JPH11351091A - Fuel injection valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection valve that can expand the range of premixed compressive-ignition combustion that offers a desirable exhaust emission characteristic. SOLUTION: The fuel injection valve comprises a fuel spray nozzle 1b formed at its pintle with two types of nozzle hole 8e and 17, the injection axes of which are crossed just outside their outlets, and which individually spray a fuel of a small cetane number and a fuel of a large cetane number out respectively, and a duplex valve needle 6 for directing both fuels together just outside both nozzle-hole outlets and spraying them to the piston situated out of its top dead center, at premixed compressive-ignition combustion. At premixed compressive-ignition combustion, this structure therefore sprays a cetane-number- lowered fuel out in the spray shape most suitable for this combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection valve suitable for homogeneous charge compression ignition combustion.

[0002]

2. Description of the Related Art In a diesel engine, a diesel combustion is generally performed in which fuel is injected near a top dead center of a compression stroke and the fuel is burned by compression heat.
In this diesel combustion, since the time until the fuel burns is considerably short, a large amount of NOx and black smoke are likely to be generated.

[0003] In order to reduce such NOx and black smoke, it has been found that, for example, lean combustion can be carried out with a lean mixed gas. Therefore, in order to realize this lean combustion, a diesel engine employing a premixed compression ignition combustion system has been proposed in recent years.

[0004] The homogeneous charge compression ignition combustion system of the engine is as follows:
The fuel is injected into the cylinder at an early stage, the fuel is mixed with the air in the cylinder over time, and the entire cylinder is made to have a uniform lean mixture before burning. Specifically, in the premixed compression ignition combustion, for example, fuel is injected into a cylinder at the beginning of the compression stroke, the fuel is vaporized and mixed in the compression stroke, and the premixed fuel is self-ignited at the end of the compression stroke. It is to try.

[0005] Incidentally, diesel engines use light oil as fuel. However, because of good ignitability (high cetane number fuel), high compression, which causes a high temperature rise in the cylinder during premixed compression ignition combustion, is used. In the operation with a high ratio or high load, there is a problem that compression self-ignition occurs in the middle of the compression stroke and knocking occurs.

For this reason, the homogeneous charge compression ignition combustion can be operated only at a low compression ratio in which knocking does not occur, and only in a narrow operating range (low load range, medium load range) in which knocking does not occur.

Therefore, as a countermeasure, it is conceivable to change the cetane number of the fuel so as to adopt the homogeneous charge compression ignition combustion even in a higher compression ratio / higher load region. For example, a premixed compression ignition is performed by using a fuel injection valve having a structure in which two types of flow paths are combined into one inside a nozzle and injected from one injection hole as shown in JP-A-7-243355 and JP-A-2538908. At the time of combustion, it is conceivable to mix a low cetane number fuel and a high cetane number fuel inside the nozzle and to inject fuel with a different cetane number from one injection hole.

[0008]

By the way, in the premixed compression ignition combustion, the piston is optimally sprayed toward the piston cavity at a point away from the top dead center without touching the surrounding wall. Is required. Specifically, a narrow injection angle, a low penetration force, a high dispersion, and the like are required.

However, if the fuel injection valve is capable of injecting a fuel having a changed cetane number or a high cetane number fuel from one injection hole, it is difficult to obtain a spray shape suitable for homogeneous charge compression ignition combustion.

That is, in the premixed compression ignition combustion, sufficient exhaust gas performance is exhibited unless the fuel is sprayed toward the piston at a point away from the top dead center so as to promote premixing. Combustion cannot be obtained.

However, it is difficult to perform spraying with a narrow spray angle, low penetration force, and high dispersion by spraying from one injection hole. In particular, the injection hole used for diesel combustion has a high penetration force in the transverse (radial) direction suitable for the piston cavity (combustion chamber) located near top dead center, so this injection hole is premixed as it is If the fuel is diverted during compression ignition combustion, the fuel is attached to the wall around the nozzle because the piston is far from the top dead center. Mixed compression ignition fuel cannot be obtained.

