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Ammonia (NH3), which can be a hydrogen carrier, is a promising alternative to fossil fuels in the future carbon-free economy. In situtechniques feasible for the remote and non-intrusive detection of NH3will provide strong support for developing clean NH3combustion. Here, we demonstrated a femtosecond two-photon laser-induced fluorescence (fs-TPLIF) technique for interference-free in situNH3measurements in laminar premixed NH3/air flames. The two-head band of NH3at ∼565 nm was observed, which verifies the feasibility of fs-TPLIF for NH3measurements in a combustion environment. The single-shot NH3fs-TPLIF images with efficient signal-to-noise ratios were obtained. The variation of the thickness of the reaction zone with the equivalence ratio of NH3flames was also obtained. As a result of the broad line width of the femtosecond laser, the OH fluorescence was also observed together with the NH3fluorescence. The potential of fs-TPLIF for simultaneous measurements of NH3and OH with only one laser was analyzed. The laser power dependence of NH3and NH emissions was investigated. The radial distributions of NH3, NH, and OH in the flame were also discussed. This work is the first attempt of fs-TPLIF for NH3measurements in a combustion environment, and the results indicate that fs-TPLIF is a feasible tool for NH3measurements in combustion diagnostics.

Ammonia (NH_3) is a sustainable fuel with excellent emission characteristics. Hence, it is important to develop diagnostic techniques for NH_3 combustion. In this paper, femtosecond laser-induced plasma spectroscopy (FLIPS) was performed in premixed NH_3/air flames. The plasma emission spectra induced by the femtosecond laser in the flame and the chemiluminescence spectra of the flame itself were both measured. Through calibration, we found that the spectral intensity ratio of NH (336  nm)/N_2 (337 nm) could be used for equivalence ratio measurements in NH_3 combustion flow fields. This work is the first attempt at using a femtosecond laser-based technique for NH_3 combustion diagnostics.

Femtosecond laser-induced plasma spectroscopy for in situ ammonia (NH_3) measurements was demonstrated in NH_3/N_2 mixtures. When a femtosecond laser at 800 nm was focused at the flow field, the parent NH_3 molecules would be photolyzed to generate electronics excited NH fragments, and then indirect measurements of NH_3 could be realized by detecting the NH fluorescence (A^3Π−X^3Σ^−) at 336 nm. A detection limit of 205 ppm was achieved. This work is the first attempt, to the best of our knowledge, for ammonia measurements with a femtosecond laser, and the results are useful for the development of ammonia diagnostics.