Modeling of a Turbulent Methanol Spray Flame by Means of an Eulerian Droplet Model and a Reaction Progress Variable gaseous Combustion Model.

2012 ◽  
Author(s):  
Jim Kok ◽  
Bram De Jager
Keyword(s):  
Combustion Model ◽  
Droplet Model ◽  
Reaction Progress ◽  
Progress Variable ◽  
Spray Flame

scholarly journals Analysis and flamelet modelling for spray combustion

2008 ◽  
Vol 612 ◽  
pp. 45-79 ◽  
Author(s):  
YUYA BABA ◽  
RYOICHI KUROSE
Keyword(s):  
Conservation Equation ◽  
Spray Combustion ◽  
Combustion Model ◽  
Flamelet Model ◽  
Jet Flame ◽  
Total Enthalpy ◽  
Progress Variable ◽  
Combustion Models ◽  
Spray Flame ◽  
Variable Approach

The validity of a steady-flamelet model and a flamelet/progress-variable approach for gaseous and spray combustion is investigated by a two-dimensional direct numerical simulation (DNS) of gaseous and spray jet flames, and the combustion characteristics are analysed. A modified flamelet/progress-variable approach, in which total enthalpy rather than product mass fraction is chosen as a progress variable, is also examined. DNS with an Arrhenius formation, in which the chemical reaction is directly solved in the physical flow field, is performed as a reference to validate the combustion models. The results show that the diffusion flame is dominant in the gaseous diffusion jet flame, whereas diffusion and premixed flames coexist in the spray jet flame. The characteristics of the spray flame change from premixed–diffusion coexistent to diffusion-dominant downstream. Comparisons among the results from DNS with various combustion models show the modified flamelet/progress-variable approach to be superior to the other combustion models, particularly for the spray flame. Where the behaviour of the gaseous total enthalpy is strongly affected by the energy transfer (i.e. heat transfer and mass transfer) from the dispersed droplet, and this effect can be accounted for only by solving the conservation equation of the total enthalpy. However, even the DNS with the modified flamelet/progress-variable approach tends to underestimate the gaseous temperature in the central region of the spray jet flame. To increase the prediction accuracy, a combustion model for the partially premixed flame for the spray flame is necessary.

Modeling of Turbulent Combustion of Lean Premixed Prevaporized Propane Using the CFI Combustion Model

2006 ◽  
Author(s):  
B. de Jager ◽  
J. B. W. Kok
Keyword(s):  
Gas Turbine ◽  
Source Term ◽  
Laminar Flame ◽  
Dimensional Space ◽  
Turbulent Flames ◽  
Combustion Model ◽  
Detailed Chemistry ◽  
Reaction Progress ◽  
One Dimensional ◽  
Progress Variable

In this paper combustion of propane under gas turbine conditions is investigated with a focus on the chemistry and chemical kinetics in turbulent flames. The work is aimed at efficient and accurate modeling of the chemistry of heavy hydrocarbons, ie. hydrocarbons with more than one carbon atom, as occurring in liquid fuels for gas turbine application. On the basis of one dimensional laminar flame simulations with detailed chemistry, weight factors are determined for optimal projection of species concentrations on one or several composed concentrations, using the Computational Singular Perturbation (CSP) method. This way the species concentration space of the detailed mechanism is projected on a one dimensional space spanned by the reaction progress variable for use in a turbulent simulation. In the projection process a thermochemical database is used to relate with the detailed chemistry of the laminar flame simulations. Transport equations are formulated in a RaNS code for the mean and variance of the reaction progress variable. The turbulent chemical reaction source term is calculated by presumed shape probability density function averaging of the laminar source term in the thermochemical database. The combined model is demonstrated and validated in a simulation of a turbulent premixed prevaporized swirling propane/air flame at atmospheric pressure. Experimental data are available for the temperature field, the velocity field and the unburnt hydrocarbon concentrations. The trends produced by CFI compare reasonable to the experiments.

Comparison of Performance of Flamelet Generated Manifold Model With That of Finite Rate Combustion Model for Hydrogen Blended Flames

2021 ◽  
Author(s):  
Sourabh Shrivastava ◽  
Ishan Verma ◽  
Rakesh Yadav ◽  
Pravin Nakod ◽  
Stefano Orsino
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Characteristics ◽  
Combustion Model ◽  
Finite Rate ◽  
Reaction Progress ◽  
Progress Variable ◽  
Combustion Models ◽  
Flamelet Generated Manifold ◽  
Chemistry Modeling

