JP2001304014A - Compression ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a two-stroke cycle internal combustion engine attaining high heat efficiency by reducing nitrogen oxide, smoke, and discharge concentration of unburned fuel in a wide range of an engine speed and a load. SOLUTION: This two-stroke cycle internal combustion engine, having compression ratio incapable of continuing normal operation by generating abnormal combustion by conception as in the past to make self ignition combustion of a combustible mixture by adjusting an amount of supplied air and residual gas, is provided with a fuel supply means capable of independently changing an amount and a degree of dispersion of fuel supplied into a cylinder, to properly set at least one of fuel injection timing, a number of fuel injection times, a supply pressure of fuel, and a number of fuel injection valves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes self-ignition of a combustible air-fuel mixture by compression, reduces the emission concentration of nitrogen oxides, smoke and unburned fuel in a wide range of engine speed and load, and achieves high thermal efficiency. The invention relates to a two-stroke cycle internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine, if an air-fuel mixture in which fuel and air are mixed in advance is burned at an appropriate time regardless of the air-fuel ratio, and the output can be adjusted, the thermal efficiency of the engine is improved. It is well known that this is achieved primarily by a reduction in pump losses and a high specific heat ratio of the lean mixture. It is also known that if the generation of heat by combustion is completed in a short period of time, that is, if the combustion period is shortened, isocapacity is improved and thermal efficiency is improved. On the other hand, it is known that the combustion of a sufficiently diluted mixture in an internal combustion engine significantly reduces the emission of nitrogen oxides. And
It is known that a compression ignition internal combustion engine employing a compression ignition combustion scheme of a lean mixture that focuses on these characteristics can achieve high thermal efficiency and suppress the emission concentration of nitrogen oxides to several ppm or less.

However, in the above-mentioned compression self-ignition type internal combustion engine,
The occurrence of the self-ignition depends on the reactivity of the air-fuel mixture and the history of pressure and temperature rise associated with piston compression, making it difficult to maintain an appropriate ignition timing over a wide range of engine speeds and required loads. . In addition, at high load, the amount of fuel supplied increases, so the emission of nitrogen oxides increases.
Since a large amount of heat is generated in a short time, pressure vibration similar to knocking and lower frequency combustion noise are generated.
Further, the emission concentrations of hydrocarbon compounds and carbon monoxide containing unburned fuel are not low, and they tend to increase at low load.

In the compression ignition type internal combustion engine, a variable compression ratio system, self ignition control based on fuel properties, and the like have been proposed for the purpose of maintaining an appropriate ignition timing in a wide range of engine speed and required load. In either case, the ignition timing can be adjusted in theory. However, it is difficult to realize a mechanism that changes the amount of movement of the piston or a mechanism that moves the cylinder head as the variable compression ratio system. Further, a system in which a sub-chamber or a sub-piston is provided in the combustion chamber to continuously change the volume of the combustion chamber has not been put into practical use due to its complicated structure. That is, it is not easy to realize a means for freely changing only the compression ratio.

Means for changing the effective compression ratio by changing the closing timing of the intake valve has been put to practical use.
Unless the lift curve is changed, the opening timing of the intake valve also changes at the same time, so it is necessary to consider the overlap period when both the intake and exhaust valves are open and the interference between the valve and the piston. It is difficult to change. Furthermore, at high loads, it is necessary to reduce the compression ratio to suppress early ignition, but at the same time, the amount of operating gas also decreases, so increasing the output requires an increase in the amount of air by the turbocharger. However, there is a problem that the mechanism and the control become complicated.

Further, the means for changing the self-ignition characteristics by changing the properties of the fuel is not a technology that can be practically used at present because the problem of the social infrastructure for providing the fuel must be solved. Furthermore, in order to reduce nitrogen oxides at high loads, a method of supplying a large amount of air by a supercharger is conceivable, but this may increase combustion noise similar to knocking. Cannot continue driving. Also, the efficiency of the entire engine system may decrease due to the increased power required to supercharge a large amount of air.

A method of reducing nitrogen oxides under high load and suppressing combustion noise similar to knocking by recirculating a large amount of exhaust gas or remaining in a cylinder has been considered. To self-ignite under high conditions, it is necessary to raise the temperature of the air-fuel mixture, that is, the temperature at the time of combustion cannot be reduced so much, and that the nitrogen oxides and combustion noise cannot be sufficiently reduced. Research (Nakano et al., "Combustion Characteristics and Auto-Ignition Control of Premixed Compression Ignition Engines", Automotive Engineering Society No.9910 Symposium, (1999), p20-25.)

Further, a method of purifying nitrogen oxides with a three-way catalyst or a selective reduction catalyst by bringing the air-fuel ratio of exhaust gas close to the stoichiometric air-fuel ratio at high load can be considered. If it is not possible to change the stoichiometric air-fuel ratio in a short period of time, it is necessary to use a condition in which the air-fuel ratio is around 18 and the emission concentration of nitrogen oxides is high. It is.

