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Research on ethanol and toluene's synergistic effects on auto-ignition and pressure dependences of flame speed for gasoline surrogates

Fan, Qinhao and Wang, Zhi and Qi, Yunliang and Liu, Shang and Sun, Xingyu (2020) Research on ethanol and toluene's synergistic effects on auto-ignition and pressure dependences of flame speed for gasoline surrogates. Combustion and Flame, 222 . pp. 196-212. ISSN 0010-2180. https://resolver.caltech.edu/CaltechAUTHORS:20200910-100850567

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Abstract

Spark-assisted compression ignition (SACI) has a promising potential to substantially improve engine's fuel efficiency. To this end, two exothermic stages in SACI combustion, flame propagation and auto-ignition, need to be well organized to increase control authority of bulk ignition timing especially in lean burn. In this study, three gasoline surrogates, namely EPRF, ETPRF and TPRF, formulated through blending ethanol/toluene with primary reference fuel (PRF) and having the same research octane number (RON) and octane sensitivity (S), were used to conduct experiments in a rapid compression machine (RCM) under lean engine-relevant conditions (10–30 bar and 722–862 K). Under different ethanol blending ratios, both ethanol's synergistic effect during auto-ignition and its stronger pressure dependence of flame speed (S_(Flame)) than toluene were observed. The ethanol's synergistic effect is mainly attributed to its more HO₂ production and then faster consumption by benzyl which results in more OH radical production. As for the stronger pressure dependence of S_(Flame) of ethanol, at 722 K, it is primarily determined by the stronger pressure dependence of H radical in EPRF's flame structure rather than the promotion effect from critical reactions on S_(Flame); while at 862 K, these two factors influence the pressure dependence of S_(Flame) simultaneously. Whatever the temperature is, third-body reactions have larger impacts on ethanol's S_(Flame) than on toluene's. In this study, the relative magnitude of S_(Flame)’s pressure dependence between ethanol and toluene shows rationality at lower φ and higher T, which is in line with the pressure exponents extracted from the existing high-p laminar burning velocities of ethanol and toluene. Further verification was made in a spark-ignition engine, which showed that low-carbon alcohols, exhibited stronger pressure dependence of S_(Flame) than monophenyl aromatics in commercial gasoline, represented by toluene. The aforementioned characteristics of ethanol can be utilized under different engine loads and provide a reference in fuel design for lean SACI combustion.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.combustflame.2020.08.049DOIArticle
ORCID:
AuthorORCID
Fan, Qinhao0000-0001-6127-3852
Additional Information:© 2020 The Combustion Institute. Published by Elsevier Inc. Received 30 March 2020, Revised 28 August 2020, Accepted 28 August 2020, Available online 6 September 2020. This work was supported by National Key Research and Development Program of China (Grant No. 2017YFE0102800), National Natural Science Foundation of China (Grant No. 21761142012) and Program of State Key Laboratory of Automotive Safety and Energy of China (Grant No. ZZ2019-031). The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Group:GALCIT
Funders:
Funding AgencyGrant Number
National Key Research and Development Program of China2017YFE0102800
National Natural Science Foundation of China21761142012
Program of State Key Laboratory of Automotive Safety and Energy of ChinaZZ2019-031
Record Number:CaltechAUTHORS:20200910-100850567
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200910-100850567
Official Citation:Qinhao Fan, Zhi Wang, Yunliang Qi, Shang Liu, Xingyu Sun, Research on ethanol and toluene's synergistic effects on auto-ignition and pressure dependences of flame speed for gasoline surrogates, Combustion and Flame, Volume 222, 2020, Pages 196-212, ISSN 0010-2180, https://doi.org/10.1016/j.combustflame.2020.08.049. (http://www.sciencedirect.com/science/article/pii/S0010218020303722)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105309
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:10 Sep 2020 18:18
Last Modified:10 Sep 2020 18:18

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