[0012] For this reason, even if the region of the homogeneous charge compression ignition combustion can be expanded, good exhaust gas performance as originally intended,
That is, there is a problem that the premixed compression ignition combustion that causes low NOx and low black smoke is not performed, and a technique capable of sufficiently exhibiting the effect of the premixed compression ignition combustion is demanded.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel injection valve capable of expanding a region of homogeneous charge compression ignition combustion which provides good exhaust gas performance. It is in.

[0014]

According to a first aspect of the present invention, there is provided a fuel injector having a low cetane number fuel, wherein an injection axis is arranged at a front end of the fuel injection valve so as to intersect immediately after an outlet.
A fuel spray nozzle with two types of injection holes that can independently inject high cetane number fuel is provided. During premixed compression ignition combustion, both fuels collide immediately after the exit of both injection holes, leaving top dead center In the case of premixed compression ignition combustion, the fuel with a low cetane number is sprayed in a spray shape suitable for premixed compression ignition combustion by adopting a structure provided with means for spraying fuel toward the piston. I did it.

[0015] In addition to the above objects, the fuel injection nozzle according to the second aspect of the present invention provides a pre-mixed ignition combustion so that normal diesel combustion using a high cetane number fuel can be continued when premixed ignition combustion cannot be continued. When the mixed compression ignition combustion cannot be continued, the switching means for switching to diesel combustion by spraying only from the injection hole of the high cetane number fuel is provided.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on one embodiment shown in FIGS. FIG. 1 shows a diesel engine fuel injection device to which the present invention is applied. In the figure, reference numeral 1 denotes a variable fuel injection valve mounted on a cylinder head 2.

This fuel injection valve 1 is constructed by combining a nozzle tip 1a (corresponding to a fuel injection nozzle) adopting a double needle valve structure with a nozzle holder 1b having a double rod structure.

That is, to explain each part of the fuel injection valve 1, reference numeral 3 in FIG. 1 denotes a nozzle body of the nozzle tip 1a. As shown in detail in the enlarged view of FIG. 2, the nozzle body 3 has a large-diameter cylindrical portion 3a on the upper side and a small-diameter cylindrical portion 3b on the lower side. The lower end of the small-diameter cylindrical portion 3b faces the inside of the cylinder from the lower surface of the cylinder head 2.

In a needle valve chamber 5 formed in the space inside the nozzle body 3, a double needle valve 6 in which two types of large and small needle valves are concentrically combined is housed slidably in the vertical direction. . The double needle valve 6 has a structure in which a needle-shaped inner needle valve 7 and a bottomed cylindrical outer needle valve 8 slidably fitted on the outer peripheral surface of the inner needle valve 7 are combined. Used.

Specifically, the outer needle valve 8 is provided with the large-diameter cylindrical portion 3.
has a large-diameter shaft portion 8a that fits within a and a small-diameter shaft portion 8b that fits within a small-diameter cylindrical portion 3b. A conical surface 8c is formed at the boundary between the two shaft portions 8a and 8b, and the tip is a hemisphere. It has a bottomed cylindrical shape formed in a shape. A plurality of injection holes, for example, six injection holes 8e are formed at predetermined intervals in the circumferential direction on the base side of the hemispherical portion 8d. The hemispherical portion 8d protrudes from the lower end of the small-diameter cylindrical portion 3b. On the outer peripheral surface forming the linear portion of the small diameter shaft portion 8b, slit-shaped grooves 9 extending in the axial direction are formed in parallel with each other in the circumferential direction corresponding to the injection hole positions of the hemispherical portion 8d. I have. Each groove 9
Has an upper end extending to the conical surface 8c. The upper end of each groove 9 is formed with a conical surface 8c, that is, a sheet portion using a conical surface 8c, and an outer sheet portion 12 formed by combining a conical surface 8c with a sealing surface 11 that comes into contact with and separates from the conical surface 8c. An oil reservoir 14 formed on the inner surface of the large-diameter cylindrical portion 3a so as to surround a certain pressure-receiving surface 13, and a passage 16 formed on the peripheral wall of the large-diameter cylindrical portion 3a. It is open. The lower end of each groove 9 opens into the cylinder from the lower end of the small-diameter cylindrical portion 3b, and forms an injection hole 17 at a point where the injection axis intersects immediately after the outlet of the injection hole 8e.