It is conceivable to use an occlusion reduction type catalyst as the catalyst. However, this means requires a method of forming rich exhaust gas under a wide range of required load conditions. In order to realize the combustion with a rich air-fuel mixture, a method of supplying a large amount of exhaust gas or burned gas into the cylinder or a method of reducing the amount of air by a throttle can be considered. However, there is no report that any of the methods has shifted to rich combustion in a short period of time without causing misfire in the compression ignition type internal combustion engine, and it is not easy to realize the method.

[0010] For the above reasons, an internal combustion engine that achieves both low emission of nitrogen oxides and high thermal efficiency by applying compression ignition combustion of premixed gas to a wide range of operating conditions has not yet been put into practical use.

On the other hand, a technique for mixing the combustion gas generated in the previous cycle with newly supplied air to generate self-ignition combustion is disclosed, for example, in Japanese Patent Application Laid-Open No. H11-236833. According to the invention, a four-stroke cycle type engine is provided with means for changing the opening / closing timing of intake and exhaust valves, whereby the temperature of the air-fuel mixture and the effect of dilution are adjusted to achieve desired combustion.

However, in a four-stroke cycle internal combustion engine, when the opening / closing timing of the overhead valve is greatly changed, it is necessary to avoid contact between the valve and the top surface of the piston when the piston is near top dead center. However, in order to avoid this in an internal combustion engine having a high compression ratio, a mechanism for changing the valve lift in a complicated manner is required. It has also been considered to prevent the combustion gas from being released to the outside of the cylinder by closing the exhaust valve early before the top dead center. Unless the opening time of the valve is prevented from being significantly advanced, the thermal efficiency is reduced due to the shortened expansion stroke, so that a complicated mechanism is still required for realization.

Further, in a four-stroke cycle internal combustion engine, when the combustion gas generated in the previous cycle is left in the cylinder by adjusting the opening / closing timing of the valve,
Most of the combustion gas requires a process of once being discharged into the intake passage or the exhaust passage and then re-inhaled. In this process, the temperature of the combustion gas decreases. Therefore, the effect of promoting the ignition of the combustion gas is also reduced, that is, it is difficult to adjust the self-ignition combustion in a wide operating range.

According to the invention, the air-fuel ratio of the air-fuel mixture in the cylinder is made closer to the stoichiometric ratio as the required load increases. In this case, a relatively high load causes a large amount of nitrogen oxides to be generated. It is necessary to use an air-fuel ratio of around 18, which causes a problem of emission of a large amount of nitrogen oxides. Further, in the present invention, an internal combustion engine in which the stoichiometric air-fuel ratio of the air-fuel mixture in the cylinder is used irrespective of the required load is disclosed. The inevitability of the decline is explained by basic knowledge of thermodynamics. As described above, it is not easy to realize an internal combustion engine that realizes compression ignition combustion under a wide range of operating conditions based on the method disclosed in the present invention.

On the other hand, with respect to a two-stroke cycle type diesel engine, there is an invention disclosed in, for example, JP-A-11-153043. The invention provides a means for dispersing and supplying fuel to a cylinder at an early stage of a compression stroke, and for supplying air to a cylinder without using a mechanical supercharger at least up to half of the maximum fuel amount to be supplied. The present invention combines a conventional diesel engine with high-dispersion spraying and a method for reducing smoke and nitrogen oxides under high-load conditions from a method that does not require active control of the ratio. The present invention is directed to a subject that is substantially different from the present invention.

In a two-stroke cycle internal combustion engine, ATAC (S. Ohnishi et al., "
Active Thermo-Atomosphere Combustion (ATAC)-A Ne
w Combsution Process for Internal Combustion Engin
es ", SAE Paper 790501, (1979).) and AR combustion (Y. Ishib
ashi et al., "A Low Pressure Pneumatic Direct Inje
ction Two-Stroke Engine by Activated Radical Combu
stion Concept ", SAE paper 980757, (1998).) already exists.

However, these prior arts improve irregular combustion at low load in a two-stroke cycle type internal combustion engine used near a stoichiometric ratio, and emit harmful substances and increase fuel consumption due to incomplete combustion. It is intended to solve a problem that is clearly different from the problem to be solved by the present invention.
Further, in the prior art relating to these two-stroke cycle internal combustion engines using self-ignition combustion, the compression ratio must be set to approximately 8 or less in order to avoid abnormal combustion such as knocking during operation by spark ignition combustion under high load. However, since the air-fuel ratio is set near the stoichiometric ratio, high thermal efficiency cannot be expected.

Therefore, the present inventors have disclosed in Japanese Patent Application No. 12-977.
As disclosed in No. 65, the conventional concept has a compression ratio that causes abnormal combustion and cannot continue normal operation, and appropriately adjusts the remaining amount of gas in the previous cycle and the amount of newly supplied air. Invented a two-stroke cycle internal combustion engine. As a result, sufficient in-cylinder conditions for self-ignition combustion were obtained under a wide range of operating conditions, and both high thermal efficiency and low nitrogen oxide emission concentration were successfully achieved.

