JP5838730B2 - Abnormal combustion prevention system for diesel engine - Google Patents

Description

  The present invention relates to a system for preventing abnormal combustion of a diesel engine. More specifically, the present invention can prevent the occurrence of abnormal combustion at the time of engine start due to fuel leakage into a combustion chamber in a diesel engine using liquefied gas as fuel. The present invention relates to a system for preventing abnormal combustion of diesel engines.

  As a countermeasure against air pollution caused by exhaust gas from a diesel engine, use of a liquefied gas such as dimethyl ether (DME) instead of light oil, which is a conventional fuel, has been studied (for example, see Patent Document 1).

  This liquefied gas is in the form of gas from the seat portion of the injection nozzle that injects fuel into the combustion chamber, and tends to leak to the outside. Furthermore, since the liquefied gas has a lower viscosity than that of light oil, the sheet portion of the injection nozzle is likely to be worn out, which promotes leakage to the outside.

  In particular, when the engine is stopped, the liquefied gas remaining in the injection nozzle is vaporized due to a decrease in pressure, thereby causing a leak from the seat portion to the combustion chamber. Thus, when a fuel leak of liquefied gas occurs when the engine is stopped, abnormal combustion may occur at the first explosion when the engine is started, and in the worst case, the cylinder liner or the piston ring may be damaged. This becomes more prominent when a common rail type injection device that injects fuel at a high pressure is used.

  In order to solve such problems, it is conceivable to open and close the intake and exhaust valves when starting the engine to scavenge liquefied gas that remains in the combustion chamber. However, the addition of a variable valve mechanism and control logic that controls it Therefore, the configuration of the engine is complicated and the cost is greatly increased.

  Therefore, for a diesel engine using liquefied gas as a fuel, there is a demand for a system that can prevent the occurrence of abnormal combustion at the time of engine start at a low cost.

JP 2007-239651 A

  An object of the present invention is to provide a system for preventing abnormal combustion of a diesel engine that can prevent the occurrence of abnormal combustion at the time of engine start in a diesel engine using liquefied gas as a fuel at low cost.

A system for preventing abnormal combustion of a diesel engine according to the present invention that achieves the above object is a diesel engine that prevents abnormal combustion caused by fuel leakage from an injection nozzle installed in a cylinder of a diesel engine using liquefied gas as a fuel into a combustion chamber. An abnormal combustion prevention system for an engine, comprising: a loop pipe communicating with the combustion chamber through a pipe; two check valves attached in the same direction along a circumferential direction of the loop pipe; and the pipe A release valve that opens and closes the release valve, an opening and closing means that operates the relief valve, and a control means that controls the opening and closing means. The control means rotates the crankshaft with a starter when receiving a start request for the diesel engine. Driving and opening the relief valve by the opening and closing means when the cylinder is at least in a compression stroke and an expansion stroke, It is characterized in performing control to closed at all times after the constant time period.

  The above-described abnormal combustion prevention system for a diesel engine has a fuel leak detection means, and the control means detects that the fuel leak of the liquefied gas is detected only when the fuel leak detection means detects that the cylinder is at least in the compression stroke and the expansion stroke. In some cases, the opening and closing means is used to open the relief valve, and the valve is always closed after a predetermined period of time, thereby preventing delay in starting the diesel engine.

  In addition, the control means efficiently processes the premixed mixture of liquefied gas that has been evacuated in the loop pipe by closing the relief valve in the exhaust stroke, and the abnormal combustion of the diesel engine at the next engine start-up The function of the prevention system can be prevented.

  Furthermore, the control means always closes the relief valve after 2 to 3 cycles of the cylinder, so that the premixed gas of the liquefied gas stored in the combustion chamber can be completely scavenged due to fuel leak, and the diesel engine after the start It is possible not to affect driving.

  By setting the volume of the loop pipe so that the compression ratio of the gas in the cylinder is 9 or less when the relief valve is opened in the compression stroke, the occurrence of abnormal combustion can be reliably prevented.

  The abnormal combustion prevention system for a diesel engine according to the present invention is suitably used for a general internal combustion engine using liquefied gas as fuel.

