JP2018096227A - Exhaust emission control system of lean combustion internal combustion engine and exhaust emission control method of lean combustion internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system of a lean combustion internal combustion engine which can restore a methane purification property of an oxidation catalyst device for purifying methane without impairing drivability, and an exhaust emission control method of the lean combustion internal combustion engine, in the lean combustion internal combustion engine using compressed natural gas as fuel.SOLUTION: In a lean combustion internal combustion engine using a compressed natural gas as fuel, and having an oxidation catalyst device 29 in an exhaust passage 28 and a control device 40, the control device lean-operates the lean combustion internal combustion engine during the acceleration and a cruise operation of a vehicle which is mounted with the lean combustion internal combustion engine, oxides a treatment objective component in an exhaust gas G by using the oxidation catalyst device, rich-operates the lean combustion internal combustion engine at the deceleration of the vehicle, performs purification rate restoration control for restoring a purification rate of the oxidation catalyst device, and holding a temperature of the catalyst by combustion, and when performing the purification rate restoration control, sets ignition timing so as to be retarded after a piston top dead point without generating torque.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lean combustion internal combustion engine exhaust gas purification system and a lean combustion internal combustion engine exhaust gas purification method for reducing NOx emitted from a lean combustion internal combustion engine.

In a lean burn engine using compressed natural gas as a fuel, the main component of the natural gas used as fuel is methane (CH ₄ ), and this methane has an arm of carbon (C) and hydrogen (H) due to its molecular structure. In order to cause a chemical reaction with an oxidation catalyst mainly composed of platinum and vanadium for purifying methane, a temperature of 450 ° C. or higher is required. In addition, in the oxidation catalyst, the supported noble metal may become an oxide in an oxidizing atmosphere environment in lean combustion. When this noble metal oxidation reaction proceeds, the methane purification rate decreases.

  Therefore, in order to purify this methane with an oxidation catalyst, it is difficult to maintain the oxidation reaction of methane for a long time at a temperature that can be purified, and it is difficult to maintain a high purification rate for a long time. There is. On the other hand, the oxidation catalyst of this oxidation catalyst has progressed, and the oxidation catalyst with a reduced methane purification rate can be recovered in its methane purification capacity when operated in a rich state and put into a reducing atmosphere. Yes.

  In this connection, it is not an oxidation catalyst for purifying methane but a NOx occlusion reduction type catalyst for purifying NOx, but it purifies NOx when the air-fuel ratio of the exhaust gas of a vehicle-mounted internal combustion engine is lean. In addition, an exhaust gas purification method that uses both fuel system rich control and intake system rich control when the vehicle is decelerating has been proposed for a NOx purification catalyst that recovers NOx purification capacity in a rich state (for example, a patent) Reference 1).

  This fuel system rich control is a control for adding or increasing the amount of fuel in the exhaust gas by multistage injection or post injection in cylinder injection, or injection in the exhaust pipe that supplies fuel directly to the exhaust pipe. In this exhaust gas purification method, by performing regeneration control when the vehicle is decelerating, the fuel injection amount is reduced by intake system rich control, so it is possible to prevent deterioration in riding comfort during regeneration control.

JP 2006-316757 A

  By the way, the exhaust gas purification method described above relates to a NOx occlusion reduction type catalyst used for NOx purification of diesel engines, some gasoline engines, and the like. Moreover, in multistage injection and post injection in cylinder injection, main injection is performed. As a result, the generated torque of the internal combustion engine cannot be made completely zero, and there remains room for further improving drivability. Further, the direct injection in the exhaust pipe has a problem that when the in-cylinder fuel injection is completely stopped and the generated torque of the internal combustion engine is made zero, the increase in the temperature of the exhaust gas due to the combustion in the cylinder cannot be used.

  The present invention has been made in view of the above, and an object thereof is a methane purification of an oxidation catalyst device for purifying methane without impairing drivability in a lean combustion internal combustion engine using compressed natural gas as a fuel. To provide an exhaust gas purification system for a lean combustion internal combustion engine and an exhaust gas purification method for a lean combustion internal combustion engine capable of recovering the capacity.

