Auxiliary chamber type engine

Abstract

To provide an auxiliary chamber type engine having a simple configuration, small cooling loss, and excellent energy balance.SOLUTION: In an auxiliary chamber engine 1, a piston 3 reciprocates in a cylinder 2, causing premixed compression ignition combustion in an auxiliary chamber 20 and then a main chamber 10. The main chamber 10 is an area defined by the cylinder 2 and the piston 3. The auxiliary chamber 20 is connected to the main chamber 10 by a communication hole 31a, and is provided in the piston 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pre-combustion chamber engine that obtains power through homogeneous charge compression ignition combustion. [Background technology]

[0002] In recent years, homogeneous charge compression ignition (HCCI) combustion has been attracting attention as a combustion method for internal combustion engines.

[0003] HCCI combustion is a combustion method in which fuel is injected directly into the intake passage or into the combustion chamber early in the compression stroke to form a lean premixture of fuel and air (lean premixture), which is then compressed and self-ignited near the top dead center of the piston.With HCCI combustion, the compression ratio can be set as high as that of a diesel engine, making it possible to significantly improve thermal efficiency (fuel consumption rate).However, there is a problem in that knocking (abnormal combustion) occurs due to a sudden rise in pressure (temperature) under high load, which limits the operating range to low loads.

[0004] Various studies are being conducted to prevent knocking in HCCI combustion and expand the operating range to high loads. For example, the pre-chamber engine described in Patent Document 1 has a main chamber separated by a cylinder and a piston, a pre-chamber provided in the cylinder head, and a control valve that can open and close a communication port that connects the main chamber and the pre-chamber. By dividing combustion in the pre-chamber and then the main chamber, a sudden rise in pressure (temperature) is suppressed and knocking is avoided. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-357138 A (pages 3 to 5, Figure 1) Summary of the Invention [Problem to be solved by the invention]

[0006] Although the pre-chamber engine of Patent Document 1 aims to prevent knocking, the pre-chamber provided in the cylinder head causes problems such as greater cooling loss and a poorer energy balance than an engine without a pre-chamber. Furthermore, the need for a control valve to separate the main and pre-chambers makes the engine structure complicated.

[0007] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a pre-chamber engine having a simple configuration, small cooling loss, and excellent energy balance. [Means for solving the problem]

[0008] In order to solve the above problems, the pre-chamber engine of the present invention comprises: A pre-chamber engine in which a piston reciprocates in a cylinder and homogeneous charge compression ignition combustion is performed in the pre-chamber and then the main chamber, the main chamber is a region defined by the cylinder and the piston, The auxiliary chamber is connected to the main chamber by a communication hole and is provided in the piston. This feature allows the piston to maintain a higher temperature than the cylinder, making it easier for the mixture to self-ignite and burn in the auxiliary chamber provided in the piston. This allows for a simple configuration that reduces cooling loss and results in excellent energy balance.

[0009] The piston is characterized in that one communication hole is disposed in the center of the top surface of the piston. According to this feature, the combustion gas ejected from the sub-chamber tends to spread evenly in the main chamber.

[0010] means for introducing a premixed fuel into the main chamber; and an injector that injects fuel into the sub-chamber. According to this feature, the concentration of the mixture in the pre-chamber can be made higher than the concentration of the pre-mixture in the main chamber, which makes it easier for the mixture in the pre-chamber to self-ignite and burn.

[0011] The injector is characterized by being disposed directly above the communication hole. According to this feature, it is easy to supply fuel to the auxiliary combustion chamber without significantly affecting the concentration of the premixed gas in the main combustion chamber.

[0012] The fuel is injected into the sub-chamber by the injector during the compression stroke when the crank angle is between -90° and -10°. This feature allows the concentration of the air-fuel mixture in the pre-chamber to be appropriately increased, thereby enabling combustion to occur in stages over a relatively long period of time, first in the pre-chamber and then in the main chamber, thereby achieving high thermal efficiency.

[0013] The sub-chamber is characterized in that it is formed by a cavity in the upper surface of the piston body and a plate-like attachment that is fixed to the upper surface of the piston body and has the communication hole. According to this feature, the auxiliary chamber can be configured simply.

