Computational Fluid Dynamics Simulations of Lean Premixed Methane-Air Flame in a Micro-Channel Reactor Using Different Chemical Kinetics

2016 ◽  
Vol 14 (5) ◽  
pp. 1003-1015
Author(s):  
Junjie Chen ◽  
Baofang Liu ◽  
Xuhui Gao ◽  
Deguang Xu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Kinetic Models ◽  
Reaction Rate ◽  
Flame Structure ◽  
Flame Temperature ◽  
Flame Stability ◽  
Micro Channel ◽  
Micro Scale ◽  
Lean Premixed

Abstract Flame temperature and structure are a useful tool for describing flame dynamics and flame stability, especially at the micro-scale. The objective of this study is to examine the effect of different kinetic models (that have been proven to accurately predict the macro-combustion behavior of hydrocarbons) on the combustion characteristics and the flame stability in microreactors, and to explore the applicability of these kinetic models at the micro-scale. Computational fluid dynamics (CFD) simulations of lean premixed methane-air flame in micro-channel reactors were carried out to examine the effect of different reaction mechanisms (Mantel, Duterque and Fernández-Tarrazo model) on the reaction rate and the flame structure and temperature. The time-scales with regard to homogeneous reaction and heat transfer were analyzed. The CFD results indicate that kinetic models strongly affect flame stability. Large transverse gradients in temperature and species are observed in all kinetic models, despite the small scales of the microreactor. Preheating, combustion, and post-combustion regions can be distinguished only in Duterque and Mantel model. Duterque model causes a stable elongated homogeneous flame with a considerable ignition delay as well as a dead region with cold feed accumulation near the entrance, and is inappropriate for micro-combustion studies because of the seriously overestimated flame temperature. Fernández-Tarrazo model causes a rapid extinction and a flashback risk, and is also inappropriate for micro-combustion studies due to the significantly underestimated reaction rate, without taking all kinetic factors into account. Mantel model can accurately predict the micro-flame behavior and consequently can be used for describing micro-combustion.

scholarly journals CFD Indications of Premix Flame Stability in a Gas Turbine Combustor

1996 ◽  
Author(s):  
J. Allan
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Gas Turbine ◽  
Heating Rate ◽  
Flame Stability ◽  
Cfd Model ◽  
Gas Turbine Combustor ◽  
Flow Models ◽  
Cold Flow ◽  
Primary Zone

An approach for predicting the relative tendency for weak extinction among similar gas turbine premix combustors is presented. The method involves analyzing CFD (computational fluid dynamics) solutions so as to evaluate the recirculating masses in the primary zone and the resulting potential heating rate of incoming fresh mixture. Results are illustrated for two combustor geometries which look similar but have very different behaviour. The comparison between the combustors agrees with test data when the CFD model incorporates a simulation of the flame. The inadequacy of cold flow models for the purpose is shown.

NOx emissions in direct injection diesel engines – part 1: Development of a phenomenological NOx model using experiments and three-dimensional computational fluid dynamics

2017 ◽  
Vol 19 (3) ◽  
pp. 308-328 ◽  
Author(s):  
Clemens Brückner ◽  
Sushant Sunil Pandurangi ◽  
Panagiotis Kyrtatos ◽  
Michele Bolla ◽  
Yuri Martin Wright ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Ignition Delay ◽  
Flame Temperature ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Adiabatic Flame Temperature ◽  
Mixture Preparation ◽  
Start Of Combustion

There exists a well-established correlation of exhaust NOx emissions arising from diesel engines with the adiabatic flame temperature, in particular for conventional (i.e. short ignition delay, diffusion combustion-dominated) operating conditions. Most published NOx emission models rely on this correlation. However, numerous experimental studies have identified operating conditions where this correlation fails to capture the exhaust NOx trend. In this work, a novel phenomenological NOx model concept is introduced, including a first successful validation against experimental data. The model development is based on experimental observations and is supported by three-dimensional computational fluid dynamics computations, strengthening the understanding of the underlying mechanisms leading to the discrepancy between the adiabatic flame temperature and exhaust NOx trend. For long ignition delay operating conditions, the improved mixture preparation before ignition leads to reduced mixing rates during and after combustion. Both the improved mixture preparation before ignition and the instantaneous increase of mass observed above 2000 K after start of combustion are due to compression heating of the burned gases. Key features of the model are improved description of mixture distribution at start of combustion, NOx formed in products of premixed burn, different physical treatments of premixed and diffusion sourced products, and inherent consideration of burned gas compression heating. Model results capture the NOx emissions for conventional diesel combustion, as well as for operating conditions where the NOx emissions do not follow the adiabatic flame temperature trend. Moreover, the results show that the contribution of NOx from products from premixed burn and the consideration of compression heating effects on burned (post-flame) gases are essential to capture the NOx emissions under the latter conditions.

