JP5196270B2 - Combustion control device and combustion control method for diesel engine - Google Patents

Description

  The present invention relates to a combustion control device and a combustion control method for a diesel engine, and more particularly to a combustion control device and a combustion control method for a diesel engine having two combustion modes, namely, a diffusion combustion mode and a premixed combustion mode.

  2. Description of the Related Art Conventionally, in a diesel engine, a combustion control device that controls a combustion mode of fuel in a combustion chamber according to an engine load is known. As fuel combustion modes, there are a diffusion combustion mode in which fuel is burned while injecting fuel into the combustion chamber, and a premixed combustion mode in which fuel and air are mixed in the combustion chamber before ignition of the fuel. Such a diesel engine control device controls the timing of the divided injection and the fuel injection amount according to the load of the diesel engine, that is, the timing and the fuel injection amount of the main injection and the pilot injection before this. The combustion mode is switched, and the diffusion combustion mode is used when the engine is in a high load state, while the premixed combustion mode is used when the engine is in a low load state.

  In such a diesel engine combustion control device, when switching the combustion mode from one combustion mode to the other combustion mode, the pilot injection amount and the main injection amount are controlled so as to continuously fluctuate while controlling the combustion chamber. Is known that controls the generation of nitrogen oxides (NOx), soot, noise (NVH: Noise Vibration Harshness), etc. (for example, Patent Document 1). In such a combustion control device, when shifting the combustion mode from the diffusion combustion mode to the premixed combustion mode, the pilot injection amount is continuously increased, and the main injection amount is continuously decreased, so that the premixed combustion is performed. When the mode is entered, torque is generated by pilot injection without performing main injection.

JP 2007-162544 A

  However, according to the above-described combustion control device, it is difficult to achieve both suppression of soot and noise generation at the time of transition to the combustion mode even if injection control is performed using the gas state such as the intake air amount and the EGR rate as an index. There is a fear.

  Therefore, the present invention has been made to solve the above-described problems, and provides a combustion control apparatus and combustion control method for a diesel engine that can simultaneously suppress generation of soot and noise at a higher level when shifting to a combustion mode. The purpose is to provide.

  In order to solve the above-described problems, the present invention provides a main injection in which the oxygen concentration in a combustion chamber of a diesel engine is set to a first oxygen concentration and fuel is injected into the combustion chamber at a first timing, and the main injection. The diffusion combustion mode in which pilot injection for injecting fuel into the combustion chamber is performed before, and the oxygen concentration in the combustion chamber is set to the second oxygen concentration lower than the first oxygen concentration, and the first time earlier than the first timing. The diesel engine is controlled in two combustion modes: a main injection that injects fuel into the combustion chamber at timing 2 and a premixed combustion mode that performs pilot injection that injects fuel into the combustion chamber before the main injection. The diesel engine combustion control device is configured to change the combustion mode of the diesel engine when the engine load exceeds a predetermined load. Combustion mode control means for controlling the combustion mode so that the combustion mode of the diesel engine is set to the premixed combustion mode when the engine load is less than a predetermined load, the combustion mode control means comprises: The fuel injection amount is controlled so that the pilot injection amount in the premixed combustion mode is larger than the pilot injection amount in the diffusion combustion mode, and the load of the diesel engine changes to diffuse the combustion mode. When shifting between the combustion mode and the premixed combustion mode, the pilot injection amount is increased until it becomes larger than the pilot injection amount in the premixed combustion mode, and then decreased.

  According to the present invention configured as described above, for example, the pilot injection amount before reaching the premixed combustion mode at the time of switching from the diffusion combustion mode to the premixed combustion mode is more than the pilot injection amount in the premixed combustion mode. To do more. As a result, the oxygen concentration in the combustion chamber decreases and the local oxygen equivalence ratio approaches 1, so that the generation of soot can be suppressed. As a result, it is possible to perform control advantageous for noise generation suppression at the time of switching the combustion mode, and it is possible to switch the combustion mode while achieving both suppression of soot and noise generation.

