JP2013124636A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine that improves instability of ignition caused by deterioration in an actual compression ratio due to application of a mirror cycle, in a diesel engine to which the mirror cycle is applied, that is, a compression ignition engine.SOLUTION: A diesel engine includes: a combustion chamber 9; a fuel injection valve 19 which injects a pressed fuel to the combustion chamber 9; an intake valve 15 for opening and closing an intake port 11 for causing air to flow into the combustion chamber 9; an intake valve actuating valve mechanism 16 for actuating the intake valve 15 with an opening and closing timing of the mirror cycle; an ignition plug 21 disposed in the combustion chamber 9; and an ignition plug control device 23 for controlling an ignition timing or ignition period of the ignition plug 21 and, in such an operation state that ignition property of injection fuel is deteriorated, forcibly ignites the fuel.

Description

  The present invention relates to a four-cycle diesel engine, and more particularly to improvement in ignitability when operating by applying a mirror cycle.

The Miller cycle engine is known as a technology that can achieve a high thermal efficiency, a reduction in pump loss, and an improvement in fuel consumption by suppressing the substantial compression ratio by reducing the charging efficiency of intake air.
In this mirror cycle, the timing of closing the intake valve in the intake stroke is divided into a method of shutting off the intake flow in the middle of the intake stroke by early closing and a method of releasing the intake pressure at the beginning of the compression stroke by closing the intake valve late. FIG. 9 shows an outline of a PV diagram in the case of early closing of intake air as an example.
The compression stroke volume S1 is set to be lower than the expansion stroke volume S2, so that the expansion ratio can be set large and the work amount can be increased. In addition, Vb / Va: expansion ratio, Vc / Va: actual compression ratio.

Even in a four-cycle diesel engine, application of the mirror cycle is effective as a measure for reducing NOx and improving fuel efficiency. As the mirror ratio is increased and the actual compression ratio is lowered, the compression temperature is lowered and the NOx reduction effect is obtained.
For example, the characteristic diagram of FIG. 10 shows the relationship of NOx emission when the valve is quickly closed at a position θ degrees before the bottom dead center of the intake valve. From FIG. 10, as the degree of early closing increases, the NOx emission amount decreases, and the NOx reduction effect by the mirror cycle increases.

  As described above, the application of the mirror cycle is effective as a measure for reducing NOx and improving fuel consumption. The higher the mirror degree (early closing degree) and the lower the actual compression ratio, the lower the compression temperature, and the NOx reduction effect can be obtained. On the other hand, there is a problem that the ignitability of the fuel is lowered due to the reduction of the compression temperature.

  In order to deal with this problem of ignitability, for example, Patent Document 1 (Japanese Patent Laid-Open No. 7-301107) discloses an operation of an intake valve by a rocker arm and a hydraulic cylinder in an intake valve device incorporated in an engine cylinder head. By switching between the intake valve and the engine, the engine is operated in a mirror cycle at high speeds, and the conventional cycle is operated at low speeds to stabilize ignition without lowering the effective compression ratio at low speeds. Is disclosed.

JP-A-7-301107

  However, the technique for stabilizing the ignitability disclosed in Patent Document 1 requires that both a mechanism using a rocker arm mechanism and a mechanism using a hydraulic cylinder mechanism be provided for the valve mechanism of the intake valve. There is a problem that the structure of the valve mechanism is complicated, leading to an increase in size and weight of the engine.

  Therefore, the present invention has been made in view of such problems, and in a diesel engine, that is, a compression ignition engine, in which a mirror cycle is applied, improves the instability of ignition by reducing the actual compression ratio. With the goal.

  In order to achieve the above object, a diesel engine according to the present invention includes a combustion chamber that compresses intake air with a piston, a fuel injection valve that injects pressurized fuel into the combustion chamber, and the combustion chamber. An intake valve that opens and closes an intake port through which air flows in, an intake valve valve mechanism that operates the intake valve at the opening and closing timing of a mirror cycle, an ignition plug provided in the combustion chamber, and an ignition timing of the ignition plug Or, it is provided with a spark plug control device that controls the ignition period to forcibly ignite the fuel when the ignitability of the injected fuel decreases.

According to this invention, the ignition plug control device is provided in the combustion chamber in an operating state in which a decrease in the ignitability of the fuel due to a decrease in the actual compression ratio by applying the Miller cycle leads to an engine failure. The ignition plug is operated to forcibly ignite the fuel. Therefore, even if the actual compression ratio is lowered by applying the mirror cycle, ignition can be performed reliably.
As a result, the NOx reduction effect by applying the mirror cycle can be obtained without reducing the ignitability.

