JP4779386B2 - diesel engine - Google Patents

Description

  The present invention relates to a diesel engine that switches between premixed combustion and diffusion combustion based on the operating state of the engine.

  In a four-cycle diesel engine that directly injects fuel into a cylinder, it is common to inject fuel near the compression top dead center of the piston, where the inside of the cylinder is at high temperature and high pressure. In this case, ignition starts during fuel injection to form a flame, and combustion is continued by supplying subsequent fuel to the flame. As described above, the combustion mode in which ignition starts during fuel injection is generally referred to as diffusion combustion. However, the problem that NOx, smoke, and the like are generated in this diffusion combustion has been pointed out.

  Therefore, the fuel injection timing is made earlier than the compression top dead center of the piston, and the air-fuel mixture is ignited after the fuel injection is completed (in other words, the fuel injection is ended before the air-fuel mixture is ignited) It has been proposed to realize a so-called fuel form (see Patent Document 1).

  In premixed combustion, the mixture is ignited after a certain period of time (premixing period) after the end of fuel injection, so the mixture is diluted and made uniform before ignition. Accordingly, the local combustion temperature is lowered, the NOx emission amount is reduced, and combustion in an air shortage state is also avoided, so that the occurrence of smoke is also suppressed. In particular, by reducing the oxygen concentration of the air-fuel mixture by executing EGR (exhaust gas recirculation) in conjunction with early fuel injection, the NOx reduction effect can be enhanced, and the premixing period and ignition timing are optimized. Can be achieved.

JP 2003-83119 A

  Thus, although premixed combustion is effective for improving exhaust gas, there is a problem that diesel knock becomes intense when executed in a high rotation / high load region with a large amount of fuel injection.

  In order to suppress diesel knock, it is necessary to satisfy both the supply of a large amount of oxygen suitable for the fuel injection amount into the cylinder and the maintenance of the air-fuel mixture in the cylinder at a low oxygen concentration. That is, in order to perform premix combustion in a high rotation / high load region, it is required to introduce a large amount of air (fresh air) and a large amount of inert gas (EGR gas) into the cylinder. At present, no intake system or supercharging system has been established to achieve this.

  Another reason why premixed combustion cannot be performed in a high rotation / high load region is that, in premixed combustion in which combustion is performed after all of the injected fuel is mixed, the maximum in-cylinder pressure is higher than that in diffusion combustion. Therefore, when it is executed in a high rotation / high load region where the fuel injection amount is large, the maximum in-cylinder pressure exceeds the allowable maximum in-cylinder pressure of the engine. In this case, a significant engine design change is required and the cost increases.

  Therefore, as disclosed in Patent Document 1, it is proposed that premixed combustion is performed when the engine operating state is in a low rotation / low load region, and diffusion combustion is performed when the engine is in a high rotation / high load region. Has been. However, as described above, since the amount of emission of NOx and the like is larger in the diffusion combustion than in the premixed combustion, it is desired to expand the operating range where the premixed combustion can be performed as much as possible.

  In addition, if the operating region for performing diffusion combustion is wide, a large and high-performance post-processing device for purifying exhaust gas is required, which increases costs and specially regenerates the filter of the post-processing device. There is also a problem that the fuel efficiency is deteriorated because the number of times of performing fuel injection increases.

  In view of the above, an object of the present invention is to solve the above-described problems and to expand an operation range in which premixed combustion can be performed.

To achieve the above object, the present invention provides a fuel injection device capable of injecting fuel into a cylinder at an arbitrary timing, a variable intake valve and a variable exhaust valve that can be opened and closed at an arbitrary timing, and an operating state of the engine. And a control device that controls the fuel injection device, the variable intake valve, and the variable exhaust valve based on the operation state detected by the operation state detection unit, and When the engine crankshaft makes one revolution by the control device , the variable intake valve and the variable exhaust valve are each opened twice, and each time the engine crankshaft makes two revolutions, in a diesel engine for switching the four-cycle operation of opening the intake valve and the variable exhaust valves once each respectively, the control device performs the two cycle operation Both performed fuel injection by the fuel injection device before the compression top dead center of the piston, determines the fuel injection before ignition of the mixture based on the target fuel injection amount in the 2-cycle premix combustion operation to end was, the 2 and a driving region and does not occur operating region where the diesel knocking occurs when the cycle was premixed combustion operation, has been operating state detected by the operating condition detecting means, the two-stroke premix when the case of performing the combustion operation is an operation region where the diesel knock is not generated, executes the two-cycle premix combustion operation, the operating state the operating state detected by the detection means, the two-stroke premix combustion operation When the operation range is such that diesel knock occurs, the above four-cycle operation is performed, and the upper limit is reached near the compression top dead center of the piston. It performs fuel injection by the fuel injection device, and executes a 4-cycle diffusive combustion operation in which the ignition begins in the injection of fuel.

