Laser igniter with focal point modulation and method for operating such a laser igniter

Abstract

The invention relates to a laser igniter for a combustion chamber, wherein the laser igniter has at least one optical component and is designed to focus a laser beam onto a focal point, wherein the at least one optical component is movably arranged in such a way that the focal point of the laser igniter can be changed in order to thereby increase the reliability of an ignition. The invention further relates to the use of the laser igniter for igniting a rocket engine, an internal combustion engine or an aircraft gas turbine; and to a method for operating a laser igniter having at least one optical component and for focusing a laser beam onto a focal point, comprising moving the at least one optical component in order to change the focal point.

Description

[0001] Laser igniter with focus point modulation and method for operating such a laser igniter

[0002] Technical field

[0003] The invention lies in the field of laser igniters.

[0004] background

[0005] Prior art laser igniters have a single, fixed focal point.

[0006] Summary of the invention

[0007] The invention is based on the problem of increasing the reliability of an ignition effected by means of a laser igniter.

[0008] The invention provides one of the following aspects to solve this problem:

[0009] [1]

[0010] Laser igniter for a combustion chamber, wherein the laser igniter has at least one optical component and is configured to focus a laser beam onto a focal point, wherein the at least one optical component is arranged to be movable in such a way that the focal point of the laser igniter can be changed.

[0011] The at least one optical component can be a mirror and / or a lens. The optical component can be rigid or elastically deformable, e.g., a mirror or a plastic lens. The optical component can be a transmissive component, e.g., a lens, a glass plate, etc., or a deflecting component, e.g., a mirror.

[0012] To change the focal point, the laser igniter can have an actuator arrangement comprising one or more actuators. Thus, a (different) actuator arrangement can be provided for each optical component, capable of effecting a translational movement of the optical component along one, two, and / or three mutually perpendicular axes, and / or capable of effecting a rotational movement of the optical component about one, two, and / or three mutually perpendicular axes, solely to effect or at least contribute to changing the focal point. The optical component can also be elastically deformable. In the case of an elastically deformable optical component, the actuator arrangement can additionally or alternatively be configured to elastically deform the elastically deformable optical component, solely to effect or at least contribute to changing the focal point.The actuator arrangement can consist of one actuator configured to perform the required movements of the respective optical component in order to effect a specific change in the focal point, or of several actuators configured to perform the required movement(s) of the respective optical component(s) in order to effect a specific change in the focal point.

[0013] Actuators, also known as drive units, can be piezoelectric drives, electromagnetic drives, or ultrasonic motors. These are suitable for small sizes and can be driven at high frequencies. Commercially available galvanometer scanners (galvo scanners) can also be used.

[0014] The laser igniter can be integrated with the combustion chamber in a laser igniter system. The laser igniter can include a control unit for controlling actuators. Alternatively, the control unit can be integrated with the laser igniter in a laser igniter system.

[0015] [2]

[0016] Laser igniter according to aspect [1], wherein the at least one optical component is configured to change the focal point several times per second, and wherein the focal point is repeated not once, once, twice or more frequently per second.

[0017] This means there can be no time interval between repetitions, or at least the focus can shift to a different focus point before returning to the previous one. If the focus point repeats twice or more per second, the same time interval can occur between repetitions.

[0018] [3]

[0019] Laser igniter according to aspect [2], wherein the at least one optical component is configured to repeat one focal point and another focal point with the same frequency per second or with different frequencies per second.

[0020] The frequency of repetition of one focus point can be higher compared to the frequency of repetition of another focus point if it has been determined that the probability of ignition occurring at one focus point is higher than at the other focus point.

[0021] [4]

[0022] Laser igniter according to one of the aspects [1] to [3], wherein the at least one optical component is arranged such that successively focused focal points have a distance of less than 1 mm, 1 mm or more than 1 mm.

[0023] The distance can also correspond to a distance between the points furthest apart in a combustion chamber, so that the focal point can be changed directly from one point in the combustion chamber to any other point in the combustion chamber.

[0024] [5]

[0025] Laser igniter according to one of the aspects [1] to [4], wherein the at least one optical component is arranged such that the change of the focal point within a focal point field with different focal points is limited.

[0026] This can be achieved by limiting the movement of at least one optical component through design constraints. This can be accomplished by using actuators in extreme positions and / or by a control unit that controls the actuators.

[0027] [6]

[0028] Laser igniter according to aspect [5], wherein the focus points focused in the focus point field follow a pattern.

