Patent Application
20080311009
The present invention relates to an device and a method for supplying a fuel or a reducing agent, and to a plasma torch which can be used for the device and method.
Such an injector is used also for injecting a fuel into an exhaust pipe where an exhaust gas from an internal engine is flowing. This is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-159309. Japanese Unexamined Patent Publication (Kokai) No. 2001-159309 proposes generation of an electric discharge in the exhaust pipe by using a discharging device disposed upstream a catalyst and inject a reducing agent on the more upstream side of the discharging device. According to this technique, the oxidation from NO into NO2 in the discharging device can be accelerated due to the presence of hydrocarbon (HC). Also, Japanese Unexamined Patent Publication (Kokai) No. 2001-159309 proposes injection of a reducing agent upstream of a catalyst and generation of a discharge plasma on the catalyst. According to this technique, the reaction on the catalyst is accelerated and the purification activity can be enhanced.
Use of a discharge plasma for purifying an exhaust gas of an automobile is described also in Japanese Unexamined Patent Publication (Kokai) No. 5-321634. Japanese Unexamined Patent Publication (Kokai) No. 5-321634 relates to a PM removing device of collecting a particulate matter (hereinafter referred to as a “PM”) in an exhaust gas from a diesel engine by a PM trap and regenerating the PM trap by supplying fresh air thereto. In this publication, it has been proposed to inject water into the fresh air supplied to the PM trap, generate an OH radical by providing corona discharge to the fresh air containing water, and accelerate the burning of PM trapped in the PM trap by the effect of the OH radical generated.
With respect to the use of a discharge plasma for purifying an exhaust gas of automobiles, Japanese Unexamined Patent Publication (Kokai) No. 6-343820 has proposed to supply water vapor to a plasma generating device and supply the obtained water-vapor plasma gas into an exhaust gas, whereby harmful components in the exhaust gas are oxidized and rendered harmless. In this publication, it is disclosed that active chemical species such as O, OH, H, H2O and O3 are obtained by supplying a water vapor to the plasma generating device.
Japanese Patent Publication (Kokai) No. 2002-61556 discloses an injection nozzle used for injecting gasoline to a combustion chamber of an internal combustion engine. In the injection nozzle, an electric discharge is generated in a passage for fuel, thereby electrically charging the fuel before injecting it to a combustion chamber. The patent publication document states that this charging promotes an ionization of the fuel when the fuel is mixed with air and, therefor, results in little generation of NOx, CO, etc upon combustion.
As described above, an injector for injecting a fuel or a reducing agent is being used for various uses. However, in any of these uses, particularly at low temperatures, there is a problem that the fuel or reducing agent is not satisfactorily vaporized by mere injection.
In the case where the fuel is not satisfactorily vaporized when the fuel is injected to a combustion chamber of a direct injection-type internal combustion engine, mixing, between the fuel and air, proceeds insufficiently and this tends to cause incomplete combustion of fuel and generation of PM.
In the case where the reducing agent is not satisfactorily vaporized when the reducing agent is injected to an exhaust pipe in which an exhaust gas from an internal combustion engine is flowing, diffusion to a catalyst and contact with a catalyst may become insufficient and then fail in effecting adequate purification, or the reducing agent may be unreacted and as-is released into air.
Use of a plasma for the purification of an exhaust gas is conventionally known as described in Japanese Unexamined Patent Publication (Kokai) No. 2001-159309. However, when a fuel is injected to an exhaust gas and a plasma is provided during the subsequent treatment of exhaust gas as in Japanese Unexamined Patent Publication (Kokai) No. 2001-159309, the exhaust gas flow as a whole is converted into a plasma state and, therefore, a relatively large energy is required for generating a plasma or the plasma density is decreased.
Accordingly, a device and a method for supplying a fuel or a reducing agent, wherein a fuel or reducing agent supplied by injection can be vaporized even under the condition of not allowing for sufficient vaporization of the merely injected fuel or reducing agent, and/or a fuel or reducing agent having high reactivity can be relatively easily provided, are in demand.
A device for supplying a fuel or a reducing agent of the present invention comprises a plasma torch for converting a gas into a plasma and supplying the plasma, and an injector for injecting a fuel or a reducing agent to a region whereto the plasma is supplied.