  In order to achieve the above object, an exhaust gas purification system for a lean combustion internal combustion engine according to the present invention is a lean combustion internal combustion engine that uses compressed natural gas as fuel, an oxidation catalyst device in the exhaust passage, and a control device. The control device performs lean operation during acceleration and cruising operation of a vehicle equipped with the lean combustion internal combustion engine, oxidizes the target component in the exhaust gas with the oxidation catalyst device, and A rich operation is performed during deceleration, and purification rate recovery control is performed to recover the purification rate of the oxidation catalyst device and to keep the catalyst warm by combustion.

  Further, the exhaust gas purification method for a lean burn internal combustion engine of the present invention for achieving the above object is a lean burn internal combustion engine using compressed natural gas as a fuel, and acceleration and cruise of a vehicle equipped with the lean burn internal combustion engine. During the operation, the lean operation is performed to oxidize the processing target component in the exhaust gas with the oxidation catalyst device provided in the exhaust passage, and the rich operation is performed when the vehicle is decelerated, and the purification rate of the oxidation catalyst device is increased. This is a method characterized by maintaining the temperature of the catalyst by recovery and combustion.

  According to the exhaust gas purification system of the lean combustion internal combustion engine and the exhaust gas purification method of the lean combustion internal combustion engine, the lean operation is performed during acceleration and cruise operation of the vehicle, and the oxidation catalyst device oxidizes methane in the exhaust gas. And reducing the intake air amount by the throttle when the vehicle is decelerating and recovering the purification rate during the lean operation by rich operation, and the ignition timing of the spark plug is set to the top dead center of the piston during the purification rate recovery control. Since the generation of torque is prevented later, the methane purification ability of the oxidation catalyst device for purifying methane can be recovered without impairing drivability.

It is a figure which shows typically the structure of the exhaust gas purification system of the lean combustion internal combustion engine of embodiment which concerns on this invention. It is a figure which shows an example of the control flow of the exhaust gas purification method of the lean combustion internal combustion engine of embodiment which concerns on this invention.

  Hereinafter, an exhaust gas purification system for a lean combustion internal combustion engine and an exhaust gas purification method for a lean combustion internal combustion engine according to embodiments of the present invention will be described with reference to the drawings. This lean combustion internal combustion engine is a lean burn engine using compressed natural gas (CNG) as fuel.

  In the lean burn engine using compressed natural gas as the fuel, the main component of the fuel is methane, so in order to purify unburned methane with an oxidation catalyst, methane has few H and C arms due to its molecular structure, In order to cause the oxidation reaction with the catalyst, 450 ° C. or more is required, so that it is difficult in terms of temperature and methane oxidation reaction, and it is difficult to maintain a high purification rate for a long time.

  As shown in FIG. 1, in an exhaust gas purification system 1 for a lean burn internal combustion engine according to an embodiment of the present invention, intake air A enters an intake passage 12 of an engine body 11 from an upstream side with an air cleaner 13 and an intake air amount sensor (MAF). Sensor) 14, compressor 15a of turbocharger 15, intercooler 16, intake throttle valve 17 with throttle angle sensor 17a, intake pressure / intake temperature sensor 18, and fuel temperature / pressure sensor 19b. A fuel injection device (fail injector) 19 connected to the passage 19 a is provided, and the intake air A is introduced into the combustion chamber 22 above the piston 21 of the cylinder 20 through the intake passage 12.

  The combustion chamber 22 is provided with an ignition plug 23a of the primary side ignition system 23, and natural gas, which is fuel injected from the fuel injection device 19, is ignited and burned by the ignition plug 23a. Around the cylinder 20, a knock sensor 24, an engine coolant temperature sensor 25, a crank angle sensor 26, and a cylinder discrimination sensor (cam angle sensor) 27 are provided. A turbine 15 b of the turbocharger 15, an oxidation catalyst device 29, and a catalyst temperature sensor 30 are provided in the exhaust passage 28 through which the exhaust gas G discharged from the combustion chamber 22 passes. In addition, a wastegate 15c is provided in the turbine 15b so that opening / closing thereof is adjusted by a wastegate control solenoid 15d.

