JPS6299661A - Piston for heat-insulated engine - Google Patents

Abstract

PURPOSE:To intensify the strength for thermal stresses due to the water injection for enhancing the intake charging efficiency by superposing a thin-walled hollow outer wall structure made of heat resisting metal on the upper surface of a metallic piston, and filling a heat insulating filling material in the hollow space thereof. CONSTITUTION:A piston crown part 14 consists of an outer surface excepting the upper surface side of a piston body 9 or a top wall having a hollow 17, and a thin-walled hollow outer wall structure 14a provided integrally with a cylindrical circumferential wall, and is connected with a piston body 9 via a bolt 16 integrally cast and a nut 15. The outer wall structure 14a is formed by a heat resisting alloy having a high mechanical strength and heat resisting properties, such as Incoloy, Inconel, Waspalloy, or the like, and the interior thereof is filled with a heat insulating filling material 30 having a high heat insulating effect, such as porous ceramics, cordierite compounds, titanic potassium powder, or the like. Thus, the strength for thermal stresses due to water injection from a water spray nozzle 27 can be intensified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piston suitable for an adiabatic engine that improves intake air filling efficiency by water injection.

[Prior art] Ceramic materials are used in the cylinder head, piston crown, and part of the cylinder to insulate the combustion chamber, and high-temperature exhaust gas is supplied to the turbocharger, thereby increasing the efficiency of the turbocharger. Various types of adiabatic engines have already been proposed that aim to increase output and improve the overall thermal efficiency of the engine, but this adiabaticization significantly increases the temperature of the combustion chamber and reduces the intake air charging rate of 1lJt98. However, there is a problem in that the combustion condition worsens. Therefore, in order to lower the combustion temperature, conventional methods such as Utility Model Application No. 58-1636
There is a technique disclosed in Publication No. 34. In this prior art, water is injected into the combustion chamber at the end of fuel injection to lower the maximum combustion temperature inside the cylinder, thereby reducing NOx components in the exhaust gas.

However, this only suppresses the rise in combustion temperature;
It cannot be said that this is sufficient to continue to lower the temperature inside the cylinder until the intake stroke. In other words, in the exhaust stroke that follows the combustion stroke, the inside of the cylinder is reheated by the combustion gas, so when the intake air is drawn into the cylinder in the intake stroke, it heats up and expands instantly, reducing the intake air density and reducing the intake air filling efficiency. is decreasing. In addition, when the engine generates heat, preheated air of the fuel is not accumulated, making it easy to ignite on the high-temperature wall surface, reducing the isovolumic combustion light, and reducing performance.

Therefore, by cooling the inside of the cylinder with N1 at the end of the exhaust stroke, 1. *<If the rise in intake air temperature is suppressed during the intake stroke, intake air filling efficiency can be improved, but if the top of the engine and the wall of the headliner where the wood is injected are steeply tilted, a very large Thermal stress occurs and failure 1! 'It's possible.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a piston for an adiabatic engine having a piston crown having sufficient strength particularly against thermal stress caused by water injection.

r Problems W? Means for Determining] In order to achieve the above object, the present invention has a structure in which a thin hollow outer wall structure including a combustion chamber made of a heat-resistant metal is superimposed on the upper surface of a metal piston body, and a It is filled with insulation filler.

[Function] The outer shape of the piston crown 14 is formed by the outer wall structure 14a formed from a metal plate having mechanical strength and heat resistance.
The outer wall structure 14a is pressurized with a heat insulating filler such as porous ceramics, cordierite molded body, titanium liquor potassium powder, etc., which has a heat insulating effect, and is combined with the piston body made of ordinary metal. Due to the mechanical strength and heat resistance of the structure 14a, it can sufficiently withstand the heat attack caused by water jet. This thermal shock is absorbed by the outer wall structure 14a, and the heat insulating filler 30 suppresses the release of combustion heat and protects the screw main body 9.

[Embodiments of the Invention] The present invention will be explained based on remote measurement. First, to explain the outline of an adiabatic engine, as shown in FIG. An inverted cup-shaped ceramic helad liner 6 is fitted into a large-diameter cylindrical portion 8b formed at the upper end of the cylinder through a gasket 12-13. A cast iron cylinder head 4 is superimposed on the upper wall 6a of the headliner 6 via a gasket 5, and is connected to a flange of a cylinder body 8 by head bolts (not shown). In this way, a heat insulating air layer 7 is formed between the peripheral wall of the headliner 6 and the cylinder body 8, and a heat insulating air layer 23 is formed between the upper wall 6a and the cylinder head 4. The lower end of the headliner 6 is butted against the upper end of the cylinder liner 31.

