JP2018193909A - Multistage injection type diesel engine, mechanical device equipped with the same, and control method of multistage injection type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-stage injection diesel engine capable of suppressing the amount of smoke and the emission of unburned substances by increasing the utilization rate of air, as well as realizing the improvement of thermal efficiency and the reduction of combustion noise, and the same. Provided are a mechanical device and a control method for a multi-stage injection diesel engine. A multi-stage injection diesel engine (1) is provided with a piston (2) having a cavity (20) on its top surface, and a fuel injection injector (3) capable of multi-stage fuel injection toward the cavity (20). A first combustion chamber 21 which is recessed in a substantially circular shape in a plan view with respect to the axial center of the injector 3, and a concentric circle having a diameter smaller than that of the first combustion chamber 21 and recessed at a position deeper than the first combustion chamber. The fuel injection injector 3 injects fuel into the first combustion chamber 21 at the first injection timing in the compression stroke, and the second injection near the top dead center in the compression stroke or the expansion stroke. Fuel is injected into the second combustion chamber 22 at a timing. [Selection diagram]

Description

  The present invention relates to a multi-stage injection type diesel engine that directly injects fuel into a combustion chamber in a plurality of times, a mechanical apparatus including the same, and a control method for the multi-stage injection type diesel engine.

  2. Description of the Related Art Conventionally, a multi-stage injection type diesel engine in which fuel is divided into a plurality of times and directly injected into a combustion chamber is known as a means for realizing improvement in thermal efficiency and reduction in combustion noise. For example, Japanese Unexamined Patent Application Publication No. 2014-9598 discloses a diesel engine that performs main injection and pilot injection in which a smaller amount of fuel than the main injection is injected before the piston reaches compression top dead center. (Patent Document 1).

JP 2014-9598 A

  However, in the diesel engine equipped with the conventional fuel injection system capable of multistage injection including the invention described in Patent Document 1, the subsequent fuel is placed in the high temperature and low oxygen atmosphere generated by the preceding fuel injection. It comes to be injected. For this reason, the fuel produced by the subsequent injection is not easily mixed with air, and the fuel is formed in a rich region in the combustion chamber, resulting in an increase in the amount of smoke and unburned substances. There is.

  The present invention has been made to solve such problems. In addition to improving the thermal efficiency and reducing the combustion noise, the present invention increases the utilization rate of air and releases smoke and unburned substances. It is an object of the present invention to provide a multi-stage injection type diesel engine capable of suppressing the amount, a mechanical device including the same, and a control method for the multi-stage injection type diesel engine.

  The multi-stage injection type diesel engine according to the present invention not only realizes improvement of thermal efficiency and reduction of combustion noise, but also solves the problem of suppressing the emission of smoke and unburned substances by increasing the utilization rate of air. A multi-stage injection type diesel engine comprising a piston having a cavity on the top surface and a fuel injection injector capable of multi-stage injection of fuel toward the cavity, wherein the cavity relates to an axis of the fuel injection injector A first combustion chamber recessed in a substantially circular shape in plan view; a second combustion chamber formed in a concentric shape having a smaller diameter than the first combustion chamber and recessed at a position deeper than the first combustion chamber; The fuel injection injector injects fuel into the first combustion chamber at a first injection timing in a compression stroke, and performs a compression stroke or an expansion stroke. Injecting fuel to the second combustion chamber at a second injection timing positioned near top dead center definitive.

  Moreover, as one aspect of the present invention, in order to solve the problem of appropriately setting the first injection timing and the second injection timing, the first injection timing exceeds a crank angle of 40 ° before top dead center and The second injection timing may be set in a range of less than 30 ° before top dead center, and the crank angle may be set in a range of 10 ° or more before top dead center and less than 5 ° after top dead center.

  Furthermore, as one aspect of the present invention, in order to solve the problem of appropriately setting the injection amount at the first injection timing and the second injection timing, the injection amount at the first injection timing is set to the second injection timing. It may be set to 30 to 50% of the injection amount at the timing.

Further, as one aspect of the present invention, in order to solve the problem of taking the injected fuel without omission and guiding it to the first combustion chamber, the bottom surface of the first combustion chamber becomes deeper toward the outer peripheral side. The inclination angle may be expressed by the following formula (1).
θ ≦ 90 ° −θinj / 2 Formula (1)
However, each symbol represents the following.
θ: Angle of inclination of the bottom of the first combustion chamber [°]
θinj: Fuel injector injector nozzle angle [°]

  Furthermore, as one aspect of the present invention, the problem is that the fuel is prevented from scattering into the squish area and stays in the first combustion chamber, the mixture is diluted, and the emission of unburned substances is reduced. In order to solve the problem, the inner surface of the first combustion chamber is formed in a concave curved shape, and the upper end edge of the first combustion chamber is reduced in diameter from the maximum diameter of the first combustion chamber. A fuel winding return portion for winding up the fuel injected at the injection timing may be provided.

