JPH0333424A - Inner-cylinder direct injection type two cycle engine - Google Patents

Abstract

PURPOSE:To improve scavenging operation and combustion of air-fuel mixture by arranging the ignition plug gap at a specified distance from an injector which is installed on a substantially center of a sector cavity and faces to the cylinder center. CONSTITUTION:A cavity 12 substantially sector in plan view is formed, which cavity introduced scavenge flow of a longitudinal swirl S from a substantial center part of a combustion chamber 10 to the opposite side of a discharge port. An injector 13 which jets conical spray is provided on the substantially center of the narrower part of the cavity 12, facing to the center of a cylinder 2. An ignition plug 14 is installed with inclination such that a gap 14a thereof is locates at a specified distance in the jet direction of the injector 13. The injector 13 and the gap 14a of the ignition plug 14 are scavenged well by the longitudinal swirl S. A proper air-fuel ratio is kept in the vicinity of the ignition plug 14 without influence of gas movement such as the longitudinal swirl S, so that stable ignition, combustion, and excellent lamination combustion.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an in-cylinder direct injection two-stroke engine in which fuel is directly injected into a cylinder by an injector. Regarding.

[Conventional technology]

In order to improve scavenging efficiency especially at low loads in 2-cycle engines and to prevent fuel from blowing through, only air is introduced using a scavenging pump etc. during scavenging, and after the scavenging port is closed, fuel is directly injected into the cylinder by an injector. A method has been proposed that injects

Therefore, in such an in-cylinder direct injection type, the combustion chamber is equipped with an injector and a spark plug.

Therefore, conventionally, regarding this type of two-stroke engine,
For example, there is a prior art in Japanese Patent Application Laid-Open No. 62-32214, in which the combustion chamber has a diameter of about 0.55 to 0.77 of the cylinder diameter.
It is shown that a semi-circular cavity with a depth of . Furthermore, in Japanese Patent Application Laid-Open No. 60-1322, a nozzle having two nozzles for injecting fuel in different directions is attached to the subchamber, and the spark plug gap is located in an area sandwiched between the jets from both nozzles. It is shown.

[The problem that the invention attempts to solve]

By the way, in the former of the above-mentioned prior art, the cavity of the combustion chamber is quite deep, so the amount of fresh air introduced into the cavity by the scavenging air flow is small, and therefore residual gas cannot be pushed out sufficiently. , deterioration of combustion due to poor scavenging is expected. Furthermore, since the spark plug is located deep in the cavity, flame propagation is slow, especially at high loads, and knocking is likely to occur. Moreover, since the cavity is offset from the center and has a semicircular shape, the vertical swirl is influenced by the cavity and the radius of the vertical swirl becomes small. negative pressure is likely to occur. This negative pressure pulls exhaust gas back from the exhaust port, leading to an increase in residual gas, which may result in poor combustion, an increase in scavenging air temperature due to residual gas under high load, and knocking.

Furthermore, since the injector is offset from the center of the cylinder, a large amount of fuel adheres to the cylinder wall surface under high load, which tends to cause poor diffusion, which reduces combustion efficiency.

Also, the fuel may wash away the oil on the cylinder wall,
Poor lubrication may occur. In the cavity, fuel is guided to the plug gap by vertical swirl at low loads, but due to large cycle fluctuations in gas flow, it is difficult to obtain stable ignition performance.

Furthermore, since the latter prior art technology injects fuel in the pre-chamber and ignites it, when applied to a two-stroke engine, scavenging is poor and residual gas in the pre-chamber increases, resulting in poor combustion. Furthermore, due to the reduction in thermal efficiency due to the restriction of the nozzle orifices, combustion delays, etc., it is not possible to cope with deterioration of fuel efficiency and high output.

Therefore, gas exchange and combustion in a two-stroke engine require an air supply method and direct fuel injection that increase scavenging efficiency through vertical swirl, achieve stratified combustion in low load ranges, and uniform combustion in high load ranges. It is. Accordingly, it is desired to form a combustion chamber and appropriately arrange an injector and a spark plug so as to achieve good combustion and high output.

The present invention has been made in view of these points, and its purpose is to improve the shape of the combustion chamber and the arrangement of the injector and spark plug, thereby achieving high output through consistently good scavenging action and combustion of the air-fuel mixture. The object of the present invention is to provide an in-cylinder direct injection two-stroke engine that can be

[Means to solve the problem]

In order to achieve the above object, the in-cylinder direct injection two-stroke engine of the present invention has an exhaust port and a scavenging port opened in the middle of the cylinder, and an in-cylinder direct injection type engine in which an injector and a spark plug for injecting fuel into the combustion chamber are attached. In the injection type two-stroke engine, a cavity for guiding a vertical swirl scavenging air flow is formed at least in a fan shape in a plan view from approximately the center of the combustion chamber to the opposite side from the exhaust port, and in a narrow approximately central portion of the cavity, An injector that injects a cone-shaped spray is mounted toward the center of the cylinder, and the spark plug is mounted so that the gap of the spark plug is positioned at a predetermined distance in the fuel injection direction of the injector.