[0014] The surface of the cavity is characterized in that it is covered with a heat insulating film that has higher heat insulating properties than the piston body. This feature makes it easier to maintain the pre-chamber at a high temperature. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing a combustion chamber of a pre-combustion chamber engine according to a first embodiment of the present invention. [Figure 2] 1(a) to 1(f) are schematic diagrams showing the combustion process of a multi-stage HCCI combustion system in the combustion chamber of the pre-combustion chamber engine of the first embodiment. [Figure 3] 1 is a graph showing the results of numerical analysis of the internal pressure and heat release rate of the pre-chamber engine (Type: A) of the first embodiment and a conventional pre-chamber engine (Type: HEAD). [Figure 4]1 is a graph showing the results of a numerical analysis of the energy balance in the pre-chamber engine (Type: A) of the first embodiment and a conventional pre-chamber engine (Type: HEAD). [Figure 5] FIG. 10 is a schematic diagram showing a combustion chamber of a pre-combustion chamber engine according to a second embodiment of the present invention. [Figure 6] 10(a) and 10(b) are schematic diagrams showing modified shapes of the auxiliary chamber. DETAILED DESCRIPTION OF THE INVENTION

[0016] The pre-chamber engine of the present invention uses gasoline (iso-octane) as fuel and realizes a multi-stage (two-stage) HCCI combustion system in which a piston reciprocates within a cylinder and performs homogeneous charge compression ignition (HCCI) combustion in the pre-chamber and then the main chamber. The main chamber that constitutes the combustion chamber is an area partitioned by the cylinder and piston, and the pre-chamber is connected to the main chamber by a communication hole and is attached to the piston. Due to the structure of an internal combustion engine, the piston is more likely to maintain a high temperature than the cylinder, so by providing the pre-chamber on the piston, the temperature of the mixture in the pre-chamber is higher than the pre-mixture in the main chamber, and this temperature difference makes it easier for the mixture in the pre-chamber to self-ignite and burn. This simple structure reduces cooling loss and provides excellent energy balance.

[0017] Furthermore, the pre-chamber engine of the present invention has an injector that injects fuel into the pre-chamber, which makes it possible to make the mixture concentration in the pre-chamber higher than the pre-mixture concentration in the main chamber, making it easier for the mixture to self-ignite and burn in the pre-chamber.

[0018] Furthermore, in the pre-chamber engine of the present invention, the fuel is injected into the pre-chamber by the injector during the compression stroke at crank angles between -90° and -10°, thereby appropriately increasing the mixture concentration in the pre-chamber. This allows combustion to occur in stages over a relatively long period of time, first in the pre-chamber and then in the main chamber, thereby achieving high thermal efficiency.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will now be given of an embodiment of an engine with a pre-combustion chamber according to the present invention. [Example]

[0020] A pre-combustion chamber engine according to a first embodiment will be described with reference to FIGS.

[0021] As shown in FIG. 1, the combustion chamber of the pre-combustion chamber engine 1 in this embodiment 1 is divided into a main combustion chamber 10, which is an area defined by the cylinder 2 and the upper part of the piston 3, and a pre-combustion chamber 20 provided in the piston 3, and the main combustion chamber 10 and the pre-combustion chamber 20 are connected via a communication hole 31a provided in the upper part of the piston 3.

[0022] The piston 3 is connected at one end to a connecting rod 32, the other end of which is connected to a crankshaft (not shown). The piston 3 is composed of a piston body 30 and a plate-like attachment 31 fixed to the top surface of the piston body 30 with a bolt (not shown) or the like. A single communication hole 31a is provided in the center of the plate-like attachment 31, penetrating through in the thickness direction (vertical direction). That is, in this embodiment 1, one communication hole 31a is disposed in the center of the top surface of the piston 3.

[0023] The ratio of the area of ​​the communication holes 31a to the cross-sectional area of ​​the piston is preferably 0.5 to 2.5%, and more preferably 1.0 to 2.0%.

[0024] The sub-chamber 20 is formed as a roughly bowl-shaped space by the bottom surface of a cavity 30a formed on the upper surface of the piston body 30 and the lower surface of a plate-like attachment 31 fixed to the upper surface of the piston body 30 so as to cover the cavity 30a.

