JPH10281030A - Fuel injection pump of diesel engine for dimethyl ether - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress leak from a fuel injection pump and solve a problem posed due to this leak by specifying a dimension of the diameter gap of a plunger and a plunger barrel, in a fuel injection pump of a diesel engine for which dimethyl ether is used as main fuel. SOLUTION: A fuel infection pump 2 injects fuel from an injection nozzle 3 because a plunger 6 inserted into a plunger barrel 7 moves in the vertical direction and a valve, etc., interlocks with the vertical movement. When a diesel engine is operated, dimetyl ether feel gas leaking from the gap of the plunger 6 and the plunger barrel 7 is made to be sucked within a leak gas introduction pipe 13 due to flow generated within a plunger lower part chamber 12 and to be mixed with intake gas. At this time, a radial gap between a plunger outer peripheral surface and a plunger barrel inner peripheral surface is determined for less than 3 μm. Thus, leak of combustible gas to a crank chamber 17 is suppressed, improving lubricity in the plunger lower part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection pump for a diesel engine using dimethyl ether as a main fuel.

[0002]

2. Description of the Related Art In a fuel injection pump used for a diesel engine using light oil as a fuel, a plunger made of carbon steel and a plunger barrel made of carbon steel are manufactured with a diameter gap of about 3 to 5 μm.

[0003] Fuel is supplied from the fuel tank to the injection pump under a pressure of about 2 kgf / cm ² by a feeder pump provided on a pipe connecting the fuel tank and the injection pump.

[0004] The sliding of the plunger between the plunger barrels is designed so as to perform lubrication by the slight viscosity of the fuel itself of the light oil leaking from the gap between the plunger and the plunger barrel to the fuel pump cam chamber, and the amount of leakage is generally large. Is said to be 0.01% of the injection amount.

[0005] Therefore, the amount of fuel leakage from the injection pump is not a problem in the case of a diesel engine using light oil as a main fuel in terms of lubricating oil dilution, fuel efficiency, safety and the like.

[0006] Alcohol-based diesel fuel represented by methanol is generally 1/10 to 1/20 that of light oil.
It is said to be viscous.

When such a low-viscosity fuel is used, the amount of leakage from the gap between the plunger barrel and the plunger of the injection pump increases, and the fuel is supplied via a diaphragm to avoid diluting the lubricating oil of the fuel injection pump. Has been proposed (JP-A-6-173811).

Further, when these low-viscosity fuels are used in an injection pump, seizure of the plunger and the plunger barrel poses a problem. Therefore, a solid lubricant film is formed on the plunger (Japanese Patent Laid-Open No. 4-272468), A device for holding a liquid on the surface of a plunger or a plunger barrel (Japanese Patent Publication No. 61-140172, Japanese Patent Publication No.
1-1183462) has been proposed.

Further, there is an attempt to prevent seizure by performing a sulfurating treatment on the plunger surface.

In order to adjust the properties of the low-viscosity fuel,
Attempts have also been made to add a lubricating oil as a fuel additive to an alcohol-based low-viscosity fuel to adjust the viscosity to about that of light oil.

On the other hand, a report on a diesel engine using dimethyl ether as a fuel (SAE Paper 950)
064, 950062), but the type of the injection pump is of a different type in terms of the unit injector type, and there is no detailed description of measures against DME leak gas.

[0012]

When dimethyl ether (hereinafter DME) fuel is applied to a diesel engine,
Since it has the same cetane number as light oil, it can be used not only as an alternative fuel for current diesel engines, but also has a lower NOx concentration in exhaust gas compared to light oil diesel combustion, resulting in extremely low smoke emissions in the entire power range. It is expected to be a little clean fuel.

The present inventors have focused on DME as a new fuel with low pollution for diesel engines, and have conducted intensive studies in order to commercialize it.

As a result, the following facts have been found.

