JPH0730693B2 - Fuel injection method for internal combustion engine - Google Patents

Description

The present invention relates to a fuel injection method for an internal combustion engine.

[Conventional technology]

Conventionally, in a direct injection type diesel engine, a cavity is formed on the top surface of a piston, a multi-hole injection nozzle is arranged in a cylinder head, and fuel is injected from each injection port of the injection nozzle into the cavity in four directions. In such a diesel engine, the fuel is usually not immediately ignited even when the injection of fuel is started, and is ignited after a certain ignition delay period. However, in such a diesel engine, as soon as the fuel is injected from each injection hole, it is atomized and atomized, so a large amount of fuel spray is formed in the cavity around the injection nozzle before the ignition delay period elapses. Will be. However, if a large amount of fuel spray is formed in the cavity around the injection nozzle before the ignition delay period elapses, it is formed around the injection nozzle when the ignition delay period elapses and ignition is performed. A large amount of fuel spray explosively burns all at once, resulting in combustion noise and a large amount of NOx.

To suppress the generation of such combustion noise and NOx, it is sufficient to ignite while the fuel spray formed in the cavity around the injection nozzle is small, and for that purpose the ignition delay period can be shortened. Become. Therefore, in order to shorten the ignition delay period, in addition to the conventional multiple injection holes for injecting fuel toward the periphery of the cavity, a sub injection hole is further provided, and a protrusion is formed in the center of the cavity. The fuel injected from this sub injection hole is made to collide with the upper end surface of the projection, and the collision action heats the atomized fuel by the heating means to ignite the fuel early, thereby generating combustion noise and NOx. A diesel engine that is suppressed is known (see Japanese Patent Laid-Open No. 59-79031).

In this diesel engine, it is considered that the ignition delay period can be shortened by utilizing the atomization action by the fuel collision. However, even in this diesel engine, the fuel injected from each injection hole toward the periphery of the cavity is atomized and atomized as soon as it is injected, so the ignition delay period elapses even if the ignition delay period is shortened. By the time a considerable amount of fuel spray has already been formed, thus leading to a sudden rise in pressure, resulting in combustion noise,
It is considered that a large amount of NOx is generated.

On the other hand, in order to promote atomization of the fuel and promote mixing of the injected fuel and air, a collision wall member is arranged in the center of the cavity, and the fuel injected from the fuel injection valve is applied to the upper wall surface of the collision wall member. A diesel engine that is made to collide is known (see Japanese Patent Laid-Open No. 59-211716). In this diesel engine, the fuel in the first stage is atomized when the fuel is injected from the fuel injection valve, and the injected fuel is collided with the upper wall surface of the collision wall member so that the fuel in the second stage is atomized. There is.

A diesel engine having the same structure as this diesel engine is described in Japanese Patent Application Laid-Open No. 52-40209. In this publication, there is no description of how the fuel is injected from the fuel injection valve. However, judging from the drawings of this publication, even in this diesel engine, the atomization of the fuel in the first stage at the time of fuel injection is performed. It is thought that is being done. That is, as shown in the drawing of this publication, in this diesel engine, the fuel injected from the fuel injection valve spreads in a conical shape. However, unless the injected fuel is atomized into droplets, the injected fuel does not spread conically, so in this diesel engine as well, the fuel injected from the fuel injection valve is atomized as soon as it is injected. As described above, even in this diesel engine, the fuel atomization in the first stage is performed at the time of fuel injection.

However, when the fuel atomization action of the first stage is performed when the fuel is injected from the fuel injection valve as described above, a large amount of fuel spray is formed in the cavity around the fuel injection valve when the ignition delay period elapses. Therefore, since a large amount of this fuel spray burns explosively at once, combustion noise is generated and a large amount of NOx is generated.

