Accurate Determination of Branching Fractions in Ammonia Combustion

Ammonia is a potential bridge fuel for carbon-neutral combustion. However, the combustion of ammonia can lead to various nitrogen oxides (NOx), which are major pollutants, and which can exacerbate climate change. To mitigate the impact of NOx on human health and the environment, government regulations increasingly require reduced emissions of nitrogen oxides from combustion sources. The ability to make accurate predictions of NOx formation levels will benefit engineers and scientists who need to quantify the impact of a new fuel or a new engine design on NOx emissions. These NOx submechanisms also will benefit the broader atmospheric science community, both at the local level (e.g. smog) and at the global level (e.g. climate change). The goal of this project is to measure the branching fractions for several reactions that are important in the kinetics of ammonia combustion, particularly those related to various nitrogen oxides. The investigators hypothesize that by measuring the transient concentration of two or more species simultaneously, the uncertainty in the branching fractions can be reduced relative to the current state of the art in NOx literature. To test this hypothesis, the investigators will use tunable diode laser absorption spectroscopy (TDLAS) to measure the transient concentration of NO, NO2, N2O, H2O, and/or temperature behind the reflected shock in a shock tube. These profiles will serve as validation targets for a kinetic model. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.