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Title:Autoignition study of next generation aviation fuels and components
Author(s):Min, Kyungwook
Director of Research:Lee, Tonghun
Doctoral Committee Chair(s):Lee, Tonghun
Doctoral Committee Member(s):Matalon, Moshe; Glumac, Nick; Hansen, Alan Christoper
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
alternative fuel
ignition delay
rapid compression machine
shock tube
Abstract:Addressing the energy crisis motivates our society to develop alternative sources of energy beyond fossil fuels. Alternative fuels from various feedstocks have undergone diverse pathways and have unique physical properties and chemical compositions compared to conventional fuels. Deviation in chemical composition and structure could result in different combustion performance, especially in the low temperature regime. This study is focused on evaluating the reactivity of diverse alternative fuels and related hydrocarbon components by investigating their ignition delay times at various autoignition conditions. Complex multistage ignition behavior of fuels at specific conditions are further evaluated with rapid compression machine (RCM) experimental results and CHEMKIN chemical mechanism simulations. A newly constructed shock tube is also utilized to extend experimental temperature conditions to the negative temperature coefficient (NTC) regime and higher temperatures. Category A fuels, designated in the National Jet Fuel Combustion Program, are the set of fuels that represent conventional aviation fuels in commercial and military applications. Ignition delay times of three category A fuels —Jet A-1, Jet A-2 and Jet A-3— have been measured in the heated RCM at compressed pressure Pc=20 bar, Tc=620 ~ 730 K, and equivalence ratio, ϕ, of 1.0, 0.5 and 0.25. The set of test results have been used as reference data to be compared with alternative fuels, relevant pure hydrocarbon species, and specific fuel blends. Alternative candidate fuels, relevant hydrocarbon species, and their blends that are out of jet fuel standards and not comprehensively evaluated in combustion behavior are categorized as C fuels. Category C fuels are tested at similar test conditions. C-1, also known as Gevo ATJ (Alcohol to Jet fuels), is comprised of two heavily branched alkanes; isododecane and isocetane. Due to this irregular composition, the fuel has an extremely low cetane number (~16), and an extensively long ignition delay time at most of the tested conditions. During extended period of ignition delay, multistage ignition phenomena have been more readily and frequently observed compared to other conventional jet fuels. Detailed analysis on this two-stage ignition behavior has been conducted by separating first and second stage ignition delay time. Further investigation on detailed chemical kinetics and temperature analysis using CHEMKIN simulation is planned, along with optical diagnostics for real time temperature measurements. Once the unique behavior of heavily branched species in Gevo ATJ fuel was observed, further examination on contribution of distinct chemical structure to autoignition reactivity was pursued. Normal alkanes, iso-alkanes, cycloalkanes, and aromatics are the four chemical structural groups that mainly comprise most of the transportation fuels. Five pure hydrocarbon species have been selected to represent each chemical structural group (two isomers of branched alkane have different degree of branching) and have been tested in the RCM as well. Along with octane rating, cetane number (or index) is a fuel property that directly represents the reactivity of the fuels. To isolate the contribution of cetane number to the autoignition propensity, six control fuels have been specifically formulated, with varying cetane numbers from 30 to 55, incremented by 5. Overall ignition delay time measurement results appear to follow general cetane number and reactivity relations, whereas first stage ignition delay times are observed to be relatively insensitive to cetane number. Test results on varied cetane number fuels are compared and matched with ongoing Gevo ATJ / F-24 fuel blend testing, along with additional investigations on multistage ignition behavior and intermediate state temperature analysis. Overall test results and observations will be crucial assets to the combustion research community, providing valuable and novel experimental data for alternative fuel development. Reactivity study on cetane number of fuels will be specifically relevant to practical applications such as knock studies of intermittent combustion engines or lean blow out performance of turbine engines.
Issue Date:2020-05-08
Rights Information:© 2020 Kyungwook Min
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05

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