JP2556016B2 - Dual fuel supply system - Google Patents

Description

The present invention relates to a dual fuel supply system for a diesel engine.

[Conventional technology]

When alcohol is used as a fuel instead of light oil in a diesel engine, the compression ignitability of the fuel is inferior to that of light oil. Therefore, there is an auxiliary fuel supply device that enables alcohol and light oil to be supplied separately, supplies a small amount of light oil as auxiliary fuel at the start of injection to ignite, and then supplies alcohol as main fuel. Are known. At this time, the amount of light oil required for stable ignition changes according to the engine speed. That is, the higher the speed, the greater the amount of light oil required. Therefore, it is conceivable to set the filling amount constant regardless of the engine speed, and set the fixed amount to the amount that enables stable ignition at high speed, but at low speed, it is natural that an excessive amount of light oil is filled. become. Then, on the low rotation side, excess light oil that cannot be consumed every time the fuel injection cycle is completed accumulates in the fuel injection valve and its piping system, and if acceleration or racing is performed from this state, a large amount of light oil will be injected and Occasionally smoke is seen.
The fuel injection valve is adapted to obtain a proper fuel injection amount in alcohol fuel. Therefore, the fuel injection amount becomes excessive with light oil, which has high energy generation per unit amount, and black smoke is generated. Therefore, in order to achieve both ignitability and prevention of black smoke generation by filling an appropriate amount of light oil over each rotation speed, engine load,
It has been proposed that the amount of light oil supplied is variable according to operating conditions such as the number of revolutions. For example, in Japanese Utility Model Laid-Open No. 59-190964, an auxiliary fuel pumping piston driven by the discharge pressure of a fuel injection pump that pumps the main fuel to a fuel injection valve is provided, and the auxiliary fuel formed on one side of this auxiliary fuel pumping piston. A small amount of auxiliary fuel is filled in the fuel injection valve by the pressurizing chamber prior to its injection, and when the fuel injection valve opens due to the main fuel pressure from the fuel injection pump, the filled light oil is first injected to ignite. Occurs, the alcohol as the main fuel that is subsequently injected is ignited, and the combustion stroke is performed. Further, the sub fuel pressurizing chamber is equipped with a pressure control valve that works in conjunction with the accelerator pedal, the opening of the pressure control valve is controlled according to the degree of depression of the accelerator pedal, and the fuel returned from the sub fuel pressurizing chamber to the fuel tank is controlled. The amount is changed, and as a result, the rotation speed control of the auxiliary fuel filling amount is performed.

[Problems to be solved by the invention]

In the prior art, the auxiliary fuel metering control is performed by controlling the amount of return fuel from the auxiliary fuel pressurizing chamber by means of a valve device linked to the accelerator pedal. However, this structure requires a valve device and a link system for connecting the valve device to the accelerator pedal, and thus has a drawback that the structure is complicated.

An object of the present invention is to make it possible to control the number of revolutions of the auxiliary fuel filling amount without using a valve device that works in conjunction with an accelerator pedal.

[Means for solving problems]

According to the first aspect of the present invention, the main fuel, which is not easily ignited by compression ignition, and the auxiliary fuel, which is easily ignited by compression ignition, can be separately supplied, and the injection of the auxiliary fuel is limited until the compression ignition occurs.
A dual fuel supply system for a diesel engine, which supplies main fuel after the start of compression ignition, comprising: fuel injection valve means that is opened and closed by fuel pressure; and fuel injection valve means for the fuel injection valve means in a predetermined cycle of the engine. The fuel injection valve is driven by the main fuel pressure-feeding means for supplying the main fuel having a pressure to open the valve and the main fuel pressure fed by the main fuel pressure-feeding means, and before the predetermined cycle for injecting the main fuel. Means for filling the fuel injection valve means with a small amount of auxiliary fuel at a pressure not enough to open the valve, a fuel return passage connected to the downstream side of the auxiliary fuel pressure feed means, and the fuel return passage And a throttle for controlling the flow rate of the fuel return passage in accordance with at least the engine speed.

