Diode Laser Absorption Sensor for Ammonia Detection in a Shock Tube

With the improved availability and performance of low-cost near-infrared diode lasers, quantitative assessment of ammonia (NH3) as a carbon-free fuel has been made more accessible and affordable in both laboratory research and field applications. In the present study, an absorption sensor for NH3 measurement was developed by exploiting the affordability and flexibility of a near-infrared fiber-coupled distributed feedback diode laser. The first objective of the present study was to address the incomplete spectroscopic data for the absorption feature near 2.2 mu m through the determination of line strengths and broadening coefficients with collisional partners including NH3, O2, N2, and Ar. Line shape characterization in both an absorption cell and a shock tube behind reflected shock waves was conducted to determine the temperature exponents of these broadening coefficients. The other objective was to demonstrate the capability of the sensor through NH3 detection in multicomponent mixtures and NH3 time-history measurements in the shock tube for investigating NH3 chemical kinetics at engine and gas-turbine-relevant conditions. The NH3 sensor developed in this study could serve as a cost-effective diagnostic tool for chemical kinetic measurements, combustion monitoring, and other applications where flexibility and robustness are prioritized.