  Further, as one aspect of the present invention, the fuel is smoothly introduced into the second combustion chamber, and is prevented from being scattered into the first combustion chamber so as to remain in the second combustion chamber, thereby suppressing the dilution of the air-fuel mixture. In order to solve the problem of reducing the discharge amount of unburned substances, the second combustion chamber has a concave curved inner peripheral surface and a convex curved shape at the upper edge. A fuel-introducing bulge portion is provided for guiding the fuel, which is raised and reduced in diameter from the maximum diameter of the second combustion chamber, to the bottom of the second combustion chamber, and is injected at the second injection timing. May be.

  Moreover, the mechanical apparatus which concerns on this invention is equipped with the multistage injection type diesel engine which has one of the aspects mentioned above.

  In addition, the control method for a multi-stage injection diesel engine according to the present invention not only realizes improvement in thermal efficiency and reduction of combustion noise, but also increases the utilization rate of air and suppresses the emission of smoke and unburned substances. In order to solve the problem, there is provided a control method for a multi-stage injection type diesel engine comprising a piston having a cavity on the top surface and a fuel injection injector capable of multi-stage injection of fuel toward the cavity, wherein the cavity includes: A first combustion chamber that is recessed in a substantially circular shape in plan view with respect to the axial center of the fuel injector, and a concentric circle that is smaller in diameter than the first combustion chamber and that is recessed deeper than the first combustion chamber. And the fuel injection injector injects fuel into the first combustion chamber at a first injection timing in a compression stroke. To inject fuel to said second combustion chamber at a second injection timing located near the top dead center in the compression stroke or the expansion stroke.

  According to the present invention, it is possible not only to realize improvement of thermal efficiency and reduction of combustion noise, but also to increase the utilization rate of air and suppress the discharge of smoke and unburned substances.

1 is a partial cross-sectional view showing an embodiment of a multi-stage injection type diesel engine according to the present invention. It is a top view which shows the piston of this embodiment. In the piston of this embodiment, it is a partially expanded sectional view showing the case of (a) θ> 90 ° −θinj / 2 and (b) θ ≦ 90 ° −θinj / 2. It is a partial cross section figure of a multistage injection type diesel engine in the 1st injection timing of this embodiment. It is a partial cross section figure of the multistage injection type diesel engine in the 2nd injection timing of this embodiment. It is a figure which shows the simulation result in Example 1. FIG. It is a figure which shows the simulation result in Example 2. FIG. 10 is a graph showing experimental results in Example 3. It is a figure which shows the simulation result in Example 4. 10 is a graph showing experimental results in Example 5. It is a figure which shows the simulation result in Example 5. FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of a multistage injection diesel engine according to the present invention, a mechanical device including the same, and a control method for the multistage injection diesel engine will be described with reference to the drawings. In the present invention, the mechanical device means all machines that use a diesel engine as a power source, such as automobiles, motorcycles, military vehicles, railway vehicles, ships, airplanes, generators, pumps, construction machinery, agricultural machinery, etc. It is a concept that includes a device.

  The multi-stage injection type diesel engine 1 of the present embodiment is constituted by a diesel engine that directly injects fuel into a combustion chamber. As shown in FIG. 1, a piston 2 having a cavity 20 on the top surface and a cavity 20 mainly. And a fuel injection injector 3 capable of multistage injection of fuel. Each configuration will be described below. Although not shown, the multi-stage injection diesel engine 1 has a turbocharger that increases the intake air pressure, an EGR (Exhaust Gas Recirculation) system that reintakes part of the exhaust gas after combustion, and the like. I have.

  The piston 2 is formed in a substantially cylindrical shape that reciprocates in the cylinder 4, and a concave cavity 20 that functions as a combustion chamber is provided on the top surface. In the present embodiment, the cavity 20 includes a first combustion chamber 21 and a second combustion chamber 22 for dividing the fuel injected from the fuel injector 3 into separate spaces, as shown in FIGS. 1 and 2. ing.