scholarly journals Emissions and Stability Characteristics of Flameholders for Lean-Premixed Combustion

1992 ◽  
Author(s):  
Jeffrey A. Lovett ◽  
Nesim Abuaf
Keyword(s):  
Bluff Body ◽  
Flame Temperature ◽  
Perforated Plate ◽  
Premixed Combustion ◽  
Flame Stability ◽  
Nox Emissions ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
The Stability ◽  
Lean Conditions

An experimental study was conducted to determine the NOx emissions and flame stability associated with various flameholders used to support lean-premixed combustion of natural gas at gas turbine conditions. Data were obtained for velocities of 6 to 24 m/s, initial temperatures of 533 to 650 K, and pressures of 3.4 to 13.6 atm. Bluff-body, perforated-plate, and swirl-stabilized flameholders were tested and compared. The results confirm that NOx emissions at ultra-lean conditions scale with the flame temperature and are essentially independent of flameholder geometry for typical combustor residence times. The stability behavior, however, was strongly affected by flameholder type, illustrating the influence of fluid mechanics on flame stability. The flame stability was related also to the dynamics produced by combustion instability. A swirl-stabilized flameholder demonstrated the best stability characteristics at the expense of flameholder pressure drop.

Computational fluid dynamics applied to a cement precalciner

2000 ◽  
Vol 214 (3) ◽  
pp. 269-280 ◽  
Author(s):  
D Giddings ◽  
C N Eastwick ◽  
S J Pickering ◽  
K Simmons
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Calcium Oxide ◽  
Coal Combustion ◽  
Reaction Rate ◽  
Gas Flows ◽  
Coal Particles ◽  
Computational Fluid Dynamics Cfd ◽  
Burning Coal ◽  
Future Work

This paper describes a study of the use of computational fluid dynamics (CFD) to investigate the performance of a precalciner vessel at a cement works, In this vessel, limestone, held in suspension, is calcined to calcium oxide and the endothermic reaction is supported by the combustion of coal. Results are presented from a CFD model that contains all the essential features of the precalciner as operated when burning coal. The model fully represents the reactions and fluid dynamics of the precalciner. Previously unidentified features are illustrated. Certain key features at points in the precalciner, where some limited measurements can be made, are compared with the parameters indicated by the computational model. The measurements are consistent with the results calculated by the model indicating fair validation. The CFD data show the following 1 The gases undergo distinct recirculation. 2 The coal particles entering at one inlet have significantly different trajectories and temperature histories from those entering at the second diametrically opposed inlet. 3 There is 90 per cent completion of coal combustion at the exit. 4 73 per cent limestone in the raw meal is calcined to calcined to calcium oxide at the exit from the precalciner. 5 The highest reaction rate of the raw meal is closer to one side of the vessel due to interaction with the gas flows. Future work is proposed which, firstly, will provide further validation of the results so far attained by selective measurements on the precalciner and, secondly, will model the combustion and aerodynamic behaviour of waste-derived fuels in the precalciner vessel, commencing with shredded car tyre chips.

scholarly journals Studi Perbandingan Perilaku Dalam Reaktor Kolom Gelembung Secara Non-Katalitik Dengan Simulasi CFD Terhadap Kadar ME Biodiesel

2020 ◽  
Vol 13 (1) ◽  
pp. 67-82
Author(s):  
Angga Defrian ◽  
Zulfakri Zulfakri
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reaction Rate ◽  
Cfd Simulation ◽  
Methyl Esters ◽  
Perforated Plate ◽  
Catalytic Method ◽  
Methanol Vapor ◽  
Surface Contact Area ◽  
Computational Fluid Dynamics Cfd

