Ignition delay times of NH3 /DME blends at high pressure and low DME fraction
Autor: | Paul Marshall, Sander Gersen, Dai Liming, Hamid Hashemi, Anatoli Mokhov, Peter Glarborg, Howard Levinsky |
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Jazyk: | angličtina |
Rok vydání: | 2021 |
Předmět: |
Materials science
General Chemical Engineering Ab initio theory Analytical chemistry General Physics and Astronomy Energy Engineering and Power Technology Fraction (chemistry) 02 engineering and technology 01 natural sciences law.invention Ammonia chemistry.chemical_compound 020401 chemical engineering law 0103 physical sciences Dimethyl ether 0204 chemical engineering Ammonia/DME ignition RCM measurements 010304 chemical physics Autoignition temperature General Chemistry Ignition delay Ignition system Fuel Technology chemistry Pre-ignition heat release High pressure Ignition enhancement |
Zdroj: | Combustion and Flame, 227, 120-134. HANLEY & BELFUS-ELSEVIER INC Dai, L, Hashemi, H, Glarborg, P, Gersen, S, Marshall, P, Mokhov, A & Levinsky, H 2021, ' Ignition delay times of NH 3 /DME blends at high pressure and low DME fraction : RCM experiments and simulations ', Combustion and Flame, vol. 227, pp. 120-134 . https://doi.org/10.1016/j.combustflame.2020.12.048 |
ISSN: | 1556-2921 0010-2180 |
Popis: | Autoignition delay times of ammonia/dimethyl ether (NH3/DME) mixtures were measured in a rapid compression machine with DME fractions of 0, 2 and 5 and 100% in the fuel. The measurements were performed at equivalence ratios phi=0.5, 1.0 and 2.0 and pressures in the range 10-70 bar; depending on the fuel composition, the temperatures after compression varied from 610 K to 1180 K. Admixture of DME is seen to have a dramatic effect on the ignition delay time, effectively shifting the curves of ignition delay vs. temperature to lower temperatures, up to similar to 250 K compared to pure ammonia. Two-stage ignition is observed at phi=1.0 and 2.0 with 2% and 5% DME in the fuel, despite the pressure being higher than that at which pure DME shows two-stage ignition. At phi= 0.5, a reproducible pre-ignition pressure rise is observed for both DME fractions, which is not observed in the pure fuel components. A novel NH3/DME mechanism was developed, including modifications in the NH3 subset and addition of the NH2+CH3OCH3 reaction, with rate coefficients calculated from ab initio theory. Simulations faithfully reproduce the observed preignition pressure rise. While the mechanism also exhibits two-stage ignition for NH3/DME mixtures, both qualitative and quantitative improvement is recommended. The overall ignition delay times for ammonia/DME mixtures are predicted well, generally being within 50% of the experimental values, although reduced performance is observed for pure ammonia at phi= 2.0. Simulating the ignition process, we observe that the DME is oxidized much more rapidly than ammonia. Analysis of the mechanism indicates that this 'early DME oxidation' generates reactive species that initiate the oxidation of ammonia, which in turn begins heat release that raises the temperature and accelerates the oxidation process towards ignition. The reaction path analysis shows that the low-temperature chain-branching reactions of DME are important in the early oxidation of the fuel, while the sensitivity analysis indicates that several reactions in the oxidation of DME, including cross reactions between DME and NH3 species presented here, are critical to ignition, even at fractions of 2% DME in the fuel. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved. |
Databáze: | OpenAIRE |
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