[Problems to be solved by the invention]

In this way, conventional diesel engines focus on how quickly the fuel is atomized immediately after injection,
As long as the focus is on how to quickly atomize the fuel in this way, suppress the generation of combustion noise,
It is difficult to reduce the amount of NOx generated. A similar problem occurs in an internal combustion engine using gasoline or methanol, and if fuel atomization is promoted immediately after injection, increasing the compression ratio to improve thermal efficiency causes knocking in which the air-fuel mixture explosively burns at once. It will be.

[Means for solving problems]

In order to solve the above problems, according to the present invention, the fuel injection of the internal combustion engine in which the fuel is injected from the fuel injection valve arranged at the center of the top surface of the combustion chamber into the cavity formed on the top surface of the piston. In the method, the fuel is injected from the fuel injection valve only toward the central portion of the cavity in the form of a liquid fuel flow in the shape of a liquid column that hardly spreads without being dispersedly injected toward the peripheral portion of the cavity, and then the liquid column is injected. Liquid fuel flow is collided with the center of the collision wall extending in the radial direction of the cavity at an intermediate height position in the cavity, and then the liquid fuel collided with the center of the collision wall is directed along the collision wall in the peripheral direction of the cavity. I try to scatter it.

〔Example〕

Referring to FIGS. 1 and 2, 1 is a cylinder block, 2 is a piston reciprocating in the cylinder block 1,
Reference numeral 3 denotes a cylinder head fixed on the cylinder block 1, 4 is a combustion chamber formed between the flat inner wall surface of the cylinder head 3 and the piston 2, 5 is a pair of intake valves, 6 is a pair of intake passages, and 7 is A pair of exhaust valves, 8 respectively indicate exhaust passages.
A circular cavity 9 is formed at the center of the flat top surface of the piston 2. The cavity 9 has a peripheral wall surface 9a having a cylindrical shape and a bottom wall surface 9b formed substantially flat. At the center of the bottom wall 9b of the cavity, the cylinder head 3
A projecting portion 10 projecting toward is formed. This protrusion 10
Is a circular collision surface 10 that is substantially parallel to the top surface of the piston 2.
a and a conical peripheral wall surface 10b whose cross-sectional area increases downward
And. In the embodiment shown in FIG. 1, the collision surface 10a is located on the cylinder axis. Also, this collision surface 10a is the third
It can be formed from a flat surface as shown in FIG. 3A, or can be formed from a concave surface with a concave center as shown in FIG. 3B.

A fuel injection valve 11 is attached to the center of the inner wall surface of the cylinder head 3. The fuel injection valve 11 includes a single injection hole 12, a needle 13 that controls the opening and closing of the injection hole 12, and a piezoelectric element 14 that operates the needle 13. Piezo piezoelectric element
When a voltage is applied, 14 extends in the longitudinal direction, and the extension action controls the opening and closing of the needle 13. Of course, it is also possible to use a fuel injection valve using a solenoid that has been conventionally used, or a fuel injection valve in which the opening / closing control of the needle 13 is mechanically controlled by the discharge pressure of the fuel injection pump.
The piezoelectric element of the fuel injection valve 11 is connected to the electronic control unit 20, so that the fuel injection action from the fuel injection valve 11 is performed by the output signal of the electronic control unit 20. Further, a spark plug 15 is attached to the cylinder head 3, and the spark plug 15
The discharge gap 16 is arranged so as to be extremely close to the peripheral wall surface 10b of the protrusion 10 when the piston 2 is at the top dead center position as shown in FIG.

