Combustion of a Fuel Droplet in a Mixed Convective Environment
TL;DR: In this article, the authors simulated the combustion of a fuel droplet in a mixed convective environment both theoretically and experimentally, subject to the assumptions of constant properties (except for density) and infinite rate kinetics.
Abstract: The combustion of a fuel droplet in a mixed convective environment has been simulated both theoretically and experimentally. In the theoretical model, the flow and transport equations have been solved subject to the assumptions of constant properties (except for density) and infinite rate kinetics, using the finite element method. The gas density has been treated as a variable, only to determine the buoyancy force contribution, and it has been evaluated assuming an ideal gas mixture. A porous-sphere facility has been employed for simulating the burning characteristics of a fuel droplet experimentally. The effects of airflow rate and droplet size have been studied for both upward and downward airflow configurations. Theoretical predictions for the mass burning rate and flame shape are in excellent agreement with the experimental results of the present study and also those reported in the literature. For upward airflow configuration, the mass burning rate is under-predicted by 15 to 20 percent when...
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TL;DR: In this paper, the combustion characteristics of isolated micron-sized precursor/solvent droplets are investigated experimentally, and the mechanism of disruptive droplet burning is similar to that of slurry droplets, consisting of three main steps: (1) diffusion-controlled burning of the highvolatile solvent, (2) viscous-shell formation due to decomposition of the low-volatile metal precursor, and (3) subsequent disruption due to heterogeneous nucleation.
Abstract: Flame spray pyrolysis is an established technique for synthesizing nanoparticles in the gas phase through aerosol combustion of precursor/solvent droplets. The combustion characteristics of isolated micron-sized precursor/solvent droplets are investigated experimentally. Pure solvent droplets burn uniformly and classically quasisteady, whereas precursor/solvent droplets manifest disruptive combustion behavior. The fast onset of droplet disruption, which occurs only for solutions with dissolved metal precursors, is not due to solid-particle precipitation within the droplet. Instead, the mechanism of disruptive droplet burning is similar to that of slurry droplets, consisting of three main steps: (1) diffusion-controlled burning of the high-volatile solvent, (2) viscous-shell formation due to decomposition of the low-volatile metal precursor, and (3) subsequent disruption due to heterogeneous nucleation. The time sequence of the three steps depends on the concentration and decomposition characteristics of the metal precursor, shortening with increased concentration and higher incremental decomposition temperature. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4553–4566, 2013
59 citations
TL;DR: In this paper, a fundamental experimental study to determine the burning rates of ethanol and ethanol-blended fossil fuels is presented, where pure liquid ethanol or its blends with liquid fossil fuels such as gasoline or diesel, has been transpired to the surface a porous sphere using an infusion pump.
54 citations
TL;DR: In this paper, experimental and numerical investigations of spheres burning in a convective environment have been carried out using a finite volume technique based on non-orthogonal semi-collocated grids.
51 citations
TL;DR: In this paper, an isolated droplet burning in a convective flow is reported, where HO radical and acetone droplets are injected in a steady laminar diffusion counterflow flame operating with methane.
Abstract: Experimental investigation of an isolated droplet burning in a convective flow is reported. Acetone droplets were injected in a steady laminar diffusion counterflow flame operating with methane. Planar laser-induced fluorescence measurements applied to OH radical and acetone was used to measure the spatial distribution of fuel vapour and the structure of the flame front around the droplet. High-magnification optics was used in order to image flow areas with a ratio of 1:1.2. The different combustion regimes of an isolated droplet could be observed from the configuration of the envelope flame to that of the boundary-layer flame, and occurrence of these regimes was found to depend on the droplet Reynolds number. Experimental results were compared with 1D numerical simulations using detailed chemistry for the configuration of the envelope flame. Good agreement was obtained for the radial profile of both OH radical and fuel vapour. Influence of droplet dynamics on the counterflow flame front was also investigated. Results show that the flame front could be strongly distorted by the droplet crossing. In particular, droplets with high velocity led to local extinction of the flame front whereas droplets with low velocity could ignite within the flame front and burn on the oxidiser side.
28 citations
TL;DR: In this paper, the entropy generation rate in the range of subcritical freestream velocity, where an envelope flame is present, presents a minimum value and reaches a maximum value at a critical velocity where the flame transition occurs.
24 citations
References
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Book•
01 Jan 1986
TL;DR: In this article, Rankine and Hughes-Hugoniot relations of Detonation and Deflagration Waves of Premixed Gases and Turbulent Reacting Flows with Premixed Reactants.
Abstract: Review of Chemical Thermodynamics. Review of Chemical Kinetics. Conservation Equations for Multi--Component Reacting Systems. Rankine--Hugoniot Relations of Detonation and Deflagration Waves of Premixed Gases. Premixed Laminar Flames. Diffusion Flames and Combustion of a Single Liquid Fuel Droplet. Turbulent Flames. Turbulent Reacting Flows with Premixed Reactants. Chemically Reacting Boundary--Layer Flows. Ignition. Appendix. Index.
1,990 citations
904 citations
TL;DR: In this paper, the authors present a review of spray combustion in rocket engine, gas turbine, diesel engine and industrial furnace applications, highlighting the need for improved injector characterization methods, more information of droplet transport characteristics in turbulent flow and continued development of more complete two-phase turbulent models.
507 citations
01 Jan 1979
TL;DR: In this article, the authors present a review of spray combustion in rocket engine, gas turbine, diesel engine and industrial furnace applications, highlighting the need for improved injector characterization methods, more information of droplet transport characteristics in turbulent flow and continued development of more complete two-phase turbulent models.
Abstract: The present understanding of spray combustion in rocket engine, gas turbine, Diesel engine and industrial furnace applications is reviewed. In some cases, spray combustion can be modeled by ignoring the details of spray evaporation and treating the system as a gaseous diffusion flame; however, in many circumstances, this simplification is not adequate and turbulent two-phase flow must be considered. The behavior of individual droplets is a necessary component of two-phase models and recent work on transient droplet evaporation, ignition and combustion is considered, along with a discusssion of important simplifying assumptions involved with modeling these processes. Methods of modeling spray evaporation and combustion processes are also discussed including: one-dimensional models for rocket engine and prevaporized combustion systems, lumped zone models (utilizing well-stirred reactor and plug flow regions) for gas turbine and furnace systems, locally homogeneous turbulent models, and two-phase models. The review highlights the need for improved injector characterization methods, more information of droplet transport characteristics in turbulent flow and continued development of more complete two-phase turbulent models.
410 citations
TL;DR: In this paper, a numerical study of the effects of transients and variable properties on single droplet evaporation into an infinite stagnant gas is presented, and it is found that initial size Ro is eliminated from the problem on scaling time with respect to R20 and that the evaporative process becomes quasi-steady with ( R R 0 ) 2 = ( R∗ 0 R 0 ), 2 − βt R 2 0, as suggested by experiment.
398 citations