JP3777978B2 - Fuel supply device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection device for an internal combustion engine.
[0002]
[Prior art]
Liquid fuel is supplied from the fuel tank into the mixing chamber using the fuel pump, and a mixed fluid different from the liquid fuel is supplied from the mixed fluid tank into the mixing chamber using the mixed fluid pump. Forming a mixture of mixed fluids, raising the pressure and temperature in the mixing chamber above the critical pressure and critical temperature of the mixed fluid to bring the mixed fluid in the mixture into a supercritical state, and then removing the mixture from the injector; An internal combustion engine that performs injection is known (see Japanese Patent No. 2651974).
[0003]
Although details will be described later, atomization of the liquid fuel can be promoted in this way, and thus good combustion can be ensured.
[0004]
[Problems to be solved by the invention]
The amount of liquid fuel flowing into the mixing chamber depends on the discharge pressure of the fuel pump, and the amount of mixed fluid flowing into the mixing chamber depends on the discharge pressure of the mixed fluid pump. For this reason, the amount of the liquid fuel and the fluid to be mixed flowing into the mixing chamber varies due to the pulsation of the discharge pressure of these pumps, and as a result, the mixing ratio of the mixing fuel amount to the liquid fuel amount varies. The atomization action of the liquid fuel described above depends on this mixing ratio, and therefore there is a problem that a stable atomization action cannot be obtained if the mixing ratio varies.
[0005]
Therefore, an object of the present invention is to provide a fuel supply device for an internal combustion engine that can stably obtain the atomization action of liquid fuel.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, according to the first invention, a throttle portion is provided in a fuel passage for supplying liquid fuel from a fuel tank to an injection valve, and a mixed fluid different from the liquid fuel is supplied from the mixed fluid tank. The mixed fluid passage for supply is opened in the fuel passage around the throttle portion, and the liquid mixture is fueled from the mixed fluid tank by the pressure reducing action generated around the throttle portion when the liquid fuel flows through the throttle portion. A mixture in which the fluid mixture is mixed with the liquid fuel is formed by being guided into the passage, and the mixture is formed by the supercritical state generating means disposed in the fuel passage downstream of the opening of the fluid mixture passage. The fluid to be mixed is brought into a supercritical state, the mixture is injected from the fuel injection valve , and a porous body is disposed at the outflow end of the fluid mixture passage opened in the fuel passage . That is, according to the first aspect of the invention, the mixing ratio is maintained almost constant, so that a stable atomization action of the liquid fuel is ensured.
[0007]
In the first invention, the fluid to be mixed is caused to flow out of the porous body in the form of fine particles (droplets or bubbles), so that the liquid fuel and the mixing liquid are uniformly mixed.
In the first invention according to the second aspect, to said controllable control valve opening ratio to be mixed fluid passage arranged to control based on the opening ratio of the control valve to the engine operating state I have to. That is, in the third aspect of the invention, the mixing ratio is changed based on the engine operating state.
[0008]
In general, a substance is in a supercritical state when the pressure of the substance is higher than the critical pressure and the temperature of the substance is higher than the critical temperature. However, the supercritical state referred to herein includes the case where the pressure and temperature of a substance are slightly lower than the critical pressure and temperature.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a case where the present invention is applied to a vehicle diesel engine. However, the present invention can also be applied to a spark-ignition gasoline engine or an internal combustion engine not for vehicles.
Referring to FIG. 1, the engine main body 1 includes a plurality of, for example, four cylinders 1 a, and each cylinder 1 a includes, for example, an electromagnetic injection valve 2. Each of these injection valves 2 is connected to a common mixture volume or common rail 4 with respect to these injection valves 2 via a corresponding distribution pipe 3. The common rail 4 is connected to the discharge side of, for example, an engine-driven pump 6 that can control the discharge pressure via a high-pressure pipe 5, and the suction side of the pump 6 is connected to a fuel tank 8 via a fuel supply pipe 7. . The fuel tank 8 contains liquid fuel, which is light oil in this embodiment.
