Investigation of real-fluid effects on NH$_3$ oxidation and blending characteristics at supercritical conditions via high-order Virial equation of state coupled with ab initio intermolecular potentials

TL;DR

This paper introduces a novel framework combining high-order Virial equations, ab initio potentials, and real-fluid equations to accurately model ammonia oxidation at supercritical conditions, revealing significant effects of real-fluid behavior on combustion predictions.

Contribution

The study develops and applies a new coupled modeling framework that accounts for real-fluid effects in high-pressure ammonia combustion, improving accuracy over ideal gas assumptions.

Findings

Real-fluid effects significantly alter species profiles in ammonia oxidation.

Ignoring real-fluid behavior can cause up to 85% error in species mole fractions.

The framework enables more reliable chemical kinetic modeling at supercritical conditions.

Abstract

Significant efforts have been committed to understanding the fundamental combustion chemistry of ammonia at high-pressure and low-temperature conditions with or without blending with other fuels, as these are promising to improve ammonia combustion performance and reduce NOx emission. A commonly used fundamental reactor is the jet-stirred reactor (JSR). However, modeling of high-pressure JSR experiments have been conducted assuming complete ideal gas behaviors, which might lead to misinterpreted or completely wrong results. Therefore, this study proposes, for the first time, a novel framework coupling high-order Virial equation of state, ab initio multi-body intermolecular potential, and real-fluid governing equations. The framework is further applied to investigate NH$_3$ oxidation under supercritical conditions in jet-stirred reactors, where the real-fluid effects on NH$_3$ oxidation characteristics are quantified and compared, via simulated species profiles and relative changes in simulated mole fractions, at various temperatures, pressures, dilution ratios, equivalence ratios, and with or without blending with H$_2$ and CH$_4$. Strong promoting effects on NH$_3$ oxidation from real-fluid effects are revealed, with significant shifts in simulated species profiles observed for both fuel, intermediates and product species. Sensitivity analyses are also conducted based on the new framework, with diverse influences of real-fluid effects on the contributions of the most sensitive pathways highlighted. It is found that, without considering real-fluid behaviors, the error introduced in simulated species mole fractions can reach 85% at the conditions investigated in this study. Propagation of such levels of error to chemical kinetic mechanisms can disqualify them for any meaningful modeling work. These errors can now be excluded using the framework developed in this study.