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Biomass derived chemicals may offer sustainable alternatives to petroleum derived hydrocarbons, while also enhancing engine combustion performance with co-optimization of fuels and engines. This paper presents a numerical study on the oxidation and combustion of a novel biofuel compound, cyclopentanol. Its reaction kinetics and thermochemistry are first explored using ab initio quantum chemistry methods. Thermochemical properties are calculated for cyclopentanol and a set of its key oxidation intermediates. C-H bond dissociation energies of cyclopentanol are computed for different carbon sites. For the fuel radicals, the energy barriers of their ring-opening reactions and the potential energy surfaces of their oxidation reactions are determined. Based on the theoretical results, a chemical kinetic mechanism is proposed to describe the oxidation of cyclopentanol at low and high temperatures. The model is compared against data obtained from shock tube, rapid compression machine, combustion vessel, and counterflow burner experiments over a range of initial conditions. Furthermore, reaction pathway analysis is performed using the present mechanism to give insights into the underlying oxidation chemistry of cyclopentanol. It is found that the α-radical of cyclopentanol undergoes preferably an alcohol-specific HO2 elimination reaction to form stable cyclopentanone and this reaction can strongly retard reactivity. The major reaction pathways of β- and γ-radicals are similar to those of cyclopentyl radicals that are the sequential and formally direct reactions of fuel radicals with O2 to form cyclopentenols and HO2 radicals. The existence of the hydroxy moiety affects the bond dissociation energies and reaction barriers, slightly favoring the chain-branching channel for γ-radicals at low temperatures.

In this study (Part II), the oxidation of dimethoxymethane (DMM) is investigated and a detailed chemical reaction model developed for a comprehensive description of both high- and low-temperature oxidation processes. The sub-mechanism of DMM is implemented using AramcoMech2.0 as the base mechanism. Rate coefficients are based on analogies with those for dimethyl ether, diethyl ether, and n-pentane oxidation. Furthermore, theoretical studies from recent works are also included in the present model and new calculations for the dissociation kinetics of Q ˙ OOH radicals have been carried out at the CCSD(T)/CBS(aug-cc-pVXZ; X = D, T) // B2PLYP-D3/6-311 + + G(d,p) level of theory. For validation, new ignition delay time experiments have been performed in a shock tube (ST), a rapid compression machine (RCM), and in a laminar flow reactor covering a wide range of conditions (p = 1–40 bar, T = 590–1215 K, φ = 1). In addition, the kinetic model is validated against laminar burning velocities, jet-stirred reactor, plug flow reactor and further ST and RCM experimental datasets from the literature. Pathway and sensitivity analyses were used to identify critical reaction pathways in the DMM oxidation mechanism. These show that the reactivity of DMM at intermediate temperatures is controlled by the branching between pathways initiated on the primary or secondary fuel radical. While primary fuel radicals eventually lead to chain branching, secondary fuel radical consumption is controlled by fast β-scission over a wide range of temperatures, which inhibits reactivity.

