JP5909028B2 - Apparatus and method for operating an injector of an exhaust gas aftertreatment device - Google Patents

Description

  The present invention is directed to exhaust gas aftertreatment devices for internal combustion engines and methods for operating them. More particularly, the present invention is directed to an apparatus and method for preventing coke deposits on a post-processing injector nozzle in a post-processing system.

  Automotive exhaust aftertreatment devices are used to convert or remove target substances from exhaust gases. This post-treatment device, for example, removes particulate matter in exhaust gas and oxidizes carbon monoxide and unburned hydrocarbons. Diesel particulates remove particulate matter from exhaust gas. A filter (DPF) and a selective catalytic reduction (SCR) system that injects ammonia-based reducing agent in the presence of a catalyst to convert nitrogen oxides (NOx) into nitrogen gas and water. Post-processing devices, such as SCR devices, operate only at or above a threshold temperature. Other devices, such as DPF, require periodic removal of collected particulate matter from the filter body. One such process, known as regeneration, occurs by oxidation of collected particulate matter and requires that the filter body be at a high temperature, typically above 600 ° C.

  When starting the engine, the aftertreatment components can be at or near ambient temperature, but that temperature is too low for the operation of these devices. In addition, automobile exhaust gases, particularly diesel engine exhaust gases, are not always at a sufficiently high temperature for operation of certain on-board exhaust aftertreatment systems, particularly for regeneration of the DPF. Accordingly, several devices or methods are provided for raising the temperature of the exhaust gas as needed. Methods and apparatus for heating the exhaust include engine control for controlling the temperature of the exhaust gas, an electrical resistance heating coil disposed in the exhaust pipe, and a burner. Such an apparatus is a system for injecting hydrocarbons, typically diesel fuel, into an exhaust gas, and includes an injector nozzle arranged to inject the fuel into the exhaust gas stream.

  One problem with hydrocarbon injectors is the deposition of decomposed liquefied hydrocarbons, particulate matter, and other residues that collect on the nozzle, called “coking”, onto the injector nozzle.

  The present invention proposes an apparatus and method for solving these problems.

  According to the invention, an exhaust gas aftertreatment device comprising a hydrocarbon injector includes an injector nozzle coated with a catalytic material. This catalytic coating allows hydrocarbons that collect on the nozzle to be oxidized at a lower temperature than non-catalytic oxidation.

  The device according to the invention further comprises a device for supplying and controlling the air flow via the injector according to the temperature of the exhaust gas.

  The method of the present invention for operating the injector includes (1) a state in which fuel is injected to heat the aftertreatment device, and (2) after the fuel injection, when the temperature of the exhaust gas is low, the flow of air through the nozzle Conditions to purge remaining fuel and / or cool nozzle to prevent carbon deposition and (3) exhaust gas to oxidize any deposited carbon when exhaust temperature is high enough to maintain oxidation In order to enable passive heating of the nozzle, the three states include no air flow (or less). Immediately after state (3), the method can include an additional air purge to remove ash.

  A method for operating an injector of an exhaust gas aftertreatment device to avoid coke deposition is that the injector nozzle has a catalytic coating and a hydrocarbon fluid is introduced into the exhaust gas stream for a selected period of time. Injecting, allowing the air to flow through the injector nozzle when the exhaust gas temperature is below a threshold temperature, and the air flow through the injector nozzle when the exhaust gas temperature is above a threshold temperature. Substantially stopping.

  In another aspect of the present invention, the method includes the steps of monitoring the state of the aftertreatment device, monitoring the temperature of the exhaust gas, and depending on the state of the aftertreatment device and the temperature of the exhaust gas. Controlling the injection of hydrocarbons into the stream.

  In another aspect of the invention, the air flow is preferably pulsed, and the air flow parameters, volume, frequency and duration are controlled as a function of the exhaust gas temperature.

  The present invention will be further understood by reading the following detailed description in conjunction with the accompanying drawings.

1 is a schematic drawing of an exhaust system having an internal combustion engine and an aftertreatment system of an exemplary embodiment of the present invention. 2 is a simplified drawing of an exemplary post-processing injector. 2 is a flow diagram of a method according to the invention.

  FIG. 1 illustrates an apparatus comprising an internal combustion engine 10 with an exhaust gas aftertreatment system 12 according to the present invention. The internal combustion engine 10 is connected to an exhaust gas conduit 14 that receives exhaust gas from the engine. Exhaust gas is conveyed to the aftertreatment device 16 by a pipe line, but the aftertreatment system includes a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reactor (SCR) or a lean NOx catalyst (LNC). And a device for treating nitrogen oxides. After being treated, the exhaust gas is discharged to the outside through an exhaust pipe or pipe 18.