The electronic control unit 20 is composed of a digital computer, and has a ROM (Read Only Memory) 22 and a RAM (Random Access Memory) 2 interconnected by a bidirectional bus 21.
3, a CPU (microprocessor) 24, an input port 25 and an output port 26. A crank angle sensor 27 and a rotation speed sensor 28 are connected to the input port 25. The crank angle sensor 27 generates an output signal indicating that, for example, the first cylinder is at the top dead center position. Therefore, it is judged from which output signal the crank angle sensor 27 should be injected into which cylinder. The rotation speed sensor 28 generates an output pulse each time the crankshaft rotates 30 degrees, for example. Therefore, the present crank angle can be calculated from the output signal of the rotation speed sensor 28 and the engine rotation speed can be calculated. A load sensor 30 is connected to the accelerator pedal 29, and the load sensor 30 is connected to the input port 25 via the AD converter 31. The load sensor 30 generates an output voltage proportional to the depression amount of the accelerator pedal 29. Meanwhile, output port
Reference numeral 26 denotes a piezoelectric element of the fuel injection valve 11 via the drive circuit 32.
Further, the output port 26 is connected to the spark plug 15 via the drive circuit 33 and the igniter 34.

Next, the fuel injection and ignition processing will be described with reference to FIG. Referring to FIG. 4, first, at step 40, the engine speed N calculated from the output pulse of the speed sensor 28 and the output signal of the load sensor 30 representing the engine load P are read. Next, at step 41, the fuel injection amount is calculated from the engine load P, for example. Then step
At 42, the fuel injection start timing is calculated from the engine speed N and the engine load P. The relationship between the engine speed N, the load P, and the fuel injection start timing I is stored in advance in the ROM 22 in the form of a map as shown in FIG. 5, and therefore, at step 42, the fuel injection is performed from the relationship stored in the map. The start time is calculated. Next, at step 43, the fuel injection completion timing is calculated from the fuel injection amount calculated at step 41 and the fuel injection start timing I. Next, at step 44, the ignition timing is calculated from the engine speed N and the load P. Engine speed N, load P
And the ignition timing θ are stored in advance in the ROM 22 in the form of a map as shown in FIG. 6. Therefore, in step 44, the ignition timing θ is calculated from the relationship stored in the map. Next, at step 45, data representing the fuel injection start timing I, the fuel injection completion timing and the ignition timing θ is output to the output port 26, and the fuel injection action and the ignition action are performed based on this data.

FIG. 7 shows an example of fuel injection timing when methanol is used as fuel, and FIG. 8 shows an example of ignition timing when methanol is used as fuel. In FIG. 7, A ₀ indicates the fuel injection start timing during high load operation, and A ₁ indicates the fuel injection completion timing during high load operation. Therefore, the arrow X in FIG. 7 indicates the fuel injection period during high load operation. Also,
In FIG. 7, B ₀ indicates the fuel injection start timing during low load operation, and B ₁ indicates the fuel injection completion timing during low load operation. Therefore, the arrow Y in FIG. 7 indicates the fuel injection period during the low load operation. On the other hand, in FIG. 8, C shows the ignition timing during high load operation, and D shows the ignition timing during low load operation.

As can be seen from FIG. 7, the fuel injection start timing is about 100 degrees before top dead center during engine high load operation. As described above, the fuel injection timing shown in FIG. 7 is an example, and even when methanol is used, for example, the fuel injection start timing during high load operation may be slightly delayed from 100 degrees before top dead center. , You can also speed it up. Further, when a fuel such as gasoline other than methanol is used, the fuel injection start timing during high load operation may be about 180 degrees before top dead center. However, it is a fact that the fuel injection start timing is considerably earlier than the fuel injection start timing that has been conventionally adopted when methanol is used.
The ignition timing shown in FIG. 8 is also an example, and the ignition timing varies depending on whether methanol is used or fuel other than methanol is used.

The internal combustion engine according to the present invention can have a compression ratio of 12: 0 or more, and the internal combustion engine shown in FIG. 1 has a compression ratio of 16.2.
In the present invention, good combustion can be obtained without knocking even at such a high compression ratio. Next, a method of forming a mixture and an ignition method according to the present invention will be described with reference to FIGS. 9 and 10.

