JPH0559953A - Combustion control device of engine - Google Patents

Abstract

PURPOSE:To equalize a flame collision timing in the peripheral direction of a combustion chamber in ignition gaps arranged in the outer peripheral edge part. CONSTITUTION:A first ignition gap 12a is positioned between air intake ports 3A, 3B, a second ignition gap 13a between an air intake port 3A and an exhaust port 4A, a third ignition gap l4a between an air intake port 3B and an exhaust port 4B at the outer peripheral part of a second combustion chamber 2, and the gaps between 12a and 13a and 12a and 14a are almost the same distance and the gap between 13a and 14a is the largest distance. The outer peripheral edge part in a territory between 13a and 14a is coated with oxidated catalyst as a means to promote growth of a flame between the ignition gaps 13a and 14a. Additionally, an air-fuel ratio in this territory is enriched or treated in other ways. The flames grown in each of the ignition gaps 12a-14a are coincided almost at the same time first in the circumferential direction of the combustion chamber and thereafter, in the center of the combustion chamber. HC of the outer peripheral edge part of the combustion chamber is reduced, a combustion ratio is uniformized and NOx is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control device for a multipoint ignition type engine.

[0002]

2. Description of the Related Art Some engines include a multi-point ignition type in which a plurality of ignition gaps are provided for one combustion chamber. In Japanese Unexamined Patent Publication (Kokai) No. 57-148021, an annular holding plate is interposed between a cylinder head and a cylinder block, and a large number of spark plugs are held by the holding plate, and a cylinder is provided at an outer peripheral edge of a combustion chamber. It is disclosed that a plurality of ignition gaps are arranged at intervals in the circumferential direction. As a result, rapid combustion is performed by simultaneous ignition with a large number of ignition gaps, and an ideal equivolume combustion is obtained in the Otto-type engine.

[0003]

[Problems to be Solved by the Invention] By the way, recently,
From the viewpoint of exhaust gas purification and the like, it is desired to position a plurality of ignition gaps at the outer peripheral edge of the combustion chamber at intervals in the circumferential direction of the combustion chamber. By igniting from the periphery of the combustion chamber, the combustibility at the outer peripheral edge of the combustion chamber is improved to reduce HC, and the flame is first matched in the circumferential direction of the combustion chamber and then matched at the center of the combustion chamber. By suppressing the growth of flame by this, the combustion ratio within a predetermined period is made as uniform as possible, that is, the peak value of the combustion speed is made as small as possible,
This is intended to reduce NOx.

As described above, when a plurality of ignition gaps are provided at the outer peripheral edge of the combustion chamber and at intervals in the circumferential direction of the combustion chamber, interference with the intake port and the exhaust port and support for the spark plug are provided. Considering the screw property and the like, the intervals between the adjacent ignition gaps in the circumferential direction of the combustion chamber are not always uniform in many cases. As described above, when the circumferential gaps between the adjacent ignition gaps are uneven, the matching of the flame surfaces in the combustion chamber circumferential direction is delayed particularly in the portion where the circumferential gap is large, and the HC
It is not preferable for sufficiently reducing NOx and NOx.

Accordingly, an object of the present invention is to promote the growth of flame at the portion where the circumferential gap is largest when the gaps between adjacent ignition gaps in the circumferential direction of the combustion chamber are unequal to promote ignition. It is an object of the present invention to provide a combustion control device for an engine in which flame collision timings in the circumferential direction of the combustion chamber between the gaps are substantially the same.

[0006]

To achieve the above object, the present invention has the following configuration. That is, a plurality of ignition gaps are arranged at intervals in the circumferential direction of the combustion chamber on the outer peripheral edge portion of the combustion chamber, and promotion of promoting flame spread to a portion where the intervals in the circumferential direction of the combustion chamber of adjacent ignition gaps are largest. Means are set up.

Regarding the number of ignition gaps located at the outer peripheral edge of the combustion chamber, the intake po
In the case where two ignition gaps are provided, it is preferable to use the first to third ignition gaps in order to minimize the ignition gap. More specifically, the first ignition gap is located between the two intake ports, and the second ignition gap is located between the intake port and the exhaust port and with respect to the exhaust port. It is desirable that the third ignition gap is located in one direction in the circumferential direction, and the third ignition gap is located between the intake port and the exhaust port and in the other direction in the circumferential direction of the combustion chamber with respect to the exhaust port. , Second
The combustion chamber circumferential distance between the ignition gap and the third ignition gap is maximized.

