JP3796146B2 - DME engine fuel supply system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel supply device for a DME engine using dimethyl ether as a fuel.
[0002]
[Prior art]
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.
[0003]
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.
[0004]
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 supplied to the fuel supply line by the feed pump 2 installed in the fuel tank 1. 3 to the high-pressure pump 4, and the pressure is increased to about 20 to 70 MPa by the high-pressure pump 4 to accumulate pressure on the common rail 6 via the pressure-feed line 5. And is injected into the combustion chamber 9 by valve opening control, and is combusted by compression ignition as in the case of a normal diesel engine.
[0005]
Here, the high-pressure pump 4 employs a piston-type pumping system similar to a conventional row type pump in which the plunger 10 is moved up and down by an engine drive via a cam or tappet (not shown) to compress the fuel. An electromagnetic valve 11 for controlling the discharge amount is provided for each pump cylinder.
[0006]
The solenoid valve 11 is opened during the descending stroke of the plunger 10 and fuel is introduced into the pump chamber 13. However, the solenoid valve 11 is not energized during the next ascent stroke of the plunger 10. In the opened state, the fuel taken into the pump chamber 13 from the fuel gallery 12 is discharged again to the fuel gallery 12 without being increased in pressure through the electromagnetic valve 11, and on the other hand, the timing corresponding to the required discharge amount In the state where the solenoid valve 11 is energized and closed, the retreated fuel is compressed by the plunger 10 in the pump chamber 13 and is pumped to the common rail 6 via the delivery valve 14 (check valve). It is like that.
[0007]
That is, the amount of lift of the plunger 10 after the solenoid valve 11 is closed becomes the discharge amount, and the discharge amount changes at the timing of closing the solenoid valve 11 so that the pressure of the common rail 6 is generated and controlled. It has become.
[0008]
Further, when the pressure exceeds a predetermined value in the fuel gallery 12 in the high-pressure pump 4, excess fuel is released to the fuel return line 16 by the overflow valve 15 (relief valve). Since the temperature of the fuel released in this way rises due to heat received from the engine and bubbles are easily generated, the fuel is sufficiently cooled via the fuel cooler 17 installed in the middle of the fuel and then the fuel is released via the check valve 18. Recirculation is performed in the middle of the supply line 3. In addition, the fuel cooler 17 in the drawing is an air cooling system using a battery-driven electric fan 19.
[0009]
[Problems to be solved by the invention]
However, in such a fuel supply device, when the high-pressure pump 4 is stopped when the engine is stopped and the fuel flow is stagnated, heat is transmitted from the engine or the exhaust system, the temperature of the fuel in the flow path rises, and the DME Since the combustion is vaporized regardless of the pressure when the critical temperature exceeds 127 ° C., the vaporized gas accumulates in the fuel gallery 12 in the high-pressure pump 4 and the pressure is increased, so that the sealing means 20 such as an O-ring or an oil seal is used. The fuel vaporized gas leaks to the outside (it is difficult to seal the gas leak even if it is liquid-tight), or the high pressure pump 4 is in the liquid phase when the engine is started next time. There is a possibility that seizure may be caused by being not filled with fuel.
[0010]
At present, a method for extracting fuel from the fuel supply line 3 and the fuel return line 16 and the high-pressure pump 4 when the engine is stopped has been studied as a countermeasure, but if such a method is adopted, the engine When restarting after stopping, it takes time until the fuel is filled into the fuel supply line 3, the fuel return line 16 and the high-pressure pump 4, which makes it impossible to restart the engine quickly. There was a problem.
[0011]
The present invention has been made in view of the above circumstances, and avoids leakage of fuel vaporized gas from the high-pressure pump and seizure of the high-pressure pump when the engine is stopped, and realizes quick DME engine restart. The purpose is to do.
