JP4181941B2 - Diesel engine operation method - Google Patents

Description

The present invention relates to a method of operating a diesel engine.

  Conventionally, in an automobile engine or the like, a part of the exhaust gas is extracted from the exhaust side and returned to the intake side, and the exhaust gas returned to the intake side suppresses the combustion of fuel in the engine to increase the combustion temperature. Some of them employ so-called exhaust gas recirculation (EGR) that reduces the generation of NOx by lowering.

  However, reducing NOx by exhaust gas recirculation is in a trade-off relationship with the generation of black smoke due to poor combustion in the cylinder, so from the viewpoint of suppressing the generation of black smoke. There is a problem in that the amount of exhaust gas recirculation is limited, and it is difficult to significantly reduce NOx simply by recirculating exhaust gas.

For this reason, in recent years, fuel injection that should normally be performed near the compression top dead center is performed at a timing earlier than the compression top dead center, and fuel premixing is promoted by prior injection of fuel into the cylinder. Adoption of premixed compression ignition in which ignition and combustion are performed to suppress the generation of black smoke has been studied (for example, see Patent Document 1).
Japanese Patent Application Laid-Open No. 11-107772

  That is, if combustion is performed using such premixed compression ignition, combustion is performed in a state where the fuel is well dispersed and mixed and evenly diluted, so the combustion temperature is suppressed to a relatively low level. The generation of NOx is reduced, and moreover, it is difficult to produce a fuel-rich portion locally, which is effective in suppressing the generation of black smoke.

  However, in adopting such premixed compression ignition, if the fuel is only introduced in advance near the compression top dead center, the time delay until ignition is shortened in the high load region, and sufficient fuel premixing is achieved. For example, even if the injection timing is advanced to near the bottom dead center as a countermeasure, fuel premixing is promoted, but the fuel is injected near the bottom dead center where the exhaust temperature is low. The fuel hits the cylinder liner directly without being vaporized, and the oil film formed on the cylinder liner may be washed away, which may lead to problems such as seizure and damage to the engine reliability. The reality is that there is no prospect of adopting mixed compression ignition.

  Furthermore, when combustion is performed using premixed compression ignition, it is desirable that the ignition be performed near the compression top dead center even if the fuel injection timing is advanced from the compression top dead center. In the compression ratio of the engine, there is a problem that ignition occurs at a timing earlier than the compression top dead center, resulting in a loss of heat efficiency. It is also important to be able to properly control the ignition timing of the fuel. It is one of the important issues.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to expand the operable region by premixed compression ignition as compared with the prior art and to appropriately control the ignition timing.

The present invention relates to a premixed compression ignition type diesel engine in which fuel injection is performed at a timing earlier than the compression top dead center and fuel premixing is promoted before ignition combustion is performed in a fuel chamber. A control chamber provided between the intake port and the combustion chamber and having an intake valve interposed at a communicating portion with respect to the intake port side; a control valve for opening and closing between the control chamber and the combustion chamber; An injector that injects fuel, and the control valve is normally closed so that the valve is opened only during the first half of the exhaust stroke and the first half of the intake stroke until the first half of the compression stroke. and a jetting allowed to control the fuel to the injector in a state of containment, hot captures exhaust gas in a control room while compressing by opening the control valve to the previous period of the exhaust stroke, then the control valve Close and open the exhaust valve to exhaust the exhaust gas to the exhaust port and inject fuel from the injector into the hot exhaust gas confined in the control chamber, and then open the control valve in the first half of the intake stroke to open the control chamber After opening the air-fuel mixture to the combustion chamber, the intake valve is opened, and the intake air is introduced into the combustion chamber via the control chamber.Then, the piston is opened with the control valve open with the intake valve closed in the first half of the compression stroke. Diesel engine operation characterized in that the control valve is closed at an appropriate time in the compression stroke and the temperature at the compression top dead center is controlled to ignite the mixture near the compression top dead center. Method .

  In other words, when the diesel engine is operated in this way, fuel is injected in a state where high-temperature exhaust gas is contained in the control chamber in the later stage of the exhaust stroke, so that the fuel is not used under conditions of high temperature and low oxygen. The mixture of vaporized fuel and exhaust gas generated here is released into the combustion chamber in the first half of the intake stroke, and is ignited or vaporized quickly with only a small portion burned. Subsequent introduction of the intake air causes all of the air to be scavenged from the control chamber and mixed with the intake air over a sufficient period of time, so that an air-fuel mixture can be obtained in which the fuel is well dispersed and evenly diluted.

  When the air-fuel mixture is compressed and ignited, the effective compression ratio of the diesel engine is lowered by raising the piston while the control valve is opened in the first half of the compression stroke, so that the compression temperature in the combustion chamber does not reach the ignition temperature. In this way, the compression stroke is advanced, the control valve is closed at an appropriate time in the compression stroke, the mixture is further compressed from there, and the ignition temperature is reached near the compression top dead center. Thus, ignition at a timing earlier than the compression top dead center is prevented.