  The first combustion chamber 21 is a space for burning fuel injected at a first injection timing described later. Specifically, as shown in FIGS. 1 and 2, the first combustion chamber 21 is recessed in a substantially circular shape in plan view with respect to the axial center of the fuel injector 3. Further, in the present embodiment, as shown in FIG. 1, the bottom surface of the first combustion chamber 21 is inclined so as to become deeper toward the outer peripheral side.

As shown in FIG. 3A, when the inclination angle is larger than the fuel injection angle, the fuel injected at the first injection timing hardly reaches the first combustion chamber 21, and the second combustion chamber 22. There is a risk of being easily distributed. Therefore, in the present embodiment, as shown in FIG. 3B, in order to easily guide the injected fuel to the first combustion chamber 21 without leakage, the inclination angle of the bottom surface of the first combustion chamber 21 is expressed by the following formula ( It is set to the angle represented by 1).
θ ≦ 90 ° −θinj / 2 Formula (1)
However, each symbol represents the following.
θ: Inclination angle [°] of the bottom surface of the first combustion chamber 21
θinj: the nozzle angle of the fuel injection injector 3 [°]

  Moreover, in this embodiment, as shown in FIG. 1 and FIG. 3, the 1st combustion chamber 21 is formed in the concave curve shape in the internal peripheral surface by sectional view. The upper end edge of the first combustion chamber 21 has a diameter smaller than the maximum diameter of the first combustion chamber 21 and is used for hoisting the fuel to wind up the fuel injected at the first injection timing to the cylinder 4 head side. A return portion 23 is provided. The fuel hoisting return portion 23 makes it difficult for the fuel to diffuse into the squish area formed between the cylinder head and the piston 2, and makes it easier for the fuel to stay in the first combustion chamber 21.

  The second combustion chamber 22 is a space for burning fuel injected at a second injection timing described later. Specifically, as shown in FIGS. 1 and 2, the second combustion chamber 22 is formed concentrically with a smaller diameter than the first combustion chamber 21 in a plan view, and is located deeper than the first combustion chamber 21. Is recessed. The center of the second combustion chamber 22 is raised in a substantially conical shape like the reentrant combustion chamber, and a vortex ring is generated to improve the combustion efficiency.

  In the present embodiment, as shown in FIGS. 1 and 3, the second combustion chamber 22 has an inner peripheral surface formed in a concave curved shape in a sectional view. Then, the upper end edge of the second combustion chamber 22 protrudes in a convex curve shape and is reduced in diameter from the maximum diameter of the second combustion chamber 22, and the fuel injected at the second injection timing is supplied to the second combustion chamber 22. A fuel introduction ridge 24 is provided for introduction into the bottom. The fuel that has collided with the fuel introduction ridge 24 is smoothly introduced into the second combustion chamber 22 while swirling downward along the inner peripheral surface.

  Further, in the present embodiment, the volumes of the first combustion chamber 21 and the second combustion chamber 22 are set so that the compression ratio is 14 or more and 16 or less. The smaller the compression ratio, the lower the theoretical thermal efficiency and the less work that can actually be taken out. For this reason, by setting the compression ratio to 14 or more, a decrease in thermal efficiency is suppressed to a necessary minimum. On the other hand, the higher the compression ratio, the faster the fuel ignites, and the mixing with air is not promoted. For this reason, mixing of a fuel and air is accelerated | stimulated by setting a compression ratio to 16 or less.

  Next, the fuel injection injector 3 is for injecting fuel into the cavity 20 in multiple stages. In this embodiment, as shown in FIG. 1, the axis of the fuel injection injector 3 coincides with the axis of the piston 2. The fuel injector 3 is mounted as a part of a so-called common rail system, and the fuel injection amount and injection timing are controlled by an engine control unit (ECU) (not shown).

  In the present embodiment, the fuel injection injector 3 injects fuel into the first combustion chamber 21 at the first injection timing in the compression stroke under the control of the engine control unit, and in the compression stroke or expansion stroke. The fuel is injected into the second combustion chamber 22 at the second injection timing located near the top dead center.

  Here, if the timing of the first injection timing is too early, the fuel is directly introduced into the squish area instead of the first combustion chamber 21, so that the amount of unburned substances discharged increases. On the other hand, if the timing of the first injection timing is too late, part of the fuel is also introduced into the second combustion chamber 22 to form a high-temperature and low-oxygen atmosphere field. Emissions increase. If the timing of the second injection timing is too early or too late, a part of the fuel is introduced into the first combustion chamber 21 that is in a high-temperature and low-oxygen atmosphere field by the combustion at the first injection timing, and the smoke The amount of emissions increases.

