LES Study on Spray Combustion With Renewable Fuels Under ECN Spray-A Conditions

2021 ◽  
Author(s):  
Daniel Mira ◽  
Eduardo J. Pérez-Sánchez ◽  
Anurag Surapaneni ◽  
Jesús Benajes ◽  
José M. García-Oliver ◽  
...  
Keyword(s):  
Computational Study ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Liquid Fuels ◽  
Combustion Model ◽  
Low Carbon ◽  
Present Contribution ◽  
Modelling Framework ◽  
The Difference ◽  
Lift Off

Abstract Poly-Oxymethylene Dimethyl Ethers (OMEx) are being intensively investigated because of their potentially renewable synthesis path, which make them suitable as liquid fuels for low-carbon transport applications. In the present contribution, a computational study on the difference in combustion characteristics between dodecane and OMEx-type fuels under Engine Combustion Network (ECN) Spray A conditions is reported. In particular, a blend of different OMEx fuels have been investigated and compared to dodecane, which is a more conventional diesellike fuel. The modelling framework consists of a high-fidelity LES approach together with a Eulerian-Lagrangian spray model and flamelet-based turbulent combustion model. Results indicate ignition delay time and lift-off length according to the fuel reactivity properties, with the OMEx fuel performing similarly to dodecane. Flamelet calculations show that ignition of the oxygenated fuels is in general similar to that of dodecane, but it occurs at higher mixture fraction values due to the differences in stoichiometry. One of the most relevant outcomes of the study is the important effect that the oxygenated characteristics of OMEx has on the flame structure. Results show that for OMEx the reaction front is stabilized at distances closer to the nozzle than for dodecane, and that the flame shape as well as its internal structure is clearly affected.

scholarly journals Numerical simulation of n-dodecane spray combustion based on OpenFOAM

2021 ◽  
Vol 39 (3) ◽  
pp. 539-548
Author(s):  
Wengang Li ◽  
Yinli Xiao ◽  
Yipin Lu ◽  
Zhibo Cao ◽  
Juan Wu
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Fuel Injection ◽  
Mixture Fraction ◽  
Spray Combustion ◽  
Combustion Model ◽  
Temperature Reaction ◽  
Penetration Length ◽  
Chemical Reaction Kinetics ◽  
Lift Off

For the purpose of providing the scientific insights to combustion characteristics of spray jet, numerical calculations of reacting and non-reacting spray cases are performed for ECN (engine combustion network) Spray A (n-dodecane spray combustion) which coupled finite chemistry combustion model PaSR and detailed chemical reaction kinetics based on OpenFOAM. The applicability and accuracy of the spray model is verified in the non-reacting spray case, and it is found that the predicted spray characteristics such as the penetration length of liquid and vapor and the mixture fraction are in good agreement with the test results. The two processes of low-temperature reaction and high-temperature ignition experienced by n-dodecane spray ignition are analyzed in reacting spray case, and it is found that the low-temperature reaction continues to exothermic before high-temperature ignition, and continues to proceed stably after high-temperature ignition, which promotes high-temperature ignition and flame stability. Finally, the effects of different fuel injection pressures on ignition delay time and flame lift-off length are studied.

Numerical Investigation of Flame Structure and Soot Formation in a Lab-Scale Rich-Quench-Lean Burner

2018 ◽  
Author(s):  
Andrea Giusti ◽  
Savvas Gkantonas ◽  
Jenna M. Foale ◽  
Epaminondas Mastorakos
Keyword(s):  
Numerical Simulations ◽  
Soot Formation ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Swirling Flows ◽  
Operating Conditions ◽  
Moment Closure ◽  
Combustion Model ◽  
Ethylene Flame ◽  
Soot Precursors

