JPH10141124A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine, which can restrict the generation of NOx and which can lower the discharged variable of black smoke so as to improve the fuel consumption. SOLUTION: An injection device, which performs the preparatory injection for injecting fuel into a combustion chamber at the initial time of a suction process immediately after closing an exhaust valve, the main injection for injecting fuel into the combustion chamber near the compressive top dead point, and the pilot injection for injecting a small quantity of fuel before the main injection, is provided. Since a controller for controlling the injection device in response to the operating condition of an engine is provided, partial lean premixed compressive ignition combustion is performed so as to restrict the generation of NOx, and while the discharged variable of black smoke is lowered so as to improve the fuel comsumption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine, and more particularly, to a diesel engine capable of suppressing NOx generation and reducing black smoke emission to improve fuel efficiency.

[0002]

2. Description of the Related Art In order to reduce NOx contained in exhaust gas of a diesel engine, it is effective to perform a timing retard that suppresses the generation of NOx by delaying a fuel injection timing. It has been considered effective to increase the fuel injection pressure or to employ a reentrant combustion chamber in order to reduce the pressure.

[0003] However, if timing retardation is performed to reduce NOx contained in exhaust gas, there is a concern that the amount of black smoke emitted will increase and fuel efficiency will deteriorate. Also,
In high-pressure injection, although the atomization of fuel is improved, the emission of black smoke can be improved, but the combustion temperature rises and the emission of NOx increases. Therefore, it has been considered extremely difficult to improve fuel efficiency by reducing the amount of black smoke and suppressing the generation of NOx in diesel engines.

As a means for solving such a situation, a diesel engine of a homogeneous charge compression ignition system has been proposed in recent years. This homogeneous charge compression ignition type diesel engine
Fuel is injected into the combustion chamber at the beginning of the compression stroke, the injected fuel is vaporized and mixed in the compression stroke, and ignited and combusted by spontaneous ignition at the end of the compression stroke, forming a uniform lean mixture. It is possible to prevent the emission of black smoke while suppressing the generation of NOx.

However, in the conventional homogeneous charge compression ignition type diesel engine in which fuel is injected at the beginning of the compression stroke, a special fuel having poor ignition performance is supplied to a fuel injection device having a special configuration. The engine can be operated only in a limited load / rotation region, although it is necessary to supply the engine using the engine. For this reason, it has been considered that it is practically impossible to apply the above-described homogeneous charge compression ignition method to a vehicle engine having various loads and rotation ranges.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a diesel engine capable of suppressing black NOx emission while reducing NOx generation and improving fuel efficiency. Is an issue.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a preliminary injection for injecting fuel into a combustion chamber at an early stage of a suction stroke immediately after an exhaust valve is closed, and a method for burning fuel near a compression top dead center. An injection device for performing a main injection for injecting fuel into the chamber and a pilot injection for injecting a small amount of fuel into the combustion chamber prior to the main injection, and a controller for controlling the injection device in accordance with the operating state of the engine; It is characterized by.

The present invention provides an injection amount by providing a controller that variably controls the fuel injection amount in each injection by changing the period or the number of the preliminary injection, the main injection, and the pilot injection according to the operating state of the engine. Can be simplified.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall configuration diagram showing an embodiment of a diesel engine according to the present invention, in which a supply pump 5 to which fuel is supplied from a fuel tank 1 via a pre-filter segment 2, a feed pump 3 and a fuel filter 4 is provided. ing. Further, the discharge port of the supply pump 5 is connected to a common rail 7 via a check valve 6. An injection nozzle 8 provided in a combustion chamber of the engine is connected to a common rail 7 via a flow limiter 9 to constitute a pressure-accumulation type fuel injection device.

Reference numeral 10 denotes an electromagnetic spill valve for maintaining the pressure of the common rail 7 at a predetermined value, 11 a relief valve, 12 a pressure limiter for preventing an abnormal rise in fuel pressure of the common rail 7, and 13 an electromagnetic three-way provided on the injection nozzle 8. A rotation sensor 1 provided on a crankshaft 14 of the engine.
5. The controller 19 is supplied with a signal output from a cylinder discrimination sensor 16, an accelerator sensor 17, a pressure sensor 18 provided on the common rail 7, and other control information represented by an intake air temperature or an air pressure.

The controller 19 controls the operation of the supply pump 5 by supplying control signals to the electromagnetic spill valve 10 and the electromagnetic three-way valve 13 based on the various kinds of control information. Optimally controls the amount and timing of fuel supplied to the fuel cell.

