Air Force

Low energy laser igniter enhances and sustains engine combustion

Engine manufacturers can leverage this invention to overcome the challenges inherent in spark igniters

Photonics Energy Electronics

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Engineers are seeking greater reliability and combustion stability for igniting an air-fuel mixture, and one popular approach is the use of laser light to begin engine combustion.

A low energy ultraviolet laser ignition system is poised to catch the attention of leading engine manufacturers advancing technologies for military and commercial applications. The future of performance ignition systems for internal combustion engines is shifting away from conventional spark ignition design. The industry is seeking greater reliability and combustion stability, and one popular approach has been to explore the use of laser light to begin engine combustion. While attractive, the present method raises hesitation because a high power pulsed laser is used to create a high-field breakdown of air and photoelectric effects to gain optical access to an ignition volume, introducing myriad stability of issues. Furthermore, integrating high power pulsed lasers near the engine and combustion area is concerning. Another unrealized goal in this realm is to use a laser igniter to guide a lower power laser pulse through a fiber optic cable to reliably induce ignition of an air-fuel mixture.

Behold, a breakthrough low energy laser ignition design from a research team at the Wright-Patterson Air Force Base lab demonstrates immense promise to improve the ignition qualities of gas turbine and other engines. The invention employs a low-energy single-pulsed ultraviolet laser to create a pre-ionized channel so that a smaller voltage electric field is sufficient for an electrical arc to follow in this channel. The smaller voltage electric field can be created by a single electrode near the laser output into the ignition volume of a combustion chamber with the arc following the pre-ionized channel from that electrode to the other side of the ignition volume at the ground. This way, electrodes inside the combustion chamber are not necessary. The arc follows the pre-ionized channel, so it can be directed to an optimal location inside the ignition volume for igniting the air-fuel mixture.

The low energy ultraviolet laser pulse can ionize the air-fuel flow in the ignition volume by a combination of resonant enhanced multiphoton absorption, collisional energy transfer within the gas, and finally photoionization of the excited gas.

Because the laser scheme uses resonant enhanced multiphoton ionization to generate a pre-ionized path between the electrodes, the spark can be spatially guided, even when the laser path does not follow the electric field path directly. The use of volume ionization, as opposed to a photoelectric effect method used in the present laser-induced ignition, makes this invention a more reliable and less destructive approach. This invention also addresses the shortcomings of spark ignition engines and will be increasingly valuable for restarting turbine engines after a failure. Furthermore, this advancement reduces the volume and weight of an igniter electronic package. This low energy laser-induced ignition approach will find broad application in industries where creating an ionized channel within a gas is required, for example, aerospace, aircraft, oil and gas, energy generation and surface transportation.

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