An experimental and numerical study of NOx formation mechanisms in NH3-H2-Air flames

2012 ◽  
Author(s):  
Praveen Kumar
Keyword(s):  
Numerical Study ◽  
Formation Mechanisms ◽  
Nox Formation

Analysis of the Mixing and Emission Characteristics in a Model Combustor

2018 ◽  
Author(s):  
Shan Li ◽  
Shanshan Zhang ◽  
Lingyun Hou ◽  
Zhuyin Ren
Keyword(s):  
Gas Turbines ◽  
Schmidt Number ◽  
Numerical Study ◽  
Flame Temperature ◽  
Scalar Dissipation ◽  
Mixing Process ◽  
Nox Formation ◽  
Turbulent Schmidt Number ◽  
Wide Range ◽  
Air Mixing

Modern gas turbines in power systems employ lean premixed combustion to lower flame temperature and thus achieve low NOx emissions. The fuel/air mixing process and its impacts on emissions are of paramount importance to combustor performance. In this study, the mixing process in a methane-fired model combustor was studied through an integrated experimental and numerical study. The experimental results show that at the dump location, the time-averaged fuel/air unmixedness is less than 10% over a wide range of testing conditions, demonstrating the good mixing performance of the specific premixer on the time-averaged level. A study of the effects of turbulent Schmidt number on the unmixedness prediction shows that for the complex flow field involved, it is challenging for Reynolds-Averaged Navier-Stokes (RANS) simulations with constant turbulent Schmidt number to accurately predict the mixing process throughout the combustor. Further analysis reveals that the production and scalar dissipation are the key physical processes controlling the fuel/air mixing. Finally, the NOx formation in this model combustor was analyzed and modelled through a flamelet-based approach, in which NOx formation is characterized through flame-front NOx and its post-flame formation rate obtained from one-dimensional laminar premixed flames. The effect of fuel/air unmixedness on NOx formation is accounted for through the presumed probability density functions (PDF) of mixture fraction. Results show that the measured NOx in the model combustor are bounded by the model predictions with the fuel/air unmixedness being 3% and 5% of the maximum unmixedness. In the context of RANS, the accuracy in NOx prediction depends on the unmixedness prediction which is sensitive to turbulent Schmidt number.

A Numerical Study for the Relationship between Natural Manganese Dendrites and DLA Patterns

2016 ◽  
Vol 71 (3) ◽  
pp. 225-234
Author(s):  
Tugba Ozbey ◽  
Mehmet Bayirli
Keyword(s):  
Critical Exponent ◽  
Numerical Study ◽  
Formation Mechanisms ◽  
Diffusion Limited Aggregation ◽  
Density Correlation ◽  
Diffusion Limited ◽  
Crystalline Anisotropy ◽  
The Relationship ◽  
Good Agreement ◽  
Dla Model

AbstractThe formation mechanisms and the origin of manganese dendrites on the magnesite ore have been under discussion. The growth process of the manganese dendrites is statistically studied by comparing them to aggregations obtained according to the diffusion limited aggregation (DLA) model via Monte Carlo simulations. In this case, ten manganese dendrite patterns changing from the least dense to the densest aggregations on the surface are separately selected to determine the relationship between real and simulated patterns. The sticking parameter is ranged from 0.05≤t≤1. The density–density correlation functions C(r) (their critical exponent A), fractal dimension Df, critical exponent α, and critical exponent β pertaining to the root mean square (rms) thickness have been computed for both the ten manganese dendrites and the simulated aggregations representing them. The results indicate that manganese dendrites may be determined with the general DLA model. Analyses of manganese dendrites, both scaling and simulations, suggest the growth mechanism for the macroscopic expression of crystalline anisotropy for the dendritic patterns. These results are in good agreement with the values in other literature and can be helpful in comparing natural and simulated aggregations (both dendritic and compact deposits).

