WO2009097635A2

WO2009097635A2 - Laser ignition device

Info

Publication number: WO2009097635A2
Application number: PCT/AT2009/000017
Authority: WO
Inventors: Friedrich Gruber
Original assignee: Ge Jenbacher Gmbh & Co Ohg
Priority date: 2008-02-07
Filing date: 2009-01-20
Publication date: 2009-08-13
Also published as: AT506343A1; WO2009097635A3; EP2238341A2; AT506343B1

Abstract

Disclosed is a laser ignition device comprising a base (1) and a combustion chamber window (2) for injecting laser light into the combustion chamber (4) of an internal combustion engine. The combustion chamber window (2) rests against a receiving collar (5) of the base (1) in the area of the surface (2a) from which the laser light emerges. By applying pressure, a fastening element (6) fixes the combustion chamber window (2) to the base (1) in the area of the surface (2b) on which the laser light is incident. Said fastening element (6) is designed such that the pressure applied to the combustion chamber window (2) by the fastening element (6) remains substantially constant or is increased when the temperature of the base (1) and/or the combustion chamber window (2) rises. Also disclosed is an internal combustion engine comprising such a laser ignition device.

Description

laser ignition device

The invention relates to a laser ignition device, comprising a base body and a combustion chamber window for coupling laser light into the combustion chamber of an internal combustion engine, wherein the combustion chamber window in the region of the laser light exit surface rests against a receiving collar of the base body and a fastener the combustion chamber window in the region of the laser light entry surface pressurized fixed to the body , Furthermore, the invention relates to an internal combustion engine with such a laser ignition device.

The laser ignition is an ignition concept for Otto engine operated internal combustion engines, the principle of which is based on that an intense laser pulse is coupled into the combustion chamber of the internal combustion engine and focused there on a focal point. At this focal point, the intensity of the radiation exceeds a threshold sufficient to ionize the fuel-air mixture and subsequently to ignite a plasma arc. This plasma bomb is able to ignite a fuel-air mixture in a manner similar to the spark of a conventional electric spark ignition.

For the application in internal combustion engines currently the most intensively pursued laser ignition concepts are designed in such a way that the laser pulse is generated by a solid-state laser, which is integrated together with the input and output optics in a housing attached to the cylinder head of the internal combustion engine. This unit is referred to by analogy with conventional electric spark ignition, for example, as a laser spark plug. The ignition laser is optically e.g. pumped by a semiconductor laser which may be connected to the laser spark plug by an optical fiber. Between ignition laser and combustion chamber of the internal combustion engine, the coupling optics is arranged. This consists of a suitable lens system for focusing the laser light and a so-called combustion chamber window, which represents the last optical element before the beam entrance of the laser light into the combustion chamber.

The advantage of laser ignition over conventional electric spark ignition systems is that the spark is free to the depth of the Brennraums can be placed, where optimal flaming conditions prevail. This advantage requires that laser ignition systems, especially in high-performance systems such as large engines, find use in which particularly high ignition temperatures and pressures occur. Therefore, one of the main problems with laser ignition devices is the sealing of the combustion chamber window and the ignition laser to the combustion chamber. The applicant's EP 1 820 948 A1 describes a laser ignition device with base body and combustion chamber window, the combustion chamber window abutting a receiving collar of the base body in the area of the laser light exit surface and a fastening element the combustion chamber window laterally pressurized. However, endurance tests have shown that such a system can be leaking in the event of severe temperature changes.

Object of the present invention is therefore to provide a laser ignition device of the type mentioned, in which the described problems are reduced. In particular, a laser ignition device is to be provided which remains tight in all operating states and at elevated temperatures.

This object is achieved by a laser ignition device according to claim 1.

With a laser ignition device comprising a base body and a combustion chamber window for coupling laser light into the combustion chamber of an internal combustion engine, wherein the combustion chamber window in the region of the laser light exit surface rests against a receiving collar of the base body and a fastener the combustion chamber window in the region of the laser light entrance surface pressurized fixed on the base body, wherein the fastener is designed such that the pressure exerted by the fastener on the combustion chamber window pressure remains substantially constant or increased with temperature increase of the base body and / or the combustion chamber window, it is possible the different relative changes in length between fastener, combustion chamber window and body at temperature change of cold to minimize operating temperature. An essential finding in the context of the invention is therefore that the individual elements of the laser ignition device have a different longitudinal extent, which leads to gap formations can come through which gas from the combustion chamber in the laser ignition device can penetrate.

