JP5347449B2 - Compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to premixed compression ignition combustion, particularly to a compression ignition internal combustion engine that performs compression ignition combustion by directly injecting two types of fuels having different octane numbers into a cylinder.

Patent Document 1 discloses an internal combustion engine in which a low-octane fuel and a high-octane fuel are individually injected into a cylinder. Here, fuels having different octane numbers are injected from the two fuel injection valves so that they do not substantially overlap with each other, so that an air-fuel mixture field having a uniform fuel concentration and an octane number distribution is formed. This achieves compression ignition combustion in a wide operating range.
JP-A-2005-139945

  However, in the technique of the above-described Patent Document 1, two fuels can be distributed separately, but a mixed fuel distribution having an intermediate octane number cannot be formed, so that an applicable operation range is limited. That is, in Patent Document 1, it is disclosed that the supply ratio of the low octane fuel and the low octane fuel is controlled so as to reduce the low octane fuel as the load increases, but the two fuels are not mixed. When the amount of high-octane fuel is increased as the load is increased, the high-octane fuel ignited by the low-octane fuel is ignited all at once, resulting in sharp combustion in the second half of combustion and excessive combustion noise. Further, if the low octane fuel is excessively increased with the increase in load, the low octane fuel is ignited all at once, and the first half of the combustion becomes steep combustion.

  Therefore, the present invention controls the interference state of each fuel in a cylinder in a direct-injection compression ignition internal combustion engine that directly injects a low-octane fuel and a high-octane fuel into the cylinder and performs compression self-ignition. By changing the ratio of the amount of fuel having an inherent octane number distributed without mixing with each other and the amount of fuel having an intermediate octane number generated by mixing of injected fuels according to the engine operating state, In addition, the fuel was ignited all at once and the generation of heat was prevented from becoming steep.

  That is, the fuel having a low octane number is ignited promptly after injection because the so-called ignition delay period is short after the fuel injection. On the other hand, high-octane fuel has a long ignition delay period. In general, when two octane fuels are mixed, the octane number of the mixed fuel is an octane number intermediate between the octane numbers of the two fuels. This intermediate octane fuel has an intermediate ignition delay period. Therefore, if there is an appropriate distribution in the octane number of the fuel distributed in the cylinder, a phase difference can be generated at the ignition start timing, and the combustion period can be adjusted.

  On the other hand, the fuel ignition delay period is also affected by the fuel concentration. That is, in the air-fuel mixture having a low concentration, the ignition delay period is longer than that in the air-fuel mixture having a relatively high concentration. In the case of a compression ignition internal combustion engine that starts combustion using a low-octane fuel as an ignition source, when the low-octane fuel is mixed with a high-octane fuel at a low engine load with a small amount of fuel to be injected, the octane number increases. The ignition delay becomes too long, and there is a high possibility of causing a combustion fluctuation due to misfire or instability of the ignition timing. At low engine loads, the amount of high-octane fuel is small, so even if the high-octane fuel is ignited all at once, it will not hinder operability.

  Therefore, when the engine load is low, it is desirable that fuels having different octane numbers are distributed without being mixed to realize reliable ignition with the low octane fuel. It is desirable to generate an appropriate octane number distribution by distributing an air-fuel mixture having an intermediate octane number mixed with the increase in engine load, thereby realizing combustion in an appropriate period.

  Since the low-octane fuel has a short ignition delay period, the compression ignition timing in the combustion chamber is substantially controlled by the low-octane fuel injection timing.

  As one of means for controlling the generation of intermediate octane fuel, that is, the interference state of each fuel in the cylinder, it is possible to adjust each injection timing in order to adjust the relative position of the fuel spray. is there. For example, at low engine load, the injection timing of two fuels with different octane numbers is brought close to the compression top dead center, and the interval between the injection timings is narrowed so that different fuels are ignited before they are widely distributed in the cylinder. Prevents fluctuations (increase / decrease) in octane number due to mixing. On the other hand, as the engine load increases, among the injection timings of two fuels having different octane numbers, at least the injection timing of the high octane fuel to be injected first is advanced, and the interval between the two injection timings is widened. A low-octane fuel is allowed to pass through a high-octane fuel that is relatively widely distributed in the cylinder, and an intermediate-octane fuel mixture is generated by mixing the fuel.