  In the present invention, it is preferable that the operating state in which the ignitability is lowered is when the engine is started, and the spark plug control device operates the spark plug for a predetermined time from the start of the engine.

In this way, the ignition plug is operated for a predetermined period from the start to forcibly ignite the fuel, and after a certain period of time, self-ignition by compression ignition is performed without ignition by the ignition plug. Of white smoke due to poor start-up and incomplete combustion.
Further, the ignition plug can be extended in life by performing ignition with the spark plug only at the time of start-up or warm-up with poor ignitability.

  In the present invention, it is preferable that an outside air temperature sensor for detecting the outside air temperature is provided, and the spark plug control device corrects the predetermined time according to the detection result of the outside air temperature.

  In this way, by correcting the ignition time of a certain time by the spark plug according to the outside air temperature, for example, by correcting so as to increase the set value of the certain time as the outside air temperature decreases, Improved startability and prevention of white smoke emission.

  Preferably, in the present invention, the operating state in which the ignitability decreases is when the engine is started, and the spark plug control device operates the spark plug from the start of the engine until the engine coolant temperature reaches a certain value. Good.

  Thus, since the spark plug is operated until the coolant temperature of the engine reaches a certain value from the start of the engine, the warm-up state of the engine is detected more accurately than a certain time from the aforementioned engine start, Since it can be reflected in the operation control of the spark plug, it is possible to more effectively prevent starting failure and white smoke emission when starting the engine.

  In the present invention, it is preferable that the fuel injection valve performs injection divided into two stages of main injection and pilot injection before the main injection, and the spark plug control device performs the main injection and pilot injection. It is recommended to operate the spark plug in between.

  Pilot-injected fuel that is injected earlier than the main injection is poor in ignitability because the fuel is injected during the compression of the piston. Although there is a high possibility that it will lead to an increase in fuel HC and misfire, the pilot injected fuel with poor ignitability can be reliably ignited by the spark plug. As a result, main injection is performed in an atmosphere whose temperature has been increased by the combustion of the pilot fuel, so that the combustion of the main injected fuel is promoted and the ignitability is ensured.

  In the present invention, preferably, the operation timing of the spark plug between the main injection and the pilot injection is moved to the main injection side according to the elapsed time from the start or the warm-up state.

  Since the ignition plug operation timing is moved to the main injection side according to the elapsed time from the start or the warm-up state, the ignitability of the pilot injection is improved from the initial start as the warm-up progresses. To ensure the ignition of the main injection.

  Preferably, in the present invention, a DPF (diesel particulate filter) is provided in the exhaust gas passage, and the operating state in which the ignitability is reduced is when the intake throttle valve is throttled during the forced regeneration of the DPF, and the ignition The plug control device may operate the spark plug when the intake throttle valve is throttled.

  If the intake throttle valve is throttled during the forced regeneration of the DPF, the intake flow rate is reduced and the compression pressure is reduced, so that the ignitability of the fuel is reduced. Therefore, in addition to the instability of ignition at the time of starting the engine, the instability of ignition also becomes a problem by the throttle control of the intake throttle valve at the time of forced regeneration of the DPF, but the intake throttle valve at the time of forced regeneration of the DPF is throttled. Since the ignition plug is activated when the engine is in operation, such problems are eliminated, the ignitability is lowered, and the risk of white smoke is prevented.

  In the present invention, it is preferable that at least one of a plurality of fuel injection holes formed in the circumferential direction at the tip of the fuel injection valve is provided so as to face the direction of the spark plug.

In order to face the spark plug, not only the circumferential allocation of the fuel injection holes, but also the axial injection angle of the fuel injection valve is changed to face the spark plug. Is also included.
In this way, by directing one injection hole of the multi-injection nozzle in the direction of the spark plug, fuel is collected around the spark plug, and forced ignition by the spark plug can be performed reliably.

  Also, adjust the injection angle in the axial direction of the fuel injection valve so that the fuel in the direction of the spark plug gathers around the spark plug, and arrange the other injection holes to be optimal with respect to the piston cavity. Thus, both ignitability and improved combustion can be achieved.

  In the present invention, it is preferable that the actual compression ratio formed by the intake valve opening / closing timing controlled by the intake valve control device is set in a range of 12-15.