Diethoxymethane (DEM) is a promising oxygenated fuel and fuel additive, which has similar positive combustion characteristics as dimethoxymethane. DEM contains C-C bonds and can form ethylene via beta-scission, which potentially increases its sooting tendency. Since DEM is rarely studied, however, kinetic modeling attempts are forced to rely on rate constant analogies. Therefore, we employ high level CCSD(T)/aug-cc-pV(T+D)Z//B2PLYPD3BJ/6-311++(d,p) theory along with transition state theory to predict reaction rate constants for H-abstraction by H and CH3 and the subsequent unimolecular reactions. We further prove that the DLPNO approximation to CCSD(T) leads to a deviation of less than 0.25 k/mol in barrier heights for the presently studied open-shell electronic structures and use it for the prediction of reaction rate constants for H-abstraction by C2H5 radicals. We find that H-abstraction by ethyl radicals might denote a significant pathway, which should not be neglected in kinetic modeling studies of DEM. It is also shown that reaction pathways leading to ethylene formation are of minor importance and give thereby a first insight into the fate of the C-C bonds. To the best of our knowledge, this study represents the first high-level ab-initio study of DEM, which makes the reaction kinetics and thermochemistry data provided by this study vital for future comprehensive kinetic modeling of DEM. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Functional microgels are novel materials, which can potentially be used for diverse applications such as drug delivery. Among other material properties, the radial cross-linker profile is of special importance to ensure desired product functionality. However, in the system under investigation, only a high cross-linker fraction in the center and a low cross-linker fraction in the shell is obtained in batch synthesis due to the fast reaction kinetics of the cross-linker. Other radial cross-linker fraction profiles can be synthesized in fed-batch, yet the determination of the required feeding profiles is not intuitively obvious. Based on recently developed quantitative nonlinear process models, a fed-batch synthesis can be dynamically optimized under constraints set by product quality and process limitations. Here, we apply dynamic optimization to microgel synthesis to obtain large microgels under constraints posed by the radial cross-linker profile and conversion. We present three different case studies to show in silico that a wide range of different cross-linker fraction profiles is feasible. The results show that the specified constraints are met and that various cross-linker profiles can be achieved while maintaining the microgel size.

Combustion and flame 189, 433-442 (2018). doi:10.1016/j.combustflame.2017.07.037, Published by Elsevier Science, Amsterdam [u.a.]

A novel lignocellulosic biofuel 2-butyltetrahydrofuran (2-BTHF) is investigated experimentally and numerically in the present study. Laminar burning velocities were measured in a combustion vessel. Ignition delay times were experimentally determined in a rapid compression machine and in a shock tube at high pressures covering a wide temperature range. A detailed chemical kinetic mechanism is proposed to describe the oxidation of 2-BTHF at both low and high temperatures. It is demonstrated that the model gives satisfactory results for the various experimental configurations. For a better understanding of the oxidation kinetics, the chemical model is further used to elucidate the reaction pathways of 2-BTHF. A comparison of its ignition behavior with other C 8 hydrocarbons is further presented and the impact of the tetrahydrofuranic ring on the fuel ignition characteristics is highlighted and analyzed.

Often, the first step of fuel combustion is the formation of fuel radicals. These radicals can be formed via hydrogen abstraction and are typically rovibrationally excited due to the energy release from the reaction. These excitations increase the population at high energies, thus increase the probability for β -scission of the fuel radical. Hot β -scission of such non-thermal radicals can be interpreted as well-skipping reaction from the bimolecular hydrogen abstraction reactants to the dissociation products. In the present study, the impact of non-Boltzmann radical distributions on β -scission kinetics is screened for several hundred fuels. For that purpose, the free energy release between stable stationary points is predicted using group contribution theory. Based on that screening, fuel radicals with potentially pronounced β -scission of rovibrationally excited fuel radicals are picked for more detailed study. Hot β -scission is found to significantly contribute to the CO 2 loss reactions of formate radicals formed via hydrogen abstraction. Especially for methyl formate, β -scission of non-thermal radicals is found to dominate over a wide range of temperature and pressure. This reveals the need for including the origin of reactants of β -scission reactions.

2-butanone was recently identified as a promising gasoline biofuel. Its kinetic modeling requires high-level kinetic predictions of key reactions to reduce the uncertainty in the reaction model. The present work provides rate constants for hydrogen abstraction from 2-butanone by H ˙ and C ˙ H 3 . Subsequent unimolecular reactions on the 2-butanoyl radical potential energy surface were studied using RRKM/Master Equation. The updated rate constants deviate from previous predictions by up to two orders of magnitude. The potential energy surfaces computed for hydrogen abstraction and β-scission were connected by using rovibrationally excited 2-butanoyl radicals as reactants of the β-scission reaction network. The energy distributions of these excited radicals were computed from the preceding hydrogen abstraction reactions. Though at engine-relevant conditions rovibrationally excited 2-butanoyl radicals were found to be negligible, kinetic modeling of flames at very low pressures and high temperatures would require to include reactions of excited fuel radicals. The reported rate constants significantly change the ignition delay predictions, emphasizing the need for more accurate predictions for novel fuels.