JP2003097307A - Fuel supply system of diesel engine for dimethylether - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent leakage of DME during engine stopping, and to allow usage of a fuel used at present in a case where the DME is not supplied due to incomplete infrastructure in a fuel supply system of a diesel engine using DME. SOLUTION: This system comprises: a fuel supply passage S1 connected to a fuel injector 5 of an engine from a DME tank via a selector valve 11; a fuel supply passage S2 branched at the selector valve 11 from a mixture tank 9 which mixes a diesel fuel and DME to store them and connected to the fuel injector 5; a fuel return passage R1 which connects the fuel overflowed from the fuel injector 5 to the DME tank 1 via the cut-off valve 12; a fuel return passage R2 which branches the overflowed fuel at the cut-off valve 12 to connect to the mixing tank 9; a DME concentration sensor 21 arranged to the fuel return passage R2; and a control means 30 for controlling switching of the both fuel supply passages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine fuel supply system using dimethyl ether as a fuel.

[0002]

2. Description of the Related Art Conventionally, in the field of diesel engines,
The use of dimethyl ether (hereinafter referred to as DME) as an alternative fuel for light oil, which is widely used as diesel fuel, is under study. Since DME is a gas at normal temperature and pressure, it must be used in a liquefied state when pressurized in a diesel engine, but it has a similar cetane number and less NOx than light oil. In particular, since soot generation is extremely low, it is attracting attention as a low-pollution fuel that replaces diesel oil for diesel engines.

However, since DME has an extremely low viscosity as compared with light oil, it has various problems when used as a fuel for a diesel engine. One of them is due to a high residual pressure in the fuel pipe during engine stop. DM with low viscosity from the injection hole of the fuel injector consisting of the fuel injection nozzle and the injector
There is a problem that E leaks and stays in the combustion chamber, causing abnormal combustion when the engine is started.

By the way, as disclosed in Japanese Patent Application Laid-Open No. 11-107871, the atmospheric pressure, the internal pressure of the fuel tank, and the fuel are used to prevent the DME from leaking from the injection hole of the fuel injector while the engine is stopped. There is an attempt to solve the above problem by detecting three pressure parameters of the return pipe internal pressure and utilizing the pressure difference between them.

[0005]

However, in the device disclosed in the above publication, residual DME in the fuel pipe communicating with the injection hole is removed by continuing the operation of the booster pump after the engine is stopped. However, it takes several minutes until the residual DME is completely removed, that is, until the pressure inside the fuel pipe becomes equal to the atmospheric pressure. There is a problem that DME leaks for a minute.

When DME fuel cannot be replenished due to insufficient infrastructure, it may be possible to temporarily run on diesel fuel currently in use (hereinafter simply abbreviated as diesel fuel), but the DME tank must be at atmospheric pressure. If
There is also a problem that diesel fuel cannot be replenished by a normal refueling method, and unnecessary control is continued.

The present invention has been made in view of the above-mentioned problems, and it is possible to use the injection hole D of the fuel injector while the engine is stopped.
A diesel engine for dimethyl ether that prevents the ME from leaking and, when the DME fuel cannot be replenished due to insufficient infrastructure of the DME fuel, uses diesel fuel stored in the mixing tank to make an emergency run. An object is to provide a fuel supply system for an engine.

[0008]

The present invention uses the following technical means in order to achieve the above object.

That is, the first invention according to claim 1 is the first to DME tank for storing dimethyl ether.
A first fuel supply path connected to a fuel injector for injecting high-pressure fuel into the engine via the switching valve of the first and a mixing tank for storing the diesel fuel and dimethyl ether currently in use and storing the first switching valve. Is connected to the DME tank via a second switching valve from a second fuel supply path that is branched off at and connected to the fuel injector, and a fuel recovery unit that recovers fuel that overflows from the fuel injector. First
Fuel return path, a second fuel return path branched from the fuel recovery section by the second switching valve and connected to the mixing tank, and the mixing tank via a compressor for decompressing the inside of the mixing tank. And a bypass path connected to the DME tank and a second fuel return path,
A DME concentration sensor for detecting the concentration of dimethyl ether in the fuel, a fuel remaining amount sensor provided in the DME tank for detecting the remaining fuel amount in the DME tank, and a mixing tank provided in the mixing tank A pressure sensor for detecting the internal pressure, and switching between the both fuel supply paths and between the both fuel return paths according to the detected values of the respective sensors and the respective operation categories at engine start, vehicle running, and engine stop. And a control means for controlling switching, depressurization in the mixing tank, and driving of the engine.