[0025] The auxiliary chamber 20 is configured to have a smaller volume than the main chamber 10. More specifically, the ratio of the volume of the auxiliary chamber 20 to the combined volume of the main chamber 10 and the auxiliary chamber 20 when the piston 3 is at top dead center (see FIG. 2(d)) is preferably 10 to 20%, and more preferably 13 to 17%.

[0026] The pre-chamber engine 1 of this embodiment 1 has a side injector 4 that injects fuel into the intake pipe 7 as a means for introducing a lean premixture of fuel and air into the main combustion chamber 10. That is, the method of supplying fuel to the main combustion chamber 10 in this embodiment 1 is intake pipe injection using the side injector 4.

[0027] The pre-combustion chamber engine 1 of this embodiment 1 also has a center injector 5 as an injector that injects fuel into the pre-combustion chamber 20. The center injector 5 is located directly above the communication hole 31a. That is, the method of supplying fuel to the pre-combustion chamber 20 in this embodiment 1 is a direct injection method into a pipe by the center injector 5.

[0028] Next, the combustion method of the pre-combustion chamber engine 1 in this embodiment 1 will be described with reference to Fig. 2. The pre-combustion chamber engine 1 in this embodiment 1 is a four-stroke cycle engine consisting of four strokes: intake-compression-expansion-exhaust.

[0029] 2, in the pre-combustion chamber engine 1 of the first embodiment, during the intake stroke, the intake valve 6 opens and fuel is injected from the side injector 4 into the intake pipe 7, forming a lean and homogeneous pre-mixture in the main combustion chamber 10 (see FIG. 2(a)). The pre-mixture formed in the main combustion chamber 10 is also introduced into the pre-combustion chamber 20 via the communication hole 31a.

[0030] Next, in the latter half of the compression stroke, specifically, at a crank angle of −90° to −10°, preferably −30° to −20° (see FIG. 2(b)), fuel is directly injected from the center injector 5 into the auxiliary combustion chamber 20 through a communication hole 31a provided in the center of the top surface of the piston 3 for a predetermined injection period (see FIG. 2(b)). The fuel injection is preferably terminated before top dead center in the latter half of the compression stroke, particularly before the time when autoignition and combustion occur in the auxiliary combustion chamber 20 near top dead center (see FIG. 2(c)). This ensures that fuel is supplied to the auxiliary combustion chamber 20, and the concentration of the mixture in the auxiliary combustion chamber 20 is appropriately increased compared to the concentration of the premixed mixture in the main combustion chamber 10. The amount of fuel injected from the center injector 5 into the auxiliary combustion chamber 20 is preferably 0.003 to 0.005 ml in the case of a naturally aspirated engine.

[0031] Next, as the compression stroke progresses further, near the top dead center, autoignition and combustion occur first in the sub-chamber 20 where the temperature of the mixture is high (see FIG. 2(c)). Note that a cooling means such as a cooling jacket (not shown) is provided on the outer periphery of the cylinder 2 to cool the cylinder 2, and the temperature of the inner wall of the piston 3 (cavity 30a) is more likely to be maintained at a higher temperature than that of the inner wall of the cylinder 2.

[0032] Next, at top dead center, the flame generated by combustion in the auxiliary combustion chamber 20 is ejected into the main combustion chamber 10 through the communication hole 31a (see FIG. 2(d)). The flame ejected from the communication hole 31a then causes the premixed air-fuel mixture to combust in the main combustion chamber 10 (see FIG. 2(e)). In addition, the premixed air-fuel mixture is compressed in the main combustion chamber 10 by the flame ejected from the communication hole 31a, resulting in so-called self-ignition.

[0033] After the expansion stroke, the exhaust valve 8 opens, and the combustion gas (burned gas) in the main combustion chamber 10 and the auxiliary combustion chamber 20 is discharged from the exhaust pipe 9 (see FIG. 2(f)).