  With such an actual compression ratio, at the time of cold start in a low temperature environment, the temperature in the combustion chamber does not rise and it is difficult to self-ignite the fuel. Even in such an actual compression ratio, a spark plug is employed. Thus, it is possible to improve the ignitability failure and to achieve both NOx reduction by reducing the actual compression ratio.

  According to the present invention, in a diesel engine that is operated with a mirror cycle applied, that is, a compression ignition engine, the instability of ignition is improved by reducing the actual compression ratio, and NOx is reduced by reducing the actual compression ratio. Can be achieved.

1 is an overall configuration diagram of a diesel engine according to the present invention. 1 is a control flowchart of a spark plug control device according to a first embodiment. It is a control flowchart of a spark plug control device according to the second embodiment. It is a time chart of a 2nd embodiment. 3rd Embodiment is shown and the relationship between the fuel injection mode and the ignition timing of a spark plug is shown. It is explanatory drawing of the fuel-injection direction in 4th Embodiment which shows 4th Embodiment. It is a side view of the fuel injection direction in the side view in FIG. It is explanatory drawing of 5th Embodiment. It is explanatory drawing of a mirror cycle and shows a PV diagram. It is an explanatory graph showing the relationship between the degree of early intake of the mirror cycle and the NOx reduction effect.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific examples unless otherwise specifically described. Only.

(First embodiment)
FIG. 1 shows an overall configuration diagram of a diesel engine (hereinafter referred to as an engine) 1 to which a mirror cycle is applied. In FIG. 1, a piston 5 is inserted into the cylinder liner 3, and a combustion chamber 9 is formed between the piston 5 and the cylinder head 7. An intake port 11 and an exhaust port 13 are formed in the cylinder head 7, an intake valve 15 is provided in the intake port 11, and an exhaust valve 17 is provided in the exhaust port 13.

The cylinder head 7 is further provided with a fuel injection valve 19 and a spark plug 21. The fuel injection valve 19 is installed at a substantially central portion of the combustion chamber 9 in a plan view, and injects fuel spray radially around the fuel injection valve 19. The spark plug 21 is provided as means for igniting upon receiving an ignition signal and forcibly igniting the injected fuel separately from the ignition by compression.
The ignition plug control device 23 controls the ignition timing (ignition timing within the combustion cycle) and the ignition period (period during which the ignition plug is operated) of the ignition plug 21.

  An intake valve drive mechanism 16 and an exhaust valve drive mechanism 18 that drive these valves are connected to the intake valve 15 and the exhaust valve 17, respectively.

  The engine 1 is equipped with an exhaust turbocharger 29, and the air discharged from the compressor 29a of the exhaust turbocharger 29 passes through the supply passage 31 and enters the intercooler 33, where the supply air is cooled. After that, the intake air flow rate is controlled by the intake throttle valve 35 and then flows into the combustion chamber 9 from the intake port 37 provided for each cylinder from the intake manifold 37 via the intake valve 15.

Further, the combustion gas burned in the combustion chamber 9, that is, the exhaust gas, drives the exhaust turbine 29 b of the exhaust turbocharger 29 through the exhaust manifold and exhaust passage 39 in which the exhaust ports 13 provided for each cylinder are gathered. Then, it becomes a power source for the compressor 29a and then flows into the exhaust gas after-treatment device 43 through the exhaust passage 41. The exhaust gas aftertreatment device 43 includes a DPF (diesel particulate filter).
Further, an EGR (exhaust gas recirculation) passage 45 is branched from the middle of the exhaust passage 39, and a part of the exhaust gas is cooled by the EGR cooler 47 and introduced into the downstream portion of the intake throttle valve 35 via the EGR valve 49. It has become so.

  The fuel injection valve 19 of each cylinder is provided with a fuel injection control device 51 for controlling the flow rate of fuel to be supplied and the supply timing. The fuel pressurized to a predetermined pressure by the fuel pump 53 is accumulated in the common rail 55, supplied from the common rail 55 to the fuel injection valve 19, and injected into the combustion chamber 9.

Next, the engine control device 57 will be described. The engine control device 57 includes the fuel injection control device 51 and the spark plug control device 23 described above.
A signal indicating an operating state such as the engine speed and the engine load, a signal from the cooling water temperature sensor 59 for detecting the cooling water temperature of the engine 1, and a signal from the outside air temperature sensor 61 for detecting the outside air temperature are input. . The coolant temperature sensor 59 is installed so as to detect the water temperature in the vicinity of the coolant outlet from the cylinder head 7 of the engine 1 in order to reliably detect the warm-up state of the engine 1.