According to the above invention, the first and second values are determined according to the detected values of the DME concentration sensor, the remaining fuel amount sensor, and the pressure sensor, and the respective operation categories when the engine is started, the vehicle is running, and the engine is stopped. Since the fuel supply path can be switched and the first and second fuel return paths can be switched, it is possible to respectively supply DME and diesel fuel to the fuel injection system.

Therefore, as will be described later, while the engine is stopped, the inside of the fuel pipe can be replaced with the highly viscous diesel fuel in a short time to prevent the fuel leakage from the injection hole of the fuel injector. When the DME fuel cannot be replenished as described later, the diesel fuel stored in the mixing tank can be used for emergency driving.

According to a second aspect of the present invention, when the detected value of the fuel remaining amount sensor is equal to or greater than a set value, the fuel is fed from the DME tank to the first fuel supply path when the engine is started. Is supplied and fuel is returned from the fuel recovery unit to the mixing tank via the second fuel return path, and the detection value of the DME concentration sensor becomes equal to or higher than a set value, the second switching valve Are switched and fuel is returned to the DME tank through the first fuel return path at the time of start, and when the vehicle is running, the fuel circulation mode at the time of start is continued and the compressor is Is activated and fuel is returned from the mixing tank to the DME tank via the bypass path during traveling, and when the engine is stopped, the first and second switching valves are turned off. The fuel is supplied from the mixing tank to the second fuel supply path while the engine is driven, and the fuel is returned from the fuel recovery unit to the mixing tank via the second fuel return path. And D
When the detected value of the ME concentration sensor becomes equal to or lower than a set value, a fuel circulation mode at the time of stopping the driving of the engine,
It is characterized by controlling to execute.

According to the above invention, the DME tank has a DM.
E When the minimum required amount of fuel remains, DME is supplied from the DME tank to the fuel injector at engine startup,
Initially, fuel is returned from the fuel recovery unit to the mixing tank. In this case, the fuel mainly composed of diesel fuel staying in the fuel pipe is pushed back to the mixing tank by the DME, and the DME concentration in the fuel in the fuel pipe becomes high,
If the detected value of the DME concentration sensor exceeds the set value, the second
The switching valve is switched to fuel circulation in which fuel is returned to the DME tank.

While the vehicle is running, the fuel circulation is continued and the compressor operates to reduce the pressure in the mixing tank, so that the DME dissolved and mixed in the diesel fuel in the mixing tank is vaporized and separated, D through the bypass path
The vaporized and separated DME is returned to the ME tank.

When the engine is stopped, fuel mainly composed of diesel fuel is supplied from the mixing tank while the engine is running, and is returned to the mixing tank from the fuel recovery section. In this case, the DME in the fuel pipe is pushed back to the mixing tank in a short time by the fuel mainly composed of diesel fuel, the DME concentration in the fuel in the fuel pipe becomes low, and the detected value of the DME concentration sensor becomes equal to or lower than the set value, Engine drive stops. In this case, since the fuel pipe is replaced by the fuel mainly composed of highly viscous diesel fuel, the fuel does not leak from the injection hole of the fuel injector while the engine is stopped.

A third aspect of the present invention is the fuel level sensor according to the first or second aspect of the invention.
When all the detection values of the pressure sensor and the DME concentration sensor are equal to or less than the set values, the first and second switching valves are switched, and when the engine is started and the vehicle is running, the mixing tank is used to The fuel is supplied to the second fuel supply path, the fuel is returned from the fuel recovery section to the mixing tank via the second fuel return path, and the driving of the engine is immediately stopped when the engine is stopped. It is characterized in that it is controlled as follows.

