JP2010249028A - Spark ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem on a spark ignition type internal combustion engine that the reaction of an electric field with spark discharge generates plasma to possibly improve igniting efficiency that, when using microwaves to generate the electric field, the use of a monopole type antenna as an antenna for radiating microwaves to simplify construction generates all-round directivity, and therefore, electromagnetic waves are radiated to areas other than the vicinity of an ignition plug to form the electric field, and plasma may be generated in an area other than the vicinity of the ignition plug, thus resulting in instable combustion generated by the plasma generated in an unexpected position. <P>SOLUTION: In the spark ignition type internal combustion engine, the reaction of an electric field generated in a combustion chamber by electromagnetic waves with spark discharge caused by the ignition plug 1 generates plasma to ignite a mixture. An inner diameter D of the combustion chamber 6 is set to be not larger than 1/2 of the wavelengths of the electromagnetic waves. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a spark ignition internal combustion engine that generates an electric field in a combustion chamber, generates plasma by the electric field and spark discharge by an ignition plug, and ignites an air-fuel mixture.

  2. Description of the Related Art Conventionally, in a spark ignition internal combustion engine mounted on a vehicle, particularly an automobile, an air-fuel mixture in a combustion chamber is ignited at each ignition timing by spark discharge between a center electrode and a ground electrode of a spark plug. In such ignition by an ignition plug, for example, in an internal combustion engine of a type in which fuel is directly injected into a cylinder, if the injected fuel is not distributed at the spark discharge position of the ignition plug, it rarely occurs.

  For this reason, in such an internal combustion engine, a plasma atmosphere is generated in the discharge region of the spark plug, for example, as described in Patent Document 1, in order to compensate for the spark discharge of the spark plug, and an arc is generated in the plasma atmosphere. It is known that the discharge is performed to surely ignite the air-fuel mixture in the combustion chamber without applying a higher voltage than in the past and to obtain a stable flame.

JP 2007-32349 A

  By the way, as a method of generating plasma under atmospheric pressure, an electromagnetic wave, particularly using microwaves is considered. When microwaves are used, for example, a magnetron that outputs microwaves and a monopole antenna that is provided to supply microwaves to the combustion chamber are connected via a waveguide and a coaxial cable. . In this case, the monopole antenna is installed in a state protruding from the combustion chamber. Usually, the monopole antenna only needs to radiate electromagnetic waves, so that it may be thinner than the center electrode or ground electrode of the spark plug.

  In such a monopole antenna, basically, an electric field is formed around the antenna to form plasma. However, in an antenna having directivity in all directions, such as a monopole antenna, an electromagnetic field is radiated in addition to the vicinity of the spark plug and an electric field is formed, so that plasma is formed in the vicinity of the spark plug. There is. In such a case, combustion may become unstable due to the plasma formed at such an unexpected position.

  Therefore, the present invention aims to eliminate such problems.

  That is, the spark ignition internal combustion engine of the present invention is a spark ignition internal combustion engine that generates plasma by reacting an electric field generated in a combustion chamber by electromagnetic waves and a spark discharge by an ignition plug to ignite an air-fuel mixture, The internal diameter of a combustion chamber is set to 1/2 or less of the wavelength of electromagnetic waves, It is characterized by the above-mentioned.

  According to such a configuration, when electromagnetic waves are radiated into the combustion chamber, it becomes difficult to diffuse into the combustion chamber because the inner diameter of the combustion chamber is ½ or less of the wavelength of the electromagnetic waves. For this reason, it becomes possible to form the electric field by electromagnetic waves in the desired position in a combustion chamber.

  The present invention has a configuration as described above, and can suppress the emission of electromagnetic waves to unnecessary positions in the combustion chamber, thereby suppressing the generation of plasma at unexpected positions and achieving good combustion. Can be guaranteed.

Sectional drawing which expands and shows the principal part of one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  An engine 100 that is a spark ignition type internal combustion engine with a spark plug 1 attached and shown in FIG. 1 is of, for example, a three-cylinder double overhead camshaft (DOHC) type and has an intake port 2 opening. 3 and the opening 5 of the exhaust port 4 are arranged opposite to each other centering on a spark plug 1 attached to substantially the center of the ceiling portion of the combustion chamber 6 and are opened at two locations per cylinder. That is, the engine 100 is attached to the cylinder block 7, and the camshafts 9 and 10 are attached to the intake side and the exhaust side of the cylinder head 8 forming the ceiling portion of the combustion chamber 6, respectively. The intake port 2 of the cylinder head 8 is opened and closed by an intake valve 11 that reciprocates when the camshaft 9 rotates, and the exhaust port 4 is opened and closed by an exhaust valve 12 that reciprocates when the camshaft 10 rotates. Is. In FIG. 1, the engine 100 is illustrated with the ignition coil removed from the spark plug 1.

