JPH11117746A - Lean burn method by low pressure cylinder injection for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a fuel consumption and to reduce a harmful component in exhaust gas by conducting cylinder injection under low pressure using a simple compressing means such as a compressor in a 4-cycle engine. SOLUTION: A concentrated air-fuel mixture is injected into a cylinder under the pressure of 4 atm or less via an injection valve 10 interlocked with an engine speed by a compressor 2 during a low pressure period of the inside of the cylinder ranging from its suction stroke to the first half of its compression stroke, and lean burn by in-cylinder fuel direct injection is conducted by igniting the injected mixture with a spark plug 9 in the condition that the mixture stays in a subsidiary chamber 7 as one local part of a combustion chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for lean-burning a general four-stroke engine by low-pressure in-cylinder injection.

[0002]

2. Description of the Related Art A cylinder-injected lean-burn engine, which has recently been researched and developed and put into practical use, usually employs an in-cylinder in-cylinder injection system. In this case, an injection pressure of about 5 MPa is used. Is required, and an expensive injection device is required.

[0003]

SUMMARY OF THE INVENTION The technical problem of the present invention is to improve fuel economy and reduce harmful exhaust components by performing in-cylinder injection at a low pressure using a simple compression mechanism such as a compressor in a four-cycle engine. It is an object of the present invention to provide a lean burn method capable of reducing the amount of lean burn. A more specific technical object of the present invention is to mix air and fuel,
The air-fuel injection during the low pressure in the cylinder in the first half of the intake stroke or the compression process enables the atomization and combustion of the spray at a sufficiently low pressure as compared with the anaerobic injection in which only the fuel is injected in the compression stroke. To provide a lean burn method.

[0004]

According to the present invention, there is provided a lean-burn method using low-pressure in-cylinder injection for compressing a rich mixture of air and fuel from an intake stroke in a four-cycle engine. During the low pressure in the cylinder up to the first half of the stroke, the compression mechanism injects it into the cylinder at a low pressure of 4 atm or less through an injection valve linked with the rotation of the engine by a compression mechanism,
This is characterized in that lean combustion is performed by direct injection of in-cylinder fuel by igniting with a spark plug in a state where the fuel is retained in one part of the combustion chamber. In the above-described lean burn method, it is preferable that a local portion in which the fuel supplied in the combustion chamber is retained is a sub-chamber opening to the combustion chamber.

In the lean combustion method of the present invention, air and fuel are mixed, and only the fuel is compressed by air-fuel injection during a low pressure in the cylinder in the intake stroke or the first half of the compression process. As compared with the anaerobic injection in which the injection is performed at a low pressure, the atomization can be finely performed at a sufficiently low pressure to perform lean combustion. In particular, even in a gasoline engine, A / F =
Lean combustion up to about 70 can be realized.

[0006]

FIG. 1 shows an example of the configuration of a four-cycle engine to which the lean burn method according to the present invention is applied. This engine has a main body 1 of a general-purpose side-valve four-cycle engine and a compressor 2 as a compression mechanism.
The driving of the compressor 2 is performed via a timing belt 5 by a pulley 4 attached to an output shaft 3 of the engine. In the combustion chamber in the cylinder, a small auxiliary chamber 7 is provided in communication with the main combustion chamber 6 having the piston 8, and a spark plug 9 is installed therein.
The spray of air and fuel from the injection valve (lead nozzle) 10 is blown onto it. The engine body 1 is provided with an exhaust valve (side valve) 11 at an exhaust port 12 to synchronize the exhaust discharge timing with the engine. Further, although not shown, an air supply port and an air supply valve are provided similarly to the exhaust air.

Although the engine shown in FIG. 1 is provided with a side valve, it goes without saying that a general four-stroke engine having an overhead valve and the like can be used in the present invention. As for the injection valve 10, it goes without saying that various injection valves can be used without being limited to the illustrated lead nozzle. Further, the sub-chamber 7 is provided to keep the mixture injected into the cylinder in a local portion of the combustion chamber. However, the mixture is not necessarily limited to the sub-chamber, and the rich mixture supplied to the cylinder by the compressor is not necessarily required. It suffices that a sufficient portion is formed near the spark plug to be retained. For example, it is also appropriate to provide a dent in the head of the piston 8 or to provide a dent in a part of the combustion chamber.