  Therefore, about the 1st injection timing and the 2nd injection timing, suitable timing was specified based on the result of the numerical simulation in Examples 2 and 4 mentioned below. Specifically, the first injection timing is preferably set in the range of the crank angle exceeding 40 ° before the top dead center and less than 30 ° before the top dead center, and the crank angle is most preferably 35 ° before the top dead center. preferable. The second injection timing is preferably set in a range of 10 ° or more before top dead center and less than 5 ° after top dead center in crank angle, and most preferably 5 ° before top dead center in crank angle.

  In the present embodiment, the ratio of the fuel injection amount (first injection amount) at the first injection timing and the fuel injection amount (second injection amount) at the second injection timing is the smoke emission amount. It is set as follows from the viewpoint of noise and thermal efficiency.

  Specifically, the smoke is mainly discharged from the combustion at the second injection timing. For this reason, if the second injection amount is increased and the first injection amount is relatively decreased, the smoke discharge amount increases. Therefore, if the first injection amount is secured to 30% or more of the second injection amount, the smoke discharge amount is suppressed. In addition, the afterburning period in the second combustion chamber 22 (the state in which the remaining fuel continues to burn gradually even after large combustion) does not increase, and a decrease in isovolume is suppressed, so that a decrease in thermal efficiency is prevented. .

  On the other hand, if the first injection amount is increased and the second injection amount is relatively decreased, combustion at the first injection timing becomes steep and noise is deteriorated. For this reason, if the first injection amount is suppressed to 50% or less of the second injection amount, combustion in the first combustion chamber 21 becomes gentle and noise is reduced. From the above, it can be said that the first injection amount is preferably set to 30 to 50% of the second injection amount.

  Further, in this embodiment, a system in which fuel is injected twice for one operation (intake stroke, compression stroke, expansion stroke, exhaust stroke) of the multi-stage injection type diesel engine 1 is employed. In a range where the above is achieved, multistage injection may be performed three times or more per operation. For example, as the third injection timing, the crank angle in the expansion stroke may be set around 30 ° after top dead center, and may be injected again into the first combustion chamber 21. As a result, there is a possibility that the unburnt fuel is burned or fuel is sent to the exhaust pipe so that the soot deposited on the diesel particulate filter (Diesel Particulate Filter: DPF) is burned.

  Next, the operation of the multistage injection diesel engine 1 of the present embodiment, the mechanical device including the same, and the control method of the multistage injection diesel engine 1 will be described.

  First, in the multi-stage injection type diesel engine 1 of the present embodiment, as shown in FIG. 4, the fuel injection injector 3 injects fuel into the first combustion chamber 21 at the first injection timing in the compression stroke. Thereby, the fuel takes in the air in the first combustion chamber 21 to form an air-fuel mixture. Further, in the first combustion chamber 21, the bottom surface inclined so as to become deeper toward the outer peripheral side takes in the injected fuel without leakage and guides it to the first combustion chamber 21. Further, the fuel winding return portion 23 provided at the upper edge of the first combustion chamber 21 prevents the fuel from scattering to the squish area, and most of the fuel remains in the first combustion chamber 21. Thereby, since the dilution of the air-fuel mixture is suppressed, the discharge amount of unburned substances is reduced.

  After the first injection timing, as the compression in the compression stroke proceeds, the air-fuel mixture in the first combustion chamber 21 ignites and burns. At this time, since the second combustion chamber 22 is spatially divided from the first combustion chamber 21, the fuel is hardly introduced. For this reason, in the second combustion chamber 22, a high-temperature and low-oxygen atmosphere field generated by fuel combustion is not formed, and abundant air necessary for combustion at the second injection timing remains.

  Subsequently, as shown in FIG. 5, the fuel injection injector 3 injects fuel into the second combustion chamber 22 at the second injection timing in the vicinity of the top dead center. Thereby, the fuel burns while taking in the air in the second combustion chamber 22. At this time, the fuel injected into the second combustion chamber 22 is prevented from interfering with the high-temperature and low-oxygen atmosphere field generated in the first combustion chamber 21 by the combustion at the first injection timing. For this reason, in the 2nd combustion chamber 22 in which air exists abundantly, the area | region where a fuel is rich (rich) is hard to be formed, and the discharge | emission amount of smoke reduces.

  In the present embodiment, the fuel introduction raised portion 24 raised at the upper edge of the second combustion chamber 22 smoothly introduces the injected fuel into the second combustion chamber 22, and the first combustion chamber 21. Suppresses splashing into. For this reason, most of the fuel remains in the second combustion chamber 22 and the dilution of the air-fuel mixture is suppressed, so that the amount of unburned substances discharged is reduced. Further, since the central portion of the second combustion chamber 22 is raised in a substantially conical shape, a vortex ring is generated in the second combustion chamber 22 along with the injection to improve combustion efficiency.