The inner needle valve 7 has a needle shape having a thick shaft portion 7a that fits inside the large diameter shaft portion 8a and a thin shaft portion 7b that fits inside the small diameter shaft portion 8b. A conical sealing surface 1 formed on the inner surface of the small-diameter shaft portion 8b is provided at the lower end of the thin shaft portion 7b.
A conical surface 7c is formed in combination with the inner surface 9 and constitutes an inner seat portion 20 for opening and closing the injection hole 8e in the same portion. The inner sheet portion 20 has a passage 2 formed between the outer peripheral surface of the thin shaft portion 7b and the outer peripheral surface of the small diameter shaft portion 8b.
1. An oil reservoir 23 formed on the inner surface of the large-diameter shaft portion 8a so as to surround the pressure-receiving portion 22 formed immediately above the passage end, and a relay portion formed on the outer peripheral surface of the large-diameter shaft portion 8a. Annular groove 2
4, a passage 25 formed in the peripheral wall of the larger-diameter cylindrical portion 3a
Through the upper end surface of the nozzle body 3.

The nozzle tip 1a is combined with a nozzle holder 1b which enables fuel injection from both the injection holes 8e and 17 and fuel injection only from the injection holes 8e.

If the nozzle holder 1b is described,
Reference numeral 0 denotes a holder body of the nozzle holder 1b. The holder body 30 is formed in, for example, a bottomed cylindrical shape having substantially the same diameter as the outer diameter of the nozzle tip 1a. The lower end of the holder body 30 is connected to the nozzle body 3
The holder body 30 is connected in series to the nozzle tip 1a.

In a rod chamber 32 formed by the space in the holder body 30, a double rod 33 in which two types of large and small rod members are concentrically combined so as to correspond to the double needle valve 6 in the vertical direction. It is slidably housed. The inner portion of the double rod 33 is formed by connecting an outer rod member connected to the outer needle valve 8, for example, a cylindrical outer push rod 34 a, an outer spring 34 b, and a cylindrical outer pressure piston 34 c in series. An inner rod member connected to the inner needle valve 7, for example, an inner rod 35 formed by connecting a cylindrical inner push rod 35a, an inner spring 35b, and a cylindrical inner pressure piston 35c in series is slidably fitted. Structure is used.

Using this housing structure, the double rod 33
An oil sump chamber 36 is formed at the upper end of the rod so that the rod end can move in and out. A pair of passages 37 extending along the axial direction are formed outside the double rod 33, for example, in the peripheral wall portions on both sides of the holder body 30 sandwiching the rod chamber 32. The lower end of each of these passages 37 is
And a pair of independent fuel passages 38 that communicate with the passages 16 and 25 that are open at the upper end surface of each of the needle valves.

A passage portion 37a divided from the middle of each passage 37 communicates with a fuel inlet 39 formed in a pair of boss portions 30a protruding on both sides of the holder body 30.

Of these, the fuel inlet 39 toward the inner needle valve 7
Is connected to a high cetane number fuel pumping device 27 (for example, a device configured by combining an accumulator, an oil pump, and a fuel tank for light oil) that supplies a high cetane number fuel, for example, light oil. The fuel inlet 39 is provided with a low cetane number fuel pumping device 28 (for example, an accumulator, an oil pump, a water or methanol fuel tank) for supplying a low cetane number fuel, for example, water (or methanol or the like). Device).

The upper end of each passage 37 is connected to the oil sump chamber 36 through a passage portion 37 b having a check valve 40 and an orifice 41 interposed therebetween, and the fuel supplied from each fuel inlet 39 is connected to the oil reservoir chamber 36. Pressure is applied to the tip side of each of the inner / outer needle valves 7, 8 and the inner / outer pressure piston ends. The inner / outer needle valves 7 and 8 are closed using the fuel pressure applied so as to sandwich the double needle valve 6.

