JP6044192B2 - Fuel injection method and exhaust system - Google Patents

Description

  The present invention relates to an exhaust system in which gas heated by a burner device is mixed with exhaust gas flowing through an exhaust flow path to assist oxidation of the catalyst, and a fuel injection method for injecting fuel with the burner device in the exhaust system About.

  In some cases, fuel is further burned in the exhaust gas from the engine. For example, the regeneration process of the particulate filter which removes particulate matter (PM: Particulate Matter), such as soot, contained in exhaust gas in a diesel engine corresponds to it (for example, patent document 1).

  In such regeneration treatment, the temperature of the exhaust gas is raised by an oxidation reaction via a catalyst. In order to quickly raise the catalyst to the activation temperature, the air is heated with a separate heater and introduced into the exhaust gas (for example, Patent Document 2), or fuel is injected into the exhaust passage (for example, Patent Document 3). ) The technology is known.

JP-A-5-222913 JP 2005-320880 A JP 2007-154772 A

  As a heat source that assists in raising the temperature of the catalyst, there is a burner device that raises the temperature of exhaust gas in addition to the heater and the fuel injection mechanism described above. The burner device introduces a part of the exhaust gas into the combustion chamber of the burner device itself, mixes it with air or the like, burns and raises the temperature, and returns the heated exhaust gas to the original flow path of the exhaust gas. By doing so, the downstream catalyst can be rapidly raised to the activation temperature.

  In such a burner device, for example, the outer wall of the burner device is preheated, a part of the exhaust gas is mixed with air and introduced into the combustion chamber, and fuel is injected into the combustion chamber to burn and raise the temperature. The operation is started by sequentially executing. In the combustion chamber, only a small amount of fuel is injected after the operation is started, and rated fuel is injected when the temperature of the combustion chamber rises and ignition is confirmed.

  However, when operating with low cetane number fuels or biofuels, the rate of temperature rise is relatively low in a low temperature environment, and unburned fuel that has not been burned out is included in the exhaust gas when the burner system starts operating. Sometimes it was. Further, since the temperature increase rate varies depending on the cetane number, it has been difficult to completely control the burner apparatus so as not to discharge unburned fuel.

  The present invention has been made in view of such problems, and an object thereof is to provide a fuel injection method and an exhaust system that can reduce the discharge of unburned fuel regardless of the cetane number.

  In order to solve the above problem, the temperature of the exhaust gas is raised by a particulate filter that collects particulate matter contained in the exhaust gas exhausted from the engine, and an oxidation reaction that is provided upstream of the particulate filter and through a catalyst. And a part of the exhaust gas introduced from the exhaust passage so that the catalyst reaches the activation temperature and combusted using the fuel, and a part of the combusted exhaust gas is exhausted. A fuel injection method according to the present invention, in which fuel is injected in an exhaust system including a burner device that leads to a flow path and a burner temperature detection unit that detects the temperature of the burner device, preheats the burner device and determines in advance. The fuel is started to be injected at the first injection amount, and the temperature detected by the burner temperature detection unit is determined whether the temperature detected by the burner temperature detection unit is equal to or higher than a predetermined first threshold value. It measures a passage of time from a first threshold value or more, exceeds the elapsed waiting time period is predetermined, characterized by injecting fuel in the second injection amount larger than the first injection amount.

  The waiting time may be determined based on the cetane number of the fuel.

  The exhaust system further includes a flow path temperature detection unit that detects a temperature at an arbitrary position downstream of the burner device in the exhaust flow path, and the cetane number is estimated based on a transition of the temperature detected by the flow path temperature detection unit. May be.

  The burner device includes a primary combustion chamber provided with a primary fuel supply unit, and a secondary combustion provided with a secondary fuel supply unit provided downstream of the primary combustion chamber and having a higher rated fuel injection amount than the primary fuel supply unit. A timing at which the primary fuel supply unit switches the injection amount from the first injection amount to the second injection amount and the secondary fuel supply unit switches from the first injection amount to the second injection amount. Then, fuel injection may be started.

