Experimental investigation of the intermediates of isooctane during ignition

Abstract

Direct measurements of intermediates of ignition are challenging experimental objectives, yet such measurements are critical for understanding fuel decomposition and oxidation pathways. In the current work, a new gas-sampling system is used to provide quantitative discrete measurements of 30 hydrocarbon and oxygenate species during rapid compression facility studies of isooctane ignition. Two target conditions and equivalence ratios (based on molar fuel to oxygen ratio) were studied (P = 5.2 atm, T = 1000 K, φ = 0.4 and P = 4.8 atm, T = 975 K , φ = 1.2). The results are compared with model predictions that use the detailed reaction mechanism developed by Curran et al. (Combust Flame 2002, 129, 253-280). In general, the model predictions are in excellent agreement with the experimental data, including several trace species. Isobutene (i-C 4 H 8 ) and propene (C 3 H 6 ) were the major olefin species identified in the experiments. The results are consistent with an intermediate temperature reaction path sequence, where isooctane is consumed by H-atom abstraction to yield isooctyl radicals that undergo β-scission to form olefin and alkyl radical species.

A chemical kinetically based ignition delay correlation for iso-octane covering a wide range of conditions including the NTC region

“…The UM-RCF also has the capability for rapid gas sampling, and chemical analysis of intermediates during the delay period of iso-octane charges has been reported in Ref. [27]. Tanaka and PRF + fuel additives was investigated, with iso-octane only being a small set of these.…”

“…Wooldridge and co-workers [27,42,50,68] at the University of Michigan (U. Michigan) used a rapid compression facility (RCF) to investigate the ignition behavior of mostly lean iso-octane charges in the intermediate temperature regime, 900-1025 K. Desired temperatures were achieved by adjusting the compression ratio of the machine and/or the composition of inert gas species (N 2 , Ar and CO 2 ). Equivalence ratios of φ = 0.2-1.0 (with some at φ = 1.98) were employed where the effective pressures ranged from 4.7-10 atm, with some up to 23 atm.…”

“…Speciation of charge gases during the delay period (in situ or off-line) is difficult and therefore only a few data sets of these types are currently available (e.g., see Refs. [26][27][28][29]). A limitation of RCMs and STs for advanced engine studies is that the working pressures have historically been restricted to below 40-50 atm (compressed pressure) (though some STs using very dilute conditions have achieved significantly higher pressures (e.g., see Ref.…”

Using rapid compression machines for chemical kinetics studies

“…Recent work has focused on primary reference fuels (PRFs), biofuels, and biofuel/PRF blends, including work with n-heptane [92], iso-octane [93], n-butanol [94], n-heptane/n-butanol blends [95], and methyl-butanoate [96]. These studies found that, although most chemical kinetic models are able to predict the ignition delay time fairly well (e.g., within 20% typically), the predictions of some species profiles deviate from those measured experimentally, and this may influence the model's ability to predict combustion features besides ignition delay time, e.g., soot formation and/or emissions.…”

Propene concentration sensing for combustion gases using quantum-cascade laser absorption near 11 μm

“…Direct measurement of propene has traditionally involved physical sampling using probes [21]. This approach is very effective at detecting many species within a single measurement.…”