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. However, this technique has been used extensively in hydrocarbons (HCs) and hydrogen flames, but no quantitative Raman spectroscopy is available for ammonia flames, despite the current interest in ammonia combustion.
First, this work extends Raman spectroscopy to the instantaneous and spatially resolved measurement of major species concentrations and temperatures 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 thesis introduces a novel approach to estimating the temperature dependence of the Raman signal and fluorescence interference contributions from a series of counterflow diffusion flames. Species concentrations and temperature profiles from measurements are shown, and their accuracy and precision are discussed.
Next, this work obtains the first quantitative Raman measurements of temperature, mass fractions, and mixture fractions in two turbulent ammonia/hydrogen/nitrogen diffusion jet flames simulating 14% (CAJF14) and 28% (CAJF28) partial ammonia cracking ratio with Reynolds numbers of 11,200. 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. Finally, the probability of localized extinction and the differential diffusion (diff-diff) effects are analyzed in two turbulent flames.
Lastly, an improved Raman/Rayleigh system is introduced for ammonia combustion at atmospheric pressure, which enables the 1D simultaneous laser-induced fluorescence (LIF) measurements of the amidogen (NH2) radical and interference-free Raman/Rayleigh measurements of major species and temperature in non-premixed and premixed NH3/H2-air flames.
|Date of Award||Oct 2022|
|Original language||English (US)|
- Physical Sciences and Engineering
|Supervisor||Gaetano Magnotti (Supervisor)|
- Ammonia combustion
- Raman/Rayleigh spectroscopy
- NH2 detection