Various means can be adopted as means for promoting flame spread. For example, partial enrichment of air-fuel ratio of air-fuel mixture, use of oxidation catalyst, second ignition gap, third
When the ignition gap is located in the plug hole, the direction of the flame in the combustion chamber circumferential direction is set by the shape (structure) setting of the plug hole, the ignition timing is set for each ignition gap in consideration of the swirl of the intake air, Furthermore, a fourth ignition gap is additionally provided. Of course, any one of these facilitating means may be adopted, but any two or more may be combined and adopted.

[0009]

According to the present invention configured as described above, the HC collision and NOx reduction can be more effectively performed by setting the flame collision timings in the circumferential direction of the combustion chamber to be substantially the same between the ignition gaps. You can In particular, in the case of having two intake ports, by adopting the configuration described in claim 2, it is possible to reduce the HC and NOx while minimizing the number of ignition gaps. it can.

When the construction as described in claim 3 is adopted, the promoting means can be constructed by an extremely simple method such as partial enrichment of the air-fuel ratio, that is, setting of the fuel injection direction and injection timing. .. As described in claim 4, when the oxidation catalyst is used, it is possible to easily promote flame propagation only in a necessary portion regardless of various restrictions related to the combustion chamber in designing the engine. You can
With the structure as described in claim 5, the flame spread can be promoted in a necessary portion by a simple method of setting the shape of the plug hole. With the structure as described in claim 6, it is possible to promote the flame spread of a necessary portion by an extremely simple method of adjusting the ignition timing using the intake swirl. With the configuration as described in claim 7, it is possible to surely promote the flame spread in the necessary portion utilizing the fourth ignition gap. Preferred embodiments of the invention and their advantages will be apparent from the description of the examples below.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is a cylinder head, 2 is a combustion chamber, and the cylinder head 1 has two intake ports 3A and 3B and two exhaust ports 4A which open into the combustion chamber 2, respectively. 4B are formed. Intake / exhaust port 3A,
As is known, 3B, 4A, and 4B are opened / closed at known timing by intake / exhaust valves (not shown) in synchronization with the rotation of the crankshaft.

The two intake ports 3A, 3B are connected to the combustion chamber 2
Are opened in the combustion chamber 2 on one side surface side of the cylinder head 1 with respect to the straight line L1 passing through the center of the cylinder and parallel to each other in the crank axis direction. Also, 2
The two exhaust ports 4A, 4B open into the combustion chamber 2 on the other side surface side of the cylinder head 1 with respect to the straight line L1,
They are formed in parallel with each other in the crankshaft direction. The intake ports 3A, 3B open on one side of the cylinder head,
The exhaust ports 4A, 4B are opened to the other side surface side of the cylinder head 1, and the cylinder head 1 is of a so-called cross flow type.

The two intake ports 3A, 3B have their downstream end portions, that is, the portions near the combustion chamber 2 as branch portions 3a, 3b defined by a partition wall 5, and their upstream portions gather together. It is a collecting unit 3c. Intake port 3A
From the upstream side to the downstream side, that is, the collecting portion 3c
From the to the branch portion 3a, it is formed in a substantially straight shape so as to be substantially orthogonal to the crankshaft.

The intake port 3B is curved from its branching portion 3b toward the collecting portion 3c. Explaining this curve, consider a straight line L2 that passes through the center of the combustion chamber 2 and is orthogonal to the crankshaft (orthogonal to the straight line L1). At this time, the upstream end of the partition wall 5 is on the straight line L2, and therefore the branch portion 3b is curved so as to be offset toward the intake port 3A side.

A swirl valve 6 is arranged in the collecting portion 3c. The swirl valve 6 is swingable around a rotary shaft 7 provided at the upstream end thereof. The state shown by the solid line in FIG. 1 is the fully closed state, and the state shown by the one-dot chain line is the fully opened state. is there. The rotating shaft 7 is located near the side wall of the collecting portion 3c on the side opposite to the intake port 3B.
The downstream end (free end) of the valve 6 is located at a small distance from the upstream end of the partition wall 5. Further, when the swirl valve 6 is fully opened, the swirl valve 6 is in a state of being substantially orthogonal to the crankshaft, that is, in a state of extending substantially parallel to the intake port 3A having a substantially straight shape. In the embodiment, the swirl valve 6 is fully closed when the load is low, the opening increases as the load increases when the load is medium, and is fully opened when the load is high.

