JP2021131083A - Compression ignition engine - Google Patents

Abstract

To provide a compression ignition engine that is improved in heat efficiency without impairing volumetric efficiency of intake air.SOLUTION: A compression ignition engine 1 for self-igniting the air that is compressed and heated to a point equal to or higher than an ignition point of fuel F by jetting the fuel F includes: a piston body 11 including a combustion chamber E; a heat insulation part 18 provided to a surface constituting the combustion chamber E in the piston body 11; and a medium jetting nozzle 5 for jetting a medium M having evaporative latent heat into the combustion chamber E in an intake stroke or compression stroke.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a compression ignition engine.

As a technique for improving thermal efficiency in an engine, there is a technique in which a heat insulating layer made of ceramics such as zirconia is added to a combustion chamber to suppress heat transfer from the wall surface of the combustion chamber. For example, in Patent Document 1, a heat shield layer that suppresses heat transfer from the lower part of the cylinder liner to the cylinder block is provided to reduce the temperature gradient from the upper part to the lower part of the cylinder liner.

Japanese Unexamined Patent Publication No. 2005-330873

However, when the heat insulating layer is provided to the combustion chamber, the temperature of the wall surface of the combustion chamber rises and the intake air is warmed by the wall surface, so that the volumetric efficiency of the intake air may decrease. Further, it is considered that the heat transfer coefficient of the wall surface of the combustion chamber becomes large, so that the heat transferred to the wall surface becomes large, and as a result, the intended improvement in thermal efficiency cannot be achieved. Especially for compression ignition engines, no attempt has been made to solve such problems.

The present disclosure has been made to solve the above problems, and an object of the present invention is to provide a compression ignition engine capable of improving thermal efficiency without impairing the volumetric efficiency of intake air.

The compression ignition engine according to one aspect of the present disclosure is a compression ignition engine that self-ignites air compressed and heated above the ignition point of the fuel by injecting fuel, and has a piston body having a combustion chamber and a combustion chamber in the piston body. Includes a heat insulating portion provided on the surface constituting the above, and an injection portion for injecting a medium having latent heat of evaporation into the combustion chamber in the intake stroke or the compression stroke.

In this compression ignition engine, the wall surface of the combustion chamber insulated by the heat insulating portion can be cooled by injecting a medium having latent heat of vaporization into the combustion chamber in the intake stroke or the compression stroke. Therefore, it is possible to suppress an increase in the heat transfer coefficient of the wall surface of the combustion chamber, and it is possible to enhance the effect of improving the thermal efficiency by the heat insulating portion. Further, since the intake air taken into the combustion chamber can be cooled by injecting a medium having latent heat of vaporization, it is possible to avoid impairing the volumetric efficiency of the intake air.

The injection unit may inject the medium into the combustion chamber when the piston body is located on the bottom dead center side of the midpoint between the top dead center and the bottom dead center in the compression stroke. In this case, the generation of smoke in the combustion chamber can be suppressed. In addition, the cooling effect of the wall surface of the combustion chamber can be enhanced.

The medium may include any of gasoline, alcohols, and water. When gasoline and alcohols are used, the medium can be burned together with the fuel in the combustion / expansion stroke. When water is used, the effect of cooling the wall surface of the combustion chamber can be sufficiently enhanced.

According to the present disclosure, the thermal efficiency can be improved without impairing the volumetric efficiency of the intake air.

It is sectional drawing which shows one Embodiment of a compression ignition engine. It is a figure which shows the relationship between the injection amount of a medium, and the temperature drop in a combustion chamber.

Hereinafter, preferred embodiments of the compression ignition engine according to one aspect of the present disclosure will be described in detail with reference to the drawings. In the following description, the "up" and "down" directions correspond to the reciprocating directions of the pistons in the compression ignition engine. Further, the word "upper" corresponds to the top dead center side of the piston, and the word "lower" corresponds to the bottom dead center side of the piston.

As shown in FIG. 1, the compression ignition engine 1 is, for example, a diesel engine mounted on a vehicle, and is an engine of a type in which air compressed and heated above the ignition point of the fuel F is self-ignited by injection of the fuel F. The compression ignition engine 1 includes a piston 2, a cylinder 3, a fuel injection nozzle 4, and a medium injection nozzle (injection unit) 5.

The piston 2 is a member that reciprocates inside the cylinder 3 along the extending direction of the central axis C. The piston 2 has a substantially cylindrical outer shape. The piston 2 is connected to the crankshaft of the internal combustion engine via a connecting rod. The cylinder 3 is a cylinder formed in a cylinder block. A cooling water flow path through which cooling water flows is provided around the cylinder 3. For example, a cylinder liner is mounted on the inner wall surface of the cylinder 3.

