JP5239923B2 - 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, it is difficult to achieve good compression ignition combustion in a wide operating range from low load to high load while suppressing combustion noise.

  The present invention relates to an in-cylinder direct injection type compression ignition internal combustion engine that directly injects a low octane fuel and a high octane fuel into a cylinder, and injects the low octane fuel and the high octane fuel respectively. The fuel injection valve is disposed in the center of the combustion chamber and has a cavity in the center of the piston crown surface, and one fuel injection valve injects fuel toward the cavity at least in the latter half of the compression stroke. The spray angle is narrower than that of the other fuel injection valve.

  By injecting fuel from one fuel injection valve having a narrow spray angle toward the cavity, fuel having a specific octane number injected from the one fuel injection valve is distributed in the cavity. On the other hand, outside the cavity, the fuel has a specific octane number injected from the other fuel injection valve with a wide spray angle, or has an intermediate octane number generated by mixing the fuel injected from both fuel injection valves. A concentric octane number distribution in which fuels are distributed and fuels having different octane numbers in the radial direction are distributed can be formed.

  Here, 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, as described above, a concentric octane number distribution in which the octane number changes in the radial direction in the cylinder is formed, and the mixing and interference state of the low octane number fuel and the high octane number fuel are made appropriate, so that the intermediate octane number For example, a fuel having a low octane number on the outer peripheral side of the cylinder, a fuel having a high octane number on the inner peripheral side, and a fuel having an intermediate octane number in the middle while suppressing the combustion noise due to steep combustion. By distributing in a concentric manner, combustion proceeds from the outer peripheral side of the cylinder to the inner peripheral side, suppressing the unburned fuel component remaining in the piston clevis portion etc. near the cylinder wall surface, and discharging the unburned fuel component. Can be suppressed.

  As described above, according to the present invention, by making the distribution of the octane number of the fuel in the combustion chamber appropriate, it is possible to suppress combustion noise and suppress discharge of unburned fuel components.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the compression ignition internal combustion engine which concerns on one Example of this invention. Explanatory drawing which shows the setting in the low load area | region of the said Example. Explanatory drawing which shows an example of the setting in the high load area | region of the said Example. Explanatory drawing which shows the other example of the setting in the high load area | region of the said Example. Explanatory drawing which shows typically the octane number distribution in the low-medium load (A) of the said Example, medium load (B), and medium-high load (C).

  FIG. 1 shows an embodiment of a compression ignition internal combustion engine according to the present invention. A combustion chamber 4 is formed in the cylinder 1 </ b> A by the cylinder head 2, the cylinder block 1, and the 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. The cylinder block 1 is formed with a water jacket 12 through which cooling water flows around the cylinder 1A. 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, a cavity 17 is formed at the center of the crown surface of the piston 3 so as to receive the fuel injected from the high-octane fuel injection valve 16 and form a stratified mixture. Is provided. The cavity 17 has a bottom surface 17A parallel to the piston crown surface 3A, and a cylindrical cavity wall surface 17B that rises substantially perpendicularly from the outer periphery of the bottom surface 17A. A cavity lip portion 18 that forms an inclined surface (or curved surface) that is appropriately inclined with respect to the piston crown surface 3A is formed at the corner portion between the piston crown surface 3A and the cavity wall surface 17B. The cavity lip portion 18 has an inclination angle and a piston radial direction length so that the injected fuel jumps up to the cavity lip portion 18.

  The two fuel injection valves 15 and 16 both form a conical spray centered on the cylinder center axis, but the high-octane fuel injection valve 16 injects fuel into the cavity 17. The fuel injection valve 15 for low octane fuel is configured to have a wide spray angle α1 so as to inject fuel outside the spray of the high octane fuel.

  Specifically, the fuel injection valve 15 for low-octane fuel 15 has a piston crown surface 3A in the period (BDC to 60BTDC (before top dead center)) in which the spray axis Z1 forming the spray angle α1 is from the first half of the compression stroke to the middle stage. Is directed to the wall surface of the cylinder 1A without interfering with the cylinder, and is directed to the region A of the piston crown surface 3A in the latter half of the compression stroke (60 BTDC to 30 BTDC), and near the compression top dead center (30 BTDC to TDC). It is set so as to be directed to the region B. That is, the spray angle α1 is set wide so that the cavity 17 is not directed in the compression stroke.