FIG. 9 shows the moment when fuel injection is started from the injection hole 12 of the fuel injection valve 11. The injection hole 12 is directed to the collision surface 10a, and therefore, most of the fuel injected from the injection hole 12 collides with the collision surface 10a. That is, since the injection hole 12 is a single hole nozzle, most of the fuel injected from the injection hole 12 travels toward the collision surface 10a in the form of a liquid fuel flow in the form of a liquid column with almost no spread. Since most of the injected fuel is liquid as described above, the penetration force is large. Therefore, most of the injected fuel reaches the collision surface 10a even if the distance between the injection hole 12 and the collision surface 10a is considerably large. The fuel colliding with the collision surface 10a is atomized and scattered in the radial direction, but the injected fuel has a downward inertial force, so the fuel scattered in the radial direction is the peripheral wall surface 10b of the projecting portion 10 as shown by an arrow F. Along the bottom wall surface 9b of the cavity 9
Head towards. Therefore, a region having a high fuel density is formed around the protrusion 10. Next, the fuel around the protruding portion 10 diffuses in the cavities 9 in the radial direction, so that the air-fuel mixture is gradually formed in the cavity 9 from the peripheral wall surface 10a of the protruding portion 10 toward the peripheral wall surface 9a of the cavity 9. To be done. While the piston 2 is moving upward, the air-fuel mixture or air in the cavity 9 is pressed downward and therefore does not flow upward from the cavity 9. Therefore, the air-fuel mixture layer is formed in the cavity 9, and only the air is formed in the combustion chamber 4 above the top surface of the piston 2, so that the stratification is performed. Since the fuel injection start timing is early during engine high load operation, the vaporization and diffusion of the fuel in the cavity 9 sufficiently progress before the piston 2 reaches the vicinity of the top dead center, and therefore the cavity 9 is filled with the air-fuel mixture. . On the other hand, when the engine load is low, the fuel injection start timing is delayed, so the piston 2
The fuel does not sufficiently diffuse in the cavity 9 before reaching the vicinity of the top dead center. Therefore, in this case, a rich air-fuel mixture layer is formed around the projecting portion 10, and this rich air-fuel mixture layer The surrounding area is a donut-shaped air layer. However, in any case, a mixed gas region that is denser than the other regions is formed around the peripheral wall surface 10b of the protrusion 10.

FIG. 9 shows the moment when the ignition action by the spark plug 15 is performed. As described above, the ring-shaped rich air-fuel mixture region is formed around the peripheral wall surface 10b of the protruding portion 10 as indicated by the broken line G, and the discharge gap 16 of the spark plug 15 is within this rich air-fuel mixture region during ignition. It is arranged to be located in. When the rich air-fuel mixture in the region G is ignited by the spark plug 15, the fire immediately spreads over the rich air-fuel mixture region, and then the fire spreads radially in the cavity 9 to burn the air-fuel mixture in the cavity 9. In this way, the fire is
Since it spreads from the center of the area to the surroundings, the fire propagation distance is short,
Therefore, since the fuel speed becomes faster, the thermal efficiency improves, and HC, C
O will be reduced. Further, as described above, since only the air is in the combustion chamber 4 above the top surface of the piston 2, when the piston 2 reaches the vicinity of the top dead center as shown in FIG. The combustion chamber couple K between the flat inner wall surface of the cylinder head 3 and the cylinder head 3 is made of only air. Knocking occurs when the mixture in the combustion chamber even portion K is compressed and self-ignites when combustion starts and the pressure in the combustion chamber 4 rises. Since only air is present, self-ignition does not occur in the combustion chamber even part K, and thus knocking does not occur. Therefore, in the present invention, the compression ratio can be increased, and thus the efficiency of the engine can be greatly increased. FIG. 11 shows the thermal efficiency when methanol is used in the internal combustion engine shown in FIG. It can be seen that the thermal efficiency is greatly increased compared to the conventional internal combustion engine using methanol.

