Nick Wilvert M.S. Final Exam and Defense
Friday, June 29, 2012, 01:00 PM
ERC, Classroom A210

Development and Testing of a Solid Core Fiber Optic Delivery System and Ultraviolet Preionization for Laser Ignition

Advisor: Azer Yalin Committee: Anthony Marchese, Jorge Rocca

Abstract Laser ignition of natural gas engines has shown potential to improve many facets of engine performance including brake thermal efficiency, exhaust emissions, and durability as compared with traditional spark ignition. This technology has yet to transition to industry primarily because no system for reliably and safely delivering the laser pulse to the combustion chamber exists. This thesis presents a novel fiber optic delivery approach using solid core multimode step index silica fibers with large cladding diameters (400 µm core, 720 µm cladding). Testing was done on the fibers to determine their response to bending, vibration, high energy input, and long duration beam transmission. It was found that in configurations representative of what is required on a real engine and in the presence of vibration, reliable spark formation could be achieved in pressures as low as 50 psig using a specially designed optical spark plug. Comparative tests between the fiber delivered laser ignition system and a traditional J-gap spark plug were performed on a single cylinder Waukesha Cooperative Fuel Research (CFR) engine running on bottled methane. Tests were run at three different NMEPs of 6, 8, and 12 bar at various air-fuel ratios. Results indicate reliable performance of the fiber and improved engine performance at high NMEP and lean conditions. Initial studies into the use of dual pulses for ignition are presented where a first ultraviolet pulse preionizes a volume of air followed by a second overlapped pulse which adds additional energy. Electron density measurements reveal the ultraviolet beam generates preionization with no visual breakdown, and Schlieren images are used to study the interaction between the two beams at atmospheric and lower pressures.

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Event Contact: Karen Mueller can be reached at (970) 491-3872

Sponsored by the Department of Mechanical Engineering.