  In the four-cycle engine 1, in the stroke in which the piston 5 reciprocates and repeats the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke, the compression stroke in the compression stroke, that is, the actual compression ratio (see FIG. 9, Vc / Va) In order to execute a mirror cycle in which the expansion stroke in the expansion stroke, that is, the expansion ratio (see FIG. 9, Vb / Va) is increased, the intake valve drive mechanism 16 causes the intake valve 15 to move the piston 5 to the bottom dead center. It is driven so as to perform so-called intake early closing, which closes quickly before reaching.

The actual compression ratio formed by the opening / closing timing of the intake valve 15 is preferably set in the range of 12-15.
With such an actual compression ratio, at the time of cold start in a low temperature environment, the temperature in the combustion chamber does not rise and it is difficult to self-ignite the fuel. Even in such an actual compression ratio, a spark plug is employed. Thus, it is possible to improve the ignitability failure and to achieve both NOx reduction by reducing the actual compression ratio.

  Note that the closing timing of the intake valve 15 of the four-cycle diesel engine may be set so as to execute so-called intake-air late closing that prevents the piston 5 from closing until after the bottom dead center is reached.

A control flow of the spark plug control device 23 of the spark plug 21 of the first embodiment will be described with reference to FIG.
In step S1, it is determined from the engine key switch or engine speed whether the engine 1 has been started. In step S2 it is determined that the start is set as the initial time reading the predetermined time t ₀ which is set in advance. In step S <b> 3, the outside air temperature is detected by the outside air temperature sensor 61. In step S4, using the outside air temperature correction map, a correction value corresponding to the outside air temperature, for example, a correction value for correcting the set value for a certain period of time to become longer as the outside air temperature decreases is calculated. In step S5, it calculates a correction time t ₁ by using the correction value.

Next, in step S6, a subroutine for operating the fuel injection valve 19 is executed, and the fuel injection control device 51 operates the fuel injection valve 19 at the timing of compression ignition of the diesel engine to inject fuel into the combustion chamber 9. To do.
In step S7, a subroutine for operating the spark plug 21 is executed to ignite the spark plug 21. In this spark plug operation subroutine, the ignition timing of the spark plug 21 is set, and in the first embodiment, control is performed so that ignition is performed immediately after fuel injection from the fuel injection valve 19.

In the next step S8, counts the elapsed time t from the start, in step S9, whether the elapsed time t has reached the correction time t ₁ or more is determined. In No, it returns to step S6 and repeats step S6-step S9. In the case of Yes, it progresses to step S10 and makes the ignition plug 21 non-operation. In the next step S11, the process returns to the combustion by compression ignition and ends.

According to the first embodiment described above, a decrease in ignitability due to a decrease in the actual compression ratio caused by applying the mirror cycle is caused by operating the ignition plug 21 provided in the combustion chamber 9 by the ignition plug control device 23. Since the fuel is forcibly ignited, the startability is improved and the generation of white smoke due to poor combustion is prevented.
As a result, the NOx reduction effect by applying the mirror cycle can be obtained without reducing the ignitability.

  Further, according to the present embodiment, the spark plug control device 23 ignites the spark plug 21 for a predetermined time from the start of the engine to forcibly ignite the fuel, and performs ignition by the spark plug 21 after a certain period of time has elapsed. Since self-ignition by compression ignition is performed without performing ignition by the ignition plug 21 only at the time of starting with poor ignitability or during warm-up, the life of the ignition plug 21 can be extended.

Furthermore, according to the present embodiment, the outside air temperature sensor 61 for detecting the outside air temperature is provided, and the spark plug control device 23 corrects the constant time t ₀ according to the detection result of the outside air temperature to calculate the correction time t ₁ . Then, the ignition period of the spark plug 21 (the period during which the spark plug is operated) is calculated using the correction time t ₁ to control the ignition period of the spark plug 21, so that the startability according to the outside air temperature is controlled. Improvement and prevention of white smoke emission are obtained.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. A control flow of the spark plug control device 23 of the second embodiment will be described.
In step S21, it is determined from the engine key switch or the engine speed whether the engine 1 has been started. This determination is the same as in the first embodiment.
If it is determined that the engine has started, the operation of the fuel injection valve operation subroutine is executed in step S22, and the operation subroutine of the spark plug 21 is executed in step S23. The fuel injection valve operating subroutine of step S22 and the spark plug operating subroutine of step S23 are the same as steps S6 and S7 of the first embodiment.

