Impact of Combustion Models on Emissions Predictions From a Piloted Methane-Air Diffusion Flame

2019 ◽  
Author(s):  
Chitralkumar V. Naik ◽  
Hossam Elasrag ◽  
Rakesh Yadav ◽  
Ahad Validi ◽  
Ellen Meeks
Keyword(s):  
Mixture Fraction ◽  
Flame Structure ◽  
Direct Integration ◽  
Finite Rate ◽  
Modeling Approaches ◽  
Combustion Models ◽  
Eddy Simulation ◽  
Flamelet Generated Manifold ◽  
Simulation Results ◽  
Detailed Kinetics

Abstract Combustion models can have a significant impact on flame simulations. While solving finite rate chemistry typically yields more accurate predictions, they depend significantly on the detailed kinetics mechanism used. To demonstrate the effect, Large Eddy Simulation (LES) of Sandia Flame D [1] has been performed using various combustion models. Four different detailed kinetics mechanisms have been considered. They include DRM mechanism with 22 species, GRI-mech 2.11 with 49 species, GRI-mech 3.0 with 53 species [2], and Model Fuel Library (MFL) mechanism with 29 species [3]. In addition to the mechanisms, two modeling approaches considered are direct integration of finite rate kinetics (FR) and Flamelet Generated Manifold (FGM). The performance is compared between combinations of the mechanisms and combustion-modeling approaches for prediction of the flame structure and pollutants, including NO and CO. The mesh contains about half a million hexahedral cells and LES statistics were collected over ten flow throughs. Advanced solvers including dynamic cell clustering using the Chemkin-CFD solver in Fluent have been used for faster simulation time. Based on comparison of simulation results to the measurements at various axial and radial positions, we find that the results using the FGM approach were comparable to those using direct integration of FR chemistry, except for NO. In general, the simulation results are in good agreement with the experiment in terms of aerodynamics, mixture fraction and temperature profiles. However, kinetics mechanisms were found to have the most pronounced effect on emissions predictions. NO was especially more sensitive to the kinetics mechanism. Both versions of the GRI-mech fell short in predicting emissions. Overall, the MFL mechanism was found to yield the closest match with the data for flame structure, CO, and NO.

Large eddy simulation of spark ignition of a bluff-body stabilized burner using a subgrid-ignition model coupled with FGM-based combustion models

2017 ◽  
Vol 27 (2) ◽  
pp. 400-427 ◽  
Author(s):  
Alain Fossi ◽  
Alain DeChamplain
Keyword(s):  
Bluff Body ◽  
Mixture Fraction ◽  
Aircraft Engines ◽  
Simulation Approach ◽  
Finite Rate ◽  
Content Type ◽  
Combustion Models ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ignition Kernel