  Further, an EGR passage 31 branched from the exhaust passage 28 and connected to the intake passage 12 is provided, and an EGR cooler 32 and an EGR valve 33 are provided in the EGR passage 31 to recirculate EGR gas Ge to the combustion chamber 22. ing.

  The oxidation catalyst device 29 is configured by supporting an oxidation catalyst of a noble metal catalyst such as platinum or palladium on a support such as a monolith support formed of ceramic or the like, and carbon monoxide (CO) in the exhaust gas G. It oxidizes and purifies hydrocarbons (HC) and the like. Here, it has the role which prevents that methane etc. which are unburned fuel are discharge | released in air | atmosphere. Although this oxidation catalyst can purify unburned methane, which is a component to be treated, in the stoichiometric state, the oxidation reaction is poor in the lean state, and the supported noble metal may become an oxide. The catalyst recovers its purification rate when operated in a rich state.

  Further, a control device 40 is provided, and the detection values of the various sensors 14, 17 a, 18, 19 b, 24, 25, 26, 27, and 30 are input to adjust the pressure of fuel supplied to the fuel injection device 19. A control command for controlling the fuel injection amount and fuel injection timing supplied to the combustion chamber 22 is output to the fuel injection valve 62, and the ignition timing of the spark plug 23a is controlled. The control device 40 is usually composed of an engine control device called an ECU (engine control unit) that controls the overall operation of the engine, but is formed separately from the engine control device. You may make it the structure controlled while taking cooperation between.

  In the present invention, the control device 40 performs lean operation during acceleration and cruising operation of a vehicle equipped with the lean combustion internal combustion engine, and the oxidation catalyst device 29 removes components to be treated such as methane in the exhaust gas G. At the same time as the oxidation process, the intake throttle valve 17 is closed when the vehicle is decelerated and the rich operation is performed to perform the purification rate recovery control for recovering the purification rate of the oxidation catalyst device 29 and keeping the catalyst warm by combustion. When performing recovery control, the ignition timing is set behind the piston top dead center so that torque is not generated.

  In other words, the lean burn engine is operated with lean combustion during cruising, but since no torque is required during deceleration, the intake throttle valve 17 is closed during deceleration and the oxidation catalyst device 29 is low in oxygen by performing rich operation. In a rich state, oxygen content is removed from the supported noble metal, the catalyst purification rate during the lean operation is recovered, and the temperature of the catalyst is kept by combustion. During the control period calculated from the catalyst temperature Tc and the engine speed Ne, all cylinders are injected, and then all cylinder fuel is cut. Since the purification rate of methane increases when the catalyst temperature Tc is high, the activity of the oxidation catalyst becomes active. Therefore, the rich operation time is increased, and oxygen attached to the noble metal is positively separated.

  Further, the ignition timing is set to be after the top dead center so as not to retard (delay) the fuel ignition timing, that is, the spark plug ignition timing to generate torque. As a result, it is avoided that when fuel is injected for deceleration, torque is generated and there is no feeling of deceleration. In other words, if fuel is supplied during deceleration, torque may be generated, so the ignition timing during that time is retarded to prevent torque generation.

  Then, the control device 40 determines whether or not the vehicle is decelerating from the throttle opening or the accelerator pedal opening. At the same time, the catalyst temperature Tc of the oxidation catalyst device 29 is measured by the catalyst temperature sensor 30, and the purification rate recovery control is not performed when the catalyst temperature Tc is lower than the preset temperature Tcc. In this catalyst temperature determination, the catalyst temperature Tc during operation is monitored by the catalyst temperature sensor 30 to monitor whether the temperature is equal to or higher than the temperature Tcc at which methane can be purified.

  Alternatively, when the control device 40 determines that the engine coolant temperature Tw measured by the engine coolant temperature sensor 25 is equal to or lower than a preset determination water temperature (for example, 70 ° C.) Twc, or when the idle switch is OFF, or the exhaust When the brake is ON, the purification rate recovery control is not performed.