  According to the abnormal combustion prevention system for a diesel engine of the present invention, since the combustion chamber is communicated with the loop pipe at least during the compression stroke and the expansion stroke of the cylinder at the time of starting the engine, it is stored in the cylinder due to fuel leak. The premixed gas of liquefied gas dissipates heat in the loop pipe and the temperature rise due to compression is suppressed and compression ignition does not occur, so that abnormal combustion can be prevented and the premixed gas of liquefied gas can be removed. It is possible to scavenge outside the engine so that it does not affect the operation of the diesel engine. Moreover, since the structure and function of the abnormal combustion prevention system are simple, an increase in cost can be suppressed.

It is a block diagram of the abnormal combustion prevention system of the diesel engine which consists of the 1st Embodiment of this invention. It is an enlarged view of the X section shown in FIG. It is a flowchart which shows the function of the control means in 1st Embodiment. It is an enlarged view which shows the state of the X section in a compression process. It is an enlarged view which shows the state of the X part in an expansion stroke. It is a block diagram of the abnormal combustion prevention system of the diesel engine which consists of the 2nd Embodiment of this invention. It is a flowchart which shows the function of the control means in 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2 show an abnormal combustion prevention system for a diesel engine according to a first embodiment of the present invention.

  In a diesel engine 1 equipped with this diesel engine abnormal combustion prevention system (hereinafter referred to as “abnormal combustion prevention system”), liquefied gas 2 such as dimethyl ether (DME) is supplied to a common rail 3 by a high-pressure pump (not shown). The engine piston 9 in the cylinder 8 is burned and expanded by being injected into the compressed air in the combustion chamber 7 of the cylinder 6 through an injection nozzle 5 that is accumulated in the engine and controlled by an ECU (engine control unit) 4. It is designed to reciprocate. The burned gas is sent from the combustion chamber 7 to the exhaust pipe 11 when the exhaust valve 10 is opened, and released into the atmosphere. On the other hand, when the intake valve 12 is opened, air is introduced from the intake pipe 13 into the combustion chamber 7 and is compressed by the engine piston 9.

  When the engine is started, the pinion 16 that is rotationally driven by the cell motor 15 of the starter 14 extends and fits toward the ring gear 17 to rotate the crankshaft 18 to perform cranking. Yes.

  The abnormal combustion prevention system includes a loop pipe 20 communicating with the head portion of the cylinder 8 through a pipe 19, a relief valve 22 attached to the pipe 19 and operated by an opening / closing means 21, and a control means 23.

  In the middle of the loop tube 20, two check valves 24 and 25 are attached at a predetermined distance so as to be in the same direction along the longitudinal direction of the loop tube 20. In the example of FIG. 2, two check valves 24 and 25 are attached in such a direction that the gas flows clockwise in the loop pipe 20. The attachment positions of the check valves 24 and 25 are not particularly limited, but are preferably attached in the vicinity of the connection portion with the pipe 19. In addition, in FIG. 2, although the ball catch type is illustrated as a form of the check valves 24 and 25, it is not restricted to this.

  Examples of the opening / closing means 21 of the relief valve 22 include an actuator and a motor using hydraulic pressure or pneumatic pressure.

  The control means 23 is composed of a CPU (Central Processing Unit) provided with a storage unit. Signal lines 27 a to 27 d are respectively connected to the opening / closing means 21, the starter 14, the rotational position sensor 26 that detects the stroke state of the cylinder 6, and the ECU 4. Connected through.

  In the configuration of FIG. 1, the control unit 23 and the ECU 4 are separated, but the ECU 4 may be integrated with the function of the control unit 23.

  The function of the abnormal combustion prevention system having such a configuration will be described below based on the flowchart shown in FIG.

  When the control means 23 receives from the ECU 4 that a start request has been issued to the diesel engine 1 in a stopped state (S10), the control means 23 rotates the pinion 16 with the cell motor 15 of the starter 14, and the pinion 16 The crankshaft 18 is rotated by being extended and fitted toward the ring gear 17 (S20). At this time, the relief valve 22 is closed.