Since the DME fuel has a low boiling point of about -25 ° C., it is a gas at ordinary temperature, while the fuel must be a liquid in order to be pressurized by an injection pump of a diesel engine.

[0016] The temperature in the injection pump increases during operation of the diesel engine. Even when the temperature rises, it is necessary to pressurize the fuel at such a pressure that DME, which is a low-boiling fuel, is liquid. Therefore, in order to supply a liquid to a fuel injection pump of a diesel engine, the pressure is required to be in a range of 15 kgf / cm ² to 30 kgf / cm ^2.
It is necessary to supply at a pressure as high as kgf / cm ² .

The viscosity of DME liquid fuel is 1/10 to 1/2 that of light oil, similar to alcohol fuel such as methanol.
0.

When such a DME fuel is applied to a diesel injection pump, the fuel leaking from the gap between the plunger barrel and the plunger because the pressure supplied to the injection pump is higher than that of light oil and the viscosity is low. Is much larger than when light oil is used.

DM leaking from the plunger and the plunger barrel to the injection pump cam chamber through the lower chamber of the plunger.
The E fuel is gasified, and although there is no problem with the dilutability of the lubricating oil of the injection pump, since it is released into the atmosphere in an engine crankcase open type diesel engine, fuel consumption is reduced by the amount of fuel gas released.

In a diesel engine having a closed engine crankcase, the injection pump and the crankcase have a closed structure. In the closed engine, the crankcase is connected to an engine intake pipe so that blow-by gas is not released to the atmosphere. A blow-by gas conduit 11 is provided. At that time, the engine crank chamber has a slight negative pressure.
As shown in FIG. 6, the DME fuel gas leaked from the plunger and gasified flows into the lower plunger chamber 12. At this time, the internal pressure in the plunger lower chamber 12 is about one hundred and several tens of millimeters. The fuel injection pump has a structure as shown in FIG. Flows out into the engine crank chamber 17. The DME gas flowing into the crank chamber 17 is returned to the engine intake pipe 18 through the blow-by gas conduit 11 together with the blow-by gas such as lubricating oil. As a result, the DME gas leaked from the injection pump is sucked into the engine together with the air from the intake pipe, thereby contributing to combustion,
As for the deterioration of the fuel efficiency, it is possible to obtain the same fuel efficiency as that of light oil as compared with the case of releasing the leak gas to the atmosphere.

However, in this case, the DME fuel leak gas (flammable gas) flows into the crank chamber, and the crank chamber is filled with the combustible gas. This is a safety issue.

In a diesel engine using DME fuel as the main fuel, the fuel supply pressure to the injection pump is large.
Since a large amount of leakage occurs in the plunger and the low boiling point, the DME liquid fuel is vaporized at the same time as the leakage from the plunger, and as a result, it is conceivable that the DME liquid fuel leaks at a very high flow velocity in the lower part of the plunger. For this reason,
Due to this fast gas flow, lubrication by the lubricating oil mist at the lower portion of the plunger is hindered, and there is a problem with seizure of the sliding portion of the plunger.

The plunger pump for low-viscosity fuel proposed in Japanese Patent Application Laid-Open No. 6-173811 is a compression device via a diaphragm and has a hermetically sealed structure. Is a problem.

In the conventional technique of the low-viscosity fuel plunger pump, the main focus is on the wear resistance and prevention of seizure of the plunger and the plunger barrel of the injection pump when the low-viscosity fuel is used. No leak is mentioned. In the proposed technique, when dimethyl ether fuel is used, a large amount of leakage occurs due to a large supply pressure to the injection pump, and the fuel vaporizes and leaks at a large flow rate.

An object of the present invention is to suppress a leak from a gap between a plunger and a plunger barrel of a fuel injection pump when dimethyl ether fuel is used as a diesel engine fuel, and to solve a problem caused by the leak.

Another object of the present invention is to provide a fuel injection pump capable of preventing seizure of a plunger and a plunger barrel of a fuel injection pump when dimethyl ether fuel is used as a diesel engine fuel.