In a first particularly preferred embodiment, it is provided that the fastening element has a higher thermal expansion coefficient than the main body and / or the combustion chamber window. In this case, the pressure on the combustion chamber window can be increased with a thermal expansion, that an additional pressure is exerted on the combustion chamber window, which keeps the combustion chamber window tight, by increasing the length of the fastening element. The sum of thermal expansion of the fastening element and the combustion chamber window should correspond at least to the thermal expansion over that length of the base body between which the combustion chamber window is pressurized.

In an alternative embodiment, it may be provided that the fastening element acts on the combustion chamber window by means of spring action with pressure. By means of spring action, the force or the pressure which is exerted on the combustion chamber window can be kept substantially constant even when the temperature increases.

It can be provided that the fastening element has a plate spring, since this represents a particularly simple way of exerting spring force.

The above options, namely higher coefficient of thermal expansion and spring action of the fastener, can of course be combined, which further improves the installation safety.

It can be provided that the fastening element is designed as a clamping sleeve. Further favorable embodiments provide that the fastening element is formed substantially sleeve-shaped or cylinder jacket-shaped. In a structurally very simple embodiment can further be provided that the fastening element is fixed on the side facing away from the combustion chamber window with the base body. In this case, it has proved to be advantageous if the Fastener attached to the body insoluble, preferably welded, since so the degree of attachment is particularly high.

In addition, it can be provided that at least one sealing element is arranged between the fastening element and the combustion chamber window and that at least one sealing element is arranged between the combustion chamber window and receiving collar, since an additional sealing effect is achieved in this way.

Furthermore, the fastening element may be designed in several parts, so that at least one further intermediate element would be provided which the bias of the

Fastening element favors. In this case, could be achieved with the intermediate element, a prefixing of Brennraumfesters on the body and the

Main fixation (for example, a gas-tight weld) then attach simplified. The intermediate element could for example be screwed or clamped.

In addition, the fastening element recesses, for example in the form of at least one groove, which serve to relieve the pressure.

In the simplest case, the laser ignition device is a laser spark plug.

The invention also relates to an internal combustion engine having a laser ignition device of the aforementioned type.

Further advantages and details of the invention will become apparent from the following description of figures and figures. It shows

1 shows schematically a laser ignition device, installed in a simplified illustrated internal combustion engine,

2 shows a first embodiment of a laser ignition device in cross section, FIG. 3 shows a second embodiment of a laser ignition device in cross section,

4 shows a third embodiment of a laser ignition device in cross section,

Fig. 5 shows a fourth embodiment of a laser ignition device in cross section and

Fig. 6 is a fastener according to FIG. 5 in oblique view. In Fig. 1 is roughly simplified and schematically an internal combustion engine with a cylinder 14 is shown, which has a piston 13 which is moved up and down in the cylinder 14, and which together form the combustion chamber 15.

The actual laser ignition device is shown as a simplified laser spark plug, wherein in FIG. 1, the base body 1 can be seen, in which the actual ignition laser is arranged. Since ignition lasers are known per se, will not be discussed here in detail. The ignition laser is supplied with pumping light via the light guide 11 from a pump light source 10 (e.g., a pump laser). The amplification then takes place in the ignition laser until laser light with sufficient intensity for ignition in the combustion chamber 15 can be coupled in the combustion chamber 15 via a coupling optics (not shown). The laser light is focused on the focal point 3, in which the ignition takes place. Schematically, an inlet valve 17 is further shown, via which a fuel-air mixture can be introduced into the combustion chamber 15. After combustion, the exhaust gas is discharged via an outlet valve 18.

In Fig. 2, the front portion of the laser ignition device according to the invention is shown in cross section. For reasons of clarity, the ignition laser and the coupling optics are not shown, since both can be carried out according to the prior art. The laser light is focused in the operating state of the laser ignition device from the upper part of the figure along the optical axis A via the combustion chamber window 2 to the focal point 3. The laser light is thus guided along the axis A from the ignition laser to the laser light entrance surface 2a of the combustion chamber window 2 through the combustion chamber window 2 and coupled to the laser light exit surface 2a of the combustion chamber window 2 from the laser ignition and subsequently led to the focal point 3, in which it comes to plasma ignition. The optical window 2 is transparent to laser light and has a thickness d. The combustion chamber window 2 is located in the region of the laser light exit surface 2a on the receiving collar 5 of the main body 1 of the laser ignition device. The fastening element 6 fastens the combustion chamber window 2 to the main body 1 by pressurizing the combustion chamber window 2 along the axis A in the region of the laser light entry surface 2 b. The combustion chamber window is thus clamped in some areas between the fastening element 6 and receiving collar 5 on the opposite side surfaces. In the simplest case, as shown in the left half of Fig. 2, expresses The fastener 6 has the combustion chamber window 2 to the receiving collar 5 of the base body 1. The fastener 6 has a higher coefficient of thermal expansion α as the body 1 and combustion chamber 2. The length of the fastener 6 is designated by ld, the length of fastener plus the thickness of the combustion chamber window denoted by I. The fastening element 6 is designed as a clamping sleeve and has the shape of a cylinder jacket. In the area of the side facing away from the combustion chamber window 2 6b of the fastener 6 this is attached to the base body. This is indicated by a weld 7. Conceivable but would also fasteners on additional screw etc.

