EP2841762A2

EP2841762A2 - Laser ignition device and operating method therefor

Info

Publication number: EP2841762A2
Application number: EP13711616.6A
Authority: EP
Inventors: Klaus Stoppel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-04-23
Filing date: 2013-03-18
Publication date: 2015-03-04
Also published as: US9784173B2; WO2013160017A3; US20150136049A1; WO2013160017A2; DE102012206643A1

Abstract

A laser ignition device (100) for an internal combustion engine (102) is presented, wherein the laser ignition device (100) has at least a laser spark plug (110) and a cooling device (120) for controlling the temperature, in particular cooling, the laser spark plug (110). According to the invention, the cooling device (120) has a cooling circuit (122) which contains a cooling fluid (128) and can be thermally connected to at least one component of the laser spark plug (110), wherein a volume of the cooling fluid (128) which is contained in the cooling circuit (122) is less than or equal to approximately fifty percent of a compression volume of a cylinder (132) of the internal combustion engine (102), preferably less than or equal to approximately ten percent of a compression volume of the cylinder (132) of the internal combustion engine (102).

Description

Description title

Laser ignition device and operating method for this state of the art

The invention relates to a laser ignition device for an internal combustion engine, wherein the laser ignition device has at least one laser spark plug and a cooling device for tempering, in particular cooling, of the laser spark plug.

Known cooling systems of laser ignition devices, which

Liquid cooling based, have the disadvantage that leaked from a cooling circuit of the cooling system cooling fluid, especially water

(Leakage water), flow into the cylinder shaft of the internal combustion engine and can even enter the combustion chamber when changing the laser spark plug. As a result, the compression ratio is increased during operation of the internal combustion engine, since the cooling fluid, in particular water, is known to be incompressible, so that the internal combustion engine can be destroyed as a result of the leakage water (water hammer). The cause of the leakage water are usually leaky cooling water connections or installation errors.

Disclosure of the invention

Accordingly, it is an object of the present invention, a

Laser ignition of the type mentioned to be improved so that the risk of water hammer is reduced or completely avoided.

This object is achieved with the laser ignition device of the type mentioned above in that the cooling device containing a coolant Cooling circuit which is thermally connectable to at least one component of the laser spark plug, wherein a volume of the cooling liquid contained in the cooling circuit less than or equal to about 50 percent of a

Compression volume of a cylinder of the internal combustion engine is,

Preferably, less than or equal to about 10 percent of a compression volume of the cylinder of the internal combustion engine.

The compression volume of a cylinder of the internal combustion engine corresponds to the minimum combustion chamber volume that can be set during the working cycle of the cylinder. The compression volume is reached when the piston of the cylinder in question is at the top dead center.

By the inventive measure, the volume of the cooling liquid contained in the cooling circuit is less than or equal to a predetermined proportion of the compression volume of the cylinder is advantageously achieved that no inadmissibly high combustion chamber pressure occurs in the cylinder, even if accidentally the coolant partially or completely entered the combustion chamber.

The principle of the invention therefore provides a limitation of

Liquid amount of the cooling liquid, which is advantageous to the

Compression volume of the cylinder of the internal combustion engine is related to achieve a limitation of the occurring as a result of water entering the combustion chamber overpressure. Alternatively, the principle of limiting the liquid quantity of the cooling liquid can also provide for the provision of an absolute maximum amount of cooling liquid.

Particularly advantageous is the maximum in the cooling circuit of the

Laser ignition contained amount of cooling liquid or its volume with respect to the compression volume of a cylinder set, which is to be assigned a laser spark plug of the laser ignition device according to the invention.

As a further solution of the object of the present invention, a laser ignition device according to claim 2 is given. At this

Invention variant is a volume of that contained in the cooling circuit Coolant less than or equal to about 0.1 liter, preferably less than or equal to 0.05 liters, whereby typical applications of the laser ignition device according to the invention, namely the use in stationary large gas engines, are covered. Such large gas engines usually have

Cylinder volumes between about 2 liters and about 4 liters. The inventive

Limiting the volume of the cooling liquid to about 0.1 liter or less than about 0.05 liters is particularly advantageous because in case of accidental leakage of the cooling liquid from the cooling circuit of the invention

Laser ignition in a cylinder of the large gas engine, an unacceptably high compression pressure in the top dead center of the cylinder is not to be feared.