The understanding of the processes involved in soot formation and oxidation is a critical factor for a reliable prediction of emissions in aero-engines, particularly as legislation becomes increasingly stringent. This work studies the flame structure and soot formation in a lab-scale burner, which reproduces the main features of a Rich-Quench-Lean (RQL) combustor, using high-fidelity numerical simulations. The investigated burner, developed at the University of Cambridge, is based on a bluff-body swirl-stabilised ethylene flame, with air provided in the primary region through two concentric swirling flows and quenching enabled by means of four dilution jets at variable distance downstream. Measurements for different air split between the two inlet swirling flows and dilution ports, and different height of the dilution jets, indicate noticeable differences in the soot tendency. Numerical simulations have been performed using Large-Eddy Simulation with the Conditional Moment Closure combustion model and a two-equation model for soot, allowing a detailed resolution of the mixing field and to directly take into account the effect of turbulent transport on the flame structure, which has been shown to have an important effect on the soot formation and evolution. The main objective of this work is to study the flow field and mixing characteristics in the burner’s primary region, in order to improve the understanding of the mechanisms leading to the soot behaviour observed in the experiment at different operating conditions. Results show the key role of mixing in determining the level of soot in the burner, with the soot production mainly related to the extension of the flame zone characterized by a rich mixture, with pyrolysis products and soot precursors. The presence of additional dilution air seems to improve the oxidation and leads to a leaner mixture in the primary combustion region whereas the air added through the outer swirl stream seems to have less impact on the mixture formation in the primary region. Analysis of the solution in mixture fraction space shows the importance of residence time for the soot formation and highlights the existence of a range of values of mixture fraction, between 0.1 and 0.2, where the soot production terms are maximum. High residence times and local air-to-fuel ratio in the range of high soot production should be avoided to decrease the level of soot mass fraction in the burner.

scholarly journals Numerical study of turbulent normal diffusion flame CH4-air stabilized by coaxial burner

2013 ◽  
Vol 17 (4) ◽  
pp. 1207-1219 ◽  
Author(s):  
Zouhair Riahi ◽  
Ali Mergheni ◽  
Jean-Charles Sautet ◽  
Ben Nasrallah
Keyword(s):  
Equivalence Ratio ◽  
Numerical Study ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Air Jet ◽  
Fuel Jet ◽  
Jet Velocity ◽  
Lift Off

The practical combustion systems such as combustion furnaces, gas turbine, engines, etc. employ non-premixed combustion due to its better flame stability, safety, and wide operating range as compared to premixed combustion. The present numerical study characterizes the turbulent flame of methane-air in a coaxial burner in order to determine the effect of airflow on the distribution of temperature, on gas consumption and on the emission of NOx. The results in this study are obtained by simulation on FLUENT code. The results demonstrate the influence of different parameters on the flame structure, temperature distribution and gas emissions, such as turbulence, fuel jet velocity, air jet velocity, equivalence ratio and mixture fraction. The lift-off height for a fixed fuel jet velocity is observed to increase monotonically with air jet velocity. Temperature and NOx emission decrease of important values with the equivalence ratio, it is maximum about the unity.

Simulation of Heptane Jet Fire at Low Atmosphere Pressure

2012 ◽  
Vol 516-517 ◽  
pp. 1070-1073 ◽  
Author(s):  
Chang Jian Wang
Keyword(s):  
Atmospheric Pressure ◽  
Liquid Fuel ◽  
Mixture Fraction ◽  
Combustion Model ◽  
Maximum Value ◽  
Pressure Region ◽  
Safety Consideration ◽  
Low Atmospheric Pressure ◽  
Lift Off ◽  
Centerline Temperature

Due to safety consideration of storage and transportation of liquid fuel at low atmospheric pressure region, the influence of low atmospheric pressure on heptane jet fire was numerically investigated, based on LES and mixture-fraction combustion model. Injection heptane diameters satisfy Rosin-Rammler distribution. The simulation shows that, low atmospheric pressure has an evident effect on jet fire. It extends the fire length and shortens the lift-off height. The centerline temperature rises to the maximum value more rapidly and then it decays more slowly. The maximum centerline temperature is not sensitive to various atmospheric pressure.

Comparison of Representative Interactive Flamelet and Detailed Chemistry Based Combustion Models for Internal Combustion Engines

2014 ◽  
Author(s):  
M. Wang ◽  
M. Raju ◽  
E. Pomraning ◽  
P. Kundu ◽  
Y. Pei ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Internal Combustion Engines ◽  
Mixture Fraction ◽  
Spray Cooling ◽  
Combustion Model ◽  
Combustion Engines ◽  
Detailed Chemistry ◽  
Combustion Models ◽  
Computational Fluid Dynamics Cfd ◽  
Lift Off