Purpose Safety improvement and pollutant reduction in many practical combustion systems and especially in aero-gas turbine engines require an adequate understanding of flame ignition and stabilization mechanisms. Improved software and hardware have opened up greater possibilities for translating basic knowledge and the results of experiments into better designs. The present study deals with the large eddy simulation (LES) of an ignition sequence in a conical shaped bluff-body stabilized burner involving a turbulent non-premixed flame. The purpose of this paper is to investigate the impact of spark location on ignition success. Particular attention is paid to the ease of handling of the numerical tool, the computational cost and the accuracy of the results. Design/methodology/approach The discrete particle ignition kernel (DPIK) model is used to capture the ignition kernel dynamics in its early stage of growth after the breakdown period. The ignition model is coupled with two combustion models based on the mixture fraction-progress variable formulation. An infinitely fast chemistry assumption is first done, and the turbulent fluctuations of the progress variable are captured with a bimodal probability density function (PDF) in the line of the Bray–Moss–Libby (BML) model. Thereafter, a finite rate chemistry assumption is considered through the flamelet-generated manifold (FGM) method. In these two assumptions, the classical beta-PDF is used to model the temporal fluctuations of the mixture fraction in the turbulent flow. To model subgrid scale stresses and residual scalars fluxes, the wall-adapting local eddy (WALE) and the eddy diffusivity models are, respectively, used under the low-Mach number assumption. Findings Numerical results of velocity and mixing fields, as well as the ignition sequences, are validated through a comparison with their experimental counterparts. It is found that by coupling the DPIK model with each of the two combustion models implemented in a LES-based solver, the ignition event is reasonably predicted with further improvements provided by the finite rate chemistry assumption. Finally, the spark locations most likely to lead to a complete ignition of the burner are found to be around the shear layer delimiting the central recirculation zone, owing to the presence of a mixture within flammability limits. Research limitations/implications Some discrepancies are found in the radial profiles of the radial velocity and consequently in those of the mixture fraction, owing to a mismatch of the radial velocity at the inlet section of the computational domain. Also, unlike FGM methods, the BML model predicts the overall ignition earlier than suggested by the experiment; this may be related to the overestimation of the reaction rate, especially in the zones such as flame holder wakes which feature high strain rate due to fuel-air mixing. Practical implications This work is adding a contribution for ignition modeling, which is a crucial issue in various combustion systems and especially in aircraft engines. The exclusive use of a commercial computational fluid dynamics (CFD) code widely used by combustion system manufacturers allows a direct application of this simulation approach to other configurations while keeping computing costs at an affordable level. Originality/value This study provides a robust and simple way to address some ignition issues in various spark ignition-based engines, namely, the optimization of engines ignition with affordable computational costs. Based on the promising results obtained in the current work, it would be relevant to extend this simulation approach to spray combustion that is required for aircraft engines because of storage volume constraints. From this standpoint, the simulation approach formulated in the present work is useful to engineers interested in optimizing the engines ignition at the design stage.

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.

Numerical Investigation of Combustion Instabilities in a Single Element Lean Direct Inject (LDI) Combustor Using Flamelet Based Approaches

2019 ◽  
Author(s):  
Saurabh Patwardhan ◽  
Pravin Nakod ◽  
Stefano Orsino ◽  
Carlo Arguinzoni
Keyword(s):  
Experimental Data ◽  
Equivalence Ratio ◽  
Single Element ◽  
Pressure Amplitude ◽  
Combustion Instabilities ◽  
Time Step ◽  
Impedance Boundary ◽  
Combustion Models ◽  
Flamelet Generated Manifold ◽  
Simulation Results

Abstract In this paper, high-fidelity large eddy simulations (LES) along with flamelet based combustion models are assessed to predict combustion dynamics in low-emissions gas turbine combustor. A model configuration of a single element lean-direct-injection (LDI) combustor from Purdue University [1] is used for the validation of simulation results. Two combustion models based on the flamelet concept, i.e., steady diffusion flamelet (SDF) model and flamelet generated manifold (FGM) model are employed to predict combustion instabilities. Simulations are carried out for two equivalence ratios of φ = 0.6, and 0.4 and the results in the form of mode shapes, peak to peak pressure amplitude and power spectrum density (PSD) are compared with the experimental data of Huang et al. [1]. The effect of variation in the time step size for transient simulations is also studied. The time step sizes corresponding to Acoustic Courant numbers of 4, 8 and 16 are tested. Further, two numerical solver options, i.e., pressure based segregated solver and pressure based coupled solver are used in understanding their effect on the solution convergence regarding the number of time steps required to reach the limit cycle of the pressure oscillations. An additional test for reducing the overall simulation time is explored using a truncated (half) calculation domain and applying an appropriate acoustic impedance boundary condition at the truncated location. The simulation results from this test for the equivalence ratio of φ = 0.6 are compared with the simulation results from the corresponding full domain test. Overall, the simulation results compare well with the experimental data and trends are captured accurately. A clear dominant acoustic mode of 4L is observed for the equivalence ratio of 0.6 that compares well with the experimental data. For the equivalence ratio of 0.4, simulation results show that there is no dominant frequency and the energy is distributed among the first five modes. It is consistent with the observations in the experiments. Both combustion models (SDF and FGM) used in this study capture the combustion instabilities accurately. It builds confidence in flamelet based combustion models for the use in combustion instability modeling which is traditionally done using finite rate chemistry models based on reduced kinetics.

