JP2007255390A - Premixed compression ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a premixed compression ignition internal combustion engine capable of surely suppressing the discharge of nitrogen oxide, hydrocarbon, and carbon monoxide. <P>SOLUTION: This internal combustion engine comprises a mixture jetting injector 10 for jetting a mixture into a combustion chamber 5 and an injection timing control means 12 for so controlling injection timing for the mixture that an air-fuel ratio at the center 18 of the combustion chamber 5 is equal to a predetermined value, for example, 25 to 30. The engine further comprises a premixing chamber 11 for forming the mixture, fuel supply injectors 13, 14, and fuel supply amount control means 16, 17 for controlling the supply amount of fuel. The fuel supply amount control means 16, 17 increase the supply amount of fuel with high octane number under high load, and increase the supply amount of fuel with low octane number under low load. The engine further comprises a mixture injection control means for jetting the mixture into the combustion chamber 5 by controlling the injection timing of the mixture by the injection timing control means 12, the ratio of the supply amounts of fuel by the fuel supply amount control means 16, 17, and the premixed air amount in the premixing chamber 11 independently for each cycle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a premixed compression ignition internal combustion engine.

  In recent years, compression ignition internal combustion engines represented by premixed compression ignition internal combustion engines have been studied in order to reduce fuel consumption and emissions of the internal combustion engine. The premixed compression ignition internal combustion engine compresses and self-ignites a mixture of fuel and air in a combustion chamber of the internal combustion engine.

  However, the premixed compression ignition internal combustion engine is likely to knock when the required load of the engine becomes high when fuel with a low octane number is used, and when the required load becomes low when fuel with a high octane number is used. Since it is easy to misfire, there exists a problem that the driving | operation area | region which can be drive | operated stably is narrow.

  In order to solve the above problem, conventionally, a technique for injecting two types of fuel, a low octane fuel and a high octane fuel, into the combustion chamber independently to form the air-fuel mixture in advance in the combustion chamber. Is known (see, for example, Patent Document 1). According to the technique, in the premixed compression ignition internal combustion engine, it is possible to adjust the octane number of the air-fuel mixture by properly using the two fuels according to the required load or by changing the ratio of the supply amounts of the two fuels. It can be operated stably over a wide range of required loads.

  However, in the above technique, there is a region where the fuel concentration is locally high, and in this region, the combustion rate increases and the temperature becomes very high, so that the amount of nitrogen oxide (NOx) emissions increases. There's a problem. Moreover, in the said area | region, since the fuel heated without being able to contact air increases, there also exists a problem that discharge | emission amount of unburned gas, such as hydrocarbon (HC) and carbon monoxide (CO), increases.

  Therefore, when two types of fuel, a low octane number fuel and a high octane number fuel, are independently injected into the combustion chamber, the two fuels are injected so that they do not substantially overlap each other in the combustion chamber. A technique has been proposed (see Patent Document 2). According to the technique, since the two fuels do not overlap each other in the combustion chamber, the fuel is prevented from locally becoming a high concentration, and emission of nitrogen oxides, hydrocarbons, carbon monoxide, etc. is suppressed. It is supposed to be possible.

However, even if fuel injection is performed so that a fuel having a low octane number and a fuel having a high octane number do not substantially overlap each other in the combustion chamber, in some cases, emissions of nitrogen oxides, hydrocarbons, carbon monoxide, etc. There is a disadvantage that it cannot be suppressed.
JP 2001-5070 A JP-A-2005-139945 JP 2002-339838 A

  An object of the present invention is to provide a premixed compression ignition internal combustion engine that can eliminate such inconveniences and reliably suppress emission of nitrogen oxides, hydrocarbons, carbon monoxide, and the like.

  The present inventors have repeatedly studied the inconvenience in a premixed compression ignition internal combustion engine. As a result, when the present inventors directly inject fuel into the combustion chamber of the internal combustion engine and mix the fuel with air in the combustion chamber to form an air-fuel mixture, the phantom line in FIG. As shown in the figure, it has been found that a region where the air-fuel ratio is locally small in the central portion along the axial direction of the combustion chamber, in other words, a region where the fuel concentration is high, is easily formed. In the region where the concentration of the fuel is high, the combustion rate is increased and the temperature becomes very high as described above, and thus an increase in the emission amount of nitrogen oxides is inevitable.