The piston 2 includes a piston body 11. The piston body 11 includes a top surface 12, a sliding side surface 13, a skirt 14, an oil gallery 15, and a cavity 16. As the material of the piston body 11, for example, aluminum alloy or iron is adopted. The top surface 12 is the upper end surface of the piston body 11. The top surface 12 constitutes a combustion chamber E in the piston body 11. The combustion chamber E is a space defined by the piston 2, the cylinder 3, and the cylinder head 3a.

The sliding side surface 13 is a piston side surface that slides with respect to the inner wall surface of the cylinder liner. A first piston ring groove 19a to a third piston ring groove 19c are formed on the sliding side surface 13, respectively. In the first piston ring groove 19a, the first piston ring 17A located closest to the top surface 12 side is arranged. In the second piston ring groove 19b, a second piston ring 17B located between the first piston ring groove 19a and the third piston ring groove 19c is arranged. A third piston ring 17C located closest to the skirt 14 is arranged in the third piston ring groove 19c.

The skirt 14 extends downward along the sliding side surface 13. A small end of a connecting rod is arranged in the internal space S of the skirt 14. The piston body 11 has an oil gallery 15 formed in an annular shape so as to surround the cavity 16. The oil gallery 15 is a hollow portion formed inside the piston body 11. Engine oil flows through the oil jet holes inside the oil gallery 15 to cool the piston body 11.

The cavity 16 is a recess provided on the top surface 12 of the piston body 11, and constitutes a combustion chamber E in the piston body 11. The cavity 16 has an axisymmetric shape with respect to the central axis C. The cavity 16 has a bottom surface 16a and a side wall surface 16b. The bottom surface 16a is inclined upward as it approaches the central axis C, and has a conical shape centered on the central axis C. The side wall surface 16b is a curved surface that bulges outward in the radial direction, and extends in an annular shape about the central axis C.

A heat insulating portion 18 is provided on the inner wall surface (bottom surface 16a and side wall surface 16b) of the cavity 16. The heat insulating portion 18 is formed by coating the bottom surface 16a and the side wall surface 16b with a ceramic such as zirconia to a substantially uniform thickness. The heat insulating portion 18 is interposed on the heat transfer path from the combustion chamber E to the cooling water flow path of the cylinder 3 via the piston main body 11 to insulate the combustion chamber E.

The fuel injection nozzle 4 is a portion that injects fuel F toward the combustion chamber E. The fuel injection nozzle 4 is provided so as to coincide with the central axis C, and protrudes from the cylinder head 3a toward the piston body 11 side. When the piston body 11 is displaced from the bottom dead center to the top dead center, the fuel injection nozzle 4 injects the fuel F (here, light oil) into a mist toward the combustion chamber E.

The medium injection nozzle 5 is a portion that injects the medium M toward the combustion chamber E in the intake stroke or the compression stroke. The medium injection nozzle 5 is provided at a constant inclination angle with respect to the central axis C and the fuel injection nozzle 4, and projects from a position facing the edge of the cavity 16 in the cylinder head 3a toward the piston body 11. The medium injection nozzle 5 may be arranged on either side of the intake port (not shown) or the exhaust port (not shown).

In the present embodiment, the medium injection nozzle 5 injects the medium M toward the combustion chamber E in a mist form when the piston body 11 is displaced from the bottom dead center to the top dead center in the compression stroke. More specifically, the fuel injection nozzle 4 is directed toward the combustion chamber E when the piston body 11 is located on the bottom dead center side of the midpoint between the top dead center and the bottom dead center in the compression stroke. The medium M is injected in a mist form. The timing of injection of the medium M by the medium injection nozzle 5 is earlier than the timing of injection of the fuel F by the fuel injection nozzle 4.

The medium M ejected from the medium injection nozzle 5 is a medium having latent heat of vaporization. Examples of such a medium M include gasoline (premixed mixture of gasoline and air), alcohols, and water. The tip (injection port) of the medium injection nozzle 5 may be bent with respect to the main body of the nozzle. In this case, the medium M does not directly face the bottom surface 16a of the cavity 16 but is supplied to the combustion chamber E in a more diffused state.

