Engine ignition system

Abstract

In an ignition system used in engines that premix air and fuel, compress it, and burn it, and which supplies additional fuel to the compressed mixture to form a flame kernel, this device generates a flame kernel and ignites the premixed mixture without using a spark plug. [Solution] At least two fuel injectors 4 are provided facing the ignition chamber 5 where the fuel-air mixture is compressed, and the fuel flows 18 injected from each of these at least two fuel injectors 4 collide with each other in the ignition chamber 5 to ignite and generate a flame kernel. A tapered nozzle 16 may be provided upstream of the fuel injectors 4 to make the fuel flow 18 a supersonic flow.

Description

Technical Field

[0001] The present invention relates to an ignition device for an engine.

Background Art

[0002] Conventionally, an engine (for example, an HCCI engine) that compresses and ignites a premixed air-fuel mixture is known. However, it is difficult to control the ignition timing of the premixed air-fuel mixture, and particularly during HCCI combustion, ignition occurs only under very narrow operating conditions.

[0003] On the other hand, a technique of forming a flame kernel by spark ignition using a spark plug and thereby controlling the ignition timing of the premixed air-fuel mixture is known (Patent Document 1).

[0004] Also, as this type of ignition method, one related to the proposal of the present applicant is known (Patent Document 2), which involves colliding a high-speed air flow with the fuel injected into the combustion chamber to cause ignition and combustion.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] When attempting to create a flame kernel using a spark plug or the like as in the former conventional example (Patent Document 1), there are problems in that a high-voltage current is required and a sufficient flame kernel cannot be formed in lean combustion such as HCCI combustion.

[0007] Furthermore, in the latter conventional method (Patent Document 2), almost the entire amount of fuel is injected and combusted in collision with the airflow, resulting in a large scale of detonation and a high combustion speed, making it difficult to seal the backflowing flame.

[0008] To solve these problems, the present invention involves injecting fuel from at least two fuel injectors into a premixed gas that has been adiabatically compressed, causing them to collide with each other, thereby forming a suitable flame kernel and igniting the premixed gas. [Means for solving the problem]

[0009] Specifically, the present invention is based on an ignition device used in an engine of the type that premixes air and fuel, compresses it, and burns it, and which supplies additional fuel to the compressed mixture to form a flame kernel. In this device, at least two fuel injectors are provided facing the ignition chamber where the mixture is compressed, and the fuel flows injected from these fuel injectors collide with each other in the ignition chamber and ignite, forming a flame kernel that burns the compressed mixture.

[0010] In this configuration, instead of using a spark plug, a small amount of fuel is injected into the ignition chamber, causing it to collide and ignite, thereby forming a flame kernel of an appropriate size. Unlike systems that use a spark plug, by adjusting the amount of fuel injected, it is possible to form a flame kernel of the necessary and sufficient size according to the condition of the ignition chamber.

[0011] The air-fuel mixture, adiabatically compressed by the engine's piston head, is easily ignited. When the fuel stream injected from the fuel injector collides with it, ignition occurs easily, especially in high-pressure lean mixtures such as HCCI combustion, as it approaches the stoichiometric air-fuel ratio. The resulting detonation wave reaches several times the speed of sound, causing instantaneous combustion even in lean mixtures.

[0012] The fuel supply means to the fuel injection port may include an on-off valve and a check valve that are interlocked with a shaft driven by an actuator, and the check valve may be closed when the on-off valve is open by the pressure of the combustion chamber.

[0013] In this configuration, when an on / off valve, which is linked to an actuator-driven shaft, is opened, fuel flows and is injected into the ignition chamber from at least two fuel injectors. When these injected fuel flows collide and combust, forming a flame kernel with detonation, a pressure wave attempts to flow back through the fuel injectors, but this backflow is sealed by a check valve.

[0014] The fuel supply means may include a fuel compression mechanism driven by an actuator. This is because, for example, in the case of a gaseous fuel with low pressure, it is preferable to compress the fuel using the fuel compression mechanism to a pressure higher than that of the ignition chamber in order to create a flame kernel accompanied by uniform detonation.

[0015] A tapered, widening nozzle may be provided upstream of the fuel injection port, and the fuel flow passing through this nozzle may become a supersonic flow and be injected into the ignition chamber, where it may collide with the fuel at the point of impact within the ignition chamber, accompanied by a shock wave.

