JP2002349267A - Combustion system of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the constitution for obtaining an improving effect of exhaust gas by injecting fuel in a multistage without forming a fuel injection nozzle such as a complcated structure when adopting a shallow pan-shaped combustion chamber. SOLUTION: This combustion system of a diesel engine has the combustion chamber arranged in a top surface part of a piston reciprocatably arranged in a cylinder, and having a bottom wall part and a side wall part gradually diametrally expanding toward a top surface of the piston from the outer peripheral end of the bottom wall part, and a fuel injector capable of injecting the fuel in a multistage toward the combustion chamber, and is characterized in that the fuel injector has a fuel injection nozzle having a fuel injection angle for injecting fuel toward the vicinity of a connecting part of the bottom wall part and the side wall part of the combustion chamber when the piston exists in the vicinity of the compression upper dead center, and injects the fuel as a first stage when the piston exists in the vicinity of the compression upper dead center, and the, injects it as a second stage toward the combustion chamber when the piston exists in a lowered position more than the fuel injection timing of the first stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a diesel engine combustion system for directly injecting fuel into a combustion chamber provided on a piston top surface.

[0002]

2. Description of the Related Art Diesel engines are roughly classified into a sub-combustion chamber type (hereinafter referred to as a sub-chamber type) and a direct injection type (hereinafter referred to as a direct injection type) depending on the type of combustion chamber. As a result, direct-injection diesel engines that do not have a throttle loss and have less heat loss than sub-chamber engines are increasingly used.

[0003] In a direct injection type diesel engine, a combustion chamber is provided on the top surface of a piston reciprocally disposed in a cylinder, and fuel is directly injected into the combustion chamber. Then, when the air in the combustion chamber is compressed and reaches the ignition temperature, the fuel self-ignites and starts burning, the inside of the cylinder expands, and the piston is lowered to convert it into rotational energy.

[0004] As described above, a diesel engine is self-ignited and does not have an ignition device (such as a spark plug). Therefore, it is necessary to compress the inside of a cylinder to a higher pressure than a gasoline engine. In particular, in a direct injection diesel engine, fuel is injected into a cylinder in a highly compressed atmosphere, so that the fuel injection pressure also becomes high. However, when the fuel injection pressure becomes high, the reach of the fuel spray in the combustion chamber also increases, and the amount of fuel adhering to the wall of the combustion chamber increases. As a result, atomization of the fuel and mixing with the air in the combustion chamber are hindered, so that the direct injection diesel engine may cause deterioration of the exhaust gas (black smoke) despite the large excess air ratio.

[0005] On the other hand, in recent years, many diesel fuel engines have employed pressure-accumulation type fuel injection devices which can inject fuel at an arbitrary timing and an arbitrary injection pressure and can freely set the number of injections. . As shown in FIG. 4, the pressure-accumulation type fuel injection device includes a supply pump 1 driven by an engine, a supply pump control valve 2 for adjusting a pumping amount of the supply pump 1, and a fuel pumped from the supply pump 1 through a pipe 3. A common rail 4 for accumulating high pressure, a fuel injection nozzle 6 connected to the common rail 4 by a pipe 5, a solenoid valve 10 for ON / OFF control of the start and end of fuel injection of the fuel injection nozzle, and a leak fuel from the fuel injection nozzle. A pipe 7 for discharging fuel to the fuel tank 8, a pipe 9 for sending fuel from the fuel tank 8 to the supply pump 1, a pressure sensor 11 for detecting the pressure in the common rail 4, a supply pump control valve 2 and a solenoid valve 10 for a fuel injection nozzle And an engine control unit (ECU) 12 for executing control of the engine.

[0006] Engine control unit (ECU)
Reference numeral 12 inputs detection signals from an accelerator opening sensor (not shown) and an engine rotation speed sensor, and determines the fuel injection amount using the detection values of these sensors as parameters. Then, the engine control unit (ECU) 12
The target pressure of the common rail is determined from the fuel injection amount and the engine rotation speed, and the pumping amount of the supply pump 1 is determined from the deviation from the current pressure in the common rail detected by the pressure sensor 11, so that the pumping amount of the supply pump The opening / closing timing of the solenoid valve 2 to be adjusted is controlled.