The oil sump chamber 36 has a normally closed solenoid valve 42a (leak valve:
A leak path 42 interposed with an orifice 42b is connected, and the pressure in the oil reservoir 36 can be released through a solenoid valve 42a.

An orifice 43 and a normally-closed solenoid valve 44a (leak valve: corresponding to a switching means) are provided in the middle of the passage portion 37a leading to the outer needle valve 8, for example, leading to a fuel tank (not shown). A leak path 44 is connected so that the pressure in the oil sump chamber 36 can be released through a solenoid valve 44a.

When the pressure in the oil sump chamber 36 is released by opening the solenoid valve 42a, the entire double needle valve can be lifted, and the fuel pressure applied to each tip of the double needle valve 6 allows the inner / outer valve to be opened. Light oil (high cetane number fuel) / water (low cetane number fuel) accumulated in the oil reservoirs 14 and 23 of the needle valves 7 and 8 are simultaneously injected from both the injection holes 8e and 17 and both fuels are injected immediately after the injection hole outlet. A collision jet is performed so that the spray is performed while colliding. From the collision of this lateral jet with the downward jet, the fuel adjusted to a low cetane number (fuel mixed with a high cetane number fuel and a low cetane number fuel) has a spray shape suitable for premixed compression ignition combustion. It is made to be sprayed. Specifically, when a downward jet collides with a horizontal jet,
While both fuels are mixed with each other, narrow injection angle, low penetration,
It is highly dispersed and becomes downward spray toward the piston 47 distant from the top dead center.

When both the solenoid valves 42a and 44a are opened to release the pressure in the oil reservoir 36 and the fuel pressure applied to the outer needle valve 8, the inner needle valve 7 can be lifted and the inner needle valve 7 is lifted.
With the fuel pressure applied to the tip of the inner needle valve, the oil sump 23 of the inner needle valve 7
Light oil that accumulates in the nozzle hole is injected from the injection hole 17. By the injection only from the injection holes 17, the spray suitable for normal diesel combustion, that is, the injection in the lateral (radial) direction is performed. Specifically, since the fuel is injected only from the injection hole 17, the fuel is sprayed in the lateral (radial) direction toward the inner surface (the inner surface of the combustion chamber) of the piston 47 near the top dead center.

Each of the solenoid valves 42a,
The ECU 46 (comprising, for example, a microcomputer) is connected to 44a. The ECU 46 controls the solenoid valves 42a and 44a to perform early injection of the low / high cetane number mixed fuel (from the initial stage of the intake stroke to the middle stage of the compression stroke) during premixed compression ignition combustion. During diesel combustion, normal injection of high cetane number fuel (injection near top dead center) is performed. For the switching of the injection, control for switching using the ignition delay near the top dead center is employed. Specifically, the ECU 46 stores, for example, the rotational speed of the diesel engine, the fuel injection amount, the intake temperature, the intake pressure, the water temperature,
Similarly, a function of calculating the average temperature and oxygen concentration of the in-cylinder gas near the top dead center (TDC) from the EGR rate, and from the calculation result, the vicinity of the top dead center of the fuel to be injected using the flow rate ratio of two fuels A function for calculating the ignition delay τm, for example, an ignition delay value set in advance from fuel properties and an estimated flow ratio of two flow paths for switching the spray shape between the premixed compression ignition combustion and the diesel combustion is set. . Also EC
In U46, by comparing the ignition delay value with the calculated ignition delay τm, the two injection holes 8e, 1
7 from the impingement injection, that is, premixed compression ignition combustion,
When there is no difference in ignition delay, a function is set to switch to injection only from the injection hole 17, that is, to diesel combustion.
As a result, switching between premixed compression ignition combustion using a fuel adjusted to a low cetane number and diesel combustion using a high cetane number fuel is performed. Also E
The CU 46 is provided with a function of performing switching after switching between premixed compression ignition combustion and diesel combustion via two-stage injection using both the early injection and the normal injection during one cycle, for example. Have been. With this function, in any switching from the premixed compression ignition combustion to the diesel combustion, and from the diesel combustion to the premixed compression ignition combustion, the transition is made after the intermediate transition combustion serving as a cushion is interposed.

