JPH04116224A - Direct injection type two cycle diesel engine - Google Patents

Abstract

PURPOSE:To perform a loop scavenging while to generate a swirl in a cavity by connecting a fresh air guide groove formed on a piston top face into the cavity as a tangent-line to a cavity peripheral wall surface. CONSTITUTION:A fresh air guide groove 15 is formed on a top face 2a of a piston 2 so as to guide a part of fresh air flowing in a loop form into a cavity 14. The fresh air guide groove 15 is connected to the cavity 14 as a tangent-line of a peripheral wall surface of the cavity 14. A swirl around an axis of the cavity 14 is generated by a part of the fresh air guide by the fresh air guide groove 15. The remaining fresh air flows inside a combustion chamber in a loop form to scavenge combusted gas. It is therefore possible to perform a loop scavenging so as to generate a swirl in the cavity 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a direct injection two-stroke diesel engine [Prior Art] An intake valve and an exhaust valve are arranged on the inner wall surface of the cylinder head, and the exhaust valve side is By covering the opening of the intake valve located in the combustion chamber with a mask wall, fresh air is caused to flow in a loop from the intake valve to the top surface of the piston and then to the exhaust valve, and the fuel injection is arranged on the inner wall surface of the cylinder head. A direct-injection two-stroke diesel engine is known in which fuel is injected into a combustion chamber from a valve (see Japanese Patent Publication No. 60-5770).

In this direct injection two-stroke diesel engine, scavenging efficiency is increased by flowing fresh air in a loop.

[Problem to be solved by the invention]

Increasing the scavenging efficiency in this way improves the engine output, so it is necessary to increase the scavenging efficiency in a two-stroke diesel engine, but it is difficult to obtain good ignition combustion simply by increasing the scavenging efficiency. In other words, the combustion chamber structure that can achieve good ignition combustion has been studied for a long time, and the result of this research is that a cavity is formed on the top surface of the piston, which is currently used in most four-stroke diesel engines. It has been found that it is preferable to form a fuel cavity and inject fuel into the cavity to obtain good ignition combustion. However, when fuel is injected into the cavity in this way, it is essential to generate a swirl around the cavity axis within the cavity in order to obtain good ignition combustion. This also applies to two-stroke diesel engines, and in order to obtain good ignition and combustion, it is preferable to form a cavity on the top surface of the piston. Since fuel is simply injected into the combustion chamber without forming a cavity on the top surface of the piston, the scavenging efficiency can be improved, but there is a problem that good ignition combustion cannot be obtained.

[Means for Solving the Problems] In order to solve the above problems, according to this development, the intake valve and the exhaust valve are arranged on the inner wall surface of the cylinder head, and the opening of the intake valve located on the exhaust valve side. By covering the air with a mask wall, fresh air is caused to flow in a loop from the intake valve to the top surface of the piston, then to the exhaust valve, and from the fuel injection valve located on the inner wall of the cylinder head to the inside of the combustion chamber. In a direct injection two-stroke diesel engine that injects fuel, a cavity is formed on the top surface of the piston, and a fresh air guide groove is formed on the top surface of the piston to guide part of the fresh air flowing in a loop into the cavity. A fresh air guide groove is formed in the cavity and connected tangentially to the peripheral wall surface of the cavity.

[For production]

Since the fresh air guide groove is connected within the cavity in a tangential manner to the peripheral wall surface of the cavity, a portion of the fresh air flow guided by the fresh air guide groove generates a swirl around the cavity axis within the cavity. The remaining fresh air flows in a loop within the combustion chamber to scavenge the burnt gas.

〔Example〕

Referring to FIGS. 1 to 3, 1 is a cylinder block, 2 is a piston that reciprocates within the cylinder block 1, and 3 is a cylinder block.
4 is a cylinder head, 4 is a combustion chamber formed between the flat top surface 2a of the piston 2 and the flat inner wall surface 3a of the cylinder head 3, 5 is a pair of intake valves, 6 is an intake port, and 7 is a pair of intake air ports. Exhaust valve, 8 is exhaust port, 9 is cylinder head inner wall surface 3
The fuel injection valves disposed in the center of FIG.

As shown in FIGS. 1 and 2, the cylinder head 3
A pair of grooves 10 are formed on the inner wall surface 3a of the air supply valve 1, and a valve seat 11 for each air supply valve 5 is arranged at the inner part of these grooves 10. Therefore, when the air supply valve 5 is seated on the valve seat 11, the air supply valve 5 is retracted into the groove 10. The circumferential wall of the concave groove 10 on the exhaust valve 7 side is formed in a cylindrical shape disposed close to the outer circumference of the bulk part of the air supply valve 5, and therefore this cylindrical circumferential wall covers the opening of the air supply valve 5 on the exhaust valve 7 side. A mask wall 12 is formed.

