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
Abstract
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 T's 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-Glenn's 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2013
- Accession Number
- ADA583715
Entities
People
- Andrew J. Westman
Organizations
- Air Force Institute of Technology