FIG. 3 is a flow chart showing the control for switching between the homogeneous charge compression ignition combustion and the diesel combustion. Next, switching of combustion will be described based on the flowchart.

During operation of the diesel engine, the ECU 46
Is the engine speed N as shown in step S1.
e, fuel injection amount q, intake temperature, intake pressure, water temperature, EGR
The ratio is read, and the average temperature T and the oxygen concentration C of the in-cylinder gas in the vicinity of the top dead center (TDC) are calculated using these detected values in the subsequent step S2. Then, the next step S
In step 3, the ignition delay τm is calculated from the average temperature T and the oxygen concentration C, and the ignition delay τm is calculated from the fuel flow ratio to be injected.
m (τm = α · τu + β · τl, where τ
u: high cetane number fuel, τl: low cetane number fuel, α, β =
Fuel injection amount ratio from two flow paths).

On the other hand, the ECU 46 sets an ignition delay value for switching the combustion, specifically, the ignition delay values τp and τd, which are set in advance from the fuel properties and the estimated flow ratio of the two flow paths.
And read.

Here, the set value τp is a threshold value that defines the boundary between premix combustion and diesel combustion, and the set value τd
Is a threshold value that defines a transition combustion region that smoothes the switching of combustion (τp> τd).

Then, in steps S4 and S5, the threshold τ
p and τd are compared with the calculated ignition delay τm. As a result of this comparison, if the calculated ignition delay τm is higher than the threshold value τp, and it is determined that the premixed compression combustion without knocking is possible, the ECU 46 proceeds from step S4 to step S6, and performs, for example, compression. In the middle stage of the stroke, the solenoid valve 42a is opened according to the load. Then, as shown in FIG. 4A, both the inner needle valve 7 and the outer needle valve 8 are opened in the middle stage of the compression stroke. Thereby, water, which is a low cetane number fuel, and light oil, which is a high cetane number fuel, are injected by collision from the front end of the fuel injection valve 1, that is, as shown by Y in FIG. The fuel is injected into the cylinder while colliding with each other to form an optimal spray shape for premixed compression ignition combustion. Specifically, when the downward jet (low cetane fuel) collides with the lateral jet (high cetane fuel), the fuel does not adhere to the lower surface of the cylinder block 2 and has a low penetration force. A piston 4 located at a point away from top dead center while promoting fuel miniaturization
The spraying is performed at the optimum spray angle (narrow spray angle) toward the cavity 47a of the nozzle 7.

Thus, premixed compression ignition combustion, that is, combustion in which fuel is vaporized and mixed in the compression stroke, and the premixed fuel is self-ignited at the end of the compression stroke, is performed. At this time, the fuel to be injected is a fuel whose cetane number is adjusted to be small according to the mixing ratio of the fuel (fuel which is difficult to ignite), and the spray shape is an appropriate dedicated fuel in consideration of the premixed compression ignition fuel. It is the shape of.

Therefore, even under a higher compression ratio or a higher load range, good premixed compression ignition combustion that provides a sufficiently low NOx and low black smoke is performed. Therefore, the region where the effect of the homogeneous charge compression ignition combustion can be sufficiently exhibited can be expanded.

In addition, if the homogeneous charge compression ignition combustion cannot be continued, the operation is switched to the normal diesel combustion, so that it can cope with any operation range. That is, if the previously calculated ignition delay τm becomes small, and even if a fuel whose cetane number is adjusted to a small value and a spray shape suitable for premixed compression ignition combustion is used, it becomes difficult to continue good premixed compression ignition combustion, The ECU 46 switches to normal diesel combustion as shown in FIG. 4 (c) after intervening transitional combustion as shown in FIG. 4 (b).

More specifically, if the ECU 46 determines that the ignition delay τm has become small enough that good homogeneous charge compression ignition combustion cannot be continued, the process proceeds from step S5 to step S7. 42a is opened,
The two solenoid valves 42a and 44a are opened near the top dead center of the subsequent compression stroke. Then, as shown in FIG. 4B, both the inner needle valve 7 and the outer needle valve 8 are opened in the middle stage of the suction stroke, and only the inner needle valve 7 is opened near the top dead center of the subsequent compression stroke. Is done.

