SPARK DISCHARGE IGNITION PROMOTING METHOD, SPARK DISCHARGE IGNITION PROMOTING APPARATUS, AND ENGINE WITH SPARK DISCHARGE IGNITION PROMOTING APPARATUS

Abstract

Stable combustion becomes possible even in a super-lean combustion engine or an engine that carries out a large amount of EGR. In a spark discharge ignition promoting apparatus, non-thermal plasma is generated in a cylinder by a non-thermal plasma generating unit. The non-thermal plasma generating unit is provided at a location where a processed air-fuel mixture by the non-thermal plasma reaches a spark plug after an in-cylinder flow or where the air-fuel mixture exists around an electrode of the spark plug in a time when the air-fuel mixture keeps an easy combustion state. The spark plug ignites the processed air-fuel mixture by discharge of the spark plug at timing when the processed air-fuel mixture by the non-thermal plasma of an easy combustion state reaches the spark plug after an in-cylinder flow or timing when the air-fuel mixture of the easy combustion state exists around an electrode of the spark plug in the time when the air-fuel mixture keeps the easy combustion state.

Claims

1-14. (canceled)

15. An ignition promoting method for an engine that uses premixed fuel, the method comprising: generating non-thermal plasma around a spark plug or in a region including the spark plug in a cylinder in a compressing process of the engine by a non-thermal plasma generating unit to process an air-fuel mixture, the non-thermal plasma generating unit including an embedded electrode embedded in a dielectric and an exposed electrode that faces the embedded electrode; and igniting, by discharge of the spark plug, an air-fuel mixture processed by the generated non-thermal plasma at timing when the air-fuel mixture reaches the spark plug by an in-cylinder flow or timing when the air-fuel mixture exists in a region including an electrode of the spark plug in a time when the air-fuel mixture keeps an easy combustion state.

16. The ignition promoting method according to claim 15, wherein each of the embedded electrode and the exposed electrode has an annular shape and is arranged so as to surround the spark plug, and the exposed electrode has an inner diameter larger than an outer diameter of the embedded electrode.

17. The ignition promoting method according to claim 15, wherein the non-thermal plasma generating unit is arranged within a half or lower of a cylinder radius from the spark plug.

18. The ignition promoting method according to claim 15, wherein the non-thermal plasma generating unit is configured to set an area in which the non-thermal plasma is generated to from 1 cm.sup.2 or more to 10 cm.sup.2.

19. The ignition promoting method according to claim 15, wherein the in-cylinder flow is a flow by a piston motion and/or a non-thermal plasma induced flow.

20. The ignition promoting method according to claim 15, wherein a time from generation of the non-thermal plasma to plug ignition is from 0.1 ms or more to 20 ms.

21. An ignition promoting apparatus comprising: a non-thermal plasma generating unit provided in a cylinder and configured to generate non-thermal plasma and process an air-fuel mixture of premixed fuel by the non-thermal plasma to form an air-fuel mixture of an easy combustion state, the non-thermal plasma generating unit including an embedded electrode embedded in a dielectric and an exposed electrode that faces the embedded electrode; and a spark plug fitted to the cylinder and configured to ignite the air-fuel mixture of the easy combustion state by discharge of the spark plug, wherein the non-thermal plasma generating unit is arranged at a location where the air-fuel mixture is configured to reach the spark plug by an in-cylinder flow or where the air-fuel mixture is configured to include an electrode of the spark plug in a time when the air-fuel mixture keeps the easy combustion state.

22. The ignition promoting apparatus according to claim 21, wherein each of the embedded electrode and the exposed electrode has an annular shape and is arranged so as to surround the spark plug, and the exposed electrode has an inner diameter larger than an outer diameter of the embedded electrode.

23. The ignition promoting apparatus according to claim 22, wherein the exposed electrode of the non-thermal plasma generating unit is grounded via a cylinder head and a cylinder block, and a high RF voltage is applied to the embedded electrode.

24. The ignition promoting apparatus according to claim 21, wherein the exposed electrode of the non-thermal plasma generating unit is grounded via a cylinder head and a cylinder block, and a high RF voltage is applied to the embedded electrode.