In the four-cycle engine, only air is supplied from the air supply port, and a rich mixture of air and fuel is supplied to the cylinder from the intake stroke to the first half of the compression stroke. During the low pressure, the fuel is injected into the cylinder at a low pressure of 4 atm or less, desirably 1 to 3 atm through the injection valve 10 linked with the rotation of the engine by the compressor 2, and this is accumulated in a local portion of the combustion chamber. By igniting with the spark plug 9 in the closed state, lean combustion (lean burn) by in-cylinder direct fuel injection is performed in a normal four-cycle engine. As described above, the injection method in the engine is air-fuel injection, in which air and fuel are mixed and injected in the first half of the intake stroke or the compression stroke. In comparison, it is possible to atomize the spray at a lower pressure.

The air-fuel injection may be completed just before the spark is blown by the spark plug 9. However, at what time and at what position the rich mixture is stored.
The later the injection timing, the easier it is to control, while the earlier the injection, the more difficult it is to control. Therefore,
From the viewpoint of controlling the rich mixture, it is desirable to delay the injection timing as much as possible.However, if the injection timing is delayed, it is necessary to increase the injection pressure. Therefore, the injection timing and the injection pressure are determined in consideration of their balance. Should. In order to increase the injection pressure, it is conceivable to construct a pressure-accumulation type injection system based on a compressor and inject from a needle type injection valve. In this case, the metering and timing are performed electrically, As the injection pressure, 2-3 atm is appropriate.

According to such a method of the present invention, low fuel consumption and low pollution combustion can be realized as will be understood from the embodiments described later. In addition, in the case of locally producing a rich air-fuel mixture by airless injection in which only fuel is injected in the compression stroke, 50
Injection pressure of about atmospheric pressure is required, and the injection device becomes expensive. On the other hand, in the air-fuel injection, in-cylinder injection can be performed at a very low pressure, for example, 1 to 2 atm. Will be possible. Further, as will be apparent from the embodiment described later, the air-fuel ratio of a normal engine is 1 unit.
5, it can be operated at an air-fuel ratio of 70.

[0011]

EXAMPLES Examples of the present invention will be described below. Experiments first confirmed that the method of the present invention was applied over a wide range of rotation speeds and loads, and that it was possible to operate at almost the same power and fuel efficiency as a carburetor. As a result, it has been found that in a certain operation range, lean combustion of up to about 25% is possible as compared with a carburetor. Also, it has been found that when the throttle is fully opened, the air-fuel ratio can be sufficiently increased up to a no-load operation within a certain rotational speed range. In particular, a spark plug is installed in a small sub-chamber communicating with the main combustion chamber,
It has been found that when air / fuel spray from the lead nozzle is blown onto it, stable no-load operation up to A / F = 70 is possible. In addition, the rated output 6-1
It has been confirmed that in the output range up to 8%, lean burn up to A / F = about 22 to 25 is possible.

The engine tested was a general-purpose, side-valve, four-cycle, single-cylinder gasoline engine as shown in FIG. 1, having a bore of 66 mm, a stroke of 53 mm, and a displacement of 181.
cc, the maximum output is 3.7 kw / 4200 min ^-1 ,
It is a camshaft driven engine with a compression ratio of 6.4. The air / fuel injection compressor 2 has a bore of 22.4 m.
A 4-cycle engine (for model airplanes) with m, stroke of 19 mm and displacement of 7.5 cc was modified and diverted. Specifically, the exhaust valve was used to discharge the air-fuel mixture, and the cam on the exhaust side was processed so that the injection was performed in the original compression stroke, and the engine was modified to slightly reduce the intake valve operation period. . The operating period of the exhaust valve was approximately 180 degrees. The compressor 2 sucks an air-fuel mixture from a small carburetor in its original suction stroke, compresses it in a compression stroke, and blows the air and fuel spray from an injection valve (lead nozzle) 10 to a spark plug 9. It is.

