scholarly journals Evaluation of Emission Model for Diffusion Flame, Rich/Lean, and Premixed Lean Combustors

1993 ◽  
Author(s):  
N. K. Rizk ◽  
H. C. Mongia
Keyword(s):  
Diffusion Flame ◽  
Variable Structure ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Emission Model ◽  
Nox Formation ◽  
Model Calculations ◽  
Lean Combustion ◽  
Wide Range

A recently developed emission model was used to predict the emission characteristics of a gas turbine combustor. The model involves a multiple-step reaction scheme that addresses the breakup of the fuel into an intermediate hydrocarbon compound of variable structure. The reaction rate expressions developed in the present approach simulated the results obtained using a detailed chemical kinetic mechanism over a wide range of operation that is typically encountered in a conventional diffusion flame combustor, as well as low NOx rich/quench/lean, and premixed/prevaporized lean combustion concepts. The modeling of the combustor involves dividing the combustor into a number of reactors representing various combustion and near wall regions of the combustor. The calculations showed that the fuel reaction could proceed at a completely different rate depending on the conditions prevailing in each region of the combustor. The model results also indicated that at idle power mode the initial rate of NOx formation was high. However, due to the subsequent admission of air, no further addition to the NOx concentration was predicted at downstream locations. At high power levels, the fuel rich region near the combustor dome inhibits the formation of NOx. The admission of air in this case brings the fuel/air mixture close to the stoichiometric value causing a significant amount of NOx to form. The model calculations agreed quite well with the measured data of the combustor.

Reaction Model Development of Selected Aromatics as Relevant Molecules of a Kerosene Surrogate – The Importance of M-Xylene Within the Combustion of 1,3,5-Trimethylbenzene

2021 ◽  
Author(s):  
Astrid Ramirez Hernandez ◽  
Trupti Kathrotia ◽  
Torsten Methling ◽  
Marina Braun-Unkhoff ◽  
Uwe Riedel
Keyword(s):  
Atmospheric Pressure ◽  
Burning Velocity ◽  
Model Development ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Reaction Model ◽  
Pollutant Emissions ◽  
Similar Species ◽  
Ignition Delay Times ◽  
Wide Range

Abstract The development of advanced reaction models to predict pollutant emissions in aero-engine combustors usually relies on surrogate formulations of a specific jet fuel for mimicking its chemical composition. 1,3,5-trimethylbenzene is one of the suitable components to represent aromatics species in those surrogates. However, a comprehensive reaction model for 1,3,5-trimethylbenzene combustion requires a mechanism to describe the m-xylene oxidation. In this work, the development of a chemical kinetic mechanism for describing the m-xylene combustion in a wide parameter range (i.e. temperature, pressure, and fuel equivalence ratios) is presented. The m-xylene reaction submodel was developed based on existing reaction mechanisms of similar species such as toluene and reaction pathways adapted from literature. The sub-model was integrated into an existing detailed mechanism that contains the kinetics of a wide range of n-paraffins, iso-paraffins, cyclo-paraffins, and aromatics. Simulation results for m-xylene were validated against experimental data available in literature. Results show that the presented m-xylene mechanism correctly predicts ignition delay times at different pressures and temperatures as well as laminar burning velocities at atmospheric pressure and various fuel equivalence ratios. At high pressure, some deviations of the calculated laminar burning velocity and the measured values are obtained at stoichiometric to rich equivalence ratios. Additionally, the model predicts reasonably well concentration profiles of major and intermediate species at different temperatures and atmospheric pressure.

