JP2001193465A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine of premixed compressed ignition system, capable of operation in a load/speed region over a wide range. SOLUTION: This diesel engine, having a subsidiary chamber provided with a fuel injection nozzle and an air injection nozzle, is equipped with a subsidiary chamber scavenge step injecting only air into the subsidiary chamber from the air injection nozzle after premixed fuel is injected into a cylinder by the fuel injection nozzle and the air injection nozzle and a pilot fuel injection step injecting pilot fuel into the subsidiary chamber from the fuel injection nozzle in the latter period of a compression stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine capable of suppressing the generation of NOx and the like, and more particularly to a diesel engine that ignites and burns using a premixed lean mixture.

[0002]

2. Description of the Related Art Due to recent environmental problems, in diesel engines, nitrogen oxides (NOx) contained in exhaust gas
It is desired to improve fuel efficiency by reducing the emission of black smoke and hydrocarbons (HC) while reducing the emission of black smoke and hydrocarbons (HC). As a conventional technique for solving such a problem, a premixed compression ignition type diesel engine for reducing NOx and the like by compressively igniting a premixed lean mixture (hereinafter referred to as a lean premix) is known. Proposed. This premixed compression ignition type diesel engine injects fuel such as light oil into the cylinder at the beginning of the compression stroke, vaporizes and mixes the injected fuel in the compression stroke, and ignites and burns by self-ignition at the end of the compression stroke. By forming a uniform lean air-fuel mixture, it is possible to prevent the generation of black smoke while suppressing the generation of NOx as in the case of the lean-burn spark ignition engine. Have.

[0003]

However, as described above, in a conventional homogeneous charge compression ignition type diesel engine in which fuel is injected at an early stage of the compression stroke, a large NOx is generated.
Although there is an advantage that reduction is possible, there is a problem that the engine can be operated only in a limited load / rotation region because of self-ignition. For this reason, it has been considered that it is substantially difficult to apply the above-described homogeneous charge compression ignition method to a vehicle having a wide range of load and rotation, such as a vehicle engine.

[0004] The present invention has been made in view of the above circumstances, and an object thereof is to provide a wide range of loads and loads.
An object of the present invention is to provide a premixed compression ignition type diesel engine that can be operated in a rotation range.

[0005]

The present invention employs the following means in order to solve the above-mentioned problems. The diesel engine according to claim 1 is a diesel engine including a sub-chamber provided with a fuel injection unit and an air injection unit, wherein a premixed fuel is injected into a cylinder by the fuel injection unit and the air injection unit. Thereafter, a sub-chamber scavenging step of injecting only air into the sub-chamber from the air injection means, and a pilot fuel injection step of injecting pilot fuel from the fuel injection means into the sub-chamber at a later stage of the compression stroke. It is characterized by becoming.

According to such a diesel engine,
By providing the sub-chamber scavenging stage, the fuel in the sub-chamber is almost completely scavenged and becomes only air, so premature ignition of the premixed air in the cylinder is suppressed, and steady self-ignition of pilot fuel is achieved. A possible atmosphere can be formed. And
If the pilot fuel is injected into the sub-chamber in such an atmosphere at an appropriate timing, the pilot fuel steadily ignites itself and becomes an ignition source for the lean premixed gas. The self-ignition timing and the ignition timing for the lean premixed fuel can be controlled.

In this case, the sub-chamber scavenging step is desirably continued until the air filled in the sub-chamber further flows out into a cylinder, and preferably from the late stage of the suction stroke to the early stage of the compression stroke. It is good practice. In this way, the lean premixture compressed in the compression stroke can be prevented from flowing into the sub-chamber, so that the atmosphere in which the pilot fuel formed in the sub-chamber is capable of steady self-ignition can be maintained. it can.

It is preferable that the air injection means is provided so as to form a swirling flow of air in the sub-chamber. This promotes positive mixing of the premixed fuel and air, so that the uniformity is obtained. It becomes possible to form a lean premixture. Preferably, a throttle portion is provided in a flow path for communicating the sub-chamber with the inside of the cylinder, whereby the self-ignited pilot fuel is accelerated in the throttle portion. , A torch jet serving as a high-energy ignition source can be formed.

