Chemical Reactor Network Modeling of Ammonia Rich-Quench-Lean Combustion Using a Partially Stirred Reactor Approach

Journal Article · Wed Oct 08 00:00:00 EDT 2025 · Journal of Engineering for Gas Turbines and Power

DOI:https://doi.org/10.1115/1.4069551· OSTI ID:3012906

Bedick, Clinton ^[1]; Boyette, Wesley ^[1]

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1. National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV (United States)

Ammonia is a promising alternative to hydrogen with high energy density and favorable storage and transport characteristics. However, low flammability and a propensity for high nitrogen oxide (NO_x) emissions make direct utilization challenging. Recently, two-stage rich-quench-lean (RQL) combustion strategies have shown promise in achieving low NO_x emissions with ammonia. In this approach, the rich stage serves to oxidize a portion of the fuel while thermally decomposing as much of the remaining ammonia as possible, generating hydrogen. In the second (lean) stage, air is rapidly introduced, burning out the hydrogen and residual ammonia. Two-stage RQL combustion of ammonia has been investigated in the open literature both experimentally and numerically. In general, idealized chemical reactor network (CRN) models predict NO_x concentrations below those of 2D/3D computational fluid dynamics models and experiments. The primary drivers of these discrepancies may be largely attributed to finite rate mixing nonadiabatic operation. The typical CRN model is comprised of a perfectly-stirred-reactor (PSR), followed by a plug-flow-reactor (PFR), meant to represent the flame, and postflame zones, respectively. In the two-stage RQL approach two PSR-PFR networks are arranged sequentially, corresponding to the rich and lean stages, with secondary air injection in between. In the authors' past work, this arrangement has demonstrated the significant sensitivity of exit NO_x to the rich stage equivalence ratio, while the amount of secondary air injection was shown to be less critical. In this paper, the CRN model is extended to (1) include the impacts of heat loss and (2) utilize a partially-stirred-reactor (PaSR) approach to study the impacts of mixing on emissions performance. Varying amounts of heat loss are applied to the rich relaxation zone to understand emissions performance and changes to optimization of equivalence ratio and residence time. Premixed and nonpremixed configurations are considered in the rich stage PaSR, with varying degrees of mixing intensity to study the interaction between mixing, transport, and kinetic timescales. Critically, the impact of mixing between hot products and secondary air injection is studied to understand practical injector needs. Results show unburnt ammonia leaving the rich stage as a primary contributor to NO_x emissions – driven both by increased heat loss and reduced mixing rates. Furthermore, heat losses have been shown to create conditions that are conducive to increased N₂O formation in the lean stage. In conclusion, the results of this study will be considered in the context of developing optimized two-stage RQL combustors for ammonia.

• Research Organization: National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
• Sponsoring Organization: USDOE Office of Fossil Energy and Carbon Management (FECM), Office of Carbon Management
• OSTI ID: 3012906
• Journal Information: Journal of Engineering for Gas Turbines and Power, Journal Name: Journal of Engineering for Gas Turbines and Power Journal Issue: 2 Vol. 148; ISSN 1528-8919; ISSN 0742-4795
• Publisher: ASME
• Country of Publication: United States
• Language: English

Related Subjects

Combustion
Combustion chambers
Density
Emissions
Flames
Flow (Dynamics)
Fuels
Gas turbines
Heat losses
Hydrogen
Modeling
Nitrogen oxides
Particulate matter
Relaxation (Physics)
Simulation
Temperature
ammonia
ammonia combustion
chemical reactor network
gas turbine
hydrogen
rich-quench-lean