In the right half of Fig. 2, a variant is indicated in which between the combustion chamber window 2 at the light inlet surface 2b, a sealing element 8 is applied, which is acted upon by the fastening element 6 in addition to pressure to improved sealing on the one hand and a preservation of the combustion chamber window 2 on the other achieve.

An example calculation is intended to briefly explain the effect of the invention with reference to the embodiment according to FIG. 2 (left-hand version without additional sealing elements 8) in the case of a fastening element 6 in the form of a cylinder jacket with a corresponding expansion length I from the side facing away from the combustion chamber window 2 with the base body 1 is clamped, and presses the combustion chamber window 2 to the receiving collar 5 of the base body 1. The connection of the fastening element 6 to the main body 1 can be done for example by a screw, wherein a fastening nut, which is tightened, for example, with a defined torque or with a defined angle of rotation, which braces the fastener 6 against the combustion chamber window 2. Another possibility is a welded connection, wherein the welding of fastening element 6 and basic body 1 takes place in a defined prestressed state (for example with the aid of a pretensioning device). In addition to ensuring a non-positive support of the combustion chamber window 2 on the abutment collar 5, the fastening element 6 can additionally also have a (sufficient) sealing function with respect to the combustion gases of the internal combustion engine under all possible conditions of use. However, this seal can also be done by separate Sealing elements 8, for example, between the combustion chamber window and support collar of the body done (eg by soft iron or brass sealing rings).

The material of the fastening element 6 is additionally selected so that the thermal expansion coefficient α (namely, the so-called coefficient of linear expansion) is higher than the thermal expansion coefficient of the material of the main body 1 of the laser ignition device. The design of the combustion chamber window fastening in the laser ignition device with the aid of the fastening element 6 takes place in such a way that the sum of the length expansion of the combustion chamber window 2 and fastener 6 is approximately equal to or slightly greater than the extension of the base body 1 over the length of the clamping :

Since the thermal expansion of the combustion chamber window 2 is substantially lower than that of metals, this condition can be fulfilled by selecting a material for the fastening element 6 whose

Thermal expansion coefficient is significantly higher than that of the main body. 1

For example, the material can be 1.4562 having a linear thermal expansion coefficient of 13.5 ⁴ IO ^{^"6/0} K for the main body. 1, for example, the material can then be chosen 1.4301 as the material for the fastening element 2 having a linear thermal expansion coefficient of 16.5 MO ^" ^6/0 K can be selected. The thermal expansion coefficient of the combustion chamber window 2 is about 0.5 * 10 ^"6 / ° K

This results in the following calculation:

I * 13.5 * 10 ⁶ = d * 0.5 * 10 ^"6 + (ld) * 16.5 ^{'lO" 6} or

I ^* (13.5-16.5) = d * (0.5-16.5) or I = d * 5.3 where: I = total clamping length; d = thickness of the combustion chamber window

With a thickness d of the combustion chamber window of 7 mm, this results in a minimum length of the fastening element 6 of 37 mm In principle, with sufficient space, the length of the fastening element 6 can be selected so that the temperature-induced change in length of the sum of the relevant construction elements is less than the elastic expansion or compression reserve of the clamping device. In order to increase the elasticity of this clamping device in limited space, according to the invention additionally or alternatively, an axially arched fastener is proposed (see also Fig. 3).

Fig. 3 shows a further embodiment of the laser ignition device analogous to FIG. 2, so that the same components will not be discussed in detail and reference is made to FIG. 2. In contrast to FIG. 2, the fastening element 6 is designed so that there is a spring effect on the combustion chamber window 2, on the

Laser light entry surface 2a pressurized. The fastening element 6 is as

Cup spring formed and attached to the combustion chamber window 2 side facing away 6b with the base body 1 via the weld 7. Again, a variant without additional sealing element is shown on the left side, while on the right side a variant with sealing element 8 is indicated.

