### Recent Submissions

• #### Autoignition of diethyl ether and a diethyl ether/ethanol blend

(Fuel, Elsevier BV, 2020-07-04) [Article]
Binary blends of fast-reacting diethyl ether (DEE) and slow-reacting ethanol (EtOH) are quite promising as renewable replacements for conventional fuels in modern compression ignition engines. In this work, pure diethyl ether and a 50/50 M binary blend of diethyl ether and ethanol (DEE/EtOH) were investigated in a shock tube and a rapid compression machine. Ignition delay times were measured over the temperature range of 550–1000 K, pressures of 20–40 bar, and equivalence ratios of 0.5–1. Literature reaction mechanisms of diethyl ether and ethanol were combined to simulate the reactivity trends of the blends. Species rate-of-production and sensitivity analyses were performed to analyze the interplay between radicals originating from the two fuels. Multistage ignition behavior was observed in both experiments and simulations, with peculiar 3-stage ignition visible at fuel-lean conditions. Kinetic analyses were used to identify the reactions controlling various stages of ignition. Reactivity comparison of DEE/EtOH and dimethyl ether/ethanol (DME/EtOH) blends showed that the oxidation of DEE blends is controlled by acetaldehyde whereas formaldehyde controls the oxidation of DME blends.
• #### QCL-Based Dual-Comb Spectrometer for Multi-Species Measurements at High Temperatures and High Pressures

(Sensors, MDPI AG, 2020-06-29) [Article]
<jats:p>Rapid multi-species sensing is an overarching goal in time-resolved studies of chemical kinetics. Most current laser sources cannot achieve this goal due to their narrow spectral coverage and/or slow wavelength scanning. In this work, a novel mid-IR dual-comb spectrometer is utilized for chemical kinetic investigations. The spectrometer is based on two quantum cascade laser frequency combs and provides rapid (4 µs) measurements over a wide spectral range (~1175–1235 cm−1). Here, the spectrometer was applied to make time-resolved absorption measurements of methane, acetone, propene, and propyne at high temperatures (>1000 K) and high pressures (>5 bar) in a shock tube. Such a spectrometer will be of high value in chemical kinetic studies of future fuels.</jats:p>
• #### Cool flame chemistry of diesel surrogate compounds: n-Decane, 2-methylnonane, 2,7-dimethyloctane, and n-butylcyclohexane

(Combustion and Flame, Elsevier BV, 2020-06-23) [Article]
Elucidating the formation of combustion intermediates is crucial to validate reaction pathways, develop reaction mechanisms and examine kinetic modeling predictions. While high-temperature pyrolysis and oxidation intermediates of alkanes have been thoroughly studied, comprehensive analysis of cool flame intermediates from alkane autoxidation is lacking and challenging due to the complexity of intermediate species produced. In this work, jet-stirred reactor autoxidation of four C10 alkanes: n-decane, 2-methylnonane, 2,7-dimethyloctane, and n-butylcyclohexane, as model compounds of diesel fuel, was investigated from 500 to 630 K using synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometry (SVUV-PIMS). Around 100 intermediates were detected for each fuel. The classes of molecular structures present during the autoxidation of the representative paraffinic functional groups in transport fuels, i.e., n-alkanes, branched alkanes, and cycloalkanes were established and were found to be similar from the oxidation of various alkanes. A theoretical approach was applied to estimate the photoionization cross sections of the intermediates with the same carbon skeleton as the reactants, e.g., alkene, alkenyl keto, cyclic ether, dione, keto-hydroperoxide, diketo-hydroperoxide, and keto-dihydroperoxide. These species are indicators of the first, second, and third O2 addition reactions for the four C10 hydrocarbons, as well as bimolecular reactions involving keto-hydroperoxides. Chemical kinetic models for the oxidation of these four fuels were examined by comparison against mole fraction of the reactants and final products obtained in additional experiments using gas chromatography analysis, as well as the detailed species pool and mole fractions of aforementioned seven types of intermediates measured by SVUV-PIMS. This works reveals that the models in the literature need to be improved, not only the prediction of the fuel reactivity and final products, but also the reaction network to predict the formation of many previous undetected intermediates.
• #### A Systematic Theoretical Kinetics Analysis for the Waddington Mechanism in the Low-Temperature Oxidation of Butene and Butanol Isomers

