Academic literature on the topic 'Iso-paraffins'

AbstractFour different analytical methods were used for the determination of (1) polybrominated diphenyl ethers (PBDE), (2) hexabromocyclododecanes (HBCDD), (3) chlorinated paraffins (CP) and (4) polychlorinated naphthalenes (PCN) in human milk samples of the WHO/UNEP-coordinated exposure studies. As a laboratory accredited according to EN ISO/IEC 17025, a comprehensive quality control program was applied to assure the reliability of results. This included procedural blanks, the use of numerous quality control samples as in-house reference materials and the participation in proficiency tests (PTs). Trueness was estimated from the PT samples using the assigned values.The mean absolute deviation of the sum parameters ∑PBDE6 and ∑PBDE7 from the assigned values of 53 PT samples analysed between 2006 and 2021 was 12% and 14%, respectively.For α-HBCDD as the most abundant diastereomer and the sum of α-, β- and γ-HBCDD, deviations of the reported value from the assigned value of the proficiency tests (31 samples, analysed between 2007 and 2021) were in most cases below 40% over a large concentration range, e.g., for α-HBCDD, between 0.0084 and 19 ng/g fw. For concentrations above 0.5 ng/g lipid, the deviation was in the range of approximately 0–30%.For short-chain and medium-chain CP (SCCP and MCCP) all z-scores achieved in interlaboratory comparisons during 2017–2020 were within ±2 z and therefore satisfactory (13 PT samples were analysed for ΣCP, ΣSCCP and ΣMCCP using the GC-ECNI-Orbitrap-HRMS method, eight results achieved for ΣCP using the GC-EI-MS/MS method).Due to the lack of available proficiency tests for PCN at the time of measuring the human milk samples of the 2016–2019 period, an external validation for control of the trueness was performed through an interlaboratory comparison with an independent laboratory. The deviation of the ΣPCN13 in five test samples between the external laboratory and CVUA Freiburg was in the range from 3 to 20%. At a later stage (in 2021), the laboratory participated successfully in the first interlaboratory comparison study on PCN congeners in cod liver oil. The z-scores for seven congeners and two sum parameters were within ±2 z and therefore satisfactory. Also, the results for other of the altogether 26 PCN congeners were in accordance with the median values reported by all participants.As a result, the determination of PBDE, HBCDD, CP and PCN in human milk samples of the WHO/UNEP-coordinated exposure studies followed the strict rules of the accreditation system and the general criteria for the operation of testing laboratories as laid down in EN ISO/IEC 17025.

After searching the literature and making predictions based on theory without getting sufficient satisfactory results, the next move would be to make estimates. We need the property y of substances pi from a population P that has not been investigated and reported in the literature. Fortunately, there exists a subset S of P that has been investigated, and we have the values for the property y. For instance, we may want the boiling points of all the hydrocarbons, but we have only the boiling points of the normal paraffins from 1 to 20 carbon atoms. Can we use this piece of information on normal paraffins to estimate the boiling points for the rest of the hydrocarbon population? How much effort would be involved and how accurate would the results be? The number of isomers of paraffin is very large; see table 5.1. We see that the iso-paraffins are not as well investigated as the normal paraffins. We have the boiling points of all three isomers of pentane, but not the 75 isomers of decane. It is inevitable that we have to resort to estimations. When we have obtained a good correlation for normal paraffins, we would naturally want to know if we can extend this to the branched paraffins, and onward to the population of all the saturated hydrocarbons (by including the cyclic paraffins), and onward to the population of all hydrocarbons (by including olefins, acetylenes, and aromatic compounds), and then onward to the population of all organic compounds (by including compounds with heteroatoms, such as O, N, Cl). A correlation that applies accurately to a larger domain is more useful than one that works only for a smaller domain. Another example is polychlorinated biphenyls (PCBs), which have 10 hydrogen atoms that can be substituted by chlorine atoms. There are three types of site: the four α sites near the bridge between the two phenyl fragments, the four β sites farther away from the bridge, and the two γ sites that are the farthest away from the bridge. The number of isomers is shown in table 5.2.

Ignition delay times of a “real” synthetic jet fuel (S8) were measured using an atmospheric pressure flow reactor facility. Experiments were performed between 900 K and 1200 K at equivalence ratios from 0.5 to 1.5. Ignition delay time measurements were also performed with JP8 fuel for comparison. Liquid fuel was prevaporized to gaseous form in a preheated nitrogen environment before mixing with air in the premixing section, located at the entrance to the test section of the flow reactor. The experimental data show shorter ignition delay times for S8 fuel than for JP8 due to the absence of arom

Abstract The development of advanced reaction models to predict pollutant emissions in aero-engine combustors usually relies on surrogate formulations of a specific jet fuel for mimicking its chemical composition. 1,3,5-trimethylbenzene is one of the suitable components to represent aromatics species in those surrogates. However, a comprehensive reaction model for 1,3,5-trimethylbenzene combustion requires a mechanism to describe the m-xylene oxidation. In this work, the development of a chemical kinetic mechanism for describing the m-xylene combustion in a wide parameter range (i.e. temperatu

Abstract Machine learning based predictive models are being extensively applied for predicting combustion properties like derived cetane number (DCN), which is the measure of a fuels ignition quality. In the present work, a comprehensive model was developed using artificial neural networks (ANN) that can predict the DCN of fuels containing a large number of chemical classes like paraffins, iso-paraffins, olefins, naphthenes, aromatics, alcohols, ethers, aldehydes, ketones and esters. Experimental DCN’s of 275 fuels was used as a dataset and the composition of the fuels expressed in the form of

Blowoff sets important operational limits on a combustor system. While blowoff is intrinsically a system-dependent phenomenon, it is also dependent on the chemical and physical properties of the fuel. This paper describes an experimental study of the lean blowout limits of eight liquid fuels in a swirl-stabilized combustor, with data for both a pressure atomizer and an airblast atomizer. Three of the fuels were traditional jet fuels (an average Jet-A, JP-5, and JP-8) and the remaining five fuels spanned a range of physical and kinetic properties. These experiments were performed at a combustor

Abstract With aviation’s dependence on the high volumetric energy density offered by liquid fuels, Sustainable Aviation Fuels (SAFs) could offer the fastest path towards the decarbonization of aircrafts. However, the chemical properties of SAFs present new challenges, and research is needed to better understand their injection, combustion and emission processes. While efforts such as the United States National Jet Fuel Combustion Program (NJFCP) that investigated several aspects in detail, certain processes were unfortunately beyond the reach of this program. One of them in particular is about