JPH0557406B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a combustion chamber of an internal combustion engine in which fuel is directly injected into the combustion chamber, and in particular uses low cetane number fuel such as light oil, gasoline, alcohol, etc. as fuel oil.
The present invention relates to a combustion chamber of an internal combustion engine that can use volatile fuel oil in all operating load operating ranges, including during low-temperature startup.

[Prior Art] It has been confirmed that combustion in an internal combustion engine that uses alcohol as fuel generally follows the processes shown in FIGS. 4 to 7. That is, from the fuel injection state shown in FIG. 4, as shown in FIG. 5, the fuel spray a flows in the forward direction of the swirl S to generate a combustible mixture M. When the spark plug b is discharged at a time when the mixture gasification is further progressed, a plurality of flame kernels Sp are formed in the vicinity, and from the generation position of the flame kernel Sp to the downstream of the swirl S as shown in Fig. 6. The flame propagates as if chasing the flammable mixture M to the side, and the seventh
Finish combustion as shown.

Conventionally, the combustion chamber of a direct-injection diesel engine proposed earlier by the present applicant (Japanese Patent Application No. 1983-1999) has been used to follow this combustion process and burn low cetane number and volatile fuel oils such as alcohol and gasoline.
210519).

As shown in Fig. 8, this proposal involves recessing the main combustion chamber d and the auxiliary combustion chamber e in the top surface of the piston c and arranging them side by side, and also sharing the space between the main combustion chamber d and the auxiliary combustion chamber e. A communication passage f that communicates the combustion chambers d and e is formed in the peripheral side wall of the combustion chamber, so that independent evaporative combustion is carried out in each of the main and auxiliary combustion chambers d and e.

[Problems to be Solved by the Invention] The above proposal is configured to allow good combustion in the auxiliary combustion chamber e and the main combustion chamber d, but the flame from the auxiliary combustion chamber e is transferred to the main combustion chamber. It was not sufficient to propagate to d. In other words, the flame that is rapidly generated in the auxiliary combustion chamber e that is led to the main combustion chamber d is narrowed down by the communication passage f, so that most of it flows into the gap (squeeze area) h formed between the top of the piston c and the cylinder head g. You can think about it when you are guided. As a countermeasure to this problem, it is possible to increase the passage area of the communication passage f, but in order to set the air-fuel ratio in the sub-combustion chamber e to be sufficiently rich for combustion, it is necessary to There were limits to the use of synthetic fuels. For this reason, the fuel becomes unstable with respect to the fuel injection amount, resulting in a decrease in output and a large amount of unburned methanol being discharged, which remains a problem.

[Means for Solving the Problems] The present invention aims to solve the various problems mentioned above. an auxiliary combustion chamber formed to be shallowly recessed at the top of the piston and whose volume is smaller than that of the main combustion chamber; A bank part is provided by recessing the upper part of the side wall between the main combustion chamber and the main combustion chamber, and a fuel having a low cetane number and high volatility such as alcohol is injected into the bank part facing this bank part. A fuel injection nozzle configured as shown in FIG. The auxiliary nozzle is designed to collide the atomized fuel spray with the inner wall of the main combustion chamber, scattering part of it, and causing the remaining part to swirl in the circumferential direction along the inner wall of the main combustion chamber. A nozzle formed to inject atomized fuel spray having a fuel particle size larger than that of the atomized fuel in the forward direction of the swirl and toward the inner wall outside the center of the main combustion chamber. A main nozzle whose direction is determined so that the fuel spray collides with the inner wall of the main combustion chamber, part of which is scattered, and the remaining part flows downstream of the swirl along the inner wall. The injection nozzle and the combustion flame of the auxiliary combustion chamber are provided above the main combustion chamber through the bank part, and the auxiliary combustion chamber is provided in a portion bordering the upper opening of the auxiliary combustion chamber so as to cover the auxiliary combustion chamber. a shelf, a slit-like opening radially along the shelf for introducing combustion air into the sub-combustion chamber, and an ignition part inserted into the shelf into the sub-combustion chamber. The combustion engine is equipped with a plug accommodating portion, and an ignition plug disposed in the plug accommodating portion such that its ignition portion can be inserted into the auxiliary combustion chamber.