Fuel is accumulated in the common rail 4 at a pressure corresponding to the operating state of the engine. By controlling ON / OFF of a solenoid valve 10 provided in the fuel injection nozzle 6, the common rail 4, the pipe 5, and the The injection timing and the fuel injection amount of the fuel injected through the fuel injection nozzle 6 are controlled. Further, as described above, the pressure in the common rail 4 is changed depending on the operation state of the engine, but is generally controlled so that the higher the rotation speed and the higher the load, the higher the pressure. In the pressure accumulating fuel injection device, the pressure in the common rail 4 is directly used as the fuel injection pressure due to its structure.

As described above, the high-pressure direct injection diesel engine has a problem that the exhaust gas (black smoke) is rather deteriorated due to an increase in the fuel injection pressure. As a countermeasure, multiple injection holes and small injection hole diameters have been attempted to further atomize the spray, but multi-stage injection, in which the main injection is divided into multiple injections, has also been attempted, taking advantage of the characteristics of the accumulator type fuel injection device. (For example, Japanese Patent Application Laid-Open No. 11-182313). This multi-stage injection system disturbs the combustion of the first injected fuel by the combustion of the second injected fuel, thereby improving the air utilization rate of the combustion chamber and improving the exhaust gas (black smoke) without inducing fuel consumption deterioration. It is what we are trying to figure out. FIG. 5 shows an example of the above-mentioned two-stage injection of the prior art. The combustion system shown in FIG. 5 includes a fuel injection nozzle 6, a piston P that reciprocates in a cylinder formed by a cylinder head H and a cylinder block B, and a top surface of the piston P is formed in a concave shape. A combustion chamber C is provided. The combustion chamber C is a so-called reentrant combustion chamber formed by a deep dish-shaped bottom wall part whose center is raised and a side wall part whose diameter is narrowed from the bottom wall part toward the top surface of the piston P. The injection angle β formed by the axis of the fuel injection nozzle 6 and the axis of the fuel spray is about 72.5 °. It has a combustion chamber shape widely used in recent diesel engines.

FIG. 5A shows a state in which the first-stage fuel injection is performed from the fuel injection nozzle 6 at the timing of the top dead center of the compression stroke. FIG. 5B shows a state in which the ignition is started after the ignition delay period while the spray enters the expansion stroke after the top dead center and spreads below the outer periphery of the combustion chamber C. FIG. 5 (c)
The piston P descends, and the first stage combustion gas moves downward together with the piston P while being held by the caliber of the combustion chamber C, and goes down below the outer periphery of the combustion chamber C,
Further, the second stage injection is performed from the fuel injection nozzle 6,
This shows a state in which the spray of the second stage spreads upward from the combustion gas of the first stage. FIG. 5D shows that the second-stage fuel injection proceeds upward from the combustion gas generated by the first-stage fuel injection, and ignition and combustion are not performed by the first-stage combustion gas. Indicates that it is spreading upward.

[0010] The injection angle (β angle) of the fuel injection nozzle using the combustion chamber described above is aimed at near or below the aperture restriction portion, and is generally set to about 70 ° or more. It is a target. Then, as shown in FIG. 5, the entire combustion chamber is used by performing multi-stage injection (first
The lower part of the combustion chamber is used in the second stage fuel injection and the upper part of the combustion chamber is used in the second stage fuel injection), thereby increasing the air utilization rate and suppressing the generation of smoke.

The reentrant combustion chamber shown in FIG. 5 has been used as an excellent swirl preserving agent due to its deep shape and the effect of reducing the diameter, and has been used to suppress the generation of smoke in the combustion chamber. The shape of a shallow dish-shaped combustion chamber that does not generate swirl so much has been studied. Also, attention has been paid to the fact that the shallow dish-type combustion chamber contributes to improvement in fuel efficiency by reducing heat loss because the surface area with respect to the volume of the combustion chamber is reduced. Although it is conceivable to apply the two-stage injection as shown in FIG. 5 to the shallow dish type combustion chamber, a problem in executing the combustion by the two-stage injection in the shallow dish type combustion chamber will be described with reference to FIG. explain.

FIG. 6A shows a state where the first-stage fuel injection is performed from the fuel injection nozzle 6 at a timing before the top dead center of the compression stroke. FIG. 6B shows a state in which the ignition is started after the ignition delay period while the spray enters the expansion stroke after the top dead center and spreads. In FIG. 6C, the second-stage injection is performed from the fuel injection nozzle 6, the piston P descends and the spray is spread, and the second-stage injection toward the combustion gas by the first-stage injection is performed. Indicates a state in which it is expanding.