  In order to solve the above-described problems, an exhaust system according to the present invention includes a particulate filter that collects particulate matter contained in exhaust gas discharged from an engine, and an oxidation that is provided upstream of the particulate filter and that passes through a catalyst. An oxidation catalyst part that raises the temperature of the exhaust gas by reaction, and a part of the exhaust gas is introduced from the exhaust passage so that the catalyst is at the activation temperature provided upstream of the oxidation catalyst part and burned with fuel, and burned A burner device for deriving a part of the exhaust gas to the exhaust passage, a burner temperature detection unit for detecting the temperature of the burner device, and fuel injection at a predetermined first injection amount; It is determined whether or not the detected temperature is equal to or higher than a predetermined first threshold, and the elapsed time after the temperature detected by the burner temperature detecting unit is equal to or higher than the first threshold is measured. Beyond the standby time, characterized by comprising a fuel supply unit for injecting the fuel in the second injection amount larger than the first injection amount.

  According to the present invention, it is possible to reduce the discharge of unburned fuel regardless of the cetane number.

It is explanatory drawing for demonstrating the exhaust system of a diesel engine. It is explanatory drawing for demonstrating the structure of a burner apparatus. It is explanatory drawing which compared the required air quantity at the time of idling of a diesel engine. It is a flowchart for demonstrating the fuel-injection timing in case a cetane number is high. It is a timing chart for demonstrating the fuel-injection timing in case a cetane number is high. It is a timing chart for demonstrating the fuel-injection timing in case a cetane number is low. It is a flowchart for demonstrating the other fuel-injection timing when a cetane number is low. 6 is a timing chart for explaining another fuel injection timing when the cetane number is low. It is a flowchart for demonstrating the other fuel-injection timing when a cetane number is low. 6 is a timing chart for explaining another fuel injection timing when the cetane number is low.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Exhaust system)
FIG. 1 is an explanatory diagram for explaining an exhaust system of the diesel engine 1. As shown in FIG. 1A, the diesel engine 1 is a reciprocating engine. Specifically, the air in the cylinder is compressed by a piston to increase the temperature and pressure, and the light oil and heavy oil stored in the fuel tank 2 are stored. The fuel pump 3 or the injection pump 4 is pressurized and injected into the high-temperature and high-pressure air to cause an explosion, and the energy generated by the explosion is converted into power. The supercharger 5 is a device that improves the engine output by rotating the turbine with the energy of the exhaust gas of the diesel engine 1 and compressing the intake air to increase the intake pressure.

  The exhaust passage 6 is configured by piping for exhausting the exhaust gas discharged from the exhaust port of the diesel engine 1 to the outside. The exhaust passage 6 includes a burner device 7 and a passage temperature detector in order from the upstream side. 8, Diesel Oxidation Catalyst (DOC) 9 and Diesel Particulate Filter (DPF) 10 are provided. The flow path temperature detection unit 8 is provided at an arbitrary position downstream of the burner device 7 in the exhaust flow path 6, in this embodiment, upstream of the diesel oxidation catalyst section 9, and the temperature of the exhaust flow path 6 (diesel oxidation catalyst section) 9 inlet temperature). The exhaust system includes a burner device 7, a flow path temperature detection unit 8, a diesel oxidation catalyst unit 9 as an oxidation catalyst unit, and a diesel particulate filter 10 as a particulate filter. Hereinafter, functions of the diesel particulate filter 10, the diesel oxidation catalyst unit 9, and the burner device 7 will be described in this order.

(Diesel particulate filter 10)
As shown in the longitudinal sectional view of FIG. 1B, the diesel particulate filter 10 is composed of a porous body 10a in which ceramic or metal is formed in a honeycomb structure. The diesel particulate filter 10 collects particulate matter 20 having a size of, for example, 10 microns or more contained in the exhaust gas of the diesel engine 1 (indicated by an arrow in FIG. 1B), and extracts the particulate matter 20 from the exhaust gas. The particulate matter 20 is separated. The exhaust gas from which the particulate matter 20 is thus separated is discharged to the outside. At this time, if the particulate matter 20 is excessively deposited on the diesel particulate filter 10, the porous body 10a may be clogged. Clogging causes an increase in exhaust pressure, leading to deterioration in fuel consumption and output. Therefore, the following diesel oxidation catalyst unit 9 is provided.