[Operation] At all operating loads, the atomized fuel spray supplied into the sub-combustion chamber is confined within the sub-combustion chamber by the shelves and banks without flowing into the cylinder and into the main combustion chamber. Then, a part of the atomized fuel spray collides with the inner wall of the sub-combustion chamber to be further broken down and scattered, and the remaining part swirls along the inner wall of the sub-combustion chamber due to its inertia.
Therefore, the scattered fuel instantaneously evaporates due to the high temperature atmosphere in the sub-combustion chamber and mixes with the air to form a premixture with good ignitability and flame propagation. It is evaporated by the high temperature atmosphere of the combustion chamber and becomes a flammable mixture. Therefore, when the spark plug is ignited in such a state of the mixture, the premixture ignites quickly, and
The flammable mixture burns slowly as its flame propagates.

When a predetermined load is exceeded, fuel spray is supplied not only to the sub-combustion chamber but also to the main combustion chamber. A part of this fuel spray collides with the inner wall of the main combustion chamber and scatters, and the remainder is carried downstream along the inner wall of the main combustion chamber by the swirl generated within the main combustion chamber. . The scattered fuel is stirred by the swirl and evaporated by the atmosphere inside the main combustion chamber to form a premixture, and the remainder is evaporated by the wall heat of the inner wall of the main combustion chamber and becomes a flammable mixture. However, since the fuel spray is supplied to the main combustion chamber in a state where the fuel particle size is larger than that of the atomized fuel spray, the amount of flammable mixture produced relative to the volume of the main combustion chamber is smaller than that of the sub-combustion chamber. considerably less compared to
In other words, since the amount of combustible air-fuel mixture is small, the rate of heat generation in the main combustion chamber is low, and slow combustion with a low rate of pressure increase is achieved.

Here, the shelf part guides the flame in the auxiliary combustion chamber to the upper part of the main combustion chamber via the bank part, so when the predetermined load is exceeded, the premixture generated in the main combustion chamber The flame supplied to the main combustion chamber is propagated through the bank portion and ignited quickly. Therefore, the flammable air-fuel mixture in the main combustion chamber is combusted by the propagation of this flame, and the fuel spray that has not been converted into a flammable air-fuel mixture is slowly combusted by the flame.

[Embodiment] A preferred embodiment of a combustion chamber of an internal combustion engine according to the present invention will be described below with reference to the accompanying drawings.

1 to 3, a piston 1 is housed in a cylinder (not shown) of an internal combustion engine so as to be able to reciprocate along the cylinder, and 2 is a piston top that forms the top surface of the piston 1. , 3 is a main combustion chamber, and 4 is a sub-combustion chamber.

Piston top 2 of piston 1 as shown
The main combustion chamber 3 is recessed along the axial direction of the piston 1. Piston top 2
In this embodiment, a sub-combustion chamber 4 is recessed in parallel to the main combustion chamber 3, and in this embodiment, the vertical cross section of the main combustion chamber 3 and the sub-combustion chamber 4 passing through the axis of the piston 1 is as follows. Both have a circular top with a truncated shape.
And the horizontal cross section parallel to the piston top 2 is
Both are formed into a circular shape.

Regarding the recess depth, the auxiliary combustion chamber 4 is the main combustion chamber 3.
The auxiliary combustion chamber 4 is formed to have a smaller volume than the main combustion chamber 3. A bank portion 5 forming a circumferential side wall shared between the main combustion chamber 3 and the sub-combustion chamber 4 is provided with the main combustion chamber 3 and the sub-combustion chamber
A communication path 7 is formed to communicate with the two.