A numerical study on NOx formation in laminar counterflow CH4/air triple flames

2005 ◽  
Vol 143 (3) ◽  
pp. 282-298 ◽  
Author(s):  
Hongsheng Guo ◽  
Fengshan Liu ◽  
Gregory J. Smallwood
Keyword(s):  
Numerical Study ◽  
Nox Formation

Computational Evaluation of Low NOx Operating Conditions in Arch-Fired Boilers

1999 ◽  
Vol 121 (4) ◽  
pp. 735-740 ◽  
Author(s):  
N. Fueyo ◽  
V. Gambo´n ◽  
C. Dopazo ◽  
J. F. Gonza´lez
Keyword(s):  
Computational Model ◽  
Field Measurements ◽  
Operating Conditions ◽  
Formation Mechanisms ◽  
Local Concentration ◽  
Nox Formation ◽  
Operating Modes ◽  
Computational Evaluation ◽  
Chemical Conditions ◽  
Coal Boiler

In the present paper, a computational model is used to simulate the aero-dynamic, thermal, and chemical conditions inside an arch-fired coal boiler. The model is based on the Eulerian-Eulerian concept, in which Eulerian conservation equations are solved both for the gas and the particulate phases. A NOx formation and destruction submodel is used to calculate the local concentration of NO. The model is used to simulate a range of operating conditions in an actual, 350 MW, arch-fired boiler, with the aim of reducing, using primary measures, the emissions of NOx. The model results shed some light on the relevant NOx-formation mechanisms under the several operating conditions. Furthermore, they correlate well quantitatively with the available field measurements at the plant, and reproduce satisfactorily the tendencies observed under the different operating modes.

Experimental and Numerical Study of Steady and Modulated Transverse Jets at Low Blowing Ratios

2010 ◽  
Author(s):  
Guillaume Bidan ◽  
Pierre-Emmanuel Bouladoux ◽  
Jeremiah E. Oertling ◽  
Dimitris E. Nikitopoulos
Keyword(s):  
Steady State ◽  
Numerical Study ◽  
Mie Scattering ◽  
Formation Mechanisms ◽  
Transitional Region ◽  
Vortical Structures ◽  
Coverage Metrics ◽  
Jet In Crossflow ◽  
Wide Range ◽  
Hotwire Anemometry

The effects of jet flow pulsation were investigated in the case of a fully modulated vertical jet in crossflow over a flat plate using Mie scattering visualizations, hotwire anemometry and Large Eddy Simulations (LES). A preliminary steady state study was conducted over a wide range of blowing ratios to provide a baseline comparison to pulsed results in terms of vortical structures and performance. Based on observation of the vortical structures and hotwire signatures, two distinct regimes were identified separated by a transitional region. LES using the dynamic Smagorinsky sub-grid model were carried out to provide additional insights on vortical structures formation mechanisms and their effect on heat transfer results, showing good agreement with the experimental observations and measurements. The influence of the pulsing parameters such as mean, high and low blowing ratios, forcing frequency and duty cycle was explored in terms of jet coverage metrics and spanwise adiabatic effectiveness. Average blowing ratios of 0.250, 0.350 and 0.450, duty cycles of 25, 50 and 70% and forcing frequencies of St∞ = 0.008, 0.016, 0.079, and 0.159 were investigated. While in most of the cases, forced jets show a decrease in average performance compared to steady state configurations, some improvement was found in part of the forcing cycle. Vortical structures formed at the jet onset are consistent with the classification given by previous studies in terms of stroke-ratio and high blowing ratio over an overlapping range of conditions. The dynamics of the vortical structures formed at the pulse rise are highly responsible for the decrease in performance observed under forced conditions.

scholarly journals NUMERICAL STUDY ON ACCUMULATION MECHANISM OF CORAL GRAVELS AROUND BALLAST ISLAND, THE CORAL CAY OFF THE COAST OF IRIOMOTE ISLAND

2018 ◽  
pp. 93
Author(s):  
Yoshimitsu Tajima
Keyword(s):  
Field Survey ◽  
Numerical Study ◽  
Formation Mechanisms ◽  
Physical Mechanisms ◽  
Iriomote Island ◽  
Characteristic Behavior ◽  
Protection Strategies ◽  
Accumulation Mechanism

Understanding the formation mechanisms of a coral cay or a coral beach is essentially important to consider better conservation and protection strategies and measures of coral coast. Ballast island is a coral cay formed on the isolated reef located off the coast of Iriomote island, Okinawa, Japan. While this small coral cay frequently alters its shape under the attacks of severe waves, coral gravels gather around the island and keep the island around the same location. This study carries out the field survey and the numerical study to investigate the physical mechanisms of above mentioned characteristic behavior of coral gravels.

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