Representative Interactive Flamelet (RIF) and Detailed Chemistry based combustion models are two commonly used combustion models for non-premixed diesel engine simulations. RIF performs transient chemistry calculations on a one-dimensional grid based on the mixture fraction coordinate. Hence, the chemistry calculations are essentially decoupled from the computational fluid dynamics (CFD) grid. The detailed chemistry model, on the other hand, solves transient chemistry in the 3D CFD domain. An efficient parallelization strategy is used for the computation of the multiple flamelets RIF model. The multiple flamelets RIF and detailed chemistry combustion models are applied for modeling a constant volume spray combustion case and a diesel engine case, with a view to compare the differences between the two models. Results for ignition delay, flame lift-off length, cylinder pressure, and emissions are compared with experimental data. The effect of number of flamelets is evaluated. Finally, the effect of spray cooling is investigated based on the results from the RIF model and the detailed chemistry based combustion model.

A Computational Study of H2/N2 Jet Diffusion Flame With Radiation Heat Loss

2004 ◽  
Author(s):  
M. A. Alim ◽  
W. Malalasekera
Keyword(s):  
Heat Loss ◽  
Diffusion Flame ◽  
Computational Study ◽  
Mixture Fraction ◽  
Beta Function ◽  
Flame Temperature ◽  
Chemical Species ◽  
Combustion Model ◽  
Radiation Heat ◽  
Radiation Heat Loss

In this work simulation of a turbulent H2/N2 jet diffusion flame with flamelet modeling has been presented. The favre averaged mixture fraction has been employed to model the combustion. Favre-averaged scalar quantities have been calculated from flamelet libraries by making use of a presumed Probability Density Function (PDF) method. To incorporate the effect of radiation heat transfer the combustion model has been extended using the concept of enthalpy defect. The predicted flame temperature profiles and chemical species concentrations with and without radiation heat loss are compared with experimental data. Predictions considering the radiation heat loss found to be in good agreement with temperature and chemical species measurements whereas the adiabatic model significantly overestimates temperatures in the downstream regions of flames where the significant heat loss occurs. This study shows that the combustion simulation using flamelet models considering radiation heat loss are effective for predicting the flow, temperature and chemical kinetics of H2/N2 jet diffusion flame. To account for fluctuations of mixture fraction, its distribution is presumed to have the shape of a beta-function.

Three-Dimensional Flame Structure in Wall-Fired Swirl Flame Combustors

1996 ◽  
Author(s):  
Ay Su ◽  
Ze-Chern Lee ◽  
Wu-Chi Ho
Keyword(s):  
Numerical Model ◽  
Power Plants ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Combustion Model ◽  
Reacting Flow ◽  
Inlet Conditions

A CFD solver CFX is used to analyze the complex behavior of turbulent reacting flow inside the furnace. The flow characteristics for various combustor geometries, fuel/air ratios, and injection velocities, and swirl levels are investigated. Starting with a cylindrical furnace fired with gaseous fuel from a concentric tube burner (both with and without swirl), the mixture-fraction is predicted using the k-ε and RSM turbulence models. The discrepancies between the predictions and measurements are most significant in the flame core of upstream regions. It may stem from inappropriateness of the assumed inlet conditions and the combustion model. However, the calculated results are still qualitatively acceptable. After the validation work of the numerical model, a rectangular furnace with four wall-fired swirling combustors is employed to investigate the effect of neighbouring burners and geometry on combustion characteristics. The central recirculation zone which appeared in the isothermal flowfield vanished in the combustion case. It may be attributed to the fact that the hot gas suddenly expands outward and destroys the recirculation mechanism. Thus, the central flame could not hold. In addition, the four corner flames are stretching against the wall and their shapes are similar to a “cam” profile. The results are intended to assist in the development and validation of a numerical model for predicting furnace flows in wall-fired power plants.

scholarly journals Influence of the chemical mechanism in the frame of diesel-like CFD reacting spray simulations using a presumed PDF flamelet-based combustion model

2017 ◽  
Author(s):  
Eduardo Javier Pérez-Sánchez ◽  
Francisco Payri ◽  
José María García-Oliver ◽  
Ricardo Novella
Keyword(s):  
Cfd Simulation ◽  
Flame Structure ◽  
Research Work ◽  
Combustion Process ◽  
Chemical Mechanism ◽  
Combustion Model ◽  
Key Species ◽  
Spatial Coordinates ◽  
Lift Off ◽  
Presumed Pdf

