Abstract
This work provides a kinetic and experimental investigation of excited radical OH(2Σ+) (also referred to as OH*) in NH3–H2-air flames. A counterflow burner is used to stabilize laminar diffusion flames over wide ranges of ammonia fraction in the fuel blend (0.2 ≤ xNH3 ≤ 0.8) and strain rate (40 ≤ a ≤ 200/s). Using an intensified camera or a spectrometer coupled to a Cassegrain optical system, spatially resolved and spatially integrated OH(A2Σ+-X2Π) chemiluminescence intensities are measured. These data are used to challenge a kinetic mechanism largely developed from existing literature schemes. Measurements and simulations show that two distinct OH* peaks exist in spatially resolved profiles for intermediate ammonia fractions in the fuel blend. Sensitivity analyses identified that reactions N2O+H=N2+OH* and H+O+M=OH*+M, respectively pertinent to NH3 and H2 oxidation routes, are responsible for the formation of OH*. The proposed kinetic mechanism gives a remarkable portrait of the empirical data recorded in diffusion flames as well as in premixed NH3–H2-air flames from the literature. Nevertheless, the contribution of reaction N2O+H=N2+OH* in the formation of OH* in the peak closest to the fuel side of diffusion flames is consistently overpredicted. Consequently, the frequency factor of the N2O+H[dbnd]N2+OH* reaction is adjusted to A = 1.35 × 1014 cm3mol−1s−1, which significantly improves predictions of spatially integrated and spatially resolved OH* intensities for all the diffusion and premixed flames examined.
Original language | English (US) |
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Article number | 113258 |
Journal | Combustion and Flame |
Volume | 260 |
DOIs | |
State | Published - Feb 2024 |
Keywords
- Ammonia
- Chemical kinetics
- Hydrogen
- OH* chemiluminescence
ASJC Scopus subject areas
- General Chemistry
- General Chemical Engineering
- Fuel Technology
- Energy Engineering and Power Technology
- General Physics and Astronomy