Combustion Simulation of Propane/Oxygen (With Nitrogen/Argon) Mixtures Using Rate-Controlled Constrained-Equilibrium

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Guangying Yu ◽  
Hameed Metghalchi ◽  
Omid Askari ◽  
Ziyu Wang
Keyword(s):  
Experimental Data ◽  
Energy System ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Oxygen Mixture ◽  
Free Valence ◽  
Wide Range ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
Good Agreement

The rate-controlled constrained-equilibrium (RCCE), a model order reduction method, has been further developed to simulate the combustion of propane/oxygen mixture diluted with nitrogen or argon. The RCCE method assumes that the nonequilibrium states of a system can be described by a sequence of constrained-equilibrium states subject to a small number of constraints. The developed new RCCE approach is applied to the oxidation of propane in a constant volume, constant internal energy system over a wide range of initial temperatures and pressures. The USC-Mech II (109 species and 781 reactions, without nitrogen chemistry) is chosen as chemical kinetic mechanism for propane oxidation for both detailed kinetic model (DKM) and RCCE method. The derivation for constraints of propane/oxygen mixture starts from the eight universal constraints for carbon-fuel oxidation. The universal constraints are the elements (C, H, O), number of moles, free valence, free oxygen, fuel, and fuel radicals. The full set of constraints contains eight universal constraints and seven additional constraints. The results of RCCE method are compared with the results of DKM to verify the effectiveness of constraints and the efficiency of RCCE. The RCCE results show good agreement with DKM results under different initial temperature and pressures, and RCCE also reduces at least 60% CPU time. Further validation is made by comparing the experimental data; RCCE shows good agreement with shock tube experimental data.

Theoretical Investigation of Autoignition of Combustible Gas Mixtures in Rapid Compression Machines

2002 ◽  
Author(s):  
Shaoping Shi ◽  
Daniel Lee ◽  
Sandra McSurdy ◽  
Michael McMillian ◽  
Steven Richardson ◽  
...  
Keyword(s):  
Experimental Data ◽  
Theoretical Investigation ◽  
Ignition Delay ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Independent Manner ◽  
Elementary Reactions ◽  
Chemical Kinetic Mechanism ◽  
Rapid Compression

In any theoretical investigation of ignition processes in natural gas reciprocating engines, physical and chemical mechanisms must be adequately modeled and validated in an independent manner. The Rapid Compression Machine (RCM) has been used in the past as a tool to validate both autoignition models as well as turbulent mixing effects. In this study, two experimental cases were examined. In the first experimental case, the experimental measurements of Lee and Hochgreb (1998a) were chosen to validate the simulation results. In their experiments, hydrogen/oxygen/argon mixtures were used as reactants. In the simulations, a reduced chemical kinetic mechanism consisting of 10 species and 19 elementary reactions coupled to a CFD software, Fluent 6, was used to simulate the autoignition. The ignition delay from the simulation agreed very well with that from the experimental data of Lee and Hochgreb, (1998b). In the second case, experimental data derived from an RCM with two opposed, pneumatically driven pistons (Brett et al., 2001) were used to study the autoignition of methane/oxygen/argon mixtures. The reduced chemical kinetic mechanism DRM22, derived from the GRI-Mech reaction scheme coupled to Fluent 6, was applied in the simulations. The DRM22 scheme included 22 species and 104 reactions. When methane/oxygen/argon mixture were simulated for the RCM, the ignition delay deviated about 15% from the experimental results. The simulation approaches as well as the validation results are discussed in detail in this paper. The paper also discusses an evaluation of reduced reaction models available in the literature for subsequent Fluent modeling.

Mathematical Imaging of Piloted Diffusion Methane-Air Flames Under Anisotropic Scalar Dissipation Rates

2005 ◽  
Author(s):  
Mohsen M. Abou-Ellail ◽  
Karam R. Beshay ◽  
David R. Halka
Keyword(s):  
Diffusion Flame ◽  
Dissipation Rate ◽  
Mixture Fraction ◽  
Flame Temperature ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Scalar Dissipation ◽  
Elementary Reactions ◽  
Chemical Kinetic Mechanism ◽  
Limiting Value

