The AFIT Combustion Optimization and Analysis Laser (COAL) Laboratory was designed to maximize flexibility and include as much capability in performing world-class combustion research as possible. The laboratory includes gaseous as well as liquid fuel injection, large volume air delivery systems, and both conventional and advanced diagnostic equipment. The design includes failsafe operation, remote control, and adherence to the combustion industry standard SAE ARP 1256. The AFIT facility delivers air in two separately controlled air lines at up to 530 K (500 °F), at delivery rates of 0.12 kg/s (200 SCFM) for the main line and 0.03 kg/s (60 SCFM) for the secondary. A continuous dual syringe pump can deliver liquid fuel at up to 5.67 mL/s for JP-8 with equivalence ratios up to 4.0.
The diagnostic system can be configured with a plethora of pressure and temperature sensors throughout the experiment. These sensors will give relative thermodynamic states at specified locations within a combustion device. Industry standards also suggest emissions measurements be made to determine combustion efficiencies. The COAL lab is equipped with a high accuracy California Analysis gas chromatograph and a more convenient Testo solid-state emissions analyzer to perform this task. These instruments give the basis for exploring the capability of a given system and the ability to determine performance enhancing design changes. Although quite valuable, the use of these standard instruments falls short of actually looking inside the device. The temperatures in the combusting environment are often out of the range of traditional thermocouples. Inserting a probe into the device also disrupts the flow field and changes the problem at hand. In order to look inside the flame and get supportable, valid, and quantifiable information about the combustion process, an advanced laser combustion diagnostics system was added to the laboratory. The laser system will provide instantaneous Raman and Raman spectroscopy, Coherent Anti-Stokes Raman Scattering, Planar Laser-Induced Fluorescence, Laser-Induced Incandescence, and Planar Imaging Velocimetry diagnostic techniques. These laser-measuring techniques are all non-intrusive and have proven to be useful in a wide variety of flow fields. Each of these laser techniques has been used before in laboratory combustion environments but rarely in actual engineering devices or in this combination. These measurements provide spatially resolved species concentrations, density, temperature, velocity vectors, soot production, and turbulence intensities. With these measurements, one can characterize the flame location, shape, character, energy release, and local combustion efficiency. This information will allow designers to identify specific features within the device to focus on for design improvements, reliability in ignition, and extending life by reducing surface temperatures to identify just a few possibilities.
Current plans for the COAL lab include the Ultra Compact Combustor – Cavity Vane Interaction (UCC-CVI), the rocket transpiration cooling experiment, and the jet engine augmenter dynamics experiment. The UCC-CVI will replace conventional combustion sections on jet engines as well as provide the opportunity to add a combustion section between the turbine stages. The UCC-CVI has the potential of increasing the overall engine thrust/weight ratio by 25% for the higher performing engines. The transpiration cooling experiment is currently being developed and designed with plans to characterize design tools and relationships for cooling the internal walls of the next generation kerosene rocket engines. The jet engine augmenter dynamics will be helping solve the problems of both fielded and next generation high performance jet engines. Current issues in the after-burner section of a jet engine often involve a complex, multi-physics environment without very well understood design tools. The task at hand is to characterize some of these phenomena, in particular under operational conditions where problems have been experienced.
For further information, contact Maj. Rich Branam, Assistant Professor of Aerospace Engineering, at richard.branam@afit.edu or (937) 255-3636 ext 7485.