For internal combustion engines with lower cylinder volumes, such as internal combustion engines of motor vehicles and the like, is a

to provide correspondingly smaller amount of cooling liquid in the cooling circuit. For example, for conventional internal combustion engines of

For motor vehicles, the amount of the cooling liquid to values less than about 0.05 liters, for example, values less than about 0.02 liters or even less than 0.01 liters are limited.

In an advantageous embodiment of the invention, it is provided that the cooling circuit has a first heat exchanger, which is thermally connectable to at least one component of the laser spark plug, wherein the cooling circuit has a second heat exchanger, which is thermally connectable with a heat sink, and wherein funding is provided, to cause a circulation of the cooling liquid in the cooling circuit. The volume of the conveying means which can be acted upon with cooling liquid is advantageously included in the dimensioning according to the invention of the maximum volume of the coolant.

For example, the first heat exchanger may advantageously be connected directly to a housing of the laser spark plug to be cooled or to a component of the laser spark plug. Particularly advantageous is a direct thermal connection of the first heat exchanger to a heat source of the laser spark plug, for example to a semiconductor laser or the like. The second heat exchanger is advantageously arranged remotely from the

Laser spark plug and with a heat sink connectable or connected. As a heat sink, for example, the following components can serve:

1 . Metal housing of an intake manifold of the internal combustion engine. The

Temperature of the heat sink in this case corresponds to the temperature of the intake air, which is usually between about 20 ° C and about 35 ° C.

2. A plurality of cylinders associated heat conduction, for example, metal tube or stainless steel corrugated hose or the like, which in turn is cooled by means of coolant, for example, flows through cooling water of the internal combustion engine associated intercooler or mixture cooler. In this case, the maximum temperature of the heat sink is about 45 ° C in typical

Applications.

3. A housing of the internal combustion engine itself can serve as a heat sink, wherein the maximum temperature corresponds approximately to the cooling water temperature of the engine cooling of the internal combustion engine, that is about 85 ° C.

4. An air-flow pipe, which is acted upon by ambient air, so that in turn results in the temperature of the heat sink about ambient air temperature between 20 ° C and 35 ° C. Optionally, surface enlarging measures in the

air-flow pipe are taken, for example, the integration of cooling fins in the air-conducting cross-section of the tube.

5. Another alternative to forming a heat sink for the

Use with the laser ignition device according to the invention consists in a metal tube or a stainless steel corrugated hose, wherein these elements are flowed through by cooling water of a primary cooler, which is provided for the laser ignition device on the internal combustion engine. This primary cooler can be for example a so-called chiller (with constant temperature selection) or an air-water cooler (temperature depends on ambient temperature). This design of the heat sink is slightly more complex and expensive than the above four variants. Other designs for the heat sink and combinations of

above measures 1 to 5 are also conceivable.

In order to achieve an improved temperature gradient between the cooling circuit and the heat source or the heat sink, optionally one or more Peltier elements can be provided in series, wherein the Peltier elements or either in the laser spark plug between the heat source (semiconductor laser) and the first heat exchanger of the cooling circuit or be arranged outside the laser spark plug. For example, the or the Peltier elements can also be arranged between the second heat exchanger and the heat sink or elsewhere in the cooling circuit. Peltier elements can generally be characterized by the following

Connection techniques with the components of the invention

Laser ignition device or its cooling circuit to be connected: by clamping with two-sided application of thermal grease and / or

Wärmeleitkleber and / or heat conducting foil or by soldering on both sides metallized surfaces of the Peltier element.

It is also possible to apply a surface of the Peltier elements with thermal paste and to solder another surface of the Peltier elements, which is metallized. Combinations of the above

Connection techniques are also conceivable.

In order to set the temperature difference provided by the Peltier element exactly, a control or regulation is necessary. The control operates, for example, with a temperature sensor, which is preferably fastened near a cold side of the Peltier element.

In a further advantageous embodiment, it is provided that the cooling circuit has at least one fluid line for guiding the cooling liquid, wherein the fluid line is preferably designed to be flexible. The

Provision of one or more fluid lines advantageously allows a spatially separate arrangement of the first and second heat exchangers such that the waste heat of the laser spark plug to be cooled can be transported to a remote heat sink. Particularly advantageously, the cooling circuit has a first fluid line, which from the heat sink or the second heat exchanger to the first heat exchanger, ie, the "hot" end of the cooling circuit, and a second fluid line, which leads the cooling fluid heated in the area of the first heat exchanger back to the heat sink. Circulation of the cooling liquid in the cooling circuit is provided by provision of conveying means, in particular a pump preferably a miniaturized electric motor

driven pump, realized. In a particularly preferred

Embodiment, this pump has a maximum electrical

Power consumption of about eight watts. Other funding

(Diaphragm pump, etc.) are also conceivable.