According to the second aspect of the present invention, the main fuel, which is not easily ignited by compression ignition, and the auxiliary fuel, which is easily ignited by compression ignition, can be separately supplied, and the injection of the auxiliary fuel is limited until the compression ignition occurs.
A dual fuel supply system for a diesel engine, which supplies main fuel after the start of compression ignition, comprising: fuel injection valve means that is opened and closed by fuel pressure; and fuel injection valve means for the fuel injection valve means in a predetermined cycle of the engine. The fuel injection valve is driven by the main fuel pressure-feeding means for supplying the main fuel having a pressure to open the valve and the main fuel pressure fed by the main fuel pressure-feeding means, and before the predetermined cycle for injecting the main fuel. A fuel injection valve means for filling the fuel injection valve means with a small amount of auxiliary fuel at a pressure at which the means does not cause the valve to open, and the auxiliary fuel pressure-feeding means is housed in the casing and supplies the main fuel. Normally, a first piston that responds to the pressure and sends the auxiliary fuel under pressure and a side of the first piston that is separated from the side on which the supply pressure of the main fuel is applied are placed at a predetermined interval. A second piston that interlocks with the first piston to pump the sub fuel, a first spring that biases the first piston against the supply pressure of the main fuel, and a second piston that supplies the main fuel to the main fuel. A second spring, which is urged against the supply pressure and is stronger than the first spring, is provided until the first piston engages with the second piston due to the main fuel supply pressure when the main fuel pressure is low. A supply amount of the sub fuel corresponding to the stroke of the first piston when moving against the first spring is obtained, and during operation where the main fuel pressure is high, the main fuel supply pressure causes the first piston to move first. A secondary fuel corresponding to the total stroke of the first piston until it is combined with the second piston against the first spring and then against the second spring until the second piston engages its stopper. Is obtained.

[Action]

In the operation of the first aspect of the present invention, when the engine is running at low speed, the fuel feeding interval becomes long, and the amount of sub fuel discharged through the throttle provided in the fuel return passage becomes relatively large.
The amount of sub fuel filled in the fuel injection valve is relatively small. On the other hand, when the engine is running at high speed, the fuel feeding interval is shortened, the amount of sub fuel discharged through the throttle provided in the fuel return passage is relatively small, and the sub fuel filled in the fuel injection valve is relatively small. Is relatively large. By such an operation, it is possible to fill the optimum amount of auxiliary fuel according to the engine speed.

In the operation of the second aspect of the invention, the main fuel pressure is low at low rotation speed, and the main fuel supply pressure causes the first piston to move against the first spring until it engages with the second piston. A relatively small amount of sub fuel corresponding to At high revolutions, the main fuel pressure is high and the main fuel supply pressure causes the first piston to first resist the first spring and then merge with the second piston to resist the second spring and the second piston A large stroke is obtained until the stopper is engaged, and a relatively large amount of auxiliary fuel corresponding to the large stroke is obtained.

〔Example〕

FIG. 1 shows the whole first embodiment of the multiple fuel supply system of the invention applied to a four-cylinder diesel engine. In FIG. 1, 1 is a tank for storing alcohol as a main fuel, while 2 is a tank for storing light oil as a sub fuel. Reference numeral 3 is a pre-compression pump for alcohol, and 4 is a pre-compression pump for light oil, which is supplied to the fuel injection valve 5 fixed to the cylinder head of each cylinder by the dual fuel supply system of the present invention. The fuel injection valve 5 includes a valve casing 6 and a needle 7, and the needle 7 is biased to be seated on the valve seat 8 by a spring (not shown). An annular fuel passage 9 is formed around the needle 7 and receives the supply of alcohol, which is the main fuel, from a fuel injection pump described later. The needle 7 has a pressure receiving portion 7a that receives the main fuel pressure,
When the pressure of the main fuel overcomes the spring force, the needle 7 opens and the fuel is vigorously injected from the nozzle 10 at the lower end of the valve casing 6. An auxiliary fuel passage 11 is formed in the center of the needle 7, and the lower end of the auxiliary fuel passage 11 is open to the annular passage 9 around the needle 7. In the sub fuel passage 11, as described later,
Light oil is filled in other than the injection cycle of the cylinder,
The filled light oil is ejected from the nozzle 10 into the cylinder bore prior to the injection of alcohol during the fuel injection cycle. As a result, the light oil is first compressed and ignited, and then the alcohol is ignited to perform combustion.