[0012]
[Means for Solving the Problems]
The present invention relates to a fuel supply device for a DME engine in which fuel in a fuel tank is boosted by a high-pressure pump and accumulated in a common rail, and the fuel is guided from the common rail to an injector and injected into a combustion chamber. A fuel supply line that guides the fuel delivered by the pump to the high-pressure pump; and the fuel supply line that cools excess fuel released when the pressure exceeds a predetermined value in the fuel gallery in the high-pressure pump via the fuel cooler. A fuel return line that is recirculated in the middle of the fuel return line, a bypass line that appropriately draws fuel from the downstream side of the fuel cooler of the fuel return line and returns it to the fuel tank, and a connection point of the bypass line to the fuel return line The fuel that has passed through the fuel cooler is changed only when the switching command is input. A flow path switching valve that selectively distributes to the ipass line side, a temperature sensor that detects a fuel temperature of a fuel gallery in the high-pressure pump, a switching command that is output to the flow path switching valve when the engine is stopped, and the temperature sensor A control device that inputs a detection signal and outputs a start command to the feed pump and the fuel cooler only under a condition that the detected temperature exceeds a predetermined set temperature when the engine is stopped, and the control device comprises: Each time the feed pump and fuel cooler started when the engine is stopped stop due to a decrease in the temperature detected by the temperature sensor, the set temperature for outputting the next start command is set to a higher set temperature than the previous start. It is characterized by being comprised so that it may change.
[0013]
In this way, when the engine is stopped, a switching command is output from the control device to the flow path switching valve, the flow path switching valve is switched, and the fuel that has passed through the fuel cooler is selectively distributed to the bypass line side. At the same time, start commands are also output to the feed pump and fuel cooler at the same time, and the feed pump and fuel cooler are started. Therefore, even when the engine is stopped, fuel is pumped from the fuel tank by the feed pump. The fuel flows into the fuel supply line and flows into the fuel return line via the fuel gallery in the high-pressure pump. The fuel flowing into the fuel return line is cooled through the fuel cooler. After that, it is returned to the fuel tank via the flow path switching valve.
[0014]
Here, regarding the start of the feed pump and the fuel cooler when the engine is stopped, the feed pump and the fuel cooler are started when the fuel temperature of the fuel gallery in the high-pressure pump is raised to a dangerous temperature range close to the critical temperature. Since the control is performed by the control device, it is possible to significantly reduce the power consumption by limiting the drive time of the feed pump and the fuel cooler to the necessary minimum.
[0015]
In addition, even if the temperature detected by the temperature sensor falls below the set temperature and the feed pump and fuel cooler are stopped until the engine or exhaust system cools down after the engine stops, the fuel gallery of the high-pressure pump stops. The fuel temperature in the engine rises again, but the set temperature for outputting the next start command is changed to a set temperature higher than that at the previous start. A situation in which start and stop are frequently repeated is avoided.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0017]
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.
[0018]
With respect to the fuel supply device for the DME engine configured in substantially the same manner as in FIG. 3 described above, in this embodiment, as shown in FIG. 1, fuel is appropriately extracted from the downstream side of the fuel cooler 17 of the fuel return line 16 and a fuel tank. The bypass line 21 for returning to 1 is newly provided, and the bypass line 21 is connected to the fuel return line 16 at a position where the fuel that has passed through the fuel cooler 17 is input to the bypass line 21 only when the switching command 22a is input. A flow path switching valve 22 that selectively distributes to each other is provided.
[0019]
Further, the high-pressure pump 4 is newly equipped with a temperature sensor 23 for detecting the fuel temperature in the fuel gallery 12, and a detection signal 23a of the temperature sensor 23 is input to a control device 24 provided at a predetermined location. It is like that.
[0020]
The control device 24 outputs a switching command 22a toward the flow path switching valve 22 when the engine is stopped, and the detected temperature exceeds a predetermined set temperature T ₁ based on the detection signal 23a from the temperature sensor 23. The start commands 2a and 19a are appropriately output to the feed pump 2 and the electric fan 19 of the fuel cooler 17 only under the conditions.