In the two-stroke cycle type internal combustion engine described above, it is possible to realize self-ignition combustion under a wide range of operating conditions, and it is not necessary to use the occurrence of pump loss due to throttle reduction for adjusting output. Therefore, the thermal efficiency is high, so that the output can be generated with a smaller amount of fuel as compared with the conventional spark ignition type internal combustion engine. However, due to the high thermal efficiency of the two-stroke cycle internal combustion engine, the amount of supplied fuel used under extremely low load conditions is small, and the number of explosions of the two-stroke cycle internal combustion engine is essentially reduced to four stroke cycle internal combustion engine. Since it is twice the number of times the engine has exploded, it is necessary to burn with less than 1/2 the supplied fuel amount as compared with a 4-stroke cycle type internal combustion engine having the same displacement.

However, in the two-stroke cycle type internal combustion engine described above by the present inventors, the method of forming the air-fuel mixture is not changed irrespective of the change in the load. Is formed as a sparse mixture that is widely dispersed, and has a problem that auto-ignition becomes unstable. Conversely, in a fuel supply mode in which a mixture having an air-fuel ratio appropriate for self-ignition is formed in a narrow space region under low load conditions, particulate matter typified by soot and SOF and nitrogen oxides under high load conditions There is the problem of increased emissions.

Further, in the two-stroke cycle type internal combustion engine, essentially, fresh air blows into the exhaust passage during the scavenging stroke. If the fuel flows out into the exhaust passage together with the blown air, not only high thermal efficiency is not obtained, but also the concentration of hydrocarbons in the exhaust is increased.

In view of the above problems, the present invention provides a two-stroke internal combustion engine (Japanese Patent Application No. 12-97) by the present inventors.
No. 765), it is possible to expand the operable range by self-ignition combustion, reduce the emission of particulate matter and nitrogen oxides, and at the same time, prevent the flow of newly supplied fuel into the exhaust passage in the scavenging process. Things.

[0023]

According to the conventional concept, the present inventors have a compression ratio at which abnormal combustion occurs so that normal operation cannot be continued, and the remaining amount of gas in the previous cycle and the amount of newly supplied air are reduced. For a two-stroke cycle internal combustion engine that appropriately adjusts the amount, there is provided fuel supply means capable of independently changing the fuel amount and the degree of dispersion of the fuel supplied to the cylinder, and the fuel supply means The above-mentioned problem was solved by changing the fuel amount and the degree of dispersion of the fuel supplied to the fuel cell.

Further, the above-mentioned problem has been solved by using the fuel supply means as a fuel injection valve for directly injecting fuel into the cylinder.

That is, according to the first aspect of the present invention, if a uniform stoichiometric air-fuel mixture formed by air and fuel is supplied to a cylinder without heating, the stoichiometric air-fuel mixture can self-ignite or correspond to knocking. While supplying a fuel amount smaller than the fuel amount used to form the stoichiometric mixture in the cylinder, and changing at least one of the air amount and the residual gas amount of the cylinder to change the inside of the cylinder. A two-stroke cycle type internal combustion engine having a reciprocating piston for generating self-ignition of an air-fuel mixture, comprising: a fuel supply means capable of changing a fuel amount and a degree of dispersion of fuel supplied to a cylinder; By changing the fuel amount and the degree of dispersion of the fuel supplied into the cylinder, self-ignition of the air-fuel mixture within the cylinder can be generated within a wide range of air-fuel ratios according to the engine speed and the supplied fuel amount It is a two-stroke-cycle internal combustion engine, characterized in that the configuration was.

More specifically, if a uniform theoretical mixture composed only of air and fuel is supplied to a cylinder without heating by a special device, the theoretical mixture can be self-ignited only by piston compression. Compression ratio, or a compression ratio at which the theoretical air-fuel mixture is piston-compressed, spark-ignitions from one point in the cylinder near top dead center and combustion occurs by flame propagation, and knocking occurs. A self-ignition of the air-fuel mixture is generated in the cylinder by supplying a smaller amount of fuel than the amount of fuel used to form the air-fuel mixture and changing one or both of the air amount and the residual gas amount of the cylinder. A two-stroke cycle type internal combustion engine having a reciprocating piston capable of changing a fuel amount and a degree of dispersion of fuel supplied into a cylinder independently. Fuel supply means capable of supplying fuel into the cylinder by changing the fuel amount and the degree of dispersion of the fuel supplied into the cylinder by the fuel supply means. It is a two-stroke cycle type internal combustion engine capable of generating self-ignition of an air-fuel mixture within the engine.

Here, the degree of dispersion of the fuel is expressed in terms of the diffusion range of the fuel molecules supplied to the fresh air in the cylinder or the volume in which the fuel molecules are present. Quantitative definition is a difficult measure. That is,
In the case where fuel is directly injected into the cylinder, the spatial concentration of fuel molecules becomes non-uniform due to the shape and particle size of the spray. It is possible that the rich mixture is unevenly distributed only in the region of the part. Considering this special case,
It is not easy to quantitatively define the degree of fuel dispersion. Therefore, in the present invention, the degree of dispersion of the fuel is defined as a high degree of dispersion when a relatively lean mixture is burned as a result in a combustion cycle in which the same amount of fuel is supplied. Is defined as having a low degree of dispersion. For example, when the same amount of fuel is injected by a fuel injector having the same shape, the state in which fuel molecules diffuse in a relatively wide space range has a high degree of dispersion, while the state in which fuel molecules diffuse in a narrow range is high. It can be said that the degree of dispersion is low. In the following description,
Low dispersion spray refers to a state of fuel spray with a low degree of dispersion, and high dispersion spray refers to a state of fuel spray with a high degree of dispersion. In addition, a low dispersion injector refers to a fuel injection valve characterized in that the injected fuel spray has a low dispersion degree, and a high dispersion injector refers to a state in which the injected fuel spray has a high dispersion degree. Refers to a fuel injection valve characterized by the following.