In step S24, the coolant temperature T is detected based on the detection signal from the coolant temperature sensor 59. In step S25, the detection value determines whether the threshold value T ₀ or more cooling water temperature. This threshold value T ₀ is the coolant temperature at which the engine 1 is warmed up to the extent that it does not lead to defects such as white smoke even if the actual compression ratio is reduced due to the application of the mirror cycle. .

In step S25, still, if it does not reach the threshold value or more T ₀ of the cooling water temperature, repeated control of the forced ignition by the spark plug 21 returns to step S22. In step S25, when the cooling water temperature reaches the threshold value _{T 0} or more, by deactivating the ignition plug 21 at step S26. And it ends.

FIG. 4 shows a time chart of the coolant temperature T at the start of the second embodiment, the ignition state of the spark plug 21 and the operating state of the fuel injection valve 19. fuel injection valve 19 starts to operate in ON with the beginning of startup in t _a. At t _b , the cooling water temperature threshold T ₀ is reached, and the spark plug 21 is turned off. Thereafter, at t _c , the cooling water temperature is maintained at a constant temperature by the operation of a thermostat provided in the cooling water circuit of the engine 1.

  As described above, according to the second embodiment, since the spark plug 21 is operated from the start of the engine 1 until the cooling water temperature reaches a constant value, the spark plug 21 according to a predetermined time from the start of the engine 1 of the first embodiment. Since the warm-up state of the engine 1 can be reflected with higher accuracy than the above-described operation control, it is possible to more effectively prevent starting failure and white smoke emission when starting the engine 1.

(Third embodiment)
Next, a third embodiment will be described with reference to FIG. The third embodiment is another example of steps S6 and S7 of the first embodiment, the fuel injection valve operating subroutine of steps S22 and S23 described in the second embodiment, and the spark plug subroutine.

  As shown in FIG. 5, the fuel injection valve 19 performs the injection divided into two stages of the main injection 65 and the pilot injection 67 of the injection earlier than the main injection 65 by the fuel injection control device 51. The spark plug control device 23 is controlled at the timing at which the spark plug 21 is operated between the main injection 65 and the pilot injection 67.

The fuel of the pilot injection 67 injected earlier than the main injection 65 is poor in ignitability because the fuel is injected during the compression of the piston 5, and in the state where the actual compression ratio is lowered by adopting the mirror cycle, the ignition delay Is likely to lead to an increase in unburned HC and misfire.
However, the ignition plug 21 can reliably ignite the fuel of the pilot injection 67 having poor ignitability. As a result, the main injection 65 is performed in an atmosphere whose temperature is increased by the combustion of the fuel of the pilot injection 67, so that the combustion of the main injected fuel is promoted and the ignitability is ensured.

  Further, the operation timing of the spark plug 21 between the main injection 65 and the pilot injection 67 is set according to the elapsed time from the start or the warm-up state, that is, as the elapsed time t elapses, and the coolant temperature It is good to move to the main injection 65 side as T rises.

  Since the operation timing of the spark plug 21 is moved to the main injection 65 side according to the elapsed time from the start or the warm-up state, the ignitability of the pilot injection 67 is improved from the initial start as the warm-up progresses. By moving to the main injection 65 side and contributing to the ignitability of the main injection 65, the ignitability of the main injection 65 can be further improved.

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to FIGS. In the fourth embodiment, at least one of the plurality of fuel injection holes 69 formed in the circumferential direction at the tip of the fuel injection valve 19 is provided so as to face the direction of the spark plug 21. In other words, the fuel injection holes 69 are provided so that the circumferential direction of the fuel injection holes 69 faces the direction of the spark plug 21.

Furthermore, not only the circumferential allocation of the fuel injection holes 69 is performed, but the axial injection angle α of the fuel injection valve 19 is also changed to face the spark plug 21. That is, the injection angle α ′ is set so as to face the spark plug 21 as shown in FIG.
In this way, by directing one injection hole of the multi-injection nozzle toward the ignition plug 21, fuel gathers around the ignition plug 21, and forced ignition by the ignition plug 21 can be performed reliably.