[0016] This allows for the generation of a supersonic flow using a tapered nozzle, which collides with the surrounding air-fuel mixture to generate a shock wave. The supersonic flow and shock wave from at least two fuel injectors then collide at the fuel collision point in the ignition chamber, more reliably forming a flame kernel and igniting the premixed fuel.

[0017] Furthermore, the scale of the detonation should be sufficient to ignite the surrounding premixed gas, and the detonation wave should be large enough to compress and burn the surrounding premixed gas.

[0018] The fuel supply means preferably supplies fuel to the fuel supply port in a gaseous state. Specifically, a heater may be provided in the fuel passage upstream of the fuel injection port to vaporize the liquid fuel or maintain the vaporized state of the gaseous fuel.

Advantages of the Invention

[0019] The advantage of the present invention is that a sufficient flame kernel for the combustion of a lean premixed gas can be formed in the ignition chamber without using an ignition plug with a high-voltage current. That is, by bringing the air-fuel ratio of the lean premixed gas closer to the theoretical air-fuel ratio by additional fuel injection and causing collision combustion while mixing with the lean premixed gas, an appropriate flame kernel can be formed even in lean combustion, thus solving the problem of poor formation of the flame kernel by the ignition plug.

[0020] Therefore, even in a lean combustion method such as HCCI combustion where it is difficult to time the compression ignition normally, in the present invention where additional fuel is injected to mix with the lean mixture and cause collision combustion, a flame kernel necessary and sufficient for instantaneously compression-combusting the lean mixture can be formed.

[0021] In particular, if the fuel flow is made into a supersonic flow with a tapered nozzle and caused to collide with the generated shock wave, the detonation phenomenon can be more reliably caused, and the pressure wave propagates at supersonic speed to instantaneously combust the air-fuel mixture in the engine.

Brief Description of the Drawings

[0022] [Figure 1] It is a schematic configuration diagram of an engine ignition device according to Embodiment 1 of the present invention. [Figure 2] It is a modification of Embodiment 1, in which a fuel compression mechanism is added to the fuel supply system. [Figure 3] It is a diagram corresponding to FIG. 1 according to Embodiment 2 in which a supersonic fuel flow is generated by a tapered nozzle. [Figure 4] It is a view of the layout of a plurality of fuel injection ports in Embodiment 2 as seen from below. [Figure 5]It is a diagram showing the layout of the fuel injection ports of a modified example. [Figure 6] It is a diagram showing a modified example in which a concave reflector facing the fuel injection port is provided. [Figure 7] It is a schematic diagram showing the configuration of a fuel supply device in an engine of Embodiment 3 that supplies liquid fuel, vaporizes it, and then injects it.

Mode for Carrying Out the Invention

[0023] FIG. 1 is a schematic configuration diagram of an ignition device for an engine according to Embodiment 1 of the present invention, and as an example, it is applied to the cylinder head of a reciprocating engine in which a piston 12 reciprocates. In this example, the engine is of a type that premixes, compresses, and burns air and fuel. Depressions are provided on the lower surface of the cylinder head that forms the ceiling of the combustion chamber and on the upper surface of the opposing piston 12, and an ignition chamber 5 is formed therebetween.

[0024] When an intake port (not shown) is opened in synchronization with the reciprocating motion of the piston 12 in this engine, a lean mixture of air and fuel is supplied to the combustion chamber, and then it is compressed by the upward movement of the piston 12. In this specification, the terms "up" and "down" refer to the top dead center side in the reciprocating motion of the piston 12 as "up" and the bottom dead center side as "down", and are not limited to the up and down in the direction of gravity.

[0025] And in the combustion chamber where the mixture is compressed as described above, particularly facing the ignition chamber 5, a plurality of fuel injection ports 4 are provided so as to open on the lower surface of the cylinder head. These fuel injection ports 4 open side by side, for example, on the circumference in the depression on the lower surface of the cylinder head. As shown by an arrow 18 in FIG. 1, the fuel flows 18 injected from the respective fuel injection ports 4 collide with each other and ignite, forming a flame kernel that burns the compressed mixture.

[0026] In the example shown in the figure, a volume chamber 6 provided in the cylinder head so as to communicate with the upstream side of the fuel injection port 4 serves as the fuel passage, and an on-off valve 1 and a check valve 2 are provided to open and close this passage, forming a fuel supply means. Specifically, the valve body of the check valve 2 is provided at the lower end of a vertically extending shaft 9, and the valve body of the on-off valve 1 is provided above it at a distance, and when the shaft 9 driven by the actuator 8 swings up and down, the on-off valve 1 and the check valve 2 move in conjunction with it.

