 or 2, characterized in that the heating member (61) is a candle. 4. Exhaust line according to any one of the preceding claims, characterized in that it comprises a turbo compressor (23) interposed between the exhaust manifold (19) and the oxidation catalyst (25). 5. Exhaust line according to claim 4, characterized in that the turbo compressor (23) comprises a turbine (35) provided with a gas inlet (34) connected to an exhaust gas outlet (33). ) of the exhaust manifold (19), a gas outlet (36) connected to the oxidation catalyst (25), and a rotor (37) adapted to be rotated by the exhaust gases flowing from the gas inlet (34) to the gas outlet (36). 6. Exhaust line according to any one of the preceding claims, characterized in that the vaporizer (47) is mounted on the manifold (19) with the vaporization chamber (55) at least partially located inside the collector exhaust (19). 7. Exhaust line according to any one of the preceding claims, characterized in that the fuel is gas oil. 8. Exhaust line according to any one of the preceding claims, characterized in that it comprises a particulate filter (43) interposed downstream of the oxidation catalyst (25), and a member (31) for controlling the fuel introduction device (29) with estimation means for estimating whether the particulate filter (43) needs to be regenerated, and means for controlling the introduction of fuel into the exhaust manifold (19) when the estimating means estimates that the particulate filter (43) needs to be regenerated. 9. Exhaust assembly with a diesel engine (1) having combustion chambers (3), and an exhaust line (5) according to any one of the preceding claims, the exhaust gas inlets (21). exhaust manifold (19) being connected to exhaust gas outlets (11) of said combustion chambers (3).