Oxidation of 2,7-Dimethyloctane and n-Propylcyclohexane in the Low to Intermediate Temperature Regime with a Pressurized Flow Reactor

摘要

The Pressurized Flow Reactor (PFR) at Drexel University was used to study the low to intermediate temperature oxidation of 2,7-Dimethyloctane (2,7-DMO)/air and n-Propylcyclohexane (n-PCH)/air. 2,7-DMO is a symmetric lightly branched alkane (an isomer of n-Decane) and n-PCH is a cycloalkane; both are possible surrogate components of their respective chemical classes commonly used for chemical kinetic model development and validation. The experimental conditions studied were: temperature of 550-850 K; pressure of 8.0 atm; residence time of 120 ms. The initial hydrocarbon mole fractions were: 843 ppm 2,7-DMO (equivalence ratio of 0.31) and 824 ppm n-PCH (equivalence ratio of 0.27). The oxidation intermediates were extracted from the PFR and then identified and quantified with a Gas Chromatograph/Flame Ionization Detector (GC/FID) coupled to a Mass Spectrometer (MS). Carbon monoxide (CO) levels were measured online to monitor fuel reactivity and map the Negative Temperature Coefficient (NTC) regime. For n-PCH oxidation NTC start was at approximately 690 K, as indicated by maximum CO and minimum O_2 mole fractions. Over 60 intermediate species were measured and carbon balances were greater than 90% for all sample temperatures. Similar intermediates were previously measured for n-Butylcyclohexane (n-BCH) oxidation which suggests that similar reaction pathways exist between n-PCH and n-BCH, as expected. For 2,7-DMO, NTC start was approximately 695 K. Overall fuel reactivity was less than n-Decane, likely resulting from the methyl group substitution. Carbon balances were higher than 70% with about 50 intermediate species measured. During the oxidation of 2,7-DMO, high levels of butene were produced near the NTC region. Lower reactivity of 2,7-DMO in comparison to n-Decane and n-BCH can be explained by the high stability of butene.