  Further, in the premixed compression ignition internal combustion engine, the compression pressure is high, and the heat transfer coefficient on the wall surface of the combustion chamber is increased, so that heat release is large, the combustion temperature is lowered, and hydrocarbons, carbon monoxide, etc. Gas emissions are expected to increase.

  The present invention is based on the above knowledge, and in order to achieve the above object, in a premixed compression ignition internal combustion engine in which a mixture of fuel and air is compressed and self-ignited in a combustion chamber of the internal combustion engine. An air-fuel ratio injector that injects a mixture of fuel and air into the combustion chamber, and an air-fuel ratio at a central portion within 50% of the diameter of the combustion chamber along the axial direction of the combustion chamber; For example, an injection timing control means for controlling the injection timing of the air-fuel mixture so as to have a value in the range of 25-30. In the present specification, the air-fuel ratio is indicated by the weight ratio of air and fuel (air / fuel).

  In the premixed compression ignition internal combustion engine of the present invention, the preformed mixture is injected into a combustion chamber by the mixture injection injector, and the injection timing of the mixture is controlled by the injection timing control means. The air-fuel ratio is set to a predetermined value, for example, a value in the range of 25 to 30, at a central portion along the axial direction of the combustion chamber, that is, around the central axis of the combustion chamber and within 50% of the diameter. If it does in this way, it can prevent that a fuel becomes high concentration in the said center part of the said combustion part, and can suppress discharge | emission of nitrogen oxide reliably.

  When the value of the air-fuel ratio in the central portion of the combustion chamber is 25 or less, the fuel becomes high in concentration, and nitrogen oxide emissions may not be sufficiently suppressed. Further, unlike the spark ignition type internal combustion engine, the premixed compression ignition internal combustion engine does not require the fuel concentration in the vicinity of the spark plug to be the stoichiometric air-fuel ratio, but if the air-fuel ratio exceeds 30, the premixed compression ignition internal combustion engine You may not be able to take full advantage of.

  Further, according to the premixed compression ignition internal combustion engine of the present invention, the air-fuel ratio in the central portion of the combustion portion is set to the predetermined value, so that air is relatively disposed in an outer peripheral region of the central portion. A region having a high concentration is formed. As a result, a heat insulating effect is obtained by the region having a high air concentration, and heat radiation from the wall surface of the combustion chamber is reduced, so that it is possible to reliably suppress discharge of unburned gases such as hydrocarbons and carbon monoxide. it can.

  In addition, the technique itself which injects the said air-fuel mixture formed beforehand to a combustion chamber by the said air-fuel mixture injector is well-known (for example, refer patent document 3).

  In the premixed compression ignition internal combustion engine of the present invention, the previously formed mixture is injected into a combustion chamber by the mixture injection injector. Therefore, the premixed compression ignition internal combustion engine of the present invention independently supplies a premixing chamber for forming the mixture to be introduced into the mixture injector and two fuels having different octane numbers to the premixing chamber. The first fuel supply injector, the second fuel supply injector, and the amount of fuel supplied from each fuel supply injector are controlled so that the octane number and the calorific value of the air-fuel mixture formed in the premixing chamber are It is preferable to provide a fuel supply amount control means for adjusting

  Further, when the premixed compression ignition internal combustion engine of the present invention has the above-described configuration, the fuel supply amount control means supplies the fuel supply amount having a relatively high octane number to the fuel supply having a relatively low octane number at a high load. It is preferable that the amount of fuel supplied with a relatively low octane number be larger than the amount of fuel supplied with a relatively high octane number when the load is low. By doing so, the premixed compression ignition internal combustion engine of the present invention can prevent knocking at high load and misfire at low load, and can operate stably over a wide range of required loads. Can do.

  Furthermore, the premixed compression ignition internal combustion engine of the present invention includes an injection timing of the air-fuel mixture by the injection timing control means, a ratio of two fuel supply amounts having different octane numbers by the fuel supply amount control means, It is preferable that an air-fuel mixture injection control means for injecting the air-fuel mixture into the combustion chamber by independently controlling the amount of air mixture in the mixing chamber for each cycle.

  The premixed compression ignition internal combustion engine of the present invention can be precisely controlled by providing the mixture injection control means, and can more reliably suppress emissions of nitrogen oxides, hydrocarbons, carbon monoxide, and the like. it can.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory sectional view showing the configuration of the premixed compression ignition internal combustion engine of the present embodiment, and FIG. 2 is a graph showing the air-fuel ratio distribution in the combustion chamber of the premixed compression ignition internal combustion engine shown in FIG.