A bulging portion 8 bulging upward is formed on the upper wall of the collecting portion 3c, and a fuel injection valve (not shown) is attached to the bulging portion 8. The downstream portion of the bulging portion 8 is branched into a branch portion 8a extending toward the intake port 3A side and a branch portion 8b extending toward the intake port 3B side. The fuel injection valve is of the two-hole type that directs the injected fuel in the two directions of the branch portions 8a and 8b, but is approximately the same as the branch spread of the branch portions 8a and 8b. It is also possible to use one injection hole type having a spray width of.

In the fully closed state of the swirl valve 6, most of the intake air is supplied only from the intake port 3B, so that the intake air swirl in the clockwise direction in FIG. The swirl becomes weaker as the swirl valve 6 opens. Even when the swirl valve 6 is fully closed, a small amount of intake air flows into the intake port 3A, which prevents a large amount of fuel from adhering to the inner wall of the intake port (branch portion 3a). Even when the swirl valve 6 is fully open, the swirl is formed by the bending of the intake port 3B. At this time, the swirl valve 6
Becomes substantially parallel to the intake port 3A, which is preferable in minimizing the intake resistance of the swirl valve 6 and ensuring a fully open output.

There are a total of four ignition gaps 1 in the combustion chamber 2.
1a, 12a, 13a, 14a are located. Of the four ignition gaps, the ignition gap 11a is located at the center of the combustion chamber 2 and the other three ignition gaps 12a to 12a.
14 a are respectively located on the outer peripheral edge of the combustion chamber 2.

The ignition gap 12a serves as a first ignition gap and is located between the two intake ports 3A and 3B, more specifically, below the upstream end of the partition wall 5. One of the ignition gaps 13a and 14a serves as a second ignition gap and the other serves as a third ignition gap. Of these, the ignition gap 13a is provided in the intake port 3
It is located between A and the exhaust port 4A. The ignition gap 14a is located between the intake port 3B and the exhaust port 4B. These are located at the outer peripheral edge of the combustion chamber 3
In the two ignition gaps 12a to 14a, the intervals between the adjacent ignition gaps in the combustion chamber circumferential direction are set to be substantially equal between 12a and 13a and between 12a and 14a.
And the distance between 14a and 14a are the largest. Therefore, promotion of flame spread in the circumferential direction of the combustion chamber between the ignition gaps 13a and 14a is desired.

Of the above ignition gaps 11a to 14a, when the load is low, ignition is performed by the peripheral ignition gaps 12a to 14a. As a result, combustion is performed from the vicinity of the combustion chamber 2, and HC easily generated around the combustion chamber is reduced. Then, the flame surfaces are matched with each other in the circumferential direction of the cylinder before they are matched with each other in the center of the combustion chamber 2, or are brought into a state close to such a flame growth mode, and the flame surfaces are changed within a short time. The rapid spread is suppressed, the combustion ratio is made uniform within a predetermined period, and the increase of NOx is also suppressed.

At high load, all ignition gaps 11a
Ignition by ~ 14a is performed. Thereby, rapid combustion is performed and knocking is prevented. Note that when the load is extremely low, ignition may be performed by all the ignition gaps 11a to 14a to increase the combustion speed at the initial stage of combustion to ensure combustion stability.

Spark plug 1 having a spark gap 12a
The mounting hole 22 for 2 is inclined below the intake ports 3A, 3B with respect to the straight line L2, and is formed on one side surface of the cylinder head 1 (side surface on the side where the intake ports 3A3B are open). Has been formed. More specifically, the mounting hole 22
The opening of the cylinder head 1 to the outside of the cylinder head 1 is arranged closer to the intake port 3B than the straight line L2. As a result, the spark plug 12 is attached to the cylinder head 1 while avoiding interference with the intake pipes connected to the intake ports 3A and 3B. By setting the mounting mode of the spark plug 12 as described above, it is not necessary to form a mounting hole for mounting the spark plug 12 in the partition wall 5, and the partition wall 5 can be thinned to reduce intake resistance. Is preferred.

The spark plugs having the ignition gaps 11a, 13a and 14a are not shown, but the mounting holes formed in the cylinder head 1 are shown in FIGS. (Each spark plug is attached to the cylinder head 1 by extending it in the direction in which the attachment hole extends). That is, the reference numeral 2 is a mounting hole for the central spark plug having the ignition gap 11a.
Reference numeral 23 denotes a mounting hole for the spark plug having the ignition gap 13a, and reference numeral 24 denotes a mounting hole for the spark plug having the ignition gap 14a.