[0013]

As described above, in a normal fuel injection nozzle, the fuel injection angle of multiple injections performed a plurality of times is large and the injection direction is the same, and in a shallow dish type combustion chamber, the aperture is reduced. When the piston moves, the combustion gas is not retained in the combustion chamber when the piston moves, and the swirl is small, so that the second-stage fuel injection rushes toward the combustion gas by the first-stage fuel injection, and the air utilization rate is rather reduced. A problem arises in that the effect of reducing exhaust gas (black smoke) cannot be obtained. In order to solve this problem, the injection direction of the first stage and the second stage is changed in the multistage injection, and the combustion of the first stage and the second stage are performed.
It is conceivable that the combustion of the stage is performed in different space parts, but it is extremely difficult to change the direction while making the injection of the fuel injection nozzle in multiple stages, and even if it can be realized, the structure becomes complicated. This is not preferable in terms of cost. In other words, when a shallow dish-type combustion chamber is adopted, the structure for performing the fuel injection in multiple stages without obtaining a complicated structure of the fuel injection nozzle to obtain the above-described effect of improving the exhaust gas is still available. Not disclosed.

[0014]

In order to achieve the above technical object, according to the present invention, a piston is provided on a top surface portion of a piston reciprocally movable in a cylinder, and a bottom wall portion and the bottom wall portion are provided. Combustion of a diesel engine comprising: a combustion chamber having a side wall portion whose diameter is gradually increased from the outer peripheral end of the portion toward the top surface of the piston; and a fuel injection device capable of injecting fuel into the combustion chamber in multiple stages. A fuel injection nozzle having a fuel injection angle for injecting fuel toward a vicinity of a connection between the bottom wall and the side wall of the combustion chamber when the piston is near a compression top dead center. When the piston is near the compression top dead center, the first stage is injected. When the piston is located at a position lower than the first stage fuel injection timing, the second stage is directed toward the combustion chamber. It is specially designed to inject eyes. To provide a combustion system of the diesel engine to be.

The fuel injection angle in the combustion system is an angle formed by the axis of the fuel injection nozzle and the axis of the fuel spray, and is preferably from 62.5 degrees to 67.5 degrees.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment according to the present invention, in which a piston P which reciprocates in a cylinder formed by a cylinder head 30 and a cylinder block 32 is provided. The combustion chamber 20 provided in the piston P is formed such that the center of the bottom wall portion 21a is formed in a convex shape (conical shape), and the combustion chamber 20 passes through the connection portion 22a located at the outer peripheral end of the bottom wall portion 21a. It is formed by a side wall 23a that expands in a curved shape to the top surface of the chamber. Then, the top surface 24 of the piston P and the cylinder head 30
A combustion space is formed by the space formed by the lower surface 31 of the cylinder head and the combustion chamber 20, and the injection angle β formed by the axis F1 of the fuel spray formed by the fuel injection and the axis of the fuel injection nozzle is equal to the piston angle. Is set to about 62.5 ° so that the fuel injection angle is directed toward the connection portion 22a when is at the top dead center position.

Further, in the combustion system according to the present invention,
When the piston P rises near the compression start point, the first stage fuel is injected, and the injection angle β of the fuel spray along the axis F1 is near the connection portion 22a between the bottom wall 21a and the side wall 23a of the combustion chamber 20. The spray is set to collide.
After the first-stage fuel injection is performed, when the piston P further descends, the second-stage fuel injection is executed toward the combustion chamber.

The progress of combustion when the first and second stages of fuel injection according to the present invention are executed in the combustion system shown in this embodiment will be described with reference to FIG.
In this embodiment, the engine is in a high load state, and is set so that 50% of the fuel is injected in the first stage and the remaining 50% is injected in the second stage. The injection timing is crank angle (CA) with the compression top dead center set to 0 °.
Indicated by

FIG. 2A: CA = 0 °: The piston P is at the compression top dead center, and the first stage fuel injection is executed at this timing. The fuel spray from the first-stage fuel injection is directed to the vicinity of the connection 22a between the bottom wall 21a and the side wall 23a. Then, it collides with the vicinity of the connection portion 22a, changes its traveling angle, and moves upward along the side wall portion 23a of the combustion chamber 20.

FIG. 2B: CA = 4 °: The first-stage fuel injection is completed and the spray spreads upward from the contact side portion 22a along the side wall portion 23a. Further, the ignition starts after an ignition delay period.