In the present invention, it is preferable that the combustion mode control means keeps the oxygen concentration in the combustion chamber substantially constant when the pilot injection amount is changed between the injection amount in the premixed combustion mode and the injection amount larger than that. It is like that.
According to the present invention thus configured, the amount of torque generated by the diesel engine can be kept constant when the pilot injection amount is changed.

  In the present invention, it is preferable that the combustion mode control means gradually changes the oxygen concentration in the combustion chamber when the pilot injection amount is gradually changed.

  In the present invention, preferably, the combustion mode control means is configured such that the interval between the pilot injection and the main injection in the premixed combustion mode is larger than the interval between the pilot injection and the main injection in the diffusion combustion mode.

  The present invention also provides a main injection for injecting fuel into the combustion chamber at a first timing with the oxygen concentration in the combustion chamber of the diesel engine as the first oxygen concentration, and the combustion chamber before the main injection. A diffusion combustion mode in which pilot injection is performed to inject fuel, and an oxygen concentration in the combustion chamber is set to a second oxygen concentration lower than the first oxygen concentration, and at a second timing earlier than the first timing, Combustion control of a diesel engine in which the diesel engine is controlled in two combustion modes: a main injection that injects fuel and a pilot injection that injects fuel into the combustion chamber before the main injection. A method for changing the combustion mode of the diesel engine when the engine load changes from less than a predetermined load to more than a predetermined load. The combustion mode is controlled so that the mixed combustion mode is changed to the diffusion combustion mode, and the combustion mode of the diesel engine is changed from the diffusion combustion mode to the premixed combustion mode when the engine load changes from a predetermined load to a predetermined load. The fuel injection amount is controlled so that the pilot injection amount in the premixed combustion mode is larger than the pilot injection amount in the diffusion combustion mode. A first step of increasing the pilot injection amount until it becomes larger than the pilot injection amount in the premixed combustion mode when the engine load changes and the combustion mode is shifted between the diffusion combustion mode and the premixed combustion mode; And a second step of reducing the pilot injection amount increased in the first step. To.

  According to the present invention configured as described above, for example, the pilot injection amount before reaching the premixed combustion mode at the time of switching from the diffusion combustion mode to the premixed combustion mode is more than the pilot injection amount in the premixed combustion mode. Can also be more. And, by increasing the pilot injection amount before reaching the premixed combustion mode more than the pilot injection amount in the premixed combustion mode, the local oxygen concentration is reduced and the oxygen equivalence ratio approaches 1, so Occurrence of wrinkles can be suppressed. As a result, it is possible to perform control advantageous for noise generation suppression at the time of switching the combustion mode, and it is possible to switch the combustion mode while achieving both suppression of soot and noise generation.

  Thus, according to the present invention, at the time of transition to the combustion mode, both noise and soot generation can be suppressed.

It is the schematic which shows the engine system to which the combustion control apparatus of the diesel engine by embodiment of this invention was applied. It is a map which shows the fuel-injection mode according to the state of the diesel engine by embodiment of this invention. In embodiment of this invention, it is a graph which shows the target value of the oxygen concentration in a combustion chamber when performing each combustion mode. It is a graph of the relationship between the timing when changing between the diffusion combustion mode and the premixed combustion mode in the conventional combustion control apparatus, and the change of a fuel injection form. It is a map used when changing between the diffusion combustion mode and the premixed combustion mode in the conventional combustion control apparatus. It is a graph of the relationship between the pilot injection quantity in the state close | similar to the premix combustion mode in embodiment of this invention, and the quantity of Soot. It is a graph of the relationship between the amount of pilot injection in the state close to the premixed combustion mode, and the amount of NVH in the embodiment of the present invention. It is a graph of the relationship between the timing when changing between the diffusion combustion mode and the premix combustion mode in the combustion control apparatus by embodiment of this invention, and a fuel injection form. 5 is a map used by the combustion control device according to the embodiment of the present invention when shifting to a combustion mode. It is a flowchart which shows a series of processes of ECU when shifting combustion mode in embodiment of this invention.