[0027] More specifically, an annular portion 3 is formed that protrudes inward from the inner circumferential surface of the volume chamber 6, i.e., toward the shaft 9, surrounding the constricted portion between the valve body of the on-off valve 1 and the valve body of the check valve 2, which are separated vertically. The valve seat of the on-off valve 1 is formed on the upper surface of this annular portion 3, while the valve seat of the check valve 2 is formed on the lower surface of the annular portion 3. The vertical oscillation stroke of the shaft 9 is set so that the valve body of the on-off valve 1 and the valve body of the check valve 2 can contact the annular portion 3, respectively.

[0028] Then, from the state shown in Figure 1, the shaft 9 is driven downward, and although not shown in the figure, when the valve body of the on-off valve 1 contacts (seats) the valve seat on the upper surface of the annular portion 3, it enters a closed state that seals the fuel. In this example, gaseous fuel at a pressure higher than the maximum compression pressure of the air-fuel mixture in the ignition chamber 5 is supplied to the fuel supply port 7 upstream of the on-off valve 1. For example, when the air pressure in the ignition chamber 5 decreases as the piston 12 descends, the on-off valve 1 is closed and the fuel is sealed.

[0029] As the fuel flow toward the fuel injection port 4 is sealed, the shaft 9 is driven upward, and as shown in Figure 1, a gap is created between the valve body and valve seat of the on-off valve 1, allowing fuel to flow through this gap. Then, as schematically shown by the arrows in the figure, the fuel flows 18 injected into the ignition chamber 5 from each of the multiple fuel injection ports 4 collide at the fuel collision point 19 and ignite, forming a flame kernel accompanied by detonation.

[0030] In other words, the fuel streams 18 injected from each of the multiple fuel injectors 4 mix with the lean mixture in the ignition chamber 5, collide with each other, and ignite, forming a flame kernel. Since the compressed premix is ​​easily ignited, and this, combined with the air-fuel ratio approaching the stoichiometric air-fuel ratio, ignition occurs easily. The resulting detonation wave reaches several times the speed of sound, triggering the autoignition of the compressed premix throughout the combustion chamber.

[0031] Furthermore, a flame kernel is formed instantaneously, and flames from detonation attempt to flow back from the fuel injection port 4, but this is sealed by the check valve 2. That is, a pressure wave acts on the valve body of the check valve 2 via the fuel injection port 4, and the check valve 2 closes in response to this pressure. In other words, the stroke and gap of the shaft 9 of the fuel supply means are set so that the backflow of flames from the ignition chamber 5 is sealed by the check valve 2.

[0032] Therefore, in the ignition system of the engine of this embodiment, by bringing the lean premix closer to the stoichiometric air-fuel ratio through additional fuel injection and causing impingement combustion, it is possible to form a flame kernel that is necessary and sufficient to instantaneously compress and burn the lean mixture, even in combustion where it is normally difficult to time ignition, such as HCCI. Thus, it is not necessary to use a spark plug that requires high voltage current. With a spark plug, there is a disadvantage in that it is difficult to create a sufficient flame kernel in a lean mixture, but this problem of poor flame kernel formation does not occur.

[0033] Moreover, unlike systems that use spark plugs, in this embodiment, by adjusting the amount of additional fuel injected, it is possible to form a flame kernel that is necessary and sufficient according to the state of the ignition chamber 5. In other words, because the scale of detonation does not become too large, the flame flowing back from the ignition chamber 5 through the fuel injection port 4 can be sealed by the sealing valve 2.

[0034] Figure 2 shows a modified version of Embodiment 1 described above, in which a gaseous fuel compression mechanism is added to the fuel supply means. This fuel compression mechanism compresses the gaseous fuel using a pressurizing piston 11 driven by an actuator 10 without significantly increasing the base pressure of the fuel supplied to the fuel supply port 7, thereby raising the pressure to a level higher than the maximum compression pressure of the air-fuel mixture in the ignition chamber 5.

[0035] Figure 3 is a schematic diagram of the ignition system of an engine according to Embodiment 2 of the present invention. A tapered nozzle 16 (Laval nozzle) is provided that communicates with the upstream side of the fuel injection port 4 of Embodiment 1 to generate a supersonic fuel flow. Accordingly, the configuration of the on-off valve and check valve that open and close the fuel flow path, and the volume chamber 6 that houses them, has also changed. As shown in the figure, the on-off valve and check valve are provided integrally.

