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Title: Premixed ignition behavior of C{sub 9} fatty acid esters: A motored engine study

Abstract

An experimental study on the premixed ignition behavior of C{sub 9} fatty acid esters has been conducted in a motored CFR engine. For each test fuel, the engine compression ratio was gradually increased from the lowest point (4.43) to the point where significant high temperature heat release (HTHR) was observed. The engine exhaust was sampled and analyzed through GC-FID/TCD and GC-MS. Combustion analysis showed that the four C{sub 9} fatty acid esters tested in this study exhibited evidently different ignition behavior. The magnitude of low temperature heat release (LTHR) follows the order, ethyl nonanoate > methyl nonanoate >> methyl 2-nonenoate > methyl 3-nonenoate. The lower oxidation reactivity for the unsaturated fatty acid esters in the low temperature regime can be explained by the reduced amount of six- or seven-membered transition state rings formed during the oxidation of the unsaturated esters due to the presence of a double bond in the aliphatic chain of the esters. The inhibition effect of the double bond on the low temperature oxidation reactivity of fatty acid esters becomes more pronounced as the double bond moves toward the central position of the aliphatic chain. GC-MS analysis of exhaust condensate collected under the engine conditions where onlymore » LTHR occurred showed that the alkyl chain of the saturated fatty acid esters participated in typical paraffin-like low temperature oxidation sequences. In contrast, for unsaturated fatty acid esters, the autoignition can undergo olefin ignition pathways. For all test compounds, the ester functional group remains largely intact during the early stage of oxidation. (author)« less

Authors:
; ;  [1]
  1. EMS Energy Institute, The Pennsylvania State University, University Park, PA 16802 (United States)
Publication Date:
OSTI Identifier:
21177445
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 156; Journal Issue: 6; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CARBOXYLIC ACID ESTERS; COMBUSTION; DIESEL FUELS; PRESSURE RANGE KILO PA; AUTOIGNITION; HEAT; ENGINES; TEMPERATURE RANGE 0400-1000 K; BIOFUELS; QUANTITATIVE CHEMICAL ANALYSIS; COMBUSTION PROPERTIES; COMPRESSION RATIO; ACTIVATION ENERGY; INHIBITION; Low-temperature heat release; High- temperature heat release; Low-temperature oxidation; Motored engine

Citation Formats

Zhang, Yu., Yang, Yi, and Boehman, Andre L.. Premixed ignition behavior of C{sub 9} fatty acid esters: A motored engine study. United States: N. p., 2009. Web. doi:10.1016/J.COMBUSTFLAME.2009.01.024.
Zhang, Yu., Yang, Yi, & Boehman, Andre L.. Premixed ignition behavior of C{sub 9} fatty acid esters: A motored engine study. United States. doi:10.1016/J.COMBUSTFLAME.2009.01.024.
Zhang, Yu., Yang, Yi, and Boehman, Andre L.. Mon . "Premixed ignition behavior of C{sub 9} fatty acid esters: A motored engine study". United States. doi:10.1016/J.COMBUSTFLAME.2009.01.024.
@article{osti_21177445,
title = {Premixed ignition behavior of C{sub 9} fatty acid esters: A motored engine study},
author = {Zhang, Yu. and Yang, Yi and Boehman, Andre L.},
abstractNote = {An experimental study on the premixed ignition behavior of C{sub 9} fatty acid esters has been conducted in a motored CFR engine. For each test fuel, the engine compression ratio was gradually increased from the lowest point (4.43) to the point where significant high temperature heat release (HTHR) was observed. The engine exhaust was sampled and analyzed through GC-FID/TCD and GC-MS. Combustion analysis showed that the four C{sub 9} fatty acid esters tested in this study exhibited evidently different ignition behavior. The magnitude of low temperature heat release (LTHR) follows the order, ethyl nonanoate > methyl nonanoate >> methyl 2-nonenoate > methyl 3-nonenoate. The lower oxidation reactivity for the unsaturated fatty acid esters in the low temperature regime can be explained by the reduced amount of six- or seven-membered transition state rings formed during the oxidation of the unsaturated esters due to the presence of a double bond in the aliphatic chain of the esters. The inhibition effect of the double bond on the low temperature oxidation reactivity of fatty acid esters becomes more pronounced as the double bond moves toward the central position of the aliphatic chain. GC-MS analysis of exhaust condensate collected under the engine conditions where only LTHR occurred showed that the alkyl chain of the saturated fatty acid esters participated in typical paraffin-like low temperature oxidation sequences. In contrast, for unsaturated fatty acid esters, the autoignition can undergo olefin ignition pathways. For all test compounds, the ester functional group remains largely intact during the early stage of oxidation. (author)},
doi = {10.1016/J.COMBUSTFLAME.2009.01.024},
journal = {Combustion and Flame},
number = 6,
volume = 156,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2009},
month = {Mon Jun 15 00:00:00 EDT 2009}
}
  • Autoignition of two biodiesel surrogates, methyl heptanoate and ethyl hexanoate, was studied in a motored CFR engine at an equivalence ratio of 0.25 and an intake temperature of 155 C. The engine compression ratio was gradually increased from the lowest point (4.43) to the point where significant high temperature heat release (HTHR) occurred. Within the test range of this work, both of the two esters exhibited evident cool flame behavior. At the same compression ratio, methyl heptanoate was observed to have both an earlier onset and a higher magnitude of low temperature heat release (LTHR) than ethyl hexanoate, indicating thatmore » methyl heptanoate is more reactive in the low temperature region than ethyl hexanoate. GC-MS analyses of the reaction intermediates from the oxidation of the two esters showed that the alkyl chain of fatty acid esters experiences the typical paraffin-like low temperature oxidation sequence. Based on the observations from GC-MS analyses, major low temperature oxidation pathways of ethyl hexanoate are proposed in this work. Also, it is observed that the abstraction of H-atoms on the {alpha}-carbon of the ester carbonyl group plays an important role in the oxidation of fatty acid esters. In addition, the identification of hexanoic acid among the reaction intermediates from low temperature oxidation of ethyl hexanaoate together with the observation of more fuel carbon being converted to C{sub 2}H{sub 4} during ethyl hexanoate oxidation than during methyl heptanoate oxidation provide evidence for the existence of the six-centered unimolecular elimination reaction during low temperature oxidation of ethyl esters. (author)« less
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