Further, the premixed fuel is preferably mixed with supply air having a reduced oxygen concentration in a cylinder, whereby premature ignition of the lean premixed fuel can be prevented. In addition, as a suitable means for lowering the oxygen concentration, there is EGR for recirculating exhaust gas to air supply.
Alternatively, the premixed fuel may be mixed with the supply air in the cylinder, and water may be injected into the premixed gas before combustion to lower the compression temperature to prevent premature ignition of the lean premixed gas.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a diesel engine according to the present invention will be described below with reference to the drawings. In FIG. 2, reference numeral 1 denotes a cylinder, 2 denotes a piston, 3
Is an air supply port, 4 is an air supply valve, 5 is an exhaust port, and 6 is an exhaust valve. In this diesel engine, a sub-chamber 7 having a circular cross section is provided at an upper portion of the cylinder 1. The sub-chamber 7 and a combustion chamber 8 formed above the piston 2 are communicated with each other through a flow path 9, and the flow path 9 has a throttle portion 9 a having a narrow flow path cross-sectional area.
Is provided. The outlet 9b where the flow channel 9 opens into the cylinder 1 is formed with an inclined surface such that the cross-sectional area of the flow channel gradually increases.

In the sub-chamber 7, the fuel injection nozzle 10 of the fuel injection means is provided at the upper part, and the air nozzle 11 of the air injection means is provided at the side. The one fuel injection nozzle 10 has a function of injecting a premixed fuel and a pilot fuel described later at a high pressure. The air injection nozzle 11 is connected to an air cylinder 14 via a solenoid valve 12 and a regulator 13 and receives a supply of compressed air adjusted to a predetermined pressure by the regulator 13. Also,
A compressor may be used instead of the air cylinder 14 and the regulator 13. The air stored in the air cylinder 14 is preferably pure air containing no impurities such as exhaust gas.

Reference numeral 15 indicates a water injection nozzle.
It is provided for the purpose of injecting water into the cylinder 1 at an appropriate timing before ignition to take away heat of vaporization and lower the temperature in the cylinder during the compression stroke. In addition, air supplied from the air supply port 3 includes:
Exhaust gas recirculation (so-called EGR) for reducing the oxygen concentration by introducing a part of the exhaust gas discharged from the exhaust port 5 is performed.

Next, a configuration example of the air injection nozzle 11 provided in the sub chamber 7 will be described with reference to FIG. The air injection nozzle 11 is disposed with a predetermined injection direction so as to form a swirling flow of air in the sub chamber 7. Preferably, a plurality of air injection nozzles 11 are arranged at an appropriate pitch so as to inject air in a tangential direction of a plane intersecting the fuel injection direction. In the example shown in the figure, for fuel that is injected vertically downward,
Three air jet nozzles 11 are arranged at a pitch of 120 degrees in a tangential direction of a circular horizontal plane perpendicular or substantially perpendicular to the air jet nozzle. The air injection nozzle 11 opens and closes when a valve seat 11b urged by a spring 11a moves up and down. When the solenoid valve 12 is closed, the urging force of the spring 11a wins and the valve seat 11b is pushed up to the position indicated by the broken line, closing the inlet 11c having a smaller diameter than the seat surface. However, when the solenoid valve 12 is opened, the regulator 1
Since the air pressure adjusted in Step 3 acts, the valve seat 11b receiving this pressure is pushed down against the bias of the spring 11a. As a result, the valve seat 11
The space 11d formed by cutting out the side surface of b serves as an air flow path, and the compressed air flowing from the inlet 11c is injected into the sub chamber 7 through the space 11d and the outlet 11e.

The operation of the four-stroke diesel engine constructed as described above will be described with reference to FIG. 1 together with the crank angle. In FIG. 1,
(1) shows the fuel injection timing of the fuel injection nozzle 10,
(2) the air injection timing of the air injection nozzle 11;
(3) shows the internal pressure in the cylinder 1, (4) shows the opening and closing timing of the exhaust valve 6, (5) shows the opening and closing timing of the air supply valve 4, (6) shows the crank angle, and (7) shows the stroke.

