Showing papers on "Diffusion flame published in 2014"
TL;DR: In this article, numerical simulations with detailed chemistry and different radiation models are con- ducted to examine the effects of radiation on spherical flame propagation, and a method to obtain the radiation-corrected flame speed (RCFS) is presented and it can be used for laminar flame speed measurement using the propagating spherical flame method.
160 citations
TL;DR: In this article, a skeletal mechanism for n-dodecane with 105 species and 420 reactions was developed for spray combustion simulations, which was coupled with well-established spray models and further validated in 3-D turbulent spray combustion simulation under engine-like conditions.
Abstract: n-Dodecane is a promising surrogate fuel for diesel engine study because its physicochemical properties are similar to those of the practical diesel fuels. In the present study, a skeletal mechanism for n-dodecane with 105 species and 420 reactions was developed for spray combustion simulations. The reduction starts from the most recent detailed mechanism for n-alkanes consisting of 2755 species and 11,173 reactions developed by the Lawrence Livermore National Laboratory. An algorithm combining direct relation graph with expert knowledge (DRGX) and sensitivity analysis was employed for the present skeletal reduction. The skeletal mechanism was first extensively validated in 0-D and 1-D combustion systems, including auto-ignition, jet stirred reactor (JSR), laminar premixed flame and counter flow diffusion flame. Then it was coupled with well-established spray models and further validated in 3-D turbulent spray combustion simulations under engine-like conditions. These simulations were compared with the re...
136 citations
TL;DR: In this article, an improved chemical mechanism of PAH growth was developed and tested in soot computations for a laminar co-flow non-premixed ethylene-air diffusion flame.
134 citations
TL;DR: In this paper, the formation, growth, and transport of soot was investigated via large scale numerical simulation in a three-dimensional turbulent non-premixed n-heptane/air jet flame at a jet Reynolds number of 15,000.
133 citations
TL;DR: In this paper, a comparison of two different combustion models that were recently implemented by the authors in an open-source code is presented, where the first assumes each cell to be a homogeneous reactor and neglects interaction between turbulence and chemistry, while the second, multiple laminar flamelets are used to represent the structure of a turbulent diffusion flame.
Abstract: The application of detailed chemistry to the computational fluid dynamics simulation of combustion process in diesel engines has many potentials, including the possibility to predict auto-ignition, diffusion flame structure, stabilisation and soot formation in a wide range of operating conditions, also taking into account the effects of different fuel types. Among the approaches that were proposed over the years, the ones that are mostly used in practical calculations can be divided into two main categories: the first assumes each cell to be a well-stirred reactor, while the second employs the flamelet assumption to describe both auto-ignition and turbulent diffusion flame propagation. Despite the fact that both types of model have been widely validated over the years, a detailed comparison between them appears to be very useful in order to understand better the relevant parameters governing auto-ignition, flame stabilisation and the formation of pollutant emissions. This work is focused on a comparison of two different combustion models that were recently implemented by the authors in an open-source code. The first assumes each cell to be a homogeneous reactor and neglects interaction between turbulence and chemistry, while in the second, multiple laminar flamelets are used to represent the structure of a turbulent diffusion flame. Suitable techniques for online reaction rate tabulation and chemical mechanism reduction are also incorporated, to make the use of bigger mechanisms possible (up to 150 species). The two models are compared and validated by simulating constant-volume diesel combustion in a wide range of operating conditions, including variations of ambient temperature and oxygen concentration. Comparison between the computed and experimental data on flame structure, auto-ignition and flame lift-off enables an understanding of the main relevant differences between the models in the way both auto-ignition and flame stabilisation processes are predicted.
124 citations
TL;DR: In this paper, laser induced fluorescence (LIF) has been applied to probe PAHs in two atmospheric sooting flames: a premixed flat flame of methane and a Diesel turbulent spray one.
121 citations
TL;DR: In this article, high-speed fuel, flow, and flame imaging are combined with spark discharge measurements to investigate the causes of rare misfires and partial burns in a spray-guided spark-ignited direct-injection (SG-SIDI) engine over a range of nitrogen dilution levels.