FIGS. 2A and 2B show the structure of the lead nozzle. In this lead nozzle 20, a reed valve 23 attached so as to close an injection hole 22 in a valve body 21 is cut out of a stainless steel material having a thickness of 0.2 mm to a length of 16 mm and a width of 9 mm. 5 mm. The valve opening pressure of the reed valve is approximately 0.2 MPa. Although the engine is provided with a carburetor, when performing air-fuel injection from the lead nozzle 20, no fuel was supplied to the carburetor, and only the function of the throttle valve was used.

FIG. 1 shows a structure in which a lead nozzle 20 and a spark plug 9 are provided in a sub-chamber 7 connected to a main combustion chamber 6, and air and fuel spray are blown from the lead nozzle 20 to the spark plug 9. Although this structure is shown, this structure is used at the time of no-load and light-load operation described in FIG.
A structure in which air and fuel spray were sprayed from a lead nozzle mounted on a cylinder head to a spark plug was used.

[0015] The fuel injection timing is low because the injection pressure is low.
As shown in FIG. 3, the injection stroke is set in the first half of the compression stroke from the intake stroke of the engine. However, at the time of partial load, consideration was given to delaying the injection timing as much as possible. In addition, the injection timing in the figure shows the top dead center of the compressor for convenience of the experiment. An eddy current dynamometer was used to absorb the engine power. The air flow rate of the engine was measured by a round nozzle, and the air flow rate of the compressor was measured by a dry gas meter.

In the experiment, the engine speed was 3000
A continuous photograph of the spray at min ^-1 was taken, and it was found that the spray was fan-shaped, and that the spray was sprayed over a fairly wide range, especially in the latter half of the spray. In addition, when inferred from this photograph and the result of measurement performed by attaching a strain gauge to the lead nozzle, the injection period is considered to be 160 to 200 ° CA.

[0017] (A) ~ in FIG 4 (E) are those output during full throttle, fuel efficiency, HC, and CO and NO _X concentration plotted against air, the performance was compared with the vaporizer It is. At the time of measurement, the engine performance was measured by changing the fuel injection timing in advance, but almost no change in the output performance due to the injection timing was recognized. However, since slight changes were observed in the HC and CO concentrations, the injection timing at which the HC concentration became the lowest was set as the optimal injection timing. When the top dead center of the compressor piston is adopted as a value representing the injection timing, this injection timing is 280 ° CA-BTD.
C. As shown in the figure, there was no significant difference between the carburetor and the output in terms of power and fuel consumption. However, the output is corrected by measuring the drive loss of the compressor separately. At 3600 min ⁻¹ , no-load operation can be performed with the throttle fully open, and it has been found that a certain stratification can achieve a maximum of about 25% lean burn compared to a carburetor. In the case of this experiment, the injection was performed in opposition to the air flow, so that the air-fuel mixture was appropriately stirred and good mixing was obtained. It is considered that good combustion was performed.

FIGS. 5A to 5E show the engine performance at a throttle opening of 1/4. Compared with the full-open operation, good results were obtained over a wider range of injection timing, but this is probably because the in-cylinder pressure was reduced at partial load, resulting in better spraying. .
In general, with respect to the output and the fuel efficiency, it can be said that the injection provided a performance almost equal to that of a carburetor, and enabled a slight lean burn as compared with the carburetor.

In the above, when a reed valve is attached to a side-valve engine and air / fuel injection is performed, almost the same performance as that of the carburetor is obtained.
Although lean combustion of about 5% was possible, it was difficult to achieve further lean combustion as it is. Therefore, a sub-chamber 7 having a capacity of 7.7 cc as shown in FIG.
Was put in it and tried to operate the engine. However, in this case, the compression ratio dropped to 6.1. The diameter of the communication passage between the sub chamber and the main combustion chamber is 12 mm. The ignition of the engine drives the distributor with the crankshaft,
The ignition was performed by a semi-transistor method.

FIG. 6 shows a comparison of the flammability limits during the no-load operation at a rotational speed of 1300 min ^-1 , and plots the operable A / F with respect to the ignition timing. As can be seen from the figure, the carburetor can only operate up to A / F = 14, while the in-cylinder injection method uses the A / F.
A considerably stable lean burn of about = 70 was possible. FIG. 7 is a graph in which the cycle fluctuation rate of the combustion pressure in this case is plotted with respect to the ignition timing. Although the fluctuation rate increases as the ignition timing is delayed, in the case of fuel / air injection, better results are obtained than in the carburetor over a wide range of ignition timing. (A) to (C) of FIG.
C, in which CO and NO _X concentrations were plotted against the ignition timing. As shown in the figure, in the case of air-fuel injection, stable operation with less pollution than a carburetor is possible in a wide range of ignition timing.