As shown in FIG. 2, in this embodiment, the communication passage 7 is connected to the central axis O ₁ of the main combustion chamber 3 and
It is formed by moving the central axis _O2 of the piston 1 toward the center of the piston 1. That is, depending on the distance moved, the main combustion chamber 3 and the sub-combustion chamber 4
The degree of wrap of the bank portion 5 shared with the bank portion 5 increases, and a communication path 7 corresponding to the wrap is formed in the upper portion of the bank portion 5.

As described above, the main combustion chamber 3 and the sub-combustion chamber 4, which communicate with each other and have an open top, are arranged in parallel in the piston top 2. The main combustion chamber 3 also has a lip portion 2 at the top of the opening that protrudes appropriately inward in the radial direction along the top opening edge 9a to generate an independent swirl _S1 and squish inside the main combustion chamber 3.
5 is formed.

In the embodiment of the present invention, the fuel injection nozzle is of the type shown in FIG. 3, for example.

The fuel injection nozzle 12 has a cylindrical nozzle body 13 that is integrally housed in a cylinder head (not shown), and a valve seat 14 that is formed on the distal end side of the nozzle body 13.
a throttle part 1 which is housed in a valve seat 14 so as to be movable up and down, and which closes a nozzle, which will be described later, when seated on the valve seat 14;
8, a sub-nozzle 16 opened in the valve seat 14, and the needle valve 15 has a sub-nozzle 16 opened in the valve seat 14;
The diameter of the main nozzle 17 opened at the tip of the nozzle body 13, which is opened when a predetermined lift value l is exceeded, and the upper housing portion 26 in the nozzle body 13 facing the needle valve 15 are expanded in diameter. The lift value of the needle valve 15 is adjusted by applying fuel oil pressure to the upper throttle portion (not shown) of the needle valve 15 according to the fuel oil pressure supplied from the fuel injection pump (not shown). fuel oil chamber (not shown)
It mainly consists of. Nozzle diameter d ₁ of sub-nozzle 16
is formed extremely small compared to the nozzle diameter d ₂ of the main nozzle 17, and the main nozzle 17 is configured to eject fuel spray with large penetration force and dispersion, whereas the sub nozzle 16 is The structure is such that the penetration force is weakened by atomization to improve evaporation, and the direction of fuel spray can be reliably set.

As described above, until the lift value of the needle valve 15 reaches a predetermined value, the fuel injection nozzle 12 is operated by the sub-nozzle 16.
When the lift value exceeds the lift value, the sub nozzle 16 and the main nozzle 17 are opened. In other words, there is 1 sub-nozzle for 17 main nozzles.
It is of the so-called pintalk type, in which the pin 6 is opened first.

Now, the feature of the combustion chamber of the internal combustion engine of the present invention is that the flame generated in the auxiliary combustion chamber 4 is guided to the main combustion chamber 3 without escaping to the squish area for stable combustion.

Therefore, a shelf 10 is formed at the upper opening edge 9b of the sub-combustion chamber 4, and extends radially inward along the opening edge 9b. A slit 11 is formed in the shelf portion 10 at an intermediate portion passing through the center O ₂ of the sub-combustion chamber 4 to guide combustion air into the sub-combustion chamber 4 . Further, a housing portion 31 for housing a spark plug 30 is opened on the upper opening edge 9b side of the shelf portion 10. Furthermore, a curved portion 32 is formed on the side of the communication path 7 of the shelf portion 10, which serves as a relief for the injection nozzle 12. spark plug 30
is accommodated in the housing section 31, and PG is the discharge section of the spark plug 30.

As shown in FIGS. 1 and 2, the fuel injection nozzle 12 is integrally disposed in a cylinder head (not shown) with its injection port side facing the communication passage 7, and the sub injection port 16 is used for sub-combustion. Inside the chamber 4, a main nozzle 17 faces into the main combustion chamber 3, and the main nozzle 17 is
It faces the forward direction of the swirl S ₁ in the main combustion chamber 3. Furthermore, the main and sub-nozzles 16 and 17 are connected to each combustion chamber 3,
The inner walls 3a, 4a of the respective combustion chambers 3, 4 are faced outward from the centers _O1 , _O2 of the combustion chambers 4.