Abstract International Air Transport Association (IATA) sets a 50% reduction in 2005 CO2 emissions levels by 2050, with no increase in net emissions after 2020 [1]. The association also expects the global aviation demand to double to 8.2 billion passengers per year by 2037. These issues have prompted the aviation industry to focus intensely on adopting sustainable aviation fuels (SAF). Further, reduction in CO2 emission is also an active area of research for land-based power generation gas turbine engines. And fuels with high hydrogen content or hydrogen blends are regarded as an essential part of future power plants. Therefore, clean hydrogen and other hydrogen-based fuels are expected to play a critical role in reducing greenhouse gas emissions in the future. However, the massive difference in hydrogen’s physical properties compared to hydrocarbon fuels, ignition, and flashback issues are some of the major concerns, and a detailed understanding of hydrogen combustion characteristics for the conditions at which gas turbines operate is needed. Numerical combustion analyses can play an essential role in exploring the combustion performance of hydrogen as an alternative gas turbine engine fuel. While several combustion models are available in the literature, two of the most preferred models in recent times are the flamelet generated manifold (FGM) model and finite-rate (FR) combustion model. FGM combustion model is computationally economical compared to the detailed/reduced chemistry modeling using a finite-rate combustion model. Therefore, this paper aims to understand the performance of the FGM model compared to detailed chemistry modeling of turbulent flames with different levels of hydrogen blended fuels. In this paper, a detailed comparison of different combustion characteristics like temperature, species, flow, and NOx distribution using FGM and finite rate combustion models is presented for three flame configurations, including the DLR Stuttgart jet flame [2], Bluff body stabilized Sydney HM1 flame [3] and dry-low-NOx hydrogen micro-mix combustion chamber [4]. One of the FGM model’s essential parameters is to select a suitable definition of the reaction progress variable. The reaction progress variable should monotonically increase from the unburnt region to the burnt region. The definition is first studied using a 1D premixed flame with different blend ratios and then used for the actual cases. 2D/3D simulations for the identified flames are performed using FGM and finite rate combustion models. Numerical results from both these models are compared with the available experimental data to understand FGM’s applicability. The results show that the FGM model performs reasonably well for pure hydrogen and hydrogen blended flames.

A New Combustion Model Based on Transport of Mean Reaction Progress Variable in a Spark Ignition Engine

2008 ◽  
Author(s):  
Dongkyu Lee ◽  
Insuk Han ◽  
Kang Y. Huh ◽  
Je-Hyung Lee ◽  
Sung-Jun Kim ◽  
...  
Keyword(s):  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Combustion Model ◽  
Reaction Progress ◽  
Progress Variable ◽  
Model Based

Numerical Simulations of a Premixed Turbulent Confined Jet Flame Using the Flamelet Generated Manifold Approach With Heat Loss Inclusion

2013 ◽  
Author(s):  
A. Donini ◽  
S. M. Martin ◽  
R. J. M. Bastiaans ◽  
J. A. van Oijen ◽  
L. P. H. de Goey
Keyword(s):  
Heat Loss ◽  
Computational Effort ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Conductive Heat ◽  
Jet Flame ◽  
Reaction Progress ◽  
Progress Variable ◽  
Air Jet ◽  
Flamelet Generated Manifold

In the present paper a computational analysis of a confined premixed turbulent methane/air jet flame is presented. In this scope, chemistry is reduced by the use of the Flamelet Generated Manifold (FGM) method [1, 2], and the fluid flow is modeled in a RANS context. In the FGM technique the reaction progress of the flame is generally described by a few control variables, for which a transport equation is solved during runtime. The flamelet system is computed in a pre-processing stage, and a manifold with all the information about combustion is stored in a tabulated form. In the present implementation the reaction evolution is described by the reaction progress variable, the heat loss is described by the enthalpy and the turbulence effect on the reaction is represented by the progress variable variance. The turbulence-chemistry interaction is considered through the use of a presumed pdf approach. A generic lab scale burner for high-velocity preheated jets is used for validation [3, 4]. It consists of a rectangular confinement, and an off-center positioning of the jet nozzle enables flame stabilization by recirculation of hot combustion products. The inlet speed is appropriately high, in order to be close to the blow out limit. Flame structures were visualized by OH* chemiluminescence imaging and planar laser-induced fluorescence of the OH radical. Laser Raman scattering was used to determine concentrations of the major species and the temperature. Velocity fields were measured with particle image velocimetry. The important effect of conductive heat loss to the walls is included in the FGM chemistry reduction method in a RANS context, in order to predict the evolution and description of a turbulent jet flame in high Reynolds number flow conditions. Comparisons of various mean fields (velocities, temperatures) with RANS results are shown. The use of FGM as a combustion model shows that combustion features at gas turbine conditions can be satisfactorily reproduced with a reasonable computational effort.

scholarly journals Assessment of Extrapolation Relations of Displacement Speed for Detailed Chemistry Direct Numerical Simulation Database of Statistically Planar Turbulent Premixed Flames

2021 ◽  
Author(s):  
Nilanjan Chakraborty ◽  
Alexander Herbert ◽  
Umair Ahmed ◽  
Hong G. Im ◽  
Markus Klein
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Premixed Flames ◽  
Turbulent Premixed Flames ◽  
Reaction Progress ◽  
Progress Variable ◽  
Stretch Rate ◽  
Non Linear ◽  
Displacement Speed ◽  
Curvature Dependence