25. The ignition promoting apparatus according to claim 21, wherein the non-thermal plasma generating unit is arranged within a half or lower of a cylinder radius from the spark plug.

26. The ignition promoting apparatus according to claim 21, wherein the non-thermal plasma generating unit is configured to set an area in which the non-thermal plasma is generated to from 1 cm.sup.2 or more to 10 cm.sup.2.

27. The ignition promoting apparatus according to claim 21, wherein the in-cylinder flow is a flow by a piston motion and/or a non-thermal plasma induced flow.

28. The ignition promoting apparatus according to claim 21, wherein a time from when the non-thermal plasma generating unit generates the non-thermal plasma to when the spark plug ignites the air-fuel mixture is from 0.1 ms or more to 20 ms.

29. The ignition promoting apparatus according to claim 21, wherein the non-thermal plasma is generated by applying a high RF voltage between the embedded electrode and the exposed electrode.

30. An engine comprising: a cylinder; a non-thermal plasma generating unit provided in the cylinder and configured to generate non-thermal plasma and process an air-fuel mixture of premixed fuel by the non-thermal plasma to form an air-fuel mixture of an easy combustion state, the non-thermal plasma generating unit including an embedded electrode embedded in a dielectric and an exposed electrode that faces the embedded electrode; and a spark plug fitted to the cylinder and configured to ignite the air-fuel mixture of the easy combustion state by discharge, wherein the non-thermal plasma generating unit is arranged at a location where the air-fuel mixture is configured to reach the spark plug by an in-cylinder flow or where the air-fuel mixture is configured to include an electrode of the spark plug in a time when the air-fuel mixture keeps the easy combustion state.

31. The engine according to claim 30, wherein each of the embedded electrode and the exposed electrode has an annular shape and is arranged so as to surround the spark plug, and the exposed electrode has an inner diameter larger than an outer diameter of the embedded electrode.

32. The engine according to claim 30, wherein the exposed electrode of the non-thermal plasma generating unit is grounded via a cylinder head and a cylinder block, and a high RF voltage is applied to the embedded electrode.

33. The engine according to claim 30, wherein the exposed electrode of the non-thermal plasma generating unit is grounded via a cylinder head and a cylinder block, and a high RF voltage is applied to the embedded electrode.

34. The engine according to claim 30, wherein the non-thermal plasma is generated by applying a high RF voltage between the embedded electrode and the exposed electrode.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0050] FIG. 1 is a view showing the whole configuration according to the first embodiment.

[0051] FIG. 2 is a view of an ignition promoting apparatus according to the first embodiment when viewed from a combustion chamber side.

[0052] FIG. 3 is a view showing a relationship between a spark plug and the ignition promoting apparatus.

[0053] FIG. 4 is a view showing a cross-section drawing and electric connection of the ignition promoting apparatus.

[0054] FIG. 5 is a view showing an outline of a second embodiment.

[0055] FIG. 6 is a view showing a relationship of ignition timing of a spark plug, discharge timing by an ignition promoting apparatus, and discharge duration.

[0056] FIG. 7 is a view showing an outline of an experiment for examining effects of non-thermal plasma treatment for air-fuel mixture.

[0057] FIG. 8 is a view showing experimental data regarding a pressure history.

[0058] FIG. 9 is a view showing a result of Schlieren measurement in a case where a reactor of the ignition promoting apparatus is not operated in experimental equipment.

[0059] FIG. 10 is a view showing a result of Schlieren measurement in a case where the reactor of the ignition promoting apparatus is operated in the experimental equipment.

[0060] FIG. 11 is a view showing the whole configuration in a case where the ignition promoting apparatus is mounted in a four-cylinder engine.