Abstrak. Biodiesel dihasilkan melalui reaksi transesterifikasi atau reaksi esterifikasi asam lemak bebas dan tergantung dari kualitas minyak nabati yang digunakan sebagai bahan baku. Teknologi produksi biodiesel memiliki 2 metode yaitu metode katalis dan non katalis. Salah satu metoda produksi biodiesel tanpa katalis adalah metoda superheated methanol vapor (SMV). Namun metode inimenghasilkan kadar biodiesel yang rendah dari SNI. Salah satu cara untuk meningkatkan kadar biodiesel dengan meningkatkan luas kontak permukaan antara gelembung metanol dengan minyak. Hal ini dilakukan dengan memberikan perforated plate (obstacle) di dalam kolom reaktor. Perancangan desain obstacle sangat mempengaruhi luas kontak permukaan antara metanol uap dan minyak. Beberapa jenis obstacle yang dirancang di simulasikan dengan metode Computational Fluid Dynamics (CFD), karena CFD dapat menggambarkan distribusi gelembung di dalam kolom reaktor, sehingga pembuatan obstacle dapat lebih tepat dan memudahkan menganalisa perilaku gelembung di dalam kolom reaktor. Hasil simulasi di-dapatkan luas kontak permukaan yang tertinggi menunjukkan desain obstacle A-4 dengan nilai sebesar 0.013635 m2/det. Namun kadar metil ester pada obstacle tersebut masih rendah dibandingkan dengan SNI yaitu sebesar 67.73% (w/w). Untuk kadar metil ester yang mendekati SNI adalah obstacle D-4 yaitu 94.55 % (w/w).Comparative Study Of Behavior In Non-Catalytic Bullet Column Reactors With CFD Simulation on Content me biodieselAbstract. Biodiesel is produced through transesterification reaction triglycerides or esterification of free fatty acids depending on the FFA content of the feedstock. The reaction normally requires a catalyst, even though the non-catalytic reaction has attracted significant attention recently. One of the non-catalytic method by using superheated methanol vapor (SMV). However, this method still has a low reaction rate and thereby needs to be improved by increasing the surface contact area between methanol vapor and oil. In this study, the utilization of a perforated plate (obstacle) in the reactor column was studied using computational fluid dynamics (CFD).  Several types of obstacles were designed and their influence on the reaction rate was evaluated through CFD simulation. The result shows that obstacle design A4 gave the highest contact surface (0.013635 m2/s), even though methyl ester concentration in the reaction product is still low (67.73 %w/w). For methyl esters which are close to SNI is design obstacle D-4, which is 94.55 %(w/w).  

Toward Machine Learned Highly Reduced Kinetic Models for Methane/Air Combustion

2021 ◽  
Author(s):  
Mark Kelly ◽  
Stephen Dooley ◽  
Gilles Bourque
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Kinetic Models ◽  
Laminar Flame ◽  
Error Function ◽  
Chemical Kinetic ◽  
Operating Conditions ◽  
Flux Analysis ◽  
Detailed Model ◽  
Computational Fluid Dynamics Cfd

Abstract Accurate low dimension chemical kinetic models for methane are an essential component in the design of efficient gas turbine combustors. Kinetic models coupled to computational fluid dynamics (CFD) and chemical reactor networks (CRN) provide quick and efficient ways to test the effect of operating conditions, fuel composition and combustor design compared to physical experiments. However, detailed chemical kinetic models are too computationally expensive for use in computational fluid dynamics (CFD). We propose a novel data orientated three-step methodology to produce compact kinetic models that replicate a target set of detailed model properties to a high fidelity. In the first step, a reduced kinetic model is obtained by removing all non-essential species from the NUIG18_17_C3 detailed model containing 118 species using path flux analysis (PFA). This reduced model is so small that it does not retain fidelity in calculations to the detailed model. Thus, it is numerically optimised to replicate the detailed model’s prediction in two rounds; First, to selected species (OH,H,CO and CH4) profiles in perfectly stirred reactor (PSR) simulations and then re-optimised to the detailed model’s prediction of the laminar flame speed. This is implemented by a purposely developed Machine Learned Optimisation of Chemical Kinetics (MLOCK) algorithm. The MLOCK algorithm systematically perturbs all three Arrhenius parameters for selected reactions and assesses the suitability of the new parameters through an objective error function which quantifies the error in the compact model’s calculation of the optimisation target. This strategy is demonstrated through the production of a 19 species and a 15 species compact model for methane/air combustion. Both compact models are validated across a range of 0D and 1D calculations across both lean and rich conditions and shows good agreement to the parent detailed mechanism. The 15 species model is shown to outperform the current state-of-art models in both accuracy and range of conditions the model is valid over.

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