The controller 19 determines the operating state of the engine based on the signals output from the rotation sensor 15 and the accelerator sensor 17. And the controller 1
By outputting a pre-injection signal from 9, pre-injection is performed at the beginning of the suction stroke immediately after the exhaust valve is closed. By outputting a main injection signal from the controller 19, the main injection is performed near the compression top dead center, and a pilot injection signal is output prior to the main injection to perform the pilot injection.

That is, the pressure-accumulation type fuel injection device having the above-described configuration and a conventionally known Hall type fuel injection nozzle are mounted on a direct injection type diesel engine, and the suction is performed based on a preliminary injection signal output from the controller 19. At the beginning of the stroke, an amount of fuel corresponding to 0 to 5% of the total injection amount is injected from the injection nozzle 8 into the combustion chamber. Subsequently, in the middle or late stage of the compression stroke, the controller 19 outputs a pilot injection signal to pilot-inject an amount of fuel corresponding to 2 to 15% of the total injection amount, and then outputs the main injection signal to output the compression top dead center. The remaining amount of fuel was injected near the point. FIG. 2 shows the valve opening characteristics of the injection nozzle 8.

As described above, at the beginning of the suction stroke, the total supply amount becomes zero.
If the fuel is pre-injected in an amount corresponding to ５5%, the pilot injection of the fuel in the amount of 2 to 15% in the middle or late stage of the compression stroke, and the main injection of the remaining amount of fuel, the pre-injection is performed. The fuel spray is diffused widely into the combustion chamber under the influence of the turbulence of the intake air and is sufficiently mixed. Then, when the temperature of the intake air rises due to the progress of the compression stroke, the vaporization of the fuel spray is promoted using the intake air whose temperature has risen as a heat source, so that a lean mixture having an equivalence ratio of less than 1 is formed.

The lean mixture formed as described above has no excess soot because it has excess oxygen.
In addition, since the heat capacity is large, the degree of heat generation due to the compression is low, so that it is difficult to ignite. Then, when the piston rises to the vicinity of the compression top dead center and the temperature becomes higher, a part of the lean air-fuel mixture self-ignites, but the remaining air-fuel mixture is left unburned.

When pilot injection is performed based on the pilot injection signal output from the controller 19, the pilot injection fuel is quickly vaporized and partially self-ignites. Then, since the remaining fuel is injected based on the main injection signal output following the pilot injection, the main injected fuel is quickly vaporized in the combustion chamber whose temperature has increased due to the combustion of the preliminary injection fuel and the pilot injection fuel. And burns the lean mixture formed by the preliminary injection fuel and the pilot injection fuel at once. At this time, since the lean mixture formed by the preliminary injection fuel and the pilot injection fuel contains excess oxygen, the generation of black smoke is suppressed.

In the combustion as described above, the combustion gas generated by igniting a part of the lean air-fuel mixture formed by the pre-injection fuel and the pilot injection fuel is present in the combustion chamber to bring about an internal EGR effect. For this reason, generation of NOx during combustion of the pilot injection fuel and the main injection fuel is reliably suppressed.

The present invention can suppress the generation of black smoke as described above. Therefore, it is possible to use a conventionally known EGR together, and it is possible to use NOx
And the effect of reducing CO and HC can be further enhanced.

The controller 19 variably controls the total fuel injection amount in accordance with the operating state of the engine, similarly to the case of a conventionally known diesel engine. Is also optimally controlled.

That is, when the engine is operated in the full load range, for example, the ratio of the amount of the pre-injection fuel, the amount of the pilot injection fuel, and the amount of the main injection fuel is set to 3-5: 2-
5: Set to about 95 to 90. When the engine is operated in the medium load range, the ratio of the amount of the pre-injection fuel, the amount of the pilot injection fuel, and the amount of the main injection fuel is set to 2 to
4: 5 to 10:93 to 86. When the engine is operated in the light load region, the ratio of the amount of the pre-injection fuel, the amount of the pilot injection fuel, and the amount of the main injection fuel is set to about 0-3: 7-15: 93-82. As a result, the emission of black smoke was reduced while the generation of NOx was suppressed, and the fuel economy was improved. FIG. 3 shows the characteristics of the exhaust gas concentration and the fuel consumption rate with respect to the NOx emission amount.

When the engine is operated in a light load region where the total fuel supply is extremely small, preliminary injection is performed at the beginning of the intake stroke, and pilot injection and main injection are performed at the middle or late stage of the compression stroke. And the air-fuel ratio of the lean air-fuel mixture becomes too large, so that the combustion flame is not smoothly diffused by the pilot injection fuel and the main injection fuel. There is a concern that the amount of emissions will increase.

