EP2053711A2

EP2053711A2 - Spark plug

Info

Publication number: EP2053711A2
Application number: EP08466027A
Authority: EP
Inventors: Stanislav Beroun; Josef Blazek
Original assignee: Technicka Univerzita v Liberci
Current assignee: Technicka Univerzita v Liberci
Priority date: 2007-10-23
Filing date: 2008-10-22
Publication date: 2009-04-29
Also published as: CZ2007738A3; EP2053711A3

Abstract

The spark plug, especially for the spark ignition piston engine, comprising the center electrode of spark-gap and the shell forming the second electrode of spark-gap and provided with means for connection of the spark plug to dead space of cylinder in combustion engine, while inside the shell the ignition chamber is performed, whose face adjacent to the dead space of the cylinder being respective to the spark plug comprises at least one connecting orifice. The center electrode is passing through the space of ignition chamber and it finishes in the connecting orifice in the face of ignition chamber, while between surface of circumference of the connecting orifice and surface of circumference of the end of center electrode there is the gap.

Description

Technical field

The spark plug, especially for the spark ignition piston engine, comprising the center electrode of spark-gap and the shell forming the second electrode of spark-gap and provided with means for connection of the spark plug to dead space of cylinder in combustion engine, while inside the shell the ignition chamber is performed, whose face adjacent to the dead space of the cylinder being respective to the spark plug comprises at least one connecting orifice.

Background art

The spark-ignition engines (petrol, gas) mostly work with external creating of mixture, i.e., into engine cylinders the mixture is brought in a state of high level preparedness: for completion of creation and homogenization of mixture in engine cylinder (in case of petrol after then also its full evaporating and mixing of fuel vapours with the air), a relatively long period of full filling stroke and substantial part of compression stroke is available. Prepared homogenous mixture then together with the enclosed volume forms suitable conditions for kinetic course of combustion process in engine cylinder.
Initiation of combustion process in spark-ignition engines is realised through the mechanism of high-temperature inflammation of a very small volume of prepared mixture. By a high-voltage (HV) discharge on electrodes of spark plug the temperature is increased extremely in a very small volume of combustible mixture which starts the pre-oxidation reactions in fuel. Due to high temperature the molecules of hydrocarbon fuel, which were in contact with oxygen, change to radicals with peroxide bond, which decompose quickly and energetic rich activated particles - free radicals are created, which initiate process of further chain reactions. After a sufficient concentration of activated particles is created, the whole process culminates by generating the ignition focus. From the ignition focus the combustion starts to spread by effect of heat transfer and by gradual increasing of concentration of products of pre-oxidation reactions in the area closely before the combustion zone in the ignition focus. Concentration of activated particles in the unburned mixture is increased through the heat effect (thermal conduction) from the face of the flame, and also into the unburned mixture activated particles from the combustion zone penetrate: by this suitable conditions for flame spreading into the surrounding mixture are created. Spread of flame up to entire mixture burnout in the whole volume of combustion space (of engine cylinder) is ensured by spreading and development of oxidation reactions first from ignition focus and subsequently also from further areas of spreading combustion.
Kinetic combustion of homogenous prepared mixture and seemingly definite conditions for ignition as well as the subsequent combustion nevertheless in reality are complicated by a series of effects, that cause a poor reproducibility of working cycles, showing itself by their high inter-cycle variability. Inter-cycle variability is a long-term problem of spark-ignition engines and its cause lies in considerable variability of conditions for achievement of necessary concentration of free radicals in the ignition focus being created, which is caused by a greater number of effects: considerably acts the fact, that in engine cylinder, thus also in the closest vicinity of electrodes of the spark plug there is a turbulent environment, in which the activated particles are dispersed in a broader surroundings, thus slowing down the process of ignition. Therefore due to impact of turbulence, the conditions for creating of ignition focus are of an accidental nature. The course of subsequent mixture combustion, which strongly depends on the initial phase of combustion, thus in the spark-ignition engines features by the already mentioned inter-cycle variability, showing itself cycle from cycle by relatively big differences in the course of pressure in the engine cylinder. Inter-cycle variability complicates the optimisation in adjustment of the spark-ignition engine and deteriorates its efficiency as well as performance and emission parameters.
Some vehicle spark-ignition engines, to improve the conditions for reliable ignition and more stable course of the combustion process, use mixture ignition by means of 2 spark plugs, positioned in opposite places of combustion space. This solution is complicated as to its construction and therefore not widely spread. Other groups of spark-ignition engines (e.g. stationary gas engines) for more quality and reliable ignition of mixture use so called indirect mixture ignition in the combustion space in engine cylinder by flashing out of burning mixture from the ignition chamber. The ignition chamber is a separate space of a very small volume, in which through a special inlet of gas an enriched mixture is created, which after ignition by a high voltage discharge on the spark plug (positioned in ignition chamber) begins to burn very quickly (burning-out within cca 1 ms) and burned gases together with burning mixture flash out from the chamber through the connecting channels into the main combustion space and on many places ignite the mixture in the main combustion space - nearly simultaneous ignition of the mixture in more places together with initiated turbulence support development of a relatively very stable process in the main combustion space in engine cylinder. By a suitably designed indirect ignition it is possible to ignite and combust reliably very weak mixtures with high excess of air (λ ≅ 2÷2,4) at relatively low inter-cycle variability. Nevertheless this device and its accessories is rather complicated, thus expensive.
For example the solution according to DE 19714796 A1 uses ignition chamber without independent fuel delivery. The spark-gap of the spark plug arranged in ignition chamber ignites the mixture, which into the chamber was delivered through the connecting channels from engine cylinder at compression stroke. Mixture ignition in the spark-ignition engine by means of the ignition chamber without independent fuel delivery into the chamber is used also at some engines of the GDI type (FSI - spark-ignition engines with direct fuel injection and combustion of layered heterogenous mixture), where through a special modification in shape of the dead space and through suitable arrangement of inlet and flash-out channels in the chamber an important improvement of ignition quality is achieved. Such arrangements of ignition chambers are described for example also in documents DE 102005017186 , JP 2006144648 , US 20050211217 and elsewhere.
In the spark-ignition engines according to the above mentioned solutions which combust the prepared homogenous mixture, the ignition chamber without independent fuel delivery into the chamber improves energetic and performance parameters of engine in the modes of higher loading. At idle running or at low engine loading, the activity of this ignition chamber is deteriorated by pressure drop in engine cylinder, due to which a lower quantity of mixture gets into the chamber.
The goal of the invention is to eliminate or at least substantially reduce shortcomings of the background art.

