JPWO2013102947A1 - Exhaust heating method - Google Patents

Abstract

Fuel is supplied from the fuel addition valve (27) to the exhaust passage (23a) toward the heat generating portion (28a) of the glow plug (28) disposed in the exhaust passage (23a) on the upstream side of the exhaust purification device (26). The method according to the present invention for heating the exhaust led to the exhaust purification device (26) by injecting and igniting this directly contacts the heat generating part (28a) of the fuel injected from the fuel addition valve (27). The fuel ratio was set within the range of 8% to 55%.

Description

  The present invention heats the exhaust led to the exhaust purification device by injecting fuel into the exhaust passage from the fuel addition valve arranged in the exhaust pipe upstream of the exhaust purification device, and heating and igniting the fuel. On how to do.

  In recent years, in order to cope with strict exhaust regulations for an internal combustion engine, it is necessary to promote activation of an exhaust purification device at the start of the internal combustion engine or to maintain the active state during operation of the internal combustion engine. . For this reason, Patent Document 1 and the like propose an internal combustion engine in which an exhaust heating device is incorporated in an exhaust passage upstream of the exhaust purification device. The exhaust gas heating device generates a heating gas in the exhaust gas, and supplies the generated heating gas to the exhaust gas purification device on the downstream side, thereby promoting activation of the exhaust gas purification device or maintaining an active state. Is. For this reason, the exhaust heating device generally includes a fuel addition valve that injects fuel into the exhaust passage, and an ignition device such as a glow plug that generates heated gas by heating and igniting the fuel. Further, in the conventional exhaust heating device disclosed in Patent Document 1, since the ignition device is arranged in the vicinity of the fuel addition valve, the fuel and exhaust injected from the fuel addition valve to the exhaust passage are mixed. May not be sufficient, and the ignited fuel may be incompletely combusted. For this reason, Patent Document 1 proposes that a receiving plate that receives the fuel injected from the fuel addition valve and scatters the fuel into the exhaust passage is incorporated in the exhaust passage.

JP 2010-084710 A

  In the exhaust heating apparatus disclosed in Patent Document 1, it has been confirmed from recent research that fuel that collides with the heat generating portion of the ignition means from the fuel addition valve is not directly ignited by the heat generating portion. That is, after the fuel that has collided with the heat generating part is vaporized by receiving heat from the heat generating part, it is ignited and ignites the mixture of fuel droplets floating around the heat generating part and the exhaust flowing from the upstream side of the exhaust passage. It has been found that combustion spreads. For this reason, when fuel is injected toward the heat generating part of the ignition means and collides with the fuel, the heat generating part is cooled by the fuel depending on conditions such as the amount and ratio of the fuel, and the ignitability is reduced. Even if burned, the combustion diffusivity may not be good. In such a case, there is a possibility that the amount of unburned HC generated increases and flows directly downstream of the exhaust passage, or the amount of soot generated increases.

  An object of the present invention is to provide a method capable of suppressing the generation of unburned HC and soot when compared with a conventional one when an exhaust heating apparatus is used.

  The present invention is based on the novel knowledge of the present inventors that the ratio of the fuel directly in contact with the heat generating part of the ignition means among the fuel injected from the fuel addition valve is important for the generation of unburned HC and soot. It is. In other words, the fuel is injected from the fuel addition valve to the exhaust passage toward the heat generating portion of the ignition means arranged in the exhaust passage upstream of the exhaust purification device, and the exhaust led to the exhaust purification device by igniting the fuel. The method according to the present invention for heating the fuel is characterized in that the proportion of the fuel directly in contact with the heat generating portion of the fuel injected from the fuel addition valve is set in the range of 8% to 55%. is there.