  DPF filters the exhaust gas to collect soot and other particulate matter, which must be removed at intervals or when the DPF is clogged. One common method of removing primarily carbon-based particulate matter is to raise the temperature of the DPF filter body to a temperature sufficient to oxidize the particulate matter. As is well known, the temperature of the DPF filter body can be raised by various methods. One way is to add hydrocarbon (or fuel) to the exhaust gas, which oxidizes and releases thermal energy. An injector 20 connected to a hydrocarbon source 22 is shown in FIG. 1 for such purpose. The injector 20 includes a nozzle 24 that introduces hydrocarbons into the exhaust gas flow. The injector 20 of the illustrated embodiment is also connected to an air source 26. Controller 28 is programmed to control the flow of hydrocarbons and air through injector 20 as will be described in more detail below. The temperature sensors 30 and 34 are respectively arranged at the inlet and the outlet of the aftertreatment device 16 in order to monitor the temperature of the exhaust gas entering and leaving the device. Instead, in an aftertreatment device including a DOC and a DPF, temperature sensors can be arranged upstream of the DOC, downstream of the DOC, upstream of the DPF, and downstream of the DPF. In addition, pressure sensors 32 and 36 are respectively disposed at the inlet and the outlet of the aftertreatment device 16 in order to monitor the pressure change of the exhaust gas passing through the DPF. The difference in exhaust pressure between the input and outlet is useful for determining soot build-up in the DPF.

  The injector 20 is exposed to the exhaust gas carrying the particulate matter by being upstream of the aftertreatment device 16. In addition, the injector nozzle 24 and the hydrocarbon liquid in and out of the injector nozzle 24 are exposed to the heat of the exhaust gas. This can result in nozzle coking as the hydrocarbon liquid and particulate deposits form on the nozzle.

  Maintaining the nozzle at a relatively low temperature does not eliminate coking, but can help prevent it. Coke deposits can be removed by heating the nozzle to a sufficiently high temperature to oxidize the carbon, and devices for heating the nozzle are known. However, these add cost and complexity to the injector system.

  In accordance with the present invention, the injector nozzle 24 is provided with a coating of catalytic material that allows oxidation of coke deposits at relatively low temperatures. Suitable catalyst materials include noble metal catalysts such as platinum and palladium. Referring to FIG. 2, the injector nozzle 24 includes a nozzle pipe 40 having a flow path 42 for liquid fuel. The flow path 42 terminates within the tip 44, but the tip 44 may include, for example, a fluid distributor that controls the flow rate or induces a vortex or spray angle. Injector 20 can be any suitable fluid injector and is intended to control injector body 50 having an internal passage 52 for the ejected fluid and flow into nozzle flow path 42 and to tip 44. A spring 56 and a needle 54 movable within the internal passage 52 operable by an actuator device (not shown) can be included.

  The catalyst coating is preferably applied to the surface exposed to the heat of the exhaust gas and the fuel injected by the nozzle 24. Such surfaces include the outer surface 46 of the nozzle 24, the tip 44, and the surface 48 that defines the flow path 42.

  The catalytic coating on these surfaces reduces the temperature required to oxidize the carbon deposits on those surfaces. FIG. 3 is a flow diagram of the method of the present invention for preventing injector coke deposition. According to this method, the operating condition of the aftertreatment (AT) device is monitored by monitoring the pressure difference between the inflow and outflow of exhaust gas and / or by monitoring the temperature of the device (S100). . Further, the temperature of the exhaust gas flowing into the AT device is also monitored (S102).

  This method determines whether the exhaust gas is above a temperature threshold at which the exhaust gas can heat the catalyst coating nozzle to a temperature sufficient to oxidize the deposited carbon (S104). By using a noble metal as a catalyst, heating the nozzle to about 240 ° C. or higher promotes oxidation.

  Although described in a continuous manner, it should be understood that rather than performing the entire method of the present invention continuously, the steps of monitoring the AT device, monitoring the exhaust gas temperature, The step of determining whether the gas temperature is above a threshold is to be performed continuously or in an iterative order when performing the rest of the method.