Principle of the invention

The goal of the invention has been reached by the spark plug comprising the ignition chamber according to the invention, whose principle consists in that the center electrode is passing through the space of ignition chamber and it finishes in the connecting orifice in the face of ignition chamber, while between surface of circumference of connecting orifice and surface of circumference of the end of center electrode there is a gap.
This gap forms both wetted cross-section between volume of the ignition chamber and the compression volume in engine cylinder, and it is simultaneously the spark-gap of the spark plug. Through this arrangement of the spark-gap, a simultaneous ignition of mixture in ignition chamber and in the dead space of engine cylinder is secured.
It is also advantageous, if the end of center electrode in the area of connecting orifice of the ignition chamber with respect to the section of the center electrode passing through the ignition chamber has a smaller diameter, while this end of the center electrode may have cylindric, or conical surface, possibly its surface is a combination of truncated cone tied up to the diameter of the center electrode and becoming narrower in direction towards the end of center electrode, at the same time it is connected to a cylindric surface, whose diameter is smaller than diameter of the center electrode.
By this shape of end of the center electrode upon preservation of the required function of the spark-gap also advantageous streaming through the connecting orifice during filling the chamber with mixture and flash-out the burned gases after ignition may be achieved.
It is also advantageous, if in the face of the ignition chamber adjacent to the dead space of cylinder being respective to the spark plug at least one further connecting hole is performed.
By this the total clear opening for filling the ignition chamber with mixture may be enlarged and to ensure an optimum direction of flash-out or more flashes-out after ignition.
Further it is advantageous, if the connecting orifice into which the center electrode enters is non-circular, preferably in the form of a star.
By the star-like and to it similar shape there may be preserved a suitable distance of circle inscribed into a star from surface of end of the center electrode, which is a flashover distance of the spark-gap, while the wedges of the star with advantage increase the clear opening of such performed connecting slot.

