Titel: Experimental and kinetic modeling study on ammonia fuel blends from low to high temperatures
Autoren: Li, Mengdi, Physikalisch-Technische Bundesanstalt (PTB), Fachbereich 3.3, Physikalische Chemie, ORCID: 0000-0002-4555-2074
Beitragende: HostingInstitution: Physikalisch-Technische Bundesanstalt (PTB), ISNI: 0000 0001 2186 1887
Seiten:121
Sprache:en
DOI:10.7795/110.20241024
Art der Ressource: Text / Dissertation
Herausgeber: Physikalisch-Technische Bundesanstalt (PTB)
Rechte: Download for personal/private use only, if your national copyright law allows this kind of use.
Beziehungen: IsPartOf: ISSN 2941-1297
IsIdenticalTo: ISBN 978-3-944659-38-1
Daten: Verfügbar: 2024-11-07
Erstellt: 2024-11
Datei: Datei herunterladen (application/pdf) 14.97 MB (15700910 Bytes)
MD5 Prüfsumme: 4ac8bf18fe880260e9e61f03a1fc756b
SHA256 Prüfsumme: 389830467826f2c9b1a975dd0f3cf3dccea4f63469335d4d8b8e31a3752c6a28
Schlagworte Ammonia ; Jet-stirred reactor ; Rapid compression machine ; Shock tube ; Combustion ; Reaction kinetics
Zusammenfassung: The combustion of fossil fuels has significantly contributed to global warming and the subsequent rise in extreme weather events. Consequently, the pursuit of carbon-free alternative fuels has become imperative for future transportation and energy systems. Ammonia, in particular, offers advantages such as zero carbon emissions, compatibility with existing infrastructure, and ease of production from renewable energy sources. However, challenges such as high ignition temperature and low burning velocity hinder its independent use as a fuel. Blending NH3 with reactive promoter fuels presents a feasible solution to enhance its combustion performance for specific applications. Nevertheless, recent studies have highlighted issues with low efficiency and high NOx emissions when using ammonia fuel blends in conventional internal combustion engines (ICEs).
Given the limited generalizability of practical application results to other energy systems, there is a strong need to comprehend the fundamental reaction kinetics behind the oxidation of ammonia and ammonia fuel blends, which include ammonia oxidation reactions and cross-reactions between promoters and ammonia. Such understanding is critical for attaining high efficiencies and low emissions across various combustion facilities utilizing ammonia fuels. Fundamental combustion experiments with homogenous reactors (reactors without fluid dynamics effects) can play a key role in developing and validating intricate reaction mechanisms.
This study investigates the oxidation properties of NH3/promoter fuel blends, with a specific focus on blending NH3 with C2-hydrocarbon fuels, i.e., ethane (C2H6), ethanol (C2H5OH), and dimethyl ether (DME, CH3OCH3). A wide range of temperatures (450 - 2500 K), pressures (1 - 40 bar), fuel blends ratios (1 - 50 %), equivalence ratios (ϕ = 0.5 - 2.0), and dilution ratios (70 - 95 %) have been explored by utilizing diverse facilities, including a jet-stirred reactor (JSR), a rapid compression machine (RCM), and a shock tube (ST). Based on obtained experimental data, namely ignition delay times and speciation data, a comprehensive chemical kinetic mechanism, PTB-NH3/C2 mech, was developed and validated. Consequently, kinetic analyses based on this mechanism were employed to identify the key reaction steps, with regard to comprehending combustion performances and optimizing combustion conditions for further development of the advanced ammonia combustion systems.
Experimental and simulation findings indicate that blending C2-hydrocarbons can enhance ammonia’s reactivity, e.g., decreasing the ignition delay times (IDTs) under RCM and ST conditions and lowering the oxidation onset temperature under JSR conditions. Detailed observations will be concisely discussed in the main text based on different temperature intervals. In brief, at low-to-intermediate temperatures (450 - 1180 K), speciation experiments under JSR conditions reveal three different oxidation regimes (1st, 2nd, and 3rd) for NH3. Namely, the unique contribution of DME promotes NH3 oxidation in the 1st regime (600 K), which only occurs in the NH3/DME fuel mixtures due to the low-temperature combustion properties of DME. In the 2nd oxidation regime (900 K), NH3 consumption is initiated by the radicals from promoter fuels’ chemistry, while the rapid NH3 consumption in the 3rd oxidation regime (1050 K) is triggered by high temperatures. Both 2nd and 3rd oxidation regimes are generally observed across different C2-hydrocarbon additives. Besides, the IDT measurements from RCM at intermediate temperatures (820 - 1120 K) demonstrate that C2-hydrocarbon addition has a substantial effect on ammonia ignition, with the following promotional effects compared to other blended fuels: 5% C2H5OH > 5% CH3OH > 5% C2H6 > 5% H2 > 10% CH4. At intermediate-to-high temperature (1320 - 1960 K) under ST conditions, speciation and IDT results from NH3/C2H6 and NH3/C2H5OH mixtures show comparable promotional effects on ammonia oxidation, as well as a reverse dependence of IDT at ST conditions compared to RCM conditions, namely IDT decreases as the equivalence ratios decrease in the high-temperature ST condition.
Finally, kinetic analyses based on PTB-NH3/C2 mech, have been employed to investigate the underlying reasons for C2-hydrocarbon promotion and interpret the differences from the various conditions. This research contributes to advancing the understanding of NH3/alkane/alcohol/ether fuel blend reaction kinetics and can serve as a valuable resource for further studies on ammonia combustion and its practical application.
Informationen zur Reihe: PTB-Bericht Diss-8
Zitierform: Mengdi L., 2024. Experimental and kinetic modeling study on ammonia fuel blends from low to high temperatures. Dissertation, Technische Universität Carolo-Wilhelmina zu Braunschweig. Braunschweig: Physikalisch-Technische Bundesanstalt. PTB-Bericht Diss-8. ISBN 978-3-944659-38-1. Verfügbar unter: https://doi.org/10.7795/110.20241024