  Hereinafter, a combustion control apparatus for a diesel engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an engine system to which a combustion control device for a diesel engine is applied.

  As shown in FIG. 1, the engine system includes a diesel engine 1 and an intake passage 3 and an exhaust passage 5 extending from the diesel engine 1. The diesel engine 1 is a multi-cylinder diesel engine, and includes a combustion chamber 7, a piston 9 that moves in the combustion chamber 7, and an injector 11 that injects fuel into the combustion chamber 7 at a predetermined timing. An intake valve 13 is provided between the combustion chamber 7 and the intake passage 3, and an exhaust valve 15 is provided between the combustion chamber 7 and the exhaust passage 5.

  An intake throttle valve 17 for adjusting the intake air amount, a compressor 21 of the turbocharger 19, an intercooler 23, and an intercooler (I / C) passage throttle valve 25 are provided in the intake passage 3 from the upstream side. It has been. The intake passage 3 communicates with the intake side of the combustion chamber 7 of the diesel engine 1 via the manifold 27.

  From the upstream side of the exhaust passage 5, the turbine 29 of the turbocharger 19, an oxidation catalyst 31 for oxidizing HC, CO, NOx, soot and the like in the exhaust, and particulate matter (PM) in the exhaust A DPF (Diesel Particulate Filter) 33 is provided for collecting the.

  A first EGR passage 35 and a second EGR passage 37 are provided between the intake passage 3 and the exhaust passage 5. The first EGR passage 35 is configured to recirculate exhaust gas from the downstream side of the DPF 33 to the upstream side of the compressor 21 of the turbocharger 19. Specifically, the first EGR passage 35 extends from the downstream side of the DPF 33 to between the intake throttle valve 17 and the compressor 21 of the turbocharger 19. The first EGR passage 35 is provided with a first EGR cooler 39 that lowers the temperature of the exhaust, and a first EGR valve 41 that adjusts the recirculation amount of the exhaust. The first EGR passage 35 is used in a high load operation region where the load of the diesel engine 1 is relatively high.

  The second EGR passage 37 is configured to recirculate exhaust gas from the downstream side to the upstream side of the diesel engine 1. Specifically, the second EGR passage 37 extends from between the diesel engine 1 and the turbine 29 of the turbocharger 19 to between the I / C passage throttle valve 25 and the manifold 27. The second EGR passage 37 is provided with a second EGR cooler 43 that lowers the exhaust temperature and a second EGR valve 45 that adjusts the recirculation amount of the exhaust.

  The ECU 47 controls intake, exhaust, and fuel injection of the diesel engine 1. Specifically, the ECU 47 controls the intake air amount to the diesel engine 1 by controlling the opening degree of the intake throttle valve 17 and the I / C passage throttle valve 25. Further, the ECU 47 controls the EGR amount recirculated to the diesel engine 1 by controlling the opening degrees of the first EGR valve 41 and the second EGR valve 45. The ECU 47 controls the oxygen concentration in the combustion chamber 7 by controlling the opening degree of the intake throttle valve 17, the I / C passage throttle valve 25, the first EGR valve 41, and the second EGR valve 45.

The ECU 47 controls the timing and amount of main injection and pilot injection for supplying fuel into the combustion chamber 7 by controlling the injector 11. Here, the main injection is to generate a torque by injecting a relatively large amount of fuel into the combustion chamber 7 and igniting this fuel. Compared with the pilot injection performed before the main injection, A small amount of fuel is injected into the combustion chamber 7 to mix the fuel and air. Each control by the ECU 47 includes a crank angle sensor 49 for detecting the crank angle (CA) of the piston 9, an intake pressure sensor 51 for detecting the pressure state of the intake air, and an O ₂ for detecting the oxygen concentration of the exhaust gas. Sensor 53, an air flow sensor 55 for detecting the flow rate of air flowing into the diesel engine 1, an intake air temperature sensor 57 for detecting the temperature of air flowing into the diesel engine 1, and an amount of depression of an accelerator (not shown) (accelerator opening) This is performed based on the detection result of the accelerator opening sensor 59 that detects the degree). In addition, a differential pressure sensor 61 that detects the differential pressure between the upstream side and the downstream side of the DPF 33 is provided near the DPF 33, so that the amount of PM collected by the DPF 33 can be detected. ing.