(The Journal of Physical Chemistry A, American Chemical Society (ACS), 2020-06-23) [Article]
The Waddington mechanism, or the Waddington-type reaction pathway, is crucial for low-temperature oxidation of both alkenes and alcohols. In this study, the Waddington mechanism in the oxidation chemistry of butene and butanol isomers was systematically investigated. Fundamental quantum chemical calculations were conducted for the rate constants and thermodynamic properties of the reactions and species in this mechanism. Calculations were performed using two different ab initio solvers: Gaussian 09 and Orca 4.0.0, and two different kinetic solvers: PAPR and MultiWell, comprehensively. Temperature- and pressure-dependent rate constants were performed based on the transition state theory, associated with the Rice Ramsperger Kassel Marcus and master equation theories. Temperature-dependent thermochemistry (enthalpies of formation, entropy, and heat capacity) of all major species was also conducted, based on the statistical thermodynamics. Of the two types of reaction, dissociation reactions were significantly faster than isomerization reactions, while the rate constants of both reactions converged toward higher temperatures. In comparison, between two ab initio solvers, the barrier height difference among all isomerization and dissociation reactions was about 2 and 0.5 kcal/mol, respectively, resulting in less than 50%, and a factor of 2−10 differences for the predicted rate coefficients of the two reaction types, respectively. Comparing the two kinetic solvers, the rate constants of the isomerization reactions showed less than a 32% difference, while the rate of one dissociation reaction (P1 ↔ WDT12) exhibited 1−2 orders of magnitude discrepancy. Compared with results from the literature, both reaction rate coefficients (R4 and R5 reaction systems) and species’ thermochemistry (all closed shell molecules and open shell radicals R4 and R5) showed good agreement with the corresponding values obtained from the literature. All calculated results can be directly used for the chemical kinetic model development of butene and butanol isomer oxidation.
• #### PAH formation from jet stirred reactor pyrolysis of gasoline surrogates

(Combustion and Flame, Elsevier BV, 2020-06-20) [Article]
Soot particles and their precursor polycyclic aromatic hydrocarbon (PAH) species, formed during combustion, are responsible for particulate emissions in gasoline direct injection (GDI) engines. To better understand the effects of fuel composition on formation of soot in GDI engines, the pyrolysis of several gasoline surrogates was studied in a jet-stirred reactor across a broad temperature range at atmospheric pressure and 1 s residence time. Fuel and intermediate species, including aromatics up to naphthalene, were measured using gas chromatography (GC). PAH concentrations from pyrolysis of surrogate fuels were compared to gain insight into the effects of fuel composition on PAH formation. In addition, synergistic effects were observed in pyrolysis experiments of binary blends. A detailed kinetic model, recently developed at Lawrence Livermore National Laboratory (LLNL), successfully captured the effects of blending and the concentration of major PAHs. Major reaction pathways are discussed, as well as the role of important intermediate species, such as acetylene, and resonantly stabilized radicals such as allyl, propargyl, cyclopentadienyl, and benzyl in the formation of PAH.
• #### Effects of soot volume fraction on local gas heating and particle sizing using laser induced incandescence

(Journal of Aerosol Science, Elsevier BV, 2020-06-19) [Article]
Several decades of developing laser induced incandescence (LII) as a combustion diagnostic have led to great advances in understanding soot formation. The bulk of diagnostic development has focused on time-resolved LII (TiRe-LII) where heating of soot particles using a laser, and the subsequent particle cooling, can be measured and matched to a model to determine soot primary particle size. These models vary significantly in both complexity and accuracy. This work focuses on the effect of local gas heating during the soot cooling process. Multi-color pyrometry is performed 5 μs following laser heating on flames ranging in soot volume fraction (SVF) of 10 ppm up to 43 ppm with laser fluences of 0.09 J/cm2, 0.07 J/cm2, and 0.05 J/cm2. Both laser fluence and SVF had significant effects on the local gas heating as measured by the soot temperature. Simulations were performed implementing local gas heating and showed prediction errors depend on pressure and soot volume fraction. As SVF increases, the errors in primary particle size predictions show a nearly linear rate of increase that can become significant at higher SVF values.
• #### Multi-stage heat release in lean combustion: Insights from coupled tangential stretching rate (TSR) and computational singular perturbation (CSP) analysis