[0034] In this way, in the pre-combustion chamber engine 1 of the present embodiment 1, by providing the pre-combustion chamber 20 to the piston 3, the temperature of the mixture in the pre-combustion chamber 20 is made higher than the pre-mixture in the main combustion chamber 10, and by injecting fuel into the pre-combustion chamber 20 from the center injector 5, the mixture concentration in the pre-combustion chamber 20 is made high, making it easier for self-ignition and combustion to occur in the pre-combustion chamber 20.

[0035] Furthermore, in the pre-combustion chamber engine 1 of this embodiment, fuel is directly injected from the center injector 5 into the pre-combustion chamber 20 through the communication hole 31a provided in the center of the top surface of the piston 3 during the compression stroke at crank angles of -90° to -10°, thereby appropriately increasing the mixture concentration in the pre-combustion chamber 20. This allows HCCI combustion to occur in stages over a relatively long period of time, first in the pre-combustion chamber 20 and then in the main combustion chamber 10, thereby achieving high thermal efficiency. More specifically, the pre-combustion chamber engine 1 of this embodiment can achieve a multi-stage HCCI combustion system in which auto-ignition and combustion occurs in the pre-combustion chamber 20 before top dead center (BTDC), and combustion occurs in the main combustion chamber 10 after top dead center (ATDC).

[0036] Next, a combustion calculation is performed using 3D-CFD (CONVERGE v3.0) for the pre-chamber engine 1 of the first embodiment, and the feasibility of multi-stage HCCI combustion at high loads is examined.

[0037] FIG. 3 shows the results of a comparison of the numerical analysis results of the pipe internal pressure and heat release rate between the pre-chamber engine 1 (Type: A) of the first embodiment and a conventional pre-chamber engine (Type: HEAD) in which the pre-chamber is provided in the cylinder head. large : Main chamber excess air ratio, λ small : Pre-chamber excess air ratio, T in : intake air temperature, IMEP: indicated mean effective pressure, ISFC: indicated fuel consumption rate.

[0038] The specifications of the pre-chamber engine 1 (Type: A) of this embodiment 1 are shown in Table 1. Note that a conventional pre-chamber engine (Type: HEAD) has the same specifications except that the pre-chamber is provided in the cylinder head.

[0039] [Table 1]

[0040] The compression ratio (CR) and the volume ratio of the auxiliary chamber (VR) are defined as in the following equations 1 and 2. Here, V swept is the total displacement, V large is the volume of the main chamber at top dead center, V small is the volume of the antechamber.

[0041]

number

[0042]

number

[0043] Table 2 shows the calculation conditions for the numerical analysis.

[0044] [Table 2]

[0045] The heat release rate of the pre-chamber engine 1 (Type: A) of this embodiment 1 was calculated using the following formula 3. The heat release rate of the conventional pre-chamber engine (Type: HEAD) was calculated using the following formula 4. Here, κ is the specific heat ratio, P large is the pressure in the main chamber, P small is the pressure in the antechamber.

[0046]

number

[0047]

number

[0048] As shown in Figure 3, it was confirmed that the ignition timing in the auxiliary combustion chamber 20 of the auxiliary combustion chamber engine 1 (Type: A) of this embodiment 1 is earlier at -20° than the ignition timing (-5.5°) in the auxiliary combustion chamber of the conventional auxiliary combustion chamber engine (Type: HEAD).

[0049] In the pre-combustion chamber engine 1 (Type: A) of this embodiment, the pre-combustion chamber 20 is formed as a generally bowl-shaped space (see FIG. 1 ). This allows a relatively dense mixture to remain at the outer periphery of the pre-combustion chamber 20, allowing the mixture concentration and temperature required for ignition to be achieved early. Specifically, during the compression stroke, before the ignition timing in the pre-combustion chamber 20, a longitudinal vortex is generated near the area of ​​the communication hole 31a located in the center of the pre-combustion chamber 20. This prevents the inflow of oxygen-rich pre-mixture from the main combustion chamber 10, and the flow rate stagnates at the outer periphery of the pre-combustion chamber 20. As a result, the equivalence ratio (mixture concentration) at the outer periphery of the pre-combustion chamber 20 is maintained at a high level. Because ignition in the pre-combustion chamber 20 occurs at a location where the equivalence ratio is high, the pre-combustion chamber engine 1 (Type: A) of this embodiment is presumed to easily achieve the mixture concentration and temperature required for ignition, resulting in an early ignition timing in the pre-combustion chamber 20.