According to the second aspect of the present invention, the degree of dispersion of the fuel is reduced in order to advance the ignition timing or to avoid misfire,
2. The internal combustion engine according to claim 1, wherein the degree of dispersion of the fuel is increased in order to delay the ignition timing or to reduce the emission of particulate matter and nitrogen oxides.

According to a third aspect of the present invention, there is provided the internal combustion engine according to the first aspect, further comprising a fuel injection valve for directly injecting fuel into the cylinder through an injection hole as the fuel supply means.

According to a fourth aspect of the present invention, there is provided the internal combustion engine according to the third aspect, wherein the injection pressure is reduced to reduce the degree of dispersion of the fuel, and the injection pressure is increased to increase the degree of dispersion of the fuel. is there.

According to a fifth aspect of the present invention, the injection pressure is reduced under low-rotation or low-load operating conditions, and the injection pressure is increased under high-rotation or high-load operating conditions. 4. The internal combustion engine according to claim 3, wherein the emission of particulate matter and nitrogen oxides under the conditions is reduced, and the work of the injection pump under the operation conditions of low rotation or low load is reduced.

According to a sixth aspect of the present invention, the degree of dispersion of the fuel is reduced by bringing the injection timing close to the top dead center, and the degree of dispersion of the fuel is increased by lengthening the period between the injection timing and the ignition. An internal combustion engine according to claim 3.

The invention according to claim 7 is the internal combustion engine according to claim 3, wherein the fuel is supplied two or more times or two or more times from the injection holes of the fuel injection valve to increase the degree of dispersion of the fuel. .

The invention according to claim 8 is a process in which the volume of the combustion chamber continues to increase, and the fuel supplied to the cylinder is supplied to the exhaust passage without supplying the fuel within 20 degrees before the bottom dead center. The internal combustion engine according to claim 3, wherein the outflow of fuel is suppressed.

[0035]

The internal combustion engine to which the present invention is applied, that is, the conventional concept has a compression ratio that causes abnormal combustion and cannot continue normal operation, and the amount of residual gas that is a residual gas in the previous cycle. A two-stroke cycle internal combustion engine that appropriately adjusts the amount of newly supplied air achieves operation by self-ignition combustion at a wide range of engine speeds. Since auto-ignition combustion is strongly influenced by the chemical reaction of the combustible mixture, it is important to control the progress of the chemical reaction in controlling auto-ignition combustion. In the conventional invention, the progress of the chemical reaction is adjusted by changing the amount of air and residual gas in the cylinder.In the present invention, in addition to this effect, the degree of dispersion of the fuel in the cylinder is adjusted. It is characterized by enhancing the effect of regulating the progress of a chemical reaction.

That is, under operating conditions in which the amount of fuel to be supplied is small, the self-ignition reaction in the combustible air-fuel mixture region is promoted by allowing the fuel to exist in a narrow space region in the cylinder, so that the ignition timing is advanced and the misfire is suppressed. Can be realized. Conversely, under operating conditions where the amount of fuel supplied is large, the progress of the auto-ignition reaction is slowed by widely dispersing the fuel in the cylinder,
Prevention of early ignition and reduction of harmful emissions are realized. Increasing the degree of dispersion of the fuel under operating conditions in which the amount of supplied fuel is large forms a lean mixture, and thus has a high effect in reducing particulate matter and nitrogen oxides.

Further, in the configuration having a fuel injection valve for directly injecting fuel into the cylinder as fuel supply means,
By changing the injection pressure, the injection timing, and the number of injections, the degree of dispersion of the fuel in the cylinder can be adjusted. That is, by increasing the injection pressure, atomization of the fuel is promoted, and the fuel molecules can be dispersed over a wide range. Conversely, by reducing the injection pressure, the dispersion of the fuel over a wide range can be suppressed. . Further, by making the injection timing earlier, a sufficient time for the diffusion of the fuel spray can be obtained, and since the injection can be performed under the condition where the pressure in the cylinder is low, the diffusion effect of the spray is high. The fuel is distributed over a wider area to receive the fuel. Conversely, by delaying the injection timing toward the top dead center, it is possible to suppress the fuel from being dispersed over a wide range. In addition, by performing the fuel injection in a plurality of times, the fuel is injected at a plurality of timings having different cylinder volumes, that is, the possibility that the gas mass in which the spray is mixed is different for each injection is increased. The degree of dispersion increases.

Further, by providing the fuel injection valve for directly injecting fuel into the cylinder as described above, fuel can be supplied into the cylinder regardless of the inflow of fresh air in the scavenging stroke. Therefore, by injecting the fuel at an appropriate time, it is possible to prevent the unburned fuel from flowing out into the exhaust passage without impairing the highly efficient self-ignition combustion realized by the present invention, and thereby, the unburned carbon in the exhaust gas is suppressed. Fuel consumption can be reduced while reducing hydrogen.