(Combustion and Flame, Elsevier BV, 2020-06-17) [Article]
There is a growing interest in leaner burning internal combustion engines as an enabler for higher thermodynamic efficiency. The extension of knock-limited compression ratio and the increase in specific heat ratio with lean combustion are key factors for boosting efficiency. Under lean burning conditions, there is emerging evidence that certain fuels exhibit unusual heat release characteristics. It has been reported that fuel/air mixtures undergo three-stage heat release or delayed high temperature heat release: starting with an initial low temperature heat release, similar to the one observed in two stage ignition, followed by an intermediate stage where thermal runaway is inhibited, and then advances to a relatively slow third stage of combustion. The focus of this study is to examine the conditions under which various fuels exhibit three stage ignition or delayed high temperature heat release. The auto-ignition of hydrocarbons/air mixtures is simulated in a closed adiabatic homogenous batch reactor where the charge is allowed to auto-ignite at constant volume vessel under predefined initial temperature and pressure. The simulations cover pressures of 10–60 bar, temperatures of 600 K–900 K, and fuel to air ratio from stoichiometry (equivalence ratio) of 0.3–1.0. Tangential stretching rate (TSR) and the computational singular perturbation Slow Importance Indices for temperature are used to identify important reactions contributing to the temperature growth rate at critical time instants of the auto-ignition process. Overall, three-stage ignition or delayed high temperature heat release is found to be present for most fuels under lean fuel/air mixtures, high pressures, and low temperature conditions. The radical termination reactions of H, OH, and HO2 during the high temperature heat release are leading factors for the distinct separation of heat release stages.
• #### Analysis of ECN spray A ignition in a Rapid Compression Machine using simultaneous OH* chemiluminescence and formaldehyde PLIF

(Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, EDP Sciences, 2020-06-15) [Article]
<jats:p>The canonical diesel spray A is characterized in an optical Rapid Compression Machine (RCM) at high temperature and density conditions (900 K and 850 K, <jats:italic>ρ</jats:italic> = 23 kg/m$\{3}$) using simultaneous high-speed OH* chemiluminescence and two-pulse 355 nm Planar Laser Induced Fluorescence (PLIF). The focus is on the time evolution and the repeatability of the early stages of both cool flame and hot ignition phenomena, and on the time evolution of the fluorescing formaldehyde region in between. In particular, time resolved data related to the cool flame are provided. They show the development of several separated kernels on the spray sides at the onset of formaldehyde appearance. Shortly after this phase, the cool flame region expands at high velocity around the kernels and further downstream towards the richer region at the spray head, reaching finally most of the vapor phase region. The position of the first high temperature kernels and their growth are then characterized, with emphasis on the statistics of their location. These time-resolved data are new and they provide further insights into the dynamics of the spray A ignition. They bring some elements on the underlying mechanisms, which will be useful for the validation and improvement of numerical models devoted to diesel spray ignition.</jats:p>
• #### Collaborative investigation of the internal flow and near-nozzle flow of an eight-hole gasoline injector (Engine Combustion Network Spray G)

(International Journal of Engine Research, SAGE Publications, 2020-06-11) [Article]
<jats:p> The internal details of fuel injectors have a profound impact on the emissions from gasoline direct injection engines. However, the impact of injector design features is not currently understood, due to the difficulty in observing and modeling internal injector flows. Gasoline direct injection flows involve moving geometry, flash boiling, and high levels of turbulent two-phase mixing. In order to better simulate these injectors, five different modeling approaches have been employed to study the engine combustion network Spray G injector. These simulation results have been compared to experimental measurements obtained, among other techniques, with X-ray diagnostics, allowing the predictions to be evaluated and critiqued. The ability of the models to predict mass flow rate through the injector is confirmed, but other features of the predictions vary in their accuracy. The prediction of plume width and fuel mass distribution varies widely, with volume-of-fluid tending to overly concentrate the fuel. All the simulations, however, seem to struggle with predicting fuel dispersion and by inference, jet velocity. This shortcoming of the predictions suggests a need to improve Eulerian modeling of dense fuel jets. </jats:p>
• #### LES/PDF modeling of swirl-stabilized non-premixed methane/air flames with local extinction and re-ignition