In the suction stroke in which the piston 2 goes down from the top dead center (TDC) to the bottom dead center (BDC), as shown in FIG. 1A, the air supply valve 4 is opened to supply air. The exhaust valve 6 is closed at an early stage close to the top dead center. During this time, the premixed fuel is injected from the fuel injection nozzle 10 into the sub chamber 7, and the air in the air cylinder 14 is injected from the air injection nozzle 11. At this time, the air injection nozzle 1
The fuel injection nozzle 10 starts the air injection first, and injects the premixed fuel from the fuel injection nozzle 10 at a slightly delayed timing. The premixed fuel thus injected into the sub-chamber 7 merges with the air flow forming the swirling flow, so that active mixing of the premixed fuel and air is promoted. As a result, the premixed fuel and the air are uniformly mixed and supplied to the combustion chamber 8 formed in the cylinder 1 through the flow path 9.

The premixed fuel and air supplied to the combustion chamber 8 are mixed with the supply air sucked from the supply port 3 and have an equivalent ratio of 1
The following homogeneous lean mixture is obtained. Here, as the intake air, a part of the exhaust gas (combustion gas) discharged in the exhaust stroke is circulated and introduced to reduce the oxygen concentration. The injection of the premixed fuel by the fuel injection nozzle 10 ends in the latter half of the suction stroke, but the air injection to the sub chamber 7 continues even after the suction stroke ends, and the air supply valve 4 is compressed by a compression valve (described later). Open until the beginning of the journey.

FIG. 1B shows a sub-chamber scavenging stage in which only air is injected into the sub-chamber 7 after the injection of the premixed fuel by the fuel injection nozzle 11 is completed. This sub-chamber scavenging step is continued until the air injected from the air injection nozzle 11 and filled in the sub-chamber 7 flows out to the combustion chamber 8 in the cylinder 1. This sub-chamber scavenging phase is generally performed from the late stage of the suction stroke in which the piston 2 approaches the bottom dead center to the beginning of the compression stroke in which the piston 2 starts rising toward the top dead center.

By performing this sub-chamber scavenging step,
The premixed fuel injected into the sub-chamber 7 and mixed with the air is almost completely delivered to the combustion chamber 8. Therefore, substantially only air (indicated by hatching in the figure) exists in the sub-chamber 7. This sub-chamber scavenging step is preferably continued until the air filled in the sub-chamber 7 flows out to the combustion chamber 8 in particular.
As shown in (2), even if the piston 2 rises toward the top dead center after entering the compression stroke, it is possible to prevent the lean premixed gas from flowing back into the sub chamber 7. As a result, only the air supplied from the air cylinder 14 is filled in the inside of the sub chamber 7, and a favorable atmosphere suitable for self-ignition of the pilot fuel described later is formed.

On the other hand, since the lean premixture in the combustion chamber 8 in the compression stroke has a reduced oxygen concentration, it is possible to prevent premature ignition by compression. Furthermore, water is injected from the water injection nozzle 15 at an appropriate timing to the lean premixture before ignition to lower the compression temperature, thereby preventing premature ignition. In this way, the lean premixed gas in the compression stroke is in an environment in which self-ignition is difficult such as low oxygen concentration and low compression temperature, and does not self-ignite until torch jet ignition described later is performed.
In this embodiment, premature ignition is prevented by using both oxygen concentration reduction by EGR and compression temperature reduction by water injection, but these can be appropriately selected in consideration of operating conditions and the like. For example, if the driving range is narrow,
The operation may be performed without reducing the oxygen concentration and the compression temperature, or only one of them may be adopted in consideration of various conditions.

Subsequently, as shown in FIG. 1D, in the latter half of the compression stroke in which the piston 2 has risen to the vicinity of the top dead center, the pilot fuel enters the sub chamber 7 filled with air from the fuel injection nozzle 10. Inject. At the time of performing such a pilot fuel injection stage, a sub-chamber 7 filled with pure air and in an atmosphere suitable for self-ignition of the pilot fuel,
A combustion chamber 8 in which the compressed lean premixture is filled with premature ignition prevented is separated in a flow passage 9.
The pilot fuel injected into the sub-chamber 7 steadily self-ignites in a good ignition atmosphere where sufficient oxygen can be obtained, and thereafter functions as a high-energy ignition source for the lean premixture.