[0027]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, in the case of DME fuel, even if the gap between the plunger and the plunger barrel of the fuel injection pump is less than 3 μm, the leakage will occur. It has been found that lubricating properties can be ensured by the DME performed, while troubles caused by leaked DME can be improved.

That is, the present invention relates to a fuel injection pump for a diesel engine using dimethyl ether as a main fuel, wherein a diameter gap between a plunger and a plunger barrel is less than 3 μm.

It has also been found that by spraying a nickel-based or chromium-based alloy on the surface of the plunger, seizure problems can be greatly reduced.

Therefore, the present invention is characterized in that in the above fuel injection pump, both the plunger and the plunger barrel are made of carbon steel, and a nickel-based or chromium-based alloy is thermally sprayed on the outer peripheral surface of the plunger. A fuel injection pump is also provided.

[0031]

DETAILED DESCRIPTION OF THE INVENTION The radial gap between the plunger and the plunger barrel, that is, the radial distance between the outer peripheral surface of the plunger and the inner peripheral surface of the plunger barrel is less than 3 μm, preferably 2.5 μm or less, particularly preferably 2.5 μm or less. 2.0
μm or less. On the other hand, the lower limit is 1.0 μm or more, preferably 1.2 μm or more from the viewpoint of lubricity and workability.

The upper limit of the leak amount of DME is 10%, preferably 5%, particularly preferably 3% of the supplied DME amount, and the lower limit is 1%.

In order to prevent cohesive wear on the plunger surface, it is preferable to use a dissimilar metal from the plunger barrel so that the plunger does not form an alloy.

Therefore, when processing the conventional plunger, the gap is adjusted by spraying a nickel-based alloy or a chromium-based alloy on the outer peripheral surface to form a coating, thereby reducing sintering troubles. be able to. Nickel-based alloys include nickel-chromium-boron alloys such as Ni-Cr-B-Si alloys and Ni-Cr-W-M
o Alloys such as nickel-chromium-molybdenum alloys
(Including a self-fluxing alloy.) The chromium-based alloy may be, for example, a chromium-cobalt-tungsten alloy. The thickness of the coating is usually sprayed about 1 mm, and after spray coating, reworked so as to obtain a design interval.
mm.

This will be described with reference to FIGS. 1 and 2. FIG. 2 shows a state in which the plunger 6 is inserted into the plunger barrel 7, and in FIG. Is formed.

FIG. 3 is a structural view of a main part of the diesel engine used in the test of the present invention, FIG. 4 is an enlarged view showing a connection state between the injection pump and an intake pipe, and FIG. 5 shows a structure of a general injection pump. FIG.

The device shown in FIG. 3 comprises a fuel tank 1, a fuel injection pump 2, and a diesel engine main body 9.

The fuel tank 1 has a pressurized DME supply pipe 5
And a connecting pipe 10 for supplying this pressurized DME to the injection pump.
Is connected.

The fuel injection pump 2 has a structure as shown in FIG. The plunger 6 inserted into the plunger barrel 7 moves up and down by the cam mechanism, and the valve 20 and the like open and close in conjunction therewith, thereby injecting fuel from the injection nozzle 3 into the combustion chamber 19 of the diesel engine. The lower part of the plunger 6 is a plunger lower chamber 12, and the lower part of the plunger 6 is a cam chamber 15 via a tappet part 14 that pushes up the plunger 6. A cover plate 21 is mounted on the left side wall of the plunger lower chamber 12 in the drawing.
One end is welded there.

FIGS. 3 and 4 schematically show the fuel injection pump 2. As shown in FIGS.
The number of fuel injection pumps 2 corresponding to the number of cylinders is arranged in series.