  Here, when the two-cycle premixed combustion operation is executed, the control device may start fuel injection by the fuel injection device at 30 degrees or more before the compression top dead center of the piston.

  In the control device, when the two-cycle premixed combustion operation is performed, the period during which the variable exhaust valve is opened may be a period in which a predetermined amount of burned gas remains in the cylinder.

  Further, a supercharging device for increasing the intake pressure may be further provided.

  According to this invention, the outstanding effect that the operation area | region which can perform premixed combustion can be expanded compared with the former is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view of a diesel engine according to the present embodiment. Although FIG. 1 shows a single cylinder engine for the sake of clarity, the present invention is applicable regardless of the number of cylinders of the engine.

  In the figure, reference numeral 1 denotes an engine body. The engine body 1 includes a cylinder 2, a cylinder head 3, a piston 4, an intake port 5, an exhaust port 6, an intake valve 7, an exhaust valve 8, an injector 9 (fuel injection device), and the like. I have. A combustion chamber 10 is formed in a space surrounded by the cylinder 2, the cylinder head 3 and the piston 4. A cavity 11 is recessed at the top of the piston 4, and fuel is directly injected from the injector 9 provided facing the combustion chamber 10 toward the cavity 11. The fuel injection angle of the injector 9 is designed so that the injected fuel always reaches the cavity 11 regardless of the later-described diffusion combustion operation and premix combustion operation. This is because if the fuel adheres to the side wall of the cylinder 2, it may be discharged as unburned HC.

  The injector 9 is connected to the common rail 24, and high-pressure fuel (for example, 20 to 200 MPa) stored in the common rail 24 is constantly supplied to the injector 9. Fuel pumping to the common rail 24 is performed by a high-pressure supply pump 25.

  The intake valve 7 and the exhaust valve 8 are provided with variable valve mechanisms 7a and 8a, respectively, and the opening / closing timing thereof can be arbitrarily adjusted. That is, the intake valve 7 and the exhaust valve 8 of the engine of the present embodiment are a variable intake valve and a variable exhaust valve that can be opened and closed at an arbitrary timing.

  The intake port 5 and the exhaust port 6 are respectively connected to an intake pipe 12 and an exhaust pipe 13, and a turbocharger 14 (supercharger) is interposed in the intake pipe 12 and the exhaust pipe 13.

  The turbocharger 14 includes a turbine 15 provided in the exhaust pipe 13 and a compressor 16 provided in the intake pipe 12 so that the intake air can be pressurized using the energy of the exhaust. An intake air amount sensor 17 for detecting the intake air flow rate is provided on the upstream side of the compressor 16, and an intercooler 18 for cooling the intake air is provided on the downstream side.

A continuous regeneration type DPF 32 as an exhaust gas aftertreatment device is provided downstream of the turbine 15 in the exhaust pipe 13. The continuous regeneration type DPF 32 includes an oxidation catalyst 30 that oxidizes NO in exhaust gas to NO ₂ and a DPF 31 that collects PM in exhaust gas. The PM in exhaust gas is captured by the DPF 31 during engine operation. At the same time, the collected PM is burned by NO ₂ flowing from the oxidation catalyst 30 to regenerate the DPF 31.

  The oxidation catalyst 30 is, for example, coated with activated alumina or the like on the surface of a support made of honeycomb cordierite or heat-resistant steel to form a washcoat layer, and this coat layer is made of a noble metal such as platinum, palladium, or rhodium. Those having a catalytically active component made of or the like are used.

  The DPF 31 is a so-called wall flow type honeycomb filter in which a number of cells are formed in parallel with porous cordierite or silicon carbide, and the inlets and outlets of the cells are alternately closed. A fiber type filter wound around a porous tube is used.