FIG. 2- (c) CA = 12 °: The fuel injected at the first stage further progresses the combustion, and the momentum when injected from the fuel injection nozzle 6 causes the fuel to be injected from the connection portion 22a to the side wall portion 23a. , And further to the top surface 24 of the piston P.

FIG. 2- (d) CA = 20 °: The combustion gas generated by the first-stage fuel injection is formed from the side wall 23a of the combustion chamber 20 by the top surface 24 of the piston P and the lower surface 31 of the cylinder head. , And unused air areas are formed in the central part and the lower part of the combustion chamber 20.
At this time, the air area in the combustion chamber 20
The fuel injection of the stage is executed. It is preferable that the second-stage fuel injection is performed at a fuel injection timing that is directed at least into the combustion chamber 20.

FIG. 2E: CA = 24 °: The side wall 23a of the combustion chamber 20 due to the combustion gas from the first stage fuel injection.
The vicinity and the space surrounded by the cylinder head lower surface 31 and the top surface 24 of the piston P are at high temperature and high pressure, the penetration force of the second stage fuel spray is hindered, and the fuel spray does not reach the outer periphery but near the center. It is held down. On the other hand, the combustion gas due to the first stage fuel injection is more likely to remain above the bottom of the combustion chamber 20 or to the top of the piston P due to the injection pressure of the second stage fuel injection. The piston 24 is pushed up into a space formed by the surface 24, the cylinder head lower surface 31, and the top surface 24 of the piston P.

FIG. 2- (f) CA = 28 °: The combustion gas generated by the first stage fuel injection is mainly above the combustion chamber 20, the top surface 24 of the piston P and the lower surface 31 of the cylinder head P.
The combustion proceeds in the space formed by the
The combustion gas produced by the fuel injection in the first stage is mainly burned in the vicinity of the center and the bottom in the combustion chamber 20.

As is apparent from FIG. 2 and the above description, the first stage fuel injection is set to be narrower than the fuel injection angle in the conventional combustion system, and the fuel injection direction is the opening of the top surface 31 of the piston. Further, the fuel is injected not to the vicinity of the lower part but to the vicinity of the connection part 22a between the bottom wall part 21a and the side wall part 23a of the combustion chamber 20, and the combustion chamber 20 is formed by the side wall part 23a having the outer peripheral end of the bottom wall part 21a. , And is formed so as to increase in diameter toward the upper end of the combustion chamber, that is, has a shape having no aperture restriction. With this shape,
When the fuel spray by the first-stage fuel injection performed near the compression top dead center of the piston P reaches the vicinity of the outer peripheral end of the bottom wall 21a, that is, the vicinity of the connection 22a with the side wall 23a, the fuel spray from the bottom wall 21a. It changes smoothly at an angle toward the side wall 23a and proceeds smoothly. Since the side wall portion 23a is formed such that there is no throttle while expanding the diameter, the side wall portion 23a flows directly above the piston P by the momentum at the time of fuel injection. Therefore, a space that is not used for combustion is formed at the center or lower portion of the combustion chamber 20. The combustion chamber 2
By performing the second-stage fuel injection in a direction below 0, the combustion gas generated by the first-stage fuel injection is further pushed upward by the momentum of the fuel injection, and the fuel spray generated by the second-stage fuel injection Are pressed to the center and lower part of the combustion chamber 20. As a result, the combustion gas generated by the first-stage fuel injection burns mainly in the space formed by the upper part of the combustion chamber 20 and the top surface 24 of the piston and the lower surface 31 of the cylinder head. Combustion gas is burned in the space in the central part and lower part inside the combustion chamber 20, and the combustion space inside the cylinder is used without bias as a whole, so that the air utilization rate is improved and the smoke is deteriorated. The combustion can proceed without any change.

Further, the fuel injection angle β of the fuel injection nozzle, which is formed by the axis of the fuel injection nozzle and the axis of the fuel spray, is set between 62.5 ° and 67.5 °. When the piston is near the top dead center, if the shape is set so as to collide with the vicinity of the connection between the bottom wall and the side wall of the combustion chamber at this injection angle, the fuel spray by the first stage fuel injection and The combustion gas moves more quickly to the space above the combustion chamber and to the space surrounded by the lower surface of the cylinder head and the top surface of the piston, so that the combustion space by the second-stage fuel injection is more efficiently created. .

