An experimental investigation of ammonia combustion at subzero temperatures
Ignition and early flame propagation study of NH3 and NH3-blends in a custom-designed combustion chamber
A.F. Aversa (TU Delft - Aerospace Engineering)
F. De Domenico – Mentor (TU Delft - Flight Performance and Propulsion)
M. Pini – Graduation committee member (TU Delft - Flight Performance and Propulsion)
V. Grewe – Graduation committee member (TU Delft - Operations & Environment)
J. H. Mack – Mentor (UMass Lowell)
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Abstract
The sustainability issue has intensified interest in low-carbon alternatives to conventional hydrocarbon fuels for transport and power, where combustion is still expected to play a role. Ammonia is a promising carbon-free energy carrier, but it is difficult to ignite and exhibits slow early flame propagation, limitations that become more severe at low temperature and high pressure. Experimental data in this combined regime remain scarce, motivating this work to establish a validated basis for assessing ammonia and ammonia–hydrogen combustion under subzero conditions.
A custom constant-volume chamber was designed, commissioned, and validated for controlled subzero operation, with pressure-based diagnostics used to infer laminar burning velocity during early spherical flame growth. Results show that lowering the initial temperature from room temperature to \SI{-50}{\degree C} produces a strong penalty in neat-ammonia burning velocity across the investigated equivalence ratios, pushing the flame into a regime where losses and stretch effects become increasingly influential and ignition robustness is reduced. Hydrogen blending at \SI{-50}{\degree C} provides a marked performance recovery, with 20% and 30% H$_2$ producing substantial increases in burning velocity and restoring behaviour comparable to neat ammonia at room temperature near stoichiometric conditions. Minimum ignition energy could not be quantified reliably due to electrical signal variability, but ignition threshold settings indicate a strong increase in ignition difficulty as temperature decreases. Overall, the results show that subzero temperatures penalise neat-ammonia early combustion more strongly than predicted by kinetic models, while modest hydrogen enrichment can recover performance and improve robustness under cold-start-relevant conditions.