In a further advantageous embodiment it is provided that at least one fluid line has an inner diameter of at most about 4 mm (millimeters), preferably at most about 3 mm, whereby on the one hand a measure is implemented which limits the total volume of the cooling liquid in the cooling circuit, and on the other hand advantageous one

Speed is limited, runs out with the coolant in the event of leakage from the cooling circuit, for example, in the cylinder shaft of the

Internal combustion engine.

It is also conceivable to provide fluid lines for the cooling circuit according to the invention, which have a maximum inner diameter of less than 3 mm.

In a further advantageous embodiment, it is provided that an aggregated total length of all fluid lines of the cooling circuit amounts to a maximum of about 4 m (meters), preferably about 2 m, whereby flow-dynamic effects impairing the circulation of the cooling fluid are limited. In addition, a limitation of the total volume of the cooling liquid is made possible by the choice or limitation of the aggregated total length of all fluid lines of the cooling circuit.

In a further advantageous embodiment it is provided that the cooling circuit has a flow rate of cooling fluid per time of at least about 2 ml / min (milliliters per minute), preferably at least about 50 ml / min. The fluid then circulates preferably once a minute in the

Cooling circuit. In a further advantageous embodiment, it is provided that at least one fluid line for guiding the cooling fluid and / or

Conveying means for the cooling liquid are at least partially integrated in a wiring harness of the laser spark plug. The wiring harness usually contains for the

Operation of the laser spark plug required control lines, which may be formed electrically and / or optically. By integrating the fluid line or the conveying means for the cooling liquid in the wiring harness a particularly simple installation of the laser ignition device according to the invention is made possible. At the same time, the fluid lines of the invention

Laser ignition are protected by the same mechanical means for protecting the wiring harness, as provided for the electrical or optical lines of the laser spark plug anyway. In addition, the cooling fluid in the fluid lines allows a cooling function of

Harness.

In a further embodiment of the laser ignition device, at least one fluid line for guiding the cooling liquid and / or conveying means for the

Coolant at least partially thermally isolated from an environment. For example, on surfaces of the fluid lines a

Heat insulation arranged, which prevents unwanted heating of the cooling fluid due to irradiation of radiated heat by the internal combustion engine. Particularly preferred is according to another embodiment of the

Cooling circuit formed closed. That means no

Fluid connections between the components of the refrigeration cycle

(Fluid line (s), funding, heat exchanger) are provided, which are to be opened or closed for the inclusion or expansion of the laser ignition device according to the invention. Rather, the advantage can be

Assembly of the laser ignition device according to the invention in one

Production operation take place, so that an opening of the fluid circuit of the cooling device according to the invention locally, that is in the region of

Internal combustion engine, not required. This further reduces the risk of leakage. As further solutions of the object of the present invention, an internal combustion engine according to claim 1 1 and operating method according to claim 12 and 13 are provided.

Further features and embodiments of the invention can be found further in the following drawings and the accompanying description, wherein the features both alone and in different

Combinations may be important for the invention, without being explicitly referred to again.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

Figure 1 is a simplified sectional view of arranged on a combustion chamber of an internal combustion engine housing sections and a laser ignition device in a first embodiment; and

Figure 2 is an alternative to Figure 1 arrangement with a second

Embodiment of the laser ignition device.

The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

FIG. 1 shows a first embodiment of a device according to the invention

Laser ignition device 100 for an internal combustion engine 102 in the installed position in

Area of a cylinder head 108 of the internal combustion engine 102th Die

Laser ignition device 100 has a laser spark plug 110, which is arranged in a manner known per se in a cylinder shaft 104 of the internal combustion engine 102. Furthermore, the laser ignition device 100 comprises a

Cooling device 120 for tempering, in particular cooling, the

Laser spark plug 1 10. For this purpose, the cooling device 120 has a cooling circuit 122 which contains a cooling liquid 128. The cooling circuit 122 is thermally connectable or connected to at least one component of the laser spark plug 110. In the present case, the laser spark plug 110 includes, inter alia, a housing 12, in which a semiconductor laser 14 and a first heat exchanger WT1 of the cooling circuit 122 are arranged. The heat exchanger WT1 and the semiconductor laser 1 14 are presently adjacent and thermally coupled. Furthermore, the cooling circuit 122 in a top right area of the drawing on a second heat exchanger WT2, which is thermally coupled to a heat sink 126.

