An Analysis of the Performance of Various Equations of State for Ammonia and Hydrogen as Pure Fluids
File(s)
Published version (ahead of print)
Author(s)
Duarte Nunes, Catarina
Aleiferis, Pavlos
Type
Journal Article
Abstract
Hydrogen and ammonia are both promising alternative fuels. The devel
opment of new technologies utilizing these fuels will require their
accurate thermodynamic modeling. In this work, several equations of
state (EOS) were evaluated for hydrogen and ammonia modeling. In
total, 13 different EOS were considered, including the ideal gas law, 4
cubic EOS, 4 Helmholtz EOS, and 4 statistical associating fluid theory EOS
(SAFT). These equations were assessed against experimental density
measurements from literature. Temperatures ranged between 14 K to
1500 K and 223 K to 406 K and pressures between 1 bar to 18710 bar,
and 0.3 bar to 9500 bar for hydrogen and ammonia, respectively. For
hydrogen, the ideal gas law presents an error below 5%, compared to
experimental data, if pressures are kept below 100 bar and temperatures
above 100 K. Therefore, it is suitable for most engineering applications
involving hydrogen, if Joule–Thomson effects are considered negligible.
For ammonia, the ideal gas law is only suitable for pressures below 10
bar and at the gaseous state, while the cubic EOS considered are only
applicable in the superheated region. A Helmholtz based EOS had the
widest ranges of temperature and pressure with density errors below
5%, but its unphysical Joule–Thomson inversion curve suggests it can
not be used for calculating other thermodynamic properties. Certain
SAFT EOS are applicable across all phase regions, and result in a realistic
inversion curve, but their pressure and temperature ranges are more
limited than the most recently formulated Helmholtz EOS evaluated in
this study.
opment of new technologies utilizing these fuels will require their
accurate thermodynamic modeling. In this work, several equations of
state (EOS) were evaluated for hydrogen and ammonia modeling. In
total, 13 different EOS were considered, including the ideal gas law, 4
cubic EOS, 4 Helmholtz EOS, and 4 statistical associating fluid theory EOS
(SAFT). These equations were assessed against experimental density
measurements from literature. Temperatures ranged between 14 K to
1500 K and 223 K to 406 K and pressures between 1 bar to 18710 bar,
and 0.3 bar to 9500 bar for hydrogen and ammonia, respectively. For
hydrogen, the ideal gas law presents an error below 5%, compared to
experimental data, if pressures are kept below 100 bar and temperatures
above 100 K. Therefore, it is suitable for most engineering applications
involving hydrogen, if Joule–Thomson effects are considered negligible.
For ammonia, the ideal gas law is only suitable for pressures below 10
bar and at the gaseous state, while the cubic EOS considered are only
applicable in the superheated region. A Helmholtz based EOS had the
widest ranges of temperature and pressure with density errors below
5%, but its unphysical Joule–Thomson inversion curve suggests it can
not be used for calculating other thermodynamic properties. Certain
SAFT EOS are applicable across all phase regions, and result in a realistic
inversion curve, but their pressure and temperature ranges are more
limited than the most recently formulated Helmholtz EOS evaluated in
this study.
Date Issued
2026-03-20
Date Acceptance
2026-02-17
Citation
Combustion Science and Technology, 2026
ISSN
0010-2202
Publisher
Taylor and Francis Group
Journal / Book Title
Combustion Science and Technology
Copyright Statement
© 2026 The Author(s). Published with license by Taylor & Francis Group, LLC. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.
License URL
Publication Status
Published online
Date Publish Online
2026-03-20