  Here, of the fuel injected from the fuel addition valve, the ratio of the fuel that directly contacts the heat generating part of the ignition means (hereinafter, this ratio is referred to as the fuel collision ratio with the heat generating part), the amount of increase in the exhaust temperature, FIG. 6 shows the relationship, and FIG. 7 shows the relationship between the fuel collision rate with respect to the heat generating portion and the amount of soot produced per 1 cc of fuel. As is clear from FIGS. 6 and 7, when the fuel collision rate with respect to the heat generating portion is lower than 8%, the fuel is ignited in the heat generating portion, but the air-fuel mixture cannot be effectively produced around the heat generating portion, and combustion occurs. Diffusivity is low. For this reason, the amount of unburned HC passing through the exhaust heating device without being ignited increases, and the combustibility deteriorates rapidly. On the contrary, when the fuel collision ratio with respect to the heat generating part exceeds 55%, the amount of soot generated increases rapidly.

In the exhaust heating method according to the present invention, it is preferable to set the injection amount per time of the fuel addition valve for intermittently injecting the fuel into the exhaust passage within a range of 10 mm ³ to 75 mm ³ .

  It is preferable to set the injection period per one time of the fuel addition valve in a range from 1.5 ms to 15 ms.

  The amount of fuel injected from the fuel addition valve per unit time is preferably set within a range from 80 cc / min to 1000 cc / min.

  The fuel injected from the fuel addition valve diffuses in a conical shape, and with respect to the area of the injection region projected onto a plane perpendicular to the center line of the fuel injection region forming the conical shape and including the axis of the heat generating portion, The area of the heat generating portion overlapping with this can be set within the range of 8% to 55%.

  The fuel injected from the fuel addition valve may be light oil or biofuel.

  It is preferable to heat the heat generating portion of the ignition means and inject fuel from the fuel addition valve into the exhaust passage only when the flow rate of the exhaust gas flowing through the exhaust passage is 50 g / sec or less.

  According to the present invention, since the ratio of the fuel directly in contact with the heat generating portion of the fuel injected from the fuel addition valve is set within the range of 8% to 55%, the heat generating portion can be cooled without excessive cooling. It becomes possible to form a sufficient mixture around the periphery. As a result, it is possible to suppress an increase in the amount of soot generated while maintaining good flammability.

When the injection amount per time of the fuel addition valve for injecting fuel intermittently into the exhaust passage is set within the range of 10 mm ³ to 75 mm ³ , the good combustibility is maintained and the more reliable soot It is possible to suppress the increase in the production amount of.

  When the injection period per one time of the fuel addition valve is set within a range from 1.5 ms to 15 ms, it is possible to maintain the ignitability of the fuel and ensure good combustibility.

  When the amount of fuel injected from the fuel addition valve per unit time is set within the range from 80cc / min to 1000cc / min, good initial flame formation and good flame propagation can be maintained. Therefore, good combustibility can be realized more reliably.

  By setting the area of the heat generating portion within the range of 8% to 55% with respect to the area of the injection region projected onto the plane perpendicular to the center line of the fuel injection region and including the axis of the heat generating portion, A preferable relative position between the addition valve and the heat generating portion of the ignition means can be easily set.

  Even when the fuel injected from the fuel addition valve is light oil or biofuel, ignition delay is unlikely to occur, and good flame propagation can be realized and good combustibility can be maintained.

  Only when the flow rate of the exhaust gas flowing through the exhaust passage is 50 g / s or less, the air-fuel ratio around the heat generating portion is made rich by heating the heat generating portion of the ignition means and injecting fuel from the fuel addition valve to the exhaust passage. The ignitability of the fuel can be kept good.

FIG. 1 is a conceptual diagram of an engine system in an embodiment in which an exhaust heating method according to the present invention is applied to a vehicle equipped with a compression ignition type multi-cylinder internal combustion engine. FIG. 2 is a control block diagram of the main part in the embodiment shown in FIG. FIG. 3 is an enlarged cross-sectional view of a main part of the exhaust heating apparatus in the embodiment shown in FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a flowchart showing the control procedure of the exhaust gas heating process in the present embodiment. FIG. 6 is a graph showing the relationship between the rate of collision of fuel with the heat generating portion and the amount of increase in exhaust temperature. FIG. 7 is a graph showing the relationship between the rate of fuel collision with the heat generating portion and the amount of soot generated.