[0010]
On the other hand, a mixed fluid different from fuel is accommodated in the mixed fluid tank 9. Any fluid may be used as the fluid to be mixed. However, at least one selected from hydrocarbons such as water, carbon dioxide, hydrogen, alcohol, methane, and ethane can be used as the fluid to be mixed. A mixed fluid supply pipe 10 extends from the mixed fluid tank 9, and an outflow end thereof is connected to the fuel supply pipe 7. Next, this connection part will be described.
[0011]
Referring to FIG. 2 together with FIG. 1, the fuel supply pipe 7 includes an upstream pipe 7a extending from the fuel tank 8, a downstream pipe 7b extending from the pump 6, and a connecting pipe 7c connecting the upstream pipe 7a and the downstream pipe 7b to each other. The mixed fluid supply pipe 10 is connected to the connection pipe 7c. More specifically, a fuel passage 11 that connects the upstream pipe 7a and the downstream pipe 7b to each other is formed in the connection pipe 7c, and a throttle portion 12 is formed in the fuel passage 11. Further, a mixed fluid passage 13 extending from the fuel passage 11 in the throttle portion 12 is formed in the connection pipe 7 c, and this is communicated with the mixed fluid supply pipe 10. That is, the outflow end of the mixed fluid passage 13 is opened in the fuel passage 11 at the throttle portion 12.
[0012]
Referring to FIG. 3 showing a partially enlarged view of the outflow end of the mixed fluid passage, a porous body 14 is attached to the outflow end. The porous body 14 can be formed of, for example, ceramic, but the porous body 14 can also be formed of a metal plate having a large number of pores, a cloth made of metal fibers or ceramic fibers, or a non-woven cloth.
Referring to FIG. 1 again, an electromagnetic control valve 15 capable of controlling the valve opening ratio by controlling the duty ratio, for example, is disposed in the mixed fluid supply pipe 10.
[0013]
The electronic control unit (ECU) 30 is a digital computer, and is connected to each other via a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a constant time. A B-RAM (backup RAM) 35 connected to a power source, an input port 36, and an output port 37 are provided. A pressure sensor 38 that generates an output voltage proportional to the pressure in the common rail 4 is attached to the common rail 4. In addition, a load sensor 39 that generates an output voltage representing an engine load such as an intake air amount or an accelerator pedal depression amount is provided. The output voltages of these sensors 38 and 39 are input to the input port 36 via the corresponding AD converter 40, respectively. Further, a rotational speed sensor 41 that generates an output pulse representing the engine rotational speed is connected to the input port 36.
[0014]
On the other hand, the output port 37 is connected to the injection valve 2, the pump 6, and the control valve 15 through corresponding drive circuits 42.
Further, a temperature control device 43 for controlling the temperature of the mixture in the common rail 4 is attached to the common rail 4. The temperature control device 43 is composed of, for example, an electric heater as a heating device, and is connected to the output port 37 via a corresponding drive circuit 42.
[0015]
When the pump 6 is operated, the liquid fuel in the fuel tank 8 is allowed to flow through the fuel supply pipe 7 toward the pump 6. As a result, the mixed fluid in the mixed fluid tank 9 is guided into the fuel passage 11 through the mixed fluid supply pipe 10 by the pressure reducing action generated around the throttle portion 12. Therefore, a mixture in which the fluid to be mixed is mixed in the liquid fuel is formed, and this mixture then goes to the pump 6.
[0016]
Here, the flow rate of the mixed fluid flowing into the fuel passage 11 increases as the pressure reducing action or pressure drop acting on the outflow end of the mixed fluid passage 13 increases, and this pressure reducing action flows through the fuel passage 11. It increases as the liquid fuel flow rate increases. Therefore, in this embodiment, if the opening ratio of the control valve 15 is constant, the mixing ratio that is the amount of fluid to be mixed with respect to the amount of liquid fuel can be maintained substantially constant.
[0017]
At this time, the mixed fluid flows into the fuel passage 11 after flowing through the pores of the porous body 14. As a result, the mixed fluid flows into the liquid fuel flow in the form of droplets or bubbles. As a result, the liquid fuel and the fluid to be mixed can be mixed uniformly.
