JP2004183520A - Premixed compression self-ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand a region in which an appropriate operation is enabled to both a low load side and a high load side. <P>SOLUTION: This premixed compression self-ignition type internal combustion engine 1 comprises a first intake port In1 and a second intake port In2. The first intake port In1 serves as a straight port and is constituted such that an intake air flowing in a cylinder 3 via that first intake port In1 flows along a cylinder wall to generate a swirl Sw1. The second intake port In2 is constituted such that the intake air is made to flow in the vicinity of a center part of the cylinder, and is arranged in a helical port so as to generate a swirl Sw2 which is in the same direction as the swirl Sw1. A fuel injection port 10 is arranged so as to supply a fuel to the second intake port In2. As a result, in a pre-mixed gas inside the cylinder 3, a fuel concentration nonuniformity is formed such that the pre-mixed gas is thick near the center part and is thin at an outside of the cylinder 3. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technology for improving ignition stability of a homogeneous charge compression ignition internal combustion engine.
[0002]
[Prior art]
The premixed compression self-ignition type internal combustion engine is an internal combustion engine of a type in which a mixture of fuel and air outside the cylinder is flowed into a cylinder and compression ignition (self-ignition) is performed by compression of a piston. This engine is similar to a diesel engine in that compression ignition is performed without using a spark plug, while it is common to a gasoline engine in that fuel is premixed before ignition (premixing). It can be said that the engine has an intermediate property between the engine and the gasoline engine.
This type of internal combustion engine has various merits such as high thermal efficiency, low fuel consumption, and reduction of harmful substances such as soot and NOx. Research and development have been advanced in recent years.
[0003]
One of the major obstacles to the practical use of this homogeneous charge compression self-ignition internal combustion engine is that it is difficult to control ignition and combustion as compared with general engines.
In other words, in diesel engines and gasoline engines, it is possible to cause ignition at the most appropriate time near the top dead center of the piston by adjusting the timing of injecting fuel into the cylinder or generating sparks in the spark plug. Have been. On the other hand, in the case of a premixed compression self-ignition type engine, fuel and air are preliminarily mixed and then compressed and self-ignited, so that self-ignition occurs near the top dead center of the piston. As described above, various control factors including temperature, pressure, and fuel concentration must be appropriately controlled, and there is a problem that the control is extremely difficult.
[0004]
In connection with such a problem, there is an Otto cycle internal combustion engine disclosed in Patent Document 1.
In this technology, a main and auxiliary intake systems are provided, a relatively rich air-fuel mixture is sucked from an auxiliary air intake valve toward the center of a combustion chamber, and a relatively thin air-fuel mixture is sucked from a main air intake valve into a cylinder. A swirl flow that draws a rich mixture at the center of the cylinder and a thin mixture outside is distributed to the rich mixture near the spark plug, allowing lean combustion to reduce exhaust gas and improve thermal efficiency. It is intended.
[0005]
Further, the compression self-ignition gasoline internal combustion engine disclosed in Patent Document 2 uses an injection device that directly injects fuel into a cylinder, distributes fuel so that the center of the combustion chamber becomes dense, and assists compression ignition. It has become.
[0006]
[Patent Document 1]
JP-A-49-46008 [Patent Document 2]
JP 2001-342883 A
[Problems to be solved by the invention]
However, the technique disclosed in Patent Literature 1 is a technique for assisting ignition by a spark ignition engine, and is not originally intended to be applied to a homogeneous charge compression self-ignition type internal combustion engine.
[0008]
In addition, the technique disclosed in Patent Document 2 discloses a technique for, when employing a gaseous fuel such as natural gas as a fuel, a gas for injecting the fuel into the cylinder at a pressure that is not inferior to the extremely large pressure in the cylinder. A compression device is required, which causes a significant increase in cost.
[0009]
[Means for Solving the Problems]
The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.
[0010]
That is, in claim 1, the premixed compression ignition internal combustion engine includes two or more intake ports including a first intake port and a second intake port, and the first intake port is a straight port, The intake air flowing into the cylinder through one intake port flows along the cylinder wall to generate swirl, and the second intake port is configured to allow intake air to flow near the center of the cylinder, and the fuel injection port Is arranged to supply fuel to one of the first intake port and the second intake port.
[0011]
According to the configuration of the first aspect, the premixed gas supplied into the cylinder through the first intake port and the second intake port in the intake stroke is dense (or thin) near the center of the cylinder and thin near the cylinder wall ( Or dark) as in the above. Then, this density unevenness is preserved up to the piston top dead center in the compression stroke by swirl formed by the intake air from the first intake port.