[0039]

1 and 2 show an embodiment in which the present invention is realized as an overhead valve type two-stroke cycle type internal combustion engine having a charge supercharger and a fuel injection valve for supplying fuel directly into a cylinder. Is shown. Referring to FIGS. 1 and 2, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, and 6 is an electronically controlled fuel injection valve for directly injecting fuel into a cylinder. Attachment position, 8 is a scavenging valve, 9 is a scavenging port, 10 is an exhaust valve, 11
Indicates exhaust ports, respectively. The scavenging port 9 is connected to a surge tank 13 via a corresponding air supply branch 12, and the surge tank 13 is connected to an air cleaner 17 via an air supply duct 14, an air supercharger 15 and an air supply duct 16. .
The supercharger 15 is driven by an electric motor 18. On the other hand, the exhaust port 11 is connected to an exhaust duct 20 via an exhaust manifold 19. A squish portion is formed near the exhaust valve 10 on the surface of the piston 4 facing the cylinder head 3 so that the gap between the piston 4 and the cylinder head 3 is 1.5 mm at the top dead center. The area of this squish area is about 5 times the bore area including the exhaust valve.
It is configured to correspond to 0%.

The electronic control unit 50 is composed of a digital computer, and a ROM (read only memory) 52, a RAM (random access memory) 53, and a CPU (microprocessor) 5 connected to each other by a bidirectional bus 51.
4, an input port 55 and an output port 56 are provided. The output voltage of the required load sensor 61 that generates an output voltage proportional to the amount of depression of the accelerator pedal is output from the corresponding A / D converter 5.
7 to the input port 55. Further, the input port 55 is connected to a crank angle sensor 62 that generates an output pulse every time the crankshaft rotates, for example, by 10 °. The output form of the crank angle sensor may be any as long as it can calculate or express the rotational speed of the engine and the TDC and injection timing of each cylinder.

On the other hand, the output port 56 is connected to an electric motor 18 for driving the air charge supercharger 15 through a corresponding drive circuit 58.
And an electronically controlled fuel injection valve installed at the mounting position 6 of the electronically controlled fuel injection valve and a fuel pump for supplying high-pressure fuel to the electronically controlled fuel injection valve. FIG. 3 shows, as an embodiment showing the basic effects of the present invention, an embodiment of the present invention realized by the configuration shown in FIGS. 1 and 2 at a fuel supply amount corresponding to a load of about 5%. Changes in the emission concentration of nitrogen oxides (NOx) and ignition timing when the air supply ratio is changed when the two-stroke cycle internal combustion engine is operated, with the air-fuel ratio (A / F) plotted on the horizontal axis. It is. FIG. 3 compares the results of an injection valve with a high degree of dispersion of the injected fuel and an injection valve with a low degree of dispersion, and shows the effect of changing the degree of dispersion on auto-ignition combustion.

As shown in FIG. 3, under the condition of a load of about 5%, the amount of supplied fuel is extremely small, so that when a highly dispersed injection valve that forms a highly dispersed spray is used, the air-fuel ratio is reduced. It can be seen that misfire suddenly occurs. On the other hand, when using a low-dispersion injection valve that forms a low-dispersion spray,
It can be seen that the self-ignition timing is advanced by the air-fuel mixture formed relatively densely in a narrow range, and even if the average air-fuel ratio is reduced by increasing the air supply ratio, it is difficult to misfire. This indicates that the ignition timing can be delayed by increasing the degree of dispersion of the fuel, and conversely, the ignition time can be advanced by decreasing the degree of dispersion of the fuel.

Further, as shown in FIG. 3, the emission concentration of nitrogen oxides is low even with a relatively high air-fuel ratio in a high dispersion spray, but a locally rich mixture burns at a high temperature in a low dispersion spray. It can be seen that the emission concentration of nitrogen oxides is high under the influence.

FIG. 4 shows an embodiment showing the basic effects of the present invention. The embodiment of the present invention realized by the configuration shown in FIGS. 1 and 2 at a fuel supply amount corresponding to a load of about 40%. In the case of operating the two-stroke cycle type internal combustion engine according to the embodiment, changes in the smoke emission concentration and the ignition timing when the air supply ratio is changed are shown with the air-fuel ratio (A / F) on the horizontal axis. FIG. 4 compares the results of an injection valve with a high degree of dispersion of the injected fuel and an injection valve with a low degree of dispersion, and shows the effect of changing the degree of dispersion on auto-ignition combustion.

As shown in FIG. 4, under the condition of a load of about 40%, the amount of supplied fuel is relatively large, so that when a low-dispersion injection valve that forms low-dispersion spray is used, a locally rich mixture is used. Is formed and smoke is discharged. The discharged smoke decreases the air-fuel ratio and rapidly increases as the average air-fuel ratio approaches the stoichiometric air-fuel ratio. On the other hand, when an injection valve with a high degree of dispersion that forms a highly dispersed spray is used, the self-ignition timing is delayed due to a relatively lean mixture over a wide range, and the air-fuel ratio is reduced to reduce the average air-fuel ratio. It can be seen that almost no smoke is emitted even when approaching the stoichiometric air-fuel ratio. From this, it is understood that the ignition timing can be delayed and the smoke emission can be reduced by increasing the degree of dispersion of the fuel.

