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

ABSTRACT:The objectives of the proposed Phase-II research effort are to develop and deliver three probes (immersion probe, backscatter probe, imaging probe) and integrate them into the existing AFRL hyperspectral absorption spectroscopy sensors, the high-speed cameras systems, and the hyperspectral imaging sensor. The integrated probes will be implemented and tested in AFRL rigs. Automated software will be developed for processing the acquired high-speed data. The Phase-II goals will be accomplished through five key technical objectives: (1) Design and build a fully integrated immersion probe, backscatter probe, and imaging probe for measurements at AFRL test rigs. (2) Assess available absorption spectroscopy methods and wavelengths to maximize the range of conditions that can be measured using the immersion and backscatter probes. (3) Validate temperature and species concentration measurements for the immersion and backscatter probes using well-calibrated flame sources. (4) Perform single-port detections of localized temperature, H2O and CO/CO2 concentrations, high-speed flame images, and 2D fuel-air ratios in AFRL augmentor and combustor rigs. (5) Develop automated software to process the acquired high-speed data. The successful demonstration of aforementioned measurements in AFRL test articles using the developed fiber-based probes will allow the researcher to determine localized gas combustion in practical high-combustion facilities and provide useful high-speed diagnostics into unsteady combustion reaction characteristics.BENEFIT:The primary challenge for optical sensors (e.g., laser absorption spectroscopy and chemiluminescence imaging sensors) in practical augmentors and combustors is optical access. Presently, a general-purpose optical sensor is not a viable commercial product because most applications require customized optical access, particularly for high-temperature and/or highpressure combustion facilities. The research effort to develop three single-port fiber-optic spectroscopic and imaging probes will alleviate this deficiency; these probes will utilize a single common penetration into the test article and will be easily interchangeable, thereby enabling multiple diagnostics to be used at full performance in practical devices during a single measurement campaign. We anticipate that the novel three probes developed under this program will enable an array of new marketable products and technologies for real-time combustion measurements in practical gas-turbine engines. 1. Immediate benefits to Air Force test facilities and OEMs: The development outlined in this proposal will enable the optimization of intelligent control strategies through real-time sensing used to obtain understanding of high-speed time-evolving phenomena related to ignition, flame growth, and stability in high-pressure combustors. Potential applications for defense missions include the reduction of combustion instabilities, pollution reduction, and fuel and fuel additive studies that enhance the performance and facilitate the design of next-generation combustion and propulsion systems. Additionally, the toolkit developed under this SBIR project will be instrumental to fully investigate lean and ultra-lean combustion concepts in next generation fighter engines and hence will be an invaluable asset to U. S. Air Force. The proposed flexible compact probe systems should be applicable for nearly all combustion environments and as such will have broad commercial appeal covering most of the Government laboratories, engine companies (OEMs), and University etc. 2. Scientific discovery Better understanding of the fundamental behaviors of ignition, turbulent flame and flow interactions, thermoacoustic-driven combustion instabilities, flame chemistry, and flame propagation in practical combustors/augmentors promises a rich field of intellectually stimulating scientific challenges, which in turn can quickly result in revolutionary technologies for advanced gas turbine combustors and augmentors that provide societal benefits via higher propulsion efficiencies, reduced weight, low emissions, improved durability, increased ease of manufacturing, and decreased cost. 3. Economic security and prosperity: Issues such as combustion instabilities, low temperature combustion (LTC), and pollutant emissions have enormous effects on the overall performance of modern gas turbine engines. Even a slight improvement in propulsion efficiency coupled with a minor reduction of combustion instabilities and pollutant via the use of advanced fiber-optic measurements in practical test engines will have huge economic impacts when those improvements are implemented nation-wide. The successful development of these commercial products will help extend the global leadership of the US in R&D and manufacturing of engine technologies.