The diesel engine body 9 has a fuel chamber 19 inside.
A cylinder having a fuel injection nozzle 3, an intake pipe 18, and exhaust gas is provided on a top surface of the cylinder. A tube is attached. A fuel pipe 4 from a discharge port of the fuel injection pump 2 is connected to the fuel injection nozzle 3. Further, the other end of the leak gas introducing pipe 13 is connected to the intake pipe 18 as shown in FIG. Although not shown in FIG. 3, the blow-by gas conduit 11 from the crank chamber 17 is also connected to the intake pipe 18 as shown in FIG.

When this diesel engine is operated, the leak gas introduction pipe 13 is connected to the intake pipe 18 at a negative pressure, so that the atmosphere gas reaching the intake pipe 18 through the leak gas introduction pipe 13 in the lower plunger chamber 12. A flow occurs, and the pressure becomes approximately the same as the negative pressure in the intake pipe 18. The vaporized DME fuel gas leaking from the gap between the plunger 6 and the plunger barrel 7 is supplied to the plunger lower chamber 12.
The gas is sucked into the leak gas introduction pipe 13 along with the flow generated therein, and is mixed with the intake gas. Therefore, through the tappet portion 14 of the injection pump 2, the injection pump cam chamber 15
The flow of DME fuel gas from the engine into the engine crank chamber 17 disappears, and the DME leak gas fuel in the plunger 6 is drawn into the intake pipe 18 through the almost 100% leak gas introduction pipe 13.

The lower plunger chamber 12 is provided with an intake pipe 18.
When the pressure becomes as low as the inside pressure, the expansion gas flow due to the vaporization of the DME fuel and the inside of the plunger lower chamber 12 become 10
Due to the positive pressure of about 0 mm water column, the lubricating oil mist blown up from the cam chamber 8 of the injection pump 2 is easily supplied to the lower part of the plunger 6.

In the above embodiment, one end of the leak gas introducing pipe 13 is connected to the cover plate 21 of the lower plunger chamber 12, which is connected to the lower plunger chamber 12.
It goes without saying that it may be connected anywhere.
Further, the other end of the leak gas introduction pipe 13 is connected so as to protrude inside the intake pipe 18, but does not have to protrude inside. On the other hand, it is also preferable to project and bend its end in the airflow direction in the intake pipe.

Further, the other end of the leak gas introducing pipe may be connected directly to the combustion chamber by providing a valve which is linked to the blow-by gas pipe or the valve of the intake pipe.

In addition, a bypass may be provided in the intake pipe so that the bypass passes through the lower plunger chamber.

[0047]

EXAMPLE The apparatus shown in FIG. 1 was used.

The fuel supply method is such that the secondary pressure attached to the outlet of the nitrogen gas cylinder, which is the pressurizing means of the DME, is increased by 15 kgf.
/ Cm ² -30kgf / cm ^{2 is} a pressure regulator that is constant and can adjust the pressure.
The fuel supply method is such that a nitrogen gas pressure exceeding the vapor pressure of the E fuel is applied to pump the DME fuel as a liquid fuel to the fuel injection pump.

The plunger 6 includes a conventional plunger having a gap of 5 μm between the plunger barrel 7 and the plunger 6 shown in FIG. 4 and a sulfide (Na ₂ S ₂₎ added to a neutral salt bath or a reducing salt bath. and those sulphurized O _2, etc.) and a salt bath treatment plus, the surface of the plunger, nickel-based alloys 8
(In general, a nickel self-fluxing alloy (nickel-chromium-boron-based (Ni-Cr-B-Si alloy))) is sprayed and re-worked to reduce the gap between the plunger and the plunger barrel by about 2 mm.
Each injection pump having a size of μm was used.

Each injection pump has a fuel pressure of 25 kgf
When an injection test of DME fuel from the injection pump was performed at / cm ² , the leakage amount of dimethyl ether fuel from the plunger at this time was as follows. The leak amount is a ratio to the injection amount.

[0051]

[Table 1]

As shown in the above table, an experiment was also conducted on a plunger whose surface was sulfurized, but there was no improvement in the amount of leakage.