In the drawing below the cylinder head 108, a cylinder 132 is arranged, which has a combustion chamber 106 and a piston 134 of the cylinder 132.

According to the invention, it is provided that a volume of the cooling liquid 128 contained in the cooling circuit 122 is less than or equal to approximately fifty percent of a compression volume of the cylinder 132 of the internal combustion engine 102, preferably less than or equal to approximately ten percent of the compression volume of the cylinder 132 of the internal combustion engine 102. By this measure , the volume of the cooling liquid 128 contained in the cooling circuit 122 is less than or equal to a predetermined proportion of the compression volume of the

To hold cylinder 132 is advantageously achieved that no impermissibly high combustion chamber pressure occurs in the cylinder 132, even if accidentally the cooling liquid 128 has entered partially or completely into the combustion chamber 106. In this way, even in the worst case scenario, if that is the case

Coolant 128 as a result of leakage or failure in the maintenance of the laser ignition 100 completely flowed into the combustion chamber 106, damage to the internal combustion engine 102 (for example, by

Water hammer) are substantially avoided.

The principle of the invention therefore provides a limitation of

Liquid amount of the cooling liquid 128 before, which is advantageous to the

Compression volume of the cylinder 132 of the internal combustion engine 102 is related to achieve a limitation of the occurring as a result of water entering the combustion chamber 106 overpressure.

In an alternative variant of the invention, a volume of the cooling liquid 128 contained in the cooling circuit 122 is less than or equal to about 0.1 liter, preferably limited to less than or equal to 0.05 liters. As a result, typical applications of the laser ignition device 100 according to the invention, namely the use in stationary large-scale gas engines, can be covered.

Such large gas engines usually have cylinder volumes between about 2 liters and about 4 liters. The limitation of the volume of the cooling liquid 128 to about 0.1 liter or less than about 0.05 liter is particularly advantageous because in an accidental leakage of the cooling liquid 128 from the cooling circuit 122 of the laser ignition device 100 in a cylinder 132 of the large gas engine an impermissibly high compression pressure in the top dead center of the cylinder 132 is hardly to be feared.

In order to effect a circulation of the cooling liquid 128 in the cooling circuit 122 and thus a heat transfer from the first heat exchanger WT1 to the second, preferably remote heat exchanger WT2, the cooling circuit 122 further comprises a pump P ("conveying means"). A first and a second fluid line 122a and 122b of the cooling circuit 122 are connected to an end region of the laser spark plug 110 remote from the combustion chamber or to the heat exchanger WT1. The fluid lines 122a and 122b are preferably flexible and, in FIG. 1, lead upward out of the cylinder shaft 104.

The heat sink 126 in the present case is a metal housing of an air feed (intake manifold) of the internal combustion engine 102. The intake manifold is flowed through by the ambient air required for operating the internal combustion engine 102 and thus generally has a temperature of approximately + 20 ° C. to + 35 ° C.

In an alternative embodiment of the laser ignition device 100, which is not shown in FIG. 1, the heat sink 126 is a continuous metal tube arranged on a cylinder bank of the internal combustion engine 102 or a stainless steel corrugated hose. This element is derived from the cooling water of a

Charge air cooler or mixture cooler flows through, which generally has a temperature below + 45 ° C.

In a further alternative embodiment of the laser ignition device 100, the heat sink 126 is a housing of the internal combustion engine 102, which as As a result of the engine cooling a temperature of generally not more than + 85 ° C has. In yet another embodiment, the heat sink 126 is a tube through which the ambient air flows (approximately + 20 ° C. to + 35 ° C.), the tube preferably having integrated cooling fins.

In yet another embodiment, the heat sink 126 is a

Metal tube or a stainless steel corrugated hose, which is flowed through with cooling water from a primary cooler. This primary cooler is designed specifically for cooling the laser ignition device 100 and is for example a so-called "chiller" with a constant temperature setpoint. Alternatively, the primary cooler may also be an air-water cooler, the temperature depending on the ambient temperature. This latter embodiment of the heat sink 126 can be comparatively expensive and also cause comparatively high operating costs.