Therefore, even during the low load operation in which the fuel supply amount is reduced, the self-ignition can be started from the portion where the fuel concentration is high, so that the ignition stability is improved. In addition, during a high-load operation in which a large amount of fuel is supplied, a relatively gentle combustion mode in which the fuel is first ignited and the fuel is ignited in a thin portion can be taken, so that noise generation and engine Can reduce the thermal and mechanical burden of the device. That is, the region where the engine can be operated properly can be expanded to the low load side and the high load side.
[0012]
In claim 2, the fuel injection port is arranged so as to supply fuel to the second intake port.
[0013]
According to the configuration of claim 2, since the fuel injection port is arranged to supply fuel to the second intake port,
Since the fuel concentration unevenness can be formed such that the area near the center of the cylinder where the temperature is high becomes dense, ignition stability during low load operation is further improved. In addition, since combustion is performed near the center of the cylinder, heat generated by the combustion is hard to escape from the cylinder wall, and the heat efficiency is excellent.
[0014]
In claim 3, the second intake port is configured as a helical port that generates a swirl in the same direction as the swirl generated by the intake air flowing from the first intake port.
[0015]
According to the configuration of the third aspect, a stronger swirl can be generated as compared with the configuration in which the swirl is formed only by the intake from the first intake port. Further, since the relative speed difference between the vicinity of the center of the cylinder and the outside becomes small, it is possible to suppress the premixed air in the cylinder from being mixed around the center of the cylinder and the outside. As a result, the fuel concentration unevenness can be more stably maintained up to the piston compression top dead center, and the region where the engine can be operated properly can be further expanded to the low load side and the high load side.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the invention will be described.
FIG. 1 is a schematic plan view showing the overall configuration of a homogeneous charge compression ignition engine according to one embodiment of the present invention.
FIG. 2 is a perspective view showing the flow of air and fuel gas during the intake stroke of the engine. FIG. 3 is a perspective view showing a state in which the premixed gas is compressed while maintaining the concentration unevenness in the compression stroke.
[0017]
The compression ignition engine 1 shown in FIG. 1 is configured to drive a compressor of an outdoor unit in a gas heat pump, and uses city gas as fuel. The cylinder 3 of the engine 1 has two intake ports (first intake port In1 and second intake port In2) and two exhaust ports (first exhaust port Out1 and second exhaust port Out2). I have.
A piston 4 is fitted inside the cylinder 3 so as to be able to reciprocate freely. The piston 4 is connected to a crankshaft of the engine 1 via a connecting rod 8 (FIGS. 2 and 3).
[0018]
Each of the intake ports In1 and In2 and the exhaust ports Out1 and Out2 is provided with a valve 9. The valve 9 is opened and closed by a camshaft (not shown) that is operatively connected to the crankshaft via a timing belt or the like. Is controlled.
[0019]
The intake ports In1 and In2 are mounted side by side on one side of the ceiling surface of the cylinder 3. The intake path 5 serving as a path for taking in air into the cylinder 3 is branched from the middle into two, a first branch path 5a and a second branch path 5b. The first branch 5a is connected to the first intake port In1, and the second branch 5b is connected to the second intake port In2.
The fuel supply pipe 11 protrudes into the second branch passage 5b to form a fuel injection port 10 facing the second intake port In2. The fuel supply pipe 11 is connected to a carburetor (fuel mixer) (not shown), and the carburetor is supplied with city gas from a gas outlet pipe.
[0020]
The first intake port In1 is configured as a straight port (tangential inflow type), and is connected to the cylinder 3 in a direction close to the tangent to the inner wall of the cylinder 3 in plan view. As a result, the air supplied from the first branch passage 5a into the cylinder 3 via the first intake port In1 generates the swirl Sw1 along the inner wall of the cylinder 3.
The second intake port In2 is formed as a helical port (spiral inflow type port) whose tip is spirally curved in plan view. Therefore, the air and the fuel gas supplied to the second branch passage 5b are introduced into the internal space of the cylinder 3 while forming a vortex through the second intake port In2, and the swirl Sw2 in the same direction as the swirl Sw1 is formed. It is configured to generate.
[0021]
The first exhaust port Out1 and the second exhaust port Out2 are connected to the first branch 7a and the second branch 7b, respectively. The two branch paths 7a and 7b join to form a collective exhaust path 7, and are connected to a muffler for silencing.