DETAILED DESCRIPTION

(Outline)

[0061] (1) Non-thermal plasma is generated in a cylinder by a non-thermal plasma generating unit; the non-thermal plasma generating unit configured to generate the non-thermal plasma at a location (in which plasma exists by making retroactive time) in order for a processed air-fuel mixture by the non-thermal plasma to reach a spark plug after an in-cylinder flow or exist around an electrode of the spark plug in a time when the air-fuel mixture keeps an easy combustion state; and ignition is made by the spark plug at timing when the air-fuel mixture of the easy combustion state reaches the electrode of the spark plug or timing when the air-fuel mixture exists around the electrode of the spark plug. Otherwise, easy ignitibility of the air-fuel mixture is not sufficient even in the case of processing by the non-thermal plasma, and stable ignition of a lean/dilution air-fuel mixture is impossible.

[0062] Therefore, a spark discharge ignition promoting method and a spark discharge ignition promoting apparatus generates non-thermal plasma in a cylinder by a non-thermal plasma generating unit; provides the non-thermal plasma generating unit at a location where the processed air-fuel mixture by the non-thermal plasma reaches a spark plug after an in-cylinder flow or where the air-fuel mixture exists around an electrode of the spark plug in a time when the air-fuel mixture keeps an easy combustion state; and ignites by discharge of the spark plug at timing when the processed air-fuel mixture by the non-thermal plasma of an easy combustion state reaches the spark plug after an in-cylinder flow or timing when the air-fuel mixture of the easy combustion state exists around an electrode of the spark plug in the time when the air-fuel mixture keeps the easy combustion state.

[0063] (2) In a time from a compressing process for the air-fuel mixture to ignition by the spark plug, it is hardly possible for the air-fuel mixture to move by a distance of a half or lower of a cylinder radius in the in-cylinder flow.

[0064] Therefore, the spark discharge ignition promoting method and the spark discharge ignition promoting apparatus are required so that a location where the non-thermal plasma is generated is the half or lower of the cylinder radius from the spark plug.

[0065] (3) In a case where an area in the cylinder in which the non-thermal plasma is generated by the non-thermal plasma generating unit is smaller than 1 cm.sup.2, an effect of non-thermal plasma treatment becomes insufficient. On the other hand, in a case where the area in the cylinder in which the non-thermal plasma is generated by the non-thermal plasma generating unit exceeds 10 cm.sup.2, an easy combustion region becomes too wide, whereby there is a risk that abnormal combustion occurs.

[0066] Therefore, the spark discharge ignition promoting method and the spark discharge ignition promoting apparatus are required so that the area in the cylinder in which the non-thermal plasma is generated is from 1 cm.sup.2 or more to 10 cm.sup.2.

[0067] (4) In a normal engine with only a spark plug, an in-cylinder flow is a flow that occurs by means of a piston motion until a mixed gas in the compressing process is caused to ignite (by the spark plug). Part of the air-fuel mixture is subjected to the non-thermal plasma treatment until the mixed gas in the compressing process is caused to ignite (by the spark plug). Therefore, a flow by a non-thermal plasma induced flow also occurs.

[0068] Therefore, the in-cylinder flow is a flow that occurs by means of the piston motion and/or the non-thermal plasma induced flow until the mixed gas in the compressing process is caused to ignite (by the spark plug). Generally, the in-cylinder flow can technologically be grasped by measurement, or can be predicted even by computer simulation to an extent.

[0069] (5) In an air-fuel mixture in a cylinder of a gasoline engine, radicals and the like are generated immediately after non-thermal plasma is generated in non-thermal plasma treatment. Then, reaction proceeds from the radicals in a time of about 10 microseconds to generate partial oxides, whereby a region with a combustible state is generated.

[0070] It is desirable that the easy combustion state suitable for ignition by the spark plug has a time of 0.1 ms or longer for the ignition by the spark plug. On the other hand, metastable chemical species thus formed such as the partial oxides have a life of several seconds, and an easy combustion characteristic is lost. Therefore, it is necessary that a time for the ignition by the spark plug is no longer than 20 ms since the non-thermal plasma was generated.

[0071] Namely, the spark discharge ignition promoting method and the spark discharge ignition promoting apparatus are required so that as timing to ignite by the spark plug in the time when the processed air-fuel mixture by the non-thermal plasma keeps the easy combustion state, the time of plug ignition is from 0.1 ms or more to 20 ms since the non-thermal plasma is generated.

