Investigation of a Burner Function with Methane-Air Fuel Mixture (original) (raw)
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NO formation analysis of turbulent non-premixed coaxial methane/air diffusion flame
International Journal of Environmental Science and Technology, 2015
Natural gas combustion is one of the primary sources of harvesting energy for various processes and has gained a wide attention during the past decade. One of the most recent applications of natural gas combustion can be found in non-premixed combustion of methane in a coflow burner system. One of the main environmental concerns that arises from the natural gas combustion is the formation of NO produced by thermal NO and prompt NO mechanisms. Current paper is devoted on an examination of a 2D numerical simulation of turbulent non-premixed coaxial methane combustion in air enclosed by an axisymmetric cylindrical chamber to study the effects of species concentrations of reactants on NO formation, their individual contributions, and the chamber outlet temperature. A finitevolume staggered grid method is utilized to solve conservation equations of mass, energy, momentum, and species concentrations. In order to handle radiation heat transfer, discrete transfer method is used to solve radiation equation. Utilizing weighted-sum-of-gray-gases model, based on the newly obtained high-temperature molecular spectroscopic data, local variations of species absorption coefficients are taken into account. To calculate NO concentration, a single-or joint-variable probability density function in terms of a normalized temperature, mass fractions of species, or a combination of both is employed. Plus, published relevant experimental data are used to validate temperature and species concentration fields. It is shown that a decrease in N 2 concentration contributes to reducing NO. More importantly for higher O 2 mass fraction, thermal NO formation becomes the dominant mechanism responsible for NO emission.
A two-dimensional axis-symmetric numerical model was solved to investigate the effect of four turbulence models on combustion characteristics, such as the velocity, the pressure, the turbulent kinetic energy and the dissipation rate in a methane-air no-premixed flame. Based on the commercial CFD code Ansys fluent 17.0, different turbulence models including the standard k-ε model, the RNG k-ε model, the realizable k-ε model and the standard k-ω model were used to simulate the flow field in a simple burner. The eddy dissipation model with the global reaction schema was applied to model the turbulence reaction interaction in the flame region. A finite volume approach was used to solve the Navier-Stokes equations with the combustion model. Particularly, the effect of these turbulence models on the combustion characteristics was analyzed. The numerical predictions were validated by comparison with anterior experimental results. Moreover, the predicted axial and radial gradients of velocity in the standard k-ε are overall agreement with literature results. Cite This Article: O. Moussa, and Z. Driss, " Numerical Investigation of the Turbulence Models Effect on the Combustion Characteristics in a Non-Premixed Turbulent Flame Methane-Air.
A numerical simulation of none-premixed methane-air combustion is performed. The purpose of this paper is to provide information concerning the effect of inlet-air velocity (dry air) on the exhaust gas emissions of oxides of nitrogen (NO), for a simple type of combustor. Effects of increased inlet-air velocity on NOx formation are examined. Numerical results show that NO formation mechanisms, decrease, with increasing inlet-air velocity. The simulation has been performed using the Computational Fluid Dynamics (CFD) commercial code ANSYS CFX release 15, including laminar flamelet model, for simulating the methane combustion mixing with air (none-premixed combustion) and predicting concentration of (CH-CH2-CH2O-CH3-CH4-CHO-CO-CO2-O-O2-H-H2-H2O-HO2-N2-H2O2-OH).k-ε model was also investigated to predict the turbulent combustion reaction, which indicated the simulation results of velocities, temperatures and concentrations of combustion productions. A thermal and prompt Nox formation is performed for predicting NO emission characteristics. A comparison between the various inlet-air velocity, and their effects on NO emission characteristics and temperature fields are presented.
Thermal Science and Engineering Progress, 2018
The present work reports on the numerical investigation of NOx in three turbulent piloted diffusion flames of different levels of extinction. The study involves two-dimensional axisymmetric modeling of combustion in these flames with fairly detailed chemistry, i.e. GRI 3.0 mechanism. The main focus of the study is to analyze the effects of the two different combustion model approaches, such as infinitely fast chemistry based unsteady flamelet and finite rate chemistry based EDC, in predicting the NOx formation in three piloted methane jet flames (Sandia D, E, and F). The EDC approach is able to predict the passive scalar quantities but shows over-prediction in the reactive scalar quantities and NO prediction, while the unsteady flamelet modeling is found to be essential in predicting the accurate formation of slow kinetic species like NOx. The inability of flamelet and EDC approach in capturing localized flame extinction is observed, which lead to an over-prediction of NOx at larger downstream locations. Further, the dominance of NOx formation pathways is investigated in all three flames.