According to the method of operating a diesel engine of the present invention described above, it can achieve a variety of excellent effects such as the following.

  (I) By injecting the fuel into the high-temperature exhaust gas enclosed in the control chamber, the fuel can be quickly evaporated without being ignited under conditions of high temperature and low oxygen, and the vaporized fuel The mixture of gas and exhaust gas can be introduced into the combustion chamber from the first half of the intake stroke and allowed to mix with the intake air over a sufficient amount of time, so fuel can be premixed without any problem even in regions with higher loads than before. Therefore, it is possible to greatly expand the operable range by the premixed compression ignition as compared with the prior art.

  (II) Lowering the effective compression ratio of the diesel engine by raising the piston while the control valve is open in the first half of the compression stroke, and compressing the ignition timing of the air-fuel mixture by closing the control valve at an appropriate time in the compression stroke Since it can be controlled in the vicinity of the top dead center, it is possible to avoid the possibility that the air-fuel mixture is ignited at a timing earlier than the compression top dead center to cause a heat efficient loss.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 8 show an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a premixed compression ignition type diesel engine, 2 denotes a cylinder head, 3 denotes a cylinder block, 4 denotes a piston, Reference numeral 5 denotes a combustion chamber, 6 denotes an exhaust port, 7 denotes an exhaust valve, 8 denotes an intake port, and 9 denotes an intake valve. The intake valve 9 and the exhaust valve 7 are provided on an engine-driven camshaft (not shown). The valve is opened by a cam at an appropriate timing according to the stroke of each cylinder via a push rod or a rocker arm.

  Between the intake port 8 and the combustion chamber 5 in the cylinder head 2, a control chamber 10 having an intake valve 9 is provided at a communication location with respect to the intake port 8 side. A control valve 11 for opening and closing a communication point with respect to the combustion chamber 5 and an injector 12 for injecting fuel into the control chamber 10 are provided.

  Here, as shown in FIG. 2, regarding the opening / closing operation of the control valve 11 and the injection operation of the injector 12, a valve opening command 11a and a fuel injection command from a control device 13 constituting an engine control computer (ECU: Electronic Control Unit). More specifically, the control valve 11 is normally closed, and the electromagnetic of the control valve 11 is only between the first half of the exhaust stroke and the first half of the intake stroke until the first half of the compression stroke. The valve opening command 11a is output to the type actuator 14 to open the valve, and the fuel injection command 12a is output to the injector 12 in the later stage of the exhaust stroke to inject fuel.

  The control device 13 includes an accelerator opening signal 15a from an accelerator sensor 15 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and a rotation sensor 16 that detects the engine speed of the diesel engine 1. The engine speed signal 16a is input, and the operation state of the diesel engine 1 is constantly monitored to execute various engine controls.

  The operation method of the diesel engine 1 configured as described above will be described in detail below with reference to FIGS. 1 and 3 to 8.

  First, FIG. 1 shows the first half of the exhaust stroke. At this timing, the control valve 11 is opened and high-temperature exhaust gas is compressed into the control chamber 10, and then the control valve 11 is turned on as shown in FIG. The fuel is injected from the injector 12 into the high-temperature exhaust gas confined in the control chamber 10 while the exhaust valve 7 is closed and the exhaust valve 7 is opened to exhaust the exhaust gas to the exhaust port 6.

  Then, as shown in FIG. 4, after the exhaust valve 7 is closed and the intake / exhaust top dead center is reached, the control valve 11 is opened in the first half of the intake stroke as shown in FIG. After opening to the combustion chamber 5, as shown in FIG. 6, subsequently, the intake valve 9 is opened to introduce the intake air into the combustion chamber 5 through the control chamber 10.

  Next, as shown in FIG. 7, the piston 4 is lifted while the control valve 11 is opened in the first half of the compression stroke that has come after the intake valve 9 is closed, and as shown in FIG. 11 is closed, whereby the temperature in the combustion chamber 5 at a compression top dead center (not shown) is controlled, and the mixture is ignited near the compression top dead center.

  Note that the stroke from the compression top dead center to the later stage of the expansion stroke in FIG. 8 and after is performed as in the case of the ordinary diesel engine 1 with the control valve 11 closed, and is shown in the first half of the exhaust stroke after the expansion stroke. It will return to the state of 1.