In the internal combustion engine according to the present invention, as described above, a rich air-fuel mixture region is formed around the peripheral wall surface 10b of the protruding portion 10 regardless of the load of the engine, and the air-fuel mixture in the rich air-fuel mixture region is ignited by the spark plug 15. As a result, it is possible to secure stable ignition of the air-fuel mixture and subsequent stable combustion regardless of the engine load. Therefore, it is possible to secure a stable idling operation without causing a misfire, and it is possible to improve thermal efficiency and reduce HC.

Further, in the internal combustion engine of the present invention, the intake passage 6 is not provided with a throttle valve, and the load control is performed by the fuel injection amount. Since no throttle valve is provided in this way, it is possible to improve thermal efficiency during partial load operation.

FIGS. 12 to 17 and 10 show various modifications, and each modification will be described below in order from FIG.

In the embodiment shown in FIG. 12, a glow plug is used instead of the spark plug 15.
17 is used. The glow plug 17 is arranged so as to be located in the rich air-fuel mixture region G at the time of ignition. That is,
The tip of the glow plug 17 is arranged so as to be located very close to the peripheral wall surface 10b of the protrusion 10 when the piston 2 reaches the top dead center. In this case, the piston 2 rises and the rich air-fuel mixture region G comes into contact with the tip of the glow plug 17, and then the rich air-fuel mixture is ignited.

In the embodiment shown in FIG. 13, the protrusion 10 has a protrusion 10c slightly protruding from the bottom wall 9b of the cavity 9, and the protrusion 10c.
And a collision member 18 fixed on the top. The collision member 18 is made of a wear-resistant material different from that of the piston 2, and has a heat insulating structure so that the collision surface 10a of the collision member 18 has a high temperature. Methanol has a large latent heat of vaporization, and therefore the collision member 18 has a heat insulating structure so that the temperature of the collision surface 10a does not drop too much when methanol is used. By raising the temperature of the collision surface 10a, atomization of the fuel that has collided with the collision surface 10a can be promoted.

In the embodiment shown in FIG. 14, the peripheral wall surface 9c of the cavity 9 is formed in a polygonal shape. On the other hand, in the embodiment shown in FIG. 15, the collision surface 10a is arranged eccentrically with respect to the cylinder axis, and the fuel is injected toward this collision surface 10a. In these embodiments, the propagation distance of the fire to the peripheral wall surfaces 9a and 9c of the cavity 9 differs depending on the direction of the fire propagation, and therefore the combustion time can be controlled.

In the embodiment shown in FIG. 16, an intake control valve 19 is provided in the intake passage 6. FIG. 17 shows the relationship between the opening θ of the intake control valve 19 and the engine load P. As shown in FIG. 17, the intake control valve 19 is in a half-open state when the engine load is small or no load, and fully opens immediately when the engine load increases. In the present invention, it is necessary to form a rich air-fuel mixture region G (FIG. 9) around the protruding portion 10. However, if a very strong swirling flow or turbulence is generated in the combustion chamber 4, an engine with a particularly small amount of injected fuel is generated. It may be difficult to form the rich air-fuel mixture region G around the protrusion 10 during low load operation. In such a case, it is preferable that the intake air control valve 19 be closed to about half-open during the engine low load operation to reduce the intake air amount and not generate a very strong swirling flow or turbulence.

FIG. 10 shows an embodiment in which carbon is prevented from adhering to the collision surface 10a. When a fuel with a large latent heat of vaporization such as methanol is used as the fuel, the collision surface 10a is cooled, so it is difficult for carbon to adhere to the collision surface 10a, but as with gasoline, the latent heat of vaporization is relatively small. When fuel is used, the collision surface 10a is not sufficiently cooled, so that carbon easily adheres to the collision surface 10a. When carbon adheres to the collision surface 10a, the collision fuel is less likely to scatter in all directions, and only the area around the collision surface 10a becomes rich. Therefore, it is necessary to prevent carbon from adhering to the collision surface 10a as much as possible. In the embodiment shown in FIG. 10, when the piston 2 reaches the top dead center, the gap S between the collision surface 10a and the tip end surface of the fuel injection valve 11 becomes small, for example, 2 mm or less Will be placed. If the gap S is made smaller than about 2 mm in this way, the gap S becomes equal to or shorter than the quench distance when the piston 2 reaches the top dead center.
As a result, since the flame does not propagate into the gap S, the collision surface 10a
It is possible to prevent carbon from adhering to the top. Further, in the embodiment shown in FIG. 10, a space 35 is formed in the protrusion 10. By spraying the lubricating oil into the space 35, the collision surface 10a can be cooled, thereby further preventing carbon from adhering to the collision surface 10a.

