NH2 Planar Laser-Induced Fluorescence in a Laminar Non-premixed NH3/H2 Flame

Abstract

The spatial distribution of the NH2 radical in a laminar non-premixed NH3/H2/air flame is investigated using planar laser-induced fluorescence (PLIF). The NH2 radical is a key intermediate in ammonia combustion that affects NOx formation and is thought to contribute to surface nitridation reactions in metals, yet its spatial distribution in NH3/H2 flames remains incompletely characterized. The A2A1(0, 12, 0) ← X2B1(0, 2, 0) transition at 609 nm was excited using a Nd:YAG-pumped Rhodamine B dye laser, with fluorescence in the 645-750 nm range collected on an intensified CCD camera. Images were acquired at a range of heights above the burner and at 18 lateral depths to characterize the NH2 distribution in the flame. At ϕ = 1.5, NH2 LIF intensity peaked at approximately 2 mm above the burner surface, with a full width at half maximum of 2.3 mm, and decayed exponentially with a characteristic length of λ = 1.9 mm. Above 5 mm, the signal became horizontally uniform. The 3D scan demonstrates that qualitative three-dimensional NH2 mapping is achievable under these flame conditions, though future research is required to quantitatively describe the concentration distribution. This paper presents, for the first time, qualitative height/depth NH2 LIF distribution reconstructions in a non-premixed NH3/H2 flame, and it provides critical validation data to understand NOx formation and metal surface nitridation by NH2 radicals.