FIG. 5 shows the feasible range of the self-ignition combustion with respect to the load when the two-stroke cycle type internal combustion engine according to the embodiment of the present invention, which is realized by the configuration shown in FIGS. 1 and 2, is operated. . FIG. 5 shows a comparison result of the injection valve having a low degree of dispersion and the injection valve having a high degree of dispersion when the injection start timings are made equal and the number of injections is one. According to FIG. 5, it can be seen that by using a low-dispersion injector that forms a spray with a low degree of dispersion, the feasible range of auto-ignition combustion at a low load is expanded.

FIG. 6 shows the feasible range of the self-ignition combustion with respect to the load when the two-stroke cycle type internal combustion engine according to the embodiment of the present invention, which is realized by the configuration shown in FIGS. 1 and 2, is operated. is there. In FIG. 6, the low-load condition where auto-ignition combustion could not be realized when the pressure at which fuel was supplied to the fuel injector was 12 MPa was changed to the fuel spray pressure by setting the pressure at which fuel was supplied to the fuel injector to 6 MPa. An example is shown in which the degree of dispersion is reduced, thereby increasing the feasible range of the auto-ignition operation.

FIG. 6 shows that the self-ignition combustion can be realized even under the idling condition of zero load by reducing the fuel supply pressure to 6 MPa. As described above, lowering the fuel supply pressure at low load is effective in expanding the feasible range of the auto-ignition operation, but reducing the fuel supply pressure at low load reduces the pumping work of the fuel pump. Since it also has the effect, the reduction of the pumping work, which is relatively large at a low load, is realized, and the effect of improving the efficiency of the engine is also obtained.

Therefore, changing the fuel supply pressure according to the load as shown in FIG. 7 is effective for improving the efficiency of the engine. That is, at low loads, the fuel supply pressure is set low,
The fuel supply pressure will increase as the load increases. FIG. 8 is a graph showing the relationship between the emission concentration of nitrogen oxides and the fuel supply pressure when the two-stroke cycle type internal combustion engine according to the embodiment of the present invention realized by the configuration shown in FIGS. The results of examining the effects are shown. At a low rotation speed, even if the fuel supply pressure is low, there is a large time margin for dispersing the fuel. Therefore, even if the fuel supply pressure is increased, the effect of reducing nitrogen oxides is not high. On the other hand, it has been shown that, when the rotational speed is high, formation of a spray having a high degree of dispersion by increasing the fuel supply pressure is effective for reducing nitrogen oxides.

FIG. 9 shows the relationship between the number of revolutions and the smoke emission concentration when the two-stroke cycle type internal combustion engine according to the embodiment of the present invention, which is realized by the structure shown in FIGS. The result of the examination of the influence of the above will be described based on the result measured by a Bosch smoke meter. As shown in FIG. 9, when the fuel supply pressure is low, the smoke emission concentration tends to increase as the rotation speed increases, but when the fuel supply pressure is high, the smoke emission concentration increases even when the rotation speed increases. No change in concentration is shown.

The results shown in FIG. 8 and FIG. 9 show that nitrogen oxides and smoke can be reduced at a high rotation speed by using a high fuel supply pressure. Therefore, as shown in FIG. 10, by adjusting the fuel supply pressure so as to increase as the number of revolutions increases, the emission of nitrogen oxides and smoke is reduced without increasing the pumping work of the fuel pump at low revolutions. This makes it possible to improve the efficiency of the engine. FIG.
The change in the fuel supply pressure shown in FIG. 10 and FIG. 10 is an example, and it should be understood that the change should be optimally set according to various characteristics of the engine such as the shape of the fuel injection valve and the combustion chamber.

FIG. 11 shows that when the two-stroke cycle type internal combustion engine according to the embodiment of the present invention realized by the configuration shown in FIG. 1 and FIG. An example in which the operation by the self-ignition combustion is realized up to the load 0 by approaching to the condition shown in FIG. In the example of FIG. 11, under a condition of a load of 25% or more, fuel is injected at a constant injection timing close to the bottom dead center. Under the condition where the load is lower than 25%, as described above, since the fuel is dispersed in a wide range and a lean mixture is formed, stable auto-ignition combustion cannot be obtained. Therefore, by delaying the injection timing to a time close to the top dead center, self-ignition can be generated before the fuel is widely dispersed. Further, under such a low load condition, since the amount of fuel to be supplied is small, even if the self-ignition combustion in which the fuel injection timing is delayed to suppress the dispersion of the fuel is generated, as shown in FIG. The concentration is kept low enough.

When the fuel injection timing is delayed to suppress the dispersion of the fuel, self-ignition is likely to occur, and in addition, a region where the fuel is dense may be locally generated. Therefore,
As shown in FIG. 11, it is possible to make the average air-fuel ratio lean by delaying the injection timing and at the same time increasing the air supply ratio, thereby realizing an appropriate self-ignition timing and reducing the emission of nitrogen oxides.