  An embodiment in which an exhaust heating method according to the present invention is applied to a vehicle equipped with a compression ignition type multi-cylinder internal combustion engine will be described in detail with reference to FIGS. However, the present invention is not limited to such an embodiment, and the configuration can be freely changed according to required characteristics. For example, the present invention is also effective for a spark ignition type internal combustion engine in which gasoline, alcohol, LNG (liquefied natural gas) or the like is used as fuel and is ignited by a spark plug.

  A main part of the engine system in the present embodiment is schematically shown in FIG. 1, and a control block of the main part is schematically shown in FIG. In FIG. 1, in addition to a valve mechanism and a silencer for intake and exhaust of the engine 10, a general exhaust turbo supercharger, an EGR device, and the like are omitted as auxiliary equipment of the engine 10. It should be noted that some of the various sensors required for smooth operation of the engine 10 are omitted for convenience.

  The engine 10 according to the present embodiment is a compression ignition type multi-cylinder that spontaneously ignites by directly injecting light oil, biofuel, or a mixed fuel thereof as fuel into the combustion chamber 10a in a compressed state from the fuel injection valve 11. It is an internal combustion engine. However, a single cylinder internal combustion engine may be used due to the characteristics of the present invention.

The cylinder head 12 formed with the intake port 12a and the exhaust port 12b facing the combustion chamber 10a has a valve operating mechanism (not shown) including an intake valve 13a for opening and closing the intake port 12a and an exhaust valve 13b for opening and closing the exhaust port 12b. It has been incorporated. The previous fuel injection valve 11 facing the center of the upper end of the combustion chamber 10a is also assembled to the cylinder head 12 so as to be sandwiched between the intake valve 13a and the exhaust valve 13b. The amount and injection timing of fuel supplied to the combustion chamber 10a from the fuel injection valve 11, the ECU (E lectronic C ontrol U nit ) 15 based on operating conditions of the vehicle including the depression amount of the accelerator pedal 14 by the driver Be controlled. The amount of depression of the accelerator pedal 14 is detected by the accelerator opening sensor 16, and the detection information is output to the ECU 15.

  The ECU 15 is based on information from the accelerator opening sensor 16 and various sensors to be described later, an operation state determination unit 15a for determining the operation state of the vehicle, a fuel injection setting unit 15b, and a fuel injection valve drive unit 15c. Have The fuel injection setting unit 15b sets the fuel injection amount and the injection timing from the fuel injection valve 11 based on the determination result in the operation state determination unit 15a. The fuel injection valve drive unit 15c controls the operation of the fuel injection valve 11 so that the amount of fuel set by the fuel injection setting unit 15b is injected from the fuel injection valve 11 at the set time.

A surge tank 18 is formed in the middle of the intake pipe 17 connected to the cylinder head 12 so as to communicate with the intake port 12a and defining the intake passage 17a together with the intake port 12a. A throttle valve 20 for adjusting the opening degree of the intake passage 17 a is incorporated in the intake pipe 17 upstream of the surge tank 18 via a throttle actuator 19. Further, the intake pipe 17 upstream of the throttle valve 20, an air flow meter 21 which outputs the detected flow rate Q _A of the intake air flowing through the intake passage 17a to the ECU15 is attached. Instead of the air flow meter 21, an exhaust flow sensor having the same configuration may be attached to a portion of the exhaust pipe 23 located between an exhaust heating device 22 described later and the exhaust port 12b of the cylinder head 12.

  The previous ECU 15 further includes a throttle opening setting unit 15d and an actuator driving unit 15e. The throttle opening setting unit 15d sets the opening of the throttle valve 20 based on the determination result of the previous operation state determination unit 15a in addition to the depression amount of the accelerator pedal 14. The actuator driving unit 15e controls the operation of the throttle actuator 19 so that the throttle valve 20 has the opening set by the throttle opening setting unit 15d.

  A crank angle sensor 25 that detects the rotational phase of the crankshaft 24c to which the piston 24a is connected via the connecting rod 24b, that is, the crank angle, and outputs it to the ECU 15 is attached to the cylinder block 24 in which the piston 24a reciprocates. It has been. Based on the information from the crank angle sensor 25, the driving state determination unit 15a of the ECU 15 grasps the traveling speed of the vehicle in addition to the rotational phase of the crankshaft 24c and the engine speed in real time.