[0029] For example, the pattern can consist of 50 or more focus points. Naturally, the pattern can be stored in a control unit (not shown) with 50 or more focus points, but the focusing during ignition can be limited to a selection of these focus points, with focus points within this selection potentially being refocused multiple times per second. The pattern can be determined spatially and / or temporally from a fuel distribution in a mixing zone of the combustion chamber. The pattern can be understood as the spatial and temporal sequence in which the focus point changes. This can be stored in a control unit for the actuators. The pattern can repeat multiple times within an ignition cycle. It can repeat zero, one, two, or more frequently per second.

[0030] The pattern can extend exclusively along a line or exclusively in a plane. The plane can extend parallel to a free end of an injection element in the combustion chamber, for example, in a radial direction to the injection element. The plane can be parallel to the direction of propagation of the laser beam immediately before it focuses onto a focal point. The pattern can be located entirely within, partially within, or entirely outside a projection of an injection element. A projection of an injection element refers to the space that would be occupied if the injection element were to extend further through the combustion chamber in its axial direction to the corresponding end of the combustion chamber. Furthermore, the pattern can have a two-dimensional shape (e.g., the shape of a rectangle) or a three-dimensional shape (e.g., the shape of a cuboid).The pattern can thus exhibit a wave-like shape in its extent. The distance between immediately adjacent focal points can always be the same. The pattern can have several parallel rows of focal points, with each row comprising several focal points along a line. The distance between immediately adjacent rows of focal points and the distance between immediately adjacent focal points within a row can be the same or different. The position of the focal points in one row can be offset from the position of the focal points in an immediately adjacent row, meaning they are not located on a common line extending perpendicularly through the two immediately adjacent rows. This offset can be such that focal points in one row are equidistant from two immediately adjacent focal points in an immediately adjacent row.The number of focus points of the pattern can be in a range of 2 to 50, for example in a range of 2 to 16, 4 to 16, 8 to 16, or 12 to 16, or exactly 16.

[0031] [7]

[0032] Laser igniter according to Aspekt [6], wherein the pattern has a maximum extent of 2 mm and a minimum extent of 0.1 mm. The maximum extent of the pattern can be 1.9 mm, 1.8 mm, 1.7 mm, 1.6 mm, 1.5 mm, 1.4 mm, 1.3 mm, 1.2 mm or 1.1 mm. The minimum extent of the pattern can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm or 1.0 mm.

[0033] [8]

[0034] Laser igniter according to aspect [6] or [7], wherein the pattern has one or more parallel lines, with several spaced-apart focal points on each line.

[0035] [9]

[0036] Use of a laser igniter according to one of the aspects [1] to [8] for the ignition of a rocket engine, an internal combustion engine or an aircraft gas turbine.

[0037]

[0010]

[0038] Method for operating a laser igniter with at least one optical component and for focusing a laser beam onto a focal point, comprising moving the at least one optical component to change the focal point.

[0039] The features described in this disclosure can be reformulated as steps to further develop the process accordingly.

[0040] Description of the drawings

[0041] Fig. 1 shows a laser igniter designed to change the focal point of a laser beam.

[0042] Fig. 2 shows in the upper area a perspective view of a rocket injection head with a rocket combustion chamber, within which the focal point from Fig. 1 can be changed, and in the lower area an enlarged view of a section in which the focal point from Fig. 1 is located.

[0043] Detailed description Fig. 1 shows a laser igniter 1 which is designed to change a focal point 3 of a laser beam 5.

[0044] In the example shown, the laser igniter 1 comprises a mirror 7, which deflects the beam path of the laser beam 5 and is movable by both a translational mirror actuator 9 and a rotational mirror actuator 11, and a lens 15, movable by a translational and / or rotational lens actuator 13, through which the laser beam 5 is focused onto the focal point 3. The movable mirror 7 and the movable lens 15 have the function of allowing the focal point 3 of the laser beam 5 to be variably determined by their adjustable position and / or orientation.

[0045] The focal point 3 is changed several times per second by movements of actuators 9, 11, and 13. This rapid movement of the focal point 3 is necessary because the laser igniter 1 is typically intended to ignite the combustion chamber, such as a rocket combustion chamber, within one second. Since the laser igniter 1 typically emits 50 pulses or more per second, the modulation / change of the focal point 3 will also occur 50 times or more per second. Each pulse generates a plasma spot sufficient for ignition if it hits a suitable location in the mixing zone. This increases the reliability of the ignition by covering a larger ignition area within the allotted time.