  The engine of the present embodiment further includes an EGR device 19 for returning a part of the exhaust gas flowing in the exhaust pipe 13 into the combustion chamber 10. The EGR device 19 includes an EGR pipe 20 connecting the intake pipe 12 and the exhaust pipe 13, and an EGR valve for adjusting the flow rate of EGR gas (exhaust gas) recirculated into the combustion chamber 10 through the EGR pipe 20. 21 and an EGR cooler 22 for cooling the EGR gas on the upstream side of the EGR valve 21. The intake pipe 12 is provided with an intake throttle valve 23 for appropriately restricting intake air upstream of the connection portion with the EGR pipe 20.

  An ECU 26 (control device) for electronically controlling the various devices of the engine is provided. The ECU 26 determines the operating state of the engine based on the detection values of various sensors, and the injector 9 based on the engine operating state. The variable valve mechanisms 7a and 8a, the EGR valve 21, the intake throttle valve 23, the high pressure pump 25 and the like are controlled. Sensors include the above-described intake air amount sensor 17, accelerator opening sensor 33, engine rotation speed sensor 34, crank angle sensor 35, common rail pressure sensor 36, and the like. Detection values of these sensors, that is, intake air amount, The accelerator opening, engine speed, crankshaft angle, common rail pressure, and the like are transmitted to the ECU 26.

  In the present embodiment, the accelerator opening sensor 33, the engine rotation speed sensor 34, and the like constitute the operating state detection means in “Claims”.

  The injector 9 has an electromagnetic solenoid (not shown) that is ON / OFF controlled by the ECU 26 so that the ECU 26 can arbitrarily adjust the fuel injection timing (timing), the injection period, the injection amount, and the like by the injector 9. It has become. The ECU 26 determines target values such as fuel injection timing and injection period based on detection values of the engine speed sensor 34, the accelerator opening sensor 33, and the like, and turns on / off the electromagnetic solenoid of the injector 9 according to these target values. To do. Target values such as the injection timing and the injection period are previously input to the ECU 26 in the form of a map or the like.

  The variable valve mechanisms 7a and 8a also have electromagnetic solenoids (not shown) that are ON / OFF controlled by the ECU 26. The ECU 26 controls the opening timing (timing) and opening period of the intake valve 7 and the exhaust valve 8. It can be adjusted arbitrarily. The ECU 26 turns on and off the electromagnetic solenoids of the variable valve mechanisms 7a and 8a based on the detection value of the crank angle sensor 35 and the like.

  The engine according to the present embodiment switches between premixed combustion and diffusion combustion based on the operating state of the engine detected by the accelerator opening sensor 33, the engine rotational speed sensor 34, and the like.

  More specifically, the ECU 26 of the present embodiment determines that “target fuel injection amount Q (corresponding to engine load)” determined from a map or the like based on detection values of the accelerator opening sensor 33 and the engine speed sensor 34 and the like. The engine operating state is determined based on the “detected value of the engine rotational speed sensor 34”, and the operating state is lower than the predetermined operating state (switching line A) shown in FIG. In some cases, each time the crankshaft of the engine rotates, the variable intake valve 7 and the variable exhaust valve 8 are opened once, and fuel is injected by the injector 9 before the compression top dead center of the piston 4. A two-cycle premixed combustion operation in which fuel injection ends before the mixture is ignited and the engine operating state is higher than the predetermined operating state (switching line A). When the engine speed is high and the load is high, each time the engine crankshaft rotates twice, the variable intake valve 7 and the variable exhaust valve 8 are opened once and the piston 9 is driven by the injector 9 near the compression top dead center. Fuel injection is performed, and a four-cycle diffusion combustion operation in which ignition starts during fuel injection is performed.

  Hereinafter, the 2-cycle premixed combustion operation and the 4-cycle diffusion combustion operation performed by the ECU 26 will be described.

<2-cycle premixed combustion operation>
When the engine operating state is a lower rotational speed and a lower load than the predetermined operating state (switching line A in FIG. 4), the ECU 26 performs two-cycle premixing as shown in FIGS. Perform combustion operation.

  As can be seen from these figures, in the two-cycle premixed combustion operation, four strokes of expansion-exhaust-intake-compression are performed every time the crankshaft of the engine makes one revolution.

  Specifically, when the fuel injected in the previous cycle ignites near the compression top dead center of the piston, the expansion stroke starts, and then the crank angle exceeds 90 degrees (ATDC 90 ° CA) after the top dead center. The exhaust valve 8 is opened by the ECU 26 and the exhaust stroke starts (burned gas is discharged).