In adjusting the fuel injection timing, it is important to take into account the outflow of newly supplied fuel into the exhaust passage, which is an essential problem of the two-stroke cycle internal combustion engine, and this is shown in FIGS. The same applies to the case where the two-stroke cycle type internal combustion engine according to the embodiment of the present invention realized by the configuration is operated. FIG. 12 shows an example of the concentration of hydrocarbons in exhaust gas in the two-stroke cycle type internal combustion engine shown in FIGS. 1 and 2 when fuel supply timing is changed from a fuel injection valve arranged in a cylinder. It is. FIG. 12 shows that a large amount of fuel flows into the exhaust passage when fuel is injected between before the exhaust valve opens and near the bottom dead center. From our experiments, it has been found that not injecting fuel at least 20 degrees before bottom dead center is important in reducing the outflow of newly supplied fuel into the exhaust passage.

When an injection valve for directly supplying fuel into a cylinder is used, dividing the fuel injection into a plurality of injections is effective in increasing the distribution of fuel in the cylinder. This is the same when the two-stroke cycle type internal combustion engine according to the embodiment of the present invention realized by the configuration shown in FIGS. 1 and 2 is operated. FIG. 13 is an example showing changes in the self-ignition timing and smoke emission concentration when the number of times of fuel injection is changed at a fuel supply amount corresponding to a load of about 40%. According to FIG. 13, it is shown that by dividing the fuel supply into a large number of times, the timing of occurrence of self-ignition can be delayed, and at the same time, the emission concentration of smoke can be reduced. FIG. 4 shows a result in which the self-ignition timing is delayed and the smoke emission concentration is reduced by increasing the degree of dispersion of the fuel. Therefore, the fuel injection is performed in a plurality of times. This shows that the dispersion of the fuel in the cylinder can be increased.

An effect similar to the effect of increasing the distribution of fuel in the cylinder by dividing the fuel injection into a plurality of injections can also be realized by supplying the fuel from a plurality of injection valves. FIG. 14 shows a configuration example in which two injection valves are provided above the combustion chamber. 14, the same components as those of the embodiment shown in FIG. 2 are denoted by the same reference numerals. In FIG. 14, the second injection valve is arranged at the mounting position 7 of the second electronically controlled fuel injection valve.

The same effect as that obtained by arranging a plurality of fuel injection valves or the same effect as that obtained by injecting fuel in a plurality of injections is obtained by Of course, it can be realized by increasing the number of injection holes. Further, it is obvious that the present invention can also realize the internal combustion engine according to the embodiment by providing a fuel injection valve having a mechanism capable of adjusting the number of injection holes and the injection hole area.

In the embodiment described above, not only the fuel supply amount and the air supply ratio but also at least one of the fuel supply pressure, the fuel injection timing, and the number of fuel injections are changed with respect to the change in the load and the rotation speed. I have. That is, the basic control factors in the two-stroke cycle type internal combustion engine of the present invention realized in the above embodiment include, in addition to the supplied fuel amount and the supply ratio, at least one of the fuel supply pressure, the fuel injection timing, and the number of fuel injections. Will be added. As a control method for operating the engine smoothly by appropriately controlling these three or more basic control factors, a control amount of each basic control factor with respect to the load and the number of revolutions is determined in advance, and this is used as a map. Can be considered.

Therefore, the digital computer 50 shown in FIG. 1 controls the amount of fuel injected from the fuel injection valve and the amount of air supplied by the supercharger with respect to the engine speed and the required load. It is necessary to control at least one of the number of fuel injections.
Here, a specific embodiment will be described for the case where all of the fuel supply pressure, the fuel injection timing, and the number of times of fuel injection are controlled. The number of injections is limited to one or two.

The rotational speed A of the electric motor for driving the supercharger with respect to the engine rotational speed N and the required load L is previously obtained from an experiment and stored in the ROM 52 in the form of a map as shown in FIG. deep. Further, the fuel supply pressure B with respect to the engine speed N and the required load L is previously obtained from an experiment, and FIG.
It is stored in the ROM 52 in the form of a map as shown in FIG. Further, the first fuel injection amount C, the first fuel injection timing D, the second fuel injection amount E, and the second fuel injection timing F are also determined with respect to the engine speed N and the required load L. 14 (C) (D)
(E) The information is stored in the ROM 52 in the form of a map as shown in (F). As a result, an appropriate amount of air is supplied into the cylinder in accordance with the engine speed and the required load, and at the same time, an appropriate amount of fuel is supplied into the cylinder with an appropriate supply pressure at an appropriate time.

The internal combustion engine according to the present invention can be subjected to various changes and modifications without departing from the spirit thereof. For example, it is a matter of course that a different scavenging means such as a crankcase scavenging method and a chenille scavenging method or a uniflow scavenging method can be applied.

[Brief description of the drawings]

FIG. 1 is an overall view of a two-stroke cycle type internal combustion engine claimed by the present invention.

FIG. 2 is a side sectional view of an engine body and an inner view of a cylinder head viewed from a combustion chamber side.

FIG. 3 is a diagram showing the relationship between the emission concentration of nitrogen oxides, the self-ignition timing, and the air-fuel ratio with respect to the degree of dispersion of different sprays.