Effect of multistage combustion on NOx emissions in methane–air flames
Combustion and Flame, 2007
Coflow and counterflow methane-air flames are simulated over a complete partially premixed regime in order to characterize the effects of dominant combustion modes (i.e., single-, two-, and three-stage combustion) on NO x emissions. Simulations employ a comprehensive numerical model that uses detailed descriptions of transport and chemistry (GRI-2.11 mechanism) and includes radiation effects. It is demonstrated that a complete partially premixed regime, which extends from premixed flames to triple flames and then to double flames, can be simulated by suitably varying the equivalence ratios in the fuel-rich and fuel-lean streams, while maintaining the global equivalence ratio fixed. Both counterflow and coflow simulations show that NO x emissions decrease significantly from the premixed to the triple flame regime, and then increase from the triple to the double flame regime. Therefore, triple flames not only extend the rich and the lean flammability limits, but also exhibit superior NO x characteristics compared to the corresponding premixed flames and double flames, with thermal, prompt, NNH-intermediate, and N 2 O-intermediate routes being the important contributors (in descending order) to NO x formation. Coflow and counterflow flames exhibit qualitatively similar NO x characteristics in the entire partially premixed regime and an optimum level of partial premixing that yields the lowest NO x emission. The quantitative differences in NO x emissions between the two configurations can be attributed to geometry-dependent effects. In particular, compared to counterflow flames, the coflow flames have significantly larger flame volume and therefore lower peak temperature and NO x emission index in the triple flame regime.
Energies, 2021
This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by t...
Detailed Multi-dimensional Study of Pollutant Formation in a Methane Diffusion Flame
Energy & Fuels, 2012
This paper describes a method to produce chemical reactor networks (CRNs) consisting of large numbers of perfectly stirred reactors (PSRs) from computational fluid dynamics (CFD) simulations to predict pollutant emissions from combustion systems accurately, flexibly, and efficiently using detailed kinetic schemes and the kinetic post-processor (KPP) developed at Politecnico di Milano. Benefits of the method described here include its applicability to a wide range of combustion systems, its ability to predict emissions of a variety of pollutant species, and its speed. CFD and CFD−CRN simulation results of the Sandia D piloted methane−air diffusion round-jet flame are successfully validated against experimental data for axial velocity, mixture fraction, temperature, and speciation, including CO and NO mass fractions. A CRN consisting of a large number of PSRs is found to be required to simulate the system accurately, while ensuring independence of the solution from CRN size. The results of CFD−CRN analysis for a 1114 PSR network are used to study the pathways (thermal, prompt, N 2 O, and NO 2) by which NO and NO 2 , the constituents of NO x , are formed in the flame. Results of CFD−CRN analysis show that NO is produced in the high-temperature (T > 1850 K) flame brush by a combination of the prompt, N 2 O, and thermal pathways and in the intermediate-temperature (1000 < T < 1600 K) post-flame region by a reversal of the NO 2 pathway. NO is consumed in the fuelrich (mixture fraction, f > 0.43) region, where a low O atom concentration encourages a reversal of the prompt pathway (i.e., NO reburning), and in low-temperature (T < 1000 K) regions by the NO 2 pathway, which oxidizes NO to NO 2. Rate of production analysis, performed using CHEMKIN PRO at specified locations throughout the flame, shows that the trends of NO production and consumption observed in these simulations agree with expected and published results. Finally, the study predicts that, of the total NO x produced by the Sandia D flame, 47% is due to the prompt pathway, 32% is due to the N 2 O pathway, and 21% is due to the thermal pathway. As future steps in this work, the CFD−CRN method will be adapted and used to predict and study emissions from a range of more complex combustion systems.
Energy, 2013
A numerical study of NOx emission in hydrogenemethane non-premixed flame has been conducted under the moderate or intense low-oxygen dilution (MILD) conditions. In the simulation, the Eddy Dissipation Concept (EDC) model is applied. The predictions are validated by the experimental results for the three flames with the oxygen mass fraction varying from 3% to 9%. The model with the detailed chemical mechanisms can succeed in capturing the trend lines of NO level and predicting the NO formation at the low oxygen level. The simulation indicates that the low oxygen level leads to suppression of the NO formation. Analysis of the NO formation mechanisms shows that the NNH and prompt routes play a significant role in the NO formation under the MILD conditions. The effects of the coflow air temperature and hydrogen concentration in the fuel mixture on the NO formation are taken into account in the study. The results demonstrate that a decrease in fuel hydrogen concentration or a low coflow air temperature contributes to suppression of the NO formation.
Advances in Mechanical Engineering, 2020
A methodology for combustion modeling with complex mixing and thermodynamic conditions, especially in thrusters, is still under development. The resulting flow and propulsion parameters strongly depend on the models used, especially on the turbulence model as it determines the mixing efficiency. In this paper, the effect of the sigma-type turbulent diffusion coefficients arriving in the diffusion term of the turbulence model is studied. This study was performed using complex modeling, considering the conjugate effect of several physical phenomena such as turbulence, chemical reactions, and radiation heat transfer. To consider the varying turbulent Prandtl, an algebraic model was implemented. An adiabatic steady diffusion Flamelet approach was used to model chemical reactions. The P1 differential model with a WSGG spectral model was used for radiation heat transfer. The gaseous oxygen (GOX) and methane (GCH4) operating thruster developed at the Chair of turbomachinery and Flight prop...