Soot emissions in combustion are unwanted consequences of burning hydrocarbon fuels. The presence of soot during and following combustion processes is an indication of incomplete combustion and has several negative consequences including the emission of harmful particulates and increased operational costs. Efforts have been made to reduce soot production in combustion engines through utilizing oxygenated biofuels in lieu of traditional nonoxygenated feedstocks. The ongoing Co-Optimization of Fuels and Engines (Co-Optima) initiative from the US Department of Energy (DOE) is focused on accelerating the introduction of affordable, scalable, and sustainable biofuels and high-efficiency, low-emission vehicle engines. The Co-Optima program has identified a handful of biofuel compounds from a list of thousands of potential candidates. In this study, a shock tube was used to evaluate the performance of soot reduction of five high-performance biofuels downselected by the Co-Optima program. Current experiments were performed at test conditions between 1,700 and 2,100 K and 4 and 4.7 atm using shock tube and ultrafast, time-resolve laser absorption diagnostic techniques. The combination of shock heating and nonintrusive laser detection provides a state-of-the-art test platform for high-temperature soot formation under engine conditions. Soot reduction was found in ethanol, cyclopentanone, and methyl acetate; conversely, an α-diisobutylene and methyl furan produced more soot compared to the baseline over longer test times. For each biofuel, several reaction pathways that lead towards soot production were identified. The data collected in these experiments are valuable information for the future of renewable biofuel development and their applicability in engines.
Cyclopentanone is
a promising biofuel that can enable more efficient
engine operation and increase the fuel economy of the light duty fleet
over current and planned technology developments. While the ignition
of cyclopentanone has been investigated in detail, more studies on
the laminar burning velocities of cyclopentanone are called for. In
this work, the laminar burning velocities of cyclopentanone (C5H8O) have been measured using the heat flux and
spherical flame methods at 1 atm, equivalence ratios from 0.7 to 1.6,
and initial temperatures of 328, 353, and 428 K. To further investigate
the relationship between the molecular structure and laminar burning
velocity, identical experiments were also performed for binary mixtures
of cyclopentanone with ethanol and n-propanol at
1:1 (mol). The consistency between the experimental data sets obtained
in this work and literature data sets has been evaluated. A recently
published mechanism of cyclopentanone was used for simulation after
adopting the submechanism of n-propanol. Good agreement
has been seen between experimental and simulated results for all flames.
To qualitatively explain the characteristics of the laminar burning
velocity of cyclopentanone and the differences with those of ethanol
and n-propanol, sensitivity analysis and reaction
pathway analysis have been performed to compare the chemistry of the
fuels under flame conditions, which revealed how the molecular structure
of cyclopentanone could affect its laminar burning velocity. Compared
to ethanol and n-propanol, cyclopentanone does not
have primary carbon atoms in its molecule, leading to lower production
of methyl radicals. Meanwhile, the carbonyl group in the cyclopentanone
molecule is mostly released as CO in the decomposition of multiple
intermediates accompanied by the production of unsaturated C2 and C4 species, especially C2H4 and C2H3. Both features contribute to the
high laminar burning velocity of cyclopentanone.
Fentanyl is a potent synthetic opioid pain reliever with a high bioavailability that can be used as prescription anesthetic. Rapid identification via non-contact methods of both known and emerging opioid substances in the fentanyl family help identify the substances and enable rapid medical attention. We apply PBEh-3c method to identify vibrational normal modes from 0.01 to 3 THz in solid fentanyl and its selected analogs. The molecular structure of each fentanyl analog and unique arrangement of H-bonds and dispersion interactions significantly change crystal packing and is subsequently reflected in the THz spectrum. Further, the study of THz spectra of a series of stereoisomers shows that small changes in molecular structure results in distinct crystal packing and significantly alters THz spectra as well. We discuss spectral features of synthetic opioids with higher potency than conventional fentanyl such as ohmefentanyl and sufentanil and discover the pattern of THz spectra of fentanyl analogs.
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