[0072] An ignition apparatus has a location relationship with an engine body, a size relationship, and a relationship between an operation of the non-thermal plasma generating unit and an operation of the spark plug timing in addition to a location relationship between the non-thermal plasma generating unit and the spark plug. Therefore, effects as an engine with the spark discharge ignition promoting apparatus are exerted.

[0073] Hereinafter, embodiments will be described in detail.

First Embodiment

[0074] FIG. 1 shows the whole configuration according to the first embodiment. A spark plug 2 is mounted on a cylinder head 1. An ignition promoting apparatus 3 is installed around the spark plug 2. The ignition promoting apparatus 3 is configured to generate an induced flow with discharge of non-thermal plasma. In the first embodiment, an electrode of non-thermal plasma generating means is provided along a surface of the inside of a cylinder. Therefore, it is a configuration in which a size of an area in which the non-thermal plasma is generated is flexibly set and easily installed on the cylinder surface.

[0075] FIG. 2 is a view of the cylinder head 1 when viewed from a combustion chamber side. In the present embodiment, the spark plug 2 is arranged at a central portion that is encircled by intake valves 4 and exhaust valves 5.

[0076] In this regard, a fuel supplying method may be either a port injection method or a direct injection method.

[0077] FIG. 3 shows a relationship between the spark plug 2 and the ignition promoting apparatus 3. They are arranged so that a central electrode and an earth electrode of the spark plug 2 protrude from an opening of the ignition promoting apparatus 3 which is annular.

[0078] The spark plug 2 is screwed to a plug hole formed in the cylinder head 1 in the similar manner to that of a conventional engine.

[0079] As shown in FIG. 1, a concave portion is formed along a circumference of the plug hole on a combustion chamber side wall surface of the cylinder head 1. The annular ignition promoting apparatus 3 is fitted into this concave portion so as not to cause a step in the combustion chamber, whereby no influence is applied to a shape of the combustion chamber.

[0080] In this regard, it is desirable that the ignition promoting apparatus 3 is installed at an upstream side in a case where an extremely fast flow is formed in the vicinity of the plug by adopting a special combustion chamber shape.

[0081] FIG. 4 is a view showing a cross-section drawing and electric connection of the ignition promoting apparatus 3. An annular embedded electrode 3b is also embedded in an annular dielectric 3a, which is molded from a material with high durability against combustion chamber temperature, such as alumina ceramic, sapphire and the like. The electrode 3b is arranged substantially parallel at a location of a depth d (from about several hundred microns to several millimeters) from a bottom surface of the dielectric 3a which faces the combustion chamber.

[0082] On the other hand, an exposed electrode 3c is mounted on the combustion chamber side bottom surface of the annular dielectric 3a facing the combustion chamber and at a circumferential side of the embedded electrode 3b so as to be separated in a radius direction by a distance L (from 0 to about several millimeters). In this regard, the embedded electrode 3b may also be formed by a material having high durability against the combustion chamber temperature and some degree of conductivity, such as a metal or the like that is used for the central electrode of the spark plug, and may form an earth electrode via a cylinder block. The cylinder block itself may be used as the exposed electrode.

[0083] When an alternating high RF voltage is applied to the embedded electrode 3b by a pulse voltage applying apparatus 6, non-thermal plasma resulting from discharge is generated between the grounded exposed electrode 3c and the embedded electrode 3b and under the embedded electrode 3b in the combustion chamber, whereby radicals, ions, partial oxides and the like are generated in premixed fuel that passes through the non-thermal plasma. Further, rapid rise of temperature is caused due to the ions formed in the non-thermal plasma and/or energy relaxation of an excited state. This premixed fuel flows in a direction of an arrow by means of an induced flow resulting from plasma generation, that is, from a circumferential side of the combustion chamber toward a central portion of the combustion chamber. For this reason, an air-fuel mixture containing radicals and partial oxides with a high concentration gathers around the spark plug. When discharge occurs by the spark plug, the air-fuel mixture starts combustion from this point, and the combustion propagates toward the circumferential side of the combustion chamber.