(Combustion and Flame, Elsevier BV, 2020-06-08) [Article]
Turbulent non-premixed flames with local extinction and re-ignition exhibit multiple combustion modes including ignition waves, diffusion flames, partially premixed flames, and ignition-assisted partially premixed flames. The mechanisms of local extinction and re-ignition are not well understood and numerical modeling of multi-mode combustion is a challenging task. In this work, a specially designed swirl-burner was used to study local extinction and re-ignition of non-premixed turbulent methane/air flames. High speed Particle Image Velocimetry (PIV) and laser induced fluorescence of OH radicals (OH-PLIF) measurements along with Large Eddy Simulation (LES) were carried out to investigate the mechanisms of extinction and re-ignition processes in the burner. LES is based on a transported probability density function model within the framework of Eulerian Stochastic Fields (PDF-ESF). It is found that local extinction occurs when the scalar dissipation rate around the stoichiometric mixture fraction is high. The characteristic time scale for local extinction and re-ignition in the present flames is an order of magnitude longer than the characteristic time scale of diffusion/extinction of laminar flamelets. There are two mechanisms for flame hole re-ignition in the present flames. First, under low degree of local extinction conditions (i.e., for small flame holes surrounded by flames) the flame hole re-ignition is due to the mechanism of turbulent flame folding. Second, under high degree of extinction conditions (i.e., with large regions of extinction and lifted flames), re-ignition of the locally extinguished flame is due to the mechanism of ignition assisted partially premixed flame propagation. The results show that the PDF-ESF model is capable of simulating the quenching and re-ignition process found in the experiments.
• #### Quenching distance of laminar methane-air flames at cryogenic temperatures and implications for flame arrester design

(Applications in Energy and Combustion Science, Elsevier BV, 2020-06-08) [Article]
Understanding flame quenching is needed to develop efficient flame arresters. Here, the quenching distance of methane-air laminar flames is measured at atmospheric pressure for temperatures of the quenching surface down to the cryogenic, Tw = 138 K to 293 K, for two configurations: head-on and tube quenching. Fuels or flammable mixtures in contact with surfaces at temperatures below 293 K are, for example, representative of aircraft during cruise, cryogenic rocket engines, fuel distribution pipes at high altitude, or cryogenic storage of liquified natural gas and hydrogen. The experimental methods are first validated for Tw = 293 K by comparing measured quenching distances to that available in the literature. Then, quenching distances are measured for Tw = 138 K to 293 K. The quenching distance increases when temperature decreases. In the head-on quenching configuration, the quenching distance is almost multiplied by two, from δq = 0.17 mm for Tw = 290 K to δq = 0.32 mm for Tw = 175 K. In the tube quenching configuration, the quenching diameter increases by 40%, from 2.5 mm for Tw = 293 K to 3.5 mm for Tw = 138 K. Experiments conducted in tubes demonstrate that reducing the wall temperature allows quenching with larger tube diameters, yielding lower pressure drops in tubes, which is of practical interest.
• #### High-pressure direct injection of methanol and pilot diesel: A non-premixed dual-fuel engine concept

(Fuel, Elsevier BV, 2020-06-05) [Article]
In order to reduce the climate impacts, methanol produced from carbon-neutral methods plays an important role. Due to its oxygen content and high latent heat, methanol combustion can achieve low soot and NOx emissions. In the present study, direct injection (DI) of methanol is investigated in a non-premixed dual-fuel (DF) setup with diesel pilot. The present DF engine study is carried out via a specially-designed new cylinder head operating with a centrally located methanol injector and with an off-centered diesel pilot injector. The target is to inject methanol close to top dead center (TDC) in a similar fashion as in standard diesel combustion enabling robust operation with high efficiency. The ignition of the DI methanol is achieved with an almost simultaneously injected diesel pilot. The experiments were conducted in a single-cylinder heavy-duty research engine at a constant engine speed of 1500 rpm with a compression ratio of 16.5. The indicated mean effective pressure (IMEP) varied between 4.2 and 13.8 bar while the methanol substitution ratio was swept between 45 and 95%. In addition, the diesel pilot and methanol injection timings were varied for optimum efficiency and emissions. The introduced non-premixed DF concept using methanol as the main fuel showed robust ignition characteristics, stable combustion, and low CO and HC emissions. The results indicate that increasing both the load and the methanol substitution ratio can increase the thermal efficiency and the stability of combustion (lower COV) together with decreased CO and HC emissions.
• #### A comprehensive study of spray and combustion characteristics of a prototype injector for gasoline compression ignition (GCI) application