[0022]
Next, the operation of the engine 1 will be described.
That is, the engine 1 is of a four-cycle type, and passes through four strokes of (1) an intake stroke, (2) a compression stroke, (3) an expansion stroke, and (4) an exhaust stroke in order, as described below. Complete one cycle.
[0023]
{Circle around (1)} In the intake stroke, the piston 4 is descending, and the valves 9 of the intake ports In1 and In2 are controlled to be opened. Therefore, air is sucked into the negative space of the cylinder 3 through the first intake port In1, and air and fuel gas are sucked through the second intake port In2. When the lowering of the piston 4 is completed and the bottom dead center is exceeded, the process proceeds to the next compression stroke.
[0024]
{Circle around (2)} In the compression stroke, the piston 4 moves up. In this state, all four ports (In1, In2, Out1, Out2) are closed by the valve 9, so that the premixed gas is compressed. Become. The compression ratio is about 17-18. Then, at the timing when the rising piston reaches the top dead center, the premixed gas self-ignites (self-ignites), and the process proceeds to the next explosion step.
[0025]
(3) In the expansion stroke, the ignited premixed air rapidly expands. Also in the expansion stroke, all four ports (In1, In2, Out1, Out2) remain closed by the valve 9, so that the expanding premixed gas pushes down the piston 4 to rotate the crankshaft. . When the piston 4 has finished descending and has passed the bottom dead center position, the next exhaust step is started.
[0026]
(4) Since the exhaust ports Out1 and Out2 are opened in the exhaust stroke, the exhaust gas in the cylinder 3 is pushed out by the ascending piston 4, and is exhausted through the exhaust ports Out1 and Out2. One cycle is completed when the piston 4 reaches the top dead center, and the process returns to the suction process again.
[0027]
In the present embodiment, in the above (1) suction stroke, air simply flows into the cylinder 3 from the first intake port In1, while air and fuel gas flow from the second intake port In2.
The air flowing from the first intake port In1 forms a swirl Sw1 along the inner wall surface of the cylinder 3. On the other hand, the fuel-air mixture from the second intake port In2 forms a swirl Sw2 in the same direction as the swirl Sw1, while being introduced near the center of the cylinder 3.
As a result, the air-fuel mixture in the cylinder 3 has a non-uniform fuel concentration such that the outside of the cylinder is thin and the area near the center of the cylinder is dense (FIG. 3). In addition, the generated fuel concentration unevenness is maintained by the swirl Sw1 and Sw2 formed in the cylinder 3 even when the air-fuel mixture is compressed by raising the piston 4 in the next (2) compression stroke. become.
[0028]
Therefore, (2) at the end of the compression stroke (near the piston top dead center), first self-ignition occurs in the vicinity of the cylinder center where the fuel concentration is high, and the outside of the cylinder where the fuel concentration is low burns behind the ignition in the center portion. It takes the form of burning.
As a result, even at the time of high load operation, even when it is necessary to inject a large amount of fuel, first, the fuel is ignited from the central portion where the fuel concentration is high, and the pressure and temperature in the cylinder increase, thereby causing the surrounding lean premixed gas to increase. Since the combustion is induced, the combustion is relatively slow, and the noise can be reduced as compared with the multipoint simultaneous ignition combustion by the uniform compression of the fuel mixture. Further, the thermal load and the mechanical load on the cylinder head and the piston can be reduced, and the durability of the cylinder head and the piston is improved.
That is, according to the configuration of the present embodiment, it means that the operable region of the engine 1 can be expanded to the high load side.
[0029]
Also, during low-load operation in which the fuel injection amount should be reduced, if the fuel is mixed evenly, the fuel concentration should be such that the piston does not self-ignite (combustion) even if compressed until it reaches the top dead center. Even so, by forming the fuel concentration unevenness so that the center side becomes dense as described above, self-ignition occurs at the cylinder center side during compression, thereby inducing the combustion of the lean mixture around it and causing misfire. Can be suppressed.
Further, the temperature distribution of the internal space of the cylinder generally has a higher temperature on the center side of the cylinder than on the side (outside) closer to the inner wall of the cylinder because heat escapes along the inner wall of the cylinder. . In the present embodiment, by supplying the fuel from the second intake port In2 side, concentration unevenness near the stoichiometric mixture ratio is formed in the vicinity of the central portion of the cylinder where the temperature is high as described above. Can be made easier.
