Michael P. Burke

Auto-generates LMR-R reactions (and mechanisms) from a user-provided chemical input file. Contains first edition of third-body efficiency database, which will be expanded in future versions.

Chemical kinetic coupling effects between NH 3 and liquid hydrocarbon fuels on extinction limits of diffusion flames are experimentally and numerically investigated. Three n-alkanes (n-heptane, n-decane, and n-dodecane), isooctane as a representative fully branched isoalkane, and toluene as a representative mono-aromatic are each tested, along with their blends with NH 3 . The measured extinction strain rates are analyzed, employing transport-weighted enthalpy and radical index to demonstrate relative changes of chemical kinetic potentials for each fuel evaluated. The results show a significantly lower chemical kinetic potential for NH 3 , compared to hydrocarbon fuels. Comparison of extinction limits as a function of transport-weighted enthalpy multiplied by radical index for fuel/NH 3 mixtures shows potential promotive effects for n-alkanes and no significant coupling for isooctane and toluene. Planar laser-induced fluorescence is applied to quantify OH concentrations for n-heptane, isooctane, and their mixtures with NH 3 , and data are modeled to test the fidelity of chemical kinetic model predictions. It is found that including interaction reactions of n-alkyl and isoalkyl fragments with NH 2 , and the reactions involving methylamine and cyanide are critical to predicting OH production rates, as well as extinction limits for hydrocarbon/NH 3 blends. Promotive effects of NH 3 blending on n-alkanes diffusion flame extinction limits are primarily from higher flame temperatures due to the reduced fraction of CO 2 found in the flame products. In the case of isooctane blended with NH 3 , the formation of two main isoalkyl fragments, CH 3 and C 3 H 6 , are found to interact with NH 2 , resulting in the suppression of the reactive radical pool population and kinetic inhibition. A significantly weaker reactive radical pool in toluene oxidation leads to more significant inhibitive kinetic coupling from NH 3 -related reactions.

With growing desire to destroy per- and poly-fluoroalkyl substances (PFAS) now known to be detrimental to human health, a sound understanding of fluorocarbon combustion chemistry is important to efficient thermal destruction within incinerators. While most fluorocarbon combustion models and the sets of reactions contained within them were originally developed for the high temperatures encountered in flame suppression applications, they have often been used to assess PFAS destruction in incinerators, which emphasize a lower range of temperatures. We present results that demonstrate that low-temperature fluorocarbon oxidation pathways—not yet known to play a role in fluorocarbon combustion—impact key incinerator performance metrics, including: PFAS surrogate mole fractions, products of incomplete destruction, and waste destruction efficiencies. The results further point to the utility of NO as a potential additive. The present results show the influence of these pathways for CF3O2, for which some data are available, but analogous pathways would also occur for other fluoroalkylperoxy radicals, for which little is known. The results demonstrate the need for future work to identify and characterize low-temperature pathways more generally, consider such pathways in kinetic model development, and experimentally probe intermediate temperature conditions to better understand, design, and control thermal destruction technologies for improved PFAS management.

Achieving minimal levels of nitrogen oxides (NO x ) during combustion is a major constraint in the design of advanced high-efficiency engines. NO x can be formed during combustion of any fuel—including those without fuel-bound nitrogen—in air, where radicals can attack molecular nitrogen (N 2 ) present in air to break the strong N N bond to ultimately form NO x . Paramount to the goal of minimizing NO x formation is knowledge of the fundamental routes by which the strong N N bond in N 2 can be broken. Historically, there have been four known routes for breaking the strong N N bond in N 2 to ultimately form NO x . We have recently posited that another route—mediated by an HNNO intermediate—may also play a role, particularly at the high pressures and low peak temperatures relevant to high-efficiency, low-NO x engines. Our previous theoretical and modeling studies show HNNO to be a major product of the N 2 O + H reaction at high pressures and low temperatures; once formed, HNNO is likely to react with radicals in barrierless reactions that would occur quickly and with high NO x yields. In the present paper, we report measurements of H 2 , O 2 , H 2 O, N 2 O, NO, NO x , and NH 3 in jet-stirred reactor experiments for an H 2 /O 2 /N 2 O/NO/N 2 /Ar mixture that specifically target HNNO pathways. Importantly, we observe significant formation of NO and NH 3 —both of which provide signatures of the HNNO mechanism that are not predicted by previous models without it. Flame simulations using a new sub-model describing pressure-dependent formation and consumption of HNNO show these pathways to be among the most prominent formation routes at high pressures and low peak temperatures. However, exact quantification of the role of HNNO in NO x formation and quantitative predictions of NO x in general require more accurate rate constants for both HNNO pathways and mixture rules for pressure-dependent reactions.

Recent high-level theoretical calculations predict a mild temperature dependence for HO 2 + HO 2 inconsistent with state-of-the-art experimental determinations that upheld the stronger temperature dependence observed in early experiments. Via MultiScale Informatics analysis of the theoretical and experimental data, we identified an alternative interpretation of the raw experimental data that uses HO 2 + HO 2 rate constants nearly identical to theoretical predictions─implying that the theoretical and experimental data are actually consistent, at least when considering the raw data from experimental studies. Similar analyses of typical signals from low-temperature experiments indicate that an HOOOOH intermediate─identified by recent theory but absent from earlier interpretations─yields modest effects that are smaller than, but may have contributed to, the scatter in data among different experiments. More generally, the findings demonstrate that modern chemical theories and experiments have progressed to a point where meaningful comparison requires joint consideration of their data simultaneously.