Flame extinction and low-temperature combustion of isolated fuel droplets of n-alkanes

Cuoci, Alberto; Saufi, Abd Essamade; Frassoldati, Alessio; Dietrich, Daniel L.; Williams, Forman A.; Faravelli, Tiziano

doi:10.1016/j.proci.2016.08.019

Cited by 25 publications

(15 citation statements)

References 19 publications

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“…It is possible that intermediates with even higher oxygen content may be produced under low-temperature and high-pressure combustion conditions. This autooxidation mechanism also has implications for the formation of cool flames in alkane fuel droplets under microgravity conditions ( 45 ). This chemistry is important in liquid hydrocarbon degradation in the temperature range of 400–500 K ( 7 ), which is relevant to the oxidative stability of lubricants and other industrial fluids.…”

Section: Discussionmentioning

confidence: 99%

Unraveling the structure and chemical mechanisms of highly oxygenated intermediates in oxidation of organic compounds

Wang

Popolan-Vaida

Chen

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

128

106

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SignificanceHighly oxygenated molecules are involved in autooxidation reactions leading to the formation of secondary organic aerosols (SOAs); they are also critical intermediates in autooxidation processes for liquid hydrogen degradation and the ignition of fuels in advanced combustion systems. However, these reactions are still poorly understood. In this study, we unveil a generalized reaction mechanism involving the autooxidation of peroxy radicals with at least three stages of sequential O2 addition. We elucidate important underlying kinetics and structural characteristics of autooxidation processes used for developing new technologies including those aimed at reducing climatically active SOAs and pollutants from fuel combustion. We show that advances can be made by bridging experimental and theoretical methods used by atmospheric and combustion scientists.

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Section: Discussionmentioning

confidence: 99%

Unraveling the structure and chemical mechanisms of highly oxygenated intermediates in oxidation of organic compounds

Wang

Popolan-Vaida

Chen

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

128

106

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“…Hereafter, the model used to simulate heating, evaporation, and combustion of spherical droplets in 1D geometry is briefly summarized. In this 1D model, 17 already validated in previous papers 34 , 35 for droplet evaporation and combustion, the following assumptions are made: spherically symmetric droplet constant pressure equilibrium conditions at the liquid/gas interface absence of reactions in the liquid phase Conservation equations for species, energy, and velocity in the droplet in the liquid phase are solved. For the liquid phase, equations are formulated as where the subscript L refers to liquid-phase properties.…”

Section: Methodsmentioning

confidence: 99%

Kinetic Modeling of the Ignition of Droplets of Fast Pyrolysis Bio-oil: Effect of Initial Diameter and Fuel Composition

Stagni

Calabria

Frassoldati

et al. 2021

Ind. Eng. Chem. Res.

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Fast biomass pyrolysis is an effective and promising process for high bio-oil yields, and represents one of the front-end technologies to provide alternative, sustainable fuels as a replacement of conventional, fossil-based ones. In this work, the effect of droplet initial diameter on the evaporation and ignition of droplets of crude fast pyrolysis bio-oil (FPBO) and FPBO/ethanol blend (50% vol) at ambient pressure is discussed. The experimental tests were carried out in a closed single droplet combustion chamber equipped with optical accesses, using droplets with a diameter in the range of 0.9–1.4 mm. The collected experimental data show a significant effect of droplet diameter and initial fuel composition on the evaporation and combustion of the droplets. At the same time, 1-dimensional modeling of the evaporation and ignition of different droplets of crude FPBO and its blend with ethanol is performed to understand the complex physical and chemical effects. To this purpose, an 8-component surrogate was adopted, and a skeletal mechanism (170 species and 2659 reactions) was obtained through an established methodology. The comparison of numerical and experimental results shows that the model is able to capture the main features related to the heating phase of the droplet and the effect of fuel composition on droplet temperature and evaporation, particularly the increased reactivity following ethanol addition and the variation of diameter with time. Also, a sensitivity analysis highlighted the reactions controlling the autoignition of the droplets in the different conditions. It was found that the autoignition of pure FPBO droplets is governed by dimethyl furane (DMF), because of its high volatility and in spite of not being the most abundant species. On the other side, ethanol chemistry drives the gas-phase ignition in the case of the blended (50/50 v/v) mixtures, due to its higher volatility and reactivity.

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“…In this section DropletSMOKE++ is validated in microgravity conditions (imposing g = 0), against the numerical results of the solver developed by Cuoci et al [13]. This latter code has been validated in a wide range of operating conditions over the last 10 years [22,21] and represents a reliable reference for comparison. This validation is done in order to assess the validity of the equations (in terms of diameter decay, temperature profiles and vaporization velocity) before the activation of the gravity field.…”

Section: Validation Of Microgravity Casesmentioning

confidence: 99%

“…The absence of gravity allows to adopt a simple 1D mathematical description and to focus on physical aspects such as differential species diffusion, non-ideal thermodynamics and combustion kinetics. In particular, the implementation of detailed mechanisms for gas-phase chemistry in 1D models has paved the way for a better understanding of low-T chemistry [18,19,20] , ignition and extinction phenomena [21,22].…”

Section: Introductionmentioning

confidence: 99%

DropletSMOKE++: A comprehensive multiphase CFD framework for the evaporation of multidimensional fuel droplets

Saufi¹,

Frassoldati²,

Faravelli³

et al. 2019

International Journal of Heat and Mass Transfer

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This paper aims at presenting the DropletSMOKE++ solver, a comprehensive multidimensional computational framework for the evaporation of fuel droplets, under the influence of a gravity field and an external fluid flow. The Volume Of Fluid (VOF) methodology is adopted to dynamically track the interface, coupled with the solution of energy and species equations. The evaporation rate is directly evaluated based on the vapor concentration gradient at the phase boundary, with no need of semi-empirical evaporation sub-models.The strong surface tension forces often prevent to model small droplets evaporation, because of the presence of parasitic currents. In this work we by-pass the problem, eliminating surface tension and introducing a centripetal force toward the center of the droplet. This expedient represents a major novelty of this work, which allows to numerically hang a droplet on a fiber in normal gravity conditions without modeling surface tension. Parasitic currents are completely suppressed, allowing to accurately model the evaporation process whatever the droplet size. DropletSMOKE++ shows an excellent agreement with the experimental data in a wide range of operating conditions, for various fuels and initial droplet diameters, both in natural and forced convection. The comparison with the same cases modeled in microgravity conditions highlights the impact of an external fluid flow on the evaporation mechanism, especially at high pressures.Non-ideal thermodynamics for phase-equilibrium is included to correctly capture evaporation rates at high pressures, otherwise not well predicted by an ideal gas assumption. Finally, the presence of flow circulation in the liquid phase is discussed, as well as its influence on the internal temperature field. DropletSMOKE++ will be released as an open-source code, open to contributions from the sci-

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Flame extinction and low-temperature combustion of isolated fuel droplets of n-alkanes

Cited by 25 publications

References 19 publications

Unraveling the structure and chemical mechanisms of highly oxygenated intermediates in oxidation of organic compounds

Unraveling the structure and chemical mechanisms of highly oxygenated intermediates in oxidation of organic compounds

Kinetic Modeling of the Ignition of Droplets of Fast Pyrolysis Bio-oil: Effect of Initial Diameter and Fuel Composition

DropletSMOKE++: A comprehensive multiphase CFD framework for the evaporation of multidimensional fuel droplets

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