(Diesel oxidation catalyst part 9)
The diesel oxidation catalyst unit 9 is provided upstream of the diesel particulate filter 10 and is made of a catalyst such as platinum or palladium. Then, the oxygen contained in the exhaust gas of the diesel engine 1 is utilized to raise the temperature of the exhaust gas by catalytic combustion of unburned fuel (oxidation via the catalyst). The heated exhaust gas flows to the downstream diesel particulate filter 10, burns (oxidizes) the particulate matter 20 deposited on the diesel particulate filter 10 and exhausts it as carbon dioxide, and the diesel particulate filter 10 Clear clogging. Such a series of processing is referred to as filter regeneration processing in the present embodiment.

  Such a filter regeneration process is a batch process that is executed for a desired time at a desired timing until the clogging of the diesel particulate filter 10 exceeds a predetermined threshold and the clogging is eliminated to some extent. It is. However, the diesel oxidation catalyst unit 9 may not reach an activation temperature at which the temperature of the exhaust gas is low and oxidation is promoted when the diesel engine 1 is started or when the load is low, and the exhaust gas cannot be heated up. In the diesel particulate filter 10 located downstream, the filter regeneration process may not be performed at a desired timing. Therefore, in the present embodiment, the following burner device 7 is provided.

(Burner device 7)
FIG. 2 is an explanatory diagram for explaining the structure of the burner device 7. In the present embodiment, the X axis, the Y axis, and the Z axis that intersect perpendicularly are defined as shown in FIG. The burner device 7 raises the temperature of the gas and raises the temperature of the exhaust gas in addition to the exhaust gas discharged from the exhaust port of the diesel engine 1. In this way, the temperature increase of the diesel oxidation catalyst unit 9 can be assisted. That is, it is possible to perform the filter regeneration process by raising the diesel oxidation catalyst unit 9 to the activation temperature at a desired timing.

  The specific structure of the burner device 7 will be described. The outer wall 50 of the burner device 7 is formed in, for example, a rectangular tube shape, and the lower end in the direction along the Z axis communicates with the exhaust flow path 6. The end is occluded. A first partition member 52 that partitions the inside of the outer wall 50 in the X-axis direction is disposed inside the outer wall 50. The first partition member 52 is made of, for example, a rectangular plate, and three of the outer peripheral side surfaces are fixed to the closed surface of the outer wall 50 and the inner peripheral surface in the Y-axis direction, and the other one side surface is the exhaust flow. It protrudes to the path 6 (flame holding plate 52a). The outer wall 50 and the first partition member 52 form an inflow path 54. The inflow passage 54 has an opening 54 a that opens to the exhaust passage 6, and a part (for example, about 20%) of the exhaust gas flowing through the exhaust passage 6 is directly or the exhaust passage 6. It collides with the flame-holding plate 52a protruding in the direction and flows into the inflow path 54 from the opening 54a.

  Of the spaces partitioned by the first partition member 52 inside the outer wall 50, the space located downstream in the X-axis direction is further partitioned by the second partition member 56 in the Z-axis direction. The second partition member 56 is made of, for example, a rectangular plate material, and the outer peripheral side surface is fixed to the first partition member 52 and the inner peripheral surface of the outer wall 50. The space above the Z axis partitioned by the second partition member 56 is a primary combustion chamber 58 for generating a flame, and the space below the Z axis is a secondary combustion chamber 60 for promoting combustion.