The present work is a numerical simulation of the, piloted, non-premixed, methane–air flame structure in a new mathematical imaging domain. This imaging space has the mixture fraction of diffusion flame Z1 and mixture fraction of pilot flame Z2 as independent coordinates to replace the usual physical space coordinates. The predications are based on the solution of two–dimensional set of transformed second order partial differential conservation equations describing the mass fractions of O2, CH4, CO2, CO, H2O, H2 and sensible enthalpy of the combustion products which are rigorously derived and solved numerically. A three–step chemical kinetic mechanism is adopted. This was deduced in a systematic way from a detailed chemical kinetic mechanism by Peters (1985). The rates for the three reaction steps are related to the rates of the elementary reactions of the full reaction mechanism. The interaction of the pilot flame with the non-premixed flame and the resulting modifications to the structure and chemical kinetics of the flame are studied numerically for different values of the scalar dissipation rate tensor. The dissipation rate tensor represents the flame stretching along Z1, the main mixture fraction, and in the perpendicular direction, along Z2, the pilot mixture fraction. The computed flame temperature contours are plotted in the Z1-Z2 plane for fixed values of the dissipation rate along Z1 and Z2.These temperature contours show that the flame will become unstable when the dissipate rates along Z1 and Z2 increase, simultaneously, to the limiting value for complete flame extinction of 45 s−1. However, the diffusion flame will extinguish for dissipate rates less than 20 1/s, if unpiloted. It is also noticed that the flame will remain stable if the dissipation rate along Z2 is increased to the limiting value, while the dissipation rate, along Z2, remains constant at a value less than 30 s−1.

Validated F-T Fuel Surrogate Model for Simulation of Jet-Engine Combustion

2010 ◽  
Author(s):  
Chitralkumar V. Naik ◽  
Karthik V. Puduppakkam ◽  
Abhijit Modak ◽  
Cheng Wang ◽  
Ellen Meeks
Keyword(s):  
Laminar Flame ◽  
Laboratory Data ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Reduction Techniques ◽  
Auto Ignition ◽  
Wide Range ◽  
Fuel Behavior ◽  
Detailed Kinetics ◽  
Surrogate Fuel

Validated surrogate models have been developed for two Fisher-Tropsch (F-T) fuels. The models started with a systematic approach to determine an appropriate surrogate fuel composition specifically tailored for the two alternative jet-fuel samples. A detailed chemical kinetic mechanism has been assembled for these model surrogates starting from literature sources, and then improved to ensure self-consistency of the kinetics and thermodynamic data. This mechanism has been tested against fundamental laboratory data on auto-ignition times, laminar flame-speeds, extinction strain rates, and NOx emissions. Literature data used to validate the mechanism include both the individual surrogate-fuel components and actual F-T fuel samples where available. As part of the validation, simulations were performed for a wide variety of experimental configurations, as well as a wide range of temperatures and equivalence ratios for fuel/air mixtures. Comparison of predicted surrogate-fuel behavior against data on real F-T fuel behavior also show the effectiveness of the surrogate-matching approach and the accuracy of the detailed-kinetics mechanisms. The resulting validated mechanism has been also reduced through application of automated mechanism reduction techniques to provide progressively smaller mechanisms, with different degrees of accuracy, that are reasonable for use in CFD simulations employing detailed kinetics.

An Experimental Study on Methane/Oxygen-Air Combustion With a Rapidly Mixed Type Tubular Flame Burner

2011 ◽  
Author(s):  
Baolu Shi ◽  
Tatsuya Kowari ◽  
Daisuke Shimokuri ◽  
Satoru Ishizuka
Keyword(s):  
Experimental Study ◽  
Diffusion Flame ◽  
Turbulent Combustion ◽  
Mixed Type ◽  
Diffusion Flames ◽  
Kinetic Mechanism ◽  
Pure Oxygen ◽  
Extinction Limit ◽  
Wide Range ◽  
Flame Burner

