A Flow Reactor Study of Neopentane Oxidation at 8 Atmospheres: Experiments and Modeling SUQING WANG, DAVID L. MILLER, and NICHOLAS P. CERNANSKY Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA 19104 HENRY J. CURRAN,* WILLIAM J. PITZ, and CHARLES K. WESTBROOK Lawrence Livermore National Laboratory, Livermore, CA 94551 An existing detailed chemical kinetic reaction mechanism for neopentane oxidation [1] is applied to new experimental measurements taken in a flow reactor [2] operating at a pressure of 8 atm. The reactor temperature ranged from 620 K to 810 K and flow rates of the reactant gases neopentane, oxygen, and nitrogen were 0.285, 7.6, and 137.1 standard liter per minute (SLM), respectively, producing an equivalence ratio of 0.3. Initial simulations identified some deficiencies in the existing model and the paper presents modifications which included upgrading the thermodynamic parameters of alkyl radical and alkylperoxy radical species, adding an alternative isomerization reaction of hydroperoxy-neopentyl-peroxy, and a multistep reaction sequence for 2-methylpropan-2-yl radical with molecular oxygen. These changes improved the calculation for the overall reactivity and the concentration profiles of the following primary products: formaldehyde, acetone, isobutene; 3,3-dimethyloxetane, methacrolein, carbon monoxide, carbon dioxide, and water. Experiments indicate that neopentane shows negative temperature coefficient behavior similar to other alkanes, though it is not as pronounced as that shown by n-pentane for example. Modeling results indicate that this behavior is caused by the -scission of the neopentyl radical and the chain propagation reactions of the hydroperoxyl-neopentyl radical. © 1999 by The Combustion Institute INTRODUCTION Preignition of hydrocarbons has been studied in internal combustion engines [3–5]. However, the detailed mechanism of preignition chemis- try, under relevant conditions ( T  1000 K, P  1 atm), is not well understood. In view of this, we have developed a program to investi- gate the detailed kinetic mechanism of hydro- carbons under these conditions. Neopentane, because of its unique molecular structure, i.e. all hydrogen atoms are equivalent with only one parent alkyl radical formed via H atom abstraction, has been the subject of several oxidation studies [6 –10]. In addition, neopen- tane does not form a C 5 conjugate olefin from its hydroperoxy-alkyl radical. Conjugate olefins have been identified as controlling intermedi- ates in the preignition process of hydrocarbons. Specifically, formation of the conjugate olefin is considered the key step in the unique phenom- enon of low- and intermediate-temperature hy- drocarbon oxidation called negative tempera- ture coefficient (NTC) behavior. During the transition from low- to intermediate-tempera- ture oxidation, the overall reactivity of the hy- drocarbon oxidation decreases as reaction tem- perature increases. In previous neopentane oxidation experiments [6, 11] cool flames of neopentane were observed, implying that neo- pentane oxidation should also exhibit NTC be- havior. In the recent experimental study of neopentane oxidation at Drexel University us- ing a pressurized flow reactor [2], NTC behavior has been confirmed. In our previous detailed modeling study [1], an intermediate-temperature oxidation mecha- nism for the combustion of neopentane was developed and compared to the experimental results of Baker et al. [9, 10]. The detailed model matched both primary and secondary products measured in those studies. However, the experiments covered a limited range of conditions: (1) the reaction temperature was constant at 753 K and (2) the pressure was subatmospheric at 0.65 atm. In the present work, simulations using the detailed neopen- tane oxidation mechanism will be compared to new experimental data with the purpose of *Corresponding author: E-mail: curran6@llnl.gov COMBUSTION AND FLAME 118:415– 430 (1999) © 1999 by The Combustion Institute 0010-2180/99/$–see front matter Published by Elsevier Science Inc. PII S0010-2180(99)00014-0