  Next, the stroke of each cylinder 6 is detected from the rotational position sensor 26 (S30), and when the cylinder 6 is in the compression stroke, the relief valve 22 is opened by the opening / closing means 21 as shown in FIG. 4 (S40). ). Thereby, when there is a fuel leak of the liquefied gas 2 from the injection nozzle 5 into the combustion chamber 7 when the engine is stopped, at least a part of the premixed gas of the liquefied gas 2 staying in the combustion chamber 7 is connected to the pipe 19. Flows through the one check valve 24 to the loop pipe 20. At this time, since the other check valve 25 is closed, the premixed gas is temporarily stored in the loop pipe 20.

  Next, also in the expansion stroke of the cylinder 6, as shown in FIG. 5, the relief valve 22 is continuously opened (S50). As a result, the premixed gas temporarily saved in the loop pipe 20 passes through the other check valve 25 into the cylinder 8 through the other check valve 25 due to a pressure drop in the cylinder 8 due to the piston 9 being lowered. Sucked. At this time, since one check valve 24 is closed, the premixed gas in the loop pipe 20 is sucked into the cylinder 8 smoothly. Finally, the relief valve 22 is normally closed after a predetermined period (S60).

  Thus, in the compression stroke at the time of starting the engine, the relief valve 22 is opened so that the loop pipe 20 communicates with the combustion chamber 7, so that the premixing is performed in the loop pipe 20 where the surface area of contact with the outside increases. Since the heat is released and the temperature rise due to compression is suppressed and compression ignition does not occur, abnormal combustion can be prevented. At this time, suppression of compression ignition of the premixed gas due to a temporary decrease in the compression ratio in the cylinder 8 can be expected. Further, since the relief valve 22 is opened even in the expansion stroke following the compression stroke, the premixed gas of the liquefied gas 2 evacuated in the loop pipe 20 in the subsequent exhaust stroke is scavenged to the outside of the engine. The operation of the diesel engine 1 can be prevented from being affected. Furthermore, since the configuration and function of the abnormal combustion prevention system are simple, an increase in cost can be suppressed.

  Note that the premixed gas of the liquefied gas 2 leaking into the combustion chamber 7 is processed by appropriately opening and closing the relief valve 22 in the strokes other than the compression stroke and the expansion stroke during steps S50 to S60. For example, by closing the relief valve 22 in the exhaust stroke following the compression stroke and the expansion stroke, the premixed gas of the liquefied gas 2 is discharged out of the cylinder 9 through the combustion chamber 7 and the exhaust pipe 11. The premixed gas of the liquefied gas 2 saved in 20 can be efficiently processed so as not to disturb the function of the abnormal combustion prevention system at the next engine start.

  In particular, when the relief valve 22 is opened in all strokes when the engine is started, the opening / closing means 21 can be easily controlled with a simple mechanism.

  The predetermined period until the relief valve 22 is normally closed is desirably 2 to 3 cycles of the cylinder 6 from the start of the engine start. By doing so, it is possible to completely scavenge the premixed gas of the liquefied gas 2 stored in the combustion chamber 7 due to fuel leak, and it is possible to prevent the operation of the diesel engine 1 from being affected.

  Further, in order to reliably prevent the occurrence of abnormal combustion, the volume of the loop pipe 20 is set so that the premixed gas of the liquefied gas 2 stored due to fuel leaks when the relief valve 22 is opened during the compression stroke. It is necessary to make the temperature such that the temperature is lower than the temperature that causes compression ignition. Specifically, the size should be such that the compression ratio when the relief valve 22 is opened in the compression stroke is 9 or less, preferably 5 or less.

  FIG. 6 shows an abnormal combustion prevention system for a diesel engine according to the second embodiment of the present invention.

  In the embodiment shown in FIG. 1, this abnormal combustion prevention system has an oxygen sensor 28 as a fuel leak detection means attached to each of an intake pipe 13 and an exhaust pipe 11 communicating with each cylinder 6, and a control means 23 and a signal line. 27e is connected.

  The function of the abnormal combustion prevention system having such a configuration will be described below based on the flowchart shown in FIG.