  The gas supply unit 62 is configured by, for example, an air pump, and supplies a gas other than the exhaust gas, that is, air in the present embodiment, to the primary combustion chamber 58, and assists the generation of a flame in the primary combustion chamber 58. The gas supply unit 62 is not limited to an air pump, and may be configured with a fan, a compressor, or the like. Here, the first partition member 52 is provided with a hole 52b penetrating from the inflow path 54 to the primary combustion chamber 58, and air is guided to the primary combustion chamber 58 by the hole 52b. The hole 52b also serves to limit the air flow rate.

  However, if only air is introduced into the primary combustion chamber 58, the temperature of the air must be raised to some extent, and the absolute amount of air required to generate a flame increases. Therefore, in the present embodiment, as described above, a part of the exhaust gas is caused to flow from the exhaust passage 6 to the inflow passage 54 to generate an air-fuel mixture (hereinafter simply referred to as an air mixture). Then, the air mixture is introduced into the primary combustion chamber 58.

  FIG. 3 is an explanatory diagram comparing the required amount of air when the diesel engine 1 is idling. As can be understood with reference to FIG. 3, when the exhaust gas is mixed with the air, the required amount of air can be reduced at each engine speed as compared with the case where only the air is introduced without using the exhaust gas.

  Returning to FIG. 2, the first partition member 52 is provided with a hole 52 c penetrating from the inflow path 54 to the secondary combustion chamber 60, and the exhaust gas is guided to the secondary combustion chamber 60 by the hole 52 c. It is burned. The holes 52 c also serve to limit the flow rate of the exhaust gas that is guided to the secondary combustion chamber 60.

  Further, the second partition member 56 is provided with a hole 56a penetrating from the primary combustion chamber 58 to the secondary combustion chamber 60, and the air mixture burned in the primary combustion chamber 58 by the hole 56a is subjected to secondary combustion. Guided to chamber 60. The hole 56a also serves to limit the flow rate of the air-fuel mixture. Thus, the flow rate of the air-fuel mixture in the primary combustion chamber 58 and the secondary combustion chamber 60 is suppressed, so that the ignitability and flame holding performance are improved in the primary combustion chamber 58, and the flame in the secondary combustion chamber 60 is improved. The temperature range and oxygen concentration range where combustion can be started can be expanded.

  The primary fuel supply unit (fuel supply unit) 70 is constituted by a fuel injection device such as an injector having a nozzle, for example, and supplies the fuel to the primary combustion chamber 58 in the form of a mist. The ignition unit 72 is configured by an ignition device such as a glow plug, for example, and is heated to a temperature equal to or higher than the ignition temperature of the fuel to ignite the fuel and air mixture vaporized by the heat of the ignition unit 72.

  The fuel holding part 72a is disposed in the vicinity of the ignition part 72, for example, at a position covering one end of the ignition part 72, and is, for example, porous such as a wire mesh, sintered metal, metal fiber, glass cloth, ceramic porous body, ceramic fiber, pumice, etc. The air mixture is guided from the hole 52b, and the fuel is temporarily held until the fuel supplied from the primary fuel supply unit 70 is combusted. Here, the fuel holding portion 72a may be a catalyst formed as a porous body.

  The baffle plate 74 is made of, for example, a rectangular plate material, one end is fixed to the closing surface of the outer wall 50, and the other end side is disposed at a position facing the hole 52b. The baffle plate 74 prevents the air mixture flowing into the primary combustion chamber 58 through the holes 52 b from directly colliding with the ignition unit 72. With this configuration, the flow velocity of the air-fuel mixture in the vicinity of the ignition unit 72 can be suppressed, and the ignitability is improved.

  Similar to the primary fuel supply unit 70, the secondary fuel supply unit 76 is configured by a fuel injection device such as an injector and supplies the fuel into the secondary combustion chamber 60 in the form of a mist. In the present embodiment, the secondary fuel supply unit 76 has a higher rated fuel injection amount than the primary fuel supply unit 70. In the secondary combustion chamber 60, in order to amplify the seed fire generated in the primary combustion chamber 58, fuel is further injected by the secondary fuel supply unit 76, and combustion of the air-fuel mixture is promoted while entraining exhaust gas. At this time, the flame holding plate 52 a protruding into the exhaust passage 6 is located upstream of the secondary combustion chamber 60 and prevents the exhaust gas from flowing directly into the secondary combustion chamber 60 from the exhaust passage 6. Thus, stable combustion is maintained in the secondary combustion chamber 60.