[0050] It was also confirmed that the ignition timing in the main chamber 10 of the pre-combustion chamber engine 1 (Type: A) of this embodiment 1 is delayed by 5° compared to the ignition timing (3°) in the main chamber of a conventional pre-combustion chamber engine (Type: HEAD). In other words, it was confirmed that the pre-combustion chamber engine 1 of this embodiment 1 causes combustion to occur in stages over a longer period of time, in the pre-combustion chamber 20 and then the main chamber 10, compared to a conventional pre-combustion chamber engine (Type: HEAD).

[0051] Furthermore, it was confirmed that the pre-chamber engine 1 (Type: A) of this embodiment 1 has a significantly smaller first-stage heat release peak due to ignition in the pre-chamber 20, and a smaller second-stage heat release peak due to ignition in the main chamber 10, compared to a conventional pre-chamber engine (Type: HEAD).

[0052] Furthermore, the IMEP of 550 kPa in the pre-chamber engine 1 (Type: A) of this embodiment 1 is higher than the maximum IMEP of 512 kPa in the conventional pre-chamber engine (Type: HEAD), and it was confirmed that the operating range can be expanded to higher loads.

[0053] Next, the results of a comparison of the numerical analysis results of the energy balance between the pre-chamber engine (Type: A) of this embodiment 1 and a conventional pre-chamber engine (Type: HEAD) are shown in FIG. 4. Regarding the notation in FIG. 4, φ unburnt : Unburnt loss ratio, φ cool : Cooling loss rate, φ ex : Exhaust loss ratio, η i :Indicated thermal efficiency.

[0054] As shown in FIG. 4, the cooling loss of the conventional pre-chamber engine (Type: HEAD) is 34.0%, whereas the cooling loss of the pre-chamber engine (Type: A) of this embodiment 1 is 21.4%, confirming that the cooling loss is reduced by 10% or more.

[0055] Furthermore, while the indicated thermal efficiency of a conventional pre-chamber engine (Type: HEAD) is 41.4%, the indicated thermal efficiency of the pre-chamber engine (Type: A) of this embodiment 1 is 46.0%, confirming an improvement of 4% or more in indicated thermal efficiency. This is presumably because, as shown in Figure 3, the heat release peak of the second stage associated with combustion in the main combustion chamber 10 is shifted after top dead center.

[0056] Considering that the thermal efficiency of a conventional HCCI engine without a pre-chamber is approximately 40% and the cooling loss is approximately 30% in the same load range as the conditions of the above numerical analysis, the thermal efficiency and cooling loss of the pre-chamber engine 1 of this embodiment 1, in which the piston 3 is provided with the pre-chamber 20, exceed those of a conventional HCCI engine.

[0057] As explained above, the pre-chamber engine 1 of this embodiment 1 can realize a multi-stage HCCI combustion system using a single fuel (gasoline) in the practical rotation range, and achieves an indicated thermal efficiency of 46.0% and an IMEP of 550 kPa, making it possible to expand the thermal efficiency of HCCI combustion and the operating range to higher loads than conventional pre-chamber engines (TYPE: HEAD). Furthermore, the pre-chamber engine 1 of this embodiment 1 can expand the operating range to higher loads by using multi-stage HCCI combustion to appropriately lengthen the combustion period compared to a normal HCCI engine and suppressing sudden combustion.

[0058] In this way, in the auxiliary combustion chamber type engine 1 of the first embodiment, the auxiliary combustion chamber 20 is connected to the main combustion chamber 10 by the communication hole 31a and is also attached to the piston 3, so that the piston 3 is more likely to be maintained at a higher temperature than the cylinder 2, making it easier for the air-fuel mixture to self-ignite and burn in the auxiliary combustion chamber 20 attached to the piston 3, and thus the cooling loss can be reduced with a simple configuration, resulting in an excellent energy balance.