  FIG. 2 is a map showing a fuel injection mode corresponding to the state of the diesel engine. As shown in FIG. 2, in the diesel engine 1, two types of fuel injection modes, a diffusion combustion mode and a premixed combustion mode (PCI combustion mode), are switched according to the diesel engine load and the diesel engine speed.

  In the diffusion combustion mode, the ECU 47 performs the pilot injection and the main injection when the piston 9 is in the vicinity of the top dead center in the compression process of the combustion chamber 7 so that the fuel is injected into the combustion chamber 7. To control. Specifically, in the diffusion combustion mode, pilot injection is performed immediately before the piston 9 reaches top dead center, and main injection is performed immediately after the piston reaches top dead center. Are performed in parallel.

  On the other hand, in the premixed combustion mode, the ECU 47 controls the injector 11 so that fuel is injected into the combustion chamber 7 at a timing earlier than in the diffusion combustion mode. In the premixed combustion mode, the pilot injection and the main injection are performed before the piston 9 reaches the top dead center, and the fuel injection is finished before the fuel is ignited. Thereby, before the fuel ignites, the fuel can create a uniform atmosphere, and the equivalent ratio of the fuel and air can be made relatively low to suppress incomplete combustion of the fuel or generation of soot. This premixed combustion mode is used when the engine load is comparatively low and the rotational speed is comparatively low because it is necessary to secure time for making the fuel uniform. The ECU 47 switches the fuel injection mode between the premixed combustion mode and the diffusion combustion mode in accordance with the engine load and the engine speed.

FIG. 3 is a graph showing the target value of the oxygen concentration in the combustion chamber in each combustion mode. In this graph, the oxygen concentration transfer rate is shown on the X axis, and the oxygen concentration in the combustion chamber is shown on the Y axis. As shown in this figure, the oxygen concentration C ₁ when executing the diffusion combustion mode is higher than the oxygen concentration C ₂ when executing the premixed combustion mode. This is because when the diffusion combustion mode is executed, if the equivalent ratio of oxygen increases (oxygen decreases), CO, HC, or soot is likely to be generated. This is because it is necessary to suppress the incomplete combustion by setting the concentration of oxygen supplied to the gas to be higher than that in the case of executing the premixed combustion mode. Then, when moving from the premix combustion mode to the diffusion combustion mode, along the path L ₁ is gradually increased oxygen concentration in the combustion chamber 7, while, when the transition from the diffusion combustion mode to the premix combustion mode Gradually decreases the oxygen concentration in the combustion chamber 7 along the path L ₁ . When the oxygen concentration transfer rate in the diffusion combustion mode is 0.0 and the oxygen concentration transfer rate in the premixed combustion mode is 1.0, the oxygen concentration transfer rate increases or decreases in proportion to the oxygen concentration in the combustion chamber 7. To do.

  FIG. 4 is a graph showing the relationship between the timing of changing between the diffusion combustion mode and the premixed combustion mode and the change in the fuel injection mode in the conventional combustion control device, and FIG. It is a map used when changing between a mode and a premix combustion mode.

In FIG. 4, the horizontal axis indicates the crank angle (CA) of the piston 9, and the vertical direction indicates the fuel injection amount. As shown in this figure, in the conventional combustion control device, when shifting the combustion mode from the diffusion combustion mode to the premixed combustion mode, the pilot injection timing is gradually delayed and the pilot injection amount is gradually increased. Thus, the pilot injection amount is brought close to the pilot injection amount in the premixed combustion mode. In addition, when the combustion mode is shifted from the diffusion combustion mode to the premixed combustion mode, the pilot injection timing is gradually advanced and the pilot injection amount is gradually decreased to obtain the pilot injection amount in the diffusion combustion mode. It is designed to approach the amount. The pilot injection amount in the diffusion combustion mode and the premixed combustion mode is in the range of about 1.5 to 2.5 mm ³ / st.