According to the above invention, when the detected value of the fuel remaining amount sensor is less than or equal to the set value, it is determined that the DME storage amount in the DME tank has decreased to the use limit amount, and the pressure sensor detected. If the value is less than or equal to the set value, it is determined that the fuel in the mixing tank is diesel fuel that has a vapor pressure and is substantially separated from the DME. Therefore, when the engine is started and the vehicle is running, the fuel is injected from the mixing tank to the fuel injection system. Fuel circulation (see FIG. 5) is performed in which diesel fuel is supplied and overflowed diesel fuel is returned to the mixing tank.

In this case, when the detected value of the DME concentration sensor is less than the set value, when the engine is started and the vehicle is running.
The above fuel circulation is controlled so that when the engine is stopped, the drive of the engine is stopped immediately, so the diesel fuel from the mixing tank can be used to temporarily drive the vehicle. Becomes

According to a fourth aspect of the present invention, in the second or third aspect of the invention, the compressor is controlled so as to operate when the detected value of the pressure sensor is equal to or more than a set value. It is a feature.

According to the above invention, when the detected value of the pressure sensor is equal to or higher than the set value, it is determined that the DME dissolved and mixed in the diesel fuel in the mixing tank is not yet sufficiently vaporized and separated. Therefore, the compressor is operated to vaporize and separate the DME. On the contrary, when the detected value of the pressure sensor becomes equal to or lower than the set value, it is determined that the vaporization separation of the DME is completed, so the operation of the compressor is stopped, and unnecessary power consumption is saved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, 1 is about 0.5 MP at 20 ° C.
a DME tank for storing DME having a vapor pressure of a, 2
Is a feed pump that pressurizes and feeds DME in the DME tank 1 to about 3 MPa, is connected from the feed pump 2 to the high-pressure pump 3 via the electromagnetic first three-way valve 11, and Through a common rail 4 for accumulating high-pressure fuel pressurized at 20 MPa and pressure-fed, a fuel injector (hereinafter, referred to as an injector) 5 provided in each cylinder (not shown) of an engine 6 is connected and distributed. Of the fuel supply path S1.

On the other hand, the first three-way valve 11 is branched from the mixing tank 9 which stores the light oil, which is frequently used as diesel fuel, and a slight amount of DME in a dissolved and mixed state, and the high pressure pump 3, the common rail 4 and A second fuel supply path S2 that is distributed and connected to each injector 5 is configured.

In addition, the fuel recovery section 7 for recovering the fuel overflowed from the injector 5 while traveling is passed through the electromagnetic second three-way valve 12 and the check valve 8 to the DM.
A first fuel return route R1 connected to the E tank 1 is configured. When the internal pressure of the DME tank 1 becomes higher than the internal pressure of the pipe of the first fuel return path R1, the check valve 8 transfers fuel from the DME tank 1 to the first fuel return path R1.
It is to prevent the backflow to.

On the other hand, a second fuel return path R2 is formed which branches from the second three-way valve 12 and is connected to the above-mentioned mixing tank 9 through the DME concentration sensor 21 for detecting the DME concentration in the fuel. There is. Further, a bypass route R3 connected from the mixing tank 9 to the aforementioned DME tank 1 via a compressor 10 for decompressing the inside of the mixing tank 9 is formed.

A fuel level sensor 22 for detecting the fuel level of the DME is provided in the DME tank 1.
A pressure sensor 23 for detecting the pressure inside the tank is provided in the mixing tank 9.

The above-mentioned first and second three-way valves 11 and 12,
The DME concentration sensor 21, the fuel remaining amount sensor 22, the pressure sensor 23, the feed pump 2, the high-pressure pump 3, the solenoid valve (not shown) built in each injector 5, the compressor 10, and the like are electronic control units (hereinafter, ECU). 30)
Are connected to the first, second, and third operation sections according to the respective operation classifications when the engine is started, when the vehicle is running, and when the engine is stopped, and the detected values of the DME concentration sensor 21, the fuel remaining amount sensor 22, and the pressure sensor 23. The switching of the three-way valves 11 and 12 and the operation of the feed pump 2, the high-pressure pump 3, the electromagnetic valve built in each injector 5, the compressor 10, and the like are performed by the ECU 3.
It is controlled by 0.

