JP2005030327A6 - Fuel supply system for liquefied gas engine - Google Patents

Abstract

To provide a fuel supply device for a liquefied gas engine capable of avoiding excessive fuel release in a common rail as much as possible while reliably preventing abnormal combustion when the engine is restarted.
A fuel supply apparatus for a liquefied gas engine having a purge line for extracting fuel from a common rail to a fuel tank through a purge control valve when the engine is stopped, and a temperature at which the fuel temperature and pressure in the common rail are detected. A sensor 17, a pressure sensor 18, and a water temperature sensor 20 that detects the temperature of the cooling water 19 are provided. Based on the detection signals 17 a, 18 a, and 20 a from these sensors, the amount of gas leakage from the injector 7 is abnormal when restarted. The control device 21 calculates a waiting time T that is expected to reach a warning value that may cause combustion, and opens from the control device 21 to the purge control valve 9 only under a condition in which no restart request is made within the waiting time T. The valve command 9a is output.
[Selection] Figure 1

Description

  The present invention relates to a fuel supply apparatus for a liquefied gas engine that uses liquefied gas such as dimethyl ether as fuel.

  In recent years, dimethyl ether (hereinafter abbreviated as DME), which smokelessly burns with a high cetane number (55 or more), has been attracting attention as an alternative fuel for petroleum and light oil, and in particular, achieved low NOx with EGR (exhaust gas recirculation) and catalysts. From the viewpoint of satisfying strict exhaust regulations in the future, studies are underway as alternative fuels for diesel engines.

  However, since DME has a characteristic that its boiling point is as low as −25 ° C. and is easy to evaporate, the characteristics of DME are fully taken into consideration in the practical use of a DME engine using DME as fuel. It is considered that a fuel supply device is required. For example, a fuel supply device for a DME engine as shown in FIG. 3 has already been proposed.

  In the example shown here, the fuel (DME) stored in the fuel tank 1 at a pressure of about 0.4 to 1 MPa is sent to the feed line 3 by the feed pump 2 and installed in the middle of the feed line 3. The high pressure pump 4 increases the pressure to about 15 to 50 MPa and accumulates the pressure in the common rail 5. The fuel is guided from the common rail 5 to the injector 7 of each cylinder through the injection line 6 and injected into the combustion chamber 8 by valve opening control. It is made to burn by compression ignition as in the case of a normal diesel engine.

  In addition, when the pressure exceeds a predetermined value in the fuel gallery in the high-pressure pump 4, surplus fuel is released to the return line 3 ′ via the overflow valve and returned to the fuel tank 1.

  In such a fuel supply device, when the flow of the fuel stops when the engine is stopped, heat is transmitted from the engine side, the temperature of the fuel in the system rises, and the common rail 5 side expands due to the temperature rise of the fuel. However, since the fuel remaining in the nozzle of the injector 7 having particularly severe thermal conditions is vaporized, the fuel from the injector 7 to which pressure from the common rail 5 side is continuously applied is burned. Leak into the gas (it is difficult to seal the gas leak even if it is liquid-tight), and the leaked vaporized gas accumulates in the combustion chamber 8 and may cause abnormal combustion the next time the engine is started. There is.

  Therefore, in order to avoid such abnormal combustion, a purge line 11 is provided for extracting fuel from the common rail 5 by the purge control valve 9 and returning it to the fuel tank 1 through the check valve 10 when the engine is stopped. In the example shown here, a branch line 13 is also provided for extracting fuel from the downstream side of the purge control valve 9 of the purge line 11 and leading it to the purge tank 12.

  That is, when the fuel in the common rail 5 is recovered in the fuel tank 1, the pressure on the common rail 5 side gradually decreases and it becomes difficult for the fuel to flow into the fuel tank 1 side. 14 is opened and the remaining fuel is recovered from the fuel tank 1 side to the low pressure purge tank 12, and the fuel extracted to the purge tank 12 and decompressed to 0 to 0.3 MPa is recirculated by the compressor 16 through the communication line 15. It is liquefied and returned to the fuel tank 1.

The prior art document information related to this type of liquefied gas engine fuel supply apparatus includes the following information by the same applicant as the present invention.
JP 2003-56393 A JP 2003-56409 A

  However, in the fuel supply system for a liquefied gas engine as described above, if the purge control valve 9 is opened every time the engine is stopped to release the fuel in the common rail 5, the fuel will be restarted after the engine is stopped. Since it takes time until the fuel is filled into the common rail 5 and rapid restart cannot be performed, a predetermined waiting time is set after the engine is stopped and the fuel is released in a relatively short stop time as much as possible. Although it is considered necessary to avoid this, the amount of heat received by the fuel in the system after the engine stops from the engine side is not constant, and varies greatly depending on the engine operating conditions immediately before the engine stops. Even if it is only set, the fuel can be released quickly even though there is still sufficient time for the vaporized gas to leak from the injector 7. Or worse is fuel released there is a possibility that may or may not be performed for the vaporized gas from the injector 7 is already beginning to leak.