The pilot fuel thus self-ignited is
From the sub-chamber 7 toward the combustion chamber 8, at this time, it is accelerated when passing through the throttle 9 a of the flow passage 9. For this reason, the self-ignited pilot fuel becomes a high-energy ignition source called a torch jet, and as shown in FIG. 1 (e), flows into the combustion chamber 8 and is compressed into a lean premixed gas. Ignite. This ignition is performed at the beginning of the expansion stroke in which the piston 2 is near the top dead center. By adjusting the timing of injecting the pilot fuel earlier or later, the ignition is optimized according to the operating condition of the diesel engine. The ignition timing can be set. Further, since the outlet 9b of the flow passage 9 is formed as an inclined surface having an increased flow passage area, the torch jet flowing into the combustion chamber 8 of the cylinder 1 spreads in an annular shape and efficiently ignites in the radial direction. The lean premix can be burned. Thereafter, as shown in FIG. 1 (f), the lean premixture in the combustion chamber 8 burns and the piston 2
Is performed to push down to the bottom dead center. In the latter half of the expansion stroke, the exhaust valve 6 is opened to start exhausting the combustion gas.

In the exhaust stroke shown in FIG. 1 (g), the piston 2 rises from the bottom dead center to the top dead center, and exhausts exhaust gas from the exhaust port 5 in the open state. In the latter half of the exhaust stroke, the air supply valve 4 is opened to start air supply. Thereafter, after returning to the above-described air supply process, each process is sequentially repeated to operate the four-cycle diesel engine.

According to the above-described diesel engine, since the sub-chamber scavenging stage which is performed from the latter stage of the intake stroke to the early stage of the compression stroke is provided, the premixed fuel in the sub-chamber 7 is almost completely scavenged, and only pure air is provided. Is present. Therefore, an atmosphere in which the pilot fuel injected later from the fuel injection nozzle 10 can steadily self-ignite can be formed in the sub chamber 7. When pilot fuel is injected from the fuel injection nozzle 10 into the sub-chamber 7 in such an atmosphere at an appropriate timing, the pilot fuel steadily ignites itself and becomes an ignition source for the lean premix. The self-ignited pilot fuel is accelerated when passing through the throttle section 9a to form a torch jet. Since this torch jet is a high-energy ignition source that extends annularly in the combustion chamber 8, the ignition timing for the pilot fuel and the ignition timing for the lean premixed fuel can be adjusted by appropriately adjusting the injection timing of the pilot fuel. Can be controlled.

As described above, when the ignition timing of the lean premixed fuel can be controlled, the operable range of the diesel engine of the premixed compression ignition type which has an advantage that the NOx can be greatly reduced is expanded. be able to. That is, since the ignition control can be performed by selecting the optimal ignition timing according to the operating condition, the operation can be performed over a wide range without being limited by the load / rotational region which is limited due to self-ignition. Becomes possible.

In order to make this possible, among the main technical problems, the first technical problem of forming a uniform lean premixed air is that air is injected from the air injection nozzle 11 so as to generate a swirling flow. The problem is solved by actively promoting the mixing of the premixed fuel and the air injection in the sub chamber 7. Regarding the second technical problem of preventing premature ignition of a uniform lean premixed gas, the oxygen concentration of the premixed gas is reduced by EGR that recirculates exhaust gas to the supply air, and the premixed gas before ignition is reduced. This is solved by injecting water to lower the compression temperature. Regarding the third technical problem of steady ignition of the pilot fuel, a sub-chamber scavenging stage is provided to remove the premixed fuel from the sub-chamber 7 and to provide an atmosphere that is easy to ignite in which only the pure air is filled. The problem is solved by forming the sub chamber 7 and separating it from the lean premixture in the combustion chamber 8.
Regarding the fourth technical problem of igniting a uniform lean premix, the pilot fuel self-ignited in the sub-chamber 7 is ignited by a high energy ignition source of a torch jet formed by passing through the throttle 9a. Is solved.