[0084] Herewith, the combustion is carried out smoothly all over the combustion chamber without generating knocking or misfire even in the case of a super lean air-fuel mixture. In this regard, as will be described later, timing of the high RF voltage applied to the embedded electrode 3b, a voltage value, and an applied time of the pulse voltage applying apparatus 6 are controlled by a control device 7 that works together with an ignition timing control device.

[0085] FIG. 6 shows a relationship of ignition timing of the spark plug, discharge timing by the ignition promoting apparatus 3, and discharge duration. Basically, discharge by the ignition promoting apparatus 3 is started from t before the ignition timing of the spark plug, and the discharge is terminated at the ignition timing, whereby an induced flow is formed around the spark plug at the ignition timing.

[0086] For example, when the number of revolutions of the engine is 1,200 rpm, the discharge is started from 10 before a top dead center of a crank angle. When the number of revolutions is 2,400 rpm, the discharge is started from 20 before the top dead center of the crank angle. About 1 ms is ensured as the discharge duration.

[0087] The engine with the spark discharge ignition promoting apparatus according to the first embodiment has the configuration described above. Therefore, the effects of promotion of the ignition by the spark discharge ignition promoting apparatus can be exerted even in the case of a lean or super lean air-fuel mixture, and it is possible to ignite surely and stably.

[0088] Further, the non-thermal plasma generating means merely acts on promotion of the ignition by the spark plug. Therefore, it is possible to ignite with energy saving without supplying particularly high electric power.

[0089] Therefore, a load on the electrodes and the like for generating plasma can be made smaller; a life of the apparatus is made longer; and there is no need to make it including a power source thereof larger. Therefore, it is possible to realize the apparatus at low cost.

First Comparative Example

[0090] In a case where the engine according to the first embodiment is operated without activating the non-thermal plasma generating means, it becomes an operation based on ignition of only the spark plug, and is the similar operation to that of a conventional engine.

[0091] In a case where an air-fuel mixture used for the operation is caused to become lean or super lean, the ignition by only the spark plug cannot be carried out stably, whereby the operation becomes impossible.

Second Comparative Example

[0092] Japanese Patent Application No. 2015-542682 as the prior art by the inventors of the present application discloses a configuration of a conventional internal-combustion engine for a premixing combustion method in which a spark plug is provided in a combustion chamber of a cylinder and a non-thermal equilibrium plasma generating apparatus is further provided in an air-fuel mixture supplying system to an intake port.

[0093] In a case where a lean or super lean air-fuel mixture is used for the engine according to the second comparative example, ease of ignition is improved compared with the conventional engine according to the first comparative example. However, the ignition is not stabilized, and it may become inoperable in the case of super lean or super dilution.

[0094] Compared with the first embodiment, in the configuration of the engine according to second comparative example, a route of the flow of the air-fuel mixture during the processes from non-thermal plasma treatment in the air-fuel mixture supplying system to ignition (by the spark plug), including intake and compression, in the cylinder is long. Thus, the air-fuel mixture that is subjected to non-thermal plasma treatment in the air-fuel mixture supplying system advances mixture with an air-fuel mixture that is not subjected to the non-thermal plasma treatment and diffusion, whereby an easy combustion characteristic is easily lost.

[0095] In order to stabilize an operation (ignition) of the engine according to the second comparative example even in the case of the lean or super lean air-fuel mixture, it is necessary to make a volume percent of the air-fuel mixture, which is to be subjected to the non-thermal plasma treatment, larger.

[0096] Namely, in order to facilitate ignition of the lean air-fuel mixture, reforming by plasma must be carried out over a large volume so that the partial oxides and the like described above with a prescribed concentration are contained in almost of the intake air-fuel mixture.

[0097] Therefore, the engine according to the second comparative example requires large non-thermal plasma generating means and a large power source configured to supply electric power thereto. However, since they generate a large amount of air-fuel mixture of an easy combustion state for intake, abnormal combustion may occur at timing before the ignition by the spark plug, whereby a risk such as knocking is increased.

