Chemical Reactor Network Modeling Of Ammonia Rich-Quench-Lean Combustion Using A Partially Stirred Reactor Approach

Abstract Ammonia, a promising high-energy-density hydrogen alternative, faces challenges for direct utilization due to low flammability and high NOx emissions. Two-stage rich-quench-lean (RQL) combustion mitigates this, utilizing a rich stage to oxidize fuel and decompose ammonia into hydrogen, followed by a lean stage where air rapidly combusts the generated hydrogen and residual ammonia. Despite extensive RQL investigation, idealized chemical reactor network (CRN) models typically underpredict NOx compared to experiments or 2D/3D simulations due to finite rate mixing and non-adiabatic conditions. Standard CRN models use sequential perfectly-stirred-reactor (PSR) and plug-flow-reactor (PFR) stages; prior work showed rich stage equivalence ratio's significant impact on exit NOx. This paper extends the CRN model to include heat loss and uses a partially-stirred-reactor (PaSR) to study mixing effects on emissions. Varying heat loss was applied to the rich relaxation zone. Premixed and non-premixed rich-stage PaSR configurations explored mixing intensities and their interaction with transport and kinetic timescales, focusing on hot products and secondary air mixing. Results show unburnt ammonia from the rich stage, driven by heat loss and reduced mixing, is a key NOx contributor. Heat losses also foster N2O formation in the lean stage. These findings are crucial for optimizing two-stage RQL ammonia combustors.