Methane/oxygen-air combustion has been attempted by using a rapidly mixed type tubular flame burner with four slits, from two of which a fuel is injected and from another two an oxidizer is injected. The oxygen concentration (molar) in the oxygen-air oxidizer has been varied from 21% (air) to 100% (pure oxygen). Results show that uniform tubular flame combustion can be obtained for a wide range of equivalence ratios, if the oxygen molar concentration in the oxygen-air oxidizer is less than about 50%. Above 50%, however, very intense turbulent combustion occurs frequently and the circular-shaped tubular flame is deformed as oval-shaped for most equivalence ratios. The uniform tubular flame range is reduced and quite limited in the vicinity of lean condition. Detailed observations show that for pure (or near pure) oxygen oxidizer, two diffusion flames are established between the fuel and oxidizer streams at the exits of the fuel slits, which prevents fuel from mixing with oxygen, resulting in a violent turbulent combustion downstream the slits. With use of a burner with smaller slit width, however, formation of the diffusion flame is inhibited and a uniform tubular flame can be established, although still limited close to the lean extinction limit. To fully understand the flame characteristics above, the burning velocities are calculated for various equivalence ratios as well as for various oxygen concentrations in the oxygen-air oxidizer using the CHEMKIN PREMIX code with the GRI kinetic mechanism.

scholarly journals Semianalytical Correlations for NOx, CO, and UHC Emissions

1992 ◽  
Author(s):  
N. K. Rizk ◽  
H. C. Mongia
Keyword(s):  
Kinetic Scheme ◽  
Large Data ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Emission Model ◽  
Future Goals ◽  
Unburned Hydrocarbon ◽  
Annular Combustor ◽  
Analytical Approaches ◽  
Detailed Chemical

To meet the future goals of reduced emissions produced by gas turbine combustors, a better understanding of the process of formation of various pollutants is required. Both empirical and analytical approaches are used to provide the exhaust concentrations of pollutants of interest such as NOx, CO, and unburned hydrocarbon with varying degrees of success. In the present investigation, an emission model that simulates the combustor by a number of reactors representing various combustion zones is proposed. A detailed chemical kinetic scheme was used to provide a fundamental basis for the derivation of a number of expressions that simulate the reaction scheme. The model addresses the combined effects of spray evaporation and mixing in the reaction zone. The model validation included the utilization of a large data base obtained for an annular combustor of a modern turbopropulsion engine. In addition to the satisfactory agreement with the measurements, the model provided insight into the regions within the combustor that could be responsible for the excessive formation of emissions. Methods to reduce the emissions may be implemented in light of such information.

Predictions of NOx Formation Under Combined Droplet and Partially Premixed Reaction of Diffusion Flame Combustors

1999 ◽  
Vol 124 (1) ◽  
pp. 31-38 ◽  
Author(s):  
N. K. Rizk ◽  
J. S. Chin ◽  
A. W. Marshall ◽  
M. K. Razdan
Keyword(s):  
Diffusion Flame ◽  
Liquid Droplet ◽  
Mixture Distribution ◽  
Fuel Vapor ◽  
Nox Emissions ◽  
Gas Temperature ◽  
Nox Formation ◽  
Primary Zone ◽  
Wide Range ◽  
Partially Premixed