Due to the warping, the fastening element 6 springs during the clamping process, whereby a high elastic expansion range is achieved, which can accommodate the different changes in length of the components within the elastic stretch region, without the contact pressure of the combustion chamber window 2 on support collar 5 of the body drops below a permissible level. Again, the fastening element 6, the clamping sleeve in addition to the bias and the sealing function relative to the combustion chamber pressure and the combustion gases have. However, a separate component (for example in the form of a sealing ring with corresponding properties and of a suitable material) may also be provided for the sealing function here.

In Fig. 4, a further embodiment is shown, which corresponds to the embodiment of FIG. 2 of the essential components. The essential difference is that the fastening element 6 has an additional recess 10 in the form of a groove, which serves for the pressure relief. From the combustion chamber 4 originating exhaust gas, which is under high pressure, via the sealing elements. 8 between base body 1, combustion chamber window 2 and possibly fastener 6 penetrate. The recess 10 favors that such exhaust gas can flow out of the laser ignition device and via the additional pressure equalization openings 11. The recesses 10 are arranged between the base body and fastener 6 and are in communication with the pressure equalization opening 11. (The embodiment shows additional sealing elements (9 ) between combustion chamber window 2 and receiving collar 5).

The embodiment of FIG. 5 corresponds substantially to the embodiment of FIG. 4, wherein the fastening element 6 is formed in two parts and has an intermediate element 12, the first prefixed by means of the lower part 6 of the fastener, the combustion chamber window 2 under bias. Subsequently, welding takes place here (for example by means of laser welding) to form the gas-tight laser seam 7.

In the exemplary embodiments of both FIG. 4 and FIG. 5, the pressure compensation opening 11 naturally has to be arranged in an area in which it is not exposed to combustion chamber pressure. This means that the base body must be installed in such a way in the cylinder head of a cylinder of an internal combustion engine, that the pressure equalization opening 11 is sealed to the combustion chamber. In practice, this can be achieved, for example, by the base body 1 protruding into the combustion chamber only up to the lower edge or only slightly above the lower edge of the base body 1 and laterally screwed into a nut thread on the cylinder head, for example via a screw thread with optionally additional sealing elements the pressure compensation opening 11 is arranged above the thread and any sealing elements.

Fig. 6 shows the fastener 6 of the embodiment of FIG. 4 and the lower part of the fastener 6 of FIG. 5 with a direct view of the recess 10, which is clearly seen formed as an elongated groove.

Claims

claims:

1. Laser ignition device, comprising a base body (1) and a combustion chamber window (2) for coupling laser light in the combustion chamber (4) of an internal combustion engine, wherein the combustion chamber window (2) in the region of

Laser light exit surface (2a) against a receiving collar (5) of the base body (1) and a fastener (6) the combustion chamber window (2) in the region of the laser light entry surface (2b) pressurized on the base body (1) fixed, characterized in that the fastening element (6) is designed such that the of

Fastening element (6) to the combustion chamber window (2) applied pressure at a temperature increase of the base body (1) and / or the combustion chamber window (2) remains substantially constant or increased.

2. laser ignition device according to claim 1, characterized in that the

Fixing element (6) has a higher coefficient of thermal expansion than the base body (1) and / or the combustion chamber window (2).

3. laser ignition device according to claim 1 or claim 2, characterized in that the fastening element (6) is designed as a clamping sleeve.

4. laser ignition device according to one of claims 1 to 6, characterized in that the fastening element (6) by means of spring action, the combustion chamber window (2) pressurized.

5. laser ignition device according to claim 4, characterized in that the fastening element (6) has a plate spring.

6. laser ignition device according to one of claims 1 to 5, characterized in that the fastening element (6) on the

Combustion chamber window (2) facing away from (6b) is attached to the base body (1).

7. laser ignition device according to claim 6, characterized in that the fastening element (6) permanently attached to the body, preferably welded.

8. laser ignition device according to one of claims 1 to 7, characterized in that the fastening element is formed substantially sleeve-shaped or cylinder jacket-shaped.

9. laser ignition device according to one of claims 1 to 8, characterized in that between the fastening element (6) and

Combustion chamber window (2) at least one sealing element (8) is arranged.

10. laser ignition device according to one of claims 1 to 9, characterized in that between the combustion chamber window (2) and receiving collar at least one sealing element is arranged.

11. Internal combustion engine, comprising a laser ignition device according to one of claims 1 to 10.