Session: 03-02 Ammonia as Fuel and Hydrogen Carrier – Combustion, Storage, and Safety II

Submission Number: 176919

Comparative Spray Flame Dynamics of Ammonia and Diesel at Low Momentum-Flux Ratio in a Multi-Jet Non-Uniform Crossflow 

This study presents a numerical comparison of diesel and ammonia spray flames in a non-uniform crossflow environment at low momentum-flux ratio conditions. A three-jet configuration was employed within a constant geometry combustion chamber, with identical air flow boundary conditions for both fuels. To achieve comparable flame temperatures, the liquid flow rates and nozzle diameters were adjusted to compensate for energy content, momentum ratio and Weber number differences between diesel and ammonia. A two-step computational workflow was adopted: (i) spray formation and evolution using a coupled Volume-of-Fluid (VOF)–Discrete Phase Model (DPM) [1], and (ii) spray combustion simulations incorporating laminar finite rate model. For ammonia, flash-boiling effects were modelled via a User-Defined Function (UDF) [2] based on the Adachi correlation. In contrast to prior work [3] (2023), where diesel combustion was modelled using a single-step chemistry with the Eddy Dissipation Model (EDM), the present study revisits diesel with a detailed finite-rate chemistry approach and validates against experimental high-speed imaging. This advancement enables a higher-fidelity prediction of ignition transients, flame stabilization mechanisms, and detailed flame-structure evolution, thereby establishing a robust baseline for comparing conventional and alternative fuels.

The results reveal distinct fuel-dependent phenomena. Diesel flames show strong local momentum coupling and compact flame stabilization dominated by diffusion-controlled burning. Ammonia flames, by contrast, display broader spray dispersion and extended premixed-dominated regions, with higher sensitivity to turbulence–chemistry interactions. In addition, ammonia operated in a flashing regime (P_v(T_inj)/P_back > 1), which induced auto-secondary atomization. Relative to diesel, ammonia exhibited a smaller Sauter mean diameter, a shorter liquid breakup length, and a higher near-field vapor fraction, yielding faster fuel–air mixing and reduced wall-wetting propensity in crossflow. This fundamental difference in spray behaviour between the two fuels strongly influences local flame location, heat release distribution, and the overall combustion stability within crossflow configurations, leading ammonia flames to form closer to the walls than those of diesel. Mean static temperature at the outlet for the ammonia case is 1129 K and 1033K for the diesel case. Ignition characteristics of the two fuels are not within the scope of the current study.

Overall, this study demonstrates a physically consistent numerical framework that enables high-fidelity comparison between hydrocarbon and carbon-free alternative fuels under realistic mixing regimes. While diesel ensures predictable anchoring and robust flame holding, ammonia’s flashing-driven micro-atomization promotes distributed, premixed-lean heat release that can partially offset its low flammability and slow ignition chemistry. Importantly, practical strategies such as small hydrocarbon pilots to ensure reliable ignition or hydrogen addition to accelerate flame propagation can further mitigate ammonia’s limitations. These factors suggest that, rather than being sidelined by ignition challenges, ammonia—leveraging its natural flashing behaviour and strategic blending—can emerge as a strong contender in the portfolio of next-generation low- and zero-carbon fuels for aero- and power-generation gas turbines.

References

[1] Ansys Inc., Ansys Fluent User’s Guide. Release  2025R1, Canonsburg, PA, USA, 2025

[2] Ansys Inc., Ansys Fluent Customization Manual. Release 2025R1, Canonsburg, PA, USA, 2025

[3] NUMERICAL MODELLING OF COMBUSTION OF MULTIPLE LIQUID JET IN NON-UNIFORM CROSSFLOW, Proceedings of ASME Turbo Expo 2023 Turbomachinery Technical Conference and Exposition GT2023, June 26-30, 2023, Boston, Massachusetts

Presenting Author: Homayoon Feiz GE Vernova

Presenting Author Biography: Homayoon Feiz is a Technical Leader at GE Power in Greenville, South Carolina. Currently, Feiz works for Combustion Engineering organization and he is leading combustion lab testing, CFD and physics-based modeling activities for gas turbine combustor design. He has a PhD in Aerospace engineering from Georgia Institute of Technology with a focus on Large Eddy Simulations.

Prior to joining GE, Feiz was a technical leader at Northrop Grumman Company and contributed to the design of NASA’s next generation Crew Exploration Vehicle by conducting Wind Tunnel Testing and performing CFD simulations.

Authors:

Homayoon Feiz GE Vernova
Vivek Kumar Ansys (Part of Synopsys)
Harshrajsinh Jadeja Ansys (Part of Synopsys)
Sourabh Shrivastava Ansys (Part of Synopsys)
Markus Lambert Ansys (Part of Synopsys)
Predrag Popovic GE Vernova
Subhasish Bhattacharjee GE Vernova