  In addition, in order to control the interference state of each fuel in the cylinder, means for variably controlling the intensity of gas flow (for example, swirl or tumble) in the cylinder can be used. For example, at a low engine load, by increasing the gas flow, the previously injected high-octane fuel is distributed at a position different from the injection direction when the gas flow is weak, and then the low-octane fuel is injected. . Since the low-octane fuel has a short ignition delay period, the distribution position in the cylinder does not vary greatly due to the influence of flow. In contrast, high-octane fuel with a long ignition delay period is susceptible to gas flow. For example, by setting the directing direction of each fuel spray so that they can easily generate an intermediate octane number when the gas flow strength is weak, the mixing of the intermediate octane numbers depends on the gas flow strength in the cylinder. It is possible to adjust the gas generation amount.

  As described above, it is possible to reduce the amount of fuel with an intermediate octane number in the low load region of the engine and to increase the amount of fuel with an intermediate octane number in the high load region. From the viewpoint of optimization of the combustion period in the high load range. In particular, in a low load region below a predetermined load, in order to perform reliable ignition, the octane number of the low octane number fuel actually distributed in the cylinder is the unique octane number of the low octane number fuel supplied to the fuel injection valve. That is, the lowest octane number that can be supplied is desirable.

  According to the present invention, the distribution of the octane number of the fuel in the combustion chamber can be made suitable for the operating state of the engine, and, for example, reliable ignition can be performed in a low load region and steep in a high load region. Generation of heat can be avoided and combustion noise can be suppressed.

  FIG. 1 shows a first embodiment of a compression ignition internal combustion engine according to the present invention. A combustion chamber 4 is formed by a cylinder head 1, a cylinder block 2 and a piston 3. The combustion chamber 4 communicates with the intake port 6 via the intake valve 5 and communicates with the exhaust port 9 via the exhaust valve 7. The intake valve 5 and the exhaust valve 7 are opened and closed by an intake valve cam 10 and an exhaust valve cam 11, respectively. Two fuel injection valves, that is, a low-octane fuel injection valve 15 and a high-octane fuel injection valve 16 are arranged side by side in the center of the upper surface of the combustion chamber 4.

  Each of the fuel injection valves 15 and 16 is individually supplied with a low-octane fuel and a low-octane fuel via separate fuel pipes and a fuel pump (not shown). Opposite these fuel injection valves 15, 16, the central part of the piston 3 has an appropriate center so that a stratified mixture can be formed by receiving the fuel injected from the high-octane fuel injection valve 16. A shaped cavity 17 is provided. Both of these two fuel injection valves 15 and 16 form a conical spray centered on the cylinder center axis, but the high-octane fuel injection valve 16 injects fuel into the cavity 17. Thus, the fuel injection valve 15 for low-octane fuel is configured to have a wide spray angle so as to inject fuel outside the high-octane fuel spray. The fuel injection valves 15 and 16 are usually multi-hole fuel injection valves that form a conical spray as a whole. However, the present invention is not necessarily limited to this, and a single hole that forms a conical spray is used. It may be that of a nozzle hole.

  Next, the operation of the above configuration will be described. FIG. 3 shows the fuel injection timing (injection period) of the fuel injection valves 15 and 16 with the horizontal axis as the engine load and the vertical axis as the crank angle. FIG. 2 is an explanatory view schematically showing the fuel distribution realized by such fuel injection for three cases of low load, medium load, and high load.

  First, FIG. 2 will be described. For example, when the load is low, it changes as (a1) → (a2) → (a3) in the figure. The high-octane fuel F1 (in the figure, the high-octane fuel region or spray is indicated by dots) is injected from the fuel injection valve 16 with a narrow spray angle, but is injected toward the cavity 17 in the latter half of the compression stroke. After the fuel F <b> 1 collides with the bottom surface of the cavity 17, the fuel F <b> 1 moves toward the outer periphery of the cavity 17 and jumps up above the combustion chamber 4.

  Under a low engine load, before the high-octane fuel F1 is rolled up from the cavity 17, the low-octane fuel F2 (in the figure, the low-octane fuel region or spray is shown by cross-hatching) is injected toward the periphery of the cylinder. Is done. Therefore, the low-octane fuel F2 does not interfere with the high-octane fuel F1 and goes to the piston crown surface area outside the cavity 17, and the high-octane fuel and the low-octane fuel are placed in the cylinder as shown in FIG. Each can be distributed with little mixing.

  On the other hand, when the engine load increases and becomes a medium load, the high octane fuel F1 is injected toward the cavity 17 in the latter half of the compression stroke as in the case of the low load. However, as shown in FIG. The low-octane fuel F2 is injected after or immediately before F1 winds up from the cavity 17 to the spray axis (height position) of the fuel injection valve 15 for low-octane fuel. As a result, the low-octane fuel F2 goes to the area outside the cavity 17 while interfering with the high-octane fuel F1, and the high-octane fuel and the low-octane fuel both having a unique octane number locally in the cylinder. A fuel having an intermediate octane number can be distributed.