The multiple fuel supply system includes a so-called distribution type fuel injection pump. For the sake of simplicity, the distributed fuel injection pump 13 will be described by its schematic configuration. The housing 14, a cylinder 15, a plunger 16 fitted into the cylinder 15, and a front cam 18 formed at one end of the plunger 16. And the housing
A roller 20 as a cam follower mounted on a ring (not shown) rotatably mounted on 14 and a plunger
16 A spill ring 22 that slides on the left and right is provided. A main fuel pressurizing chamber 24 is formed by the tip of the plunger 16 and the cylinder 15. At the tip of the plunger 16, a number of oil supply grooves 26 equal to the number of cylinders are formed at angular intervals. A drive shaft 30 is connected to the plunger 16 via a joint 28.
The drive shaft 30 is also responsible for driving the main fuel supply pump 3, and is connected to a crank shaft (not shown),
Is driven to rotate. When the plunger 16 makes one rotation, the front cam 18 and the roller 20 work to reciprocate the plunger left and right as many times as the number of cylinders. In each of the reciprocations, when the plunger moves to the left, one oil supply groove 26 is communicated with the oil supply hole 34 formed in the cylinder 15, and the alcohol introduced into the fuel storage chamber 36 of the housing 14 by the rotation of the pump 3. The fuel is introduced into the main fuel pressurizing chamber 24 through the oil supply passage 38, the oil supply hole 34, and the oil supply groove 26. When the plunger 16 moves to the right, the communication between the oil supply groove 26 and the oil supply hole 34 is cut off, and the fuel in the main fuel pressurizing chamber 24 is pressurized by the plunger 16. When the discharge port 42 formed in the plunger 16 is communicated with one of the discharge passages 44 formed radially around the plunger 16 by the number equal to the number of cylinders, the fuel in the main fuel pressurizing chamber 24 becomes The central hole 40, the discharge hole 42, the discharge passage 44 and the discharge valve 48 of the plunger 16 are pushed open, and the fuel is pressure-fed to the annular fuel passage 9 of the fuel injection valve 5 of the cylinder via the main fuel discharge passage 49. The spill ring 22 is provided to control the maximum fuel injection amount, and is installed on the plunger 16 so as to be slidable left and right. The spill ring 22 is linked to an adjust lever 52 via a link mechanism 50 which is schematically shown for the sake of simplicity, and the adjust lever 52 is linked to an accelerator pedal (not shown). Thus, the position of the spill ring 22 changes from side to side depending on the accelerator pedal, and the further the accelerator pedal is depressed, the more the spill ring 22 moves to the right, and the opening of the spill port 54 is delayed. The main fuel (ie
Alcohol) injection amount increases.

Next, an auxiliary fuel pressure feeding means for filling the fuel injection valve 5 of each cylinder with light oil as an auxiliary fuel prior to the fuel injection will be described. This auxiliary fuel pumping means is a casing 60 fixed to the housing 14, a piston 62 arranged in the casing 60, a spring 64 for urging the piston 62, and a check valve.
It consists of 66 and 68. The piston 62 is communicated with the main fuel pressurizing chamber 24 by the communication passage 70. The piston 62 is located in the auxiliary fuel pressurization chamber 72, and is normally provided by a spring 64.
62 is held at a position where it abuts on the stopper 74. The sub fuel supply pump 4 communicates with the sub fuel pressurizing chamber 72 via the sub fuel suction passage 74 and the check valve 66. Further, the auxiliary fuel pressurizing chamber 72 is connected to the auxiliary fuel discharge passage 78 via the check valve 68.
The sub fuel discharge passage 78 is connected to the sub fuel distribution passage 81 of each cylinder via a common passage 80. This sub fuel distribution passage 81 is connected to the corresponding central passage 11 of the fuel injection valve 5 via a check valve 82. As described below, the piston 62 is
When a certain fuel injection valve is considered, the fuel injection valve fills the auxiliary fuel before performing the fuel injection.

According to the present invention, since the amount of the sub fuel filled by the piston 62 is controlled according to the engine speed, the discharge passage 78 downstream of the piston 62 as the sub fuel pressure feeding means has the sub fuel return passage 83. Is connected to the sub fuel tank 2 via
In addition, the throttle 84 is arranged in the sub fuel return passage 83. As described later, the amount of fuel discharged from the discharge passage 78 to the sub fuel tank 2 changes according to the engine speed, and the amount of sub fuel filled in each fuel injection valve is controlled according to the engine speed. To be done.

The operation of the multiple fuel supply system of the invention will be described below.
The plunger 16 is rotated by the rotation of the engine, and reciprocates left and right in the same number of times as the number of cylinders during one rotation, and the discharge valve
Fuel injection valve 5 for each cylinder from 48 via main fuel discharge passage 49
The main fuel is sequentially supplied to and is injected from the nozzle 10.

