Ammonia combustion kinetics: From multi-species measurements to reaction mechanism optimization and validation by global kinetic parameters

• Applicants: Dr. Mustapha Fikri; Professor Dr. Gernot Friedrichs
• Subject Area: Chemical and Thermal Process Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546036961

Direct combustion of ammonia is discussed as a promising renewable and carbon-free future energy source with high energy density and low cost for transport and storage. Related challenges are a potentially high emission of nitrogen oxides (NOx) and low flammability, the latter is overcome in technical applications by fuel additives such as hydrogen and hydrocarbons. As a prerequisite for the development of advanced ammonia combustion concepts, a fundamental understanding of the underlying detailed chemistry is needed. However, reaction mechanisms available to date are not yet capable to describe ammonia combustion over a wide range of experimental conditions (temperature, pressure, fuel mixture composition and equivalence ratio) and often even fail to accurately predict global combustion parameters such as ignition delay time, overall NOx emission, not to mention the concentration profiles of the various combustion intermediates. In this context, this project aims to significantly contribute to the development of reliable reaction mechanisms by extending the database with controlled validation experiments and by addressing specific research gaps in ammonia combustion chemistry. By combining the expertise of the two shock tube labs in Duisburg and Kiel, complementary measurements of ignition delay times, NOx yield, and sensitive detection of various combustion intermediates with a focus on nitrogen containing intermediates (NH3, NH2, NH, HNO, HCN, NCN, CN) will be performed for both neat ammonia oxidation as well as dual fuel ignition with various additives including alkanes, hydrogen, diethylether, and ozone. Moreover, a focus is set on the formation of alkylamines that have been postulated as important cross-intermediates in alkane/ammonia flames. A wide range of experimental methods, including low- and high-pressure shock tubes, fast valve sampling, time-resolved laser absorption by UV/Vis and Mid-IR frequency modulation spectroscopy, and CO thermometry, form the basis for the analysis, optimization, and validation of ammonia combustion mechanism. Support from a Mercator fellow in terms of quantum-chemistry / statistical rate theory to predict rate constants of unknown and key reaction steps complete the project.

• DFG Programme: Research Grants