115 citations
TL;DR: In this article, the mechanism of tulip flame formation in horizontal combustion chambers closed at the ignition end is explained based on the PIV images and direct visualization of the process, which is shown to be a purely hydrodynamic phenomenon which results from the competition between the backward movement of deflected burned gases expanding from the lateral flame skirts and the forward movement of unburned gases accelerated in the phase of finger-shaped flame.
112 citations
TL;DR: In this paper, the authors used large eddy simulation and detailed chemical kinetics to investigate the autoignition and stabilization of n-Dodecane spray combustion under diesel engine like conditions.
100 citations
TL;DR: In this article, the global combustion characteristics of 2,6,10-trimethyl dodecane, a synthetic fuel candidate species, have been experimentally investigated by measuring extinction limits for strained laminar diffusion flames at 1m and reflected shock ignition delays at 20m.
100 citations
TL;DR: In this paper, the authors investigate the mechanism of the laminar premixed flame anchoring near a heat-conducting bluff-body and show that a shear-layer stabilized flame anchors at an immediate downstream location near the bluff body where favorable ignition conditions are established; a region associated with (1) a sufficiently high temperature impacted by the conjugate heat exchange between the heat conductance and the hot reacting flow and (2) locally maximum stoichiometry characterized by the preferential diffusion effects.
TL;DR: In this article, a kinetic model of n-decane with 234 species and 1452 reactions was developed for applications in intermediate and high temperature regions, and was validated against the experimental results in the present work.
TL;DR: In this article, the effects of adding water vapor to the air stream on flame properties and soot volume fraction were investigated numerically in a laminar coflow ethylene/air diffusion flame at atmospheric pressure.
TL;DR: In this article, the authors measured the black carbon content of soot formed in premixed and diffusion flames and emitted by light duty gasoline and diesel vehicles, and compared with particle size distributions.
Abstract: This article investigates the black carbon (BC) content of soot formed in premixed and diffusion flames and emitted by light duty gasoline and diesel vehicles. BC is measured photoacoustically and compared with particulate mass collected by filter and calculated from particle size distributions. The BC fraction of soot from rich premixed ethylene flames increases with height above the burner, but can remain well below unity in modestly sooting flames. The BC fraction produced by a propane diffusion flame soot generator (combustion aerosol standard, CAST) falls as the fuel is diluted with nitrogen, the principal means used to adjust the desired particle size. Thermally treating the soot to remove possible condensed semivolatile species does little to change these trends. Transmission electron microscopy (TEM) images show that despite low BC content, these particles display the characteristic fractal-like agglomerate morphology of soot. Particle mass spectra reveal polycyclic aromatic hydrocarbon (PAH) and ...
TL;DR: In this paper, a review of recent works published on Syngas combustion at lean-premixed and Gas Turbine relevant conditions are reviewed, classified according to their objectives, and remarks are concluded.
TL;DR: In this article, a conservative analytical estimate of the effects of radiation heat loss is derived and validated against detailed numerical simulations, and a solver with a graphical interface is provided in the Supplemental material to allow implementation of these analytical results.
TL;DR: In this paper, the laminar flame speeds of CH4/O2/CO2 mixtures in atmospheric conditions (300 k and 1 k) were studied using a Bunsen burner.
TL;DR: In this paper, transmission electron micrographs of soot samples from various sources are examined and it is shown that primary particle sizes are not well mixed within an aerosol population, and the variation in size is much larger between aggregates than within aggregates.
Abstract: For decades, soot has been modeled as fractal-like aggregates of nearly equiaxed spherules. Cluster–cluster aggregation simulations, starting from a population of primary particles, give rise to structures that closely match real aerosols of solid particles produced in flames. In such simulations, primary particle size is uncorrelated with aggregate size, as all aggregates contain primary particles drawn from the same population. Aerosol measurements have been interpreted with this geometric model. Examination of transmission electron micrographs of soot samples from various sources shows that primary particle sizes are not well mixed within an aerosol population. Larger aggregates tend to contain larger primary particles and the variation in size is much larger between aggregates than within aggregates. The soot sources considered here are all substantially not well-mixed (aircraft jet engine, inverted diffusion flame, gasoline direct injection engine, heavy-duty compression ignition engine). The observe...
TL;DR: In this paper, two large-eddy simulation (LES) models are proposed to predict autoignition delays and heat release of an autoigniting liquid α-methylnaphthalene/n-decane jet injected into a constant-volume chamber under Diesel-like conditions.