  If the exhaust gas temperature is higher than the threshold in step S104, the method stops the air flow through the injector in step S106, or prevents, for example, exhaust gas from entering the nozzle but does not effectively cool the nozzle. The air flow is substantially stopped to minimize the air flow. The absence of air flow or the low flow rate of air allows the nozzle to be heated to a temperature sufficient to oxidize any carbon deposits. A timer can be started to measure the period during which the nozzle is heated and oxidation occurs. Instead, according to this method, the air flow is stopped or kept at a minimum while the temperature of the exhaust gas is higher than the threshold value determined in step S104.

  When the heating / oxidation period has elapsed (step S108) or when the exhaust gas temperature falls below a threshold temperature, the method increases the flow of air through the nozzle for cooling to prevent coking (S110). .

  Returning to step S104, if the exhaust gas temperature is lower than the threshold temperature, the state of the AT device is evaluated to determine whether the temperature of the exhaust gas needs to be increased (step S112). For example, a DPF device may require a regeneration procedure to remove the collected particulate matter.

  If the AT device does not require heating, the method allows air to flow through the nozzle (step S114). The air flow helps cool the nozzle and prevents or hinders coke deposition.

  When the AT device needs to be heated, hydrocarbons are injected through the injector while monitoring the temperature of the exhaust gas (step S116). The amount of hydrocarbons and the frequency of injection are controlled relative to the exhaust gas temperature which maintains the temperature for a period of time sufficient to heat the DPF device to the target temperature and regenerate the DPF. Alternatively, the DPF can be heated until the pressure difference of the exhaust gas between the inlet and the outlet is below a threshold value.

  When the regeneration process is completed, the injection of hydrocarbons is stopped and air is allowed to flow through the nozzle (step S114). The air flow after injecting the hydrocarbons helps remove the remaining hydrocarbons from the nozzles, and the continuous air flow helps cool the nozzles and helps prevent or prevent coke deposition.

  It should be noted here that, according to the present invention, air flows continuously through the nozzle at a low exhaust temperature that is not high enough to oxidize the carbon, slowing the carbon deposition. Therefore, the nozzle temperature should be kept as low as possible. At an exhaust temperature high enough to maintain the oxidation of the carbon adhering to the nozzle, the air flow through the nozzle is completely or substantially completely stopped, avoiding nozzle cooling and any coking. Be able to oxidize.

  In this application, the use of the term “including”, for example, is open and has the same meaning as the term “comprising”, and is not intended to exclude the presence of other structures, materials or acts. ing. Similarly, for example, use of the term “can do” or “can do” is intended to be open and imply that a structure, material, or act is not necessarily indispensable. The lack of use of simple terms is not intended to indicate that structure, material, or work is essential. To the extent that structure, material, or work is currently considered essential, they are perceived as such.

  While the invention has been illustrated and described based on preferred embodiments, it will be appreciated that modifications and changes can be made without departing from the invention as set forth in the appended claims.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Exhaust-gas aftertreatment system 14 Pipe line 16 Aftertreatment device 18 Pipe 20 Injector 22 Hydrocarbon supply source 24 Nozzle 26 Air supply source 28 Control device 30 Temperature sensor 32 Pressure sensor 34 Temperature sensor 36 Pressure sensor 40 Nozzle pipe 42 Flow path 44 Tip 46 Outer surface 48 Surface 50 Injector body 52 Internal passage 54 Needle 56 Spring

Claims (5)

A method of operating an injector of an exhaust gas aftertreatment device to prevent adhesion of coke,
The injector nozzle has a catalyst coating;
Selectively injecting a hydrocarbon fluid into the exhaust gas stream to raise the temperature of the exhaust gas stream;
Allowing air to flow through the injector nozzle when no hydrocarbons are being injected and the temperature of the exhaust gas is below a threshold temperature; and
Substantially stopping the flow of air through the injector nozzle when no hydrocarbons are being injected and when the temperature of the exhaust gas is higher than the threshold temperature;
Including methods. Monitoring the condition of the aftertreatment device;
Monitoring the temperature of the exhaust gas; and
The method of claim 1, further comprising controlling injection of the hydrocarbons into the exhaust gas stream in response to a state of the aftertreatment device and in response to the temperature of the exhaust gas.   The method of claim 1, comprising removing residual hydrocarbons from the injector by allowing air to flow through the injector immediately after injecting hydrocarbons.   The air flow through the injector nozzle is substantially stopped when the exhaust gas temperature is above the threshold temperature until the exhaust gas temperature is below the threshold temperature. Method.   The method of claim 1, wherein the flow of air through the injector nozzle is substantially stopped for a predetermined period of time when the temperature of the exhaust gas is higher than the threshold temperature.

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