In the internal combustion engine according to the present invention, various fuels such as gasoline, other alcohols, LPG gas, natural gas and mixed fuels thereof can be used as well as methanol. Particularly, in the present invention, substantially all the injected fuel is the cavity 9
Since the lubricating oil adhering to the cylinder inner wall surface is not diluted by the injected fuel because it is fed into the cylinder, it is possible to prevent rust from occurring on the cylinder inner wall surface even when using these various fuels. You can

Further, since the single-hole nozzle can be used as the fuel injection valve 11, the injection 12 does not become clogged, and the fuel injection pressure does not need to be so high. Therefore, not only the reliability and durability of the engine are improved, but also the manufacturing cost can be reduced.

It has been found that when methanol is used as the fuel, particulate matter does not exist in the exhaust gas at all, and NOx as well as HC and CO is extremely small.

〔The invention's effect〕

Since the fuel is injected from the fuel injection valve only toward the central part of the cavity in the form of a liquid fuel flow in the form of a liquid column that does not spread substantially without being dispersedly injected toward the peripheral part of the cavity, the fuel injection valve The fuel injected from is hardly atomized until it collides with the collision wall surface. Therefore, explosive combustion as in the past does not occur, combustion noise occurs due to explosive combustion, a large amount of NOx is generated,
It is possible to prevent knocking from occurring.

[Brief description of drawings]

1 is a side sectional view of an internal combustion engine according to the present invention, FIG. 2 is a plan sectional view of a cylinder head, FIG. 3 is a side sectional view showing various shapes of protrusions, and FIG. 4 is a fuel injection and ignition process. FIG. 5 is a diagram showing the fuel injection start timing, FIG. 6 is a diagram showing the ignition timing, FIG. 7 is a diagram showing the fuel injection timing, and FIG. 8 is a line showing the ignition timing. Fig. 9 is a side sectional view of an internal combustion engine at ignition, Fig. 10
FIG. 11 is a side sectional view of an internal combustion engine showing another embodiment, FIG. 11 is a diagram showing thermal efficiency, FIG. 12 is a side sectional view of an internal combustion engine showing another embodiment, and FIG. 13 is still another embodiment. Example side sectional view,
FIG. 14 is a plan view of a piston showing another embodiment, FIG. 15 is a plan view of a piston showing still another embodiment, FIG. 16 is a plan sectional view of a cylinder head showing another embodiment, and FIG. The figure is a diagram showing changes in the opening of the intake control valve. 2 ... Piston, 3 ... Cylinder head, 4 ... Combustion chamber, 9 ... Cavity, 10 ... Projection, 10a ... Collision surface, 11 ... Fuel injection valve, 12 ... Injection hole, 15 ... Spark plug.

Claims (1)

[Claims] 1. A fuel injection method for an internal combustion engine in which fuel is injected from a fuel injection valve arranged in the center of the top surface of a combustion chamber into a cavity formed on the top surface of a piston. It is injected only toward the central part of the cavity in the form of a liquid fuel liquid in the form of a liquid column that hardly spreads out toward the peripheral part of the cavity, and then this liquid fuel flow in the liquid column is formed in the middle of the cavity. At the height position, the liquid fuel that collides with the center portion of the collision wall surface extending in the radial direction of the cavity and then the liquid fuel that collides with the center portion of the collision wall surface is scattered along the collision wall surface in the peripheral direction of the cavity. Fuel injection method.