Dario Alviso

Experimental and Numerical Characterization of the Methyl Decanoate Combustion in Laminar Counterflow Spray Premixed Flames

Biodiesel is a mixture of long chain fatty acid methyl esters used mainly in compression ignition engines. In order to improve engine performance, an understanding of its fundamental properties and the combustion pathways is required. A surrogate fuel: methyl decanoate (MD) is used in order to simplify the models and experiments. This study presents new data for MD combustion in a laminar counterflow premixed flame configuration (spray MD/air against methane/air) at atmospheric pressure, for different strain rate and equivalence ratio conditions. The visible and UV chemiluminescence of the excited radicals CH* (A2Δ) and OH* (A2Σ+) as well as Planar Laser-Induced Fluorescence (PLIF) of OH are employed experimentally to analyze the flame structure. The counterflow spray flame is simulated by choosing a MD skeletal reaction mechanism, to which we add CH* and OH* reactions. The numerical predictions of the CH* concentration are very close to the experimental profiles along the central axis. The numerical and experimental results indicate differences in the OH* production routes between MD and methane flames.Copyright

FLAME STRUCTURE OF DIESEL SURROGATE COMBUSTION IN A COUNTERFLOW DIFFUSION FLAME

In 2014, Mario Molina Center performed a study concerning air pollutants in Asunción. The results showed that population of Asunción is exposed to high levels of air pollution particles (ranging between 2.5 and 10 microns) and nitrogen dioxide that threatens their health. In addition, the study showed that transport has an important role in this problem, due to the fact that emission of particles is one of the main problems of Diesel engines (about 80 % of the total fleet in Paraguay). Most of experimental studies of Diesel fuel combustion are performed using internal combustion engines, in order to characterize the emission and performance of the engine. From the numerical point of view, many studies are performed using homogeneous reactors. However, mainly due to the complexity of its chemical composition, there are only few studies on kinetic modeling of such fuel in a 1D configuration. This paper presents numerical studies of Diesel surrogate combustion in laminar counterflow diffusion flame configuration. The key objective of the study is to understand the flame structure of Diesel fuel and validate the kinetic models used in the simulations. The kinetic modelling for Diesel oxidation in the counterflow diffusion flame was performed using the COUNTERFLOW code within the REGATH package developed at EM2C laboratory (Centrale Supelec, France), that takes into account the detailed kinetic and transport phenomena (heat and mass transfer) through a numerical predictive 1D code. A kinetic model was chosen to carry the simulations. This model consists of 150 species and 759 reactions. A surrogate Diesel fuel composed of n-heptane and toluene was chosen to represent Diesel chemistry. Different equivalence ratios and strain rates of Diesel counterflow diffusion flames were studied. The flames structures were analysed and presented.

Comparison between n-butanol and ethanol combustion kinetic models through one-dimensional premixed flame simulations

The alcohol n-Butanol is an organic substance being proposed as an alternative fuel for internal combustion engines. Improvements in its production as a bio-fuel, through fermentation processes, and its combustion characteristics, close to those of gasoline and diesel, grow attention to its viability as a renewable and economically interesting substitute to petrol-based fuels. However, few is known about its combustion characteristics, thus motivating research in that area. Ethanol is a bio-fuel widely used in commercial engines, specially in Brazil and the United States, and is a proposed blending agent for n-butanol. The present study compares chemical kinetic models for n-butanol, ethanol and their mixtures through numerical simulation in order to generate information for a future experiment, to be developed in a counter-flow laminar burner. In this equipment a mixture of fuel and air is injected through an axi-symmetric convergent burner against either the same mixture or a methane/air mixture. Hot gases are located between two flame fronts parallel to the stagnation plane. The flame front structure depends on the equivalence ratio and the strain rate. Strain rate can be changed by varying the injection velocities. In the present study,1-D formulation is employed to describe the premixed flame configuration. After that, further analysis in 1-D counter-flow configuration shall be done. The system is modeled by considering detailed chemical kinetics and multi-component transport properties.

Numerical characterization of different n-decane-ethanol blends combustion

Research and investments in renewable energy are important to reduce oil dependence, to improve energetic safety and to reduce environmental and public health damages caused by combustion emissions. Currently, diesel is the most popular fossil fuel in several countries, including Brazil, Paraguay and France. Sugar cane ethanol is widely used as fuel in Brazil, but only in Otto cycle engines. Nevertheless there are diverse researches revealing that it can be added to diesel and reduce particulate matter emissions of Diesel cycle engines among other advantages. Due to diesel chemical complexity, n-decane is usually used as a diesel simplified surrogate fuel. The objective of this work is to unveil the effects of ethanol addition in n-decane combustion. REGATH package was used in numerical simulation. A new chemical scheme was developed putting together two already validated chemical schemes simulating 1D premixed laminar flames. This scheme allows prediction of several combustion characteristics. Blends ranging from 5% to 30% ethanol (mol) were simulated with equivalence ratios ranging from 0.8 to 1.4. For each blend, flame speed, flame thickness, maximum temperature and CO and CO2 emissions were obtained. Blend’s results were similar to n-decane results, unveiling that the studied combustion properties did not change for ethanol proportions added.

Image processing and correction of the apparent broadening of species concentration profiles in laminar counterflow flames

This work study the influence of the light refraction in the apparent broadening of species experimental profiles in counterflow premixed flames. In fact, in a counterflow premixed flame, is generated a layered medium by the temperature gradient which induces a change in the milieu refractive index, causing a deviation of rays emitted by each point of the flame, and therefore producing a broadening of species experimental profiles. The Gladstone-Dale relation was used to estimate the medium refractive index along the burner axis, taking into account the gas density and composition. And then Snells law for an inhomogeneous medium was used in order to estimate the light refraction, due to the variation of the medium refractive index. As it will be shown, for counterflow premixed flames, the light refraction is negligible, due to the low variation of the medium refractive index along the counterflow burner. However, the same procedure described here can be used to study the light refraction in other experimental configurations, where the medium refractive index varies considerably.

Image representation of flames from data processing of an optical multichannel analyzer spectrometer

The aim of this paper is the analysis of flames by means of a high spectral resolution (OMA spectrometer), which provides information about the spectral intensity of the excited species CH* and C2*. The spectral data resolved in space are used for an image representation resolved in wavelength. The experimental configuration consisted of a premixed methane conical flame.