Single-port Fiber-optic Probe for Imaging and Spectroscopy in Practical Combustion Systems

ABSTRACT: The aim of this Phase-I SBIR research effort is to design an optical probe platform for incorporating hi-fidelity optical diagnostics into advanced combustion systems such as gas turbine combustors and augmentors that typically offer very limited optical access. Three unique, fiber-optic-based probes are envisioned, each with its own measurement paradigm, but all will be housed in the same form factor to allow plug-and-play style use and will only require a single penetration to the test article. Two of the probes will utilize near-IR absorption spectroscopy of H2O vapor for temperature and H2O concentration sensing and the third probe will use the naturally occurring luminescence for UV/VIS imaging. One of the H2O absorption spectroscopy probes will have a small protrusion into the flow path to incorporate a retro-reflecting element for high signal return. The other near-IR probe will use scattering from a surface opposite the probe for signal return. The imaging probe will be based on a specialized fiber consisting of thousands of individual fiber cores enabling coherent image transmission. All three probes will be designed to incorporate some form of active cooling to accommodate the extreme temperatures encountered in a practical combustion environment. The feasibility of combining the two probe measurement techniques into a single probe will be addressed as well. BENEFIT: The primary challenge for combustion sensors based on H2O absorption spectroscopy is optical access. The present situation is that a general-purpose H2O sensor is not a viable commercial product because most applications have customized optical access requirements. This research effort will change this situation dramatically by requiring only that each application can accommodate a single probe insertion somewhere adjacent to the gas under test. This is the key benefit of the interchangeable probe approach and will allow investigations of high-pressure reacting flow phenomena. The approaches outlined in this proposal will also allow for devising of intelligent control strategies through real-time sensing for understanding of high-speed time-evolving phenomena related to ignition, flame growth, and stability in high-pressure combustors. This research effort will make real time sensing and control of combustion and other flow phenomena a reality. The proposed hardware system should be applicable for nearly all combustion environments, and as such will have broad commercial appeal covering most of the Universities, Government laboratories, engine companies, etc.