In order to prevent a drop in exhaust gas temperature, the cylinder head 4 is formed with one (intake) and exhaust passage made of a double metal liner 22 coated with ceramics or integrally cast with a heat insulating air layer therebetween. This (intake) exhaust passage 19 is connected to an (intake) exhaust boat that is opened and closed by an (intake) exhaust valve 25 provided on the upper wall 6a of the headliner 6.

The (intake) exhaust valve 25 is slidably supported by a valve guide 26 of the cylinder head 4. Note that the <suction/exhaust valves 25 are shown in an overlapping manner to simplify the explanation.

The piston 29 has an upper surface of a metal piston body 9 fitted with a piston ring 11 projected in a chevron shape, and a piston crown portion 14 (described later) is superimposed on this projected surface, and the bolt 16
and are connected by a nut 15. A connecting rod 33 is connected to the piston body 9 by a piston pin 10.

A fuel injection nozzle 24 is supported on the cylinder head 4,
This tip portion is supported by the upper wall 6a of the helad liner 6.

Similarly, a water injection nozzle 27 is supported by the cylinder head 4, and its tip protrudes from the upper wall 6a into the combustion chamber. Fuel is injected from the fuel injection nozzle 24h) into the combustion chamber through the injection pipe 21 from the well-known fuel injection pump 20. Also,
Water is injected from the water injection nozzle 27 through the water pump 2, the injection pipe 3, the combustion chamber, the upper surface J5 of the screw crown 14, and the lower surface of the upper wall 6a of the headliner 6. There is.

According to the present invention, the piston crown 14 is a thin hollow outer wall structure 14a that integrally includes a top wall having a recess 17 and a cylindrical peripheral wall.
and a heat insulating filler 30 filled into the inside of this outer wall structure 14H and coupled to the piston body. The outer wall structure 14a is press-formed or molded from a metal plate having high mechanical strength and heat resistance. As the material, heat-resistant alloys such as Incoloy, Inconel, and Waspaloy are used. When casting the outer wall structure 14a, it is preferable to cast the bolts 16 integrally.

As the heat insulating filler 30, a porous ceramic molded body having an excellent heat insulating effect, a cordierite molded body which is a ceramic having low thermal conductivity, or a potassium titanate powder having low thermal conductivity is used.'1. In the case of a molded body such as cordierite, it is bonded to the outer wall structure 14a by suitable means.

Porous silicon nitride, which has a low thermal conductivity, is preferably used as the porous ceramic, and porous silicon nitride is filled into the inside of the outer wall structure 14a formed from an Incoloy alloy plate, and the porous silicon nitride is bonded by heating and pressing. Since the Incoloy alloy and silicon nitride have approximately the same thermal conductivity, thermal deformation between the two can be avoided.

In addition, a heat insulating filler 3 is prepared from porous silicon nitride into a predetermined shape.
When molding o and joining it to the outer wall structure 14a made of Inconel alloy, a copper oxide coating is formed on the surface of the heat insulating filler 30 made of silicon nitride by a metallization method, and this is bonded to the outer wall structure 14a made of Inconel alloy. It is fitted inside the structure 14a with silver solder interposed therebetween, and is bonded by heating and pressurizing.

In the case of potassium titanate powder, it is press-molded with potassium titanate and a binder, filled inside the outer wall structure 14a, combined with the piston body 9 and pressurized, and in this state is tightened with the bolt 16 and nut 15. Outer wall structure 14
a and the screw main body 9 are connected.

Next, the operation of the piston for an adiabatic engine according to the present invention will be explained. The fuel injected from the fuel injection nozzle 24 during the combustion stroke is passed through the ceramic helad liner 6.
Combustion takes place in a combustion chamber surrounded by the piston crown 14 having heat insulating properties, and the release of this combustion heat to the outside is prevented. The fuel injection timing is almost the same as a normal engine.

