Recently, ammonia is emerging as a potential source of energy in power generation and industrial sectors. One of the main concerns with ammonia combustion is the large amount of NO emission. Air staging is a conventional method of reducing NO emission which is similar to the Rich-Burn, Quick-Mix, Lean-Burn (RQL) concept. In air-staged combustion, a major reduction of NO emission is based on the near zero NO emission at fuel-rich combustion of NH₃/Air mixture. A secondary air stream is injected for the oxidation of unburned hydrogen and NH_x. On the other hand, in fuel-staged combustion, NO emission is reduced by splitting NH₃ injection, which promotes the thermal DeNO_x process. In this study, NO_x emission characteristics of air-staged and fuel-staged combustion of partially cracked ammonia mixture are numerically investigated. First, the combustion system is modeled by a chemical reactor network of a perfectly stirred reactor and plug flow reactor with a detailed chemistry mechanism. Then, the effects of ammonia cracking, residence time, and staging scheme on NO_x emission are numerically analyzed. Finally, the limitations and optimal conditions of each staging scheme are discussed.

Combustion characteristics of partial cracking ammonia gas were investigated using a tangential injection burner. As the cracking ratio increased, the stable operational regime expanded, leading to the blowout limit of ∅=0.17. Higher injection velocities increased the wall peak temperature due to augmented heat transfer but lowered temperatures near the injector as the high-temperature reaction zone shifted downstream. NO exhibited peak values at 40-60% cracking ratio, attributed to enhanced radical formation with hydrogen addition. Numerical simulations, employing a perfectly stirred reactor model and a steady laminar flamelet model, demonstrated that these models, based on different assumption of flame structure, accurately reproduce NO levels in low and high cracking ratio conditions, respectively.

A numerical framework for efficient and robust simulation of supercritical Diesel combustion is developed in this study. One major problem in supercritical flow simulation is appearance of non-physical pressure oscillation at the interface of fluids with a large magnitude density gradient. To simulate supercritical flow without the spurious pressure oscillation, the pressure based SLAU2 scheme is implemented using OpenFOAM library. Also, the flamelet progress variable model with real fluid equation of state is utilized to efficiently describe combustion process. The numerical framework is applied for the Spray A benchmark case of the Engine Combustion Network. The simulation results indicate that the proposed numerical framework can capture basic features of supercritical Diesel spray mixing and combustion.