  When the crank angle reaches just before the bottom dead center, the ECU 26 opens the intake valve 7 while keeping the exhaust valve 8 open. As a result, fresh air and EGR gas are introduced into the combustion chamber 10 from the intake port 5. This period is an overlap period of the exhaust stroke and the intake stroke.

  When the crank angle exceeds the bottom dead center, the exhaust valve 8 is closed by the ECU 26 and the exhaust stroke ends.

  When the crank angle becomes near 90 degrees after bottom dead center (before top dead center), the intake valve 7 is closed by the ECU 26, the intake stroke is completed, and the compression stroke is started.

  Thereafter, when the crank angle reaches a predetermined angle before the top dead center, the ECU 26 executes fuel injection from the injector 9 and ends before the top dead center. Note that the air-fuel mixture does not ignite at this stage.

  After the fuel injection from the injector 9 is completed, when a predetermined period (a mixture premixing period) elapses and the crank angle reaches near the top dead center, the mixture is ignited and burned, and the process proceeds to the expansion stroke again. To do.

  Thus, in the two-cycle premixed combustion operation, each time the crankshaft of the engine makes one revolution, the intake and exhaust valves 7 and 8 are opened once each.

  The fuel injection by the injector 9 is performed for a predetermined period before the compression top dead center of the piston 4 every rotation of the crankshaft, and before the ignition timing of the air-fuel mixture (basically near the compression top dead center). The injection ends.

  In the engine of the present embodiment, when performing the two-cycle premixed combustion operation, the ECU 26 performs fuel injection by the injector 9 between 30 degrees before compression top dead center of the piston (BTDC 30 ° CA) and compression top dead center. To start. This is because if the fuel injection timing is too early (before BTDC 30 ° CA), the fuel is injected in a state where the temperature and density of the air in the cylinder 2 is low, so that the mixture is premixed ( (Diluting / homogenizing) is not sufficiently performed, and the improvement effect of exhaust gas becomes low, and it becomes difficult to control the ignition timing. In addition, if the fuel injection timing is too early, the fuel is injected with the position of the piston 4 being far away from the top dead center. There is also a possibility that fuel HC will be discharged.

  When executing the two-cycle premixed combustion operation, the ECU 26 executes a relatively large amount of EGR by the EGR device 19 and controls so that the EGR rate of the mixture becomes relatively large (for example, about 60% or more). This reduces the oxygen concentration of the air-fuel mixture and suppresses NOx emission. Further, the premixing period and the ignition timing are appropriately controlled by appropriately controlling the EGR rate of the air-fuel mixture.

<4-cycle diffusion combustion operation>
On the other hand, when the engine operating state is higher in rotational speed and higher load than the predetermined operating state (switching line A in FIG. 4), the ECU 26 performs four-cycle diffusion combustion similar to a general diesel engine. Do.

  Since this combustion is general, detailed description is omitted, but each time the crankshaft of the engine rotates twice, four strokes of expansion-exhaust-intake-compression are performed. In the four-cycle diffusion combustion operation, every time the crankshaft of the engine makes two revolutions, the intake and exhaust valves 7 and 8 are opened once each, and fuel injection by the injector 9 is performed by the compression top dead center (TDC) of the piston 4. ) Perform in the vicinity. The fuel injected by the injector 9 is ignited and becomes a flame before the injection ends, and combustion is continued by supplying subsequent fuel to the flame.

  The engine of the present embodiment is characterized in that pre-mixed combustion is performed in two cycles when the engine operating state is a lower rotational speed and a lower load than the predetermined operating state, and the engine operating state is higher than the predetermined operating state. However, when the rotation speed is high and the load is high, the diffusion combustion in 4 cycles is executed. That is, the engine of the present embodiment switches between premixed combustion and diffusion combustion based on the operating state of the engine, and switches between 2 cycles and 4 cycles in accordance with the switching.

  In a conventional diesel engine, regardless of whether premixed combustion or diffusion combustion is performed, as shown in FIG. 2 (b), each time the crankshaft of the engine makes two rotations, expansion-exhaust-intake-compression (In other words, each time the crankshaft makes two revolutions, the intake and exhaust valves 7 and 8 are opened once each). When performing the mixed combustion, the operation is switched to the two-cycle operation. FIG. 2B shows an example of the control content of the 4-cycle premixed combustion.