  The present invention has been made in view of the above circumstances, and a fuel supply apparatus for a liquefied gas engine capable of avoiding excessive fuel release in the common rail as much as possible while reliably preventing abnormal combustion when the engine is restarted. The purpose is to provide.

The present invention includes a feed line that boosts fuel introduced from a fuel tank by a high-pressure pump and accumulates the fuel in a common rail, an injection line that directs fuel from the common rail to an injector and injects the fuel into a combustion chamber, and a purge control valve from the common rail. A liquefied gas engine fuel supply device comprising a purge line for extracting fuel through the fuel line and returning it to the fuel tank;
A temperature sensor for detecting the fuel temperature in the common rail, a pressure sensor for detecting the pressure in the common rail, a water temperature sensor for detecting the cooling water temperature, and the temperature sensor, the pressure sensor, and the water temperature sensor from when the engine is stopped. Based on the detection signal, the purge time is calculated only when the amount of gas leakage from the injector is expected to reach a warning value that may cause abnormal combustion at the time of restart and there is no restart request within this wait time. And a control device that outputs a valve opening command toward the control valve.

  Thus, in this way, when the engine is stopped, based on detection signals from the temperature sensor, pressure sensor, and water temperature sensor, the amount of gas leakage from the injector may cause abnormal combustion at the time of restart. The waiting time that is expected to reach the value is calculated by the control device, and when this waiting time has passed without a restart request, a valve opening command is output to the purge control valve to open the purge control valve. The fuel accumulated in the common rail is released and extracted to the purge line, and the fuel vaporized gas leaks from the injector into the combustion chamber, preventing the possibility of abnormal combustion when the engine is restarted. It will be.

  That is, if the temperature of the fuel in the common rail is high, the time until the fuel remaining in the injector evaporates becomes shorter. If the temperature of the fuel in the common rail is low, the time until the fuel remaining in the injector evaporates becomes longer. Become.

  Further, if the pressure of the fuel in the common rail is high, the fuel remaining in the injector is likely to leak, and if the pressure of the fuel in the common rail is low, the fuel remaining in the injector is difficult to leak.

  Further, if the temperature of the cooling water is high, sufficient warm-up of the engine has already been completed, so that heat transfer from the engine side increases, and if the temperature of the cooling water is low, sufficient warm-up of the engine is still not possible. Is not completed (it is in a state immediately after starting), the heat transfer from the engine side becomes small.

  Therefore, regarding the temperature and pressure of the fuel in the common rail having such a tendency and the coolant temperature, the relation between the actual gas leakage amount on the injector side is grasped beforehand by a preliminary experiment or the like, and a relational expression is set. If this is the case, the waiting time is calculated based on detection signals from the temperature sensor, pressure sensor, and water temperature sensor until the amount of gas leakage from the injector reaches a warning value that would cause abnormal combustion during restart. Will be.

  Then, until the standby time calculated by the control device has elapsed, even if the engine is stopped, the release of the purge control valve is retained, and if it is in this retained state, the accumulated pressure of the common rail is retained. As long as there is a margin in the necessity to release the fuel in the common rail, the release of the fuel in the common rail is avoided as much as possible, and a quick restart of the liquefied gas engine is realized.

  Further, in the present invention, the input heat amount within the latest unit time is calculated based on the engine speed and the commanded fuel injection amount diverted from the fuel injection control system, and the standby time is appropriately corrected based on this input heat amount. It is preferable that a control device is configured.

  In this way, it is possible to accurately estimate the amount of heat received by the fuel in the system from the engine side based on the amount of heat input immediately before the engine is stopped, and the standby time is shortened when the amount of heat received is large. Further, by correcting so that the standby time is extended when the amount of heat received is small, it is possible to set a further optimal standby time, and to suppress the opportunity for releasing the fuel in the common rail to the minimum necessary.

  According to the fuel supply apparatus for a liquefied gas engine of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, the waiting time is shortened and the common rail is shortened when it is necessary to quickly release the fuel in the common rail in consideration of the engine operating conditions immediately before the stop. Make appropriate adjustments to extend the waiting time when there is room to perform the fuel release within, and perform the fuel release within the common rail only under conditions where there is no restart request within this waiting time. Therefore, it is possible to avoid excessive fuel release in the common rail as much as possible while reliably preventing abnormal combustion when the engine is restarted. Can be enlarged.