The exhaust pipe 23 connected to the cylinder head 12 so as to communicate with the exhaust port 12b defines an exhaust passage 23a together with the exhaust port 12b. An exhaust purification device 26 for detoxifying harmful substances generated by combustion of the air-fuel mixture in the combustion chamber 10a is provided in the middle of the exhaust pipe 23 upstream of the silencer (not shown) attached to the downstream end side. It is attached. Exhaust purification apparatus 26 of this embodiment includes an oxidation catalyst which is not least illustrated, it is also possible to incorporate the like In addition to this DPF (D iesel P articulate F ilter ) and _the NO _x storage catalyst. The oxidation catalyst is mainly used to oxidize, that is, burn, unburned HC contained in the exhaust gas.

  In the middle of the exhaust pipe 23 upstream of the exhaust purification device 26, a heated gas is generated and supplied to the exhaust purification device 26 disposed downstream, thereby maintaining the activation and active state of the oxidation catalyst. An exhaust heating device 22 is provided. The main part of the exhaust heating device 22 is extracted and enlarged and shown in FIG. 3, and an enlarged cross-sectional structure along the IV-IV arrow is shown in FIG. The exhaust heating device 22 in this embodiment includes a fuel addition valve 27 and a glow plug 28.

The fuel addition valve 27 has the same basic configuration as that of the normal fuel injection valve 11, and supplies an arbitrary amount of fuel to the exhaust passage 23a in a pulsed manner at arbitrary time intervals by controlling the energization time. Can be done. In this case, the injection amount per one time of the fuel addition valve that injects the fuel intermittently into the exhaust passage is set within a range from 10 mm ³ to 75 mm ³ , and the injection period per time is 1.5 ms. To 15 ms. When the fuel injection amount per time is less than 10 mm ³ or the injection period is less than 1.5 ms, the air-fuel ratio around the heat generating portion 28a of the glow plug 28 becomes too lean, and the combustion diffusion performance is deteriorated. On the contrary, if this exceeds 75 mm ³ or longer than 15 ms, the surface temperature of the heat generating portion 28a decreases due to the latent heat of vaporization of the fuel, leading to deterioration of emissions due to a decrease in combustibility and an increase in the amount of soot generation.

Therefore, by setting the injection amount per one time of the fuel addition valve within the range from 10 mm ³ to 75 mm ³ and setting the injection period per one time within the range from 1.5 ms to 15 ms, The ignitability can be maintained. In addition, it is possible to more reliably maintain good combustibility and to more reliably suppress an increase in the amount of soot generated.

  The amount of fuel per one time supplied from the fuel addition valve 27 to the exhaust passage 23a is based on the operating state of the vehicle including the intake air amount and air-fuel ratio detected by the air flow meter 21, and the fuel addition setting unit of the ECU 15 It is set by 15f. However, the amount of fuel injected from the fuel addition valve 27 per unit time is set within a range from 80 cc / min to 1000 cc / min. When the amount of fuel injected from the fuel addition valve 27 per unit time is less than 80 cc per minute, the air-fuel ratio around the heat generating portion 28a of the glow plug 28 becomes too lean, and the combustion diffusion performance is degraded. On the other hand, if this exceeds 1000 cc / min, the surface temperature of the heat generating portion 28a is lowered due to the latent heat of vaporization of the fuel, leading to deterioration in emissions due to a decrease in combustibility and an increase in the amount of soot generation.

  Therefore, by setting the injection amount per unit time of the fuel injected from the fuel addition valve 27 within a range from 80 cc / min to 1000 cc / min, a good initial flame formation and a good flame propagation state are maintained. can do. As a result, good combustibility can be more reliably realized.

  The fuel addition valve drive unit 15g of the ECU 15 controls the operation of the fuel addition valve 27 so that the amount of fuel set by the fuel addition setting unit 15f is injected from the fuel addition valve 27 at a set cycle.