As shown in FIG. 4, on the wall surface of the combustion chamber between the second and third ignition gaps 13a and 14a where the circumferential distance of the combustion chamber is the largest, combustion is performed over the length S. A known oxidation catalyst 31 that promotes is coated. Thereby, in the circumferential direction of the combustion chamber, between the ignition gaps 12a and 13a, between 12a and 14a, 13
The flame growth rates between a and 14a are almost the same (the ignition timings of the ignition gaps 12a to 14a are the same). That is, when only the peripheral ignition gaps 12a to 14a are ignited, the flames first match in the circumferential direction of the combustion chamber.
And 13a, 12a and 14a, 13a and 14
Almost the same time as a. Then, after this, the flame is matched in the center of the combustion chamber. By such combustion, HC which is likely to occur at the outer peripheral edge of the combustion chamber is greatly reduced, the combustion ratio is made as uniform as possible over the entire combustion period, that is, the peak value of the combustion speed is reduced, and NOx is reduced. To be done. It should be noted that the oxidation catalyst 31 can be coated not only on the cylinder head 1 but also on the cylinder block and further on the piston upper surface as long as it is a wall surface which is the area portion indicated by the reference symbol S.

In FIG. 5, the ignition gaps 13a and 1
4a, the air-fuel ratio of the air-fuel mixture supplied to this portion is made richer than the air-fuel ratio supplied to other portions in order to promote the flame spread, and the rich portion is shaded. It is indicated by reference numeral 32. In order to partially make the air-fuel ratio rich in this way, when the intake port (intake valve) is almost fully opened, the fuel injection valve is directed to the region indicated by reference numeral 32 so as not to interfere with the intake valve. It is sufficient to inject the fuel (setting of the direction of injection of the fuel injection valve).

FIGS. 6 and 7 show one ignition gap 13a.
The shape (structure) of the plug hole is set so that the flame ignited in (14a) grows mainly toward the other ignition gap 14a (13a). That is, when the ignition gap 13a is taken as an example, the plug hole 33 formed in the cylinder head 1
Is an ignition part 33a in which the ignition gap 13a is located, and two communication parts 3 for communicating the ignition part 33a with the combustion chamber 2.
3b and 33c. Therefore, the flame generated in the ignition part 33a is injected into the combustion chamber 2 through the communication parts 33b and 33c.

The communicating portion 33b is oriented substantially tangentially to the outer peripheral edge of the combustion chamber so that the flame injected from the communicating portion 33b is directed toward the ignition gap 12a. In addition, in the communication portion 33c, the flame injected from here communicates with the ignition gap 14
It is oriented substantially tangentially to the outer peripheral edge of the combustion chamber so as to be in the direction a. The cross-sectional area of the communication portion 33c is set to be considerably larger than that of the communication portion 33b. Therefore, the growth speed of the flame generated in the ignition gap 13a is higher toward the ignition gap 14a side than toward the ignition gap 12a side. This promotes flame spread between the ignition gaps 13a and 14a.

The plug hole of the ignition gap 14a is also constructed in the same manner as the ignition gap 13a, but in this case, the cross-sectional area toward the flame on the side toward the ignition gap 13a is the cross-sectional area of the ignition gap 13a. It is made larger than the cross-sectional area of the communication portion on the side toward 12a. Incidentally, the setting of the plug hole as described above may be made not only for both the ignition gaps 13a and 14a but only for one of them.

FIG. 8 shows the case where the ignition gap 15a near the center of the combustion chamber 2 is used as the promoting means. That is, the ignition gap 15a is set in place of the ignition gap 11a shown in FIG.
Is near the center of the combustion chamber 2, but is set at a position offset closer to the exhaust ports 4A, 4B than the center. Unlike the ignition gap 11a shown in FIG. 1, the ignition gap 15a is always involved in ignition. By providing the ignition gap 15a, flame transfer between the ignition gaps 13a and 14a is promoted, but in FIG. 8, the area of the last burned portion is shaded and the area of the burned portion is outlined. It is indicated by.

FIG. 9 and FIG. 10 show the case where the flame spread between the ignition gaps 13a and 14a is promoted by setting the ignition timing using the intake swirl. That is, although the intake swirl is clockwise as shown by the arrow in FIG. 9, of the ignition gaps 13a and 14a,
Ignition timing of the ignition gap 14a on the swirl upstream side,
Is set to be earlier than the ignition timing of the other ignition gaps 12a and 13a. The state of flame growth in this case is shown at times t1 to t5.