(Fuel, Elsevier BV, 2020-06-04) [Article]
In this study, the spray and combustion characteristics of high reactivity gasoline (HRG) fuel of RON 77 were tested and compared with E10 certification fuel under the gasoline compression ignition (GCI) engine conditions using a high-pressure multi-hole GCI engine injector. A comprehensive characterization in terms of the rate of injection, spray morphology under flash boiling conditions, penetration lengths under both nonevaporative and evaporative conditions, and ignition delay at reactive conditions was performed. It was found that both the high reactivity gasoline and E10 certification fuel exhibit very similar characteristics. The ignition delay times were found to be very similar between both the fuels tested under ambient temperatures higher than 800 K. This work further serves as an extensive database to validate and calibrate the spray models, combustion models and reaction mechanisms for computational fluid dynamics (CFD) driven development of GCI engines.
• #### Oxidation kinetics of n-pentanol: A theoretical study of the reactivity of the 1‑hydroxy‑1-peroxypentyl radical

(Combustion and Flame, Elsevier BV, 2020-06-04) [Article]
n-Pentanol has been considered as a promising alternative fuel for compression-ignition engines due to its potential to reduce greenhouse gases and pollutant emissions. Engine performance is strongly dominated by fuel oxidation chemistry, and thus a more accurate determination of the coefficients of the reactions ruling its oxidation is essential for the utilization of n-pentanol in combustion engines. The reactions involving 1‑hydroxy‑1-pentyl and molecular oxygen were found to play an important role in controlling the low temperature oxidation chemistry, but have not been investigated experimentally or theoretically; this is also the case for the reactions of the 1‑hydroxy‑1-peroxypentyl radical, which is formed by the addition of oxygen to the radical center of 1‑hydroxy‑1-pentyl. This work presents a theoretical study with high level ab initio calculations at the CCSD(T)/aug-cc-pVTZ//M06-2X/cc-pVTZ level of theory to shed light on the fate of the 1‑hydroxy‑1-peroxypentyl radical. The rate coefficients of all the possible intra-molecular hydrogen shift reactions of that radical were computed using variational transition state theory with small curvature tunneling corrections. For certain reactions, tunneling and variational effects are very pronounced, proving the need for robust methodologies to account for these effects. The hydrogen shift reaction leading to a concerted HO2 elimination and formation of n-pentanal is the dominant pathway and governs the reactivity of 1‑hydroxy‑1-peroxypentyl radical at any temperature. The reverse of this reaction was thereby investigated as well. For this prominent pathway, the effects of multistructural (multiple conformers) torsional anharmonicity of the stationary points were taken into account in order to refine the forward and reverse rate coefficients. The rate coefficients calculated at room temperature are compared to those calculated using a previously developed cost-effective multi-conformer transition state theory approach. The system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) theory was used to compute the pressure-dependent rate coefficients, which indicate significant pressure dependence at intermediate and high temperatures. Implementation of the calculated reaction rate coefficients in chemical kinetics models of n-pentanol revealed that our computed rate coefficients enable better insights into the chemistry of n-pentanol, and help to understand how n-pentanal is formed.
• #### Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture

(Flow, Turbulence and Combustion, Springer Science and Business Media LLC, 2020-05-29) [Article]
The effects of turbulence on knock development and intensity for a thermally inhomogeneous stoichiometric ethanol/air mixture at a representative end-gas autoignition condition in internal combustion engines are investigated using direct numerical simulations with a skeletal reaction mechanism. Two- and three-dimensional simulations are performed by varying the most energetic length scale of temperature, lT, and its relative ratio with the most energetic length scale of turbulence, lT/ le, together with two different levels of the turbulent velocity fluctuation, u′. It is found that lT/le and the ratio of ignition delay time to eddy-turnover time, τig/ τt, are the key parameters that control the detonation development. An increase in either lT or le enhances the detonation propensity by allowing a longer run-up distance for the detonation development. The characteristic length scale of the temperature field, lT, is significantly modified by high turbulence intensity achieved by a large le and u′. The intense turbulence mixing effectively distributes the initial temperature field to broader scales to support the developing detonation waves, thereby increasing the likelihood of the detonation formation. On the contrary, high turbulence intensity with a short mixing time scale, achieved by a small le and a large u′, reduces the super-knock intensity attributed to the finer broken-up structures of detonation waves. Either τig/ τt less than unity or le= lT even with a large u′ is found to have no significant effect on super-knock mitigation. Finally, high turbulent intensity may induce high-pressure spikes comparable to the von Neumann spike. Increased temperature and pressure by combustion heating, noticeably after the peak of heat release rate, significantly enhance the collision and interaction of multiple emerging autoignition fronts near the ending combustion process, resulting in localized high-pressure spikes.
• #### Identification of volatile constituents released from IQOS heat-not-burn tobacco HeatSticks using a direct sampling method.

(Tobacco control, BMJ, 2020-05-28) [Article]
OBJECTIVES:To identify the chemicals released in I Quit Ordinary Smoking (IQOS) heat-not-burn tobacco aerosol and to assess their potential human health toxicity. METHODS:The heating temperature window of the IQOS heat-not-burn device was determined using a thermographic camera over a period of 100 s. Qualitative studies were performed using a novel real-time gas chromatograph-mass spectrometer set-up. Aerosols from six tobacco-flavoured IQOS HeatSticks (Amber, Blue, Bronze, Sienna, Turquoise and Yellow) were collected in a 1 mL loop via a manual syringe attached to the sample-out port of the valve. The gas transport line was heated to 200°C in order to prevent the condensation of volatile species. Compound identification was performed using the NIST11 mass spectrometry database library (US National Institute of Standards and Technology), where only chemicals with a match of 70% and above were listed as identifiable. RESULTS:The temperature profile of the IQOS device revealed a non-combustive process employed in generating the tobacco aerosol. Real-time qualitative analysis revealed 62 compounds encompassing a broad spectrum of chemicals such as carbonyls, furans and phthalates, which are highly toxic. DISCUSSION:Our findings complement the qualitative studies previously performed by Philip Morris International and others via indirect sampling methods. By analysing the aerosols in real time, we have identified a total of 62 compounds, from which only 10 were in common with previous studies. Several identified species such as diacetyl, 2,3-pentanedione, hydroxymethylfurfural and diethylhexyl phthalate are classified as highly toxic, with the latter considered carcinogenic.
• #### Investigating the effects of C3 and C4 alcohol blending on ignition quality of gasoline fuels

(Energy & Fuels, American Chemical Society (ACS), 2020-05-28) [Article]
The study of the ignition quality of alcohol blends with petroleum fuels is a subject of practical interest. It is well known that the ignition delay time (IDT), as well as octane number (ON), increases when gasoline fuels are blended with ethanol. This study focuses on the impact on inverse ignition delay time (IDT-1) when alcohols, such as n-propanol and n-butanol, are blended with gasoline fuels. A non-linear decrease in the IDT-1 of the blends was observed. Predicting the extent of non-linearity in blends is complicated because it involves unknown inter-molecular interactions between base fuel components and the blended components. The purpose of this study is to establish the dependence of base fuel composition (in terms of functional groups) on observed non-linearity. Gasoline fuel contains hundreds of compounds (predominantly hydrocarbons), making it a challenge to understand observed non-linearity when they blend with other components. In this study, the IDT of primary reference fuels (PRF, a binary mixture of iso-octane and n-heptane) and FACE gasolines (fuels for advanced combustion engines) blended with two alcohols (n-propanol and n-butanol) were obtained with an ignition quality tester (IQT) following ASTM D6890 standards. A mole-based Gaussian fit was used to model the blending effects of alcohol with gasoline. The synergistic effect of the different mixtures tested in this study was investigated by analyzing the Gaussian parameters. A multiple linear regression model was formulated to provide information about the impact of the structural composition (functional group) on the synergistic blending effects of gasoline-alcohol mixtures. Constant volume homogenous batch reactor simulations were also conducted, using Chemkin-Pro for alcohols blended with a FACE J surrogate mixture to provide kinetic information about the blending effects observed in the IQT measurements.
• #### Separation and detection of meta- and ortho- substituted benzene isomers by water-soluble pillar[5]arene