  Further, in the present embodiment, the first injection amount is set to 30 to 50% of the second injection amount. For this reason, the amount of smoke discharged is suppressed, the decrease in thermal efficiency is prevented, and the noise is reduced. In the present embodiment, the volumes of the first combustion chamber 21 and the second combustion chamber 22 are set so that the compression ratio is 14 or more and 16 or less. For this reason, a decrease in thermal efficiency is suppressed to a necessary minimum, and mixing of fuel and air is promoted.

  As described above, in the present invention, the fuel to be injected in a plurality of times is spatially divided by the two combustion chambers (the first combustion chamber 21 and the second combustion chamber 22), and is separately provided for each combustion chamber. Causes combustion independently. This avoids interference between the high-temperature and low-oxygen atmosphere field generated by the preceding combustion and the fuel injected subsequently, and promotes the utilization rate of air in each combustion chamber. Is reduced.

  Further, in the present invention, for one operation (intake stroke / compression stroke / expansion stroke / exhaust stroke) of the multi-stage injection diesel engine 1, the fuel is injected in multiple stages. For this reason, like a diesel engine that performs combustion by conventional multi-stage injection, thermal efficiency is improved and combustion noise is reduced.

According to the multistage injection type diesel engine 1 according to the present invention as described above, the mechanical device including the same, and the control method for the multistage injection type diesel engine 1, the following effects can be obtained.
1. In addition to realizing improved thermal efficiency and reduced combustion noise, it is possible to increase the air utilization rate and suppress the emission of smoke and unburned substances.
2. The above effect 1 can be enhanced by appropriately setting the first injection timing and the second injection timing.
3. By appropriately setting the injection amounts at the first injection timing and the second injection timing, it is possible to suppress the smoke discharge amount, prevent the thermal efficiency from decreasing, and reduce noise.
4). The inclined bottom surface of the first combustion chamber 21 can take in the injected fuel without omission and guide it to the first combustion chamber 21.
5. The fuel hoisting return portion 23 suppresses the fuel from scattering to the squish area and stays in the first combustion chamber 21 to suppress the dilution of the air-fuel mixture and reduce the amount of unburned substances discharged. Can do.
6). The fuel introduction ridge 24 smoothly introduces the fuel into the second combustion chamber 22, suppresses the fuel from scattering into the first combustion chamber 21, stays in the second combustion chamber 22, and dilutes the air-fuel mixture. Can be suppressed, and the amount of unburned substances discharged can be reduced.

  Next, specific examples of the multi-stage injection type diesel engine 1 according to the present invention, a mechanical apparatus including the same, and a control method for the multi-stage injection type diesel engine 1 will be described.

  In the present Example 1, the numerical simulation for confirming the effect of the multistage injection type diesel engine 1 which concerns on this invention was performed.

  Specifically, in the multi-stage injection type diesel engine 1 including the piston 2 of the above-described embodiment, the first injection timing is set to 35 ° before top dead center (−35 ° CA ATDC) as a crank angle, The distribution of the gas phase equivalence ratio in the cylinder 4 when the 2 injection timing was set to the top dead center (0 ° CA ATDC) was calculated every 5 ° as the crank angle. Note that CA is a crank angle, and ATDC means After Top Dead Center.

  As a comparative example, in a diesel engine having a conventional piston with only one combustion chamber, the first injection timing and the second injection timing were set in the same manner, and the distribution of the gas phase equivalence ratio in the cylinder was calculated. . The result is shown in FIG. The gas phase equivalent ratio indicates the mass ratio of air and fuel in the air-fuel mixture, and the larger the numerical value, the more fuel in the air-fuel mixture.

  As shown in FIG. 6, in the multistage injection diesel engine 1 of the first embodiment, most of the fuel injected at the first injection timing forms an air-fuel mixture in the first combustion chamber 21. For this reason, since the dilution of the air-fuel mixture is suppressed in the first combustion chamber 21, it is presumed that the discharge amount of unburned substances is reduced. Further, most of the fuel injected at the second injection timing is introduced into the second combustion chamber 22, and interference with the high temperature and low oxygen atmosphere field (first combustion chamber 21) is avoided. For this reason, in the 2nd combustion chamber 22, since fuel is well mixed with air, it is estimated that the amount of smoke discharged is reduced.