  Then, the high-temperature air mixture after the temperature rises flows into the exhaust passage 6 and mixes with the exhaust gas that has not flowed into the burner device 7 to increase the temperature of the exhaust gas. Thus, the diesel oxidation catalyst unit 9 is heated to the activation temperature, and the filter regeneration process can be performed in the diesel particulate filter 10.

  By the way, when the operation of the burner device 7 is started, the primary fuel supply unit 70 injects a predetermined small amount (first injection amount) of fuel and starts combustion. While the primary fuel supply unit 70 is injecting the first injection amount of fuel, the burner temperature detection unit 78 causes the inside of the primary combustion chamber 58 or the secondary combustion chamber 60 (in the present embodiment, the primary combustion chamber). 58) is detected, and when the temperature is equal to or higher than a predetermined first threshold value, it is considered that the fuel has been ignited (a flame has been generated), and the primary fuel supply unit 70 and the secondary fuel supply unit 76 The final injection quantity is adjusted by adjusting the injection quantity. Below, the fuel-injection method which shows the timing of the fuel-injection in the burner apparatus 7 is demonstrated concretely.

(Fuel injection method)
FIG. 4 is a flowchart for explaining the fuel injection timing when the cetane number is high, and FIG. 5 is a timing chart for explaining the fuel injection timing when the cetane number is high. Hereinafter, the detailed operation at the start of operation will be described with reference to FIGS. 4 and 5. Here, the cetane number indicates the ignitability of the fuel, and the higher the cetane number, the easier it is to ignite spontaneously, and the lower the cetane number, the harder it is to ignite. When the operation of the burner device 7 is started, first, the ignition unit 72 is turned on (S200). As shown in FIG. 5 (a), the ignition unit 72 causes the outer wall 50 of the burner device 7, particularly the primary combustion chamber 58 and The part corresponding to the secondary combustion chamber 60 is preheated.

  For example, 30 seconds after the ignition unit 72 is turned on (YES in S202), the gas supply unit 62 starts supplying air, and an air mixture is supplied to the primary combustion chamber 58 as shown in FIG. 5B. Is introduced (S204). For example, 10 seconds after the air-fuel mixture is introduced (YES in S206), the primary fuel supply unit 70 injects a first injection amount of fuel and starts combustion as shown in FIG. 5C. (S208). Then, as shown in FIG. 5 (d), the temperature of the burner device 7 detected by the burner temperature detector 78 is slightly lowered by the heat of vaporization, and then rises according to combustion.

  Subsequently, the temperature of the burner device 7 is monitored (S210). When the temperature of the burner device 7 is equal to or higher than the first threshold (YES in S210), it is considered that the fuel has been ignited (a flame has been generated). The injection amount of the primary fuel supply unit 70 is set to the second injection amount that is the rated injection amount as shown in FIG. 5C, and the injection of the secondary fuel supply unit 76 is started as shown in FIG. The injection amount is set as the rated injection amount (S212).

  At this time, the primary fuel supply unit 70 and the secondary fuel supply unit 76 do not set the second injection amount and the rated injection amount at a time, but gradually increase them along a predetermined inclination. This is because unburned fuel is not discharged due to a sudden increase in fuel. Here, as shown in FIGS. 5 (c) and 5 (e), the inclination of the primary fuel supply unit 70 is larger than the inclination of the secondary fuel supply unit 76 because the primary combustion chamber 58 is in the secondary combustion chamber. This is because it is easier to warm than 60, and unburned fuel is not discharged even if the inclination angle is increased.