In the map shown in FIG. 5, the oxygen concentration transfer rate is shown in the X-axis direction, the injection mode transfer rate is shown in the Y-axis direction, and the point (X, Y) = (0, 0) is the diffusion combustion mode. X, Y) = (1, 1) is the premixed combustion mode. Further, as shown in this figure, NOx increases when the amount of oxygen is large (EGR rate is low) and the combustion temperature is high, and NVH increases when the amount of oxygen is large and the injection timing is advanced, soot and HC increases when the amount of oxygen is small and the injection timing is delayed. Then, the conventional combustion control device controls the oxygen concentration transition rate and the injection mode transition rate, and moves along the transition path L _{2 in} which NOx, NVH, Soot, and HC are generally reduced.

  FIG. 6 is a graph showing the relationship between the pilot injection amount and the soot amount in a state close to the premixed combustion mode, and FIG. 7 shows the pilot injection amount and NVH in a state close to the premixed combustion mode. It is a graph of the relationship with quantity.

First, as shown in FIG. 6, in a state close to the premixed combustion mode, the soot amount decreases as the fuel injection amount of pilot injection increases. Further, as shown in FIG. 7, in a state close to the premixed combustion mode, the amount of NVH increases as the fuel injection amount of pilot injection increases. Further, when the fuel injection amount of the pilot injection in the state close to the premixed combustion mode is increased from, for example, about 1.5 to 2.5 mm ³ / st, the absolute value of the decrease rate of the soot is increased by NVH. It can be seen that the ratio is larger than the absolute value. That is, by increasing the fuel injection amount of the pilot injection in a state close to the premixed combustion mode, it is possible to significantly reduce the soot while suppressing an increase in NVH.

  FIG. 8 is a graph of the relationship between the timing when changing between the diffusion combustion mode and the premixed combustion mode and the change in the fuel injection mode in the combustion control apparatus according to the present embodiment, and FIG. 9 relates to the present embodiment. It is a map which a combustion control apparatus uses at the time of transfer to combustion mode.

First, as shown in FIG. 8, when shifting from the diffusion combustion mode to the premixed combustion mode, the ECU 47 gradually increases the pilot injection timing and changes the pilot injection amount from, for example, about 1.5 mm ³ / st. Increase in proportion. At this time, the ECU 47 corrects and increases the pilot injection amount by the conventional combustion control device. When the injection mode transition rate becomes 1.0 (immediately before the transition to the premixed combustion mode is completed), the ECU 47 sets the pilot injection amount to about 2.5 mm ³ / It is set to about 8 mm ³ / st larger than st. During the transition from the diffusion combustion mode to the premixed combustion mode by such control, the pilot injection amount becomes larger than the normal pilot injection amount of about 2.5 mm ³ / st, and as shown in FIG. The soot area can be reduced. Further, the ECU 47 controls the oxygen concentration in the combustion chamber 7 so that the oxygen concentration shift rate becomes 1.0 when the pilot injection amount is about 4 mm ³ / st. Thereafter, the ECU 47 reduces the pilot injection amount to about 2.5 mm ³ / st which is a normal fuel injection amount while keeping the oxygen concentration in the combustion chamber 7 substantially constant. Further, at this time, the main injection amount is gradually decreased and then increased so that the sum of the pilot injection amount and the main injection amount of the main injection immediately thereafter is uniform throughout the entire process at the time of transition to the combustion mode. It is like that.

  In this way, by reducing the pilot injection amount when the premixed combustion mode is shifted to, it is possible to ignite at an appropriate ignition timing and to suppress the amount of pilot fuel spilling from the combustion chamber. Thereby, since the fuel which contributes to generation | occurrence | production of torque increases, the operating efficiency of a diesel engine can be improved.