By the two-stage injection of the fuel adjusted to a low cetane number and the high cetane number fuel performed during this one cycle, the intermediate combustion (for smooth transition from the premixed compression ignition combustion to the diesel combustion) is performed. (Transition combustion) is performed.

When the ignition delay τm exceeds the set value τd for shifting to diesel combustion, the ECU 46 proceeds to step S8, where the two solenoid valves 42 near the top dead center of the compression stroke.
a, 44a are opened according to the load. Then, FIG.
As shown in (c), only the inner needle valve 7 opens near the top dead center. As a result, light oil (high cetane number fuel) is injected laterally from the injection hole 17 as shown by X in FIG. 2, and the cavity 47a (forming the combustion chamber) on the piston upper surface is formed in a spray shape suitable for diesel combustion. The fuel is sprayed into the part, which switches to diesel combustion. Since this diesel combustion covers an operation region in which the homogeneous charge compression ignition combustion cannot be continued, any operation condition can be handled.

In the above-described embodiment, as the transitional combustion, the total injection amount is divided into the collision injection from the injection holes 8e and 17 and the injection from the injection hole 17, and the injection is performed in two stages ( Although the injection amount is adjusted), the invention is not limited to this.
From 17, the fuel ratio may be changed between the premixed compression ignition combustion and the diesel combustion.

In the above-described embodiment, the nozzle holder 1b that closes by utilizing the pressure applied before and after the needle valve and opens by leaking the pressure on the rear end side is employed. Alternatively, a nozzle holder may be employed in which the needle valve is urged in the valve closing direction by an elastic member and the needle valve is opened by fuel pressure.

In the above-described embodiment, the present invention is applied to an engine that injects fuel directly into a cylinder, but may be applied to other engines, for example, an engine that injects fuel into an intake pipe.

[0048]

As described above, according to the first aspect of the present invention, during the premixed compression ignition combustion, the fuel whose cetane number is adjusted to be low is sprayed in a spray shape suitable for the premixed compression ignition combustion. Therefore, it is possible to obtain a good premixed compression ignition combustion that provides a sufficiently low NOx and a low black smoke under a higher compression ratio and a higher load range.

Therefore, the region where the effect of the homogeneous charge compression ignition combustion can be sufficiently exhibited can be expanded. According to the second aspect of the present invention, in addition to the above-described effects, when the homogeneous charge compression ignition combustion cannot be continued, the operation is switched to normal diesel combustion using a high cetane number fuel. It has the effect of being able to respond.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a fuel injection valve according to one embodiment of the present invention.

FIG. 2 is a sectional view showing a structure around a nozzle tip of the injection valve together with a spray shape of collision injection / single injection from the tip of the nozzle tip.

FIG. 3 is a flowchart for explaining control for switching a spray pattern between premixed compression ignition combustion and diesel combustion.

FIG. 4 is a view for explaining an injection timing accompanying the switching.

[Explanation of symbols]

 Reference Signs List 1 fuel injection valve 1a nozzle tip (fuel injection nozzle) 7 inner needle valve 8 outer needle valve 8e, 17 injection hole 33 double rod 38 pair of fuel passages (two types of flow passages) 42a 44a... Solenoid valve (switching means).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 61/10 F02M 61/10 A P 61/18 320 61/18 320A

Claims (2)

[Claims] 1. Each of the flow paths having two types of flow paths through which a low cetane number fuel and a high cetane number fuel are supplied, and having an injection axis arranged at a front end thereof so as to intersect immediately after the outlet. A fuel injection nozzle having two types of connected injection holes, and during premixed compression ignition combustion, the two fuels collide immediately after the exits of the two injection holes, and the fuel is sprayed toward the piston away from the top dead center. A fuel injection valve. 2. The fuel cell system according to claim 1, further comprising a switching means for switching to diesel combustion by spraying only from a high cetane number fuel injection hole when the homogeneous charge compression ignition combustion cannot be continued. Fuel injection valve.