On the other hand, a peripheral wall portion 13 of the groove 10 on the opposite side to the mask wall 12
is formed into a conical shape that expands toward the inside of the combustion chamber 4.

FIG. 5 shows the opening timings of the intake valve 5 and the exhaust valve 7.

As can be seen from FIG. 5, in the embodiment shown in FIGS. 1 to 3, the exhaust valve 7 opens before the intake valve 5 and closes before the intake valve 5.

When the exhaust valve 7 opens, the burnt gas in the combustion chamber 4 is rapidly discharged into the exhaust boat 8. Next, when the intake valve 5 opens, fresh air starts flowing into the combustion chamber 4 from the intake port 6. At this time, since the opening of each air supply valve 5 located on the exhaust valve 7 side is covered by the mask wall 12, most of the fresh air flows through the mask wall 12 as shown by arrow S in FIGS. It flows into the combustion chamber 4 along the opposite conical wall section 13 . Next, the fresh air descends along the inner wall surface of the cylinder, then crosses the top surface 2a of the piston 2 along the top surface 2a of the piston 2, and then rises again along the inner wall surface of the cylinder. A strong loop scavenging air flow S is generated. The burnt gas in the combustion chamber 4 is sequentially pushed out into the exhaust port 8 via the exhaust valve 7 by this loop scavenging air flow S.

FIG. 4 shows a loop fresh air flow S flowing along the top surface 2a of the piston 2. As shown in Figure 4, the loop scavenging air flow S
crosses the center of the piston top surface 2a. As shown in FIGS. 1 and 4, a cavity 14 is formed in the center of the piston top surface 2a across which the loop scavenging air flow S crosses. Furthermore, the flow axis a of the loop scavenging air flow S along the piston top surface 2a
A fresh air guide groove 15 extending to the cavity 14 in the flow direction of the loop scavenging air flow S is formed on the top surface 2a of the piston located on one side of the piston (FIG. 4). The fresh air guide groove 15 gradually becomes deeper toward the cavity 14 and is then connected within the cavity 14 tangentially to the peripheral wall surface of the cavity 14 . Therefore, a portion of the loop scavenging air flow S is guided by the fresh air guide groove 15 and flows into the cavity 14 as shown by the arrow S1, thereby generating a swirl around the cavity axis within the cavity 14. The remaining portion of the loop scavenging air flow S flows through the cavity 14 as shown by arrow S2.
After passing above the exhaust valve 7, it rises along the inner wall surface of the cylinder below the exhaust valve 7.

When the piston 2 approaches top dead center, fuel is injected from the fuel injection valve 9 into the cavity 14. At this time, a swirl around the cavity axis is generated within the cavity 14, so that good ignition combustion is performed. Further, since the scavenging efficiency is increased by the loop scavenging air flow S2, high engine output can be obtained.

〔Effect of the invention〕

Since swirl can be generated within the cavity while performing loop scavenging, high engine output can be ensured while ensuring good ignition and combustion.

[Brief explanation of drawings]

Figure 1 is a side sectional view of a two-stroke diesel engine;
3 is a sectional plan view of the cylinder head, FIG. 4 is a plan view of the piston, and FIG. 5 is a diagram showing the opening timings of the intake valve and the exhaust valve. 5... Air supply valve, 9... Fuel injection valve, 14... Cavity, 7... Exhaust valve, 12... Mask wall, 15... Fresh air guide groove.

Claims (1)

[Claims] An intake valve and an exhaust valve are arranged on the inner wall surface of the cylinder head, and the opening of the intake valve located on the exhaust valve side is covered by a mask wall, so that fresh air is transferred from the intake valve to the piston top surface in the combustion chamber, and then to the exhaust valve. A cavity is formed on the top surface of the piston in a direct injection two-stroke diesel engine in which the fuel flows in a loop to the valve and is injected into the combustion chamber from the fuel injection valve located on the inner wall surface of the cylinder head. A fresh air guide groove is formed on the top surface of the piston to guide a part of the fresh air flowing in the loop shape into the cavity, and the fresh air guide groove is formed in the cavity in a line tangential to the cavity peripheral wall surface. Direct-injection two-stroke diesel engine connected to.