  Thereafter, through PID (Proportional Integral Differential) control, the injection amounts of the primary fuel supply unit 70 and the secondary fuel supply unit 76 are finely adjusted so that the temperature of the burner device 7 becomes the target temperature (S214). As shown in (f), a stable temperature transition of the exhaust passage 6 (inlet of the diesel oxidation catalyst unit 9) can be obtained. Thus, the diesel oxidation catalyst unit 9 can be heated to the activation temperature.

  However, when the temperature of the burner device 7 becomes equal to or higher than the first threshold as described above, the fuel injection amount of the primary fuel supply unit 70 and the secondary fuel supply unit 76 starts to increase uniquely. When a fuel having a low cetane number is used, unburned fuel may be discharged.

  FIG. 6 is a timing chart for explaining the fuel injection timing when the cetane number is low. The timing chart of FIG. 6 is substantially the same as the timing chart of FIG. 5 except for the transition related to the difference in cetane number, and therefore, detailed description thereof is omitted here, and only the transition regarding the difference in cetane number is described. .

  In FIG. 6, as in FIG. 5, the operation of the burner device 7 is started, and when the temperature of the burner device 7 becomes equal to or higher than the first threshold, it is considered that the fuel has been ignited, and as shown in FIG. The injection amount of the unit 70 is set as the second injection amount that is the rated injection amount, and the injection of the secondary fuel supply unit 76 is started as shown in FIG. However, a fuel having a low cetane number has a relatively low temperature rising rate as compared with a fuel having a high cetane number, so that the temperature gradient of the exhaust passage 6 becomes small as shown in FIG. It takes time to reach the temperature (second threshold value) at which sufficient combustion occurs.

  Then, when the temperature is not sufficiently raised, the rated injection amount of fuel is injected from the primary fuel supply unit 70 and the secondary fuel supply unit 76 as shown in FIGS. 6C and 6E. The low cetane number causes the fuel indicated by hatching to be discharged as unburned fuel, resulting in white smoke. Here, the injection timings of the primary fuel supply unit 70 and the secondary fuel supply unit 76 are adjusted so as to suppress the discharge of unburned fuel.

  FIG. 7 is a flowchart for explaining another fuel injection timing when the cetane number is low, and FIG. 8 is a timing chart for explaining another fuel injection timing when the cetane number is low. The flowchart of FIG. 7 and the timing chart of FIG. 8 are substantially the same as the flowchart of FIG. 4 and the timing chart of FIG. 6 except for the injection timing of the primary fuel supply unit 70 and the secondary fuel supply unit 76. Detailed description is omitted, and only the injection timings of the primary fuel supply unit 70 and the secondary fuel supply unit 76 are described.

  Here, as in FIGS. 4 and 6, the operation of the burner device 7 is started, and when the temperature of the burner device 7 becomes equal to or higher than the first threshold (YES in S210), it is considered that the fuel has been ignited. However, the injection amount of the primary fuel supply unit 70 maintains the first injection amount as it is, and the secondary fuel supply unit 76 does not start the injection. And the outer wall 50 of the burner apparatus 7 is preheated only with the fuel of the 1st injection quantity. Here, since the cetane number of the fuel is low, the temperature of the exhaust passage 6 only rises gradually as shown in FIG. 8 (f), but the temperature of the exhaust passage 6 also increases as the time elapses. The temperature rises to a sufficient level for burning.

  At this time, in the burner device 7, after the temperature of the burner device 7 becomes equal to or higher than the first threshold, a timer (not shown) is operated to measure the elapsed time (S250). Then, as shown in FIG. 8C, when the elapsed time exceeds a predetermined standby time t1 (YES in S252), the injection amount of the primary fuel supply unit 70 is set to the second injection amount that is the rated injection amount. At the same time, as shown in FIG. 8E, the injection of the secondary fuel supply unit 76 is started (S212).

  With such a configuration, the fuel in the primary fuel supply unit 70 and the secondary fuel supply unit 76 is increased after the temperature of the exhaust passage 6 rises to a temperature at which the fuel is sufficiently combusted, so that unburned fuel is discharged. (Or very little unburned fuel is emitted).