However, according to the present invention, the ratio of the pre-injection fuel, the pilot injection fuel and the main injection fuel is variably controlled according to the operating state of the engine as described above, so that the light load region where the total fuel supply amount is extremely small. During the operation at, the pre-injection is omitted and the conventionally known pilot injection and main injection are performed, or the same combustion as that of the conventionally known ordinary diesel engine is performed only as the main injection to discharge HO and CO. Increase can be prevented,
In addition, for example, by selecting a normal fuel supply mode even when the engine is started in cold weather, it is possible to secure startability and suppress excessive generation of white smoke.

Further, in controlling each of the injected fuels as described above, the total injection amount of the fuel is controlled by variably controlling the injection period or the number of injections of the preliminary injection, the pilot injection, and the main injection according to the operating state of the engine. And the ratio of each injection amount can be easily changed.

As described above, according to the present invention, each injection amount of the preliminary injection, the pilot injection or the main injection can be arbitrarily changed by variably controlling the respective injection periods or the number of injections. Accordingly, the injection timing can also be changed and the supply operation can be switched to the same supply mode as that of a normal diesel engine, so that the fuel supply characteristics can be optimally controlled according to the operating state of the engine.

In the above-described embodiment, a case has been described in which a part of the fuel is supplied by using a pressure-accumulation type fuel injection device suitable for lean premixed combustion. Premixed pilot injection combustion can be performed using a mechanical injection pump that performs injection and main injection, or in the case where two types of pumps are used, fuel with a low cetane number is injected in preliminary injection. On the other hand, the combustion timing can be more reliably and optimally controlled by injecting fuel having a high cetane number in the pilot injection and the main injection.

The combustion in a lean premixed combustion type diesel engine largely depends on the temperature and oxygen concentration of the combustion chamber. Therefore, it is possible to provide an intake air temperature adjusting means for variably controlling the intake air temperature in accordance with the operation state of the engine, thereby performing more stable combustion even in a light load region.

Incidentally, since it is necessary to make the fuel injection timing earlier in order to perform lean combustion, fuel may be injected with the piston lowered. Therefore, when an injection nozzle having a large injection cone angle, such as a conventionally known injection nozzle, is used as it is, the amount of fuel spray reaching and adhering to the wall surface of the cylinder liner increases. Then, there is a concern that the vaporization of the fuel spray deteriorates, the HC and CO emissions are increased more than necessary, or the oil film is deteriorated by the attached fuel.

However, according to the present invention, it is possible to arbitrarily set the number of times of the preliminary injection and the pilot injection, which are likely to be performed in a state where the piston is lowered, so that the number of these injections is increased. By doing so, the amount of fuel injected at one time can be extremely reduced, so that the momentum of the fuel spray can be reduced and the fuel spray adhering to the wall surface of the cylinder liner can be made almost zero.
Therefore, according to the present invention, deterioration of HC and CO can be suppressed, and inconveniences such as deterioration of an oil film can be avoided.

[0029]

As is apparent from the above description, in the present invention, the pilot injection and the main injection are performed in the presence of the lean air-fuel mixture of the pre-injected fuel to cause ignition and combustion. In addition, the emission of black smoke can be reduced while suppressing the generation of NOx, thereby improving fuel efficiency.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a diesel engine according to the present invention.

FIG. 2 is an opening / closing characteristic diagram of an injection nozzle shown in FIG.

3 is a characteristic diagram of a flue gas concentration and a fuel consumption rate with respect to a NOx emission amount of the combustion according to the injection characteristic shown in FIG. 2 and the combustion according to the conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel tank 2 pre-filter segmenter 3 feed pump 4 fuel filter 5 supply pump 6 discharge valve 7 common rail 8 injection nozzle 9 flow limiter 10 electromagnetic spill valve 11 relief valve 12 pressure limiter 13 electromagnetic three-way valve 14 crankshaft 15 rotation sensor 16 cylinder Discrimination sensor 17 Accelerator sensor 18 Pressure sensor 19 Controller

Claims (2)

[Claims] 1. A preliminary injection for injecting fuel into a combustion chamber at an early stage of an intake stroke immediately after closing of an exhaust valve, a main injection for injecting fuel into the combustion chamber near a compression top dead center, and a small amount prior to main injection. A diesel engine comprising: an injection device for performing pilot injection for injecting the fuel into a combustion chamber; and a controller for controlling the injection device in accordance with an operating state of the engine. 2. The controller according to claim 1, wherein the controller changes the period or the number of times of the preliminary injection, the main injection, and the pilot injection in accordance with the operation state of the engine, and variably controls the fuel injection amount in each injection. The diesel engine according to claim 1.