When the control device 40 performs the purification rate recovery control, the rich combustion fuel injection time is set based on the temperature of the oxidation catalyst device 29 measured by the catalyst temperature sensor 30. Further, it is preferable that the fuel injection time and the fuel injection amount are changed by the catalyst temperature Tc and the engine speed Ne. In other words, the fuel injection time is preferably set by determining the fuel injection time during which the catalyst is activated from the catalyst temperature Tc and the engine speed Ne using map data set in advance through experiments or the like.
Further, when the control device 40 is performing the purification rate recovery control, when the idle switch is turned off, or the engine speed Ne is equal to or less than a preset engine speed (fuel cut return engine speed) Ns. When it becomes, it is comprised so that purification rate recovery | restoration control may be complete | finished. That is, when this cancellation condition is satisfied, both the fuel injection and ignition control are canceled and the normal control is resumed. Normally, the engine is stalled if it is decelerated, so that when the engine speed Nc reaches the fuel cut return engine speed Nc at the idling position, it is configured to return to normal control. When the fuel cut return engine speed Nc is reached, the purification rate recovery control is terminated.

  Next, an exhaust gas purification method for a lean combustion internal combustion engine according to an embodiment of the present invention will be described. This method uses a lean combustion internal combustion engine that uses compressed natural gas as a fuel, performs lean operation during acceleration and cruise operation of a vehicle equipped with this lean combustion internal combustion engine, and uses an oxidation catalyst device 29 provided in an exhaust passage 28. In this method, the component to be treated in the exhaust gas G is oxidized and the rich operation is performed when the vehicle is decelerated to recover the purification rate of the oxidation catalyst device 29.

  In the following, the exhaust gas purification method for the lean combustion internal combustion engine will be described in more detail with reference to the control flow of FIG. The control flow of FIG. 2 is called and executed from the advanced control flow when the operation of the lean combustion internal combustion engine is started, and returns to the advanced control flow when the operation of the lean combustion internal combustion engine is stopped. It is shown as ending with the end of the advanced control flow.

  When the control flow of FIG. 2 starts, it is determined in step S11 whether or not the vehicle is in a deceleration state. If the vehicle is not in a deceleration state (NO), the process returns to step S11 after a preset time has elapsed. If it is determined in step S11 that the vehicle is decelerating (YES), the process proceeds to step S12. The determination in step S11 is determined from the throttle opening, the accelerator pedal opening, and the like.

  In step S12, it is determined whether or not the oxidation catalyst of the oxidation catalyst device 29 is sufficiently active based on whether or not the catalyst temperature Tc measured by the catalyst temperature sensor 30 is equal to or higher than a preset temperature Tcc. If “Tc <Tcc” is determined in step S12 (NO), the process returns to step S11. If “Tc ≧ Tcc” is determined in step S12 (YES), the process goes to step S13.

  In step S13, it is determined whether or not a prohibition condition for prohibiting the purification rate recovery control is satisfied. The prohibition conditions are that the engine coolant temperature Tw is equal to or lower than a preset determination coolant temperature Twc, the idle switch is OFF, and the exhaust brake is ON. If any one of these conditions is satisfied, the prohibition condition is satisfied (YES). Further, when all of these conditions are not satisfied, the prohibition condition is not satisfied (NO). If the prohibition condition is satisfied in step S13 (YES), the process returns to step S11. If the prohibition condition is not satisfied in step S13 (NO), the process goes to step S14.

  In step S14, map data (table) MP1 based on the catalyst temperature Tc from the catalyst temperature Tc and the engine speed Ne inputted as the measured value at the time of the current control, the fuel injection time in the rich operation performed in the purification rate recovery control, The map data (table) MP2 based on the engine speed Ne is set with reference to each. At this time, the higher the catalyst temperature Tc, the more active the oxidation catalyst and the higher the methane purification rate. Therefore, the rich operation time is lengthened to actively separate oxygen attached to the noble metal catalyst. Further, the fuel injection amount is set from the catalyst temperature Tc and the engine speed Ne with reference to the map data (table) MP3 based on the catalyst temperature Tc base and the engine speed Ne.