In the embodiment shown in FIG. 1, the bottom wall 2
Although the combustion system using the combustion chamber 20 in which 1a is formed in a convex or conical shape is shown, the shape of the combustion chamber is not necessarily limited to this, and the combustion chamber is formed flat as shown in FIG. A combustion system having a bottom wall portion 21b and a side wall portion 23b formed so as to increase in diameter from the outer peripheral end of the bottom wall portion 21b, that is, the connection portion 22b toward the top surface of the piston P may be used. Even with such a combustion chamber shape, two-stage injection as shown in FIG. 2 is performed after setting the injection angle at the first stage of fuel injection toward the connection portion 22b according to the present invention. For example, the effects intended by the present invention can be obtained. However, considering that the purpose is to improve the air utilization rate in the combustion space, the shape of the bottom wall 21a of the combustion chamber 20 in the embodiment shown in FIG. Since the volume of the lower central portion can be reduced, more favorable results can be expected.

[0028]

According to the present invention, the diameter of the combustion chamber provided on the top surface of the piston is increased from the bottom wall and the outer peripheral end of the bottom wall, that is, the connection portion, toward the top surface of the piston P. The fuel injection is divided into a first stage and a second stage. The first stage of the fuel injection is performed when the piston is near the compression top dead center. The fuel injection angle is such that it collides with the vicinity of the connection between the bottom wall and the side wall, and the second stage fuel injection toward the combustion chamber is performed at a position where the piston is lower than at the time of the first stage fuel injection. After the fuel spray and the combustion gas from the first-stage fuel injection collide near the connection portion, the space portion formed immediately above the combustion chamber and between the piston top surface and the cylinder head lower surface is formed. And formed in the center and lower part of the combustion chamber. It will perform the fuel injection in the second stage the space portion that is not used in the combustion of the first stage. That is, the combustion gas produced by the first stage fuel injection is
The air in the entire combustion space can be efficiently used without fuel injection at the stage, and multistage injection can be performed without causing deterioration of black smoke.

[Brief description of the drawings]

FIG. 1 shows a combustion system according to an embodiment of the present invention.

FIG. 2 is a diagram showing two-stage injection fuel spray and combustion gas diffusion performed by the combustion system of the present invention.

FIG. 3 shows a combustion system according to another embodiment of the present invention.

FIG. 4 is an accumulator type fuel injection device used in a direct injection type diesel engine.

FIG. 5 is a diagram showing two-stage injection of a direct injection diesel engine in a conventional reentrant combustion chamber.

FIG. 6 is a diagram showing a two-stage injection of a direct injection diesel engine in a conventional shallow dish type combustion chamber.

[Explanation of symbols]

 1: Supply pump 2: Supply pump control valve 3, 5, 7: Piping 4: Common rail 6: Fuel injection nozzle 8: Fuel tank 10: Solenoid valve 11: Pressure sensor 12: Controller 20: Combustion chamber 21a, 21b: Bottom wall Part 22a, 22b: Connection part 23a, 23b: Side wall part 24: Top surface part of piston 30: Cylinder head 31: Lower surface of cylinder head 32: Cylinder block

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02M 61/18 320 F02M 61/18 320Z F term (reference) 3G023 AA03 AA04 AB05 AC05 AD02 AD09 AD29 3G066 AA07 AB02 AC09 AD12 BA24 CC06U CC48 CE22 DA09 DC04 DC09 3G301 HA02 JA21 JA24 LB11 MA18 PE01A PF03A

Claims (2)

[Claims] 1. A piston provided on a top surface of a piston reciprocally movable in a cylinder, and a bottom wall portion and a side wall portion gradually enlarged from an outer peripheral end of the bottom wall portion toward the top surface of the piston. And a fuel injection device capable of injecting fuel in multiple stages toward the combustion chamber, wherein the fuel injection device has a piston near compression top dead center. A fuel injection nozzle having a fuel injection angle for injecting fuel toward the vicinity of the connection between the bottom wall and the side wall of the combustion chamber, wherein the first stage is performed when the piston is near a compression top dead center; A second stage of fuel is injected toward the combustion chamber when the piston is at a position lower than the first stage fuel injection timing. 2. The fuel injection angle is an angle formed between the axis of the fuel injection nozzle and the axis of the fuel spray.
The combustion system for a diesel engine according to claim 1, wherein the temperature is 5 degrees to 67.5 degrees.