Water is injected from the water injection nozzle 27 into the combustion chamber at the end of the exhaust stroke following the combustion stroke, that is, just before the piston 29 reaches top dead center. Therefore, water is injected onto the upper surface of the outer wall structure 14a of the piston crown 14 and the peripheral surface and lower surface of the headliner 6, and the temperature of these walls is reduced by about 100° C., and the injected water is converted into water vapor. Become. In this way, the wall temperature of the combustion chamber is instantly lowered by the injection of water with a small amount of H.

Before the water injection, the temperature distribution is as shown by line a in Fig. 2, but if we look at the headliner 6, we can see that the water is lIn0
A, as shown by sob in FIG. 3, the internal temperature of the wall becomes higher than the surface temperature at each step as the wall surface temperature decreases. At this time, the intake stroke begins, and intake air is drawn into the cylinder from the intake passage. At this time, since the wall surface temperature of the headliner 6 has decreased as described above, the temperature rise and expansion of the air taken into the cylinder are suppressed, and a large amount of intake air with a correspondingly higher density is taken in. Continued compression 1
In the process, the wall surface temperature is recovered by the heat capacity of the headliner 6, as shown by line C in FIG. 4, and the intake air temperature is increased, which helps the compression work. Therefore, at the end of the exhaust stroke due to water injection, the cylinder wall temperature only temporarily decreases, and this heat is absorbed as water vapor, and the amount of heat released to the outside through the wall of the headliner 6 is the same as that without water injection. There is almost no difference compared to Furthermore, since the water injection is performed at the end of the exhaust stroke, most of the exhaust gas is supplied to the turbocharger in a high temperature state.

Therefore, in the 4-noise engine shown by the solid line in Figure 5, the intake air temperature T increases by the amount of increase in intake air temperature due to absorption of heat energy from the wall of the combustion chamber during the compression stroke, and a reheat cycle is added. The amount of work increases and thermal efficiency improves.

During the compression stroke, the intake air receives thermal energy from the combustion wall and its temperature rises by 1.5 degrees, which increases the end Obi and increases the intake air temperature, which increases the fuel combustion speed, improving fuel efficiency and engine performance. You can get an increase in output.

According to the present invention, as described above, a heat insulating filler made of a molded body or powder with low thermal conductivity and excellent heat insulation effect is bonded to the hollow part of the thin outer wall structure whose piston crown is made of a super heat-resistant alloy. The piston crown is connected to the main body made of ordinary metal with bolts and nuts, so the inside of the cylinder is When lowering the temperature and increasing the intake air filling efficiency, the outer wall structure in contact with water exhibits sufficient strength against thermal shock caused by a sudden temperature drop, and the temperature drop is limited to the outer wall structure, resulting in insulation. The temperature of the filler material changes little, preventing combustion heat from dissipating to the outside.

Furthermore, the temperature inside the cylinder decreases throughout the cycle due to the water injection compared to a case where water is not injected, so that sufficient durability is exhibited against oxidative corrosion of the outer wall structure.

[Effects of the Invention] According to the present invention, the thermal shock resistance is greatly improved compared to a piston crown formed entirely of ceramics, and an adiabatic engine with high practical reliability can be obtained. In a typical adiabatic engine, even if a super heat-resistant alloy is used for the surface of the piston crown, the surface will oxidize and corrode due to high temperatures, but by injecting water, the surface temperature can be suppressed.

[Brief explanation of drawings]

Fig. 1 is a front cross-sectional view of an adiabatic diesel engine equipped with an adiabatic engine piston according to the present invention, and Figs. 2 to 4 are combustion! FIG. 5 is a T-s diagram of the adiabatic diesel engine. FIG. 5 is a T-s diagram of the adiabatic diesel engine. 4 Nijilinda head 6: Helad liner 8 Nijilinda body 14. Piston crown 14a: Outer wall structure 3
0: Heat insulation filler 31 Niji Linda Life

Claims (3)

[Claims] (1) A piston for an insulated engine, characterized in that a thin hollow outer wall structure with a combustion chamber made of heat-resistant metal is superimposed on the upper surface of a metal piston body, and the hollow part is filled with an insulating filler. . (2) The piston for an adiabatic engine according to claim (1), wherein the outer wall structure is formed from an Incoloy alloy plate. (3) According to claim (1), a copper oxide coating is formed on the inner surface of the outer wall structure formed from an Incoloy alloy plate, and a heat insulating filler made of a porous silicon nitride molded body is brazed to the hollow part. Piston for the insulated engine described.