Highly efficient laser ignition device

Abstract

A highly efficient laser ignition device is provided. The highly efficient laser ignition device fundamentally includes: a pumping light source adopting a multi-chip single emitter-packaged optical fiber output laser diode; a laser medium to which ytterbium is added; and a saturated absorber as a passive Q-switch medium, wherein a pulse of 100-999 ps as the passive Q-switch laser output can be obtained. According to the disclosed, the problems of high cost/low efficiency/low reliance/non-uniformity, which are disadvantages for replacing an ignition device using an electric spark with a laser ignition device, can be solved.

Claims

1. A laser ignition device comprising: (a) a pumping light source including a multi-chip single emitter-packaged optical fiber output laser diode using a first focusing lens and a fiber to combine an output power of multiple single-emitters, the first focusing lens focuses light emitted by multichip single emitters, and the fiber to gather the multiple laser outputs from the first focusing lens; (b) a laser medium to which ytterbium (Yb) is added; and (c) a saturable absorber used as a passive Q-switch medium, wherein a 100 to 999 picosecond pulse is obtained as an output of the saturable absorber; wherein the pumping light source has a wavelength band of 900 to 990 nm, wherein the pumping light source is operated at a pumping pulse width between 1,200 to 2,000 s.

2. The laser ignition device of claim 1, wherein: the saturable absorber includes a chromium-doped yttrium aluminium garnet (Cr:YAG) saturable absorber.

3. The laser ignition device of claim 1, comprising a plurality of sets each including the components (a) to (c), and further comprising a multi-focused ignition point generation unit at a next stage of the saturable absorber of each set.

4. The laser ignition device of claim 1, further comprising a reverse flowing heat blocking unit.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 is a schematic configuration diagram illustrating a pumping light source used in a highly efficient laser ignition device according to embodiments of the the present invention used for ignition in an internal combustion engine of a vehicle or the like;

(3) FIG. 2 is a schematic configuration diagram illustrating a highly efficient laser ignition device according to a first embodiment of the present invention; and

(4) FIG. 3 is a schematic configuration diagram illustrating a highly efficient laser ignition device according to a second embodiment of the present invention.

REFERENCE NUMERALS

(5) 10: MULTICHIP SINGLE EMITTER

(6) 12: FIRST FOCUSING LENS

(7) 14: PUMP FIBER INPUT

(8) 16: PUMP FIBER DELIVERY

(9) 18, 18-1, 18-2: PUMP FIBER OUTPUT

(10) 20: LASER DIODE OUTPUT LIGHT

(11) 22, 22-1, 22-2: SECOND FOCUSING LENS

(12) 24, 24-1, 24-2: YTTERBIUM ADDED LASER MEDIUM

(13) 24A: TOTAL REFLECTION COATING OF LASER MEDIUM

(14) 24B: ANTI-REFLECTIVE COATING OF LASER MEDIUM EMISSION SURFACE

(15) 26, 26-1, 26-2: SATURABLE ABSORBER

(16) 26A: ANTI-REFLECTIVE COATING OF SATURABLE ABSORBER

(17) 26B: OUTPUT GLASS COATING OF SATURABLE ABSORBER

(18) 28, 28-1, 28-2: THIRD FOCUSING LENS

(19) 30, 30-1, 30-2: INCIDENT WINDOW

(20) 30B: TOTAL REFLECTION COATING OF INCIDENT WINDOW FOR PREVENTING REVERSE MOVEMENT.