  Further, the injection angle α in the axial direction of the fuel injection valve 19 is adjusted so that the fuel from the fuel injection holes 69 is collected around the spark plug 21, and the other injection holes are formed at the top of the piston 5. By arranging it to be optimal with respect to the piston cavity, it is possible to achieve both ignitability and improved combustion.

(Fifth embodiment)
Next, a fifth embodiment will be described with reference to FIG. In the fifth embodiment, the first and second embodiments are controls at the time of starting, but in the fifth embodiment, control is performed to throttle the intake throttle valve 35 during forced regeneration of a DPF (diesel particulate filter). The ignition plug 21 is ignited when

  As shown in FIG. 8, the spark plug control device 71 ignites the spark plug 21 for a predetermined time when receiving a regeneration signal from the DPF regeneration control device 73 that controls regeneration of the DPF constituting the exhaust gas aftertreatment device 43. .

  If the intake throttle valve 35 is throttled during the forced regeneration of the DPF, the intake flow rate decreases and the compression pressure decreases, so that the ignitability of the fuel decreases. Therefore, in addition to the instability of ignition at the start of the engine, the instability of ignition also becomes a problem by the throttle control of the intake throttle valve 35 at the time of forced regeneration of the DPF, but the intake throttle valve 35 at the time of forced regeneration of the DPF Since the spark plug 21 is operated when it is throttled, such a problem is solved, the ignitability is lowered, and the risk of white smoke generation is prevented.

  According to the present invention, in a diesel engine that is operated with a mirror cycle applied, that is, a compression ignition engine, the instability of ignition is improved by reducing the actual compression ratio, and NOx is reduced by reducing the actual compression ratio. Therefore, it is suitable for use in a compression value ignition engine.

DESCRIPTION OF SYMBOLS 1 Diesel engine 5 Piston 9 Combustion chamber 11 Intake port 15 Intake valve 16 Intake valve valve mechanism 17 Exhaust valve 18 Exhaust valve valve mechanism 19 Fuel injection valve 21 Spark plug 23 Spark plug controller 29 Exhaust turbocharger (supercharger) Machine)
35 Intake throttle valves 39, 41 Exhaust gas passage 43 Exhaust gas aftertreatment device 51 Fuel injection control device 59 Cooling water temperature sensor 61 Outside air temperature sensor 65 Main injection 67 Pilot injection 69 Fuel injection hole α Injection angle

Claims (9)

  A combustion chamber that compresses intake air with the piston; a fuel injection valve that injects pressurized fuel into the combustion chamber; an intake valve that opens and closes an intake port through which air flows into the combustion chamber; An intake valve valve mechanism that operates the valve at the opening and closing timing of a mirror cycle, an ignition plug provided in the combustion chamber, and a forced operation when the ignition plug is controlled to reduce the ignitability of the injected fuel A diesel engine comprising an ignition plug control device for igniting the engine.   2. The diesel engine according to claim 1, wherein the operation state in which the ignitability is lowered is when the engine is started, and the spark plug control device operates the spark plug for a predetermined time from the start of the engine. engine.   The diesel engine according to claim 2, wherein an outside air temperature sensor for detecting an outside air temperature is provided, and the spark plug control device corrects the predetermined time according to a detection result of the outside air temperature.   2. The operating state in which the ignitability decreases is when the engine is started, and the spark plug control device operates the spark plug from the start of the engine until the coolant temperature of the engine reaches a constant value. The listed diesel engine.   The fuel injection valve performs injection divided into two stages of main injection and pilot injection before the main injection, and the spark plug control device operates a spark plug between the main injection and pilot injection. The diesel engine according to claim 1.   The diesel engine according to claim 5, wherein the operation timing of the spark plug between the main injection and the pilot injection is moved to the main injection side in accordance with an elapsed time from the start or a warm-up state.   An operating state in which a DPF (diesel particulate filter) is provided in the exhaust gas passage and the ignitability is reduced is when the intake throttle valve is throttled during the forced regeneration of the DPF, and the spark plug control device The diesel engine according to claim 1, wherein the spark plug is operated when the throttle is throttled.   8. The fuel injection valve according to claim 1, wherein at least one of a plurality of fuel injection holes formed in a circumferential direction at a tip portion of the fuel injection valve is provided so as to face a direction of the spark plug. Diesel engine as described in   The diesel engine according to any one of claims 1 to 8, wherein an actual compression ratio formed by an intake valve opening / closing timing controlled by the intake valve control device is set in a range of 12-15. .

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