  On the other hand, in the diesel engine of the comparative example, the fuel injected at the first injection timing also enters the squish area and forms an air-fuel mixture. For this reason, in the combustion chamber of the comparative example, a large amount of unburned substances are discharged due to the dilution of the air-fuel mixture, and there is a concern that the thermal efficiency is lowered. Further, at the second injection timing, fuel is injected into a high-temperature and low-oxygen atmosphere field generated by the first injection timing. For this reason, the fuel at the second injection timing is unlikely to be mixed with air, and an excessively rich region is formed in the combustion chamber, so that it is presumed that the amount of smoke discharged increases.

  According to the first embodiment described above, the multistage injection diesel engine 1 including the piston 2 of the present embodiment promotes the air utilization rate in each combustion chamber by the two combustion chambers that spatially divide the fuel. It has been shown that smoke and unburned material emissions can be reduced.

  In Example 2, a numerical simulation for specifying a suitable range of the first injection timing according to the present invention was performed.

  Specifically, in the multi-stage injection type diesel engine 1 including the piston 2 of the present embodiment described above, four cases were set in which the first injection timing was varied while the second injection timing was fixed. Then, for each case, the distribution of the gas phase equivalence ratio in the cylinder 4 in the case of performing the multistage combustion according to the control method of the present embodiment described above was calculated every 5 ° in terms of the crank angle. The result is shown in FIG.

  As the first injection timing, the crank angle is 40 ° before top dead center (−40 ° CA ATDC), 35 ° before top dead center (−35 ° CA ATDC), and 30 ° before top dead center (−30 (° CA ATDC) and 25 ° before top dead center (−25 ° CA ATDC). The second injection timing was set to top dead center (0 ° CA ATDC) in any case.

  As shown in FIG. 7, when the first injection timing is 40 ° before top dead center, most of the injected fuel enters the squish area instead of the first combustion chamber 21, and the equivalence ratio is low near the cylinder wall. A lean air-fuel mixture is formed. For this reason, it is presumed that good combustion cannot be obtained with the lean air-fuel mixture, and a large amount of unburned substances are discharged.

  On the other hand, when the first injection timing is 30 ° before top dead center and 25 ° before top dead center, the injected fuel enters not only the first combustion chamber 21 but also the second combustion chamber 22. For this reason, combustion also occurs in the second combustion chamber 22, and a high temperature and low oxygen atmosphere field is formed. Therefore, it is estimated that the amount of smoke discharged increases in the combustion at the subsequent second injection timing.

  In this regard, when the first injection timing is 35 ° before top dead center, as shown in FIG. 7, most of the injected fuel stays in the first combustion chamber 21 and forms an appropriate air-fuel mixture. I understand that. Therefore, according to the second embodiment described above, the first injection timing according to the present invention is preferably set in the range of the crank angle exceeding 40 ° before top dead center and less than 30 ° before top dead center. It was shown that the crank angle is most preferably 35 ° before top dead center. According to this first injection timing, the injected fuel is sprayed onto the upper surface side of the fuel introduction ridge 24.

  Next, in the third embodiment, an experiment was performed to confirm a suitable range of the first injection timing using an actual engine.

  Specifically, a test operation was performed on four cases with different first injection timings using the actual multistage diesel engine 1 to which the piston 2 of the present embodiment was attached. For each case, four items were measured: carbon monoxide (CO) emissions, smoke emissions, unburned hydrocarbon (THC) emissions, and indicated thermal efficiency.

  As a comparative example, a test operation was performed at the same first injection timing using a diesel engine equipped with a conventional piston having only one combustion chamber, and the above four items were measured. The result is shown in FIG. As the first injection timing, the crank angle is 40 ° before top dead center (−40 ° CA ATDC), 35 ° before top dead center (−35 ° CA ATDC), and 30 ° before top dead center (−30 (° CA ATDC) and 25 ° before top dead center (−25 ° CA ATDC).

  As shown in FIG. 8, in the third embodiment, when the first injection timing is 35 ° before top dead center, which is the optimal timing specified in the second embodiment, not only the smoke emission amount but also carbon monoxide and The amount of unburned hydrocarbon emissions is also greatly reduced, and the thermal efficiency shown in the figure is increased. On the other hand, in the comparative example, when the first injection timing is 35 ° before the top dead center, the smoke emission amount is reduced, but a large amount of carbon monoxide and unburned hydrocarbons are emitted, and the illustrated thermal efficiency is also improved. It has dropped significantly.