The rightward and leftward movements of the plunger 16 increase or decrease the pressure in the pressure chamber 24, whereby the piston 62 moves to the right against the spring 64 or is pushed back to the left by the spring 64. When the discharge pressure (about 2 kg) of the auxiliary fuel pump 4 becomes higher than the pressure of the auxiliary fuel pressurizing chamber 72, the check valve 66 is opened to open the auxiliary fuel by the leftward movement of the piston 62. It is introduced into the pressure chamber 72. When the piston 62 moves to the right, the fuel in the auxiliary fuel pressurizing chamber 72 is pressurized by the piston 62, and the pressure is the set load of the check valve 68 (about 80 kg).
When the fuel injection valve 5 exceeds the fuel injection valve 5, the check valve 82
As a result, the auxiliary fuel is supplied to these fuel injection valves 5, and this supplied fuel is filled in the fuel injection valves via the central passage 11. Of course, this filling pressure is not sufficient to cause the needle 7 to open.

In this way, the auxiliary fuel with which the fuel injection valve of each cylinder is filled is injected from the nozzle 10 into the cylinder bore prior to the main fuel during the injection operation of the fuel injection valve of a certain cylinder. That is,
Immediately before fuel injection into a cylinder, the annular passage 9 above the valve seat 8 is somewhat filled with auxiliary fuel, and the plunger 16
When the main fuel is discharged to the passage 49 by the, the needle 7 is lifted by the pressure of the main fuel, and the sub fuel filled above the valve seat is injected from the nozzle. Since the pressure of the main fuel is higher than the pressure of the auxiliary fuel, the injection of the main fuel is continued after the injection of a small amount of the auxiliary fuel.

A part of the auxiliary fuel discharged from the auxiliary fuel chamber to the passage 78 is returned to the auxiliary fuel tank 2 side through the throttle 84. The amount of fuel returned per unit time is determined by the size of the throttle 84. The filling amount of the auxiliary fuel in the fuel injection valve 5 is the fuel discharged from the auxiliary fuel pressurizing chamber 72 less the fuel discharged to the tank 2. When the plunger 16 makes one reciprocation, the piston 62 makes one reciprocation and the fuel is discharged from the auxiliary fuel pressurizing chamber 72, and the discharge amount thereof is substantially constant and is not related to the engine speed. That is, the discharge amount of the sub fuel from the sub fuel pressurizing chamber 72 after each operation cycle of the fuel injection valve 5 hardly changes with the engine speed. On the other hand, the time interval between each reciprocation of the plunger 16, that is, the operation interval of the fuel injection valve 5 becomes shorter as the engine speed increases. This means the following: That is, at the time of low engine speed, the amount of sub fuel returned to the sub fuel tank 2 via the throttle 84 becomes relatively large, and the amount of sub fuel filled in the fuel injection valve 5 itself becomes small. on the other hand,
When the engine speed is high, the operation interval of the fuel injection valve is short, so that the amount of the sub fuel returned to the sub fuel tank 2 through the throttle 84 is relatively small, and the filling amount of the sub fuel in the fuel injection valve 5 is large. Become. In this way, it is possible to change the filling amount of the sub fuel into the fuel injection valve according to the rotation speed, and fill the fuel injection valve with the optimum amount of the sub fuel over each rotation speed.

FIG. 2 shows the equal oil supply amount characteristics for each rotation speed at this time.