The operation of this embodiment will be explained below based on the attached drawings.

As shown in FIG. 1, a swirl of combustion air supplied from a swirl port (not shown) is formed into an independent swirl S ₁ along the inner wall 3a of the main combustion chamber 3.
is generated.

In a light load operating range including when starting and idling the internal combustion engine, only the sub-nozzle 16 is opened because the needle valve 15 shown in FIG. 3 is below a predetermined lift value. When the sub-nozzle port 16 is opened, atomized fuel spray f ₁ is ejected toward the inner wall 4a of the sub-combustion chamber 4. When this atomized fuel spray f ₁ collides with the inner wall 4a of the sub-combustion chamber 4, a part of it is further atomized and scattered, and is instantaneously vaporized by the heat of the compressed air. , mixed with air. This becomes a flammable mixture m with good ignitability and combustibility. Further, the remainder of the atomized fuel spray f ₁ is on the inner wall 4a of the sub-combustion chamber 4.
The result is a spray layer _F1 flowing along the injection direction.
This spray layer F ₁ is vaporized by the high temperature heat of the compressed air and the wall heat. This steam is also mixed with the air in the secondary combustion chamber 4 to produce a combustible mixture m, as also shown in FIG.

When starting the engine or idling, when the needle valve lift operation is in an extremely low speed range and the cranking speed of the starter is small, the amount of fuel is increased from the skin nozzle 16, so if the fuel used is low-temperature, such as gasoline or alcohol, Even if the fuel oil has a cetane number and is volatile, the air-fuel ratio in the sub-combustion chamber 4 becomes small during this period, resulting in rich conditions. At this time, shelf 1
0. A predetermined air-fuel ratio can be set by the bank portion 5. As a result, when the spark plug 30 is discharged, a large number of flame kernels are quickly and reliably formed in the auxiliary combustion chamber 4 to start combustion, and the thermal energy generated by the combustion is transferred to the spray layer on the inner wall 4a.
The flame is rapidly propagated and combusted so as to promote the evaporation of F ₁ and follow the combustible mixture m flowing in the swirl direction.

Therefore, in this embodiment, combustion is relatively rapid and the combustion temperature is increased, so the average combustion temperature in the sub-combustion chamber 4 is increased, thereby reducing the generation of smoke, blue-white smoke, and HC. can be kept low. The flame and combustion gas generated in the auxiliary combustion chamber 4 cannot escape to the combustion area by the shelf 10, so they are blown out into the main combustion chamber 3 through the oxygen-rich side, that is, the communication passage 7. . In a medium/high load operating range where the lift value of the needle valve 15 exceeds a predetermined lift value, not only the sub nozzle 16 but also the main nozzle 17 is opened.

As shown in Figures 1 and 2, the main nozzle 1
The fuel spray f ₂ from the sub-nozzle 7 has a longer flight distance and a larger diffusion area than the atomized fuel spray f ₁ from the sub-nozzle 16 . A part of this fuel spray f ₂ is atomized by colliding with the inner wall 3a of the main combustion chamber 3, and the remaining part spreads toward the downstream side along the inner wall 3a in the swirl direction of the main combustion chamber 3. This results in a spray layer F ₂ that is flowed away. The atomized fuel spray f ₂ is instantaneously vaporized by the heat of the compressed air and the flame energy of the auxiliary combustion chamber 4 to become a flammable mixture m, which forms a spray layer.
_F2 is also vaporized by the compressed air and the wall heat, forming a flammable mixture m. At this time, since the particle size of the fuel in the fuel spray ff ₂ is relatively large, it does not result in excessive flammable mixture m being generated in the main combustion chamber 3, so the combustion is a relatively slow evaporative combustion. It is done. Further, the main combustion chamber 3 is reliably ignited by the combustion gas and flame from the auxiliary combustion chamber 4 as described above. Furthermore, as the load becomes higher, the proportion of fuel injected from the main nozzle 17 increases to a maximum of 90% or more, so that slow evaporative combustion is ensured. Therefore, it suppresses ignition delay, which causes a sudden increase in cylinder pressure and combustion peak temperature, and reduces combustion noise, vibration, and
NOx, smoke, and unburned aldehyde can be kept low.