The glow plug 28 as the ignition means in the present invention is connected to an on-vehicle power supply (not shown) via a glow plug drive unit 15h of the ECU 15 as an on / off switch. Therefore, switching between energization and non-energization for the glow plug 28 is controlled by the glow plug drive unit 15h of the ECU 15 in accordance with a preset program. The glow plug 28 has a heat generating portion 28a for igniting the fuel injected into the exhaust passage 23a. The heating unit 28a is injected from the fuel addition valve 27 so as to be positioned in the injection region Z _F of the fuel disperses conically, it is arranged in the exhaust passage 23a. In this case, the area of the injection region Z _F projected onto a plane containing the axis C _H of the vertical and the heat generating portion 28a with respect to the center line C _F of the injection region Z _F of the fuel (in FIG. 4, shown in a circular dashed line) in On the other hand, the area (indicated by hatching in FIG. 4) of the heat generating portion 28a overlapping with this is set in the range of 8% to 55%. When the ratio of the fuel directly in contact with the heat generating portion 28a of the glow plug 28 is less than 8%, even if the fuel colliding with the heat generating portion 28a is ignited, the oxygen concentration in the surrounding exhaust is low, so that the diffusion of the flame is suppressed. It will misfire. If this ratio is secured to 8% or more, combustion can be continued by the propagation of flame to the surrounding fuel. On the other hand, if the proportion of fuel directly in contact with the heat generating portion 28a of the glow plug 28 exceeds 55%, fuel droplets having a large particle size intervene in the flame, so that the amount of soot generated is significantly increased. By suppressing this ratio to 55% or less, a large amount of soot can be suppressed.

Therefore, by setting the area of the heat generating portion 28a to the area of the injection region Z _F 8% to 55%, without unduly cool the heat generating portion 28a, can be sufficiently form a mixture to around Thus, an increase in the amount of soot generated can be suppressed while maintaining good flammability.

  It is also possible to arrange a collision plate as disclosed in Patent Document 1 on the downstream side of the heat generating portion 28a of the glow plug 28 with respect to the fuel injection direction from the fuel addition valve 27. Due to the presence of the collision plate, the fuel supplied from the fuel supply valve 26 can be received, and the atomization and scattering toward the glow plug 28 can be promoted.

In the exhaust passage 23a on the outlet side of the exhaust purification device 26, there is a catalyst temperature sensor 29 that detects the temperature of the exhaust gas that has exited the exhaust purification device 26 (hereinafter referred to as catalyst temperature) and outputs it to the ECU 15. It has been incorporated. An exhaust temperature sensor 30 is attached to a portion of the exhaust pipe 23 located upstream from the exhaust purification device 26 and downstream from the exhaust heating device 22. The exhaust temperature sensor 30 detects the exhaust gas temperature T _E flowing through the exhaust passage 23a immediately before flowing into the exhaust purification device 26, and outputs the detected information to the ECU 13.

  The operation state determination unit 15a of the ECU 13 in the present embodiment determines the necessity of operation of the exhaust heating device 22, that is, the presence or absence of a fuel addition request, based on information from the catalyst temperature sensor 29 and the exhaust temperature sensor 30. Usually, it is determined that there is a fuel addition request when the catalyst temperature is predicted to be lower or lower than the minimum temperature at which the oxidation catalyst can maintain an active state. However, other conventionally known determination methods other than this can be appropriately employed.

In the present embodiment, when the engine 10 is in a motoring state, that is, when the opening of the accelerator pedal 14 becomes 0 and the fuel is not injected from the fuel injection valve 11 while the engine 10 is operating, the exhaust heating process is performed. Is executed as needed. That is, when it is determined that the oxidation catalyst needs to be activated or maintained, the fuel injection from the fuel addition valve 27 described above is performed to heat the exhaust flowing through the exhaust passage 23a. Therefore, when the engine 10 is in a fuel cut state, fuel is injected from the fuel addition valve 27 into the combustion chamber 30 via the fuel injection chamber 31, thereby increasing the temperature of the exhaust gas flowing through the exhaust passage 23a. However, when the flow rate Q _A of the exhaust gas flowing through the exhaust passage 23a exceeds per 50 grams, the portion of the fuel is likely also misfires as ignited by the heat generating portion 28a, so continuous combustion of the fuel is difficult The exhaust heat treatment is not performed.