Further, when the ECU 47 shifts from the premixed combustion mode to the diffusion combustion mode, the ECU 47 first changes the pilot injection amount from about 2.5 mm ³ / st, which is the normal fuel injection amount in the premixed combustion mode, to about about more than that. Increase to 4 mm ³ / st. Thereafter, the ECU 47 reduces the pilot injection amount to about 1.5 mm ³ / st, which is the fuel injection amount in the diffusion combustion mode, while gradually delaying the pilot injection timing.

  FIG. 10 is a flowchart showing a series of processes of the ECU when the combustion mode is shifted. In FIG. 10 and the following description, the symbol “S” indicates “step”.

  When a series of processes starts, the ECU 47 determines in S1 whether or not there is a request for shifting to the combustion mode. This process is performed by the ECU 47 reading the detection result of the accelerator opening sensor 59 and comparing the relationship between the engine load and the engine speed with the map of FIG. When the relationship between the engine load and the engine speed changes and the relationship shifts from the premixed combustion mode region on the map of FIG. 2 to the diffusion combustion mode region, the ECU 47 starts from the premixed combustion mode. It is determined that there is a request to shift to the diffusion combustion mode. The ECU 47 also changes from the diffusion combustion mode when the relationship between the engine load and the engine speed changes and the relationship shifts from the diffusion combustion mode region to the premixed combustion mode region on the map of FIG. It is determined that there is a request for transition to the premixed combustion mode. And when there exists any transfer request | requirement, ECU47 performs the process after S2.

In S2, the ECU 47 corrects the pilot injection amount. Thereby, the transition form of the fuel injection by the injector 11 is corrected from the transition form as shown in FIG. 4 to the transition form as shown in FIG. Next, in S3, the ECU 47 shifts the injection mode based on the oxygen concentration shift rate. Specifically, in S3, the ECU 47 increases the accelerator depression amount from less than a predetermined amount to a predetermined amount or more, and when there is a request to shift from the current premixed combustion mode to the diffusion combustion mode, the premixed combustion is performed. Processing for shifting from the mode to the diffusion combustion mode is performed. On the other hand, when the accelerator depression amount decreases from a predetermined amount or more to less than a predetermined amount and there is a request to shift from the current diffusion combustion mode to the premixed combustion mode, the diffusion combustion mode is changed to the premixed combustion mode. Perform the process to migrate. In this process, first, the ECU 47 controls the opening degree of the first EGR valve 41 and the second EGR valve 45, the intake throttle valve 17 and the I / C passage throttle valve 25, and the combustion of the diesel engine 1 according to the graph shown in FIG. The oxygen concentration in the chamber 7 is shifted. Thereby, the oxygen concentration in the combustion chamber 7 is gradually shifted. At this time, the ECU 47 controls the opening degrees of the first EGR valve 41 and the second EGR valve 45 so as to increase or decrease the oxygen concentration in the combustion chamber 7 in accordance with the direction of transition. At the same time, the ECU 47 predicts the current oxygen concentration in the combustion chamber 7 based on the detection result of the oxygen concentration in the exhaust passage 5 by the O ₂ sensor 53, the opening degree of the intake throttle valve 17, and the like. Then, the ECU 47 selects the injection mode transition rate corresponding to the oxygen concentration predicted with reference to the map shown in FIG. The ECU 47 controls the injector 11 so that the fuel injection mode corresponding to the selected injection mode transition rate is executed while monitoring the detection result of the crank angle sensor 49. This process is repeated until it is determined in S4 that the transition to the combustion mode has been completed.

  In S5, the ECU 47 ends the correction of the fuel injection amount in S2, and ends the series of processes.

  Thus, by correcting the pilot injection amount when shifting to the combustion mode and shifting between the diffusion combustion mode and the premixed combustion mode, the pilot injection amount is once increased and then decreased, The soot area on the map can be reduced. In addition, when the combustion mode is shifted from the diffusion combustion mode to the premixed combustion mode, the timing of fuel ignition can be delayed by reducing the pilot injection amount, so that the operation efficiency of the diesel engine 1 is improved. Can do.