(21) 34: HEAT BLOCKING BLOCK

(22) 36, 36-1, 36-2: FOCUSED IGNITION POINT

(23) 42-1, 42-2: SIGNAL TRANSMISSION OPTICAL FIBER

DETAILED DESCRIPTION

(24) FIG. 1 is a schematic configuration diagram illustrating a pumping light source 100 used in a highly efficient laser ignition device according to embodiments of the the present invention used for ignition in an internal combustion engine of a vehicle or the like. Referring to FIG. 1, light emitted by a multichip single emitter 10 is focused by a first focusing lens 12 and input to a pump fiber input 14 in the pumping light source 100, and then the light is moved through a pump fiber delivery 16 and output through a pump fiber output 18 as laser diode output light 20. Although one lens is used as the first focusing lens 12 in FIG. 1, two or more lenses may be used thereas according to necessity. An suitable example of the pumping light source 100 illustrated in FIG. 1 is a multi-chip single emitter-packaged optical fiber output laser diode having a wavelength band of 900 to 990 nm, and has an advantage in that an entire highly efficient laser ignition device can be manufactured at low cost by realizing lower costs and smaller packaging compared to an 808 nm pumping laser diode of the conventional technology. The reason for such a pumping light source 100 being employed is that, since an upper-state lifetime of a Yb ion is 1,000 s which is about six times longer than that of an Nd ion, a pumping pulse width may be as long as 1,200 to 2,000 s when a ytterbium (Yb)-based laser medium rather than a neodymium (Nd)-based laser medium is used in the highly efficient laser ignition device, a pumping pulse energy in the range of 24 to 40 mJ per pulse may be input to a laser medium even when a 20 W pumping laser diode is used, and this will be described in detail below.

(25) FIG. 2 is a schematic configuration diagram illustrating a highly efficient laser ignition device 200 according to a first embodiment of the present invention. For convenience of illustration, in FIG. 2, only a pump fiber output 18 in the pumping light source 100 in FIG. 1 from which pumped light is output is illustrated, and the other components thereof are omitted. Referring to FIG. 2, the highly efficient laser ignition device 200 of embodiments of the the present invention employs a Yb added laser medium 24, such as Yb-doped yttrium aluminium garnet (Yb:YAG), as a component of a laser resonator. A short pulse of several hundred picoseconds is needed to obtain a high intensity laser beam required for ignition. In the highly efficient laser ignition device 200 of embodiments of the the present invention, a laser resonator includes a Yb added laser medium 24, in which a total reflection coating 24a for a 1030 nm wavelength band is applied on a pumping light incident surface side (pumping light is positioned on the left and proceeds from left to right) and an anti-reflective coating 24b for a 1030 nm wavelength band is applied on an emission surface side thereof, and a saturable absorber 26, which is a passive Q-switch medium, next to the Yb added laser medium 24. For example, a chromium-doped YAG (Cr:YAG) saturable absorber (for a 1030 nm wavelength band, the anti-reflective coating 26a is applied on a side of the laser medium and an output glass coating 26b is applied on the other side thereof) is disposed as an integrated type or separate types, and thus a several hundred picosecond pulse is obtained as the passive Q-switch laser output. At this time, when a length of the resonator needs to be adjusted, the output glass coating 26b may also be implemented by a separate output glass mirror. In FIG. 2, reference numerals 22 and 28 respectively denote a second focusing lens and a third focusing lens for focusing light, a reference numeral 30 denotes an incident window through which light output by the laser ignition device is transmitted into an engine, and a reference numeral 36 denotes an ignition point to which the light is focused by a third lens. Meanwhile, since there is a concern that high temperature heat generated around the ignition point during an explosion stroke (expansion stroke) in an engine reversely moves toward the laser ignition device 200 due to an emission spectrum, the following two reverse flowing heat blocking units are applied to prevent such a thermal transfer.

(26) (1) A total reflection coating 30b for a wavelength in the range of 300 to 900 nm configured to prevent a reverse movement of an emission spectrum of an ignition fuel is applied on a right side surface of the incident window 30, through which light output by the last laser ignition device is transmitted into an engine, to block heat due to the emission spectrum of the ignition fuel or radiant heat.

(27) (2) A heat blocking block 34, in which a zirconia-based ceramic having excellent thermal resistance, low thermal conductivity, and a thermal expansion rate similar to that of a metal at a high temperature or a similar ceramic thereto is used to prevent radiated heat from being transferred through a wall of an engine cylinder 40, is installed between a coupler positioned at a side of an engine cylinder of the laser ignition device and the engine cylinder, or is installed at a coupler positioned at the side of the engine cylinder of the laser ignition device in a single or separate type. In FIG. 2, the heat blocking block 34 is illustrated as blocking a light path because of being two-dimensionally illustrated, and since the heat blocking block 34 is manufactured and installed in a cylindrical type of which central portion is removed to prevent the light path from being interfered therewith, the heat blocking block 34 does not interfere with the light path.

