CH Kinetics Measurements and Their Importance for Modeling Prompt NOx Formation in Gas Turbines

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Sean P. Cooper ◽  
Clayton R. Mulvihill ◽  
Olivier Mathieu ◽  
Eric L. Petersen ◽  
Mark W. Crofton ◽  
...  
Keyword(s):  
Shock Tube ◽  
Chemical Kinetics ◽  
Gas Turbines ◽  
Near Infrared ◽  
Elevated Temperatures ◽  
Frequency Doubling ◽  
Tunable Laser ◽  
Detailed Chemical Kinetics ◽  
Reflected Shock ◽  
Time Histories

Abstract Recent work by the authors and others has uncovered the need for further chemical kinetic-related modeling and experiments, specifically for NOx kinetics at engine conditions. In particular, data on CH formation at realistic combustion conditions are needed for further refinement of the prompt-NOx kinetics. To this end, a series of shock-tube experiments to obtain CH concentration time histories at elevated temperatures was performed behind reflected shock waves at the Aerospace Corporation using a tunable laser. This Ti-Sapphire laser was operated in the near infrared at about 854 nm; blue light at 426.9 nm was obtained using an external, frequency-doubling crystal. The resulting light was used in a differential absorption setup with common-mode rejection to measure CH time histories. New measurements in CH4–C2H6–O2 mixtures highly diluted in argon were performed at temperatures between 1890 K and 2719 K. These new data are compared to several modern, detailed chemical kinetics mechanisms with updated NOx submechanisms. Sensitivity and rate of production analyses at the shock-tube conditions along with a gas turbine model are used to elucidate the current state of affairs in CH prediction by the literature models and its effect on NOx production, particularly through the prompt mechanism. A brief discussion of the chemical kinetics for an important reaction in the production of CH is also presented to emphasize the need for further study and refinement of reactions leading to CH production.

CH Kinetics Measurements and Their Importance for Modeling Prompt NOx Formation in Gas Turbines

2019 ◽  
Author(s):  
Sean P. Cooper ◽  
Clayton R. Mulvihill ◽  
Olivier Mathieu ◽  
Eric L. Petersen ◽  
Mark W. Crofton ◽  
...  
Keyword(s):  
Shock Tube ◽  
Chemical Kinetics ◽  
Gas Turbines ◽  
Near Infrared ◽  
Elevated Temperatures ◽  
Frequency Doubling ◽  
Chemical Kinetic ◽  
Detailed Chemical Kinetics ◽  
Reflected Shock ◽  
Time Histories

Abstract Recent work by the authors and others has uncovered the need for further chemical kinetic-related modeling and experiments, specifically for NOx kinetics at engine conditions. In particular, data on CH formation at realistic combustion conditions are needed for further refinement of the prompt-NOx kinetics. To this end, a series of shock-tube experiments to obtain CH concentration time histories at elevated temperatures was performed behind reflected shock waves at The Aerospace Corporation using a tuneable laser. This Ti-Sapphire laser was operated in the near infrared at about 854 nm; blue light at 426.9 nm was obtained using an external, frequency-doubling crystal. The resulting light was used in a differential absorption setup with common-mode rejection to measure CH time histories. New measurements in CH4-C2H6-O2 mixtures highly diluted in argon were performed at temperatures between 1890 K and 2719 K. These new data are compared to several modern, detailed chemical kinetics mechanisms with updated NOx submechanisms. Sensitivity and rate of production analyses at the shock-tube conditions along with a gas turbine model are used to elucidate the current state of affairs in CH prediction by the literature models and its effect on NOx production, particularly through the prompt mechanism. A brief discussion of the chemical kinetics for an important reaction in the production of CH is also presented to emphasize the need for further study and refinement of reactions leading to CH production.

Time-Resolved Measurements of Intermediate Concentrations in Fuel-Rich n-Heptane Oxidation Behind Reflected Shock Waves

2017 ◽  
Author(s):  
Zachary E. Loparo ◽  
Joseph G. Lopez ◽  
Sneha Neupane ◽  
Subith S. Vasu ◽  
William P. Partridge ◽  
...  
Keyword(s):  
Shock Waves ◽  
Shock Tube ◽  
Chemical Kinetics ◽  
Continuous Wave ◽  
Time Resolved ◽  
Ethylene Concentration ◽  
Reflected Shock ◽  
Concentration Time ◽  
Time Histories ◽  
Kinetics Of

