Ph.D Thesis


Ph.D StudentMosevitzky Lis Bar
SubjectCombustion Kinetics of Nitrogen-Based Alternative Fuels
DepartmentDepartment of Chemical Engineering
Supervisors PROF. Gideon Grader
DR. Gennady Shter


Abstract

The demand for renewable energies has been increasing steadily over the past decade due to a combination of health and global warming concerns. The current energy market is carbon-based, and is associated with pollutant emissions that are hazardous to both humanity and the environment. However, large-scale implementation of renewable energies is inhibited by the need for energy storage to overcome temporal and spatial supply difficulties. While renewable hydrogen is commonly suggested as such a medium, it entails hazards that limit its wide application. Nitrogen-based fuels that can be synthesized using green hydrogen could serve as energy vectors owing to their compatibility with current transport and storage infrastructure. Both aqueous urea/ammonium nitrate and ammonium hydroxide/ammonium nitrate were previously suggested as possible candidates. However, knowledge of their combustion and ignition pathways is currently lacking and requires additional research. In this thesis, several publications in which the effects of various system parameters on the combustion and ignition of these fuels are discussed. Kinetic gas-phase simulations were applied to simulate experiments, yielding results that were then compared to experimental data. Good agreement between experimental and simulative datasets was used to justify more in-depth analyses of the reaction pathways and rate determining steps of the fuel's combustion and ignition process'. As the simulation mechanism and experimental tools applied in these publications improved, additional data was revealed. The reactants (isocyanic acid, nitric acid and ammonia) were determined to react via reaction channels that were not identified as relevant in previous works. Isocyanic acid was revealed to undergo hydrolysis, while nitric acid reacted with nitrous acid to produce nitrogen dioxide. Ammonia was shown to react mostly with high oxidation state nitrogen oxides, albeit reactions with hydroxyl radicals were significant at post-ignition conditions. Ammonia activation by nitrogen dioxide and nitrate radicals were demonstrated to be the ignition promoting rate determining steps. Conversely, reduction of nitrogen dioxide and nitrate radicals was shown to inhibit the fuel's thermal autoignition. The hydrolysis of isocyanic acid was determined to be a considerable source of uncertainty in the simulation mechanism, requiring additional work to ascertain its kinetic parameters. Overall, the work described in this thesis serves to promote the current level of understanding in nitrogen-based monofuel, ammonium nitrate and urea reaction chemistry. It is our hope that this data will enable the intelligent implementation of these compounds in energy-related applications in the future.