John and Marcia Price College of Engineering
12 Computational Investigation of Ammonia/Hydrogen Combustion in Premixed Flames
Joseph Lee and Alex Novoselov
Faculty Mentor: Alex Novoselov (Mechanical Engineering, University of Utah)
Introduction
In recent decades, there has been a significant increase in interest of carbon-free fuels due to rising energy demands across the globe and their contributions to climate change. One such potential alternative is hydrogen (H2). However, due to its high mass-diffusivity, fractal flame propagation is observed at conditions relevant to practical devices. A promising solution is the inclusion of ammonia (NH3) in a hydrogen combustion system. Ammonia, also a carbon-free fuel, does not propagate in a fractal nature and can be used as both a vector for stabilization and storage of hydrogen.
Combustion systems are difficult to study physically due to their turbulent high-temperature nature, thus computational systems become a primary tool for investigating such systems. Many chemical mechanisms have been developed to try and model hydrogen/ammonia combustion, but each one is often tailored to specific conditions. To choose an appropriate mechanism from this variety of mechanisms, accuracy of said mechanisms must be validated against tangible experimental data.
The mechanisms selected in this work are based off previous analysis by Alnasif et al. [1]. Among the top performing mechanisms in Alnasif’s study are those developed by Duynslaegher [2], Glarborg [3], Gotama [4], Lamoureux [5], Nakamura [6], and UC San Diego (with nitrogen chemistry) [7]. The Glarborg mechanism focuses on nitrogen/oxygen chemistry due to its focus on nitrous oxides (NOx), with carbon species included to simulate carbon-scrubbing mechanisms [3]. Duynslaegher, being an older mechanism from 2012, focused on updating reaction rate constants and improving NH2 and N2O simulation pathways with novel results from literature [2]. Lamoureux focuses on prompt-NO formation in low-pressure flames [5], Nakamura looks at weak flames [6], and Gotama investigates fuel-rich high-pressure systems and optimizes the chemical mechanism from Han et al. [4] [8], while the mechanism developed at U.C. San Diego is tailored towards high temperature ignition and detonations [7]. These mechanisms will be referred to by first author and year of publication henceforth. This work is a preliminary investigation into a wide variety of conditions investigated by Lhuillier et al. [9], with results informing further investigations
Methods
To evaluate the accuracy of said mechanisms, simulations of one dimensional adiabatic freely propagating premixed flames were performed using the FreeFlame mode in Cantera [10] with varying ammonia/hydrogen mixtures as fuel. The laminar flame speed is observed for varying conditions corresponding to experimental conditions investigated by Lhuillier et al. [9]. All simulations are done at an unburned atmospheric pressure of 1 atm. Unburned tem