  In the next step S15, the rich operation in all cylinders is performed for a preset time by the purification rate recovery control, the process goes to step S16, and step S15 is repeated until the end condition of step S16 is satisfied (YES). As the end condition, either the elapsed time of the rich operation has passed the fuel injection time, the idle switch is turned off, or the engine speed Ne is changed to the fuel cut return engine speed Nc. It is determined that the end condition is satisfied. If the end condition of step S16 is satisfied (YES), in step S17, an end operation for cutting fuel injection in all cylinders is performed, and the process returns to step S11.

  If the engine operation is stopped in the middle of these controls, an interrupt is generated, the process goes to return, returns to the advanced control flow, and the control flow in FIG.

  According to the exhaust gas purification system 1 of the lean combustion internal combustion engine and the exhaust gas purification method of the lean combustion internal combustion engine configured as described above, the oxidation catalyst device 29 that oxidizes methane in the exhaust gas G is provided in the exhaust passage 28, and During acceleration and cruising operation of a vehicle equipped with this lean combustion internal combustion engine, lean operation is performed, methane in the exhaust gas G is oxidized by the oxidation catalyst device 29, and rich operation is performed when the vehicle is decelerated. It is possible to recover the purification rate during lean operation by removing the oxygen content from the precious metal that has been removed, and at the time of this purification rate recovery control, set the ignition timing of the spark plug after the piston top dead center. Thus, generation of torque is prevented, so that the methane purification ability of the oxidation catalyst device for purifying methane can be recovered without impairing drivability.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification system of lean-burn internal combustion engine 11 Engine main body 12 Intake passage 14 Intake amount sensor (MAF sensor)
17a Throttle angle sensor 18 Intake pressure / intake temperature sensor 19b Fuel temperature / pressure sensor 19 Fuel injection device (fail injector)
20 Cylinder 22 Combustion chamber 23a Spark plug 24 Knock sensor 25 Engine coolant temperature sensor 26 Crank angle sensor 27 Cylinder discrimination sensor (cam angle sensor)
28 Exhaust passage 29 Oxidation catalyst device 30 Catalyst temperature sensor A Intake G Exhaust gas Ge EGR gas

Claims (6)

In a lean combustion internal combustion engine that uses compressed natural gas as fuel and is provided with an oxidation catalyst device in an exhaust passage and is equipped with a control device, the control device is accelerating and cruising the vehicle equipped with the lean combustion internal combustion engine Performs a lean operation to oxidize the component to be treated in the exhaust gas with the oxidation catalyst device, and performs a rich operation when the vehicle decelerates, recovering the purification rate of the oxidation catalyst device and Perform purification rate recovery control to keep warm,
Further, when performing the purification rate recovery control, an exhaust gas purification method for a lean combustion internal combustion engine, wherein the ignition timing is set behind the piston top dead center so that torque is not generated.   The controller determines whether the throttle opening or the accelerator pedal opening is decelerating, measures the temperature of the oxidation catalyst device with a catalyst temperature sensor, and if this temperature is less than a preset temperature 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the purification rate recovery control is not performed.   When the engine cooling water temperature measured by the engine cooling water temperature sensor is equal to or lower than a predetermined determination water temperature, when the idle switch is OFF, or when the exhaust brake is ON, the purification rate is 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein recovery control is not performed.   3. The rich combustion fuel injection time is set based on the temperature of the oxidation catalyst device measured by the catalyst temperature sensor when the control device performs the purification rate recovery control. Exhaust gas purification system for internal combustion engines.   When the control device is performing the purification rate recovery control, the purification rate recovery control is performed when the idle switch is turned off or when the engine speed is equal to or lower than a preset rotation speed. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 4, wherein the process is terminated.   In a lean combustion internal combustion engine using compressed natural gas as a fuel, a lean operation is performed during acceleration and cruising operation of a vehicle equipped with this lean combustion internal combustion engine, and an object to be treated in exhaust gas by an oxidation catalyst device provided in the exhaust passage An exhaust gas purification method for a lean-burn internal combustion engine characterized by oxidizing components and performing a rich operation during deceleration of the vehicle to recover the purification rate of the oxidation catalyst device and to keep the catalyst warm by combustion.

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