As is clear from FIG. 9, first, the flame ignited in the ignition gap 14a grows toward the ignition gap 13a side due to the influence of the swirl. And
The flames are ignited in the ignition gaps 12a and 13a with a slight delay, and the flame grows, but finally, the matching of the flames in the circumferential direction of the combustion chamber is performed between 12a and 13a, between 12a and 14a, and between 13a. It is almost the same time as 14a. Figure 1
At 0, the strength of the intake swirl and each ignition gap 12a
14 shows the relationship with the ignition timings of .about.14, and as an overall tendency, the lower the load, the earlier the ignition timing of the ignition gap 14a is set to be set earlier than the ignition timings of 12a and 13a. Incidentally. The examples shown in FIGS. 4 to 8 are intake swirlers.
Are not necessarily required.

12 and 13 show the peripheral ignition gap 12
An example is shown in which the spark plugs 12 to 14 for a to 14a are held by an annular holding plate 42 interposed between the cylinder head 1 and the cylinder block 41. The holding plate 42 has an inner peripheral side portion, that is, a portion facing the combustion chamber 2 as a thin portion 42a, and an outer peripheral side portion as a thick portion 42b. On the other hand, a recess 1a is formed on the lower surface of the cylinder head 1, and a recess 41a is formed on the upper surface of the cylinder block 41. These recesses 1a and 41a
Are formed in a generally annular shape so as to surround the outer periphery of the combustion chamber 2, and the thick portion 42b of the holding plate 42 is sandwiched between the recesses 1a and 41a.

By forming the recesses 1a and 41a as described above, the thickness of the thin portion 42a of the holding plate 42 is made equal to the ignition gaps 12a-1 of the ignition plugs 12-14.
The thickness can be set to the minimum necessary thickness in consideration of the diameter of the portion 4a (thickness enough to configure the plug holes for the ignition gaps 12a to 14a). This means that the holding plate 4
This is preferable in that the thickness (height) of the portion 2 of the combustion chamber 2 facing the combustion chamber 2 is made as small as possible to secure a sufficiently high compression ratio. The thickness of the thick portion 42b is the same as that of the spark plugs 12-1.
4 has a thickness slightly larger than the maximum diameter of the hexagonal nut portion so that the spark plugs 12 to 14 can hold the spark plugs 12 to 14.
2 is screwed into the holding plate 41 from the outer peripheral side.

The piston 43 fitted in the cylinder block 41 has a shoulder at its shoulder.
The ignition gaps 12a-14
The notch 43a facing a is formed with 43c.
Thereby, the flames generated in the ignition gaps 12a to 14a can be smoothly spread into the combustion chamber 2 through the notches 43a to 43c. Spark plug 12
If any abnormality occurs in No. 14 to 14, it is necessary to remove the holding plate, but the center of the combustion chamber 2 is equipped with a spark plug 11 having a central ignition gap 11a as shown in FIG. Even if an abnormality occurs in the gaps 12a to 14a, the operation to the repair shop is secured for the time being. Of course, the central spark plug 11 can be attached and detached from above the cylinder head 1.

The high voltage secondary voltage to each ignition gap 11a-14a can be provided by the ignition coil provided for each ignition gap. In FIG. 11, FIG.
A spark plug 12-1 is attached to a holding plate as shown in FIG.
4 shows an example in which an ignition coil is provided for each ignition gap when 4 is held. That is, the ignition coil 51 is fixed to the outer surface of the cylinder block 41, and the ignition coil 51 is covered with the insulator 52. Of this ignition coil 51, the iron core 51
a, the primary coil is shown by 51b, and the secondary coil is shown by 51c. The high tension code is shown at 53, and the primary current supply line from the igniter is shown at 54. In addition,
In FIG. 11, 55 is an exhaust pipe, 56 is an exhaust gas purifying catalyst, and the insulator 52 serves to prevent the influence of exhaust heat. Of course, the ignition gap 11a-
Providing an ignition coil for each 14a can be similarly applied to the case as shown in FIG.

FIGS. 14 and 15 correspond to FIGS. 12 and 13, and in order to make the thickness of the holding plate 42 thinner, the spark plugs 12 to 14 are substantially composed of only insulators and electrodes. It is configured by removing the excess coating and the hexagon nut part. Further, an anti-stop plate 61 is fixed to the outer periphery of the holding plate 41 in order to ensure sufficient anti-stop of the spark plugs 12-14. Then, the gap between the holding plate 41 and the ignition plugs 22 to 24 is filled with glass powder and then heated to melt the glass powder and seal the gap. In the case of this example, the spark plug 12-
When replacing 14, all of the spark plugs 12 to 14 as well as the holding plate 41 are replaced.

