iso-Octane (2,2,4-trimethylpentane) is a primary reference fuel and an important component of gasoline fuels. Moreover, it is a key component used in surrogates to study the ignition and burning characteristics of gasoline fuels. This paper presents an updated chemical kinetic model for iso-octane combustion. Specifically, the thermodynamic data and reaction kinetics of isooctane have been reassessed based on new thermodynamic group values and recently evaluated

Colloquium: REACTION KINETICS / INTERNAL COMBUSTION ENGINES Word Count (Method 1): The total word count (exclusive of title page, abstract) is: 5793 words Word Count (Performed from automatic counting function in MS Word plus References/Tables/Equations/ Figures) Abstract: 235 words, not included in word count Equations: 0 words (0 equations, single column) Figures: 1030 words (4 figures with captions) 3 single 50(+10) 132 4 double 52(+10) 273 Captions 116 Total: 6055 words Supplemental Materials: One supplemental material is available. AbstractMulti-stage heat release is an important feature of hydrocarbon auto-ignition that influences engine operation. This work presents findings of previously unreported three-stage heat release in the autoignition of n-heptane/air mixtures at lean equivalence ratios and high pressures. Detailed homogenous gas-phase chemical kinetic simulations were utilized to identify conditions where two-stage and threestage heat release exist. Temperature and heat release profiles of lean n-heptane/air auto-ignition display three distinct stages of heat release, which is notably different than two-stage heat release typically reported for stoichiometric fuel/air mixtures. Concentration profiles of key radicals (HO2 and OH) and intermediate/product species (CO and CO2) also display unique behavior in the lean autoignition case. Rapid compression machine measurements were performed at a lean equivalence ratio to confirm the existence of three-stage heat release in experiments. Laser diagnostic measurements of CO concentrations in the RCM indicate similar concentration-time profiles as those predicted by kinetic modeling. Computational singular perturbation was then used to identify key reactions and species contributing to explosive time scales at various points of the three-stage ignition process.Comparisons with two-stage ignition at stoichiometric conditions indicate that thermal runaway at the second stage of heat release is inhibited under lean conditions. H+O2 chain branching and CO oxidation reactions drive high-temperature heat release under stoichiometric conditions, but these reactions are suppressed by H, OH, and HO2 radical termination reactions at lean conditions, leading to a distinct third stage of heat release.

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Gasoline anti-knock quality, defined by the research and motor octane numbers (RON and MON), is important for increasing spark ignition (SI) engine efficiency. Gasoline knock resistance can be increased using a number of blending components. For over two decades, ethanol has become a popular anti-knock blending agent with gasoline fuels due to its production from bio-derived resources. This work explores the oxidation behavior of two oxygenated certification gasoline fuels and the variation of fuel reactivity with molecular composition. Ignition delay times of Haltermann (RON = 91) and Coryton (RON = 97.5) gasolines have been measured in a high-pressure shock tube and in a rapid compression machine at three pressures of 10, 20 and 40 bar, at equivalence ratios of φ = 0.45, 0.9 and 1.8, and in the temperature range of 650-1250 K. The results indicate that the effects of fuel octane number and fuel composition on ignition characteristics are strongest in the intermediate temperature (negative temperature coefficient) region. To simulate the reactivity of these gasolines, three kinds of surrogates, consisting of three, four and eight components, are proposed and compared with the gasoline ignition delay times. It is shown that more complex surrogate mixtures are needed to emulate the reactivity of gasoline with higher octane sensitivity (S = RON-MON). Detailed kinetic analyses are performed to illustrate the dependence of gasoline ignition delay times on fuel composition and, in particular, on ethanol content.

The thermal decomposition of formic acid (HCOOH) and acetic acid (CH 3 COOH), two carboxylic acids which play an important role in oxygenate combustion chemistry, were investigated behind reflected shock waves using laser absorption. The rate constants of the primary decomposition pathways of these acids:were measured using simultaneous infrared laser absorption of CO, CO 2 and H 2 O at wavelengths of 4.56, 4.18 and 2.93 microns, respectively. Reaction test conditions covered temperatures from 1230 to 1821 K and pressures from 1.0 to 6.5 atm for dilute mixtures of acids (0.25 -0.6%) in argon. The rate constants of dehydration (R1) and decarboxylation (R2) reactions of formic acid were calculated by fitting exponential functions to the measured CO, CO 2 and H 2 O time-history profiles. These two decomposition channels were found to be in the fall-off region and have a branching ratio, ! ! , of approximately 20 over the range of pressures studied here. The best-fit Arrhenius expressions of the first-order rates of R1 and R2were found to be:! 6.5 atm = 9.12 ×10 !" exp −30275 s -1 (±32%)The rate constants for acetic acid decomposition were obtained by fitting simulated profiles, using an acetic acid pyrolysis mechanism, to the measured species time-histories. The branching ratio, ! ! , was found to be approximately 2. The decarboxylation and dehydration reactions of acetic acid appear to be in the falloff region over the tested pressure range:! 1 atm = 3.18×10 !! ×exp −28679 s -1 (±30%)! 6 atm = 3.51×10 !" ×exp −31330 s -1 (±26%)! 1 atm = 7.9 ×10 !! exp −29056 s -1 (±34%).! 6 atm = 6.34×10 !" ×exp −31330 s -1 (±31%).

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 The effect of geometrical variations in jet-stirred reactors (JSRs) on mixing is studied.  Monitoring the exit concentration of a tracer using laser absorption spectroscopy collects residence time distribution data.

Towards simultaneous calibration-free and ultra-fast sensing of temperature and species in the intrapulse mode KAUST Repository Abstract:We report on exploiting the down-chirp phenomenon seen in quantum cascade lasers (QCLs), when modulated with long pulses, for the purpose of performing calibration-free and temporally resolved measurements. Intrapulse spectra of a native species (e.g. H 2 O), common to combustion environments, were generated near λ=7.62 µm at repetition rates as high as 3.125 MHz. Two-line absorption spectroscopy was employed to infer calibration-free temperature from the chirp-induced intrapulse spectra. In this study, such temperature measurements were limited to rates of 250 kHz due to spectral distortion at higher repetition rates. We demonstrate the ease at which accurate temperatures and H 2 O compositions can be achieved using simple and compact QCLs operated in the intrapulse mode. The sensor is also applicable to other species, and has the potential to be integrated into commercial technologies.