FIG. 4 shows a modified example of the present invention described above.
a is formed. The convex portion 2a enters the outlet portion 9b of the flow passage 9 connecting between the sub-chamber 7 and the combustion chamber 8 near the top dead center, thereby forming an annular outlet flow passage that expands in the radial direction. It was made. With this configuration, the pilot fuel that has self-ignited in the sub-chamber 7 is accelerated through the throttle portion 9a, and then flows out into the combustion chamber 8 through the annular flow path formed by the convex portion 2a. You will be guided to do so. For this reason, the torch jet is formed in an annular shape that reliably expands in the radial direction in the combustion chamber 8, and can prematurely ignite and efficiently ignite the lean premixture in a compressed state. .

[0027]

According to the above-described diesel engine of the present invention, the sub-chamber is scavenged to form a favorable atmosphere suitable for the self-ignition of the pilot fuel, thereby enabling the pilot fuel to steadily self-ignite. In addition, the pilot fuel steadily self-ignited is accelerated in the throttle section to form a torch jet, and a uniform lean premixture compressed in a state where premature ignition is prevented is ignited by the torch jet. Therefore, reliable ignition by the high energy ignition source is possible. Therefore, the ignition timing can be controlled by the torch jet by adjusting the injection timing of the pilot fuel. Accordingly, the homogeneous charge compression ignition type diesel engine can be operated in a wide operating range, and for example, an excellent effect that it can be applied to a vehicle engine having a wide engine operating range such as a load and a rotation range. Is played. That is, there is an effect that it is possible to prevent the emission of black smoke while suppressing the generation of NOx, and to provide a diesel engine for vehicles that is also excellent in fuel efficiency.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing one embodiment of a diesel engine according to the present invention.

FIG. 2 is a system diagram showing a main configuration of a diesel engine according to the present invention.

3A and 3B are diagrams showing a configuration of an air injection nozzle in FIG. 2, wherein FIG. 3A is a layout view on a cylinder, FIG. 3B is a longitudinal sectional view of the air injection nozzle, and FIG. It is sectional drawing.

FIG. 4 is a sectional view showing a modified example of the diesel engine according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 cylinder (cylinder) 2 piston 2a convex part 3 air supply port 4 air supply valve 5 exhaust port 6 exhaust valve 7 sub chamber 8 combustion chamber 9 flow path 9a throttle part 9b outlet part 10 fuel injection nozzle (fuel injection means) 11 air Injection nozzle (air injection means) 15 Water injection nozzle

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/38 F02D 41/38 B (72) Inventor Hidenori Egashira 3000 Tana, Sagamihara City, Kanagawa Prefecture Mitsubishi Heavy Industries F-term (reference) in Sagamihara Seisakusho Co., Ltd. LB11 LC01 MA18 NE11 NE12 PE03A

Claims (7)

[Claims] 1. A diesel engine having a sub-chamber provided with a fuel injection means and an air injection means, wherein said fuel injection means and said air injection means inject a premixed fuel into a cylinder. A sub-chamber scavenging step of injecting only air into the sub-chamber from the means, and a pilot fuel injection step of injecting pilot fuel from the fuel injection means into the sub-chamber at a later stage of the compression stroke. Diesel engine. 2. The diesel engine according to claim 1, wherein the sub-chamber scavenging step is continued until the air filled in the sub-chamber flows out into the cylinder. 3. The diesel engine according to claim 1, wherein the sub-chamber scavenging step is performed from a late stage of an intake stroke to an early stage of a compression stroke. 4. The diesel engine according to claim 1, wherein the air injection means is installed to form a swirling flow of air in the sub-chamber. 5. The diesel engine according to claim 1, wherein a throttle portion is provided in a flow path that connects the sub-chamber with the inside of the cylinder. 6. The diesel engine according to claim 1, wherein the premixed fuel is mixed with supply air having a reduced oxygen concentration in a cylinder. 7. The diesel engine according to claim 1, wherein the premixed fuel is mixed with supply air in a cylinder, and water is injected into a premixed gas before combustion.