That is, according to the configuration of the present embodiment, the operable region of the engine 1 can be expanded to the low load side. In addition, since ignition is performed near the center of the cylinder, heat generated by combustion is hard to escape to the outside, which is advantageous in terms of thermal efficiency.
[0030]
Although the embodiment of the present invention has been described above, the present invention is not limited to the configuration of the above embodiment, and the following modifications are possible without departing from the spirit of the present invention. .
[0031]
(B) Although the present embodiment is a compression ignition type engine, a spark plug for performing forced ignition under operating conditions where stable compression ignition is difficult may be provided. In this case, the spark plug is connected to an electronic control unit (ECU), and the ECU determines whether compression ignition should be performed or forced ignition should be performed based on information (for example, rotation speed and load) input from an appropriate sensor. When it is determined that forced ignition should be performed, an ignition signal is sent to the spark plug. It is desirable that the spark plug be disposed at the center of the cylinder where the fuel is rich, since stable ignition can be realized.
Further, a configuration may be adopted in which a glow plug is provided, and the ignitability is improved by increasing the intake air temperature.
[0032]
(B) In this embodiment, the four ports (In1, In2, Out1, Out2) are arranged side by side so as to be equidistant from the center of the cylinder, but the second intake port In2 is located closer to the center of the cylinder. The arrangement is preferable in that fuel concentration unevenness having a large difference in shading can be formed.
[0033]
(C) Although the present embodiment uses city gas (natural gas) as a fuel, the same structure as in the above embodiment can be adopted even when another gas such as propane gas is used as a fuel. Further, for example, a carburetor (atomizing mixer) for atomizing gasoline may be provided to inject a mixture of atomized gasoline and air into the second branch passage 5b.
[0034]
(D) In the present embodiment, the fuel injection port 10 is disposed in the intake passage (the second branch passage 5b) communicating with the second intake port In2, but is not limited thereto, and the fuel injection port 10 is not restricted to the first intake port In1. The fuel injection port 10 may be arranged in the branch path 5a. In short, if the configuration is such that fuel is supplied to only one of the intake ports In1 and In2 and not supplied to the other, it is possible to form uneven fuel concentration in the air-fuel mixture in the cylinder 3. is there.
However, if the fuel is supplied to the second intake port In2 side where the intake air flows into the vicinity of the center of the cylinder 3, the rich air-fuel mixture is located near the center of the cylinder 3 on the high temperature side. This is advantageous in that self-ignition at the time is easy and thermal efficiency can be increased.
[0035]
(E) In the present embodiment, the number of intake ports is two (In1 · In2). However, the present invention is not limited to this, and a configuration having three or more intake ports may be used.
[0036]
(F) The fuel injection port 10 may be arranged at any position of the intake passage (second branch passage 5b) communicating with the second intake port In2, but at a position close to the end on the second intake port In2 side. It is desirable to be arranged. In this manner, the fuel can be supplied to the vicinity of the center of the cylinder 3 before the fuel is evenly mixed with the air flowing through the second branch passage 5b, and concentration unevenness having a large density difference is formed in the air-fuel mixture in the cylinder 3. Because you can.
[0037]
(G) In the present embodiment, the second intake port In2 is formed as a helical port as described above, and the pre-mixed air passing through the second intake port In2 enters the cylinder 3 while forming a spiral vortex. The swirl Sw2 is formed in the same direction as the swirl Sw1 formed by the air that is supplied and flows in from the first intake port In1 as a straight port. However, the present invention is not limited to this configuration, and the second intake port In2 can be formed as a straight port.
However, it is desirable that the second intake port In2 be a helical port in that the fuel concentration unevenness can be easily maintained up to the compression top dead center of the piston 4. That is, if the intake air from the second intake port In2 forms the swirl Sw2, the swirl Sw1 formed by the intake air from the first intake port In1 can form a stronger swirl in the cylinder 3. Further, when the fuel mixture supplied from the second intake port In2 forms the swirl Sw2 by itself, the relative velocity difference between the fuel mixture and the air from the first intake port In1 forming the swirl Sw1 outside the cylinder is smaller. This is because it is possible to suppress the strong stirring and mixing of the air outside the cylinder and the fuel mixture near the center of the cylinder.
[0038]
(H) In the present embodiment, the configuration using the carburetor and the fuel supply pipe 11 is employed, but the present invention is not limited to this. For example, an electronically controlled injector may be provided in the second branch passage 5b.
