Fiber delivered systems for laser ignition of natural gas engines

Past research has shown that laser ignition is capable of operating high bmep engines at high efficiency and with low emission levels. However, for laser ignition systems to be adopted by industry, one requires a practical (and economical) mode of beam delivery other than the conventional open-path beam delivery that has been used in much of the past research. One potential beam delivery method is via optical fibers capable of handling high peak power. This paper summarizes our recent efforts in this area. Using coated hollow fibers, our research group has demonstrated the delivery of laser pulses to form optical sparks both on the bench-top and for ignition and operation of a single cylinder of an ARES engine. When held relatively straight, the hollow fibers allow transmission of nanosecond pulse energies of 10s of milli-Joules with transmission above 90% and sufficient beam quality for spark formation. We have also been able to deliver optical sparks on the bench-top with high peak power pulsed fiber lasers. Pulse energies in those experiments were approximately 2 mJ. Other recent work has studied the transmission characteristics of recently developed photonic crystal fibers.