  Further, in Example 3, as the first injection timing deviates from the optimal timing (35 ° before top dead center), the emission amounts of carbon monoxide, smoke and unburned hydrocarbons tend to increase, and the indicated thermal efficiency is It is on a downward trend. This is considered to be caused by the fact that the fuel at the second injection timing enters the high temperature and low oxygen atmosphere generated by the combustion at the first injection timing.

  According to the third embodiment described above, the multistage injection type diesel engine 1 including the piston 2 according to the present embodiment appropriately sets the fuel injection timing as compared with the diesel engine including the conventional piston. As a result, it was proved that the amount of carbon monoxide, smoke, and unburned hydrocarbons can be suppressed while the fuel is spatially divided and maintains high thermal efficiency.

  In Example 4, a numerical simulation for specifying a suitable range of the second injection timing according to the present invention was performed.

  Specifically, in the multi-stage injection type diesel engine 1 including the piston 2 of the above-described embodiment, five cases with different first injection timings and different first injection timings were set. Then, for each case, the distribution of the gas phase equivalence ratio in the cylinder 4 when the multistage combustion was performed according to the control method of the present embodiment described above was calculated every 2.5 ° as the crank angle. The result is shown in FIG.

  The first injection timing was set to 35 ° before top dead center (−35 ° CA ATDC) in the crank angle in any case. Also, the second injection timing is 10 ° before top dead center (−10 ° CA ATDC), 5 ° before top dead center (−5 ° CA ATDC), and top dead center (0 ° CA ATDC). There were five types, 5 ° after top dead center (5 ° CA ATDC) and 10 ° after top dead center (10 ° CA ATDC).

  As described above, the second injection timing is determined such that most of the fuel enters the second combustion chamber 22, so that a smoke reduction effect can be obtained. In this regard, when the second injection timing is 5 ° after the top dead center and 10 ° after the top dead center, as shown in FIG. 9, an air-fuel mixture with a high gas phase equivalence ratio is formed in the first combustion chamber 21. Yes. In particular, in the case of 10 ° after the top dead center, since almost half of the fuel has entered the first combustion chamber 21, it is estimated that the amount of smoke discharged increases significantly.

  On the other hand, as shown in FIG. 9, when the second injection timing is in the range from 10 ° before top dead center to 0 ° top dead center, the fuel at the second injection timing has entered the first combustion chamber 21 so much. Absent. In particular, the fuel is introduced into the second combustion chamber 22 most in the case of 5 ° before top dead center, and the fuel is spatially distributed. That is, the fuel at the second injection timing does not enter the first combustion chamber 21 that is in a high-temperature and low-oxygen atmosphere due to the combustion at the first injection timing, and oxygen remains. Since it is introduced into the combustion chamber 22, it is estimated that the amount of smoke discharged is greatly reduced.

  Therefore, according to the fourth embodiment described above, the second injection timing according to the present invention is preferably set within a range of 10 ° or more before top dead center and less than 5 ° after top dead center as the crank angle. It was shown that the crank angle is most preferably 5 ° before top dead center. According to the second injection timing, the injected fuel is sprayed to the lower surface side of the fuel introduction ridge 24.

  Next, in Example 5, an experiment for confirming a suitable range of the second injection timing using an actual engine was performed.

  Specifically, a test operation was performed for three cases with different second injection timings using the actual multistage diesel engine 1 to which the piston 2 of the present embodiment was attached. And the smoke discharge | emission amount was measured about each case. The result is shown in FIG. As the second injection timing, the crank angle is 5 ° before top dead center (−5 ° CA ATDC), top dead center 0 ° (0 ° CA ATDC), and 5 ° after top dead center (5 ° CA ATDC). ).

  As shown in FIG. 10, the smoke discharge amount is most reduced when the second injection timing is 5 ° before top dead center, which is the optimal timing specified in the fourth embodiment. This result corresponds to the numerical simulation result in the fourth embodiment. Moreover, although not experimented, from the result of Example 4, when the second injection timing is set to 10 ° after the top dead center, it is presumed that the smoke emission amount increases more than 5 ° after the top dead center. The

  In the fifth embodiment, the temperature distribution in the cylinder 4 at 5 ° before top dead center and 0 ° top dead center (TDC) when the first injection timing is set to 35 ° before top dead center. Is shown in FIG. This temperature environment is caused by the combustion at the first injection timing, but the high temperature region is concentrated on the first combustion chamber 21 side.