At this time, the injector is connected to an electronic control unit (ECU) to control the fuel injection timing. For example, instead of injecting fuel at the beginning of the intake stroke, a large amount of fuel is injected just before the piston 4 reaches the bottom dead center (immediately before the end of the intake stroke). It is conceivable to control the injection timing according to the angle. By doing so, the fuel rich in the vicinity of the center of the cylinder 3 is compressed just before the end of the intake stroke and compressed without time, so that the fuel density unevenness with a large difference in the density can be formed, and the engine 1 can be appropriately controlled. Thus, the range in which the motor can be operated can be further expanded to the low load side and the high load side.
[0039]
【The invention's effect】
The present invention is configured as described above, and has the following effects.
[0040]
That is, as shown in claim 1, in a homogeneous charge compression ignition internal combustion engine, a first intake port, comprising two or more intake ports including a second intake port, the first intake port as a straight port, The intake air flowing into the cylinder through the first intake port flows along the cylinder wall to generate swirl, and the second intake port is configured to allow intake air to flow near the center of the cylinder, Since the injection port is arranged to supply fuel to one of the first intake port and the second intake port,
In the premixed gas supplied into the cylinder through the first intake port and the second intake port in the intake stroke, the fuel concentration unevenness such that the vicinity of the center of the cylinder is thick (or thin) and the vicinity of the cylinder wall is thin (or thick). Can be caused. Then, this density unevenness is preserved up to the piston top dead center in the compression stroke by swirl formed by the intake air from the first intake port.
Therefore, even during the low load operation in which the fuel supply amount is reduced, the self-ignition can be started from the portion where the fuel concentration is high, so that the ignition stability is improved. In addition, during a high-load operation in which a large amount of fuel is supplied, a relatively gentle combustion mode in which the fuel is first ignited and the fuel is ignited in a thin portion can be taken, so that noise generation and engine Can reduce the thermal and mechanical burden of the device. That is, the region where the engine can be operated properly can be expanded to the low load side and the high load side.
[0041]
As described in claim 2, since the fuel injection port is arranged to supply fuel to the second intake port,
Since the fuel concentration unevenness can be formed such that the area near the center of the cylinder where the temperature is high becomes dense, ignition stability during low load operation is further improved. In addition, since combustion is performed near the center of the cylinder, heat generated by the combustion is hard to escape from the cylinder wall, and the heat efficiency is excellent.
[0042]
As shown in claim 3, the second intake port is configured as a helical port that generates a swirl in the same direction as the swirl generated by the intake air flowing from the first intake port,
A stronger swirl can be generated as compared to a configuration in which a swirl is formed only by intake from the first intake port. Further, since the relative speed difference between the vicinity of the center of the cylinder and the outside becomes small, it is possible to suppress the premixed air in the cylinder from being mixed around the center of the cylinder and the outside. As a result, the fuel concentration unevenness can be more stably maintained up to the piston compression top dead center, and the region where the engine can be operated properly can be further expanded to the low load side and the high load side.
[Brief description of the drawings]
FIG. 1 is a schematic plan view showing an overall configuration of a homogeneous charge compression ignition engine according to an embodiment of the present invention.
FIG. 2 is a perspective view showing flows of air and fuel gas in an intake process of the engine.
FIG. 3 is a perspective view showing a state in which a premixed gas is compressed while maintaining concentration unevenness in a compression step.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Premixed compression ignition engine 3 Cylinder 4 Piston 5 Intake path 7 Collective exhaust path 10 Fuel injection port In1 First intake port In2 Second intake port Sw1 ・ Sw2 Swirl

Claims (3)

In a homogeneous charge compression ignition internal combustion engine,
A first intake port, comprising two or more intake ports including a second intake port,
The first intake port is a straight port, so that the intake air flowing into the cylinder through the first intake port flows along the cylinder wall to generate swirl,
The second intake port is configured to allow intake air to flow near the center of the cylinder,
A homogeneous charge compression ignition internal combustion engine, wherein a fuel injection port is arranged to supply fuel to one of the first intake port and the second intake port. The homogeneous charge compression ignition type internal combustion engine according to claim 1, wherein the fuel injection port is arranged to supply fuel to the second intake port. organ. 3. The helical engine according to claim 1, wherein the second intake port generates a swirl in the same direction as a swirl generated by intake air flowing from the first intake port. A homogeneous charge compression ignition internal combustion engine characterized as being configured as a port.

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