FIG. 5 shows the procedure of such exhaust heat treatment. That is, it is determined whether there is a fuel addition request in step S1. Here there is a fuel addition request, that is, when the exhaust gas purification device 26 determines that it is necessary to activate, the process proceeds to S2 of the step, the determination whether the intake flow rate Q _A is less per 50 grams is Is done. Here, when it is determined that the intake air flow rate Q _A is 50 grams or less per second, that is, there is no problem even if the exhaust heating process is performed, the process proceeds to step S3 and the exhaust heating process is executed. Then, fuel is injected from the fuel addition valve 27 into the exhaust passage 23a, and this is ignited and burned by the heat generating portion 28a of the glow plug 28, thereby raising the temperature of the exhaust gas flowing through the exhaust passage 23a.

On the other hand, if it is determined in step S1 that there is no addition request, this determination is repeated without doing anything. The intake flow rate Q _A in step S2 is exceeded per second 50g ie Similarly, when it is determined that it is preferable not to perform exhaust heat treatment, without any returns to S1 in step.

  It should be noted that the present invention should be construed only from the matters described in the scope of claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are possible other than the items described. It is. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

DESCRIPTION OF SYMBOLS 10 Engine 10a Combustion chamber 11 Fuel injection valve 12 Cylinder head 12a Intake port 12b Exhaust port 13a Intake valve 13b Exhaust valve 14 Accelerator pedal 15 ECU
15a Operation state determination unit 15b Fuel injection setting unit 15c Fuel injection valve driving unit 15d Throttle opening setting unit 15e Actuator driving unit 15f Fuel addition setting unit 15g Fuel addition valve driving unit 15h Glow plug driving unit 16 Accelerator opening sensor 17 Intake pipe 17a Intake passage 18 Surge tank 19 Throttle actuator 20 Throttle valve 21 Air flow meter 22 Exhaust heating device 23 Exhaust pipe 23a Exhaust passage 24 Cylinder block 24a Piston 24b Connecting rod 24c Crankshaft 25 Crank angle sensor 26 Exhaust purification device 27 Fuel addition valve 28 Glow plug 28a Heating section 29 Catalyst temperature sensor 30 Exhaust temperature sensor C Center line of _CF injection area C Axis line of _H heating section Q _A Intake flow rate T _E Exhaust temperature Z _F Fuel injection area

Claims (7)

Fuel is injected from the fuel addition valve to the exhaust passage toward the heat generating part of the ignition means arranged in the exhaust passage upstream of the exhaust purification device, and the exhaust led to the exhaust purification device is heated by igniting the fuel. A way to
An exhaust heating method, wherein a ratio of fuel directly in contact with the heat generating portion of fuel injected from the fuel addition valve is set in a range of 8% to 55%. 2. The exhaust heating method according to claim 1, wherein an injection amount per one time of the fuel addition valve for injecting fuel intermittently into the exhaust passage is set within a range of 10 mm ³ to 75 mm ³ .   The exhaust heating method according to claim 2, wherein an injection period per one time of the fuel addition valve is set in a range from 1.5 ms to 15 ms.   The exhaust according to any one of claims 1 to 3, wherein an injection amount of fuel injected from the fuel addition valve per unit time is set in a range from 80 cc / min to 1000 cc / min. Heating method.   The fuel injected from the fuel addition valve diffuses in a conical shape, and the area of the injection region projected onto a plane perpendicular to the center line of the fuel injection region forming the conical shape and including the axis of the heat generating portion On the other hand, the exhaust heating method according to any one of claims 1 to 4, wherein an area of the heat generating portion overlapping therewith is set within a range of 8% to 55%.   The exhaust heating method according to any one of claims 1 to 5, wherein fuel injected from the fuel addition valve is light oil or biofuel.   2. The apparatus according to claim 1, wherein the heating portion of the ignition means is heated and fuel is injected from the fuel addition valve into the exhaust passage only when the flow rate of the exhaust gas flowing through the exhaust passage is 50 grams or less per second. The exhaust heating method according to any one of 6.

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