Development of a Multi-Phase Flamelet Generated Manifold for Spray Combustion Simulations

2020 ◽  
Author(s):  
Xu Zhang ◽  
Ran Yi ◽  
C. P. Chen
Keyword(s):  
Mixture Fraction ◽  
Diffusion Reaction ◽  
Spray Combustion ◽  
Direct Integration ◽  
Interphase Heat Transfer ◽  
Similarity Reduction ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Significant Difference ◽  
Mass Fractions

Abstract In this study, a model flame of quasi-1D counterflow spray flame has been developed. The two-dimensional multiphase convection-diffusion-reaction (CDR) equations have been simplified to one dimension using similarity reduction under the Eulerian framework. This model flame is able to directly account for non-adiabatic heat loss as well as multiple combustion regimes present in realistic spray combustion processes. A spray flamelet library was generated based on the model flame. To retrieve data from the spray flamelet library, the enthalpy was used as an additional controlling variable to represent the interphase heat transfer, while the mixing and chemical reaction processes were mapped to the mixture fraction and the progress variable. The spray-flamelet/progress-variable (SFPV) approach was validated against the results from the direct integration of finite-rate chemistry as a benchmark. The SFPV approach gave a better performance in terms of temperature predictions, while the conventional gas-phase flamelet/progress-variable (FPV) approach over-predicted by nearly 20%. In terms of species mass fractions, there was no significant difference between the two, both showing good agreements with the direct integration of chemistry (DIC) model.

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.

scholarly journals Assessment of Finite Rate Chemistry Large Eddy Simulation Combustion Models

2017 ◽  
Vol 99 (2) ◽  
pp. 385-409 ◽  
Author(s):  
E. Fedina ◽  
C. Fureby ◽  
G. Bulat ◽  
W. Meier
Keyword(s):  
Large Eddy Simulation ◽  
Finite Rate ◽  
Combustion Models ◽  
Eddy Simulation ◽  
Large Eddy

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

Co Emission Modeling in a Heavy Duty Annular Combustor Operating with Natural Gas

2021 ◽  
Author(s):  
Roberto Meloni ◽  
Stefano Gori ◽  
Antonio Andreini ◽  
Pier Carlo Nassini
Keyword(s):  
Turbulent Flame ◽  
Flame Temperature ◽  
Production Region ◽  
Turbulent Flame Speed ◽  
Eddy Simulation ◽  
Extinction Limit ◽  
Flamelet Generated Manifold ◽  
Annular Combustor ◽  
Definition Of ◽  
Co Emission

Abstract The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

Comparisons of Diesel PCCI Combustion Simulations Using a Representative Interactive Flamelet Model and Direct Integration of CFD With Detailed Chemistry

2006 ◽  
Vol 129 (1) ◽  
pp. 252-260 ◽  
Author(s):  
Song-Charng Kong ◽  
Hoojoong Kim ◽  
Rolf D. Reitz ◽  
Yongmo Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Direct Integration ◽  
Computational Cell ◽  
Flamelet Model ◽  
Detailed Chemistry ◽  
Engine Simulation ◽  
Integration Approach ◽  
Simulation Results ◽  
Release Data

Diesel engine simulation results using two different combustion models are presented in this study, namely the representative interactive flamelet (RIF) model and the direct integration of computational fluid dynamics and CHEMKIN. Both models have been implemented into an improved version of the KIVA code. The KIVA/RIF model uses a single flamelet approach and also considers the effects of vaporization on turbulence-chemistry interactions. The KIVA/CHEMKIN model uses a direct integration approach that solves for the chemical reactions in each computational cell. The above two models are applied to simulate combustion and emissions in diesel engines with comparable results. Detailed comparisons of predicted heat release data and in-cylinder flows also indicate that both models predict very similar combustion characteristics. This is likely due to the fact that after ignition, combustion rates are mixing controlled rather than chemistry controlled under the diesel conditions studied.

Sign in / Sign up

Export Citation Format

Share Document