Second Embodiment

[0098] FIG. 5 shows a configuration of a second embodiment. In the second embodiment, by embedding an annular embedded electrode 3b in an insulator through which a central electrode of a spark plug 1 goes and fitting the annular exposed electrode 3c to an outer surface of the insulator, an induced flow resulting from plasma generation is injected toward the inside of a combustion chamber from a space formed between an outer circumference of the insulator and the grounded electrode.

[0099] In order to gain a ratio of a thermal plasma generating area in the cylinder, it is necessary to thicken and/or lengthen an electrically insulating tube member integrated with a plug around the plug, which is made of ceramic. However, installation to an engine cylinder is substantially similar to that of a conventional spark plug. It is easy to install and exchange it, and it is a configuration easy for maintenance.

[0100] As described above, the invention made by the inventors of the present application has been explained specifically on the basis of the embodiments. However, it goes without saying that the present invention is not limited to the embodiments, and the present invention may be modified into various forms without departing from the substance thereof.

Reference: Experiment for Examining Effects of Non-Thermal Plasma Treatment Against Air-Fuel Mixture

[0101] Hereinafter, an experiment for examining effects of non-thermal plasma treatment against an air-fuel mixture according to the present invention will be described.

[0102] FIG. 7 shows an outline of experimental equipment. In order to visualize a state to arrive from ignition to combustion, a transparent quartz window 9 is mounted on one end of a rapid compression expansion machine (RCEM) liner 8. A combustion chamber 11 is formed by an RCEM piston 10 that is configured to slide in the RCEM liner 8, whereby an air-fuel mixture therein is compressed. Pulse YAG laser light 12 is concentrated from an upper portion of the combustion chamber 11, and breakdown is formed at a center in the combustion chamber 11, thereby igniting. At this time, fuel was isooctane, an equivalence ratio was 0.5, a compression ratio was 5.5, and compression duration of the piston was equivalent to that when an engine is operated at 1,200 rpm. As a reactor 13 for generating non-thermal plasma, a commercially available spark plug is modified in order to cause an induced flow to reach a laser breakdown location. A plasma actuator that forms a jet-like induced jet flow vertically from the plasma actuator was used. An applied voltage Vpp was 7.8 kV (from a peak to a next peak of alternating voltage), and an applied time was 36 ms until ignition timing by the pulse YAG laser light 12.

[0103] FIG. 8 shows a pressure history. In a case where the reactor 13 is not operated, pressure after 40 ms elapses becomes flat as shown by a broken line. On the other hand, in a case where the reactor 13 is operated, the pressure raises up to 180 ms as shown by a solid line. Thus, it is possible to confirm that ignition and combustion are generated.

[0104] FIG. 9 and FIG. 10 show results of Schlieren measurement that are photographed every 4 ms through the quartz window 9, and respectively show, in the same operating condition, the case where the reactor 13 of the ignition promoting apparatus 3 is not operated and the case where the reactor 13 is operated.

[0105] As is apparent by comparing both drawings, when the reactor 13 is not operated, a flame hardly propagates and misfire occurs in a flow of a compression end. However, when the reactor 13 is operated, ignition is succeeded, and it is possible to confirm that the flame propagates to the air-fuel mixture in the combustion chamber.

[0106] FIG. 11 shows the whole configuration in a case where the ignition promoting apparatus 3 is mounted in a four-cylinder engine. A control device 7 is configured by a microcomputer that is used to control the ignition timing, and controls an optimal voltage value of the high RF voltage to the embedded electrode 3b and application start timing in accordance with the number of revolutions on the basis of detection of a crank angle sensor by using the ignition timing as termination timing.

[0107] Further, it is necessary to increase the induced flow rate when the number of revolutions is high. For this reason, it is effective to adopt a control in which a voltage value of the high RF voltage becomes higher in accordance with an increase in the number of revolutions of the engine. Further, when the ignition is stabilized under a high engine load or the like, activation of the ignition promoting apparatus 3 may be stopped.

[0108] In this regard, electric power required to generate non-thermal plasma by applying the high RF voltage to the embedded electrode 3b is about 3 W. When an applied time width is 15 ms and the number of revolutions is 2,400 rpm, average power is about 1 W. Thus, it is substantially ignorable in view of an output of the engine.

[0109] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.