A methodology is presented in this paper on the modeling of NOx formation in diffusion flame combustors where both droplet burning and partially premixed reaction proceed simultaneously. The model simulates various combustion zones with an arrangement of reactors that are coupled with a detailed chemical reaction scheme. In this model, the primary zone of the combustor comprises a reactor representing contribution from droplet burning under stoichiometric conditions and a mixing reactor that provides additional air or fuel to the primary zone. The additional flow allows forming a fuel vapor/air mixture distribution that reflects the unmixedness nature of the fuel injection process. Expressions to estimate the extent of deviation in fuel/air ratios from the mean value, and the duration of droplet burning under stoichiometric conditions were derived. The derivation of the expressions utilized a data base obtained in a parametric study performed using a conventional gas turbine combustor where the primary zone equivalence ratio varied over a wide range of operation. The application of the developed model to a production combustor indicated that most of the NOx produced under the engine takeoff mode occurred in the primary as well as the intermediate regions. The delay in NOx formation is attributed to the operation of the primary zone under fuel rich conditions resulting in a less favorable condition for NOx formation. The residence time for droplet burning increased with a decrease in engine power. The lower primary zone gas temperature that limits the spray evaporation process coupled with the leaner primary zone mixtures under idle and low power modes increases the NOx contribution from liquid droplet combustion in diffusion flames. Good agreement was achieved between the measured and calculated NOx emissions for the production combustor. This indicates that the simulation of the diffusion flame by a combined droplet burning and fuel vapor/air mixture distribution offers a promising approach for estimating NOx emissions in combustors, in particular for those with significant deviation from traditional stoichiometry in the primary combustion zone.

Investigating Trends in Simulated Ignition Timing Across a Wide Range of Conditions Including Fuel Reactivity

2012 ◽  
Author(s):  
Michael V. Johnson ◽  
S. Scott Goldsborough ◽  
Timothy A. Smith ◽  
Steven S. McConnell
Keyword(s):  
Ignition Delay ◽  
Equivalence Ratio ◽  
Computational Cost ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Ignition Timing ◽  
Ignition Delay Times ◽  
Wide Range ◽  
Initial Work ◽  
Ci Engines

Continued interest in kinetically-modulated combustion regimes, such as HCCI and PCCI, poses a significant challenge in controlling the ignition timing due to the lack of direct control of combustion phasing hardware available in traditional SI and CI engines. Chemical kinetic mechanisms, validated based on fundamental data from experiments like rapid compression machines and shock tubes, offer reasonably accurate predictions of ignition timing; however utilizing these requires high computational cost making them impractical for use in engine control schemes. Empirically-derived correlations offer faster control, but are generally not valid beyond the narrow range of conditions over which they were derived. This study discusses initial work in the development of an ignition correlation based on a detailed chemical kinetic mechanism for three component gasoline surrogate, composed of n-heptane, iso-octane and toluene, or toluene reference fuel (TRF). Simulations are conducted over a wide range of conditions including temperature, pressure, equivalence ratio and dilution for a range of tri-component blends in order to produce ignition delay time and investigate trends in ignition as pressure, equivalence ratio, temperature and fuel reactivity are varied. A modified, Arrhenius-based power law formulation will be used in a future study to fit the computed ignition delay times.

Semianalytical Correlations for NOx, CO, and UHC Emissions

1993 ◽  
Vol 115 (3) ◽  
pp. 612-619 ◽  
Author(s):  
N. K. Rizk ◽  
H. C. Mongia
Keyword(s):  
Kinetic Scheme ◽  
Large Data ◽  
Chemical Kinetic ◽  
Reaction Scheme ◽  
Emission Model ◽  
Future Goals ◽  
Unburned Hydrocarbon ◽  
Annular Combustor ◽  
Analytical Approaches ◽  
Detailed Chemical

To meet the future goals of reduced emissions produced by gas turbine combustors, a better understanding of the process of formation of various pollutants is required. Both empirical and analytical approaches are used to provide the exhaust concentrations of pollutants of interest such as NOx, CO, and unburned hydrocarbon with varying degrees of success. In the present investigation, an emission model that simulates the combustor by a number of reactors representing various combustion zones is proposed. A detailed chemical kinetic scheme was used to provide a fundamental basis for the derivation of a number of expressions that simulate the reaction scheme. The model addresses the combined effects of spray evaporation and mixing in the reaction zone. The model validation included the utilization of a large data base obtained for an annular combustor of a modern turbopropulsion engine. In addition to the satisfactory agreement with the measurements, the model provided insight into the regions within the combustor that could be responsible for the excessive formation of emissions. Methods to reduce the emissions may be implemented in light of such information.

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