JP7786403B2 - Injection structure of direct injection valve - Google Patents

Description

The present invention relates to the injection structure of a cylinder injection valve.

As described in Patent Document 1, a direct injection valve that injects fuel directly into the cylinder of an internal combustion engine is known.

Japanese Patent Application Laid-Open No. 2005-201074

However, when the fuel injected from the direct injection valve is gaseous fuel, the following problem may occur. Depending on the fuel injection pressure and the pressure inside the cylinder, the fuel injected from the direct injection valve may become an under-expanded jet.

As shown in Figure 5, within this under-expanded jet FLm, a Mach disk MD, a type of normal shock wave, may be generated that decelerates the jet FLm, which has been accelerated at supersonic speed from the injection hole 110 of the in-cylinder injection valve, to subsonic speed. The jet FLm converges at the point where this Mach disk MD is generated, and then expands beyond the Mach disk MD. When the jet FLm expands in this way, the fuel injected from the in-cylinder injection valve is supplied to the cylinder in an excessively dispersed state, compared to a jet FLnm where no Mach disk MD is generated and no expansion occurs. Excessively dispersed fuel has weak penetration power and causes unstable airflow, making it more likely to be carried by the tumble flow generated within the cylinder and reach the spark plug. If the fuel does reach the spark plug, it may come into contact with the high-temperature part of the spark plug, resulting in pre-ignition.

The injection structure of a direct injection valve that solves the above problem is an injection structure of a direct injection valve that directly injects gaseous fuel into the cylinder of an internal combustion engine. A cylindrical guide portion is provided between the tip of the direct injection valve, where the injection hole is formed, and the combustion chamber of the internal combustion engine. The guide portion is provided so as to satisfy the conditions "L > da {0.65 (Pa/Pb)}^(1/2)" and "D < 1.3da," where L is the length from the opening of the injection hole to the opening of the guide portion on the combustion chamber side, D is the inner diameter of the guide portion, da is the diameter of the injection hole, Pa is the injection pressure of the fuel injected from the injection hole, and Pb is the pressure inside the cylinder when fuel is injected from the injection hole.

When a Mach disk occurs in the fuel jet injected from the nozzle hole of a direct injection valve, the distance from the nozzle hole opening to the Mach disk is calculated as "da{0.65(Pa/Pb)}^(1/2)". The diameter of the Mach disk is also calculated as "1.3da" or less.

In this configuration, the guide portion is provided to satisfy the condition "L > da {0.65 (Pa/Pb)}^(1/2)." Therefore, the length L of the guide portion is longer than the distance from the nozzle hole opening to the Mach disk. Therefore, if a Mach disk occurs, it will occur inside the guide portion. In addition, in this configuration, the guide portion is provided to satisfy the condition "D ≦ 1.3 da." Therefore, the inner diameter of the guide portion is less than the maximum diameter of the Mach disk. Therefore, compared to when the inner diameter of the guide portion is larger than the maximum diameter of the Mach disk, the diffusion of the jet generated within the guide portion downstream of the Mach disk is suppressed by the inner wall of the guide portion. In this way, the diffusion of the jet downstream of the Mach disk is suppressed by the guide portion, thereby suppressing the occurrence of pre-ignition.

1 is a schematic diagram showing a configuration of the periphery of a cylinder head of an internal combustion engine equipped with an injection structure of a direct injection valve in one embodiment. FIG. 2 is an enlarged view of part A shown in FIG. 1 . FIG. 2 is a perspective view of the sleeve of the embodiment. FIG. 10 is an enlarged view showing a modified example of the embodiment. FIG. 1 is a schematic diagram illustrating an under-expanded jet.

Hereinafter, an embodiment of an injection structure for a cylinder injection valve will be described with reference to FIGS.
<Configuration of the cylinder head and its surroundings in an internal combustion engine>
1 shows the structure of a cylinder head 10 and its surroundings provided in a direct injection type internal combustion engine. The internal combustion engine of this embodiment is an engine that uses hydrogen gas as a gaseous fuel.

A combustion chamber 12 is formed on the lower surface of the cylinder head 10 .
The cylinder head 10 also has an intake port 15 for introducing intake air into the combustion chamber 12 and an exhaust port 16 for discharging exhaust gas from the combustion chamber 12 .

An intake valve 17 is disposed at the opening of the intake port 15 to the combustion chamber 12 , and opens during the intake stroke of the internal combustion engine to connect the combustion chamber 12 to the intake port 15 .
An exhaust valve 18 is disposed at the opening of the exhaust port 16 to the combustion chamber 12 . The exhaust valve 18 opens during the exhaust stroke of the internal combustion engine to connect the combustion chamber 12 to the exhaust port 16 .

In the cylinder head 10, an ignition plug 19 is attached to the center of the top surface of the combustion chamber 12, and ignites a mixture of fuel and air by spark discharge.
An in-cylinder injection valve 20 that injects hydrogen gas directly into the cylinder of the internal combustion engine is attached to the cylinder head 10. A nozzle hole 22 that injects fuel is formed in a tip portion 21 of the in-cylinder injection valve 20.

An insertion hole 13 that opens into the combustion chamber 12 is formed in the cylinder head 10. A tip portion 21 of a direct injection valve 20 is inserted into the insertion hole 13.
<Structure of the tip of the direct injection valve>
As shown in FIG. 2, a sleeve 30 that functions as a cylindrical guide portion is provided between the combustion chamber 12 and the tip portion 21 where the injection hole 22 is formed in the direct injection valve 20.