FIG. 3 is a modification of the first embodiment in which the auxiliary fuel return passage 83 and the throttle 84 are used to control the auxiliary fuel filling amount, and the fuel injection pump is changed from the distribution type shown in FIG. 1 to the column type. The fuel injection pump 13A has a series of cylinders 15A in which plungers (not shown) are housed, and the main fuel pressurizing chamber formed at the tip of the plunger (not shown) in each cylinder injects respective fuel through the passage 49. It is connected to the valve 5 by piping. As is well known, the effective stroke of the plunger, that is, the fuel injection amount is controlled by the adjust lever 52A connected to the accelerator pedal. The casing 60, which constitutes the auxiliary fuel amount adjusting means, has a piston 62, a spring 64, and check valves 66 and 68, and an auxiliary fuel pressurizing chamber 72 is formed at the tip of the piston 62. Although it is similar to the figure, the casing 60 is installed for each cylinder, which is different from FIG. Further, as in FIG. 1, the auxiliary fuel pressurizing chamber 72 is connected to the fuel injection valve 5 via the passages 78, 81 and the check valve 82, and
A sub fuel return passage 83 connecting 78 to the sub fuel tank 2 is provided, and a throttle 84 is arranged. The operation of the embodiment of FIG. 2 is similar to that of the embodiment of FIG. That is, the piston 62 is driven by the pumping of the main fuel, and each fuel injection valve 5 is filled from the auxiliary fuel pressurizing chamber 72 through the passages 78 and 81. The sub fuel thus filled is injected prior to the injection of the main fuel during the fuel injection of the cylinder. In addition, the filling amount of the auxiliary fuel is the first
According to the same principle as described with reference to the drawings, it is possible to increase / decrease according to the number of revolutions and to fill a proper amount of the auxiliary fuel over each number of revolutions.

FIG. 4 shows an auxiliary fuel supply device having a distribution type fuel injection pump 13 having an auxiliary fuel amount adjusting means according to the second embodiment of the present invention. The difference from FIG. 1 will be mainly described. In the casing 60, two pistons 62A and 90 are arranged in series. The first piston 62A receives the main fuel pressure in the main fuel pumping chamber 24 and is normally stopped by the first spring 64.
Is urged to abut. The second piston 90 is the second
The spring 91 urges the stopper 92 to contact it, and in this state, a gap is left at l ₁ between the two pistons 62A and 90. There is a gap of l ₂ between the second piston 90 and the inner end surface of the casing 60. And the first piston
The strength of the first spring 64 between 62A and the second piston 90 is weaker than that of the second spring 91 that biases the second piston 90. The auxiliary fuel pressurizing chamber 72 is connected to an auxiliary fuel discharge passage 78 to each fuel injection valve 5. Return passage 83 as in the first embodiment
And the diaphragm 84 is not installed.

The operation of the embodiment shown in FIG. 4 will be described. The first piston 62A is driven by the pressure of the main fuel pressurizing chamber 24, pumps the sub fuel from the sub fuel pressurizing chamber 72 to the passage 78, and the sub fuel is Each fuel injection valve 5 is filled with the sub fuel before the main fuel is injected at the time of fuel injection. When the engine speed is low and the load is low, the pressure in the main fuel pumping chamber 24 is set to the first piston 62A.
Second spring 91, although it can be moved against spring 64 of
Is not enough to shrink. Therefore, the first piston
It is possible to obtain a small auxiliary fuel filling amount corresponding to the stroke of l ₁ obtained by the 62A.

On the high engine speed and high load side, the pressure in the main fuel pumping chamber 24 is high, so the second piston 90 contracts against the second spring 91 via the first piston 62A, and this time l ₁ + l ₂ A large amount of auxiliary fuel is filled according to the stroke. FIG. 5 shows the auxiliary fuel filling characteristics at this time. The area above the line L in the figure is the area where the stroke is l ₁ + l ₂ and the auxiliary fuel filling amount is large, and the area below is the l ₁ The auxiliary fuel filling amount is small in the region where the stroke is obtained.

FIG. 6 shows a second embodiment in which the stroke of the piston is changed depending on the magnitude of the pressure in the main fuel pressurizing chamber 24 to change the filling amount of the auxiliary fuel by the column fuel injection pump 13A. It is a thing. The structure in which the first piston 62A and the second piston 90 are arranged in series in the casing 60 is the same as in FIG. The structure of the row pump 13A is the same as that shown in FIG. The operation will be clear from the description of the previous embodiments and will not be described in detail. That is, the main fuel is injected into the fuel injection valve 5 by the plunger in the cylinder 15A.
Is injected by the piston 62 in each casing 60.
A and 90 execute long and short two-stage strokes according to the engine speed or the magnitude of the load, and the auxiliary fuel is filled in the fuel injection valve 5 from the auxiliary fuel pressurizing chamber 72, which is the main fuel at the time of the next fuel injection. Is injected prior to the injection of. The filling amount of the auxiliary fuel is controlled according to the rotation speed and the load.