  On the other hand, in the fuel injection valve 16 for high octane fuel, the spray axis Z2 forming the spray angle α2 is directed to the region A of the piston crown surface 3A in the middle of the compression stroke (˜60 BTDC), and until the latter half of the compression stroke (60 BTDC˜ 45BTDC) is directed to the region B of the cavity lip 18 and is set to be directed to the region C in the cavity 17 during the period from the latter half of the compression stroke to the compression top dead center (45BTDC to TDC).

  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.

  FIG. 2 shows a setting example of the fuel injection timing (period) and the fuel injection rate in the low load region. In this low load range, the injection periods of the fuel injection valves 15 and 16 are set to a short period in the latter half of the compression stroke, for example, about 45 BTDC to 15 BTDC.

  With this setting, of the fuel injected from the high-octane fuel injection valve 16, the fuel injected in the first half of the injection period is injected into the region B of the cavity lip portion 18 and rolled up above it. The fuel injected in the second half of the injection period is injected into the region C in the cavity 17, and the high octane fuel Fh is distributed in the region C of the cavity 17. On the other hand, of the fuel injected from the fuel injection valve 15 for low-octane fuel, the fuel injected in the first half of the injection period is injected toward the region A of the piston crown surface 3A, and the low octane number is injected on the piston crown surface 3A. While the fuel Fl is distributed, the fuel injected in the second half of the injection period is injected into the region B of the cavity lip portion 18 and is rolled up to the above, thereby mixing with the above-described low octane number fuel and the cavity lip portion 18. An intermediate octane fuel Fm is distributed in the sky.

  Here, the state where the intermediate octane fuel Fm distributed over the cavity lip 18 is injected toward the region B of the cavity lip 18 so as not to be excessively concentrated, that is, the fuel injection valve 15 for the low octane fuel. In this case, the injection rate (injection amount) of the fuel injection valve 16 for high octane fuel is kept low in the second half of the injection period and in the first half of the injection period.

  As a result, as shown in FIG. 5A, an octane number distribution in which the fuels Fl, Fm, Fh having different octane numbers in the radial direction are concentrically distributed is formed. Specifically, the fuel Fl, A fuel Fh having a high octane number is distributed on the inner peripheral side and an intermediate octane number fuel Fm is distributed in the middle, that is, a concentric octane number distribution is formed in which the octane number increases toward the center in the radial direction. Further, in this low load region, the fuel injection period is a short period in the latter half of the compression stroke, so that the fuel distribution is compact and limited to a narrow range in the center of the combustion chamber.

  In FIG. 5 and the like, the octane fuels Fl, Fm, and Fh are drawn as if they occupy independent regions due to restrictions on the notation, but they are mixed as appropriate because they are actually one space. It will be.

  In this way, in the low-load region, a concentric compact octane number distribution with increasing octane number toward the center is formed, and low octane number fuel is distributed on the outer peripheral side without being substantially mixed, thereby ensuring reliable ignition. Since the combustion can proceed from the outer peripheral side to the inner peripheral side in the central portion of the combustion chamber 4, the piston in the vicinity of the wall surface of the cylinder 1A can be secured. Unburned fuel components remaining in the clevis portion and the like are suppressed.

  FIG. 3 shows an example of setting the fuel injection timing (period) and injection rate in the high load range. In this high load region, the injection period of the low-octane fuel fuel injection valve 15 is set to the middle / second half of the compression stroke, specifically about 75 BTDC to 50 BTDC, and the injection period of the high-octane fuel injection valve 16 is compressed. A long period from the middle of the stroke to the vicinity of compression top dead center, specifically, about 70 BTDC to 15 BTDC is set.