[Effects of the Invention] As is clear from the above explanation, the combustion chamber of the internal combustion engine of the present invention can exhibit the following excellent effects.

(1) It is possible to achieve slow combustion in the auxiliary combustion chamber using low cetane number and volatile fuels such as alcohol and gasoline, and also to propagate the flame in the auxiliary combustion chamber to the main combustion chamber through the bank part. Slow evaporative combustion in the main combustion chamber can be achieved. Therefore, the noise level is low and the emissions of NOx, HC, smoke, and unused aldehyde can be significantly reduced.

(2) Output and fuel efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a preferred embodiment of a combustion chamber of an internal combustion engine of the present invention, FIG. 2 is a cross-sectional view taken along the line - - in FIG. 1, and FIG. 3 is a partial cross-sectional view showing a fuel injection nozzle. 4 to 7 are schematic diagrams showing the fuel injection process and combustion process, and FIG. 8 is a schematic diagram showing the combustion chamber of a conventional direct injection diesel engine. In the figure, 1 is a piston, 2 is a piston top, 3 is a main combustion chamber, 4 is a sub-combustion chamber, 5 is a bank part, 7 is a communication passage, 10 is a shelf part, 11 is a slit, 12 is a fuel injection nozzle, 16 is the secondary nozzle, 17 is the main nozzle, 30
3 is a spark plug, and 31 is a housing portion.

Claims (1)

[Claims] 1. A main combustion chamber deeply recessed in the top of the piston, and a shallow recess provided in the top of the piston adjacent to the main combustion chamber, the volume of which is smaller than the main combustion chamber. an auxiliary combustion chamber;
A bank portion provided by recessing the upper part of each side wall between the sub-combustion chamber and the main combustion chamber from above in order to communicate the sub-combustion chamber and the main combustion chamber with each other;
A fuel injection nozzle facing the bank part and configured to inject a fuel with a low cetane number and high volatility such as alcohol, and is configured to inject a fuel such as alcohol that has a low cetane number and high volatility, and is designed to prevent atomization in the sub-combustion chamber during all operating loads of the engine. It is a nozzle formed to eject fuel spray, and its ejection direction is such that the atomized fuel spray collides with the inner wall outside the center of the auxiliary combustion chamber, part of which is scattered, and the remaining part is sent along the inner wall. When a predetermined load is exceeded, the atomized fuel flows into the main combustion chamber in the forward direction of the swirl and toward the inner wall outside the center of the main combustion chamber. is a nozzle formed to eject atomized fuel spray with a large fuel particle size, and its ejection direction is such that the fuel spray collides with the inner wall of the main combustion chamber, part of it is scattered, and the remaining part is directed against the inner wall. A fuel injection nozzle configured to have a main injection port that is configured to flow downstream of the swirl along with the fuel injection nozzle;
a shelf section extending over the auxiliary combustion chamber at a portion bordering the upper opening of the auxiliary combustion chamber so as to supply the combustion flame of the auxiliary combustion chamber to the upper side of the main combustion chamber through the bank section; A slit-like opening is formed along the radial direction of the shelf to introduce combustion air into the sub-combustion chamber, and a slit-like opening is provided in the shelf to insert the ignition part into the sub-combustion chamber. A combustion chamber for an internal combustion engine, comprising an opening and a spark plug disposed such that its ignition part can be inserted into the auxiliary combustion chamber through the opening.