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Title:Surrogate modeling of alternative jet fuels for study of autoignition characteristics
Author(s):Oldani, Anna
Advisor(s):Lee, Tonghun
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Alternative Jet Fuels
Rapid Compression Machine
Surrogate Models
Abstract:Recently published surrogate models are evaluated for their predictive capabilities of autoignition characteristics for alternative jet fuels. Computational simulation results are compared with published data from experimental rapid compression machine (RCM) tests for conventional jet fuel. Evaluation of these surrogate models aids in identifying differences in chemical kinetics mechanisms, helping to establish model validity across operating conditions of interest. This work incorporates two chemical kinetics solver programs: CANTERA and CHEMKIN-PRO®. The former is an open-source, object oriented chemical solver with capabilities for a range of reacting flow systems. CHEMKIN-PRO®, produced by Reaction Design, is a commercially available chemical solver. Together, these two programs are used to evaluate autoignition characteristics at compressed pressures, Pc, of 5, 10, and 20 bar and equivalence ratios, Φ, of 0.25, 0.5, 0.75, and 1.0 in air, representing lean to stoichiometric conditions. A discussion on available alternative jet fuels is provided, focusing on bio-based jet fuels, derived from plant (camelina seed) or animal (tallow) sources. These fuels are referred to as hydrotreated renewable jet (HRJ) fuels, also termed hydroprocessed esters and fatty acids (HEFA). HRJ fuels compared with traditional jet fuel, both commercial and military, have higher paraffinic and lower aromatic content. Surrogate models currently available focus on several components including n-decane, n-dodecane, 2-methylundecane, and 1,2,4-trimethylbenzene. Two chemical kinetic mechanisms are evaluated: the Ranzi mechanism from the CRECK modeling group at Politecnico di Milano and the Aachen mechanism from the Institut für Technische Verbrennung at Aachen University. The models are evaluated using two component surrogates for jet fuels, containing varying amounts of n-decane and 1,2,4-trimethylbenzene. Earlier published surrogate models are more complex, including anywhere from four to more than ten different components. The two component surrogate models were chosen for their simplicity, allowing for clearer control of reactive species by adjusting the volume percentage of components. This enables assessment of the ability for various mixtures to accurately capture the ignition behavior of the jet fuels. Simulations results indicate at what conditions surrogate fuel models can provide valid predictions in agreement with experimental data. From the results, it can be concluded that the Aachen mechanism is more appropriate for stoichiometric mixture predictions at higher compressed pressures, while the Ranzi mechanism is accurate in capturing lean mixture ignition features but does not match observed ignition times. Future mechanism model validation will then lead to the development of optimized next generation alternative fuels. Continuing this work to understand the roles chemical features play in influencing a fuel’s ignition characteristics will facilitate the development of surrogate models. These more robust models can then be used to examine alternative jet fuel performance at target engine operating conditions.
Issue Date:2014-05-30
Rights Information:Copyright 2014 Anna Oldani
Date Available in IDEALS:2014-05-30
Date Deposited:2014-05

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