A comprehensive combustion chemistry study of n-propylcyclohexane

Alkylated cycloalkanes are vital components in gasoline, aviation, and diesel fuels; however, their combustion chemistry has been less investigated compared to other hydrocarbon classes. In this work, the combustion kinetics of n-propylcyclohexane (n-Pch) was studied across a range of experiments including pressurized flow reactor (PFR), jet stirred reactor (JSR), shock tube (ST), and rapid compression machine (RCM). These experiments cover a wide range of conditions spanning low to intermediate to high temperatures, low to high pressures at lean to rich equivalence ratios. Stable intermediate species were measured in PFR over a temperature range of 550–850 K, pressure of 8.0 bar, equivalence ratio (φ) of 0.27, and constant residence time of 120 ms. The JSR was utilized to measure the speciation during oxidation of n-Pch at φ of 0.5–2.0, at atmospheric pressure, and across temperature range of 550–800 K. Ignition delay times (IDTs) for n-Pch were measured in the RCM and ST at temperatures ranging from 650 to 1200 K, at pressures of 20 and 40 bar, at φ=0.5,1.0. In addition, a comprehensive detailed chemical kinetic model was developed and validated against the measured experimental data. The new kinetic model, coupled with the breadth of data from various experiments, provides an improved understanding of n-Pch combustion

Curvature effects on NO formation in wrinkled laminar ammonia/hydrogen/nitrogen-air premixed flames

The formation of nitrogen oxide (NO) in wrinkled laminar NH3/H2/N2-air premixed flames is investigated utilizing two-dimensional Direct Numerical Simulation (DNS) with detailed chemical kinetics as well as one-dimensional freely propagating flame calculations. The spatial pattern of NO formation is observed to be closely linked to flame curvature and affected by thermo-diffusive effects acting on key chemical species. Preferential diffusion of H2 into convex-shaped portions of the flame front leads to a local increase in equivalence ratio. This change in local equivalence ratio is found to prominently affect the NO formation. If the fuel-oxidant mixture is globally lean, a local increase in equivalence ratio strengthens the NO formation (locally); in a globally rich fuel-oxidant mixture, conversely, the NO concentration will be reduced in correspondence of local increments of the equivalence ratio. A sensitivity analysis with respect to NO formation reveals that decomposition of NH2 is governed by two competing pathways: the decomposition via NH and N to N2 on the one hand and the oxidation via HNO to NO on the other hand. The local radical pool, which is affected by preferential diffusion of H2 and depletion of O2, and the local fuel-oxidant mixture ratio jointly strengthen further local differences between H2-depleted (concave-shaped) portions of the flame front and H2-enriched (convex-shaped) ones. This is confirmed across a wide range of equivalence ratios from lean to rich conditions. © 2021 The Author

Detailed examination of the combustion of diesel and glycerol emulsions in a compression ignition engine

This study examines glycerol as an additive to diesel fuel to demonstrate it has the potential to suppress the formation of soot/PM. The investigation of a diesel/glycerol emulsion included an engine trial, high-speed imaging in an optical combustion chamber and a fundamental chemical kinetic study examining soot precursor formation. The emulsion had a longer ignition delay but higher AHRR with increasing load. There was no impact on the brake thermal efficiency. CO and THC were higher with the emulsion at the lower engine loads. The emulsion emitted a smaller number of particles with diameters greater than 25 nm, with a significant drop in the number of particles at 60 nm. The number of particles with diameters greater than 25 nm is reduced by 61% at 20 Nm, by 56% at 80 Nm, and by 11% at 140 Nm. A large peak of sub 10 nm particles, 2 orders of magnitude greater than with diesel alone, was observed, hypothesised to be semi-volatile organic compounds that have started to condense. A thermogravimetric analysis supported a larger semi-volatile content. Ignition delay time, determined from the OH* flame emission, was always longer for the emulsion at all conditions. In-flame soot was always lower with the emulsion at all conditions. Flame lift-off length decreased with increasing temperature and pressure of the ambient gas whilst soot increased. The concentration of known soot precursors, C2H2 and C2H4 was reduced but the concentrations of C3H6 and PC3H4 were not significantly affected

Detailed examination of the combustion of diesel and glycerol emulsions in a compression ignition engine

This study examines glycerol as an additive to diesel fuel to demonstrate it has the potential to suppress the formation of soot/PM. The investigation of a diesel/glycerol emulsion included an engine trial, high-speed imaging in an optical combustion chamber and a fundamental chemical kinetic study examining soot precursor formation. The emulsion had a longer ignition delay but higher AHRR with increasing load. There was no impact on the brake thermal efficiency. CO and THC were higher with the emulsion at the lower engine loads. The emulsion emitted a smaller number of particles with diameters greater than 25 nm, with a significant drop in the number of particles at 60 nm. The number of particles with diameters greater than 25 nm is reduced by 61% at 20 Nm, by 56% at 80 Nm, and by 11% at 140 Nm. A large peak of sub 10 nm particles, 2 orders of magnitude greater than with diesel alone, was observed, hypothesised to be semi-volatile organic compounds that have started to condense. A thermogravimetric analysis supported a larger semi-volatile content. Ignition delay time, determined from the OH* flame emission, was always longer for the emulsion at all conditions. In-flame soot was always lower with the emulsion at all conditions. Flame lift-off length decreased with increasing temperature and pressure of the ambient gas whilst soot increased. The concentration of known soot precursors, C2H2 and C2H4 was reduced but the concentrations of C3H6 and PC3H4 were not significantly affected

Compositional Effects of Gasoline Fuels on Combustion, Performance and Emissions in Engine