  Further, the above-described standby time t1 is determined based on the cetane number of the fuel. Therefore, if the correspondence between the cetane number and the standby time t1 is tabulated or expressed as a function, the standby time t1 can be easily set in the burner device 7 if the cetane number of the fuel can be grasped in advance.

  Thus, the fuel injection timing of the primary fuel supply unit 70 and the secondary fuel supply unit 76 can be set based on the appropriate standby time t1 according to the cetane number of the fuel, and the discharge of unburned fuel can be minimized. It becomes possible to limit to the limit.

  In addition, the operating conditions of the burner device 7 may change by mixing fuels having different cetane numbers or by replacing fuels having arbitrary cetane numbers with fuels having different cetane numbers. In this case, it is also possible to estimate the cetane number using the flow path temperature detection unit 8 and automatically set the standby time t1. Since the cetane number represents ignitability and is reflected in the rate of temperature increase, it corresponds to the transition of the temperature detected by the flow path temperature detector 8, specifically, the temperature rising gradient. Therefore, the cetane number can be estimated by an arbitrary gradual increase function based on the differential value of the temperature rise detected by the flow path temperature detecting unit 8, and the standby time t1 can be automatically set accordingly.

  Further, instead of waiting for the waiting time t1 to elapse after the temperature of the burner device 7 becomes equal to or higher than the first threshold value, the primary fuel supply is performed based on the temperature of the exhaust flow path 6 using the flow path temperature detection unit 8. The fuel injection timing of the unit 70 and the secondary fuel supply unit 76 can also be determined.

  FIG. 9 is a flowchart for explaining another fuel injection timing when the cetane number is low, and FIG. 10 is a timing chart for explaining another fuel injection timing when the cetane number is low. The flowchart in FIG. 9 and the timing chart in FIG. 10 are substantially the same as the flowchart in FIG. 7 and the timing chart in FIG. 8 except for the injection timing of the primary fuel supply unit 70 and the secondary fuel supply unit 76. Detailed description is omitted, and only the injection timings of the primary fuel supply unit 70 and the secondary fuel supply unit 76 are described.

  Here, even when the operation of the burner device 7 is started and the temperature of the burner device 7 becomes equal to or higher than the first threshold value, the injection amount of the primary fuel supply unit 70 remains as it is as in FIG. The secondary fuel supply unit 76 does not start injection. And the outer wall 50 of the burner apparatus 7 is preheated only with the fuel of the 1st injection quantity. Again, since the cetane number of the fuel is low, as shown in FIG. 10 (f), the temperature of the exhaust passage 6 only rises gradually, but the temperature of the exhaust passage 6 also increases as the time elapses. The temperature rises to a sufficient level for burning.

  In the burner device 7, the temperature of the exhaust flow path 6 is monitored by the flow path temperature detection unit 8 without using a timer for measuring elapsed time as shown in FIG. It is determined whether or not this is the case (S260). As shown in FIG. 10 (f), when the temperature of the exhaust passage 6 becomes equal to or higher than the second threshold (YES in S260), the injection amount of the primary fuel supply unit 70 is changed to the rated injection amount as shown in FIG. 10 (c). And the injection of the secondary fuel supply unit 76 is started as shown in FIG. 10E (S212).

  With such a configuration, it can be directly determined that the temperature of the exhaust passage 6 has risen to a temperature at which the fuel is sufficiently combusted, and after reaching the temperature accurately, the fuel in the primary fuel supply unit 70 and the secondary fuel supply unit 76 As a result, unburned fuel is not discharged.

  Further, since it is directly determined that the temperature of the exhaust passage 6 has risen to a temperature at which the fuel is sufficiently combusted, even if the cetane number of the fuel is different and the temperature transition of the exhaust passage 6 changes, There are no parameters to be changed such as the waiting time t1. Therefore, it has versatility for fuels having different cetane numbers.