The cooling device 120, together with the fluid lines 122a and 122b, according to a particularly preferred embodiment, a closed cooling circuit 122. This means that no fluid connections between the components of the cooling circuit 122 (fluid line (s) 122a or 122b, pump P, heat exchanger WT1 and WT2 ) are provided, which are to be opened or closed for the installation or removal of the laser ignition device 100.

The fluid lines 122a and 122b are filled with the cooling liquid 128 and are integrated in a preferred embodiment together with the pump P ("mini-pump") in a wire harness 130 ("terminal strand" of the laser spark plug 1 10). The wiring harness 130 is shown in the drawing by a dashed frame. The fluid lines 122a and 122b presently have an inner diameter of at most about 4 mm (millimeters) and a total length of at most about 2 m (meters). This amounts to a volume of

Coolant 128 in the fluid lines 122a and 122b, in the pump P and in the heat exchangers WT1 and WT2 present in total only about 0.05 liters (50 ml, milliliters). In one embodiment of the laser ignition device 100, thermal insulation is arranged on surfaces of the fluid lines 122a and 122b, thereby preventing radiation of heat radiated by the internal combustion engine 102. On the pump or near the pump, a surge tank can be integrated, the pressure and

Compensates for volume fluctuations of the coolant. During operation of the internal combustion engine 102 or the laser ignition device 100, a plasma 136 is generated periodically by means of the laser spark plug 110, whereby a gas-air mixture present in the combustion chamber 106 and compressed by the piston 134 is ignited. The pump P preferably delivers the cooling liquid 128 continuously at a flow rate of approximately 5 ml / min (milliliters per minute) through the cooling circuit 122

Semiconductor laser 1 14 generated and transmitted to the heat exchanger WT1 heat conveyed by means of the circulating in the cooling circuit 122 cooling liquid 128 to the heat exchanger WT2. The heat exchanger WT2 transmits the

Heat to the heat sink 126. In this way, an operating temperature of the semiconductor laser 1 14 and the laser spark plug 1 10 are kept within acceptable limits. If necessary, the flow rate in the

Cooling circuit 122 also increased by means of appropriate dimensioning of the pump P and increased, for example, to 2000 ml / min.

FIG. 2 shows an alternative embodiment of the laser ignition device 100. In contrast to FIG. 1, the laser ignition device 100 of FIG. 2 additionally comprises a Peltier element 138, which is arranged between the semiconductor laser 14 and the heat exchanger WT1. Alternatively or additionally, a

Peltier element 138 'between the heat exchanger WT2 and the heat sink 126 may be arranged. The Peltier element 138 'is shown in dashed lines in the drawing. The Peltier element 138 or 138 'can in a first embodiment by

Clamps and be disposed between the semiconductor laser 1 14 and the heat exchanger WT1 or between the heat exchanger WT2 and the heat sink 126 using Wärmeleitpaste, Wärmeleitkleber or Wärmeleitfolie. In a second embodiment, the Peltier element 138 or 138 'may have a metallized surface on both sides and thus between the respective

Connection partners may be arranged by means of soldering. In operation, the

Peltier element 138 or 138 'preferably regulated (Peltier control). For this purpose, the cold side of the Peltier element 138 or 138 'is thermally coupled to a temperature sensor. By using the Peltier element 138 or 138 ', the heat transfer from the laser spark plug 110 to the heat sink 126 is improved, thus increasing the overall efficiency of the cooling device 120. In a further preferred embodiment, the cooling device 120 is designed such that a flow rate of coolant 128 of less than or equal to about 2000 ml / min, preferably less than or equal to about 50 ml / min, is sufficient to sufficiently cool the laser spark plug during operation.

In addition to avoiding a water hammer by the special design of the system according to the invention, the installation of the internal combustion engine is very simple, because the components 120, 122a, 122b, P are advantageously integrated into the wiring harness 130. Preferably, each cylinder of the

Internal combustion engine 102, a laser ignition device 100 according to the invention are assigned. By providing a "cylinder-individual" cooling circuit, that is to say a respective cooling circuit 122 per cylinder, with its own conveying means P, it is advantageously ensured that, even in the event of failure of the

Cooling circuit 122 in a cylinder, the other cylinders or their

Laser spark plugs remain operational.