[0021]
FIG. 2 shows a specific control procedure in the control device 24. When the engine stop is confirmed in step S1, the flow path switching valve 22 is switched by the switching command 22a in step S2, and then whether the fuel temperature in the fuel gallery 12 based on the detection signal 23a from the temperature sensor 23 at step S3 exceeds the set temperature T ₁ is determined, if it exceeds the set temperatures T ₁ to step S4 willing electric fan 19 of the feed pump 2 and the fuel cooler 17 is activated command 2a, it is started by 19a, which thereafter feed pump 2 and until drops the lower set temperature T ₁ of the detected temperature is repeated determination of the step S3 The start of the electric fan 19 of the fuel cooler 17 is continued, and on the other hand, the fuel in the fuel gallery 12 is determined in step S3. If the temperature does not exceed the set temperatures T ₁ is an electric fan 19 of the feed pump 2 and the fuel cooler 17 is adapted to be stopped proceeds to step S5.
[0022]
Here, the set temperature T ₁ used for the determination in step S3 is the value immediately before the feed pump 2 and the fuel cooler 17 that are started when the engine is stopped each time the temperature detected by the temperature sensor 23 is lowered to the set temperature. The temperature is changed to a set temperature higher than the set temperature used at the start-up.
[0023]
Thus, when the fuel supply device is configured in this way, the switching command 22a is output from the control device 24 to the flow path switching valve 22 when the engine is stopped, and the flow path switching valve 22 is switched to pass through the fuel cooler 17. The fuel is selectively distributed to the bypass line 21 side.
[0024]
When the detection signal of the temperature sensor 23 exceeds a predetermined set temperature T ₁ when the engine is stopped, the control device 24 outputs start commands 2a and 19a to the feed pump 2 and the fuel cooler 17, and the feed pump 2 and Since the fuel cooler 17 is activated, the fuel is pumped up from the fuel tank 1 by the feed pump 2 and sent out to the fuel supply line 3 even when the engine is stopped, and the fuel return is made via the fuel gallery 12 in the high-pressure pump 4. A fuel flow flowing into the line 16 is formed, and the fuel flowing into the fuel return line 16 is cooled via the fuel cooler 17 and then returned to the fuel tank 1 via the flow path switching valve 22. .
[0025]
Note that the temperature detected by the temperature sensor 23 temporarily drops below the set temperature T ₁ until the engine and exhaust system cool down and cool down after the engine is stopped, and the feed pump 2 and the fuel cooler 17 are stopped. However, the fuel temperature in the fuel gallery 12 of the high-pressure pump 4 will rise again, but the set temperature T ₁ for outputting the next start commands 2a and 19a is higher than the previous set start temperature. Therefore, the situation where the feed pump 2 and the fuel cooler 17 frequently start and stop are avoided.
[0026]
Therefore, according to the above-described embodiment, even if the high pressure pump 4 stops when the engine is stopped, it is possible to prevent the fuel flow from circulating between the fuel tank 1 and the high pressure pump 4 and stagnation of the combustion flow. Fuel vaporization in the fuel gallery 12 in the high-pressure pump 4 can be remarkably suppressed, and leakage of fuel vaporized gas from the high-pressure pump 4 and seizure of the high-pressure pump 4 when the engine is stopped can be avoided. In addition, since the fuel supply line 3, the fuel return line 16, and the high-pressure pump 4 can be kept filled with fuel even after the engine is stopped, the DME engine can be quickly restarted after the engine is stopped. Can be realized.
[0027]
Further, the control device 24 performs control so that the feed pump 2 and the fuel cooler 17 are activated when the fuel temperature of the fuel gallery 12 in the high-pressure pump 4 is raised to a dangerous temperature range close to the critical temperature. Since the drive time of the feed pump 2 and the fuel cooler 17 can be limited to the minimum necessary, the power consumption required for the feed pump 2 and the fuel cooler 17 can be significantly suppressed.