The “plasma torch” as used in the present invention means a plasma generating device of converting a gas supplied thereto into a plasma and supplying the plasma, particularly a plasma generating device capable of jetting out the plasma from the distal end part thereof.
According to the device for supplying a fuel or a reducing agent of the present invention, the fuel or reducing agent injected from an injector can be converted into a low molecular weight component having high reactivity through radical formation and cracking, and/or can be vaporized quickly even under a condition where satisfactory vaporization cannot be attained merely by injecting a fuel or reducing agent.
According to the device for supplying a fuel or a reducing agent of the present invention, a plasma can be generated only in the vicinity of an injection port of an injector for injecting a fuel or a reducing agent, namely, not in the entirety but only in a part of the space where the fuel or reducing agent is injected. Accordingly, the space to be converted into a plasma can be made to be relatively small, that is, a high plasma density can be obtained with a relatively small consumption of energy.
According to the device for supplying a fuel or a reducing agent of the present invention, the concentration of fuel or reducing agent in the plasma is decreased as compared with the case wherein a fuel or a reducing agent by itself is converted into a plasma and therefore, generation of soot can be suppressed.
Furthermore, according to the device for supplying a fuel or a reducing agent of the present invention, the gas to be converted into a plasma can be selected so that the plasma torch can be prevented from corroding.
In another embodiment of the device for supplying a fuel or a reducing agent of the present invention, the gas to be converted into a plasma is selected from the group consisting of nitrogen (N2), air, argon (Ar) and recirculated exhaust gas (EGR (exhaust gas recirculation) gas).
As nitrogen, air, argon or recirculated exhaust gas can be converted into a plasma and a fuel or a reducing agent can be injected to the plasma from an injector, the radical formation, cracking, vaporization and the like of fuel or reducing agent can be accelerated.
Particularly, in the case where air and/or EGR gas is supplied to the plasma torch and converted into a plasma, the water content contained in the air and/or EGR gas can generate an OH radical and an O radical upon being converted into a plasma. Such a radical accelerates cracking and reforming, or is bonded to the terminal of a fuel or reducing agent molecular chain broken by the plasma, thereby preventing production of unsaturated hydrocarbon or suppressing generation of soot. The fuel or reducing agent reformed or decreased in molecular weight is a very active reducing agent and is preferred in many uses. Also, in the case where air and/or EGR gas is supplied to the plasma torch and converted into a plasma, a tank or the like for storing a gas to be supplied to the plasma torch is advantageously not necessary, because the air and the EGR gas can be obtained from the atmosphere and exhaust gas flow, respectively.
In the case where EGR gas is supplied to the plasma torch and converted into a plasma, this is advantageous in that the EGR gas has a relatively low oxygen concentration to cause less oxidation and consumption of the fuel or reducing agent, and that the EGR gas has a relatively stable water content concentration of, for example, about 5 to 10%.
In still another embodiment of the device for supplying a fuel or a reducing agent of the present invention, the device comprises a water supplying means for supplying water to a region whereto the plasma is supplied.
The water supplying means may be another injector for injecting water, but the injector for injecting a fuel or a reducing agent may work at the same time as the water supplying means for supplying water.
According to this embodiment, water is converted into a plasma together with the fuel or reducing agent to produce an OH radical and an O radical, so that the cracking and reforming of the fuel or reducing agent can be accelerated and production of soot can be suppressed.
In one embodiment of the device for supplying a fuel or a reducing agent of the present invention, the plasma torch and the injector for injecting a fuel or a reducing agent are separated.
According to this embodiment, the region where the plasma is supplied is separated from the injector, so that the injector can be prevented from deterioration due to plasma.
In one embodiment of the device for supplying a fuel or a reducing agent of the present invention, an injection nozzle of the injector is disposed in the plasma torch and the gas to be converted into a plasma is passed to flow between the inner wall of the plasma torch and the injection nozzle of the injector.
According to this embodiment, contact of the plasma with the fuel or reducing agent injected from the injector can be improved.
In this embodiment, a discharge plasma can be generated in the vicinity of the injection port of the injector by using the injection nozzle of the injector as a discharge electrode and by applying a voltage between the injection nozzle and an electrode coupled therewith to generate electric discharge.
Also, in this embodiment, an inductively coupled plasma can be generated in the vicinity of the injection port by disposing an induction coil in the periphery of the injection port of the injector, supplying a high-frequency current from a high-frequency electric power source to the induction coil in the periphery of the injection port, generating a magnetic field in the vicinity of the injection port, and generating an eddy current.