Although the embodiment has been described above, the present invention is not limited to this, and can be applied to an appropriate combustion chamber structure such as one having one intake port and one exhaust port.

[Brief description of drawings]

FIG. 1 is a plan view showing a positional relationship among an intake port, an exhaust port and an ignition gap with respect to a combustion chamber.

FIG. 2 is a view of the cylinder head of FIG. 1 viewed from the bottom surface thereof.

FIG. 3 is a vertical cross-sectional view of FIG. 1 showing a mounting hole for a spark plug.

FIG. 4 is a diagram showing a coating region of an oxidation catalyst.

FIG. 5 is a diagram showing an air-fuel ratio rich portion.

FIG. 6 is a vertical cross-sectional view showing a plug hole.

FIG. 7 is a view of the plug hole shown in FIG. 6 viewed from the lower surface side of the cylinder head.

FIG. 8 is a diagram when the center ignition gap is offset to the exhaust port side.

FIG. 9 is a view showing how the flame grows by adjusting the intake swirl and the ignition timing.

FIG. 10 is a diagram showing the relationship between the strength of the intake swirl and the ignition timing adjustment.

FIG. 11 is a diagram showing an example in which an ignition coil is provided for each spark plug.

FIG. 12 is a longitudinal sectional view showing an example in which a holding plate holds an ignition plug.

13 is a cross-sectional view of the holding plate portion shown in FIG. 12 taken along the spark plug axis.

FIG. 14 is a vertical cross-sectional view showing another example in which the holding plate holds the spark plug.

15 is a cross-sectional view of the holding plate portion shown in FIG. 14 taken along the axis of the spark plug.

[Explanation of symbols]

 1 Cylinder Head 2 Combustion Chamber 3A Intake Port 3B Intake Port 4A Exhaust Port 4B Exhaust Port 11a Ignition Gap 12a Ignition Gap (First Ignition Gap) 13a Ignition Gap (Second Ignition Gap) 14a Ignition Gap (Third ignition gap) 15a Ignition gap (fourth ignition gap) 31 Oxidation catalyst 32 Rich portion 33 Plug hole 33a Ignition part 33b Communication part 33c Communication part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location F02P 13/00 302 A 8923-3G 15/08 C 8923-3G 301 M 8923-3G 302 A 8923- 3G

Claims (7)

[Claims] 1. A plurality of ignition gaps are arranged at intervals in the circumferential direction of the combustion chamber on the outer peripheral edge of the combustion chamber, and a flame spread is provided to a portion where the intervals between the adjacent ignition gaps in the combustion chamber circumferential direction are the largest. A combustion control device for an engine, wherein a promotion means for promoting is set. 2. The combustion chamber according to claim 1, wherein two intake ports are opened, and the plurality of ignition gaps are three ignition gaps including a first ignition gap, a second ignition gap and a third ignition gap. The first ignition gap is located at the outer peripheral edge of the combustion chamber and between the two intake ports, and the second ignition gap is located at the outer peripheral edge of the combustion chamber, and the intake port and the exhaust port. Is located in one direction in the combustion chamber circumferential direction with respect to the exhaust port, and the third ignition gap is located at the outer peripheral edge of the combustion chamber and between the intake port and the exhaust port. Located in the other direction of the combustion chamber in the circumferential direction of the combustion chamber and having the largest distance between the second ignition gap and the third ignition gap in the combustion chamber circumferential direction. 3. The air-fuel ratio according to claim 2, wherein the promoting means enriches the air-fuel ratio of the air-fuel mixture supplied between the second ignition gap and the third ignition gap. 4. The oxidation catalyst according to claim 2, wherein the accelerating means is an oxidation catalyst applied to a combustion chamber wall surface between the second ignition gap and the third ignition gap. 5. The second ignition gap and the third ignition gap are each located in a plug hole connected to a combustion chamber, and the accelerating means burns a flame from the plug hole. It is configured by setting the shape of the plug hole so as to be mainly between the second ignition gap and the third ignition gap in the chamber circumferential direction. 6. The ignition device according to claim 2, wherein the promoting means sets an ignition timing of an ignition gap located upstream of the intake swirl among the second ignition gap and the third ignition gap to another ignition gap. The thing that makes it fire earlier than the ignition timing of. 7. The fourth ignition gap according to claim 2, wherein the promoting means is arranged at a position near the center of the combustion chamber and offset in a direction closer to the exhaust port than the center of the combustion chamber. thing.