[0059] Furthermore, since one communication hole 31a is located in the center of the top surface of the piston 3, the combustion gas ejected from the auxiliary combustion chamber 20 tends to spread evenly in the main combustion chamber 10. This aligns the timing of self-ignition in the main combustion chamber 10, making it possible to increase the peak of heat release in the second stage associated with combustion in the main combustion chamber 10. Furthermore, in the multi-stage HCCI combustion of the auxiliary combustion chamber engine 1 of this embodiment 1, the heat release in the second stage due to combustion in the main combustion chamber 10 is higher than the heat release in the first stage due to combustion in the auxiliary combustion chamber 20, and the timing of this heat release being shifted to after top dead center leads to a high indicated thermal efficiency.

[0060] Furthermore, since the center injector 5 is disposed directly above the communication hole 31a, it is easy to supply fuel to the auxiliary combustion chamber 20 without significantly affecting the concentration of the premixed gas in the main combustion chamber .

[0061] Furthermore, the auxiliary combustion chamber 20 can be simply configured by being formed by the cavity 30a on the top surface of the piston body 30 and the plate-like attachment 31 fixed to the top surface of the piston body 30. In this way, the auxiliary combustion chamber type engine 1 of this embodiment 1 can achieve multi-stage HCCI combustion by improving only the piston 3 that forms the auxiliary combustion chamber 20 and by modifying the injection system (i.e., by converting the center injector 5 that supplies fuel to the auxiliary combustion chamber 20 to direct injection). [Example]

[0062] Next, a pre-combustion chamber engine according to a second embodiment will be described with reference to Fig. 5. Note that a description of the same configuration as in the first embodiment will be omitted.

[0063] 5, in the pre-combustion engine 101 of the second embodiment, the surface (bottom) of the cavity 30a formed in the upper surface of the piston body 30 is coated with a heat insulating film 130 having higher heat insulating properties than the piston body 30. The piston body 30 is made of an aluminum alloy, and the heat insulating film 130 is made of various ceramics, carbon, or the like.

[0064] Furthermore, the heat insulating film 130 may cover the entire upper surface of the piston body 30 or the entire surface of the piston body 30, as long as it covers at least the surface of the cavity 30a.

[0065] The thickness of the heat insulating film 130 is preferably 0.01 to 0.3 μm, and more preferably 0.1 to 0.2 μm.

[0066] Furthermore, when cooling loss was extracted from the boundary surfaces of the cylinder head, the auxiliary chamber, and the piston, it was confirmed that the piston has a greater effect on cooling loss than the auxiliary chamber in terms of total heat transfer. Therefore, by covering the surface of the cavity 30a formed on the top surface of the piston body 30 with a heat insulating film 130 that has better heat insulating properties than the piston body 30, it is easier to maintain a high temperature in the auxiliary chamber 20, and cooling loss can be effectively reduced.

[0067] Furthermore, the heat insulating film 130 prevents the temperature of the piston body 30 from decreasing due to the latent heat (heat of vaporization) generated when the fuel directly injected from the center injector 5 into the auxiliary chamber 20 vaporizes. Therefore, even if fuel is directly injected from the center injector 5 into the auxiliary chamber 20 to make the mixture concentration in the auxiliary chamber 20 higher than the premixed mixture concentration in the main chamber 10, the auxiliary chamber 20 can be kept at a high temperature, and cooling loss can be reduced.

[0068] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0069] For example, in the above-described embodiment, if the pre-chamber engine is one in which the pre-chamber 20 is provided in the piston 3 and multi-stage HCCI combustion can be achieved by the temperature difference between the mixture in the pre-chamber 20 and the pre-mixture in the main combustion chamber 10, then it is not necessary to directly inject fuel from the injector into the pre-chamber 20 to increase the mixture concentration in the pre-chamber 20.

[0070] In the above embodiment, a single communication hole 31a is disposed in the center of the top surface of the piston 3. However, the present invention is not limited to this. As long as fuel can be directly injected from the injector to the sub-chamber, multiple communication holes may be provided in the top surface of the piston.

[0071] Furthermore, the injector that injects fuel into the auxiliary chamber does not have to be located directly above the communication hole, as long as it can inject fuel directly into the auxiliary chamber through the communication hole provided in the piston.