When the system was operated with a diesel engine using DME, the temperature around the injection pump was reduced by about 10 degrees on average. This is probably because the DME vaporized when leaking from the plunger and was cooled due to heat of vaporization.

The wear resistance (adhesion wear resistance) of the nickel-based alloy due to thermal spraying has been improved, and the low boiling fuel D
Due to the cooling effect of the plunger due to the heat of vaporization at the time of ME leak, even if the gap between the plunger and the plunger barrel is smaller than before, the operation was possible without seizure.

When using a DME fuel and using a plunger having a leak amount of 5% of the injection amount of the plunger pump, the combustion of the diesel engine is stable, and the fuel efficiency is also improved.
In an engine crankcase open type diesel engine,
Compared with light oil combustion, a deterioration of about 5% corresponding to the amount of DME fuel leak gas release was observed.

Similarly, the fuel efficiency of the closed crankcase type diesel engine was almost the same as that of light oil. The fuel efficiency when the leak gas inlet pipe was connected was almost the same as that of light oil.

Next, when a combustion test was carried out with the leak gas introduction pipe removed in FIG. 3, when a DME fuel was used, a sulfuration treatment type plunger having a leakage amount of 20% by an injection pump was used for a diesel engine. Combustion was not stable.

On the other hand, when the plunger having a DME fuel leak amount of 5% is used, the combustion of the diesel engine is stable, and the fuel efficiency is lower at a low rotation speed and a low torque than at the time of light oil combustion. The extent of the deterioration was suppressed.

[0059]

According to the present invention, even if there is a fuel leak from the gap between the plunger and the plunger barrel of the fuel injection pump which occurs when DME fuel is used as the main fuel of the diesel engine, the lubricity under the plunger is improved. Improved combustible gas to the crankcase (DME leak gas)
In addition to preventing inflow, it is possible to improve the deterioration of fuel efficiency due to the release of leak gas to the atmosphere by a simple method,
Seizure between the plunger and the plunger barrel can be prevented.

[Brief description of the drawings]

FIG. 1 is a cutaway perspective view schematically illustrating a state in which a plunger having a surface sprayed with a Ni alloy is inserted into a plunger barrel.

FIG. 2 is a cutaway perspective view schematically illustrating a state in which a plunger whose surface is not thermally sprayed with a Ni alloy is inserted into a plunger barrel.

FIG. 3 is a main part configuration diagram of a diesel engine used in a test of the present invention.

FIG. 4 is an enlarged view showing a connection state between the injection pump and the intake pipe.

FIG. 5 is a sectional view showing a structure of a general injection pump.

FIG. 6 is a configuration diagram of a main part of a conventional diesel engine having a closed engine crankcase.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel tank 2 fuel injection pump 3 injection nozzle 4 fuel pipe 5 pressurized DME supply pipe 6 plunger 7 plunger barrel 8 sprayed Ni alloy 9 diesel engine body 10 connection pipe 11 blow-by gas pipe DESCRIPTION OF SYMBOLS 12 ... Lower chamber of plunger 13 ... Leak gas introduction pipe 14 ... Tappet part 15 ... Cam chamber 16 ... Camshaft 17 ... Crank chamber 18 ... Intake pipe 19 ... Combustion chamber 20 ... Valve 21 ... Cover plate

Claims (3)

[Claims] 1. A fuel injection pump for a diesel engine using dimethyl ether as a main fuel, wherein a diameter gap between a plunger and a plunger barrel is less than 3 μm. 2. The fuel injection pump according to claim 1, wherein the outer peripheral surface of the plunger and the inner peripheral surface of the plunger barrel are formed of different metals. 3. The fuel injection pump according to claim 1, wherein both the plunger and the plunger barrel are made of carbon steel, and a nickel-based or chromium-based alloy is thermally sprayed on an outer peripheral surface of the plunger.