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This work presents the first quantitative Raman measurements of temperature, mass fractions, and mixture fractions in two turbulent ammonia/hydrogen/nitrogen-air diffusion jet flames simulating 14% (CAJF14) and 28% (CAJF28) partial ammonia cracking ratio with Reynolds numbers of 11,200. The precision and accuracy of the system were validated in laminar counterflow and laminar jet flames to ensure data quality. The scalar structure in turbulent flames is examined using conditional mean and rms radial profiles, scatterplots in mixture fraction space, as well as statistics conditioned on mixture fraction and physical spaces. These results are compared with opposed diffusion flow 1D simulation with multi-component transport model and Le=1 transport model to visualize the effects of differential diffusion on the scalar structure at various axial positions. Finally, localized extinction was found in CAJF14 but not for the more stable CAJF28, and the probability of localized extinction was less than 2.5%. The dataset is provided as supplemental material and can be used for the validation of numerical models. [ABSTRACT FROM AUTHOR]

Ammonia has shown great potential as a carbon-free fuel, in particular for marine transportation and energy production. Its low laminar flame speed, and the tradeoff between ammonia slip and NOx emission, pose challenges for industrial applications, and a more in-depth understanding of the combustion of ammonia is therefore needed. Raman spectroscopy is a powerful diagnostic often employed to investigate turbulence chemistry interactions and resolve the thermo-chemical structure of hydrogen and hydrocarbon-air flames. This work extends Raman spectroscopy to the instantaneous and spatially resolved measurement of major species concentrations and temperature in ammonia flames. The lack of detailed ammonia spectra at high temperatures, the strong flame luminosity, and fluorescence interference are the major obstacles to the implementation of Raman spectroscopy to ammonia flames. This paper introduces a novel approach to estimate the temperature dependence of the Raman signal and of fluorescence interference contributions from a series of counterflow diffusion flames. This approach was first validated in high-pressure hydrogen flame, and then extended this approach to high-pressure ammonia flames to obtain the Raman response of ammonia and its crosstalk. A high-contrast optical shutter is sufficient to suppress flame luminosity. Finally, species concentrations and temperature profiles from measurements are shown, and their accuracy and precision are discussed. [ABSTRACT FROM AUTHOR]