[For production]

Based on the above configuration, the vertical swirl of fresh air flowing in from the scavenging port is collected by the fan-shaped cavity of the combustion chamber and guided to increase the speed at the center, and the vertical swirl especially injects the injector and ignition at the center of the cavity. The gap area of the plug is always well scavenged. During medium and low load conditions, the amount of air supplied is small, so the solid cone-shaped spray injected from the injector advances without being affected by the above-mentioned vertical swirl, and passes through the spark plug gap without spreading much. As a result, the flame is ignited when it passes through this gap, and the flame spreads equally in all directions without being restricted, resulting in good stratified combustion. Furthermore, when the load is high, the high speed and large amount of air supply allows the spray to freely diffuse throughout the interior of the cylinder, resulting in good uniform combustion and high output.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In Figure 1, let's talk about the case where it is applied to a two-stroke engine with in-cylinder direct injection and Schneeler reverse scavenging. Reference numeral 1 designates a crankcase, in which a piston 3 is inserted into a cylinder 2, and a combustion chamber 10 is provided in the upper part of the cylinder 2 on the cylinder head 4 side. Further, an exhaust port 5 is opened in the middle of the cylinder 2, and five scavenging ports B, for example, are opened on the opposite side of the exhaust port 5 at positions slightly shifted downward from the exhaust port 5, forming a Schneeler type.

As detailed in FIGS. 2(a) and 2(b), the combustion chamber IO has a wide spherical squish area 11 with a large radius of curvature R from the center of the cylinder 2. A cavity 12 is provided on the opposite side of the exhaust port 5 from the center. The cavity 12 has a top surface 12a
is formed in a fan shape outward from the center in a plan view, and is curved so that it gradually becomes deeper from the outside toward the center, and a hole with a width of 12 mm is located at a position slightly shifted from the center of this top surface 12a toward the exhaust port 5 side. A narrow boss surface 12b is provided at a predetermined angle that is half of the injector spray angle φ. Further, both sides of the top surface 12a and the boss surface 12b are configured to be loosely connected to the squish area 11 via a tabular member 12e.

The injector 13 is installed approximately at the center of the top surface 12a of the cavity 12 of the combustion chamber IO, facing toward the center of the cylinder 2, and the ignition plug i4 is mounted on the boss surface 12b.
is installed tilted sideways. The injector 18 is a high-pressure one-fluid electromagnetic type and has a single hole, and when fuel is injected at a constant high-pressure injection amount, an atomized portion a and an incomplete atomized portion are formed for a predetermined spray angle φ. occurs. In this atomized portion a, the fuel particles are uniformly atomized by introducing fresh air, etc., and the density of the fuel particles becomes small, so that ignition and combustion are easy to occur.

Here, the vertical swirl S flows from the wall surface of the cylinder 2 to the exhaust port 5 side via the top surface 12a of the cavity 12 and the boss surface 12b. It is injected under pressure and travels almost straight. and spark plug 14 gap 1
If the spark plug 4a is close to the injector 13, the initial velocity of the spray is relatively high, making it difficult to ignite, and if it is far away, the diffusion will progress. A gap 14a is provided.

Thereby, the gap 14a is provided in the vicinity of the center of the combustion chamber lO coming out of the cavity 12.

Further, the boss surface 12 to which the above-mentioned spark plug 14 is attached
Since b is parallel to the conical surface C on the spark plug 14 side of the spray angle φ, the spray angle φ of fuel injection is not impaired, and the spark plug 1
It becomes possible to minimize the amount of protrusion of 4.

In this way, in the low speed and low load range, the spray from the injector 13 is not disturbed by the swirl and advances forward due to the injection pressure, and as it passes through the gap 14a, it is ignited and stratified combustion occurs, and in the medium load range, The swirl speed also increases, the fuel injection timing is advanced, and as the amount of fuel injection increases, the tip of the spray diffuses and automatically enters a premixed combustion state.

In a high load range, these effects are further promoted, and when a large amount of fuel is injected immediately after the scavenging port 6 is closed, the spray is diffused throughout the interior of the cylinder 2, making it possible to achieve uniform combustion.

Next, the operation of the two-stroke engine having such a configuration will be described.

First, when the piston 3 descends and the exhaust port 5 opens, and then the scavenging port B also opens, fresh air containing only air flows into the cylinder 2 from the scavenging port 6. This fresh air is transferred to scavenging port 6.
, it reverses to the side opposite to the exhaust port 5, rises along the wall surface of the cylinder 2, and flows down to the exhaust port 5 side via the top surface 12a of the cavity 12 of the combustion chamber IO and the boss surface 12b, creating a vertical swirl S. The residual gas is pushed out by the vertical swirl S, resulting in a scavenging effect. In this case,
Due to the fan-shaped top surface 12a of the cavity 12, even if there is variation in the amount of fresh air introduced from the left and right sides from each scavenging port 6, it is collected, and furthermore, a vertical swirl S is created at the center of the top surface 12a and the narrowest part of the boss portion 12b. It flows at a high speed, so that the area between the injector 13 and the gap 14a is particularly well scavenged, resulting in an atmosphere consisting only of air.