  As shown in FIG. 1, a premixed compression ignition internal combustion engine 1 of the present embodiment includes a hollow cylindrical cylinder 2, a piston 3 that is provided in the cylinder 2 and slides up and down in the cylinder 2, and The combustion chamber 5 is formed by a space surrounded by the cylinder 2, the piston 3, and the cylinder head 4. The cylinder head 4 includes an intake port 6 and an exhaust port 7 that communicate with the combustion chamber 5, an intake valve 8 that opens and closes the intake port 6, and an exhaust valve 9 that opens and closes the exhaust port 7. An air-fuel mixture injector 10 that injects an air-fuel mixture comprising fuel and air along an axis, and a premixing chamber 11 that forms an air-fuel mixture supplied to the air-fuel mixture injector 10 are provided. The air-fuel mixture injector 10 is provided with an injection timing control device 12 that controls the injection timing of the air-fuel mixture.

  Further, the cylinder head 4 includes a first fuel supply injector 13 that injects low octane fuel into the premixing chamber 11, a second fuel supply injector 14 that injects high octane fuel into the premixing chamber 11, a fuel supply injector 13, 14 and a compressed air conduit 15 for mixing air with fuel injected from the fuel. The fuel supply injectors 12 and 13 are respectively provided with fuel supply amount control devices 16 and 17, and the compressed air conduit 15 is connected to a compressed air source (not shown).

  The injection timing control device 12 and the fuel supply amount control devices 16 and 17 are controlled corresponding to the required load of the premixed compression ignition internal combustion engine 1 by an engine control unit (ECU) (not shown). .

  Next, the operation of the premixed compression ignition internal combustion engine 1 of the present embodiment will be described.

  In the premixed compression ignition internal combustion engine 1, first, low octane fuel is injected from the first fuel supply injector 13 and high octane fuel is injected from the second fuel supply injector 14 into the premixing chamber 11. Simultaneously with fuel injection, compressed air is supplied from the compressed air conduit 15 to the premixing chamber 11 and mixed with the fuel to form the air-fuel mixture.

  Examples of the low octane fuel include naphtha and diethyl ether, and examples of the high octane fuel include gasoline and ethanol. The compressed air is supplied to the premixing chamber 11 at a pressure of 500 to 800 kPa, for example.

  The amount of fuel injected from the fuel supply injectors 13 and 14 is controlled by the ECU via the fuel supply amount control devices 16 and 17, and the octane number and the calorific value corresponding to the required load of the premixed compression ignition internal combustion engine 1 are obtained. The air-fuel mixture provided is formed. In the premixing chamber 11, the air-fuel ratio is set to about 0.1 to 3, for example.

  Next, the air-fuel mixture is supplied to the air-fuel mixture injector 10 and injected into the combustion chamber 5 at the injection timing controlled by the ECU via the injection timing control device 12. Since the air-fuel mixture injector 10 injects the air-fuel mixture along the central axis of the combustion chamber 5, as shown by a solid line in FIG. The air-fuel ratio is in the range of 25-30. The central portion 18 is a region within 50% of the diameter of the combustion chamber 5 around the central axis of the combustion chamber 5.

  At this time, since there is air introduced from the intake port 6 in the combustion chamber 5, a region having a relatively high air concentration is formed in the outer peripheral side portion 19 of the center portion 18. That is, in the combustion chamber 5, there are two regions, a region where the air-fuel ratio of the central portion 18 is substantially constant in the range of 25 to 30 and a region of the outer peripheral side portion 19 where the air concentration is relatively high. Forms a layer.

  Next, the piston 3 rises and the air-fuel mixture in the combustion chamber 5 is compressed, and the air-fuel mixture self-ignites near the top dead center of the piston 3. At this time, since the air-fuel ratio is in the range of 25 to 30 around the central axis of the combustion chamber 5 and within 50% of the diameter of the combustion chamber 5, an excessively high temperature is generated with combustion. In this case, the emission of nitrogen oxides can be suppressed. Further, since a region with high air concentration is formed on the outer peripheral side of the region of the air-fuel ratio 25-30, heat radiation from the wall surface (cylinder 2) of the combustion chamber 5 is reduced by the heat insulating action by air. , Emissions of unburned gases such as hydrocarbons and carbon monoxide can be suppressed.