(28) FIG. 3 is a schematic configuration diagram illustrating a highly efficient laser ignition device 202 according to a second embodiment of the present invention. A feature of the second embodiment compared with the first embodiment includes individual sets which are pump fiber outputs 18-1 and 18-2 included in a pumping light source 100 including a multi-chip single emitter-packaged optical fiber output laser diode, Yb added laser mediums 24-1 and 24-2, saturable absorbers 26-1 and 26-2 as passive Q-switch mediums, second focusing lenses 22-1 and 22-2 according thereto, and third focusing lenses 28-1 and 28-2. Since each of the sets generates one focused ignition point in an engine, a plurality of sets finally generate multi-focused ignition points 36-1 and 36-2, and thus simultaneous multi-focal and multi-ignition which is an advantageous in high capacity combustion can be performed. Another feature of the second embodiment is that signal transmission optical fibers 42-1 and 42-2 of which incident cross sections have angles of 90 to the direction of incident light and emission cross sections are inclined are installed between the saturable absorbers 26-1 and 26-2 and the third focusing lenses 28-1 and 28-2 as multi-focused ignition point generation units instead of a simple high refractive index optical component, and thus laser pulse energy may be stably transmitted to ignition points even when output directions of laser output pulses are finely changed or beam divergence angles are changed. For convenience of illustration, a total reflection coating layer, an anti-reflective coating layer, and the like, which are included in components, are not illustrated in FIG. 3, but coating layers are added thereto similarly as in FIG. 2, and thus a highly efficient laser ignition device is suitably operated. The same components in the first embodiment and the second embodiment serve the same roles, one of the laser mediums 24-1 and 24-2 to which Yb is added is used in the first embodiment, and both of the laser mediums 24-1 and 24-2 are used in the second embodiment, but one of the laser mediums 24-1 and 24-2 may also be commonly used in the second embodiment as long as there is no problem with laser output. In addition, design and manufacture thereof can be expanded to three or four sets, and it may also have more advantages when implemented.

(29) As described above, the highly efficient laser ignition device according to the embodiment of the present invention has operational features and advantages as follows.

(30) (1) Low cost 900 to 990 nm pumping laser diodes can be used. (2) Since an upper-state lifetime of Yb is 1000 s, a pumping pulse width is as long as about 2000 s at maximum, and thus the maximum usable pumping pulse energy is increased and the highly efficient laser ignition device is efficient. (3) Since the peak power of a pumping laser diode is low, a low current is used as input power, and thus a driving circuit becomes simple. (4) Accordingly, there is an advantage in that a total system is inexpensive and can be actually applied. (5) In addition, since a repeat rate, which is two or three times a repeat rate required as a laser output for ignition, is used, pulses between ignition pulses are used to automatically remove combustion by-products which may adhere to a laser beam emission window, the highly efficient laser ignition device has an advantage in that actual application becomes possible. When an amount of adsorbed by-product is increased, laser beams are absorbed by the by-products, laser energy transmitted to a focal point, which is an ignition point, is decreased, ignition may become unstable or impossible, and thus such automatic removal is particularly effective. (6) In addition, when multi-focal focusing is performed for multi-focal combustion which is required to be used for combustion of a high capacity combustion chamber, an optical fiber having an inclined emission cross section is used to transmit light instead of a simple high refractive index optical component, and thus there is an advantage in that even when output directions of laser output pulses are finely changed and beam divergence angles are changed, laser pulse energy can be transmitted to an ignition point. (7) In addition, since a window coating to which an emission spectrum total reflection coating is applied and a heat blocking block designed to prevent interference with a light path are used, there is an advantage in than reverse movement of radiant heat due to an ignition fuel emission spectrum and thermal transfer though an inner wall of an engine cylinder are prevented.

INDUSTRIAL APPLICABILITY

(31) Since embodiments of the present invention solves the problems of high cost/low efficiency/low reliability/non-uniformity which are disadvantages arising from the replacement of an ignition device using an electric spark with a laser ignition device, embodiments of the the present invention has high industrial applicability in the field of ignition devices.