Claims

claims

1 . Laser ignition device (100) for an internal combustion engine (102), wherein the laser ignition device (100) at least one laser spark plug (1 10) and a cooling device (120) for tempering, in particular cooling, the

Laser spark plug (1 10), characterized in that the

Cooling device (120) containing a cooling liquid (128)

Cooling circuit (122), which thermally with at least one

Component of the laser spark plug (1 10) is connectable, wherein a volume of the coolant contained in the cooling circuit (122) (128) is less than or equal to about fifty percent of a compression volume of a cylinder (132) of the internal combustion engine (102), preferably less than or equal to about ten percent of a compression volume of the cylinder (132) of the internal combustion engine (102).

2. laser ignition device (100) for an internal combustion engine (102), wherein the laser ignition device (100) at least one laser spark plug (1 10) and a cooling device (120) for tempering, in particular cooling, the

Laser spark plug (1 10), characterized in that the

Cooling device (120) containing a cooling liquid (128)

Cooling circuit (122), which thermally with at least one

Component of the laser spark plug (1 10) is connectable, wherein a volume of the cooling liquid contained in the cooling circuit (122) (128) is less than or equal to about 0.1 liter, preferably less than or equal to about 0.05 liters.

3. laser ignition device (100) according to any one of the preceding claims, wherein the cooling circuit (122) comprises a first heat exchanger (WT1), which is thermally connectable with at least one component of

Laser spark plug (1 10), wherein the cooling circuit (122) has a second

Heat exchanger (WT2), which is thermally connectable to a heat sink (126), and wherein conveying means (P) are provided to cause a circulation of the cooling liquid (128) in the cooling circuit (122).

4. laser ignition device (100) according to any one of the preceding claims, wherein the cooling circuit (122) at least one fluid line (122a, 122b) for guiding the cooling liquid (128), wherein the fluid line (122a, 122b) is preferably formed flexible.

5. laser ignition device (100) according to claim 4, wherein at least one

Fluid line (122a, 122b) has an inner diameter of at most about 4 millimeters, preferably at most about 3 millimeters.

6. laser ignition device (100) according to claim 4 or 5, wherein an aggregated total length of all fluid lines (122a, 122b) of the cooling circuit (122) is at most about 4 meters, preferably at most about 2 meters.

The laser ignition device (100) of any of the preceding claims, wherein the cooling circuit (122) has a flow rate of cooling fluid (128) per time of at least about 2 milliliters per minute, preferably at least about 50 milliliters per minute.

8. laser ignition device (100) according to any one of the preceding claims, wherein at least one fluid line (122a, 122b) for guiding the cooling liquid (128) and / or conveying means (P) for the cooling liquid (128) at least partially into a wire harness (130) of Laser spark plug (1 10) are integrated.

9. laser ignition device (100) according to any one of the preceding claims, wherein at least one fluid line (122a, 122b) for guiding the cooling liquid (128) and / or conveying means (P) for the cooling liquid (128) are at least partially thermally insulated from an environment.

10. laser ignition device (100) according to any one of the preceding claims, wherein the cooling circuit (122) is formed closed.

1 1. Internal combustion engine (102) with at least one laser ignition device (100) according to one of the preceding claims.

12. A method for operating a laser ignition device (100) for a

Internal combustion engine (102), wherein the laser ignition device (100)

at least one laser spark plug (1 10) and a cooling device (120) for tempering, in particular cooling, the laser spark plug (1 10), characterized in that the cooling device (120) has a

Cooling circuit (122) containing cooling liquid (128), which is thermally connectable to at least one component of the laser spark plug (1 10), and that a volume of cooling liquid (128) contained in the cooling circuit (122) is less than or equal to about fifty percent of a compression volume of a cylinder (132) of the internal combustion engine (102) is, preferably less than or equal to about ten percent of a compression volume of the cylinder (132)

Internal combustion engine (102).

13. A method for operating a laser ignition device (100) for a

Internal combustion engine (102), wherein the laser ignition device (100) at least one laser spark plug (1 10) and a cooling device (120) for tempering, in particular cooling, the laser spark plug (1 10), characterized in that the cooling device (120) has a

Cooling circuit (122) containing cooling liquid (128), which is thermally connectable to at least one component of the laser spark plug (1 10), and that a volume of cooling liquid (128) contained in the cooling circuit (122) is less than or equal to about 0.1 liter, preferably less than or equal to about 0.05 liter.