Toward a More Comprehensive Understanding of the Kinetics of a Common Biomass-Derived Impurity: NH₃ Oxidation by N₂O in a Jet-Stirred Reactor

Abstract

Ammonia (NH 3 ) has garnered substantial attention in recent years due to its importance across many scientific and engineering domainsincluding its potential use as a carbon-free fuel and long-term energy storage option, its use in reducing combustion-generated nitrogen oxide emissions, its role as a decomposition fragment of many energetic materials, and its presence as an important impurity during biofuel and biomass combustion that can affect overall system kinetics, among others. Yet, it is generally recognized that there are still significant gaps in the present understanding of ammonia kineticsin both experimental data sets and submodels within the overall ammonia kinetic mechanism. For example, most experimental studies of ammonia oxidation have used molecular oxygen as the primary or sole oxidizer. While large mole fractions of molecular oxygen are encountered in many combustion scenarios, there are select systems where ammonia is more likely to be oxidized via nitrogen-containing species (e.g., N 2 O), and, more generally, there are relatively untested reaction sets that would be accentuated in such conditions. To address one such gap in experimental data sets for the validation of ammonia kinetics submodels, we present results from jet-stirred reactor experiments of an NH 3 /N 2 O/N 2 mixture over an intermediate temperature range (850−1180 K). In these experiments, the mole fractions of NH 3 , N 2 O, and NO are measured through a combination of gas chromatography, chemiluminescence, electrochemical detection, and infrared absorptionwhere agreement among the different diagnostics (within 3% for N 2 O and 7% for NO) ensures high confidence in the experimental measurements. Comparison of the experimental results and model predictions suggests deficiencies in commonly used models for nitrogen kinetics. Various modeling analyses point to the central role of the N 2 O + NH 2 = N 2 H 2 + NO reaction, on which recent kinetic models all rely on the same rate constant estimate that appears to have not been tested in previous validation data sets for NH 3 kinetics.

Virtual Special Issue of Recent Advances in Fundamentals of Biomass and Biofuel Combustion

“…The last paper in the group discussed the oxidation of ammonia. Here, Cornell et al performed experiments in a jet-stirred reactor, providing kinetic results for the ammonia reaction with N 2 O being used as the oxidizer instead of O 2 . They further pointed out the importance of the N 2 O + NH 2 = N 2 H 2 + NO reaction.…”

“…The last paper in the group discussed the oxidation of ammonia. Here, Cornell et al 24 Six papers focused on the combustion of solid biomass. Three papers were interested in the reactivity of biochars.…”

Numerical Study on the Ignition and Flame Propagation of Ammonia/n-Heptane Dual Fuels

“…Recently, skeletal and reduced chemical mechanisms have been developed for ammonia/ n -heptane blends. , The combustion characteristics, including the IDTs and laminar burning velocities calculated using a homogeneous reactor, agreed well with the experimental results. However, gaps remain in our understanding of the kinetics of ammonia . Recently, numerical studies have been conducted on ammonia/diesel DF engines using the pilot injection of diesel. − An increase in the ammonia substitution ratio (ASR) leads to higher unburnt ammonia and N 2 O emissions. , The N 2 O greenhouse gas effect has been approximately 300 times higher than that of carbon dioxide over a period of 100 years.…”

“…However, gaps remain in our understanding of the kinetics of ammonia. 21 Recently, numerical studies have been conducted on ammonia/diesel DF engines using the pilot injection of diesel. 22−25 An increase in the ammonia substitution ratio (ASR) leads to higher unburnt ammonia and N 2 O emissions.…”

Upper and Lower Flammability Limits, Limit N2O Concentrations, and Minimum Inerting Concentrations of n-Alkane–N2O–Diluent Mixtures: An Experimental and Computational Study

“…Thus, despite its high ozone-depletion and global warming potential, the unique oxidizer N 2 O is being studied. , For instance, Parfenov et al delivered a new gas-phase selective oxidation of n-butenesraw materials for methyl ethyl ketonein the presence of N 2 O. Le Vaillant et al discovered a novel catalytic synthesis method for phenols, which are essential raw materials in the chemical industry, using N 2 O. Cornell et al reported a kinetic study of ammonia oxidation using N 2 O in a jet-stirred reactor, as ammonia is exclusively oxidized under conditions where N 2 O-rich O 2 oxidizers are present.…”