AbstractA three-dimensional Direct Numerical Simulation (DNS) database of statistically planar $$H_{2} -$$ H 2 - air turbulent premixed flames with an equivalence ratio of 0.7 spanning a large range of Karlovitz number has been utilised to assess the performances of the extrapolation relations, which approximate the stretch rate and curvature dependences of density-weighted displacement speed $$S_{d}^{*}$$ S d ∗ . It has been found that the correlation between $$S_{d}^{*}$$ S d ∗ and curvature remains negative and a significantly non-linear interrelation between $$S_{d}^{*}$$ S d ∗ and stretch rate has been observed for all cases considered here. Thus, an extrapolation relation, which assumes a linear stretch rate dependence of density-weighted displacement speed has been found to be inadequate. However, an alternative extrapolation relation, which assumes a linear curvature dependence of $$S_{d}^{*}$$ S d ∗ but allows for a non-linear stretch rate dependence of $$S_{d}^{*}$$ S d ∗ , has been found to be more successful in capturing local behaviour of the density-weighted displacement speed. The extrapolation relations, which express $$S_{d}^{*}$$ S d ∗ as non-linear functions of either curvature or stretch rate, have been found to capture qualitatively the non-linear curvature and stretch rate dependences of $$S_{d}^{*}$$ S d ∗ more satisfactorily than the linear extrapolation relations. However, the improvement comes at the cost of additional tuning parameter. The Markstein lengths LM for all the extrapolation relations show dependence on the choice of reaction progress variable definition and for some extrapolation relations LM also varies with the value of reaction progress variable. The predictions of an extrapolation relation which involve solving a non-linear equation in terms of stretch rate have been found to be sensitive to the initial guess value, whereas a high order polynomial-based extrapolation relation may lead to overshoots and undershoots. Thus, a recently proposed extrapolation relation based on the analysis of simple chemistry DNS data, which explicitly accounts for the non-linear curvature dependence of the combined reaction and normal diffusion components of $$S_{d}^{*}$$ S d ∗ , has been shown to exhibit promising predictions of $$S_{d}^{*}$$ S d ∗ for all cases considered here.

A Generalized FGM Progress Variable Weight Optimization Using HEEDS

2017 ◽  
Author(s):  
Graham Goldin ◽  
Yongzhe Zhang
Keyword(s):  
Constant Pressure ◽  
Operating Conditions ◽  
Weighted Sum ◽  
Weight Optimization ◽  
Reaction Progress ◽  
Optimization Software ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Variable Weight ◽  
Mass Fractions

The Flamelet Generated Manifold (FGM) model requires a reaction progress variable which is usually defined as a weighted sum of species mass fractions. This progress variable should increase monotonically as flamelet states progress from unburnt to chemical equilibrium. A favorable attribute of the progress variable is that the flamelet species should change gradually with the progress variable, which reduces sensitivity of these species to any predicted errors in the progress variable. Previous publications have presented optimization algorithms for specific flamelet operating conditions, including fuel and oxidizer compositions and temperatures, and pressures. This work applies the HEEDS optimization software to find optimal species weights for a range of fuels and operating conditions. The fuels included are methane, methane-hydrogen, n-dodecane and n-heptane, at fuel-oxidizer temperatures of 293K and 1000K, and pressures of 1 and 30 atmospheres. For manifolds modeled by constant pressure ignition reactors, the optimal progress variable weights using four species weights are {αCO2 = 1, αCO = 0.91, αH2O = 0.52, αH2 = 1}, and for eight species weights are {αCO2 = 1, αCO = 0.91, αH2O = 0.51, αH2 = 1, αC2H2 = 0.16, αOH = −0.66, αH = −0.38, αO = 0.4}.

scholarly journals Understanding the diesel-like spray characteristics applying a flamelet-based combustion model and detailed large eddy simulations

2019 ◽  
Vol 21 (1) ◽  
pp. 134-150 ◽  
Author(s):  
Eduardo J Pérez-Sánchez ◽  
Jose M Garcia-Oliver ◽  
Ricardo Novella ◽  
Jose M Pastor
Keyword(s):  
Flame Stabilization ◽  
Large Eddy Simulations ◽  
Combustion Model ◽  
Progress Variable ◽  
Auto Ignition ◽  
Large Eddy ◽  
Engine Combustion ◽  
Spatial Fields ◽  
Lift Off ◽  
Good Agreement

This investigation analyses the structure of spray A from engine combustion network (ECN), which is representative of diesel-like sprays, by means of large eddy simulations and an unsteady flamelet progress variable combustion model. A very good agreement between modelled and experimental measurements is obtained for the inert spray that supports further analysis. A parametric variation in oxygen concentration is carried out in order to describe the structure of the flame and how it is modified when mixture reactivity is changed. The most relevant trends for the flame metrics, ignition delay and lift-off length are well-captured by the simulations corroborating the suitability of the model for this type of configuration. Results show that the morphology of the flame is strongly affected by the boundary conditions in terms of the reactive scalar spatial fields and Z–T maps. The filtered instantaneous fields provided by the simulations allow investigation of the structure of the flame at the lift-off length, whose positioning shows low fluctuations, and how it is affected by turbulence. It is evidenced that small ignition kernels appear upstream and detached from the flame that eventually merge with its base in agreement with experimental observations, leading to state that auto-ignition plays a key role as one of the flame stabilization mechanisms of the flame.

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