Next, the operation of this embodiment will be described.

When the engine is started when the detected value of the fuel remaining amount sensor 22 of the DME tank 1 is equal to or more than the set value (for example, the fuel remaining amount is 10%), the ECU 30 operates the feed pump 2 and the high pressure pump 3. Then, as shown in FIG. 2, the DME tank 1 to the DME are connected to the first fuel supply path S.
1 flows as indicated by an arrow, the solenoid valve built in the injector 5 opens, and each injector 5 is connected to the engine 6
DME is injected into each of the cylinders to start the engine 6. Here, the fuel that has overflowed from the injector 5 during traveling travels from the fuel recovery unit 7 to the second fuel return route R.
2 as indicated by the arrow and returned to the mixing tank 9.

In this case, the first fuel supply path S1 and the second fuel supply path S1
The fuel mainly composed of light oil, which initially stayed in the pipe of the fuel return path R2, is pushed back into the mixing tank 9 by the DME, so that the DME in the fuel flowing through the second fuel return path R2.
The concentration increases. As a result, when the detected value of the DME concentration sensor 21 becomes equal to or higher than the set value (for example, DME concentration 90%), the ECU 30 causes the second three-way valve 12 to operate as shown in FIG.
3, the DME is returned to the DME tank 1 through the first fuel return route R1 as shown in FIG.

Next, when the vehicle is driven, as shown in FIG.
As shown in FIG. 5, the DME flows in the first fuel supply path S1 as indicated by the arrow, and is injected into each cylinder of the engine 6 from each injector 5, so that the engine 6 continues to be driven. First fuel overflow
DME is returned to the DME tank 1 by flowing through the fuel return path R1 as indicated by the arrow.

When the detected value of the pressure sensor 23 is equal to or higher than the set value (for example, the pressure is 0.15 MPa) while the vehicle is traveling, the compressor 10 is operated by the ECU 30 to reduce the pressure in the mixing tank 9, so that the mixing is performed. The DME dissolved and mixed in the light oil in the tank 9 is vaporized and separated, and the vaporized and separated DME is pumped back to the DME tank 1 through the bypass route R3. However, if the detected value of the pressure sensor 23 becomes equal to or less than the set value (for example, 0.14 MPa), it is determined that the vaporization separation of the DME dissolved and mixed in the light oil in the mixing tank 9 is completed, and thus the compressor The operation of 10 is stopped by the ECU 30, and unnecessary power consumption due to the operation of the compressor 10 is reduced.

Next, when the engine is stopped will be described with reference to the block diagram of FIG. 5 and the flowchart of FIG.

First, when the engine is stopped, the engine switch (not shown) is turned off (step 101). By the OFF signal of this engine switch, the first three-way valve 11
Is switched to the second fuel supply path S2 side (step 102), and the second three-way valve 12 is moved to the second fuel return path R2.
To the side (step 103).

Next, it is judged whether or not the detection value of the DME concentration sensor 21 is below a set value (for example, DME concentration 10%) (step 104). If it is not below the set value, the high-pressure pump 3 operates, and The solenoid valve of the injector 5 is opened (step 105), and the engine continues to be driven despite the engine switch being turned off.

As the engine continues to be driven, the fuel mainly composed of light oil flows from the mixing tank 9 through the second fuel supply path S2 as indicated by the arrow as shown by the bold line in FIG. 5, and the overflowed fuel is recovered by the fuel. It flows from the section 7 through the second fuel return route R2 as shown by the arrow and is returned to the mixing tank 9.

As a result, the DME staying in the pipes of the second fuel supply route S2 and the second fuel return route R2 is rapidly replaced by the fuel mainly composed of light oil, so that the DME in the fuel in the pipes is replaced. The density decreases rapidly, and the detected value of the DME density sensor 21 reaches a set value (for example, DME density 10
%) Or less, the operation of the high-pressure pump 3 is stopped, and the solenoid valve of the injector 5 is closed (step 106), which stops the driving of the engine (step 10).
7). The above control is all performed by the ECU 30.