  As in the engine of the present embodiment, by switching to the two-cycle operation when performing the premixed combustion, it becomes possible to execute the premixed combustion in a higher rotation speed / higher load region than in the prior art. The operating range in which mixed combustion can be performed can be expanded as compared with the conventional case.

  The reason is that the engine output is doubled in the two-cycle operation, so that the amount of fuel injection required for obtaining the same output is halved. In other words, by adopting the two-cycle operation, the fuel injection amount required at a predetermined engine load is halved, so of course, it is necessary to perform the premixed combustion (in other words, suppressing severe diesel knock) The amount of oxygen and inert gas (EGR gas) required for this is halved. Therefore, even if premixed combustion is executed in a relatively high rotation / high load region using an existing intake system or supercharging system, oxygen and EGR gas corresponding to the fuel injection amount are introduced into the combustion chamber 10. Can suppress diesel knock.

  In addition, since the maximum in-cylinder pressure is reduced by halving the fuel injection amount, the in-cylinder maximum pressure will exceed the allowable pressure even if premixed combustion is performed in a higher rotation and higher load region than before. There is nothing. This is also a factor that can expand the feasible region of premixed combustion.

  Here, the output P of the engine can be obtained from the following equation.

P = mep × D × Ne / nR
Here, mep is the in-cylinder average effective pressure, D is the displacement, and Ne is the engine speed. NR is the number of rotations of the crankshaft during one expansion stroke, which is 2 in 4 cycles and 1 in 2 cycles.

  From this equation, it can be seen that in 2-cycle operation, the engine output is twice that in 4-cycle operation.

  By the way, in the two-cycle operation, the period during which the exhaust valve 8 can be opened is shorter than that in the four-cycle operation, and there is a problem that the scavenging property (exhaust property) of the burned gas is poor. Since the remaining burnt gas acts as an internal EGR gas that reduces the oxygen concentration of the air-fuel mixture, it will rather contribute to ensuring good premixed combustion. In other words, when performing diffusion combustion, bad exhaustability in two-cycle operation will adversely affect combustion, such as the generation of smoke, but when premixed combustion and two-cycle operation are combined, On the contrary, poor exhaust performance is a merit.

  Further, by combining the two-cycle operation and the premixed combustion, it becomes possible to secure a high EGR rate that cannot be achieved by the external EGR device 19 alone, which also contributes to the expansion of the premixed combustion executable region. . From the viewpoint of securing a high EGR rate, when performing the two-cycle premixed combustion operation, a predetermined amount (appropriate amount) of burned gas is generated in the combustion chamber 10 ( It is preferable to set the period so as to remain in the cylinder 2). For example, for each operating state of the engine, an opening period and an opening time of the exhaust valve 8 necessary for causing desired burned gas to remain in the combustion chamber 10 are determined in advance, and are input to the ECU 26 in the form of a map or the like. It is possible to keep things.

  As described above, according to the engine of the present embodiment, as shown in FIG. 4, the region where the premixed combustion is performed can be expanded as compared with the conventional case.

  Accordingly, the amount of NOx and other pollutants emitted is reduced as compared with the prior art, and the cost is reduced by downsizing the post-treatment device (here, continuous regeneration type DPF 32) or reducing the amount of noble metal supported. be able to.

  Further, in the continuous regeneration type DPF 32, when the exhaust gas temperature is low, the PM trapped in the DPF 31 cannot be combusted. Therefore, when the exhaust gas temperature is low, the amount of collected PM reaches a certain amount. In addition, it is necessary to increase the exhaust gas temperature by performing special fuel injection control. However, according to the engine of the present embodiment, the amount of PM emission is reduced compared to the conventional case, so the fuel for increasing the exhaust gas temperature. The number of injections is reduced, leading to improved fuel efficiency.

  By the way, in the engine of this embodiment, when the operating state of the engine is higher than the predetermined operating state (switching line A in FIG. 4), switching to diffusion combustion is performed.

  Explaining this reason, since the fuel injection amount increases toward the high rotation / high load region, there is a region where the premix combustion cannot be maintained even in the two-cycle premix combustion operation in which the fuel injection amount can be halved. Because. That is, in the current intake and supercharging system, if the two-cycle premixed combustion operation is executed in the entire region, there will be a region where diesel knock occurs due to insufficient amounts of oxygen and inert gas.