  The spark plug 1 includes a housing 13 made of a conductive material, a center electrode 14 that is insulated and attached in the housing 13, and a ground electrode 15 that is provided at the lower end of the housing 13 away from the center electrode 14. That is, in the spark plug 1, the housing 13 supports the substantially cylindrical insulator 16, and the connection terminal 17 attached to the upper end of the insulator 16 has a center electrode 14 protruding from the lower end of the insulator 16 and a center shaft (not shown). The ground electrode 15 is integrally provided in the housing 13 at a position that is electrically connected and extends from the lower end of the housing 13 to a position facing the lower end of the center electrode 14. In this embodiment, the center electrode 14 is caused to function as an antenna for radiating microwaves that are electromagnetic waves. For this purpose, an ignition coil for spark discharge is connected to the center electrode 14 of the spark plug 1 and a magnetron (not shown) that outputs microwaves that are electromagnetic waves for generating plasma is connected. Accordingly, the microwave output from the magnetron is applied to the center electrode 14 of the spark plug 1 as described below.

  The combustion chamber 6 has a substantially conical shape with the opening 3 of the intake port 2 and the opening 5 of the exhaust port 4 closed by the intake valve 11 and the exhaust valve 12. The inner diameter (inner diameter) D of the position continuous with the lower end of the combustion chamber 6, that is, the cylinder bore 7a, is set to ½ or less of the wavelength of the microwave radiated into the combustion chamber 6 at the time of ignition. That is, the inner diameter D of the combustion chamber 6 is ½ of the wavelength of the microwave at the maximum dimension.

  In such a configuration, when the air-fuel mixture in the combustion chamber 6 is ignited using the spark plug 1, the engine 100 reacts the spark discharge of the spark plug 1 with the electric field generated in the combustion chamber 6. The spark discharge of the spark plug 1 is made larger than the spark discharge when not reacting with the electric field.

  At the time of ignition, a spark discharge is generated in the spark plug 1 by an ignition coil, and a high-frequency electric field is generated by a microwave almost simultaneously with or immediately after the spark discharge to generate plasma, thereby generating an air-fuel mixture in the combustion chamber 6. Is configured to burn rapidly.

  Specifically, the spark discharge by the spark plug 1 becomes plasma in a high-frequency electric field, and the flame becomes large.

  This is because the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge oscillate and meander due to the influence of the high-frequency electric field, resulting in a longer path length and the number of collisions with surrounding water and nitrogen molecules. This is due to a dramatic increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is ionized, in other words, a plasma state. The flame will increase dramatically.

  As a result, the air-fuel mixture is ignited by the spark discharge increased by reacting with the high-frequency electric field, so that the ignition region is expanded and the two-dimensional ignition of only the spark plug 1 is changed to the three-dimensional ignition. Therefore, the initial combustion is stabilized, and the combustion rapidly propagates into the combustion chamber 6 as the radicals increase, and the combustion expands at a high combustion rate.

  When plasma is generated in the combustion chamber 6 as described above, the center electrode 14 of the spark plug 1 functions as an antenna that radiates microwaves. The microwave radiated from the center electrode 14 forms a high-frequency electric field having the highest intensity in the vicinity of the center electrode 14. This is because the combustion chamber 6 has a substantially conical shape, and the inner method becomes larger from the substantially center of the ceiling portion of the combustion chamber 6 to which the ignition plug 1 is attached toward the cylinder bore 7a. This is to approach the dimensions in the microwave blocking region. That is, as described above, since the inner diameter D of the maximum dimension portion of the combustion chamber 6 is set to ½ or less of the wavelength of the microwave, the strength of the high-frequency electric field due to the microwave radiated from the center electrode 14 is set. Is exponentially attenuated as the distance from the center electrode 14 increases.

  As a result, the radiated microwave reaches a portion unnecessary for ignition, but forms only a high-frequency electric field having a very low intensity. That is, the high-frequency electric field is not distributed with equal intensity in the combustion chamber 6 but is most proximate to the vicinity of the center electrode 14 and the ground electrode 15 of the spark plug 1, that is, in the vicinity of a portion where a spark is generated at the timing of ignition. Distribution is such that the strength is high. Therefore, since a high-intensity high-frequency electric field is formed only at the necessary site, it is possible to achieve good ignitability and suppress the occurrence of unstable combustion without generating plasma at unexpected positions. can do.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above-described embodiment, the center electrode 14 of the spark plug 1 is made to function as an antenna, but an antenna other than the center electrode 14 may be provided.

  In the above-described embodiment, the magnetron is described as outputting microwaves. However, instead of the magnetron, a traveling wave tube or the like may be used, and a semiconductor microwave oscillation circuit may be provided.

  Further, the frequency of the electromagnetic wave is not limited to the microwave frequency range, and any frequency may be used as long as it can generate an electric field in which the polarity is alternately switched in the spark discharge portion of the spark plug to generate plasma.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  As an application example of the present invention, it can be used for a spark ignition type internal combustion engine that uses gasoline or liquefied natural gas as fuel and requires spark discharge by an ignition plug for ignition.

1 ... Spark plug 6 ... Combustion chamber D ... Inner diameter

Claims (1)

A spark ignition internal combustion engine that generates plasma by reacting an electric field generated by an electromagnetic wave in a combustion chamber with a spark discharge by an ignition plug, and ignites an air-fuel mixture,
A spark ignition internal combustion engine in which the inner diameter of the combustion chamber is set to ½ or less of the wavelength of the electromagnetic wave.

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