[0046] The selection of focus point 3 can be modulated in time and space by means of a control unit that controls actuators 9, 11, and 13. This creates a larger ignition range.

[0047] Temporal modulation of focus point 3

[0048] The same focus point 3 can be repeated zero, once, twice, or more often per second. If focus point 3 is repeated once, twice, or more often per second, there can be no time interval between repetitions, or at least one refocus point 3 can be selected before returning to the previous focus point 3. If focus point 3 is repeated two or more times per second, the same time interval can be selected between repetitions. Focus point 3 can be selected with one frequency per second, and focus point 3 can be selected with a different frequency per second. The frequency of repetition of one focus point 3 can be higher than the frequency of repetition of another focus point 3 if it has been determined that the probability of ignition occurring at one focus point 3 is higher than at the other.

[0049] Local modulation of focus point 3

[0050] Focus points 3 that are focused in immediate succession can be spaced less than 1 mm, 1 mm, or more than 1 mm apart. The space can also correspond to the distance between the most distant points in a combustion chamber described below, so that the focus point 3 can be moved directly from one point in the combustion chamber to any other point in the combustion chamber.

[0051] In addition to or instead of the optical component configured as mirror 3 and lens 15, one or more optical components may be provided. An optical component may be the described mirror 3 and / or lens 15. The optical component may be rigid or elastically deformable, e.g., a mirror or a plastic lens. An optical component may be a transmissive optical component, e.g., a lens, a glass plate, etc., or a deflecting optical component, e.g., a mirror.

[0052] The actuators 9, 11, and 13 described are only examples. For each optical component, a (different) actuator arrangement can be provided that can effect a translational movement of the optical component along one, two, and / or three mutually perpendicular axes, and / or that can effect a rotational movement of the optical component about one, two, and / or three mutually perpendicular axes, solely to effect or at least contribute to changing the focal point 3. In the case of an elastically deformable optical component, the actuator arrangement can additionally or alternatively be configured to elastically deform the elastically deformable optical component, solely to effect or at least contribute to changing the focal point 3.The actuator arrangement can consist of one actuator configured to perform the required movements of the respective optical component in order to effect a specific change in focus point 3, or of several actuators configured to perform the required movement(s) of the respective optical component(s) in order to effect a specific change in focus point 3.

[0053] The actuators, also known as drive units, can be piezoelectric drives, electromagnetic drives, or ultrasonic motors. These are suitable for small sizes and can be driven at high frequencies. Commercially available galvanometer scanners (galvo scanners) can also be used.

[0054] Fig. 2 shows in the upper area a perspective view of a rocket injection head 21 with a combustion chamber 23, which here is a rocket combustion chamber, within which the focal point 3 from Fig. 1 can be changed, and in the lower area an enlarged view of a section in which the focal point 3 from Fig. 1 is located.

[0055] The rocket injector head 21 comprises the combustion chamber 23 and numerous injection elements 25 arranged therein. Below the injection elements 25, propellant and oxidizer mix in a known manner in a mixing zone, in order to be subsequently ignited and combusted. The ignition and subsequent combustion are effected by a focal point 3 generated in the mixing zone by means of the laser igniter 1. The laser igniter 1 is arranged radially to the combustion chamber 23, so that the focal point 3 is generated from a radial side of the combustion chamber 23.

[0056] Figure 2 shows two exemplary modulations of the laser beam 5 from Figure 1, which produce different focal points 3i, 3n in a focal point field 33. This can be achieved by a design-related limitation of the movement of the optical component(s). This can be accomplished by extreme positions of the actuators 9, 11, 13 and / or by a control unit (not shown) that controls the actuators 9, 11, 13. The focal point field 33 can have any desired pattern. For example, the pattern can consist of 50 or more than 50 focal points 3, so that, according to the temporal modulation described above, each focal point 3 can be focused on once per second.Naturally, the pattern can be stored in a control unit (not shown) with 50 or more focus points, but the focusing during ignition can be limited to a selection of focus points 3, whereby focus points 3 within this selection can be focused on multiple times per second. The pattern can be determined spatially and / or temporally from a propellant distribution in the mixing zone. The pattern can be understood as the spatial and temporal sequence in which focus point 3 changes. This can be stored in a control unit for the actuators. The pattern can repeat itself multiple times within an ignition cycle of the rocket injector head 21. It can repeat zero, one, two, or more times per second.