  On the other hand, as described above, the smoke is generated by the fuel injected at the second injection timing entering the high temperature and low oxygen atmosphere generated by the combustion at the first injection timing. In this regard, referring to FIG. 9, when the second injection timing is 10 ° before top dead center and 5 ° before top dead center, the injected fuel is in a positional relationship that hardly interferes with the first combustion chamber 21. ing. Therefore, it is considered that the amount of smoke discharged when the second injection timing is 10 ° before top dead center is not significantly different from the case of 5 ° before top dead center.

  According to the fifth embodiment described above, in the multi-stage injection type diesel engine 1 having the piston 2 of the present embodiment, the fuel that enters the first combustion chamber 21 as much as possible when the second injection timing is performed near the top dead center. It has been shown that the smoke emission amount is reduced by determining the injection timing so that the amount of smoke is reduced, so that it is effective.

  The multistage injection diesel engine 1 according to the present invention, the mechanical device including the same, and the control method of the multistage injection diesel engine 1 are not limited to the above-described embodiment, and can be changed as appropriate. .

DESCRIPTION OF SYMBOLS 1 Multistage injection type diesel engine 2 Piston 3 Fuel-injection injector 4 Cylinder 20 Cavity 21 1st combustion chamber 22 2nd combustion chamber 23 Fuel raising return part 24 Fuel introduction protruding part

Claims (10)

A multistage injection diesel engine comprising a piston having a cavity on the top surface and a fuel injection injector capable of multistage injection of fuel toward the cavity,
The cavity is formed in a substantially circular shape in a plan view with respect to the axial center of the fuel injection injector, and is concentrically formed with a smaller diameter than the first combustion chamber. A second combustion chamber recessed in a deep position,
The fuel injection injector injects fuel into the first combustion chamber at a first injection timing in a compression stroke, and performs the second combustion at a second injection timing located near the top dead center in the compression stroke or expansion stroke. A multistage diesel engine that injects fuel into the chamber.   The first injection timing is set in a range of 40 ° before top dead center and less than 30 ° before top dead center in crank angle, and the second injection timing is 10 ° or more in front of top dead center in crank angle and The multi-stage injection type diesel engine according to claim 1, which is set in a range of less than 5 ° after top dead center.   The multistage injection diesel engine according to claim 1 or 2, wherein an injection amount at the first injection timing is set to 30 to 50% of an injection amount at the second injection timing. 4. The multistage according to claim 1, wherein a bottom surface of the first combustion chamber is inclined so as to become deeper toward an outer peripheral side, and an inclination angle thereof is expressed by the following formula (1). Injection diesel engine;
θ ≦ 90 ° −θinj / 2 Formula (1)
However, each symbol represents the following.
θ: Angle of inclination of the bottom of the first combustion chamber [°]
θinj: Fuel injector injector nozzle angle [°]   The first combustion chamber has an inner peripheral surface formed in a concave curved shape, and its upper end edge is reduced in diameter from the maximum diameter of the first combustion chamber, and is injected at the first injection timing. The multistage injection diesel engine according to any one of claims 1 to 4, further comprising a fuel winding return portion for winding up the fuel.   The inner surface of the second combustion chamber is formed in a concave curve, and the upper edge of the second combustion chamber is raised in a convex curve so that the diameter of the second combustion chamber is smaller than the maximum diameter of the second combustion chamber. The multistage injection type according to any one of claims 1 to 5, further comprising a fuel introduction bulge for introducing the fuel injected at a second injection timing into a bottom of the second combustion chamber. diesel engine.   A mechanical device comprising the multi-stage injection type diesel engine according to any one of claims 1 to 6. A control method for a multi-stage injection diesel engine comprising a piston having a cavity on a top surface and a fuel injection injector capable of multi-stage injection of fuel toward the cavity,
The cavity is formed in a substantially circular shape in a plan view with respect to the axial center of the fuel injection injector, and is concentrically formed with a smaller diameter than the first combustion chamber. A second combustion chamber recessed in a deep position,
The fuel injection injector injects fuel into the first combustion chamber at a first injection timing in a compression stroke, and performs the second combustion at a second injection timing located near the top dead center in the compression stroke or expansion stroke. A control method for a multi-stage injection type diesel engine in which fuel is injected into a chamber.   The first injection timing is set in a range of 40 ° before top dead center and less than 30 ° before top dead center in crank angle, and the second injection timing is 10 ° or more in front of top dead center in crank angle and The control method of a multistage injection type diesel engine according to claim 8, which is set in a range of less than 5 ° after top dead center.   The method for controlling a multi-stage injection diesel engine according to claim 8 or 9, wherein an injection amount at the first injection timing is set to 30 to 50% of an injection amount at the second injection timing.