  Further, in the engine of the present embodiment, when switching from premixed combustion to diffusion combustion, switching is performed from 2 cycles to 4 cycles. This is because evil acts as a demerit such as an increase in smoke.

  In short, the engine of the present embodiment performs a two-cycle premixed combustion operation when the engine operating state is at a lower rotation / low load side than the predetermined operating state, and has a higher rotation / high load than the predetermined operating state. By performing the four-cycle diffusion combustion operation when the engine is on the side, it is possible to minimize the discharge amount of pollutants in the entire operation region of the engine.

  In the above-described embodiment, the turbocharger 14 (supercharger) is a type that always operates regardless of the operating state of the engine. However, the present invention is not limited in this respect, and the ECU 26 activates / deactivates. A switchable type may be used. In this case, it is preferable to operate the turbocharger 14 to pressurize the intake air when performing at least a two-cycle premixed combustion operation.

  Moreover, in the said embodiment, although the intake valve 7 and the exhaust valve 8 were each provided with the variable valve mechanisms 7a and 8a, this invention is not limited in this point, The camshaft for 2 cycle premix combustion combustion, A camshaft for four-cycle diffusion combustion operation may be provided, and the camshaft that drives the intake valve 7 and the exhaust valve 8 may be appropriately selected based on the operating state of the engine.

1 is a schematic view of a diesel engine according to an embodiment of the present invention. (A) It is a figure which shows an example of the control content of the 2 cycle premixed combustion operation which the engine of one Embodiment of this invention performs. (B) It is a figure which shows an example of the control content of 4 cycle premix combustion operation. It is a figure for demonstrating the opening-and-closing timing of the intake / exhaust valve in 2 cycle premix combustion operation. It is a figure which shows the execution area | region of a premix combustion operation and a diffusion combustion operation.

Explanation of symbols

4 Piston 7 Intake valve (variable intake valve)
7a Variable valve mechanism 8 Exhaust valve (variable exhaust valve)
8a Variable valve mechanism 9 Injector (fuel injection device)
14 Turbocharger (supercharger)
19 EGR device 26 ECU (control device)
32 Continuous regeneration type DPF (post-processing equipment)
33 Accelerator opening sensor (operating state detection means)
34 Engine rotation speed sensor (operating state detection means)

Claims (4)

A fuel injection device capable of injecting fuel into the cylinder at an arbitrary timing;
A variable intake valve and a variable exhaust valve that can be opened and closed at any timing; and
An operating state detecting means for detecting the operating state of the engine;
A control device for controlling the fuel injection device, the variable intake valve and the variable exhaust valve based on the operation state detected by the operation state detection means;
With the control device , each time the crankshaft of the engine makes one revolution, the variable intake valve and the variable exhaust valve are opened once each, and the variable every time the engine crankshaft makes two revolutions. In a diesel engine that switches between four-cycle operation, in which each type of intake valve and variable exhaust valve is opened once ,
The control device
The target fuel in the two-cycle premixed combustion operation in which the two-cycle operation is performed, the fuel injection by the fuel injection device is performed before the compression top dead center of the piston, and the fuel injection is terminated before the mixture is ignited. It was determined based on the injection amount, and a driving region which does not generate an operating region where the diesel knocking occurs when performing the 2-cycle premix combustion operation,
The operating state the operating state detected by the detection means, when the case of performing the two-stroke premix combustion operation is an operation region where the diesel knock is not generated, executes the two-cycle premix combustion operation,
When the operation state detected by the operation state detection means is an operation region in which diesel knock occurs when the two-cycle premixed combustion operation is performed, the four-cycle operation is performed and the compression top dead center of the piston is performed. A diesel engine characterized by performing fuel injection by the fuel injection device in the vicinity and performing a four-cycle diffusion combustion operation in which ignition starts during fuel injection . The control device
The diesel engine according to claim 1, wherein when the two-cycle premixed combustion operation is executed, fuel injection by the fuel injection device is started after 30 degrees before compression top dead center of the piston. The control device
3. The diesel engine according to claim 1, wherein when the two-cycle premixed combustion operation is performed, a period in which the variable exhaust valve is opened is a period in which a predetermined amount of burned gas remains in the cylinder. A supercharging device for increasing the intake pressure;
The diesel engine in any one of Claims 1-3.

Images