  Further, in the premixed compression ignition internal combustion engine 1, the ratio of the supply amount of the low octane number fuel and the high octane number fuel by the fuel supply amount control devices 16 and 17 is increased. Control is performed to increase the amount of low-octane fuel supplied during loading. By doing so, the premixed compression ignition internal combustion engine 1 can prevent both occurrence of knocking at the time of high load and misfire at the time of low load, and can stably operate for a wide range of required loads. can do.

  In the premixed compression ignition internal combustion engine 1, the ECU is used as a mixture injection control means, and the injection timing of the mixture by the mixture injector 10, the low-octane fuel and the high-octane fuel by the fuel supply amount control devices 16, 17 are high. You may make it control independently the ratio of the supply amount with an octane number fuel, and the amount of mixed air in the premixing chamber 11 for every cycle.

  The control of the ECU as the air-fuel mixture injection control means includes, for example, a region where the octane number of the air-fuel mixture in the combustion chamber 5 is low and the air-fuel ratio of the central portion 18 is substantially constant, The formation of the layer with the two regions of 19 relatively high air concentration regions becomes clear, and the air-fuel ratio of the central portion 18 is moderate, for example, within the range of 25-30. When the load is high, the octane number of the air-fuel mixture in the combustion chamber 5 is high, the air-fuel ratio of the central portion 18 is substantially constant, and the region of the outer peripheral side portion 19 where the air concentration is relatively high. The formation of the layer with the two regions is loosened, and the air-fuel ratio of the central portion 18 is moderate, for example, in the range of 24-30.

  By doing so, in the premixed compression ignition internal combustion engine 1, it becomes possible to perform precise control corresponding to the operating state and the required load, and the emission of nitrogen oxides, hydrocarbons, carbon monoxide and the like is further reliably suppressed. can do.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory sectional drawing which shows one structural example of the premixed compression ignition internal combustion engine which concerns on this invention. The graph which shows the air fuel ratio distribution in the combustion chamber of the premixed compression ignition internal combustion engine shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Premix compression ignition internal combustion engine, 5 ... Combustion chamber, 10 ... Mixture injection injector, 11 ... Premix chamber, 12 ... Injection timing control means, 13 ... 1st fuel supply injector, 14 ... 2nd fuel supply Injector 16, 17, ... fuel supply amount control means.

Claims (4)

In a premixed compression ignition internal combustion engine in which a mixture of fuel and air is compressed and self-ignited in a combustion chamber of the internal combustion engine.
An air-fuel mixture injector for injecting an air-fuel mixture comprising fuel and air into the combustion chamber;
Injection timing control means for controlling the injection timing of the air-fuel mixture so that the air-fuel ratio (weight ratio) at the central portion within 50% of the diameter of the combustion chamber becomes a predetermined value along the axial direction of the combustion chamber And a premixed compression ignition internal combustion engine.   2. The premixed compression ignition according to claim 1, wherein the injection timing control means controls the injection timing of the air-fuel mixture so that the air-fuel ratio at the center is in a range of 25-30. Internal combustion engine. A premixing chamber for forming the air-fuel mixture introduced into the air-fuel mixture injector;
A first fuel supply injector and a second fuel supply injector for independently supplying two fuels having different octane numbers to the premixing chamber;
Fuel supply amount control means for controlling the amount of fuel supplied from each fuel supply injector to adjust the octane number and heat generation amount of the air-fuel mixture formed in the premixing chamber;
The fuel supply amount control means increases the supply amount of the fuel having a relatively high octane number at the time of high load than the supply amount of the fuel having a relatively low octane number, and supplies the fuel having a relatively low octane number at the time of low load. The premixed compression ignition internal combustion engine according to claim 1 or 2, wherein the amount of fuel is made larger than a supply amount of fuel having a relatively high octane number.   The injection timing of the air-fuel mixture by the injection timing control means, the ratio of the two fuel supply amounts having different octane numbers by the fuel supply amount control means, and the amount of air mixture in the premixing chamber are independent for each cycle. 4. The premixed compression ignition internal combustion engine according to claim 3, further comprising a mixture injection control means for controlling the injection to the combustion chamber and injecting the mixture into the combustion chamber.

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