Next, the piston 3 rises to close the scavenging port 6 and the exhaust port 5, and then fuel is injected from the injector 13 at high pressure. Then, at a predetermined ignition timing, the ignition plug 14 is energized to ignite the spray. Therefore, when the load is low, the fuel spray injected from the injector 13 takes on a cone shape and entrains air, and the air-fuel mixture in the atomized part a is not affected by the vertical swirl S so much that the fuel spray is injected into the spark plug I.
It is ignited when passing through the gap 14a of No. 4. Furthermore, since the fuel spray in the atomized portion a is in an atomized state and is well mixed with air and has an air-fuel ratio that is optimal for combustion, good combustion is carried out.

Furthermore, since the ignition point of the gap 14a is near the center of the combustion chamber lo and the vicinity where it exits from the cavity 12, the flame propagates in all directions without being restricted in any way, thus achieving good stratified combustion.

Further, when the load increases, the fuel injection amount increases, the injection starts earlier, and the swirl speed also increases, which causes the tip of the spray to spread and become premixed. When the load is high, this is further promoted, and the spray itself is freely diffused and spreads over the entire area of the cylinder 2, is pushed up by the piston 2, becomes uniform, and is combusted with a high utilization rate of fresh air.

Even if the temperature on the exhaust port 5 side becomes high, a strong squish effect is obtained in the squish area 11 of the combustion chamber 10, so that the knocking phenomenon is suppressed.

Referring to FIG. 3, another embodiment of the present invention will be described.

The combustion chamber shown in FIG. 3(a) is formed so that the fan-shaped top surface 12a of the cavity 12 curves the tapered surfaces 12c on both sides to further increase the divergence angle.

In the case shown in FIG. 3(b), the top surface 12a is formed with the opening angle as large as possible over substantially the entire circumference except for the boss 12b. As a result, the gathering ability of the vertical swirl S by the top surface 12a is increased, and the scavenging effect of the gap 14a between the injector 13 and the spark plug 14 is improved.

〔Effect of the invention〕

As described above, according to the present invention, the in-cylinder direct injection type 2
In a cycle engine, the cavity of the combustion chamber is formed into a fan shape, and the injector and spark plug gap are located in the narrow center, so that the injector and the gap can always be well scavenged by vertical swirl. This can improve the ignition combustibility due to the gap.

In addition, a spark plug gap is placed a predetermined distance in the fuel injection direction of the injector, and when the spray passes,
Since the air-fuel ratio near the ignition plug is maintained at an appropriate air-fuel ratio without being affected by gas flow such as vertical swirl, stable ignition combustion and good stratified combustion can be achieved.

Furthermore, the flame propagates equally in all directions, resulting in good combustion efficiency. Furthermore, uniformity during high loads is achieved well, and a high fresh air utilization rate results in good combustion and high output performance.

Furthermore, a wide squish area is provided around the cavity of the combustion chamber to create a strong squish effect, thereby preventing knocking.

Furthermore, since the gap between the injector and the spark plug is located at the center of the cylinder, the above-mentioned improvement in combustibility is promoted, and the amount of fuel adhering to the cylinder wall is reduced, so that the lubrication of the piston is not impaired.

Furthermore, the spaced arrangement of the injector and spark plug facilitates replacement of the two assembled spark plugs and maintenance of the injector.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the in-cylinder direct injection two-stroke engine of the present invention, Fig. 2(a) is an enlarged sectional view of the combustion chamber, (b> is a bottom view of the same, Fig. 3(a) , (b) is a bottom view of another embodiment. 2... Cylinder, 5... Exhaust port, 6... Scavenging port, 10... Combustion chamber, 12... Cavity, 1
2a...Top surface, 12b...Boss surface, 13...Injector, i4...Spark plug, 4a...Gap

Claims (2)

[Claims] (1) In an in-cylinder direct injection two-stroke engine in which an exhaust port and a scavenging port are opened in the middle of the cylinder, and an injector and a spark plug are attached to inject fuel into the combustion chamber, the exhaust port is opened from approximately the center of the combustion chamber. On the opposite side, a cavity for guiding the vertical swirl scavenging air flow is formed at least fan-shaped in plan view, and an injector for injecting a cone-shaped spray is installed in the narrow center of the cavity toward the center of the cylinder. An in-cylinder direct injection two-stroke engine, characterized in that the spark plug is mounted with a gap thereof tilted so as to be positioned a predetermined distance apart in the fuel injection direction of the injector. (2) The cavity of the combustion chamber is fan-shaped in plan view and has a top surface that gradually becomes deeper from the outside toward the center, and a narrow boss surface that is inclined from the center of the top surface toward the exhaust port. The in-cylinder direct injection two-stroke engine according to claim 1, wherein the injector is mounted on the central axis of the top surface, and the spark plug is mounted on the boss surface.