Technical field
[0001] 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
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] The goal of the invention is to eliminate or at least substantially reduce shortcomings
of the background art.
Principle of the invention
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] Further it is advantageous, if the connecting orifice into which the center electrode
enters is non-circular, preferably in the form of a star.
[0016] 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
[0017] 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
[0018] 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 cm
3. 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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
[0027]
- 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
1. 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).
2. 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.
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 cylindric surface.
4. 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).
5. 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).
6. 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.
7. 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.
8. The spark plug according to the claim 6, characterised in that further connecting hole or holes (122) are curved.
9. 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.
10. The spark plug according to the claim 7, characterised in that the connecting orifice (121) has a star-like shape.