[0072] In the above embodiment, the fuel is injected into the auxiliary combustion chamber 20 by the injector during the compression stroke when the crank angle is between -90° and -10°. However, the present invention is not limited to this. As long as the concentration of the mixture in the auxiliary combustion chamber 20 can be increased appropriately before top dead center, the timing of fuel injection by the injector may be freely set.

[0073] Furthermore, in the above embodiment, the method of supplying fuel to the main combustion chamber 10 is described as an intake manifold injection method in which fuel is injected from the side injector 4 into the intake manifold 7. However, the method of supplying fuel to the main combustion chamber is not limited to this, and may be a direct injection method into the pipe using a side injector or a center injector.

[0074] In the above embodiment, the piston 3 is composed of the piston body 30 and the plate-like attachment 31, and the auxiliary chamber 20 is formed by the bottom surface of the cavity 30a formed in the upper surface of the piston body 30 and the lower surface of the plate-like attachment 31 fixed to the upper surface of the piston body 30. However, the piston is not limited to this, and the piston may be composed of only the piston body, and the cavity and the communicating hole may be formed directly in the piston.

[0075] In the above embodiment, the auxiliary combustion chamber 20 is described as being formed as a generally bowl-shaped space. However, the auxiliary combustion chamber may be formed as a space of any shape. For example, as a modified auxiliary combustion chamber, an auxiliary combustion chamber formed as a generally cylindrical space, such as auxiliary combustion chamber 220 shown in FIG. 6(a), or an auxiliary combustion chamber formed as auxiliary combustion chamber 320 shown in FIG. 6(b), which is a generally cylindrical space with a raised bottom center and a peak directly below the communication hole 31a, may be used. It has been confirmed that even if the auxiliary combustion chamber shape is as shown in FIGS. 6(a) and 6(b), the auxiliary combustion chamber engine of the present invention can achieve a multi-stage HCCI combustion system using a single fuel (gasoline) by appropriately setting the intake air temperature during the combustion process, and that cooling loss can be reduced to approximately the same level as that of the auxiliary combustion chamber engine of the first embodiment.

[0076] Furthermore, it has been confirmed that by combining the multi-stage HCCI combustion method realized by the pre-chamber engine of the above embodiment with EGR (exhaust gas recirculation), it is possible to suppress sudden combustion caused by supercharging, enable combustion at high loads, and significantly reduce NOx emissions. [Explanation of symbols]

[0077] 1,101 Pre-chamber engine 2 cylinders 3 pistons 4 Side injector (means of introducing premixed fuel into the main chamber) 5 Center injector (injector that injects fuel into the pre-chamber) 6 intake valve 7 Intake pipe 8 Exhaust valve 9 Exhaust pipe 10 Main room 20 Antechamber 30 Piston body 30a cavity 31 Plate-shaped attachment 31a Communication hole 32 Connecting rod 130 Heat insulating film

Claims

1. A pre-chamber engine in which a piston reciprocates in a cylinder and homogeneous charge compression ignition combustion is performed in the pre-chamber and then the main chamber, the main chamber is a region defined by the cylinder and the piston, 1. A pre-combustion engine, comprising: a pre-combustion chamber connected to the main combustion chamber by a communication hole; and a piston provided in the pre-combustion chamber.

2. 2. The engine according to claim 1, wherein the communication hole is disposed at the center of the upper surface of the piston.

3. means for introducing a premixed fuel into the main chamber; 2. The engine according to claim 1, further comprising an injector for injecting fuel into the pre-chamber.

4. 4. The engine according to claim 3, wherein the injector is disposed directly above the communication hole.

5. 5. The engine according to claim 4, wherein the fuel is injected into the pre-combustion chamber by the injector during the compression stroke when the crank angle is between -90° and -10°.

6. 2. The engine according to claim 1, wherein the auxiliary chamber is formed by a cavity in an upper surface of the piston body and a plate-like attachment fixed to the upper surface of the piston body and having the communication hole.

7. 7. The engine according to claim 6, wherein the surface of the cavity is covered with a heat insulating film having a higher heat insulating property than the piston body.

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