[0057] The pattern can extend exclusively along a line or exclusively in a plane. The plane can extend parallel to a free end of an injection element 25, for example, in a radial direction to the injection element 25. The plane can be parallel to the direction of propagation of the laser beam 5 immediately before its focusing onto a focal point 3. The pattern can be located entirely within, partially within, or entirely outside a projection of an injection element 25. A projection of an injection element 25 refers to the space that would be occupied if the injection element 25 were to extend further through the combustion chamber 23 in its axial direction and to the corresponding end of the combustion chamber 23. Furthermore, the pattern can have a two-dimensional shape (e.g., the shape of a rectangle) or a three-dimensional shape (e.g., the shape of a cuboid) in its extent.The pattern can thus have a wave-like shape in its extent. The distance between immediately adjacent focus points 3 can always be the same. The pattern can have several parallel rows of focus points, with each row comprising several focus points 3 along a line. The distance between immediately adjacent rows of focus points and the distance between immediately adjacent focus points 3 within a row of focus points can be the same or different. The position of the focus points 3 in one row of focus points can be offset from the position of the focus points 3 in an immediately adjacent row of focus points, meaning they are not located on a common line extending perpendicularly through the two immediately adjacent rows of focus points. This offset can be such that focus points 3 in one row of focus points have the same distance to two immediately adjacent focus points 3 in an immediately adjacent row of focus points.The number of focus points 3 of the pattern can be in a range of 2 to 50, for example in a range of 2 to 16, 4 to 16, 8 to 16, or 12 to 16, or exactly 16.

[0058] The maximum pattern size can be 2 mm, 1.9 mm, 1.8 mm, 1.7 mm, 1.6 mm, 1.5 mm, 1.4 mm, 1.3 mm, 1.2 mm, or 1.1 mm. The minimum pattern size can be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm.

[0059] Naturally, the laser igniter described here can also be used in combustion engines, aircraft gas turbines, etc.

[0060] A method for operating a laser igniter with at least one optical component and for focusing a laser beam onto a focal point may include moving the at least one optical component to change the focal point. The features described in this disclosure may be reformulated as steps to further develop the method accordingly.

[0061] Advantages of the technical solution(s) described here:

[0062] • Increased probability of ignition

[0063] • More robust ignition under varying conditions

[0064] • Reduced adjustment effort

[0065] • Reduced qualification requirements

[0066] • Lower probability of failure while retaining the simple laser ignition system

[0067] • Avoiding costs due to engine failure (potential mission loss)

Claims

Claims 1. Laser igniter (1) for a combustion chamber (23), wherein the laser igniter (1) has at least one optical component (7, 15) and is designed to focus a laser beam (5) onto a focal point (3), characterized in that the at least one optical component (7, 15) is arranged to be movable such that the focal point (3) of the laser igniter (1) can be changed.

2. Laser igniter (1) according to claim 1, wherein the at least one optical component (7, 15) is configured to change the focus point (3) several times per second, and wherein the focus point (3) is repeated once, twice or more frequently per second.

3. Laser igniter (1) according to claim 2, wherein the at least one optical component (7, 15) is configured to repeat one focus point (3) and another focus point (3) with the same frequency per second or with different frequencies per second.

4. Laser igniter (1) according to one of claims 1 to 3, wherein the at least one optical component (7, 15) is arranged such that focus points (3) focused immediately one after the other have a distance of less than 1 mm, 1 mm or more than 1 mm.

5. Laser igniter (1) according to one of claims 1 to 4, wherein the at least one optical component (7, 15) is arranged such that the change of the focal point (3) within a focal point field (33) with different focal points (3i, 3n) is limited.

6. Laser igniter (1) according to claim 5, wherein the focus points (3i, 3n) focused in the focus point field (33) follow a pattern.

7. Laser igniter (1) according to claim 6, where the pattern has a maximum extent of 2 mm and a minimum extent of 0.1 mm.

8. Laser igniter (1) according to claim 6 or 7, wherein the pattern comprises one or more parallel to each other has lines, with several focus points (3) spaced apart on each line.

9. Use of a laser igniter (1) according to any one of claims 1 to 8 for the ignition of a rocket engine, an internal combustion engine or an aviation gas turbine.

10. Method for operating a laser igniter (1) with at least one optical component (7, 15) and for focusing a laser beam (5) onto a focus point (3), characterized by Moving at least one optical component (7, 15) to change the focus point (3).

Images