FIG. 4 is a diagram showing the relationship between the smoke emission concentration, the self-ignition timing, and the air-fuel ratio with respect to the degree of dispersion of different sprays.

FIG. 5 is a diagram showing that a low-dispersion injector that forms a spray with a low degree of dispersion can expand the operating range by auto-ignition combustion at a low load.

FIG. 6 is a diagram showing that the operating range by auto-ignition combustion at a low load can be expanded by lowering the fuel supply pressure to form a spray with a low degree of dispersion.

FIG. 7 is a diagram showing an example of control for increasing a fuel supply pressure with an increase in load.

FIG. 8 is a diagram showing that emission of nitrogen oxides can be reduced at high rotation speeds by increasing the fuel supply pressure.

FIG. 9 is a diagram showing that smoke emission can be reduced by increasing the fuel supply pressure at high revolutions.

FIG. 10 is a diagram showing an example of control for increasing the fuel supply pressure as the engine speed increases.

FIG. 11 is a diagram showing that at a low load, an appropriate self-ignition combustion is realized by bringing the fuel injection timing close to the top dead center and simultaneously increasing the air supply ratio.

FIG. 12 is a diagram showing a fuel injection timing and a concentration of hydrocarbons in exhaust gas.

FIG. 13 is a diagram showing the relationship between the emission concentration of nitrogen oxides, the self-ignition timing, and the air-fuel ratio when the number of times of fuel injection is changed.

FIG. 14 is a side sectional view of an engine main body and an inner view of a cylinder head viewed from a combustion chamber side, showing another embodiment in which two fuel injection valves are arranged in a cylinder.

FIG. 15 shows a map of the rotation speed of the electric motor driving the supercharger, the fuel supply pressure, the fuel injection amount, and the fuel injection timing with respect to the required load and the engine rotation speed.

[Explanation of symbols]

4 ... Piston 5 ... Combustion chamber 6 ... Mounting position of an electronically controlled fuel injection valve that injects fuel directly into the cylinder 15 ... Charge supercharger

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/02 351 F02D 41/02 351 380 380B 41/38 41/38 B F02M 45/02 F02M 45/02 61/14 310 61/14 310U F term (reference) 3G023 AA04 AA05 AA18 AB05 AC05 AD08 AF02 AG02 AG05 3G066 AA07 AA08 AA11 AB02 AD08 AD12 BA14 BA17 BA24 BA25 BA26 CC01 CD26 CD29 DA04 DA09 DC04 DC05 DC09 3G301 HA08 HA03 KA24 KA24 KA25 MA01 MA18 MA26 MA27 MA28 MA29 NC02 NE12 NE14 PA17Z PE01Z PE03Z PF03Z

Claims (8)

[Claims] 1. If a uniform stoichiometric mixture formed by air and fuel is supplied to a cylinder without heating,
The stoichiometric air-fuel mixture has a compression ratio equivalent to self-ignition or knocking, and supplies a fuel amount smaller than the amount of fuel used to form the stoichiometric air-fuel mixture in the cylinder,
And a two-stroke cycle type internal combustion engine having a reciprocating piston that changes at least one of the air amount and the residual gas amount of the cylinder to generate self-ignition of the air-fuel mixture in the cylinder, wherein the fuel amount supplied to the cylinder is And a fuel supply means capable of changing the degree of dispersion. The fuel supply means changes the fuel amount and the degree of dispersion of the fuel supplied into the cylinder, and a wide air-fuel ratio range corresponding to the engine speed and the supplied fuel amount. A self-ignition of the air-fuel mixture in the cylinder. 2. The degree of dispersion of the fuel in order to reduce the degree of dispersion of the fuel in order to advance the ignition timing or to avoid misfiring, to delay the ignition time or to reduce the emission of particulate matter and nitrogen oxides. 2. The internal combustion engine according to claim 1, wherein the internal combustion engine is configured to have a higher pressure. 3. The internal combustion engine according to claim 1, further comprising a fuel injection valve for directly injecting fuel into the cylinder as the fuel supply means. 4. The internal combustion engine according to claim 3, wherein the injection pressure is reduced to reduce the degree of dispersion of the fuel, and the injection pressure is increased to increase the degree of dispersion of the fuel. 5. The particulate matter under high rotation or high load operation conditions by lowering the injection pressure under low rotation or low load operation conditions and increasing the injection pressure under high rotation or high load operation conditions. The internal combustion engine according to claim 3, wherein the work of the injection pump under low rotation or low load operating conditions is reduced while reducing the emission of nitrogen oxides. 6. The fuel injection system according to claim 3, wherein the degree of dispersion of the fuel is reduced by bringing the injection timing closer to the top dead center, and the degree of dispersion of the fuel is increased by lengthening the period between the injection timing and the ignition. Internal combustion engine. 7. The internal combustion engine according to claim 3, wherein fuel is supplied two or more times or two or more times from an injection hole of the fuel injection valve to increase the degree of dispersion of the fuel. 8. In a process in which the volume of the combustion chamber continues to increase, and at 20 degrees before the bottom dead center, the fuel supplied to the cylinder without supplying the fuel is prevented from flowing into the exhaust passage. The internal combustion engine according to claim 3.