  With this setting, the fuel injected from the low-octane fuel injection valve 15 is injected toward the cylinder outer periphery above the piston crown, and the fuel injected from the high-octane fuel injection valve 16 is: As the piston rises during the compression stroke, it is injected into the region A of the piston crown surface 3A, the region B of the cavity lip 18 and the region C of the cavity 17. As a result, as shown in FIGS. 3D and 5C, in the combustion chamber 4, the high octane fuel Fh is widely distributed on the inner peripheral side, and the low octane fuel ( Alternatively, an intermediate octane fuel (Fl) in which high-octane fuel is mixed to some extent and an intermediate octane fuel (Fm) in which both fuels are mixed are distributed concentrically.

  In this way, although the fuel distribution range is wider in the high load region than in the low load region, a concentric octane number distribution is formed in which the octane number increases toward the center as in the low load region. Therefore, the combustion proceeds from the outer peripheral side toward the inner peripheral side over the entire combustion chamber, so that discharge of unburned fuel components can be suppressed. Further, in this high load region, the high octane fuel Fl is widely distributed to the piston crown surface 3A so that the high octane fuel Fl and the intermediate octane fuel Fm occupy most of the fuel in the combustion chamber 4. Thus, it is possible to suppress combustion noise due to sharp combustion by setting the combustion period to an appropriate one.

  FIG. 4 shows another example of setting of the fuel injection timing (period) and injection rate in the high load region, and corresponds to the setting near the full load with a higher load. In this setting, in addition to the main injection in the second half of the compression stroke, high octane fuel is injected and supplied in advance in the intake stroke (or the first half of the compression stroke). As a result, as shown in FIG. 4 (B), the high octane fuel injected in the intake stroke (or the first half of the compression stroke) is widely distributed in the combustion chamber 4 as the piston rises. In the second half of the stroke, when low-octane fuel is injected, it mixes quickly with high-octane fuel, and the octane number of the fuel distributed near the cylinder periphery becomes intermediate octane numbers Fm1, Fm2 higher than the low-octane number of the injected fuel. . That is, the lowest octane number Fm1 of the fuel distributed in the cylinder 1A can be made higher than the octane number of the fuel injected from the fuel injection valve 15 for low octane number fuel.

  Under the condition that the load becomes high and the fuel injection amount increases, as shown in FIG. 3, in the configuration in which both fuels are injected in the middle and latter half of the compression stroke, the mixing of the two fuels does not proceed sufficiently and the low octane fuel is mixed. If the remaining ratio increases without the ignition, the ignition timing may be inadvertently advanced. In such a case, as described above, high octane number fuel is injected in advance in the intake stroke (or the first half of the compression stroke), so that mixing of fuel is promoted so that fuel having an intermediate octane number or more occupies the combustion chamber. By doing so, the combustion period can be optimized and good compression ignition combustion can be realized.

  Note that the detailed description of the fuel injection timing (period) and the injection rate in the middle load range is omitted here, but the intermediate setting between the low load range and the high load range described above is used. As shown in FIG. 5B, similarly to the case of the low load region, a concentric octane number distribution in which the octane number increases toward the center can be formed, and good compression ignition combustion can be realized.

  Next, characteristic configurations of the present invention will be listed with reference to the illustrated embodiments. However, the present invention is not limited to the above embodiments, and includes various modifications and changes without departing from the spirit of the present invention. For example, the two fuel injection valves 15 and 16 do not have to be completely separated and independent from each other, and a fuel injection valve having a substantially integrated structure capable of injecting two fuels can be used. is there. In the above embodiment, the octane number increases toward the center of the octane number distribution, but conversely, the octane number can decrease toward the center.

  [1] The spray angle of one fuel injection valve 16 is narrower than that of the other fuel injection valve 15 so that fuel is injected toward the cavity 17 from the middle of the compression stroke.

  [2] More specifically, one fuel injection valve 16 having a narrow spray angle α2 injects fuel to the outside of the cavity 17 in the first half of the compression stroke, and injects fuel toward the cavity 17 in the middle of the compression stroke. Thus, the other fuel injection valve 15 having a wide spray angle α1 injects fuel to the outside of the cavity 17 from the first half of the compression stroke to the second half of the compression stroke. The spray angle α1 is set wide so that the fuel is not injected into the tank.