  When the engine load further increases and becomes a high load region, the high octane fuel F1 is supplied from the high octane fuel injection valve 16 in the first half of the intake stroke or the compression stroke so that the high octane fuel F1 is distributed outside the cavity 17. Be injected. As a result, the high-octane fuel is widely distributed in the combustion chamber 4, and in this state, the low-octane fuel F2 is injected in the second half of the compression stroke. Accordingly, the low-octane fuel is mixed with the high-octane fuel immediately after injection, and the fuel having the intermediate octane number occupies most of the fuel in the combustion chamber 4. In FIG. (C3) and the like, the low octane number fuel F2 is drawn as if it occupies an independent region due to the limitation on the notation, but in reality, it is quickly mixed. Thus, even if the fuel has only an intermediate octane number, the equivalence ratio in the cylinder is large in the high load region, and the ignitability by the low octane number fuel is good, so the ignitability is not deteriorated.

  In any load, the low octane number fuel F2 is injected toward the cylinder bore and the ignition starts with the spray of the low octane number fuel F2 as the center. Therefore, it is possible to suppress the phenomenon that unburned fuel enters the piston clevis and is discharged as unburned HC by the expansion action due to combustion.

  More specifically, the fuel injection timing from each of the fuel injection valves 15 and 16 is controlled as shown in FIG.

  First, since the low-octane fuel is injected for the purpose of starting combustion by self-ignition of itself, the injection timing is set near the compression top dead center. In the sections A and B on the low load side, the low octane number fuel injection end timing is set so as to appropriately distribute the fuel at the time of ignition with respect to the increase in load (so as not to spread too much at the ignition timing and misfire). The injection amount is increased by advancing the low-octane fuel injection start timing while keeping it constant. However, the injection amount is constant in the sections C to E where the load is a certain value or more. This is because an increase in the injection amount requires an advance in the injection timing and an increase in the injection pressure, so that the penetrating force of the low-octane fuel is excessive and prevents the cylinder bore from hitting directly.

  On the other hand, the high-octane fuel is injected before the low-octane fuel. In the section A below the predetermined engine load, the fuel injection amount is increased by advancing the injection start timing and retarding the injection end timing with respect to the load increase. The broken line S1 indicates the time when the high octane fuel collides with the piston 3 and reaches the spray axis of the fuel injection valve 15 for low octane fuel, and this time S1 is after the injection end time of the low octane fuel. In this way, interference between the two is avoided. Even when the injection start timing and the injection end timing are as indicated by broken lines S2 and S3, the timing when the high octane number fuel collides with the piston 3 and reaches the spray axis of the fuel injection valve 15 for low octane number fuel (indicated by the broken line S4). Is after the injection end timing of the low-octane fuel, but in order to ensure the ignitability of the low-octane fuel on the low load side, the characteristics shown by the solid line are better than those of the high-octane fuel. The risk of mixing is small and more preferable.

  Further, in the sections B and C above the predetermined load, the fuel injection amount is increased by advancing the injection start timing. The characteristic of the broken line S1 is determined by the injection start timing of the high octane fuel, and the degree of mixing is adjusted by adjusting the time of the broken line S1 and the amount of low octane fuel injected after the time of the broken line S1. The The injection end timing does not advance with respect to the load increase, but does advance at a constant or moderate speed in order to prevent the air-fuel mixture in the cavity 17 from becoming excessively rich at the ignition timing. In the sections D and E on the higher load side, the fuel injection timing is set to the intake stroke or the first half of the compression stroke in order to avoid the excessive air-fuel mixture in the cavity 17.

  Next, FIG. 4 shows a second embodiment in which a swirl is used to more actively control the interference state of fuel sprays having different octane numbers, and the strength of the swirl is made variable at the intake port 6. A swirl control valve 21 for control is provided. The swirl control valve 21 has a general configuration in which a part of a butterfly valve type valve body is provided with a notch, and generates a swirl in a cylinder by being in a closed position in a predetermined load region. Can do. The two fuel injection valves 15 and 16 are multi-hole fuel injection valves, both of which form a conical spray centered on the cylinder center axis as a whole. The fuel injection valve 16 for high octane fuel is configured to have a narrow spray angle so as to inject fuel into the cavity 17, and the fuel injection valve 15 for low octane fuel injects fuel outside the spray of high octane fuel. The spray angle is configured to be wide. Further, as shown in FIG. 5, the sprays of the individual nozzle holes are sprayed F2 of the fuel injection valve 15 for the low octane fuel and the spray F1 of the fuel injection valve 16 for the high octane fuel when viewed from the cylinder axial direction. However, the spray direction is almost the same.