As a result, the second fuel supply path S2 and the second fuel return path R2 communicating with the injection holes of each injector 5 are provided.
Since the fuel pipe is replaced with fuel having a high viscosity of light oil, the fuel does not leak from the injection holes of each injector 5 while the engine is stopped.

Each of the above-described fuel circulation modes at the time of starting the engine, traveling the vehicle, and stopping the engine is an operation when the DME storage amount in the DME tank 1 is equal to or more than the use limit amount (hereinafter referred to as a steady operation mode). The operation when the DME storage amount in the DME tank 1 is below the use limit amount will be described with reference to the configuration diagram of FIG. 1 and the flowchart of FIG. 7.

First, it is determined whether the detected value of the fuel remaining amount sensor 22 is less than or equal to a set value (for example, 9% of the remaining fuel amount) (step 201). If it is not less than the set value, the above-mentioned steady operation mode is executed. (Step 202). If the detection value of the fuel remaining amount sensor 22 is less than or equal to the set value, that is, if the fuel remaining amount in the DME tank 1 is less than or equal to the set value, the pressure sensor 23
It is determined whether the detected value of is less than or equal to a set value (for example, pressure 0.14 MPa) (step 203), and if it is not less than or equal to the set value, the compressor 10 operates (step 204),
DM in which the pressure inside the mixing tank 9 is reduced and dissolved in light oil
Evaporative separation of E is performed.

If the detected value of the pressure sensor 23 is below the set value, that is, if the internal pressure of the mixing tank 9 is below the set value,
The first three-way valve 11 is switched so that the high-pressure pump 3 side communicates with the second fuel supply path S2 side (step 20).
5), the second three-way valve 12 is switched so that the fuel recovery unit 7 side communicates with the second fuel return route R2 side (step 206). Next, it is determined whether the detected value of the DME concentration sensor 21 is less than or equal to a set value (for example, DME concentration 10%) (step 207), and if it is not less than or equal to the set value, the solenoid valve of each injector 5 is opened, and the high pressure is increased. The pump 3 is operated for a short time (step 208), the fuel is returned to the mixing tank 9 for a short time, and the flow returns to step 203 to repeat the subsequent flow.

If the detected value of the DME concentration sensor 21 is equal to or less than the set value, the high pressure pump 3 is activated at the time of starting the engine and running the vehicle without stopping the engine as in the above-described steady-state operation mode. The electromagnetic valve of the injector 5 is opened (step 209), whereby the light oil in the mixing tank 9 is supplied to each injector 5 and the engine is driven. The overflowed light oil is returned to the mixing tank 9 for fuel circulation. Further, when the engine is stopped, the operation of the high-pressure pump 3 is stopped and the electromagnetic valve of each injector 5 is closed (step 210).
The engine drive is stopped immediately.

As described above, when the fuel remaining amount in the DME tank 1 is less than the set value, the light oil in the mixing tank 9 is supplied, so that the DM is caused by the undeveloped infrastructure.
E Even if the fuel cannot be replenished, the mixing tank 9
By using the light oil in the vehicle, the vehicle can be run in an emergency, so there is no concern that the vehicle will be unable to run due to running out of DME fuel.

In the present embodiment, the case where the present invention is applied to the common rail type fuel injection device has been described. However, the present invention can of course be applied to a jerk type fuel injection device which has been widely used.

In the present embodiment, diesel oil was used as the diesel fuel currently used, but diesel fuel having much higher viscosity than DME may be used. Tempura oil used for pollution may be used.

In this embodiment, the electromagnetic three-way valve is used as the switching valve. However, the two commonly used electromagnetic two-way valves are replaced by two three-way valves, and two of each are used to achieve the same function. Can also have.

[0047]

Since the present invention is constructed as described above, it has the following effects.

When the engine is stopped, the fuel in the fuel pipe leading to the injection hole of the fuel injector is replaced with a fuel mainly composed of highly viscous diesel fuel in a short time. Leakage of DME from the injection holes into each cylinder is eliminated, thereby preventing abnormal combustion at engine startup.

Even when the DME fuel cannot be replenished due to the lack of infrastructure, the diesel fuel stored in the mixing tank can be used for emergency driving, so that the vehicle cannot run due to the exhaustion of DME fuel. Things can be avoided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a fuel supply system showing an embodiment of the present invention.