  [3] Typically, the spray angle α2 of the high-octane fuel fuel injection valve 16 that injects the high-octane fuel is set to be narrow, and the spray angle α1 of the low-octane fuel fuel injection valve 15 that injects the low-octane fuel is Widely set.

  [4] With the configuration as described above, by controlling at least one of the fuel injection timing, the fuel injection amount, and the fuel injection rate of each of the two fuel injection valves 15 and 16 according to the engine operating conditions, As shown in FIG. 5, it is possible to form an octane number distribution in which fuels having different octane numbers are distributed concentrically.

  [5] Also, as described in [3] above, by setting the spray angle α2 of the high-octane fuel fuel injection valve 16 to be narrow and setting the spray angle α1 of the low-octane fuel fuel injection valve 15 to be wide, the octane number distribution is The octane number increases toward the center in the radial direction. As a result, combustion proceeds from the outer peripheral side of the cylinder to the inner peripheral side, and unburned fuel remaining in the outer peripheral part of the cylinder can be suppressed, so that exhaust emission can be reduced and fuel consumption can be improved.

  [6] In the high load region, prior to the main injection in the latter half of the compression stroke, the low octane number fuel or the high octane number fuel is injected and supplied in advance in the intake stroke or the first half of the compression stroke, thereby mixing two types of fuels having different octane numbers. For example, as shown in FIG. 4, the combustion chamber occupies a fuel having an intermediate octane number or more, so that the combustion period is optimized and the ignition period is not inadvertently advanced. Compressive ignition combustion can be realized.

  [7] In addition, an inclined surface that is inclined with respect to the piston crown surface 3A at a corner portion of the piston crown surface 3A and a wall surface 17B of the cavity that forms a cylindrical surface substantially perpendicular to the piston crown surface 3A. Alternatively, a cavity lip portion 18 having a curved surface is provided. Thereby, for example, in the low load region described above, by controlling the injection timing and injection rate (injection amount) of the fuel injected toward the cavity lip portion 18, as shown in FIG. Two kinds of fuels are appropriately mixed in the sky, and an intermediate octane fuel between the high octane fuel Fh on the inner cavity 17 and the low octane fuel Fl on the outer piston crown surface 3A. Fm can be distributed well.

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 18 ... Cavity lip part

Claims (6)

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,
One fuel injection valve is configured such that the spray angle is narrower than the other fuel injection valve so as to inject fuel toward the cavity from the middle of the compression stroke ,
One fuel injection valve with a narrow spray angle has a spray angle set so that fuel is injected to the outside of the cavity in the first half of the compression stroke, and fuel is injected toward the cavity from the middle of the compression stroke,
The compression ignition internal combustion engine characterized in that the other fuel injection valve having a wide spray angle has a spray angle set so as to inject fuel to the outside of the cavity from the first half of the compression stroke to the second half of the compression stroke . One fuel injection valve with a narrow spray angle is a fuel injection valve for high octane fuel that injects high octane fuel,
2. The compression ignition internal combustion engine according to claim 1 , wherein the other fuel injection valve having a wide spray angle is a fuel injection valve for low octane fuel that injects low octane fuel. By controlling at least one of the fuel injection timing, fuel injection amount, and fuel injection rate of each of the two fuel injection valves according to engine operating conditions, concentric fuels with different octane number fuels distributed in the radial direction The compression ignition internal combustion engine according to claim 1 or 2 , wherein an octane number distribution is formed. The compression ignition internal combustion engine according to claim 3 , wherein the octane number distribution is such that the octane number increases toward the center in the radial direction. The compression ignition internal combustion engine according to any one of claims 1 to 4 , wherein a low octane number fuel or a high octane number fuel is injected and supplied in advance in the intake stroke or the first half of the compression stroke prior to the main injection in the latter half of the compression stroke. . A cavity lip portion that forms an inclined surface or a curved surface that is inclined with respect to the piston crown surface is provided at a corner portion of the piston crown surface and a wall surface of the cavity that is substantially perpendicular to the piston crown surface. compression ignition internal combustion engine according to any one of claims 1 to 5, characterized in that it has.

Images