  (II) According to the invention described in claim 2 of the present invention, the amount of heat received by the fuel in the system from the engine side can be accurately estimated based on the amount of input heat immediately before the engine is stopped. Since the standby time is shortened when the amount of heat is large and the standby time T is corrected to be extended when the amount of heat received is small, an even more optimal standby time can be set. Can be minimized.

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

  1 and 2 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIG. 3 represent the same items.

  With respect to the DME engine fuel supply apparatus configured in substantially the same manner as in FIG. 3 described above, in this embodiment, as shown in FIG. 1, the temperature sensor 17 for detecting the fuel temperature in the common rail 5 and the pressure in the common rail 5 are adjusted. A pressure sensor 18 for detection and a water temperature sensor 20 for detecting the temperature of the cooling water 19 of the DME engine are newly provided. The detection signals 17a, 18a from the temperature sensor 17, the pressure sensor 18, and the water temperature sensor 20 are provided. 20a is input to a control device 21 provided at a predetermined location.

  In the control device 21, when the engine is stopped, the amount of gas leakage from the injector 7 causes abnormal combustion when restarting based on the detection signals 17a, 18a, and 20a from the temperature sensor 17, the pressure sensor 18, and the water temperature sensor 20. A waiting time T that is expected to reach a warning value that may be reached is calculated, and a valve opening command 9a is output to the purge control valve 9 only under a condition in which there is no restart request within the waiting time T. Yes.

  That is, if the temperature of the fuel in the common rail 5 is high, the time until the fuel remaining in the injector 7 evaporates becomes shorter. If the temperature of the fuel in the common rail 5 is low, the fuel remaining in the injector 7 evaporates. The time will be longer.

  Further, if the fuel pressure in the common rail 5 is high, the fuel remaining in the injector 7 is likely to leak, and if the fuel pressure in the common rail 5 is low, the fuel remaining in the injector 7 is difficult to leak.

  Furthermore, if the temperature of the cooling water 19 is high, sufficient engine warm-up has already been completed, so that heat transfer from the engine side increases, and if the temperature of the cooling water 19 is low, the engine still has a sufficient temperature. Since the warm-up has not been completed (the state is immediately after starting), the heat transfer from the engine side becomes small.

  Therefore, regarding the temperature and pressure of the fuel in the common rail 5 having such a tendency and the coolant temperature, the relation between the actual gas leakage amount on the injector 7 side is grasped in advance by a preliminary experiment or the like and a relational expression is set. Then, based on the detection signals 17a, 18a, and 20a from the temperature sensor 17, the pressure sensor 18, and the water temperature sensor 20, a warning value that causes the amount of gas leakage from the injector 7 to cause abnormal combustion at the time of restart. The time until it reaches is calculated as the waiting time T.

  The control device 21 shown here also serves as an engine control computer (ECU: Electronic Control Unit). The control device 21 is provided in a driver's seat (not shown) and detects the accelerator opening as an engine load. The detection signal 22a and the detection signal 23a from the rotation sensor 23 that detects the engine speed are also input.

  The control device 21 outputs a fuel injection signal 7a for instructing the fuel injection timing and the injection amount to the injector 7 based on the detection signals 22a and 23a from the accelerator sensor 22 and the rotation sensor 23. Because the engine speed and the commanded fuel injection amount are always known, the amount of heat input within the most recent unit time (past several minutes) is calculated by integrating the engine speed and the commanded fuel injection amount. The standby time T is corrected as appropriate based on this input heat amount.

  In other words, this makes it possible to accurately estimate the amount of heat received by the fuel in the system from the engine side based on the input heat amount immediately before the engine stops, and when the amount of heat received is large, the waiting time T By correcting so that the standby time T is extended when the amount of heat received is small, it is possible to optimize the standby time T that reflects the input heat amount immediately before the engine is stopped.

  FIG. 2 shows a specific control procedure in the control device 21. In step S1, the detection signals 17a, 18a, 20a from the temperature sensor 17, the pressure sensor 18, the water temperature sensor 20, and the accelerator sensor are shown. 22 and detection signals 22a and 23a from the rotation sensor 23 are input, the temperature and pressure of the fuel in the common rail 5 and the cooling water temperature are grasped, and the input heat amount within the latest unit time (past several minutes) is sometimes It is calculated every moment.

  Next, in step S2, it is determined whether or not the engine has been stopped. If the engine has not been stopped, the process returns to step S1, and if the engine has been stopped, the process proceeds to the next step S3, where the waiting time T is set. Calculated.