The chemical kinetics of the oxidation of n-heptane (C7H16) — an important reference compound for real fuels — are well studied at stoichiometric and lean conditions. However, there is only limited information on the chemical kinetics of fuel-rich combustion. In order to improve the accuracy of chemical kinetic models at these conditions, the oxidation of rich n-heptane mixtures has been investigated. Combustion of n-C7H16/O2/Ar mixtures at equivalence ratios, ϕ, of 2.0 behind reflected shock waves has been studied at temperatures ranging from 1075 to 1418K and at pressures ranging from 1.6 to 1.9atm. Reaction progress was monitored by recording ethylene (C2H4) concentration time-histories and initial n-heptane decay rates at a location 2cm from the endwall of a 13.4m long, 14cm inner diameter shock tube. Ethylene and n-heptane concentration time-histories were measured using absorption spectroscopy at 10.532μm from a tunable CO2 laser and at around 3.4μm from a continuous wave distributed feedback interband cascade laser (ICL), respectively. The measured concentration time-histories were compared with modeled predictions from the Lawrence Livermore National Lab (LLNL) detailed n-heptane reaction mechanism. To the best of our knowledge, the current data are the first time-resolved n-heptane and ethylene concentration measurements conducted in a shock tube at these conditions.

scholarly journals Assessing NO2-Hydrocarbon Interactions during Combustion of NO2/Alkane/Ar Mixtures in a Shock Tube Using CO Time Histories

Fuels ◽  
2022 ◽  
Vol 3 (1) ◽  
pp. 1-14
Author(s):  
Olivier Mathieu ◽  
Sean P. Cooper ◽  
Sulaiman A. Alturaifi ◽  
Eric L. Petersen
Keyword(s):  
Natural Gas ◽  
Shock Tube ◽  
Gas Turbines ◽  
Rate Coefficients ◽  
Combustion Chemistry ◽  
Laser Absorption ◽  
Time Histories ◽  
Reduce Emissions ◽  
Main Components ◽  
Detailed Kinetics

Modern gas turbines use combustion chemistry during the design phase to optimize their efficiency and reduce emissions of regulated pollutants such as NOx. The detailed understanding of the interactions during NOx and natural gas during combustion is therefore necessary for this optimization step. To better assess such interactions, NO2 was used as a sole oxidant during the oxidation of CH4 and C2H6 (the main components of natural gas) in a shock tube. The evolution of the CO mole fraction was followed by laser-absorption spectroscopy from dilute mixtures at around 1.2 atm. The experimental CO profiles were compared to several modern detailed kinetics mechanisms from the literature: models tuned to characterize NOx-hydrocarbons interactions, base-chemistry models (C0–C4) that contain a NOx sub-mechanism, and a nitromethane model. The comparison between the models and the experimental profiles showed that most modern NOx-hydrocarbon detailed kinetics mechanisms are not very accurate, while the base chemistry models were lacking accuracy overall as well. The nitromethane model and one hydrocarbon/NOx model were in relatively good agreement with the data over the entire range of conditions investigated, although there is still room for improvement. The numerical analysis of the results showed that while the models considered predict the same reaction pathways from the fuels to CO, they can be very inconsistent in the selection of the reaction rate coefficients. This variation is especially true for ethane, for which a larger disagreement with the data was generally observed.

Numerical CFD evaluation of a flameless burner using detailed chemical kinetics

2017 ◽  
Author(s):  
Marco Antonio Nascimento ◽  
Lucilene Oliveria Rodrigues ◽  
Fagner Luis Goulart Dias
Keyword(s):  
Chemical Kinetics ◽  
Detailed Chemical Kinetics ◽  
Flameless Burner ◽  
Detailed Chemical

PARALLEL SOLVER FOR THE SIMULATIONS OF DETONATION WAVES ON UNSTRUCTURED GRIDS

2020 ◽  
Author(s):  
A. I. Lopato ◽  
◽  
A. G. Eremenko ◽  
Keyword(s):  
Chemical Kinetics ◽  
Numerical Scheme ◽  
Unstructured Grids ◽  
Numerical Study ◽  
Numerical Approach ◽  
Detonation Waves ◽  
Detailed Chemical Kinetics ◽  
Parallel Solver ◽  
Further Development ◽  
Detailed Chemical

Recently, we developed a numerical approach for the simulation of detonation waves on fully unstructured grids and applied it to the numerical study of the mechanisms of detonation initiation in multifocusing systems. Current work is devoted to further development of our numerical approach, namely, parallelization of the numerical scheme and introduction of more comprehensive detailed chemical kinetics scheme.