As described above, in the no-load operation at a rotation speed of 1300 min ^-1 , it was proved that the lean combustion up to A / F = 70 was possible. An experiment was performed to determine the possible load range. FIG.
Indicates the range of operable torque in in-cylinder injection. At the time of full opening and load operation, the spark plug is mounted on the cylinder head for operation.
Is about the same as a vaporizer. On the other hand, at the time of no-load and light-load operation, the operation is performed with the spark plug and the injection valve installed in the sub-chamber.
~ 70. However, the operating range where lean burn is possible is
Further expansion can be expected depending on various conditions.

According to the above experimental example, low-pressure air-assisted in-cylinder injection enables lean combustion similar to high-pressure injection in a four-stroke gasoline engine, thereby making it almost the same as in a carburetor. About the same output and fuel consumption rate were obtained, and even when the injection timing and the throttle opening were changed, almost the same engine performance as the carburetor could be obtained. Further, in the air-fuel mixture injection, a good spray could be obtained despite the low injection pressure. In addition, in the injection and ignition of the sub chamber, (1) during idling operation, fairly stable lean combustion with A / F = 70 was possible. (2) Regarding the operable load range, A / F = 35 to
In the range of 48, 2 to 7% of the maximum output, A / F = 22 to 3
In the range of 5, an output of 6 to 18% was obtained. In short, the low-pressure air / fuel injection system
In a cycle gasoline engine, it has been demonstrated that lean burn up to A / F = 70 is possible.

[0023]

According to the lean-burn method using low-pressure in-cylinder injection of the present invention described in detail above, in-cylinder injection is performed at a low pressure using a simple compression mechanism such as a compressor in a four-cycle engine. In order to improve fuel efficiency and reduce exhaust harmful components, and by mixing air and fuel and performing air-fuel injection during low pressure in the cylinder in the first half of the intake stroke or compression process, only fuel is injected. Compared to the anaerobic injection that is injected in the compression stroke, the spray can be made finer at a lower pressure to perform lean combustion.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a four-cycle engine to which a lean burn method according to the present invention is applied.

FIGS. 2A and 2B are a front view and a bottom view of a lead nozzle used in the engine.

FIG. 3 is an explanatory diagram of a fuel injection timing.

FIGS. 4A to 4E show outputs when the throttle is fully opened,
Fuel, CO, HC and NO _X concentration plotted against air is a graph of the experimental results of performance comparison between the carburetor.

5 (A) to 5 (E) are graphs of experimental results showing engine performance similar to FIG. 4 at a throttle opening of 1/4.

FIG. 6 is a graph of experimental results showing a comparison of flammability limits during a no-load operation at a rotational speed of 1300 min ⁻¹ by plotting an operable A / F with respect to an ignition timing.

FIG. 7 is a graph of an experimental result in which the cycle fluctuation rate of the combustion pressure in the case of FIG. 6 is plotted with respect to the ignition timing.

8 (A) ~ (C) is a graph of experimental results of plotting HC, and CO and NO _X concentration with respect to the ignition timing.

FIG. 9 is a graph showing a range of operable torque in in-cylinder injection.

[Description of Signs] 1 Engine main body 2 Compressor (compression mechanism) 6 Main combustion chamber 7 Sub chamber 9 Spark plug 10 Injection valve

Claims (2)

[Claims] In a four-stroke engine, a rich mixture of air and fuel is interlocked with rotation of the engine by a compression mechanism during a low pressure in a cylinder from an intake stroke to a first half of a compression stroke. The fuel is injected into the cylinder at a low pressure of 4 atm or less through the injection valve, and is ignited by a spark plug in a state where the fuel stays in one part of the combustion chamber to perform lean combustion by direct fuel injection in the cylinder. And a lean burn method using low-pressure in-cylinder injection of the engine. 2. The method according to claim 1, wherein a local portion for retaining the fuel supplied into the combustion chamber is a sub-chamber opening to the main combustion chamber. Lean combustion method.