TL;DR: In this article, a detailed numerical study was conducted to investigate the effects of hydrogen and helium addition to fuel on soot formation in atmospheric axisymmetric coflow laminar methane/air diffusion flame.
TL;DR: In this paper, the uncertainties associated with the extraction of laminar flame speeds through extrapolations from directly measured experimental data were assessed using one-dimensional direct numerical simulations with focus on the effects of molecular transport and thermal radiation loss.
TL;DR: In this article, the influence of chemical structure on the sooting characteristics of some paraffin class hydrocarbons which are found in gasoline and diesel fuel is studied experimentally, and the results show that the PSD of normal, iso and cyclo paraffins evolve in a similar way with flame height.
TL;DR: The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought.
Abstract: High-resolution mass spectrometry coupled with nanospray desorption electrospray ionization was used to probe chemical constituents of young soot particles sampled along the centerline of a coflow diffusion flame of a three-component Jet-A1 surrogate. In lower positions where particles are transparent to light extinction (λ = 632.8 nm), peri-condensed polycyclic aromatic hydrocarbons (PAHs) are found to be the major components of the particle material. These particles become enriched with aliphatic components as they grow in mass and size. Before carbonization occurs, the constituent species in young soot particles are aliphatic and aromatic compounds 200–600 amu in mass, some of which are oxygenated. Particles dominated by PAHs or mixtures of PAHs and aliphatics can exhibit liquid-like appearance observed by electron microscopy and be transparent to visible light. The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought. For example, the mass growth and enrichment of aliphatic components in an initial mostly aromatic structure region of the flame that is absent of H atoms or other free radicals indicates that there must exist at least another mechanism of soot mass growth in addition to the hydrogen abstraction–carbon addition mechanism currently considered in fundamental models of soot formation.
TL;DR: In this article, the authors measured the laminar flame speeds of lean premixed H 2 /CO/air mixtures in the counterflow configuration over a wide range of H 2 content at lean conditions.
TL;DR: In this article, the mechanism of repetitive extinction-ignition dynamics for lean premixed hydrogen-air mixture is studied in a microchannel with prescribed wall temperature, where the reacting flow is affected by the wall temperature and leads to ignition near walls.
TL;DR: In this article, the flame propagation behavior and a blast wave of homogeneous premixed combustible gas/air mixtures in unconfined areas were experimentally investigated using a soap bubble method at room temperature and atmospheric pressure.
TL;DR: In this paper, a Direct Numerical Simulation (DNS) study is performed to determine a quantitative indicator of imminent global extinction in spray flames ignited by a spark, where the structure of spray flames is examined, including identification of non-premixed behaviour in the core of the flame and premixed flame fronts except in the presence of droplets.
TL;DR: In this paper, the liquid fuel combustion in a meso-scale burner with porous media was experimentally investigated for n-heptane/air mixtures of varying equivalence ratios and flow speeds.
TL;DR: In this article, a premixed methane-air Bunsen flame is seeded with increasing concentrations of micron-size aluminum powder, and scanning emission spectroscopy is used to determine the flame temperature via both the continuous and aluminum monoxide spectra.
Abstract: Stabilized aluminum flames are studied in the products of methane combustion. A premixed methane–air Bunsen flame is seeded with increasing concentrations of micron-size aluminum powder, and scanning emission spectroscopy is used to determine the flame temperature via both the continuous and aluminum monoxide spectra. The flame burning velocity is measured and the condensed flame products are collected and analyzed for unburned metallic aluminum content. It was observed that, below a critical concentration of about 120 g/m3, aluminum demonstrates incomplete oxidation with a flame temperature close to the methane–air flame. Below the critical concentration, the flame burning velocity also decreases similar to a flame seeded with inert silicon carbide particles. In contrast, at aluminum concentrations above the critical value, an aluminum flame front rapidly forms and is coupled to the methane flame. The flame temperature of the coupled methane–aluminum flame is close to equilibrium values with aluminum as...
TL;DR: In this paper, the instantaneous flame front structure of turbulent premixed CH 4 /H 2 /air flames (hydrogen fraction of 0, 5, 10% and 20% by mole fraction) was investigated quantitatively using a nozzle-type Bunsen burner.