In one embodiment of the device for supplying a fuel or a reducing agent of the present invention, the plasma is a discharge plasma, and wherein when the gas to be converted into a plasma, particularly EGR gas, is at a temperature less than a predetermined temperature, particularly at a temperature of less than 100° C., more particularly less than 120° C., the gas is not converted into a plasma at the plasma torch.
When the gas to be converted into a plasma is cooled to a low temperature, the water content contained in the gas is sometimes condensed to liquid water. In particular, since the EGR gas has a relatively high water content, when it is cooled during supply to the plasma torch, it may generate liquid water. In the case where the plasma torch for use in the present invention generates a plasma by discharging, if liquid water is present in the discharging portion, a short-circuit may occur and this may cause deterioration of the device. Therefore, according to this embodiment, discharging is not performed when the temperature is less than a predetermined temperature, so that the device can be prevented from deterioration or the like.
In one embodiment of the device for supplying a fuel or a reducing agent of the present invention, when the oxygen concentration in the space to which the fuel or reducing agent is supplied exceeds a predetermined concentration, the gas is not converted into a plasma at the plasma torch.
If the oxygen concentration is high in the space, to which the fuel or reducing agent is supplied when cracking and reforming of a fuel or reducing agent, particularly, a relatively light fuel or reducing agent such as gasoline, is caused by the plasma, a relatively large amount of fuel or reducing agent may be consumed there by the oxidation or combustion reaction. Accordingly, when the oxygen concentration in this space exceeds a predetermined concentration, for example, exceeds 10%, particularly 5%, discharging is not performed, whereby the fuel or reducing agent can be effectively utilized. This is particularly preferred in view of consumption of energy in the case where for the purification of an exhaust gas, the fuel or reducing agent is injected to an exhaust pipe.
In the method for supplying a fuel or a reducing agent of the present invention, a gas is converted into a plasma and supplied, and a fuel or reducing agent is injected to the plasma.
The plasma torch of the present invention converting a gas into a plasma and supplies the plasma to the vicinity of an injection port of an injector for injecting a fuel or a reducing agent.
According to the method for supplying a fuel or a reducing agent or the plasma torch of the present invention, the fuel or reducing agent supplied by injection can be converted to a low molecular weight component having high reactivity through radical formation and cracking, and/or can be vaporized quickly even if a fuel or reducing agent is not satisfactorily vaporized merely by injecting the fuel or reducing agent.
The present invention is specifically described below based on the embodiments shown in the Figures.
Each Figure is a view showing the concept of the present invention but the present invention is not limited to these embodiments.
The device for supplying a fuel or a reducing agent of the present invention can be roughly described by referring to
In the device for supplying a fuel or a reducing agent of the present invention, the fuel or reducing agent injected from an injector can be at least partially converted into a plasma. As shown in
The plasma region can be formed by converting a gas such as nitrogen, air, argon and recirculated exhaust gas into a plasma, and then jetting out (supplying) the plasma to the vicinity of the injection port of an injector for injecting a fuel or a reducing agent.
The fuel or reducing agent injected by the device for supplying a fuel or a reducing agent of the present invention can be selected according to use but may be, for example, a hydrocarbon such as gasoline and light oil, an ether or an alcohol. Incidentally, the terms “fuel” and “reducing agent” are terms chosen according to the usage of the injector in use. Generally, the “fuel” is a term used for indicating a material supplied from the injector wherein the supplied material is intended to be explosively burned, and the “reducing agent” is a term used for indicating a material supplied from the injector wherein the supplied material is intended to be used for reducing other substances. Accordingly, these terms sometimes indicate the same object and can be used exchangeably with each other. More specifically, in some cases, a gasoline is injected as a “fuel” into a combustion chamber for generating power in an internal combustion engine and at the same time, a gasoline is injected as a “reducing agent” into an exhaust pipe for reducing NOx in the exhaust gas discharged from this internal combustion engine. Of course, the “fuel” as a power source for an internal combustion engine may be different from the “reducing agent” for the purification of an exhaust gas.