In the compression ignition engine 1 having the above configuration, air is taken into the cylinder 3 through an intake port (not shown) in the intake stroke. In the subsequent compression stroke, when the piston body 11 is displaced from the bottom dead center to the top dead center, the fuel F is injected from the fuel injection nozzle 4 toward the combustion chamber E, and the medium injection nozzle 5 is injected into the combustion chamber E. The medium M is injected toward the target. Then, just before the piston body 11 reaches the top dead center, the fuel F ignites and shifts to the combustion / expansion stroke. In the combustion / expansion stroke, the combustion gas expands due to the combustion of the fuel F, and the piston body 11 is pushed down to the bottom dead center. In the subsequent exhaust stroke, the combustion gas is discharged from the inside of the cylinder 3 through the exhaust port (not shown).

As described above, in the compression ignition engine 1, the wall surface of the combustion chamber E (the bottom surface 16a of the cavity 16 and the bottom surface 16a of the cavity 16) is insulated by the heat insulating portion 18 by injecting the medium M having latent heat of vaporization into the combustion chamber E in the intake stroke. The side wall surface 16b) can be cooled. Therefore, it is possible to suppress an increase in the heat transfer coefficient of the wall surface of the combustion chamber E, and it is possible to enhance the effect of improving the thermal efficiency by the heat insulating portion 18. Further, since the intake air taken into the combustion chamber E can be cooled by the injection of the medium M having latent heat of vaporization, it is possible to avoid impairing the volumetric efficiency of the intake air.

In the compression ignition engine 1, when the piston body 11 is located on the bottom dead center side of the midpoint between the top dead center and the bottom dead center in the intake stroke, the fuel injection nozzle 4 moves the medium M into the combustion chamber E. Inject to. As a result, the generation of smoke in the combustion chamber E can be suppressed. Further, the cooling effect of the wall surface of the combustion chamber E can be enhanced.

In the compression ignition engine 1, gasoline, alcohols, and water are used as the medium M having latent heat of vaporization. When gasoline and alcohols are used, the medium can be burned together with the fuel F in the combustion / expansion stroke. When water is used, the effect of cooling the wall surface of the combustion chamber E can be sufficiently enhanced.
FIG. 2 is a diagram showing the relationship between the injection amount of the medium and the temperature drop in the combustion chamber. In the figure, the horizontal axis represents the air-fuel ratio (A / F) and the vertical axis represents the amount of temperature decrease (° C.) in the combustion chamber, and the effect of the air-fuel ratio on the temperature decrease of the gas in the cylinder was calculated by simulation. The medium having latent heat of vaporization was (premixed mixture of gasoline and air), and the latent heat of vaporization was 75 kcal / kg. The specific heat of air was 0.24 kcal / kgK, and the specific heat of gasoline was 0.4 kcal / kgK.
From the results shown in FIG. 2, it can be seen that the amount of temperature decrease of the gas in the cylinder increases in proportion to the amount of the medium to be injected. However, when the amount of the injected medium becomes excessive, if the compression ratio of the engine is set high, the medium may self-ignite before the fuel is injected, and so-called premature ignition may occur. Therefore, the amount of the medium to be injected is preferably determined according to the compression ratio and the like within a range in which self-ignition of the medium does not occur. In the simulation of FIG. 2, it is possible to realize a temperature drop of about 7 ° C. when the A / F is 40, and a sufficient temperature drop is expected even under a relatively high condition of a compression ratio of about 17.

The present disclosure is not limited to the above embodiment. For example, the protruding position of the medium injection nozzle 5 in the cylinder head 3a is not limited to the position facing the edge of the cavity 16 in the cylinder head 3a, and may be another position such as a position adjacent to the fuel injection nozzle 4. Further, the medium injection nozzle 5 may be arranged parallel to the central axis C and the fuel injection nozzle 4.

Further, in the above embodiment, the medium injection nozzle 5 injects the medium M in the compression stroke, but the medium injection nozzle 5 may inject the medium M in the intake stroke. In this case, the medium injection nozzle 5 may be arranged close to the intake port, and the medium M may be injected at the timing when the intake port is opened in the intake stroke.

1 ... compression ignition engine, 5 ... medium injection nozzle (injection part), 11 ... piston body, 18 ... heat insulating part, E ... combustion chamber, F ... fuel, M ... medium.

Claims (3)

A compression ignition engine that self-ignites air compressed and heated above the ignition point of fuel by injecting the fuel.
A piston body with a combustion chamber and
In the piston body, a heat insulating portion provided on the surface constituting the combustion chamber and
A compression ignition engine including an injection unit that injects a medium having latent heat of vaporization into the combustion chamber in an intake stroke or a compression stroke. Claim 1 in which the injection unit injects the medium into the combustion chamber when the piston body is located on the bottom dead center side of the midpoint between the top dead center and the bottom dead center in the compression stroke. The described compression ignition engine. The compression ignition engine according to claim 1 or 2, wherein the medium includes any of gasoline, alcohols, and water.

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