El 24 de enero de 1965 fallecía en Londres el político británico más importante del siglo XX: Winston Churchill. Su figura polifacética, su olfato político y su fuerza oratoria fueron indispensables para salvar Inglaterra de la amenaza nazi. Pero también tuvo errores. Conservador, sincero y políticamente incorrecto, como recuerda en este perfil Rafael Navarro-Valls, la historia no sería justa con él si sus equivocaciones ensombrecieran el imprescindible papel que desempeñó tanto para su país como para el resto del mundo

Autoignition characteristics of oxygenated gasolines

Gasoline anti-knock quality, defined by the research and motor octane numbers (RON and MON), is important for increasing spark ignition (SI) engine efficiency. Gasoline knock resistance can be increased using a number of blending components. For over two decades, ethanol has become a popular anti-knock blending agent with gasoline fuels due to its production from bio-derived resources. This work explores the oxidation behavior of two oxygenated certification gasoline fuels and the variation of fuel reactivity with molecular composition. Ignition delay times of Haltermann (RON = 91) and Coryton (RON = 97.5) gasolines have been measured in a high-pressure shock tube and in a rapid compression machine at three pressures of 10, 20 and 40 bar, at equivalence ratios of phi = 0.45, 0.9 and 1.8, and in the temperature range of 650-1250 K. The results indicate that the effects of fuel octane number and fuel composition on ignition characteristics are strongest in the intermediate temperature (negative temperature coefficient) region. To simulate the reactivity of these gasolines, three kinds of surrogates, consisting of three, four and eight components, are proposed and compared with the gasoline ignition delay times. It is shown that more complex surrogate mixtures are needed to emulate the reactivity of gasoline with higher octane sensitivity (S = RON-MON). Detailed kinetic analyses are performed to illustrate the dependence of gasoline ignition delay times on fuel composition and, in particular, on ethanol content. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Research reported in this paper was funded by Saudi Aramco under the FUELCOM program and by King Abdullah University of Science and Technology (KAUST).2019-08-1

Kinetic modelling and experimental study of small esters : Methyl acetate and ethyl acetate

A detailed chemical kinetic mechanism comprising methyl acetate and ethyl acetate has been developed based on the previous work by Westbrook et al. [1]. The newly developed kinetic mechanism has been updated with new reaction rates from recent theoretical studies. To validate this model, shock tube experiments measuring ignition delay time have been conducted at 15 & 30 bar and equivalence ratio 0.5, 1.0 and 2.0. Another set of experiments measuring laminar burning velocity was also performed on a heat flux burner at atmospheric pressure over wide range of equivalence ratios [ ~ 0.7-1.4]. The new mechanism shows significant improvement in prediction of experimental data over earlier model across the range of experiments.In this study, a detailed chemical kinetic model for methyl and ethyl acetate (Fig. 1) has been developed. This model is advanced from the mechanism proposed for laminar premixed flames by Westbrook and coworkers in 2009 [1]. Acetates studied in this work are both high RON fuels with suitable physical and chemical properties [Table 1] to be considered as potential fuels in advanced gasoline engines [4]. Shock tube experiments measuring ignition delay time have been conducted at 15 & 30 bar and equivalence ratio 0.5, 1.0 and 2.0. Another set of experiments measuring laminar burning velocity have also been performed on a heat flux burner at atmospheric pressure over wide range of equivalence ratios. The model developed in this work shows good agreement with ignition data and laminar burning velocity data across the temperature and equivalence ratio range respectively

Small ester combustion chemistry: Computational kinetics and experimental study of methyl acetate and ethyl acetate

Small esters represent an important class of high octane biofuels for advanced spark ignition engines. They qualify for stringent fuel screening standards and could be synthesized through various pathways. In this work, we performed a detailed investigation of the combustion of two small esters, MA (methyl acetate) and EA (ethyl acetate), including quantum chemistry calculations, experimental studies of combustion characteristics and kinetic model development. The quantum chemistry calculations were performed to obtain rates for H-atom abstraction reactions involved in the oxidation chemistry of these fuels. The series of experiments include: a shock tube study to measure ignition delays at 15 and 30 bar, 1000-1450 K and equivalence ratios of 0.5, 1.0 and 2.0; laminar burning velocity measurements in a heat flux burner over a range of equivalence ratios [0.7-1.4] at atmospheric pressure and temperatures of 298 and 338 K; and speciation measurements during oxidation in a jet-stirred reactor at 800-1100 K for MA and 650-1000 K for EA at equivalence ratios of 0.5, 1.0 and at atmospheric pressure. The developed chemical kinetic mechanism for MA and EA incorporates reaction rates and pathways from recent studies along with rates calculated in this work. The new mechanism shows generally good agreement in predicting experimental data across the broad range of experimental conditions. The experimental data, along with the developed kinetic model, provides a solid groundwork towards improving the understanding the combustion chemistry of smaller esters. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.The authors at KAUST acknowledge funding support from the Office of Sponsored Research under the Future Fuels Program. The authors at NUI Galway recognize funding support from Science Foundation Ireland via their Principal Investigator Program through project number 15/IA/3177. Cavallotti acknowledges the financial support of the Chemical Sciences and Engineering Division of Argonne National Laboratories for his sabbatical. The work by authors at LLNL was performed under the auspices of the U.S. Department of Energy (DOE), Contract DE-AC52-07NA27344 and was conducted as part of the Co-Optimization of Fuels & Engines (Co-Optima) project sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies and Vehicle Technologies Offices. The authors at Lund University acknowledge financial support from the Centre for Combustion Science and Technology (CECOST), and Swedish Research Council (VR) via project 2015-04042. Part of this material is based on work at Argonne supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under Contract No. DE-AC02-06CH11357. The NREL research was conducted as part of the Co-Optimization of Fuels & Engines (Co-Optima) project sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies and Vehicle Technologies Offices.peer-reviewed2020-07-1