Description of the drawing

Exemplary embodiments of spark plug according to the invention are represented on the drawing, where Fig. 1 shows a basic embodiment of the spark plug with integrated ignition chamber, Fig. 2 embodiment with further connecting holes from the ignition chamber, Fig. 3a, 3b exemplary embodiment with non-circular connecting orifice forming the spark-gap, where Fig. 3b is the "P" view from Fig. 3a, and Fig. 4 to 6 modification of ends of the center electrode.

Examples of embodiment

The spark plug according to the invention comprises the shell 1 provided with thread 11 for fastening of the spark plug to combustion space of engine cylinder. In upper section of the shell 1 of spark plug there is tightly fastened insulator 2, through which the center electrode 3 passes. In lower section of the shell in area of its thread 11 a cavity of the ignition chamber 4 is performed whose volume in exemplary embodiment is 0,5 cm³. Upper terminal 31 of center electrode 3 extending from insulator 2 serves for connection of high-voltage cable, lower end section 32 passes through a cavity of the ignition chamber 4. In lower face 12 of cavity of ignition chamber 4 there is a central connecting orifice 121 , into which by its face the end 321 of end section 32 of center electrode 3 extends. Between the cylindric end 321 of center electrode 3 and connecting orifice 121 there is the circumferential gap 5. The shell 1 forms the ground electrode of the spark plug and the gap 5 thus forms the space of spark-gap of the spark plug.
Fig. 2 represents arrangement of the spark plug with the ignition chamber 4, whose face 12 besides the central connecting orifice 121, into which the center electrode 3 enters by its end 321, is provided with further connecting hole 122. The basic arrangement is identical as in the case of embodiment of spark plug according to Fig.1. In the not represented embodiment the face 12 is provided with several connecting holes 122. At the same time the holes 122 with the longitudinal axis of the spark plug may be parallel, trapezoidal or skew, while they need not to be straight. At the same time the holes 122 may be parallel, trapezoidal or skew also mutually one to another.
In embodiments according to Fig. 1 and 2 the central connecting orifice 121 is circular. In Fig. 3a, 3b the central connecting orifice 121 is a non-circular. In this exemplary embodiment it is performed as a star with several wedges, what may be advantageous also from the point of view of production technology. Originally tube-shaped form of lower end of the shell 1 in direction from the edge is cut, the developed shape is indicated in Fig. 3a. The face 12 with wedged connecting orifice 121 of the star-like shape is after then created by bending the wedges 123 produced by cutting, as represents the view of connecting orifice 121 in Fig. 3b.
In embodiment according to Fig. 4 the end 322 of center electrode 3 extending into the connecting orifice 121 is a cylindric one, at the same time it has a smaller diameter, than the end section 32 of center electrode 3 passing through space of the ignition chamber 4.
In embodiment according to Fig. 5 the end 323 of center electrode 3 extending into the connecting orifice 121 is a conical one, at the same time in direction from cavity of the ignition chamber 4 it becomes narrower.
In embodiment according to Fig. 6 the end 324 of center electrode 3 extending into the connecting orifice 121 at the beginning is conical, while in direction from ignition chamber 4 becomes narrower and transits into the cylindric section of a small diameter.
It is apparent, that the shape of end of the center electrode 3 in area of the connecting orifice 121 and the shape of connecting orifice 121 is not restricted to the represented exemplary embodiments.
In the course of compression stroke of piston the homogenous mixture of the liquid fuel and the air, possibly gas, is compressed, at the same time it penetrates through the connecting orifice 121 possibly through another one or through further connecting holes 122 into the ignition chamber 4. In the moment of ignition by the high-voltage discharge in area of the spark-gap between the end 321, 322, 323, 324 of center electrode 3 and the connecting orifice 121 of the shell 1 forming the ground electrode simultaneously the mixture in the compress space of the cylinder as well as in the space of ignition chamber 4 is ignited. In the unchanging volume of cavity of the ignition chamber 4 burning-out the filling of the ignition chamber 4 accelerates significantly, and the ignited and burning mixture in the ignition chamber 4 through the gap 5 between the center electrode 3 and circumference of connecting orifice 121, possibly another connecting holes 122 in the face 12 of the ignition chamber 4 is flashed-out into the combustion space in cylinder. Acceleration in development of burning in homogenous mixture in engine cylinder, improved stability of combustion process and decreasing of inter-cycle variability is secured through this. By the star-like and to it similar shape of connecting orifice 121 for example according to the Fig. 3 the necessary flashover distance, a suitable distance of the spark-gap given by the gap between the circle inscribed star and surface of end of the center electrode may be performed, while the wedges of the star advantageously increase the clear opening of the connecting orifice 121.
Due to the fact that the spark-gap according to the invention is situated on interface of the ignition chamber 4 and the dead space of cylinder, the inflammation of the mixture in the ignition chamber 4 as well as in section of the dead space neighbouring with the spark-gap occurs simultaneously. Therefore also at idle speed of engine or at low loading, when the ignition chamber 4 is not sufficiently filled with mixture, the resultant effect of mixture ignition in the dead space is, at minimum, in the quality corresponding to ignition with a classic spark plug with the spar-gap situated in the dead space. At a very quality ignition of the mixture and thus at a quality course of the combustion process at loading in conditions of operation running, the required parameters of idle speed and running with low loading are preserved. At the same time into the ignition chamber 4 there is not introduced an independent delivery of fuel.