[0036] Specifically, a fuel sealing valve body 21, which integrates the valve body of an on-off valve and the valve body of a check valve, is provided at the lower end of the shaft 9 driven by the actuator 8. Its upper and lower surfaces are capable of contacting (seat) with the upper sealing valve seat 22 and the lower sealing valve seat 23, respectively. When the lower surface of the fuel sealing valve body 21 seats with the lower sealing valve seat 23, it enters a closed state. From there, it moves upward to the open state shown in Figure 3, thereby allowing fuel to pass through and preventing backflow.

[0037] In this second embodiment, as shown in Figure 3, when the fuel sealing valve body 21 is open, fuel flows through the gap between it and the valve seats 22 and 23, and is converted into a supersonic flow 18 by the tapered-to-widening nozzle 16, which is then injected from multiple fuel injectors 4 towards the ignition chamber 5. This supersonic flow 18 collides with the surrounding air-fuel mixture, generating a shock wave, and by colliding with the fuel impact point 19 in the ignition chamber 5, it more reliably forms a flame kernel and ignites the premixed air.

[0038] Figure 4 shows a view of multiple fuel injectors 4 from below. In this example, in addition to the central fuel injector 4, six fuel injectors 4 are provided in concentric circles surrounding it. However, this is not the only option; there can be two or more fuel injectors 4, such as three to five or even seven or more. For example, Figure 5 shows a modified example in which three fuel injectors 4 are arranged in concentric circles.

[0039] Furthermore, Figure 6 shows another modified example in which, if a sufficient flame kernel cannot be formed at the fuel impact point 19 of the supersonic flow and shock wave, the wake of the impact is reflected back towards the fuel impact point 19 by the concave reflector 20, thereby more reliably forming a flame kernel. The concave reflector 20 may be provided, for example, on the piston head 17.

[0040] Figure 7 shows a schematic diagram of the fuel supply means in the engine ignition system according to Embodiment 3 of the present invention. A predetermined amount of liquid fuel is supplied from the nozzle 14 by the liquid fuel injection device 13, heated and vaporized by the heater 15, and then injected from the fuel injection port 4. Because the amount of liquid fuel supplied is small, the heating time is also very short. Although not shown in the figure, similar heaters can be added to Embodiments 1 and 2 to maintain the vaporized state of the gaseous fuel. [Explanation of Symbols]

[0041] 1. Shut-off valve 2. Check valve 3. Annular section (valve seat for on-off valves and check valves) 4 Fuel injection port 5 Ignition chamber 6 Volume chamber 7 Fuel supply port 8. Actuator for fuel supply means 9 shafts 10. Actuator of the fuel compression mechanism 11. Pressurized piston of the fuel compression mechanism 12. Engine pistons 13 Liquid fuel injection device 14 Fuel nozzle 15 Heater 16. Tapered, flared nozzle 17 Piston head 18 Fuel flow 19 Fuel collision point 20 Concave reflector 21 Fuel sealing valve body 22 Upper sealing valve seat 23 Lower sealing valve seat

Claims

1. In an ignition system used in an engine that premixes air and fuel, compresses it, and burns it, and which supplies additional fuel to the compressed mixture to form a flame kernel, Facing the ignition chamber in which the aforementioned fuel mixture is compressed, at least two fuel injection ports are provided. An ignition device for an engine, characterized in that fuel flows injected from at least two fuel injectors collide with each other in the ignition chamber, ignite, and form a flame kernel that burns the compressed fuel mixture.

2. The ignition system for an engine according to claim 1, comprising, as a means of supplying fuel to the fuel injection port, an on-off valve and a check valve that are interlocked with a shaft driven by an actuator, wherein when the on-off valve is open, the check valve is closed by the pressure of the ignition chamber.

3. The ignition device for an engine according to claim 2, wherein the fuel supply means is further provided with a fuel compression mechanism driven by an actuator.

4. An ignition system for an engine according to claim 1, wherein a tapered nozzle is provided upstream of the fuel injection port, and the fuel flow passing through this tapered nozzle becomes a supersonic flow and is injected into the ignition chamber, and is configured to collide with the fuel at the fuel collision point in the ignition chamber, accompanied by a shock wave.

5. The ignition device for an engine according to claim 2, wherein the fuel supply means supplies fuel in a gaseous state to the fuel supply port.

6. The ignition device for an engine according to claim 5, wherein the fuel supply means is equipped with a heater in the fuel passage upstream of the fuel injection port to vaporize liquid fuel or maintain the vaporized state of gaseous fuel.

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