FIG. 2 is a route diagram showing fuel circulation at the beginning of engine startup.

FIG. 3 is a path diagram showing fuel circulation from the middle of engine startup.

FIG. 4 is a route diagram showing fuel circulation when the vehicle is traveling.

FIG. 5 is a path diagram showing fuel circulation when the engine is stopped.

FIG. 6 is a flowchart showing control when the engine is stopped.

FIG. 7 is a flow chart showing a control when traveling with a diesel fuel currently in use.

[Explanation of symbols]

1 DME tank 2 feed pump 3 high pressure pump 4 common rail 5 Fuel injector (injector) 6 engine 7 Fuel recovery section 8 Check valve 9 mixing tank 10 compressor 11 First switching valve (first three-way valve) 12 Second switching valve (second three-way valve) 21 DME concentration sensor 22 Fuel level sensor 23 Pressure sensor 30 electronic control unit (ECU) S1 First fuel supply route S2 Second fuel supply route R1 First fuel return route R2 Second fuel return route R3 bypass route

Claims (4)

[Claims] 1. A first fuel supply path connected to a fuel injector for injecting high-pressure fuel from a DME tank that stores dimethyl ether to a engine through a first switching valve, and an existing diesel fuel and dimethyl ether. A second fuel supply path that is branched from the mixing tank that stores the mixture by the first switching valve and that is connected to the fuel injector; and a fuel recovery unit that recovers fuel that overflows from the fuel injector. A first fuel return path connected to the DME tank via a second switching valve, and a second fuel return path branched from the fuel recovery unit by the second switching valve and connected to the mixing tank. A bypass path connected from the mixing tank to the DME tank via a compressor for depressurizing the inside of the mixing tank; A DME concentration sensor that detects the concentration of dimethyl ether, a fuel remaining amount sensor that is provided in the DME tank and that detects the remaining fuel amount in the DME tank, and a fuel remaining amount sensor that is provided in the mixing tank. A pressure sensor that detects pressure, and the detection values of each of the sensors and when the engine is started, the vehicle is running,
A control means for controlling switching between the both fuel supply paths, switching between the both fuel return paths, depressurization in the mixing tank, and driving of the engine according to each operation classification when the engine is stopped. Diesel engine fuel supply system for dimethyl ether. 2. When the detected value of the fuel remaining amount sensor is equal to or more than a set value, fuel is supplied from the DME tank to the first fuel supply path at the time of engine start, and the fuel recovery unit performs the operation. When the fuel is returned to the mixing tank via the second fuel return path and the detection value of the DME concentration sensor becomes equal to or more than a set value, the second switching valve is switched to change the first fuel return path. The fuel circulation mode at the time of start-up in which fuel is returned to the DME tank via the fuel circulation mode at the time of start-up while the vehicle is running, and the compressor operates to pass the bypass path from the mixing tank. In the fuel circulation mode during traveling in which fuel is returned to the DME tank through the engine, and when the engine is stopped, the first and second switching valves are switched and the engine is driven. The fuel is supplied from the mixing tank to the second fuel supply path, and the fuel is returned from the fuel recovery section to the mixing tank via the second fuel return path, and the detection value of the DME concentration sensor is detected. The fuel supply system for a diesel engine for dimethyl ether according to claim 1, wherein the fuel supply system controls the fuel circulation mode at the time of stopping to stop the driving of the engine when is less than or equal to a set value. 3. When the detection values of the fuel level sensor, the pressure sensor and the DME concentration sensor are all set values or less, the first and second switching valves are switched to start the engine. The fuel is supplied from the mixing tank to the second fuel supply path at the time of driving the vehicle, and at the same time, the fuel is returned from the fuel recovery section to the mixing tank via the second fuel return path. The fuel supply system for a diesel engine for dimethyl ether according to claim 1 or 2, wherein when the engine is stopped, the driving of the engine is controlled to be immediately stopped. 4. The fuel supply system for a diesel engine for dimethyl ether according to claim 2, wherein the compressor is controlled so as to operate when the detected value of the pressure sensor is equal to or higher than a set value.