The mixture thus formed is then pressurized by the pump 6 and allowed to flow into the common rail 4. The discharge pressure of the pump 6 is controlled so that the pressure in the common rail 4 is maintained at a pressure P1 higher than the critical pressure PC of the mixed fluid, and the output of the heater 43 is controlled by the temperature of the mixture in the common rail 4. It is set in advance so as to be maintained at a temperature T1 higher than the critical temperature TC of the mixed fluid. That is, in the common rail 4, the mixture is exposed to a supercritical state generation environment that brings the mixed fluid into a supercritical state. As a result, the fluid to be mixed is brought into the supercritical state in the common rail 4, that is, the mixture is formed from the liquid fuel and the fluid to be mixed in the supercritical state.
[0018]
Here, the supercritical state generation environment described above is formed by the pump 6 and the heater 43. Therefore, the pump 6 and the heater 43 can also be regarded as forming a supercritical state generating device.
This mixture is then supplied to the injection valve 2 via the distribution pipe 3 and then injected from the injection valve 2 into the engine combustion chamber. In this way, atomization of the liquid fuel can be promoted, and therefore good combustion can be ensured.
[0019]
The mechanism of the atomization promoting action in this case is not necessarily clarified. However, it is thought that this mechanism can be explained as follows.
That is, in the supercritical state, the molecules of the mixed fluid can move much more freely than in the liquid state. For this reason, the mixed fluid molecules easily enter between the molecules of the liquid fuel, thereby reducing the surface tension of the liquid fuel. As a result, after the liquid fuel is injected, it cannot form large droplets, i.e., small droplets. In this way, atomization is promoted.
[0020]
According to this mechanism, the atomization promoting action depends on the mixing ratio of the mixed fluid amount to the liquid fuel amount. That is, as the mixing ratio increases, the atomization promoting effect increases. Therefore, if the mixing ratio varies, the atomization promoting action varies, which is not preferable.
On the other hand, in this embodiment, as described above, the mixing ratio is maintained substantially constant as long as the valve opening ratio of the control valve 15 is constant. Therefore, a stable atomization promoting effect can be obtained.
[0021]
The liquid fuel as well as the fluid to be mixed may be in a supercritical state. However, considering the mechanism described above, the atomization promoting action can be ensured if only the fluid to be mixed is brought into the supercritical state. Moreover, it is not preferable to bring both into a supercritical state from the viewpoint of energy consumption.
Therefore, in this embodiment, a mixture of the fuel that is not in the supercritical state and the mixed fluid that is in the supercritical state is formed, and this mixture is injected. In other words, the pressure and temperature in the common rail 4 are set so that the mixed fluid is in a supercritical state but the liquid fuel is not in a supercritical state.
[0022]
In order to make this possible, the mixed fluid must satisfy the following conditions. That is, at least one of the critical pressure and critical temperature of the fluid to be mixed must be smaller than the corresponding value of the liquid fuel.
Next, a method for controlling the duty ratio D of the control valve 15 will be described with reference to FIG.
[0023]
As can be seen from FIG. 4, during normal operation, the engine load L is higher than the predetermined first set load L1 and lower than the second set load L2 set higher than the first set load L1. The duty ratio D is, for example, the maximum (100%) D0. From another viewpoint, for example, the cross-sectional areas of the throttle portion 12 and the mixed fluid passage 13 are set so that the mixing ratio of the mixed fluid amount to the liquid fuel amount is optimal when D = D0. become.
[0024]
On the other hand, the duty ratio D is set to D1 smaller than D0 at the time of engine low load operation where L ≦ L1. As a result, the mixing ratio is reduced. During engine low load operation, the amount of liquid fuel injected from the injection valve 2 is small, so that combustion tends to become unstable. Therefore, the mixing ratio is reduced to reduce the absolute amount of the fluid to be mixed, thereby stabilizing the combustion.
[0025]
On the other hand, at the time of engine high load operation where L ≧ L2, the duty ratio D is set to D2, which is smaller than D0. As a result, also in this case, the mixing ratio is reduced. Since the amount of liquid fuel to be injected from the injection valve 2 is large at the time of engine high load operation, if an attempt is made to inject a mixture of this large amount of liquid fuel and an amount of mixed fluid commensurate with this, the injection of the injection valve 2 The period becomes very long. Therefore, the mixing ratio is reduced to shorten the injection time.