As for the injector used in the device for supplying a fuel or a reducing agent of the present invention, any injector can be used. For example, this injector may be a conventional injector 10 shown in
In the case where, as shown in
The device for supplying a fuel or a reducing agent of the present invention can have any mechanisms and may have, for example, mechanisms shown in
The device for supplying a fuel or a reducing agent shown in
When using this device for supplying a fuel or a reducing agent, electric discharge is generated between the duct 32 and the discharge electrode 36 by the electric power source 38, whereby a gas 23 supplied through the flow-path in the plasma torch 30 is converted into a plasma. The fuel or reducing agent is injected from an injector 10 into a plasma region 20.
In
A mechanism shown in
Also, in the case of further supplying water to the region where a plasma is generated, as shown in
In the plasma torch, the portion used as an electrode can be formed of a material which can work as a discharge electrode when a voltage is applied between electrodes. As for such a material, an electrically conducting material or a semiconductor material may be used, but a metal material such as copper, tungsten, stainless steel, iron and aluminum is preferred. Particularly, in the arc discharge, the electrode reaches a high temperature and therefore, a high-melting-point material such as tungsten is preferably used. Also, an insulating material may be disposed on such an electrically conducting or semiconductor material so as to generate barrier discharge.
The discharge plasma means a plasma generated by causing a high-energy electron produced by electric discharge between electrodes to collide with a gas molecule and thereby ionizing the gas molecule into a plus ion and a minus ion. For generating this discharge plasma, any discharge mode may be used, and arc discharge or corona discharge, such as barrier discharge, can be utilized.
In the case of generating a plasma in the plasma torch by using the arc discharge, the electric power source 38 can supply, for example, a voltage of 1 to 50 V and an electric current of 5 to 500 A. In this arc discharge, the electric discharge is maintained by electrons emitted from a cathode. As for the electric current for generating the arc discharge, not only direct current but also alternating current can be used.
The arc discharge is advantageous in that the output can be easily increased by increasing the discharge current or discharge voltage, and that stable electric discharge can continue for a long period of time. Also, the arc discharge is advantageous in that the device and technique for generating the arc discharge are simple and the cost of equipment is relatively low.
In the case of generating a plasma in the plasma torch by using corona discharge, the electric power source 38 may supply either a pulsed DC voltage or a pulsed AC voltage. As for the voltage applied between electrodes, a voltage of 1 to 100 kV and, for example, 5 to 20 kV, can be generally used. The pulse period of the applied voltage may be from 0.1 μs to 10 ms, particularly from 0.1 to 10 μs.
Incidentally, in view of stability of plasma and durability of electrode, it is preferred to perform barrier discharge by disposing an insulating material on the electrode.
The device for supplying a fuel or a reducing agent of the present invention shown in
In use of this device for supplying a fuel or a reducing agent, a high-frequency current is supplied from the high-frequency electric power source 48 to the induction coil 44 while adjusting the impedance by the matching box 49, as a result, inside the distal end portion of the duct 42, a magnetic field and then an eddy current are generated, whereby a plasma 20 is inductively generated in the duct 42 and in the vicinity thereof. As for the high-frequency current used here, for example, a current having a frequency of 2 to 50 MHz, particularly from 3 to 40 MHz, can be used.
This inductively coupled plasma is preferred in view of durability, because the electrode (metal portion) can be prevented from being directly exposed to a high-temperature plasma.
In the device for supplying a fuel or a reducing agent of the present invention utilizing an inductively-coupled plasma, similarly to the device for supplying a fuel or a reducing agent of the present invention utilizing a discharge plasma, the injection nozzle of an injector 10 for injecting a fuel or a reducing agent can be disposed in the plasma torch, and water can be further supplied to the region where a plasma is generated.
The plasma torch 50 shown in
In use of this plasma torch 50, microwaves generated by a microwave generating device such as magnetron and, for example, microwaves at a frequency of about 2.54 GHz, are passed through a waveguide and irradiated from an antenna on a gas to be converted into a plasma, whereby the electric field strength is intensified and a plasma is generated.
Particularly, in the case of generating a microwave-induced plasma under an atmospheric pressure or a gas pressure higher than that, it is advantageous to use a plasma-exciting material 55 and generate a plasma in the periphery of the plasma-exciting material by irradiating microwaves onto the plasma-exciting material.
Use of a microwave plasma is preferred in view of durability, because the electrode (metal portion) can be prevented from being directly exposed to a high-temperature plasma.