The ability of a computational fluid dynamics (CFD) simulation to reproduce the diesel-like reacting spray ignitionprocess and its corresponding flame structure strongly depends on both the fidelity of the chemical mechanismfor reproducing the oxidation of the fuel and also on how the turbulence-chemistry interaction (TCI) is modeled.Therefore, investigating the performance of different chemical mechanisms not only in perfect stirred reactors butdirectly in the diesel-like spray itself is of great interest in order to evaluate their suitability for being further appliedto CFD engine simulations.This research work focuses on applying a presumed probability density function (PDF) unsteady flamelet combustionmodel to the well-known spray A from the Engine Combustion Network (ECN), using three chemical mechanismswidely accepted by the scientific community as a way to figure out the influence of chemistry in the keycharacteristics of the combustion process in the frame of diesel-like spray simulations. Results confirm that in spiteof providing all of them correct trends for ignition delays (ID) and lift-off lengths (LOL), when comparing with experimentalresults, the structure of the flame presents noticeable differences, especially in the low and intermediatetemperatures and high equivalence ratio regions. Consequently, the selection of the chemical mechanism has animpact on the zones of influence of key species as observed in both spatial coordinates and also in the equivalenceratio-temperature maps. These differences are expected to be relevant considering the implications when couplingpollutant emissions models. The analysis of temperature and oxygen concentration parametric studies evidenceshow the observed differences are consistent and moderately dependent on the ambient conditions.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4746

Explaining the magnetism of gold

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Gas Phase ◽  
Computational Study ◽  
Formation Enthalpy ◽  
Gold Atom ◽  
Orbital Energy ◽  
Knudsen Effusion ◽  
Energy Diagram ◽  
Unpaired Electrons ◽  
The Difference ◽  
Good Agreement

<p>In the present work, a computational study is performed in order to clarify the possible magnetic nature of gold. For such purpose, gas phase Au<sub>2</sub> (zero charge) is modelled, in order to calculate its gas phase formation enthalpy. The calculated values were compared with the experimental value obtained by means of Knudsen effusion mass spectrometric studies [5]. Based on the obtained formation enthalpy values for Au<sub>2</sub>, the compound with two unpaired electrons is the most probable one. The calculated ionization energy of modelled Au<sub>2</sub> with two unpaired electrons is 8.94 eV and with zero unpaired electrons, 11.42 eV. The difference (11.42-8.94 = 2.48 eV = 239.29 kJmol<sup>-1</sup>), is in very good agreement with the experimental value of 226.2 ± 0.5 kJmol<sup>-1</sup> to the Au-Au bond<sup>7</sup>. So, as expected, in the specie with none unpaired electrons, the two 6s<sup>1</sup> (one of each gold atom) are paired, forming a chemical bond with bond order 1. On the other hand, in Au<sub>2</sub> with two unpaired electrons, the s-d hybridization prevails, because the relativistic contributions. A molecular orbital energy diagram for gas phase Au<sub>2</sub> is proposed, explaining its paramagnetism (and, by extension, the paramagnetism of gold clusters and nanoparticles).</p>

Finite Element Volume Analysis of Propane Preheated Air Flame Passing Through a Minichannel

2014 ◽  
Author(s):  
Masoud Darbandi ◽  
Majid Ghafourizadeh ◽  
Gerry E. Schneider
Keyword(s):  
Finite Element ◽  
Radiation Effects ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Current Method ◽  
Reacting Flow ◽  
Wall Functions ◽  
Flamelet Model ◽  
Combustion Modeling ◽  
Detailed Kinetics

A hybrid finite-element-volume FEV method is extended to simulate turbulent non-premixed propane air preheated flame in a minichannel. We use a detailed kinetics scheme, i.e. GRI mechanism 3.0, and the flamelet model to perform the combustion modeling. The turbulence-chemistry interaction is taken into account in this flamelet modeling using presumed shape probability density functions PDFs. Considering an upwind-biased physics for the current reacting flow, we implement the physical influence upwinding scheme PIS to estimate the cell-face mixture fraction variance in this study. To close the turbulence closure, we employ the two-equation standard κ-ε turbulence model incorporated with suitable wall functions. Supposing an optically thin limit, it needs to take into account radiation effects of the most important radiating species in the current modeling. Despite facing with so many flame instabilities in such small size configuration, the current method performs suitably with proper convergence, and the encountered instabilities are damped out automatically. Comparing with the experimental measurements, the current extended method accurately predicts the flame structure in the minichannel configuration.

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