[0026]
D1 and D2 may be zero. That is, mixing of the liquid fuel and the fluid to be mixed may be stopped at the time of engine low load or high load operation. Further, the control valve 15 can be kept closed when the engine is stopped. In this way, it is possible to prevent the mixed fluid from flowing out of the mixed fluid tank 9 particularly when the mixed fluid is a substance that can be vaporized at room temperature.
[0027]
FIG. 5 shows a routine for calculating the duty ratio D of the control valve 15. This routine is executed by interruption every predetermined time.
Referring to FIG. 5, first, at step 100, it is judged if the engine load L is equal to or less than the first set load L1. When L ≦ L1, the routine proceeds to step 101 where the duty ratio D is set to D1. On the other hand, when L> L1, the routine proceeds to step 102 where it is determined whether L is equal to or greater than the second set load L2. When L ≧ L2, the routine proceeds to step 103 where D is set to D2.
[0028]
On the other hand, if L <L2 in step 102, that is, if L1 <L <L2, then the routine proceeds to step 104 where D is set to D0. The control valve 15 is controlled so that its duty ratio becomes D.
By the way, in this embodiment, both the liquid fuel and the mixed fluid are pumped by a single pump. Alternatively, it can be considered that the fluid to be mixed is pumped by a fuel pump. In any case, there is no need to provide a pump for the mixed fluid. As a result, less space is required. An auxiliary pump for pumping liquid fuel to the pump 6 may be provided in the fuel supply pipe 7 between the throttle portion 12 and the fuel tank 8.
[0029]
In the embodiment described so far, the outflow end of the mixed fluid passage 13 is opened in the throttle portion 12 (see FIG. 2). However, as long as the pressure reducing action is applied, the outflow end can be opened downstream of the throttle portion 12.
Further, as described above, in this embodiment, the porous body 14 is provided at the outflow end of the mixed fluid passage 13 so that the liquid fuel and the mixed fluid are uniformly mixed. In order to further promote such uniform mixing, a stirring device for stirring the mixture may be provided in, for example, the fuel supply pipe 7 downstream of the throttle portion 12. This agitation device is formed of, for example, a rib extending spirally along the longitudinal axis on the inner wall surface of the fuel supply pipe 7.
[0030]
【The invention's effect】
The atomization action of the liquid fuel can be obtained stably.
[Brief description of the drawings]
FIG. 1 is an overall view of a diesel engine.
FIG. 2 is an enlarged cross-sectional view of a portion II in FIG.
FIG. 3 is an enlarged cross-sectional view of a portion III in FIG.
FIG. 4 is a diagram showing a duty ratio D of a control valve.
FIG. 5 is a flowchart showing a routine for calculating a duty ratio D.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine main body 2 ... Injection valve 6 ... Pump 8 ... Fuel tank 9 ... Mixed fluid tank 12 ... Restriction part

Claims (2)

A throttle portion is provided in a fuel passage for supplying liquid fuel from the fuel tank to the injection valve, and a mixed fluid passage for supplying a mixed fluid different from the liquid fuel from the mixed fluid tank is a fuel around the throttle portion. When the liquid fuel is opened in the passage and flows through the throttle portion, the mixed fluid is guided from the mixed fluid tank into the fuel passage by the pressure reducing action generated around the throttle portion, thereby mixing the mixed fluid with the liquid fuel. The mixed fluid in the mixture is made to be in a supercritical state by supercritical state generating means disposed in the fuel passage downstream of the opening of the mixed fluid passage, and the mixture is A fuel injection device for an internal combustion engine, wherein a porous body is disposed at an outflow end of a mixed fluid passage which is made to inject from a fuel injection valve and is opened in a fuel passage .   The fuel injection of the internal combustion engine according to claim 1, wherein a control valve capable of controlling a valve opening ratio is disposed in the mixed fluid passage, and the valve opening ratio of the control valve is controlled based on an engine operating state. apparatus.

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