In the device for supplying a fuel or a reducing agent of the present invention utilizing a microwave plasma, similarly to the device for supplying a fuel or a reducing agent of the present invention utilizing a discharge plasma, the injection nozzle of an injector 10 for injecting a fuel or a reducing agent can be disposed in the plasma torch, and water can be further supplied to the region where a plasma is generated.
For supplying a gas to be converted into a plasma to the plasma torch, any mechanism can be used. For example, a gas to be converted into a plasma, particularly, nitrogen or argon, can be supplied from a tank storing such a gas. Also, in the case of supplying a reducing agent to an exhaust pipe, when the gas to be converted into a plasma is air, as shown in
In the case of measuring the temperature of the gas to be converted into a plasma, as shown in
In the case of measuring the oxygen concentration in the area whereto a fuel or a reducing agent is supplied, not only the oxygen concentration in the area itself is measured but also, as shown in
The method for supplying a fuel or a reducing agent and the plasma torch of the present invention are as described above with respect to the device for supplying a fuel or a reducing agent.
The direct injection-type internal combustion engine shown in
When the device or method for supplying a fuel or a reducing agent or the plasma torch of the present invention is used for such a direct injection-type internal combustion, the fuel injected by the injector 10 can be converted into a low molecular weight component having high reactivity in the plasma region 20 and/or can be vaporized, so that the combustion of fuel in the combustion chamber and/or the mixing of fuel and air can be accelerated, and the emission of unburned fuel or the production of PM can be prevented.
The plasma 20 may be generated all the time, but in view of energy consumption, the plasma is preferably generated only at the moment of injecting a fuel, particularly, only at the moment of injecting a fuel at a low temperature as in the starting of the internal combustion engine.
The exhaust gas purifying system 70 shown in
In this exhaust gas purifying system 70, not only a fuel used as the power source of an internal combustion engine, such as gasoline and light oil, can be injected as a reducing agent but also a separate reducing agent can be injected. The NOx purifying catalyst usable for the exhaust gas purifying system 70 is a catalyst of accelerating the reduction of NOx in an exhaust gas, particularly in an exhaust gas from an internal combustion engine.
When the device or method for supplying a fuel or a reducing agent or the plasma torch of the present invention is used for such an exhaust gas purifying system, the reducing agent injected by the injector 10 can be converted into a low molecular weight component having high reactivity in the plasma region 20 and/or can be vaporized, so that the diffusion of the reducing agent to the catalyst on the downstream side and the contact of the reducing agent with the catalyst can be promoted. This accelerates the reducing reaction on the catalyst and in turn, the unreacted reducing agent can be prevented from being released into the atmosphere. Also, when the catalyst used in this exhaust gas purifying system is an NOx purifying catalyst, particularly, NOx storage-reduction catalyst or NOx selective reduction catalyst, the NO2 reducing reaction by the catalyst can be accelerated.
The plasma 20 may be generated all the time, but in view of energy consumption, the plasma is preferably generated only at the moment of injecting a reducing agent and, particularly, only at the moment of injecting a reducing agent under the condition that the warm-up is still insufficient.
As generally known, “plasma” means a substance in the state that two or more freely moving positive and negative charged particles are present together. Accordingly, the substance in the plasma state has a high potential energy, and a fuel or a reducing agent can be converted through radical formation and cracking into a plasma to decompose into low molecular weight components having high reactivity. Furthermore, even when supplied in a liquid droplet state, the fuel or a reducing agent can be momentarily vaporized and through radical formation and cracking, converted into a low molecular weight component having high reactivity.
The plasma generated according to the present invention can take various modes. The present invention is not limited by the means for generating a plasma but, for example, a discharge plasma, a microwave plasma and an inductively coupled plasma can be used.
Considering the very high energy state of a plasma, it would be apparent to one skilled in the art that vaporization, radical formation and cracking of a fuel or a reducing agent can be momentarily performed by converting at least a part of the fuel or reducing agent into a plasma. However, in the following, cracking and the like caused by converting a hydrocarbon (C13H28) into a plasma is confirmed by an experiment.
A testing device shown in
According to this experiment, C1 to C3 components were measured by gas chromatography only when a plasma was generated by electric discharge. This reveals that the plasma can crack a relatively large molecule (C13H28) into relatively small molecules (C1 to C3).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-188614 | Jun 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/11695 | 6/21/2005 | WO | 00 | 10/4/2006 |