Shock-tube study of the decomposition of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1395-1426 ◽  
Author(s):  
Paul Sela ◽  
Sebastian Peukert ◽  
Jürgen Herzler ◽  
Christof Schulz ◽  
Mustapha Fikri
Keyword(s):  
Mass Spectrometry ◽  
Shock Tube ◽  
High Repetition Rate ◽  
Rate Coefficients ◽  
Gas Chromatography Mass Spectrometry ◽  
High Concentration ◽  
Gas Phase Chemistry ◽  
Reflected Shock ◽  
Flight Mass Spectrometry ◽  
Phase Chemistry

AbstractShock-tube experiments have been performed to investigate the thermal decomposition of octamethylcyclotetrasiloxane (D4, Si4O4C8H24) and hexamethylcyclotrisiloxane (D3, Si3O3C6H18) behind reflected shock waves by gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) in a temperature range of 1160–1600 K and a pressure range of 1.3–2.6 bar. The main observed stable products were methane (CH4), ethylene (C2H4), ethane (C2H6), acetylene (C2H2) and in the case of D4 pyrolysis, also D3 was measured as a product in high concentration. A kinetics sub-mechanism accounting for the D4 and D3 gas-phase chemistry was devised, which consists of 19 reactions and 15 Si-containing species. The D4/D3 submechanism was combined with the AramcoMech 2.0 (Li et al., Proc. Combust. Inst. 2017, 36, 403–411) to describe hydrocarbon chemistry. The unimolecular rate coefficients for D4 and D3 decomposition are represented by the Arrhenius expressions ktotal/D4(T) = 2.87 × 1013 exp(−273.2 kJ mol−1/RT) s−1 and ktotal/D3(T) = 9.19 × 1014 exp(−332.0 kJ mol−1/RT) s−1, respectively.

scholarly journals A Neural Network-Inspired Matrix Formulation of Chemical Kinetics for Acceleration on GPUs

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2710
Author(s):  
Shivam Barwey ◽  
Venkat Raman
Keyword(s):  
Neural Network ◽  
Chemical Kinetics ◽  
Graphics Processing Units ◽  
Source Term ◽  
Turbulent Flames ◽  
Peak Performance ◽  
Computational Time ◽  
Detailed Chemical Kinetics ◽  
The Matrix ◽  
Artificial Neural

High-fidelity simulations of turbulent flames are computationally expensive when using detailed chemical kinetics. For practical fuels and flow configurations, chemical kinetics can account for the vast majority of the computational time due to the highly non-linear nature of multi-step chemistry mechanisms and the inherent stiffness of combustion chemistry. While reducing this cost has been a key focus area in combustion modeling, the recent growth in graphics processing units (GPUs) that offer very fast arithmetic processing, combined with the development of highly optimized libraries for artificial neural networks used in machine learning, provides a unique pathway for acceleration. The goal of this paper is to recast Arrhenius kinetics as a neural network using matrix-based formulations. Unlike ANNs that rely on data, this formulation does not require training and exactly represents the chemistry mechanism. More specifically, connections between the exact matrix equations for kinetics and traditional artificial neural network layers are used to enable the usage of GPU-optimized linear algebra libraries without the need for modeling. Regarding GPU performance, speedup and saturation behaviors are assessed for several chemical mechanisms of varying complexity. The performance analysis is based on trends for absolute compute times and throughput for the various arithmetic operations encountered during the source term computation. The goals are ultimately to provide insights into how the source term calculations scale with the reaction mechanism complexity, which types of reactions benefit the GPU formulations most, and how to exploit the matrix-based formulations to provide optimal speedup for large mechanisms by using sparsity properties. Overall, the GPU performance for the species source term evaluations reveals many informative trends with regards to the effect of cell number on device saturation and speedup. Most importantly, it is shown that the matrix-based method enables highly efficient GPU performance across the board, achieving near-peak performance in saturated regimes.

scholarly journals Numerical Investigation of Pressure Influence on the Confined Turbulent Boundary Layer Flashback Process

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 146 ◽  
Author(s):  
Aaron Endres ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Gas Turbines ◽  
Separation Zone ◽  
Turbulent Flame ◽  
Pressure Rise ◽  
Flame Speed ◽  
Zone Size ◽  
Detailed Chemical Kinetics ◽  
Turbulent Flame Speed ◽  
Quenching Distance

Boundary layer flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0 . 5 and 3 . It was found that the flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at flashback conditions decrease with increasing pressure, which decreases flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases flashback propensity. It is not possible to predict the occurrence of boundary layer flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer flashback.

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