Autoignition behavior of gasoline/ethanol blends at engine-relevant conditions

Abstract
Ethanol is an attractive oxygenate increasingly used for blending with petroleum-derived gasoline yielding beneficial combustion and emissions behavior for a range of internal combustion engine schemes, including stoichiometric spark-ignition and low temperature combustion (LTC). As such, it is important to fundamentally understand the autoignition behavior of gasoline/ethanol blends. This work utilizes a rapid compression machine (RCM) and a homogeneous charge compression ignition (HCCI) engine to experimentally quantify changes in fuel reactivity, through ignition delay times and preliminary heat release, for blends of 0 to 30% vol./vol. into a full boiling range research gasoline (FACE-F). Diluted/stoichiometric and undiluted/fuel-lean conditions are explored covering a wide range of compressed temperatures and pressures relevant to conventional and advanced, gasoline combustion engines. Detailed chemical kinetic modeling is undertaken using a recently updated gasoline surrogate model in conjunction with a five-component surrogate to model the RCM experiments and provide chemical insight into the perturbative effects of ethanol on the autoignition process. The diluted/stoichiometric RCM measurements reveal that within the low-temperature regime ethanol retards first-stage and main ignition delay times, and suppresses both the rates and extents of low-temperature heat release (LTHR), while within the intermediate-temperature regime ethanol only causes slight changes. Good agreement of ignition delay time and preliminary heat release prediction is found between model and experimental results. Sensitivity and flux analyses further show that ethanol blending effects are dominated by the competition between the H-atom abstraction from ethanol and other fuel components by OH radical at low temperatures, and by HO2 radical at intermediate temperatures. These findings are consistent across both fuel loading conditions explored in this study. In addition, when HCCI engine experiments are mapped onto undiluted/lean RCM measurements under a constant combustion phasing scenario, good correspondence between the two apparatuses is observed for LTHR and start of high-temperature heat release. The current study highlights the importance of characterizing LTHR in predicting fuel behaviors in high-boost/low-temperature engines, and demonstrates that RCM experiments can provide an alternative, and more-efficient avenue for such characterization.

Citation
Cheng, S., Kang, D., Fridlyand, A., Goldsborough, S. S., Saggese, C., Wagnon, S., … Vuilleumier, D. (2020). Autoignition behavior of gasoline/ethanol blends at engine-relevant conditions. Combustion and Flame, 216, 369–384. doi:10.1016/j.combustflame.2020.02.032

Acknowledgements
This manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory, a U.S. Department of Energy Office of Science laboratory, under Contract No. DE-AC02-06CH11357. The work at LLNL was performed under Contract DE-AC52-07NA27344. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The DOE will provide public access in accordance with http://energy.gov/downloads/doe-public-access-plan. This work performed under auspices of the Office of Energy Efficiency and Renewable Energy, Office of Vehicle Technology, Gurpreet Singh, Leo Breton, Michael Weismiller and Kevin Stork as program managers. The work at the University of California Berkeley was partially supported by NSF/DOE Award No. CBET-1258653 entitled “Advancing Low Temperature Combustion and Lean Burning Engines for Light- and Heavy-Duty Vehicles with Microwave Assisted Spark Plugs and Fuel Stratification.”, The authors acknowledge the assistance of Dr. Jeffrey Santner, Dr. Toby Rockstroh and Mr. Tim Rutter for their efforts to maintain and operate ANL's tpRCM. Prof. S. Mani Sarathy (KAUST) is acknowledged for providing the FACE-F gasoline to ANL and UCB.

Publisher
Elsevier BV

Journal
Combustion and Flame

DOI
10.1016/j.combustflame.2020.02.032

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S001021802030095X

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