[0028]
Further, the set temperature T ₁ for outputting the start commands 2a and 19a to the feed pump 2 and the fuel cooler 17 is changed so as to gradually increase every time the feed pump 2 and the fuel cooler 17 are stopped. Therefore, the situation where the feed pump 2 and the fuel cooler 17 repeatedly start and stop can be avoided.
[0029]
The fuel supply device for the DME engine of the present invention is not limited to the above-described embodiment, and the fuel cooler is not limited to the air-cooled type, and various modifications can be made without departing from the scope of the present invention. Of course, can be added.
[0030]
【The invention's effect】
According to the fuel supply device for a DME engine of the present invention described above, various excellent effects as described below can be obtained.
[0031]
(I) Even if the high-pressure pump is stopped when the engine is stopped, fuel can be circulated between the fuel tank and the high-pressure pump to prevent the combustion flow from stagnation, so that the fuel in the fuel gallery in the high-pressure pump can be prevented. Vaporization can be remarkably suppressed, leakage of fuel vaporized gas from the high-pressure pump when the engine is stopped, and seizure of the high-pressure pump can be avoided in advance, and the fuel supply line and Since the fuel return line and the high-pressure pump can be maintained in a state filled with fuel, the DME engine can be quickly restarted after the engine is stopped.
[0032]
(II) When the fuel temperature in the fuel gallery in the high-pressure pump is raised to a dangerous temperature range close to the critical temperature, the control device controls the feed pump and the fuel cooler to control the feed pump and the fuel. Since the drive time of the cooler can be limited to a necessary minimum, the power consumption required for the feed pump and the fuel cooler can be significantly suppressed.
[0033]
(III) Since the set temperature for outputting the start command to the feed pump and the fuel cooler can be changed so as to gradually increase every time the feed pump and the fuel cooler are stopped, the feed pump and the fuel cooler are frequently used. It is possible to avoid a situation in which start and stop are repeated.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment of the present invention.
FIG. 2 is a flowchart showing a control procedure of the control device of FIG. 1;
FIG. 3 is a schematic diagram showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel tank 2 Feed pump 2a Start command 3 Fuel supply line 4 High pressure pump 6 Common rail 8 Injector 9 Combustion chamber 12 Fuel gallery 16 Fuel return line 17 Fuel cooler 19 Electric fan 19a Start command 21 Bypass line 22 Flow path switching valve 22a Switch command 23 temperature sensor 23a detection signal 24 control device

Claims (1)

In a fuel supply device for a DME engine, fuel in a fuel tank is boosted by a high-pressure pump and accumulated in a common rail, and fuel is guided from the common rail to an injector and injected into a combustion chamber.
A fuel supply line that guides fuel delivered from the fuel tank by a feed pump to the high-pressure pump and a fuel gallery in the high-pressure pump cools excess fuel that is released when the pressure exceeds a predetermined value via a fuel cooler. A fuel return line that is recirculated in the middle of the fuel supply line, a bypass line that appropriately draws fuel from the downstream side of the fuel cooler of the fuel return line and returns it to the fuel tank, and the fuel return line of the bypass line A flow path switching valve that is selectively provided to the bypass line only when a switching command is input, and a temperature sensor that detects the fuel temperature of the fuel gallery in the high-pressure pump When the engine is stopped, a switching command is output to the flow path switching valve and the temperature sensor is detected. If the input signal and a control device for detecting the temperature when the engine is stopped and outputs a start command for the feed pump and the fuel cooler only under conditions that exceed the predetermined set temperature,
In addition, every time the feed pump and the fuel cooler started when the engine is stopped are stopped due to a decrease in the temperature detected by the temperature sensor, the set temperature for outputting the next start command is set immediately before. A fuel supply device for a DME engine, wherein the fuel supply device is configured to change to a higher set temperature than at the time of startup.

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