  As described above, according to the exhaust system and the fuel injection method of the present embodiment, it is possible to reduce the discharge of unburned fuel regardless of the cetane number. Further, since the unburned fuel is reduced, the cooling effect by the unburned fuel is reduced, the diesel oxidation catalyst unit 9 is efficiently heated to the activation temperature, and the filter regeneration process is quickly performed in the diesel particulate filter 10. And it becomes possible to carry out stably.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  Note that each step of the fuel injection method of the present specification does not necessarily have to be processed in time series in the order described in the flowchart, and may include processing in parallel or by a subroutine.

  The present invention relates to an exhaust system in which gas heated by a burner device is mixed with exhaust gas flowing through an exhaust flow path to assist oxidation of the catalyst, and a fuel injection method for injecting fuel with the burner device in the exhaust system Can be used.

1 ... Diesel engine (engine)
6 ... Exhaust flow path 7 ... Burner device 8 ... Flow path temperature detection part 9 ... Diesel oxidation catalyst part (oxidation catalyst part)
10 ... Diesel particulate filter (particulate filter)
58 ... primary combustion chamber 60 ... secondary combustion chamber 70 ... primary fuel supply section (fuel supply section)
76 ... Secondary fuel supply part 78 ... Burner temperature detection part

Claims (5)

A particulate filter that collects particulate matter contained in exhaust gas discharged from the engine, an oxidation catalyst unit that is provided upstream of the particulate filter and that raises the temperature of the exhaust gas by an oxidation reaction via a catalyst; A part of the exhaust gas is introduced from an exhaust passage so as to reach an activation temperature provided at the upstream side of the oxidation catalyst unit, and is burned with fuel, and a part of the combusted exhaust gas is discharged into the exhaust stream. A fuel injection method for injecting the fuel in an exhaust system comprising a burner device that leads to a road and a burner temperature detection unit that detects the temperature of the burner device,
Preheat the burner device;
Start fuel injection at a predetermined first injection amount;
Determining whether the temperature detected by the burner temperature detector is equal to or higher than a predetermined first threshold;
Measure the elapsed time after the temperature detected by the burner temperature detection unit is equal to or higher than the first threshold,
When the elapsed time exceeds a predetermined standby time, fuel is injected with a second injection amount that is greater than the first injection amount.   The fuel injection method according to claim 1, wherein the waiting time is determined based on a cetane number of the fuel. The exhaust system further includes a flow path temperature detection unit that detects a temperature at an arbitrary position downstream of the burner device in the exhaust flow path,
The fuel injection method according to claim 2, wherein the cetane number is estimated based on a transition of temperature detected by the flow path temperature detection unit. The burner device is provided with a primary combustion chamber provided with a primary fuel supply unit, and a secondary fuel supply unit provided downstream of the primary combustion chamber and having a higher rated fuel injection amount than the primary fuel supply unit. A secondary combustion chamber,
The primary fuel supply unit performs injection by switching an injection amount from the first injection amount to the second injection amount,
The secondary fuel supply unit, the first switched from the injection amount to the second injection amount timing, fuel according to any one of claims 1 to 3, characterized in that to start the injection of fuel Injection method. A particulate filter that collects particulate matter contained in the exhaust gas discharged from the engine;
An oxidation catalyst unit that is provided upstream of the particulate filter and that raises the temperature of the exhaust gas by an oxidation reaction via a catalyst;
A part of the exhaust gas is introduced from an exhaust passage so as to reach an activation temperature, and is burned using fuel so that the catalyst has an activation temperature, and a part of the combusted exhaust gas is discharged into the exhaust stream. A burner device leading to the road;
A burner temperature detector for detecting the temperature of the burner device;
Fuel injection is started at a predetermined first injection amount, and it is determined whether or not the temperature detected by the burner temperature detection unit is equal to or higher than a predetermined first threshold, and the burner temperature detection unit detects A fuel supply unit that measures an elapsed time after the temperature becomes equal to or higher than the first threshold and injects fuel with a second injection amount that is greater than the first injection amount when the elapsed time exceeds a predetermined standby time. When,
An exhaust system characterized by comprising:

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