〔The invention's effect〕

According to the present invention, the metering that operates only by the fluid pressure in the pure frame that controls the filling amount of the sub fuel by the reciprocating speed of the plunger 16 and the operating factors of the main fuel pressurizing means such as the pressure of the main fuel pressurizing chamber 24. Means, that is, the return passage 83 and the throttle 84, and the second piston 90 are provided to control the filling amount of the auxiliary fuel into the fuel injection valve 5 in accordance with engine operating condition factors such as engine speed and load. It is possible to improve the ignitability without generating black smoke. From a structural point of view, only the passage and the throttle or the additional piston are required, and it is not necessary to take the complicated structure of driving the control valve by the link in response to the accelerator pedal as in the prior art. , The configuration is simplified.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the first embodiment of the present invention. FIG. 2 is a relationship diagram of the engine speed and the light oil filling amount in the first embodiment. FIG. 3 is a diagram showing a case where the first embodiment is applied to a row type pump. FIG. 4 is an overall configuration diagram of a second embodiment of the present invention. FIG. 5 is a diagram showing a piston stroke with respect to a rotation speed and a load in the second embodiment. FIG. 6 is a diagram showing a case where the second embodiment is applied to a row type pump. 1 …… Alcohol tank, 2 …… Light oil tank, 3,4 …… Pump, 5 …… Fuel injection valve, 13,13A …… Fuel injection pump, 15,15A …… Cylinder, 16 …… Plunger, 24 …… Main fuel pressurization chamber, 62 ... Piston, 62A ... First piston, 64 ... First spring, 66, 68 ... Check valve, 72 ... Sub fuel pressurization chamber, 78 ... Sub fuel discharge Passage, 83 …… Sub fuel return passage, 84 …… Throttle, 90 …… Second piston. 91 …… Second spring

Claims (2)

(57) [Claims] 1. A main fuel, which is not easily ignited by compression ignition, and an auxiliary fuel, which is easily ignited by compression ignition, can be supplied separately, and the injection of the auxiliary fuel is limited until compression ignition occurs. A dual fuel supply device for a diesel engine for supplying main fuel, the fuel injection valve means being opened / closed by fuel pressure, and the fuel injection valve means opening the fuel injection valve means in a predetermined cycle of the engine. The fuel injection valve means is driven by the main fuel pressure feeding means for supplying the main fuel at a pressure and the main fuel pressure fed by the main fuel pressure feeding means, and the fuel injection valve means is opened before the predetermined cycle for injecting the main fuel. An auxiliary fuel pressure-feeding means for filling a small amount of auxiliary fuel into the fuel injection valve means at a pressure not present, a fuel return passage connected to the downstream side of the auxiliary fuel pressure-feeding means, and a fuel return passage arranged in the fuel return passage. Double fuel supply system characterized in that it is composed of a diaphragm is controlled in accordance with at least the engine speed the flow passage. 2. A main fuel, which is not easily ignited by compression ignition, and a sub fuel, which is easily ignited by compression ignition, can be separately supplied, and the injection of the sub fuel is limited until compression ignition occurs. A dual fuel supply device for a diesel engine for supplying main fuel, the fuel injection valve means being opened / closed by fuel pressure, and the fuel injection valve means opening the fuel injection valve means in a predetermined cycle of the engine. The fuel injection valve means is driven by the main fuel pressure feeding means for supplying the main fuel at a pressure and the main fuel pressure fed by the main fuel pressure feeding means, and the fuel injection valve means is opened before the predetermined cycle for injecting the main fuel. An auxiliary fuel pressure-feeding means for filling the fuel injection valve means with a small amount of auxiliary fuel at a pressure not present, the auxiliary fuel pressure-feeding means being housed in the casing and adapted to the supply pressure of the main fuel. The first piston, which moves to feed the auxiliary fuel by pressure, and the first piston, which is separated from the side on which the supply pressure of the main fuel is applied, are normally arranged at a predetermined distance from each other. A second piston that interlocks to feed the sub-fuel, a first spring that urges the first piston against the main fuel supply pressure, and a second piston that resists the main fuel supply pressure. And a second spring that is stronger than the first spring, and when the main fuel pressure is low, the first spring is engaged until the first piston engages with the second piston by the main fuel supply pressure. The supply amount of the sub fuel corresponding to the stroke of the first piston when moving against the pressure is obtained, and during operation where the main fuel pressure is high, the main fuel supply pressure causes the first piston to initially move to the first spring. And then merges with the second piston to resist the second spring and the second piston Double fuel supply system, characterized in that the supply amount of auxiliary fuel in accordance with the total stroke of the first piston until it engages the Tsu Pa is obtained.