  That is, if the diesel engine 1 is operated in this way, the fuel is injected in a state where the high-temperature exhaust gas is contained in the control chamber 10 in the latter stage of the exhaust stroke shown in FIG. FIG. 5 shows a mixture of vaporized fuel and exhaust gas generated here, in which the fuel is not ignited under a small number of conditions, or is vaporized quickly with only a small portion burned. It is opened in the combustion chamber 5 in the first half of the intake stroke, and all of the air is scavenged from the control chamber 10 by the introduction of the intake air (see FIG. 6), and the intake air takes a sufficient time in the stroke of FIGS. Therefore, an air-fuel mixture is obtained in which fuel is well dispersed and uniformly diluted.

  When this air-fuel mixture is compressed and ignited, the effective compression ratio of the diesel engine 1 is increased by raising the piston 4 while the intake valve 9 is closed and the control valve 11 is opened in the first half of the compression stroke shown in FIG. Thus, the compression stroke is advanced so that the compression temperature in the combustion chamber 5 does not reach the ignition temperature, the control valve 11 is closed at an appropriate time in the compression stroke shown in FIG. 8, and the air-fuel mixture is further compressed therefrom. Thus, since the ignition temperature is controlled to reach the compression top dead center, ignition at an earlier timing than the compression top dead center of the air-fuel mixture is prevented.

  The timing for closing the control valve 11 during the compression stroke shown in FIG. 8 is based on the accelerator opening signal 15a and the rotation speed signal 16a from the accelerator sensor 15 (load sensor) and the rotation sensor 16 in the control device 13. Since the operation state of the diesel engine 1 is monitored, an appropriate valve closing timing corresponding to the operation state may be appropriately read from the control map or the like and set.

  Therefore, according to the above-described embodiment, by injecting the fuel into the high-temperature exhaust gas confined in the control chamber 10, the fuel can be quickly evaporated without being ignited under the condition of high temperature and low oxygen. In addition, since the mixture of the vaporized fuel and the exhaust gas can be introduced into the combustion chamber 5 from the first half of the intake stroke and mixed with the intake air over a sufficient period of time, the load is higher than that in the prior art. In this case, the fuel can be premixed without any problem, and the operable range by the premixed compression ignition can be greatly expanded as compared with the prior art.

  Further, the piston 4 is raised while the control valve 11 is opened in the first half of the compression stroke to lower the effective compression ratio of the diesel engine 1 and the control valve 11 is closed at an appropriate time in the compression stroke to ignite the air-fuel mixture. Since the timing can be controlled in the vicinity of the compression top dead center, it is possible to avoid the possibility that the air-fuel mixture will ignite at a timing earlier than the compression top dead center and cause a heat efficient loss.

The method of operating a diesel engine of the present invention is not limited to the above embodiments, it is obvious that various changes and modifications may be made without departing from the scope and spirit of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is a systematic diagram regarding control of the control valve and injector of FIG. It is the schematic which shows the state of the latter half of the exhaust stroke in the diesel engine of FIG. It is the schematic which shows the state of the intake / exhaust top dead center in the diesel engine of FIG. It is the schematic which shows the state of the first half of the intake stroke in the diesel engine of FIG. It is the schematic which shows the state of the latter stage of the intake stroke in the diesel engine of FIG. It is the schematic which shows the state of the first half of the compression stroke in the diesel engine of FIG. It is the schematic which shows the state of the latter stage of the compression stroke in the diesel engine of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Cylinder head 5 Combustion chamber 6 Exhaust port 7 Exhaust valve 8 Intake port 9 Intake valve 10 Control chamber 11 Control valve 11a Valve opening command 12 Injector 12a Fuel injection command 13 Controller

Claims (1)

A cylinder head intake port and combustion are applied to a premixed compression ignition type diesel engine in which fuel injection is performed at a timing earlier than the compression top dead center and fuel premixing is promoted before ignition in the fuel chamber. A control chamber which is provided between the control chamber and which is provided with an intake valve at a communication position with respect to the intake port side, a control valve which opens and closes between the control chamber and the combustion chamber, and fuel is injected into the control chamber The injector and the control valve are normally closed, the valve is opened only during the first half of the exhaust stroke and the first half of the intake stroke until the first half of the compression stroke, and high-temperature exhaust gas is contained in the control chamber in the second half of the exhaust stroke. in a control device that allowed to inject fuel into the injector, taken into the control chamber while compressing the hot exhaust gas by opening the control valve to the previous period of the exhaust stroke, then, and closes the control valve Open the air valve and exhaust the exhaust gas to the exhaust port while injecting fuel from the injector into the hot exhaust gas confined in the control chamber, then open the control valve in the first half of the intake stroke and mix in the control chamber After opening the air to the combustion chamber, the intake valve is opened and the intake air is introduced into the combustion chamber via the control chamber, and then the piston is raised while the control valve is open with the intake valve closed in the first half of the compression stroke. closing the control valve at the appropriate time of the compression stroke Te, thereby operating method of a diesel engine, characterized in that occupied conducted near the compression top dead center ignition of the mixture to control the temperature at compression top dead center.

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