Study of Laminar Flame 2-D Scalar Values at Various Fuel to Air Ratios Using an Imaging Fourier-Transform Spectrometer and 2-D CFD Analysis
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
Pagination or Media Count:
This work furthers an ongoing effort to develop imaging Fourier-transform spectrometry IFTS for combustion diagnostics and to validate reactive-flow computational fluid dynamics CFD predictions. An ideal, laminar flame produced by an ethylene-fueled C2H4 Hencken burner 25.4 x 25.4 mm2 burner with N2 co-flow was studied using a Telops infrared IFTS featuring an Indium Antimonide InSb, 1.5 to 5.5 microns, focal-plane array imaging the scene through a Michelson interferometer. Flame equivalency ratios of Phi 0.81, 0.91, and 1.11 were imaged on a 128 x 200 pixel array with a 0.48 mm per pixel spatial resolution and 0.5 cm-1 spectral resolution. A single-layer radiative transfer model based on the Line-by-Line Radiative Transfer Model LBLRTM code and High Resolution Transmission HITRAN spectral database for high-temperature work HITEMP was used to simultaneously retrieve temperature T and concentrations of water H2O and carbon dioxide CO2 from individual pixel spectra between 3100-3500 cm-1 spanning the flame at heights of 5 mm and 10 mm above the burner. CO2 values were not determined as reliably as H2O due to its smooth, unstructured spectral features in this window. At 5 mm height near flame center, spectrally-estimated Ts were 2150, 2200, 2125 K for Phi 0.81, 0.91, 1.11 respectively, which are within 5 of previously reported experimental findings. Additionally, T H2O compared favorably to adiabatic flame temperatures 2175, 2300, 2385 K and equilibrium concentrations 10.4, 11.4, 12.8 computed by NASA-Glenns Chemical Equilibrium with Applications CEA program. UNICORN CFD predictions were in excellent agreement with CEA calculations at flame center, and predicted a fall-off in both T and H2O with distance from flame center more slowly than the spectrally-estimated values. This is likely a shortcoming of the homogeneous assumption imposed by the single-layer model. Pixel-to-pixel variations in T and H2O were observed.
- Atomic and Molecular Physics and Spectroscopy
- Combustion and Ignition