List of referential markings

1: shell
11: thread
12: face (of cavity of ignition chamber)
121: connecting orifice (central)
122: connecting hole
123: wedge
3: center electrode
31: upper terminal (of center electrode)
32: end section (of center electrode)
321: end (of center electrode - lower)
322: end (of center electrode - lower)
323: end (of center electrode - lower)
324: end (of center electrode - lower)
4: ignition chamber
5: gap

Claims

The spark plug, especially for the spark ignition piston engine, comprising the center electrode of spark-gap and the shell forming the second electrode of spark-gap and provided with means for connection of the spark plug to dead space of cylinder in combustion engine, while inside the shell the ignition chamber is performed, whose face adjacent to the dead space of the cylinder being respective to the spark plug comprises at least one connecting orifice characterised in that, the center electrode (3) is passing through the space of ignition chamber (4) and it finishes in the connecting orifice (121) in the face (12) of ignition chamber (4), while between surface of circumference of the connecting orifice (121) and surface of circumference of the end (321, 322, 323, 324) of center electrode (3) there is the gap (5).
The spark plug according to the claim 1, characterised in that the end (321, 322, 323, 324) of the center electrode (3) in area of connecting orifice (121) of the ignition chamber (4) with respect to the section (32) of the center electrode (3) passing through the ignition chamber (4) has a smaller diameter.
The spark plug according to the claim 2, characterised in that the end (321, 322, 323, 324) of the center electrode (3) in area of the connecting orifice (121) of the ignition chamber (4) has a cylindric surface.
The spark plug according to the claim 2, characterised in that the end (321, 322, 323, 324) of the center electrode (3) in area of the connecting orifice (121) of the ignition chamber (4) has a conical surface, while the peak of the cone aims to end of the center electrode (3).
The spark plug according to the claim 2, characterised in that the end (321, 322, 323, 324) of the center electrode (3) in area of the connecting orifice (121) of the ignition chamber (4) has a conical surface tied up to diameter of the center electrode (3) and becoming narrower in direction towards the end of the center electrode (3), while it is connected to a cylindric surface, whose diameter is smaller, than diameter of the center electrode (3).
The spark plug according to any of the previous claims, characterised in that in the face (12) of ignition chamber (4) adjacent to the dead space of cylinder being respective to the spark plug at least one further connecting hole (122) is performed.
The spark plug according to the claim 6, characterised in that further connecting hole or holes (122) with the longitudinal axis of the spark plug and/or mutually one to another are parallel, trapezoidal or skew.
The spark plug according to the claim 6, characterised in that further connecting hole or holes (122) are curved.
The spark plug according to any of the previous claims, characterised in that the connecting orifice (121), into which the center electrode (3) enters, is a non-circular.
The spark plug according to the claim 7, characterised in that the connecting orifice (121) has a star-like shape.