(ChemPlusChem, Wiley, 2020-05-25) [Article]
Efficient and energy-saving separation of benzene isomers bearing a diverse range of functional groups is a great challenge due to their overlapping physicochemical properties. Here, we report a water soluble pillar[5]arene (WP5) that is successfully used as a multifunctional material for the separation and detection of meta/orthosubstituted benzene isomers in water. A liquid-liquid extraction strategy was used for the separation of these benzene isomers based on their different affinity to WP5 in water. The selectivity for the metaover the ortho- isomer for xylenes, chlorotoluene and bromotoluene was 88.6%, 88.3% and 95.0% respectively, in one extraction cycle. Furthermore, a fluorescence indicator system based on WP5 and a fluorescent dye molecule (10-methylacridinium, D) was adopted and exhibited significant fluorescence and optical discrimination upon the addition of MX compared to OX, which implies that a simple “turn-on” detection can be performed prior to engaging in the separation process.
• #### Auto-ignition Characteristics of Gasoline and Diesel Fuel Blends: A High-Pressure Ignition Delay and Kinetic Modelling Study

(Hanneng Cailiao/Chinese Journal of Energetic Materials, Institute of Chemical Materials, China Academy of Engineering Physics, 2020-05-25) [Article]
The ignition delay times (IDTs) of two different certified gasoline and diesel fuel blends are reported. These measurements were performed in a shock tube and in a rapid compression machine over a wide range of experimental conditions(φ= 0.5-2.0, T=700-1400 K and p=10-20 bar) relevant to internal combustion engine operation. In addition, the measured IDTs were compared with two relevant gasoline fuels: Coryton gasoline and Haltermann gasoline systematically under the same experimental conditions. Two different gasoline surrogates a primary reference fuel (PRF) and toluene PRF (TPRF) were formulated, and two different gasoline surrogate models were employed to simulate the experiments. Typical pressure and equivalence ratio effects were obtained, and the reactivity of the four different fuels diverge in the negative temperature coefficient (NTC) regime (700-900 K). Particularly at 750 K, the discrepancy is about a factor of 1.5-2.0. For the high Research Octane Number (RON) and high-octane sensitivity fuel, the simulation results obtained using the TPRF surrogate was found to be unreasonably slow compared to experimental results, due to the large quantity of toluene (77.6% by volume) present. Further investigation including reactants'concentration profile, flux and sensitivity analyses were simultaneously carried out, from which, toluene chemistry and its interaction with alkane (n-heptane and iso-octane) chemistry were explained in detail.
• #### Screening gas-phase chemical kinetic models: Collision limit compliance and ultrafast timescales

(International Journal of Chemical Kinetics, Wiley, 2020-05-22) [Article]
Detailed gas-phase chemical kinetic models are widely used in combustion research, and many new mechanisms for different fuels and reacting conditions are developed each year. Recent works have highlighted the need for error checking when preparing such models, but a useful community tool to perform such analysis is missing. In this work, we present a simple online tool to screen chemical kinetic mechanisms for bimolecular reactions exceeding collision limits. The tool is implemented on a user-friendly website, cloudflame.kaust.edu.sa, and checks three different classes of bimolecular reactions; (ie, pressure independent, pressure-dependent falloff, and pressure-dependent PLOG). In addition, two other online modules are provided to check thermodynamic properties and transport parameters to help kinetic model developers determine the sources of errors for reactions that are not collision limit compliant. Furthermore, issues related to unphysically fast timescales can remain an issue even if all bimolecular reactions are within collision limits. Therefore, we also present a procedure to screen ultrafast reaction timescales using computational singular perturbation. For demonstration purposes only, three versions of the rigorously developed AramcoMech are screened for collision limit compliance and ultrafast timescales, and recommendations are made for improving the models. Larger models for biodiesel surrogates, tetrahydropyran, and gasoline surrogates are also analyzed for exemplary purposes. Numerical simulations with updated kinetic parameters are presented to show improvements in wall-clock time when resolving ultrafast timescales.