  When the control means 23 receives from the ECU 4 that a start request has been issued to the diesel engine in a stopped state (S10), the control means 23 rotates the pinion 16 with the cell motor 15 of the starter 14 and also to the ring gear 17. The crankshaft 18 is rotated by extending and fitting the pinion 16 (S20). At this time, the relief valve 22 is closed.

  Then, the measured values of the oxygen sensor 28 attached to the intake pipe 13 and the exhaust pipe 11 are compared (S22), and if the difference is equal to or greater than a predetermined value (S24), the combustion chamber 7 is stopped while the engine is stopped. Therefore, when the cylinder 6 is in the compression stroke and the expansion stroke, the relief valve 22 is opened (S30 to S50), and is always closed after a predetermined period (S30 to S50). S60).

  On the other hand, if the difference between the measured values of the oxygen sensor 28 is less than the predetermined value (S24), it is determined that there is no fuel leak, and the relief valve 22 is kept closed at all times (S60).

  By doing in this way, when there is no fuel leak of the liquefied gas 2 from the injection nozzle 5, since the initial explosion at the time of engine start is normally performed with a normal compression ratio, the start of the diesel engine 1 is delayed. Can be prevented.

  The attachment positions of the oxygen sensor 28 on the intake pipe 13 and the exhaust pipe 11 are not particularly limited. For example, even if the intake pipe 13 and the exhaust pipe 11 extending from each cylinder 6 are large diameter portions that converge into one, respectively. Good.

  The use of the abnormal combustion prevention system of the present invention is not limited to the automobile diesel engine 1 as described above, but can be applied to other internal combustion engines using the liquefied gas 2 as fuel.

1 Diesel engine 2 Liquefied gas 3 Common rail 4 ECU
5 Injection nozzle 6 Cylinder 7 Combustion chamber 8 Cylinder 9 Engine piston 10 Exhaust valve 11 Exhaust pipe 12 Intake valve 13 Intake pipe 14 Starter 15 Cell motor 16 Pinion 17 Ring gear 18 Crankshaft 19 Pipe 20 Loop pipe 21 Opening / closing means 22 Relief valve 23 Control Means 24, 25 Check valve 26 Rotational position sensors 27a to 27e Signal line 28 Oxygen sensor

Claims (6)

An abnormal combustion prevention system for a diesel engine that prevents abnormal combustion caused by fuel leakage from an injection nozzle installed in a cylinder of a diesel engine using liquefied gas as fuel, into a combustion chamber,
A loop pipe communicating with the combustion chamber through a pipe, two check valves attached so as to be in the same direction along a circumferential direction of the loop pipe, a relief valve for opening and closing the pipe, and the relief valve And an opening / closing means for controlling the opening / closing means, and a control means for controlling the opening / closing means.
When the control unit receives a request for starting the diesel engine, the control unit rotates the crankshaft with a starter, and opens the relief valve by the opening / closing unit when the cylinder is at least in a compression stroke and an expansion stroke. An abnormal combustion prevention system for a diesel engine, characterized in that control is performed to always close the valve after a predetermined period. The diesel engine abnormal combustion prevention system has a fuel leak detection means,
The control means opens the relief valve by the opening / closing means when the cylinder is in at least the compression stroke and the expansion stroke only when the fuel leak detection means detects the fuel leak of the liquefied gas, The abnormal combustion prevention system for a diesel engine according to claim 1, wherein control is performed so that the valve is always closed after the period.   The abnormal combustion prevention system for a diesel engine according to claim 1 or 2, wherein the control means closes the relief valve in an exhaust stroke following the compression stroke and an expansion stroke.   The abnormal combustion prevention system for a diesel engine according to any one of claims 1 to 3, wherein the control means always closes the relief valve after two to three cycles of the cylinder.   The diesel according to any one of claims 1 to 4, wherein the volume of the loop pipe is set such that a compression ratio of gas in the cylinder is 9 or less when the relief valve is opened in the compression stroke. Engine abnormal combustion prevention system.   An internal combustion engine equipped with the abnormal combustion prevention system for a diesel engine according to any one of claims 1 to 5.

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