As shown in Figure 3, the sleeve 30 is a cylindrical member. The inner diameter of the sleeve 30 is larger than the nozzle hole diameter, which is the diameter of the nozzle hole 22. The outer diameter of the sleeve 30 is equal to or smaller than the diameter of the insertion hole 13.

As shown in FIG. 2, the sleeve 30 is fixed to the end of the tip portion 21 where the nozzle hole 22 is formed.
The length from the opening 22a of the injection hole 22 to the opening 30a of the sleeve 30 on the combustion chamber 12 side is defined as length L, and the inner diameter of the sleeve 30 is defined as inner diameter D. Furthermore, the diameter of the injection hole 22 is defined as injection hole diameter da, the injection pressure of the fuel injected from the injection hole 22 is defined as Pa, and the pressure inside the cylinder when fuel is injected from the injection hole 22 is defined as Pb. Note that if the pressure Pb inside the cylinder when fuel is injected from the injection hole 22 varies, the lowest value of the pressure Pb is defined as the pressure Pb.

The sleeve 30 is formed so as to satisfy both the following conditions of formula (1) and formula (2).
Length L>da{0.65(Pa/Pb)}^(1/2)...Equation (1)
Inner diameter D≦1.3da...Formula (2)
<Action and effect>
The operation and effects of this embodiment will be described.

As shown in Figure 5, when a Mach disk MD occurs in the fuel jet injected from the nozzle hole of the direct injection valve, the distance X from the nozzle hole opening to the Mach disk MD is calculated using the right-hand side of the above equation (1), "da{0.65(Pa/Pb)}^(1/2)."

Moreover, the diameter dM of the Mach disk MD is equal to or less than "1.3da", which is the right-hand side of the above equation (2).
Therefore, in this embodiment, the length L of the sleeve 30 is set so as to satisfy the above formula (1). Therefore, the length L of the sleeve 30 is longer than the distance X from the opening 22a of the injection hole 22 to the Mach disk MD. Therefore, as shown in Fig. 2, when a Mach disk MD is generated, the Mach disk MD is generated inside the sleeve 30, which serves as a guide portion.

Furthermore, in this embodiment, the inner diameter D of the sleeve 30 is set to satisfy the above formula (2). Therefore, the inner diameter D of the sleeve 30 is smaller than or equal to 1.3 da, which is the maximum value of the diameter dM of the Mach disk MD. Therefore, compared to when the inner diameter D of the sleeve 30 is larger than the maximum value of the diameter dM of the Mach disk MD, the diffusion of the jet flow FL generated inside the sleeve 30 downstream of the Mach disk MD is suppressed by the inner wall of the sleeve 30.

In this way, the sleeve 30 suppresses the diffusion of the jet FL downstream of the Mach disk MD, making it less likely that fuel with weak penetration power and unstable airflow will be produced, and making it more difficult for the fuel to reach the spark plug 19. This reduces the occurrence of pre-ignition.

<Example of change>
The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

- The guide portion provided between the tip portion 21 of the in-cylinder injection valve 20, where the injection hole 22 is formed, and the combustion chamber 12, was a sleeve 30 fixed to the tip portion 21 of the in-cylinder injection valve 20, but other structures may also be used.

As shown in Figure 4, a hole 32 having the same shape as the inner wall surface of the sleeve 30 may be formed in the cylinder head 10. That is, the length from the opening 22a of the injection hole 22 to the opening 32a of the hole 32 on the combustion chamber 12 side is defined as length L, and the inner diameter of the hole 32 is defined as inner diameter D. The hole 32 is formed so that the length L of the hole 32 satisfies the above formula (1) and the inner diameter D of the hole 32 satisfies the above formula (2). This modified example can also achieve the same functions and effects as the above embodiment.

- Although the gaseous fuel was hydrogen gas, other gaseous fuels, such as compressed natural gas, may also be used.

REFERENCE SIGNS LIST 10 cylinder head 12 combustion chamber 13 insertion hole 15 intake port 16 exhaust port 17 intake valve 18 exhaust valve 19 spark plug 20 in-cylinder injection valve 21 tip 22 injection hole 22a opening 30 sleeve 30a opening 32 hole 32a opening 110 injection hole

Claims (3)

An injection structure of an in-cylinder injection valve that directly injects gaseous fuel into a cylinder of an internal combustion engine,
a cylindrical guide portion is provided between a tip portion of the direct injection valve, where an injection hole is formed, and a combustion chamber of the internal combustion engine,
an injection structure for a cylinder injection valve, wherein the guide portion is provided so as to satisfy the conditions "L > da {0.65 (Pa/Pb)}^(1/2)" and "D≦1.3da", where L is the length from the opening of the injection hole to the opening of the guide portion on the combustion chamber side, D is the inner diameter of the guide portion, da is the diameter of the injection hole, Pa is the injection pressure of fuel injected from the injection hole, and Pb is the pressure inside the cylinder when fuel is injected from the injection hole. The injection structure of a cylinder injection valve according to claim 1 , wherein the guide portion is a sleeve fixed to the tip portion. The injection structure of a cylinder injection valve according to claim 1 , wherein the guide portion is a hole provided in a cylinder head of the internal combustion engine.