Measurement of NH3 emission in CH4/NH3 combustion exhaust gas with the mid-infrared laser absorption

Ammonia is a promising zero-carbon fuel that has received widespread attention in recent years. However, owing to its weak reactivity, the NH₃-containing flame suffers from severe combustion instability, leading to large amounts of NH₃ emission in exhaust gas. In order to quantify the NH₃ emission, reliable and efficient diagnostic has to be developed. In this work, a mid-infrared high-sensitivity laser measurement system based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology was developed for detecting NH₃ emission of NH₃/CH₄ swirl combustion. Quantum cascade lasers (QCLs) is used to detect the optimal absorption features of NH₃ centered at 1103.45 cm⁻¹, combining with the direct absorption spectroscopy and a high temperature gas cell. Firstly, the performances of the measurement system was evaluated. The results show that the maximum relative error is less than 5 % and the measurement precision is 2.3 %. The minimum detection limit (MDL) at the optimal integration time of 49 s reaches 4.27 ppm. Subsequently, the measurement system was applied to detect NH₃ emission in exhaust gas of a swirl CH₄/NH₃ co-firing flame. The NH₃ emission were successfully discerned, with a minimum of 26 ppm and a maximum of 738 ppm under present conditions. Meanwhile, it is found that NH₃ emission rapidly increases with the increasing ammonia fraction in fuel and equivalence ratio, respectively. This work makes an effort to provide an effective means to monitor the NH₃ emission for ammonia combustion.