  Only when it is confirmed in the next step S4 that the waiting time T has elapsed, the process proceeds to step S5, where the valve opening command 9a is output to the purge control valve 9, and the step S4 When the restart request is made while the waiting time T is counted, the control for releasing the fuel in the common rail 5 is canceled.

  Thus, if the fuel supply device is configured in this way, when the engine is stopped, the detection signals 17a, 18a and 20a from the temperature sensor 17, the pressure sensor 18 and the water temperature sensor 20, and further the control of the fuel injection. When the amount of gas leakage from the injector 7 reaches a warning value that may cause abnormal combustion at the time of restart based on the engine speed diverted from the system and the input heat amount within the most recent unit time calculated from the indicated fuel injection amount An expected waiting time T is calculated by the control device 21. When the waiting time T has passed without a restart request, a valve opening command 9a is output to the purge control valve 9, and the purge control valve 9 Is opened, the fuel accumulated in the common rail 5 is released and extracted to the purge line 11, and the fuel vaporized gas leaks from the injector 7 into the combustion chamber 8 and the engine Abnormal combustion occurs possibility is to be prevented during start-up.

  Then, until the waiting time T calculated by the control device 21 elapses, the release of the purge control valve 9 is retained even if the engine is stopped. Therefore, as long as there is a margin in the necessity to release the fuel in the common rail 5, the fuel release in the common rail 5 is avoided as much as possible, and a quick engine restart is realized.

  Therefore, according to the above embodiment, the waiting time T is shortened and the fuel in the common rail 5 is released when it is necessary to execute the fuel release in the common rail 5 at an early stage in consideration of the engine operating conditions immediately before the stop. Appropriate adjustment is made so as to extend the waiting time T when there is a margin for execution, and the fuel release in the common rail 5 is executed only under the condition that there is no restart request within the waiting time T. Therefore, excessive fuel release in the common rail 5 can be avoided as much as possible while reliably preventing abnormal combustion when the engine is restarted, and the chances of restarting the engine quickly can be greatly increased. be able to.

  Particularly in the present embodiment, the control device 21 calculates the input heat amount within the latest unit time based on the engine speed and the commanded fuel injection amount diverted from the fuel injection control system, and the standby time based on this input heat amount. Since T is appropriately corrected, it is possible to accurately estimate the amount of heat received by the fuel in the system from the engine side based on the amount of heat input immediately before the engine is stopped, and when the amount of heat received is large By shortening the standby time T and correcting the standby time T to be extended when the amount of heat received is small, a further optimal standby time T can be set, and an opportunity for releasing the fuel in the common rail 5 is necessary. It can be minimized.

  The fuel supply device for the liquefied gas engine of the present invention is not limited to the above-described embodiment. The fuel may be a liquefied gas fuel other than dimethyl ether, and the control device is an engine control computer. In addition, the feed line and the return line may be appropriately equipped with a heat exchanger for cooling the fuel, and the like, within the scope not departing from the gist of the present invention. Of course, various changes can be made.

It is a systematic diagram which shows an example of the form which implements this invention. It is a flowchart which shows the control procedure of the control apparatus of FIG. It is a systematic diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel tank 3 Feed line 4 High pressure pump 5 Common rail 6 Injection line 7 Injector 7a Fuel injection signal 8 Combustion chamber 9 Purge control valve 9a Valve opening command 11 Purge line 17 Temperature sensor 17a Detection signal 18 Pressure sensor 18a Detection signal 19 Cooling water 20 Water temperature sensor 20a Detection signal 21 Control device

Claims (2)

A feed line that boosts the fuel led from the fuel tank by a high-pressure pump and accumulates it in the common rail, an injection line that guides the fuel from the common rail to the injector and injects it into the combustion chamber, and extracts the fuel from the common rail via the purge control valve A liquefied gas engine fuel supply device comprising a purge line that returns to the fuel tank.
A temperature sensor for detecting the fuel temperature in the common rail, a pressure sensor for detecting the pressure in the common rail, a water temperature sensor for detecting the cooling water temperature, and the temperature sensor, the pressure sensor, and the water temperature sensor from when the engine is stopped. Based on the detection signal, the purge time is calculated only when the amount of gas leakage from the injector is expected to reach a warning value that may cause abnormal combustion at the time of restart and there is no restart request within this wait time. A fuel supply device for a liquefied gas engine, comprising: a control device that outputs a valve opening command toward the control valve.   The control device is configured to calculate the input heat amount in the latest unit time based on the engine speed and the commanded fuel injection amount diverted from the fuel injection control system, and appropriately correct the standby time based on this input heat amount. The fuel supply apparatus for a liquefied gas engine according to claim 1, wherein

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