In the above embodiment, the oxygen concentration in the combustion chamber 7 is predicted based on the detection result of the O ₂ sensor 53 provided in the exhaust passage 5, but an oxygen concentration detection sensor is provided in the manifold 27. The ECU 47 may read the detection result of this sensor.

1 Diesel engine 7 Combustion chamber 47 ECU

Claims (6)

A main injection that injects fuel into the combustion chamber at a first timing with the oxygen concentration in the combustion chamber of the diesel engine as a first oxygen concentration, and a pilot injection that injects fuel into the combustion chamber before the main injection A diffusion combustion mode in which the oxygen concentration in the combustion chamber is set to a second oxygen concentration lower than the first oxygen concentration, and the fuel is injected into the combustion chamber at a second timing earlier than the first timing. Combustion control device for a diesel engine that controls the diesel engine in two combustion modes of a premixed combustion mode in which a main injection to be injected and a pilot injection to inject fuel into the combustion chamber before the main injection are performed Because
The combustion mode of the diesel engine is set to the diffusion combustion mode when the engine load is equal to or higher than the predetermined load, and the combustion mode is set to the premixed combustion mode when the engine load is less than the predetermined load. Comprising combustion mode control means for controlling,
The combustion mode control means controls the fuel injection amount so that the pilot injection amount in the premixed combustion mode is larger than the pilot injection amount in the diffusion combustion mode. Changing the combustion mode between the diffusion combustion mode and the premixed combustion mode, increasing the pilot injection amount until it becomes larger than the pilot injection amount in the premixed combustion mode, and then reducing the pilot injection amount;
A diesel engine combustion control device.   The combustion mode control means is configured to keep the oxygen concentration in the combustion chamber substantially constant when the pilot injection amount is changed between an injection amount in a premixed combustion mode and an injection amount larger than that. 2. A combustion control apparatus for a diesel engine according to 1.   The combustion control apparatus for a diesel engine according to claim 2, wherein the combustion mode control means gradually changes the oxygen concentration in the combustion chamber when the pilot injection amount is gradually changed.   4. The combustion mode control means according to claim 1, wherein an interval between the pilot injection and the main injection in the premixed combustion mode is made larger than an interval between the pilot injection and the main injection in the diffusion combustion mode. The combustion control apparatus of the diesel engine as described in a term. A main injection that injects fuel into the combustion chamber at a first timing with the oxygen concentration in the combustion chamber of the diesel engine as a first oxygen concentration, and a pilot injection that injects fuel into the combustion chamber before the main injection A diffusion combustion mode in which the oxygen concentration in the combustion chamber is set to a second oxygen concentration lower than the first oxygen concentration, and the fuel is injected into the combustion chamber at a second timing earlier than the first timing. Combustion control method for a diesel engine in which the diesel engine is controlled in two combustion modes: a main injection to be injected and a premixed combustion mode in which pilot injection is performed to inject fuel into the combustion chamber before the main injection. Because
When the engine load changes from less than the predetermined load to more than the predetermined load, the combustion mode is controlled so that the combustion mode of the diesel engine is changed from the premixed combustion mode to the diffusion combustion mode. The combustion mode is controlled so that the combustion mode of the diesel engine is changed from the diffusion combustion mode to the premixed combustion mode when it changes to less than the load, and the pilot injection amount in the premixed combustion mode is the diffusion combustion. The fuel injection amount is controlled to be larger than the pilot injection amount in the mode,
A first step of increasing the pilot injection amount until it becomes larger than the pilot injection amount in the premixed combustion mode when the engine load changes and the combustion mode is shifted between the diffusion combustion mode and the premixed combustion mode; ,
A second step of reducing the pilot injection amount increased in the first step,
A combustion control method for a diesel engine characterized by the above.   When the engine load is reduced and the combustion mode is shifted from the diffusion combustion mode to the premixed combustion mode, the pilot injection amount is gradually increased in the first step until the pilot injection amount becomes larger than the pilot injection amount in the premixed combustion mode. 6. The method for controlling a diesel engine according to claim 5, wherein the pilot injection amount is reduced in the second step.

Images