  FIG. 6 is an explanatory diagram for explaining the mixing of the spray in the second embodiment. In the low load region shown in FIG. 6 (a), the swirl control valve 21 increases the strength of the swirl. When the spray F1 ′ of the high octane fuel injected into the nozzle jumps up in the cavity 17 and rises like the fuel block F1, it moves downstream of the swirl. Accordingly, the low-octane fuel spray F2 injected with a delay does not overlap with the cylinder axis direction, and mixing of both is suppressed.

  On the other hand, in the high load region, the swirl strength is weakened or swirl is not applied as shown in FIG. Therefore, the fuel block F1 of the high-octane fuel injected earlier and the spray F2 of the low-octane fuel interfere with each other, and an intermediate octane fuel is generated.

  In the second embodiment, the fuel injection timing from the fuel injection valves 15 and 16 is controlled as shown in FIG. The basic concept of this injection timing control is the same as in the first embodiment, but since the mixing of two fuels can be suppressed by swirl on the low load side, the injection timing of the high octane fuel is more advanced. Can be set. Therefore, when increasing the injection amount of the high octane fuel with respect to the increase in load, only the advance angle of the injection start timing may be used.

  In the first and second embodiments described above, the two fuel injection valves 15 and 16 do not have to be completely separated and independent, and are substantially integrated so that two fuels can be injected. It is also possible to provide a fuel injection valve having the structure described above.

FIG. 2 is a configuration explanatory diagram of the first embodiment. Explanatory drawing which shows the state of the mixing of the fuel according to the load in this 1st Example. The characteristic view which shows the fuel-injection time of each fuel-injection valve. Structure explanatory drawing of 2nd Example. Explanatory drawing which shows the direction of spray of each fuel injection valve. Explanatory drawing which shows the state of the mixing of the spray in this 2nd Example. The characteristic view which shows the injection timing of each fuel injection valve of 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Piston 4 ... Combustion chamber 15 ... Fuel injection valve for low octane fuel 16 ... Fuel injection valve for high octane fuel 17 ... Cavity 21 ... Swirl control valve

Claims (3)

In-cylinder direct injection type compression ignition internal combustion engine that directly injects low octane number fuel and high octane number fuel into the cylinder and performs compression self-ignition,
Two fuel injection valves for respectively injecting low octane number fuel and high octane number fuel are arranged in the center of the combustion chamber, and have a cavity in the center of the piston crown surface,
The fuel injection valve for high octane fuel is configured to have a narrow spray angle so that fuel is injected toward the cavity, and the fuel injection valve for low octane fuel is designed to inject fuel outside the spray of high octane fuel. The spray angle is widely configured,
While injecting low octane fuel near compression top dead center,
In the low load range below the predetermined load, high octane fuel that is wound up from the cavity is injected in the second half of the compression stroke toward the cavity and the low octane fuel with the inherent octane number is distributed without mixing. And set the injection timing at the time when there is no interference with the low-octane fuel,
In a low load or medium load range that is larger than the predetermined load, high octane fuel is injected into the cavity in the latter half of the compression stroke, and has a unique octane number locally in the cylinder, as well as between low octane fuel and low octane fuel. Each injection timing is set at the time when the interference between the high octane fuel and the low octane fuel that are wound up from the cavity occurs so that the mixed fuel having the octane number of
A compression ignition internal combustion engine characterized by injecting high-octane fuel in the first half of the intake stroke or compression stroke so that the low-octane fuel is injected into the high-octane fuel widely distributed in the cylinder in the high load range . 2. The compression ignition internal combustion engine according to claim 1, further comprising means for variably controlling the intensity of gas flow in the cylinder, and controlling an interference state of both fuels in the cylinder by the intensity of the gas flow. The means for variably controlling the gas flow intensity is a swirl control valve,
  The direction of spraying of the fuel injection valve for high octane fuel and the fuel injection valve for low octane fuel consisting of multi-hole type fuel injection valves is set in substantially the same direction when viewed in the cylinder axis direction,
  By increasing the swirl strength in the low load range, the spray direction of the high-octane fuel that jumped up in the cavity does not overlap with the spray direction of the low-octane fuel as seen in the axial direction.
  The compression ignition internal combustion engine according to claim 2, wherein the swirl strength is relatively weakened in a high load range so that both sprays overlap each other when viewed in the axial direction.

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