An Improved Core Reaction Mechanism for C0-C4 Unsaturated Fuels and C0-C4 Fuel Blends

2012 ◽  
Author(s):  
Chitralkumar V. Naik ◽  
Karthik V. Puduppakkam ◽  
Ellen Meeks
Keyword(s):  
Reaction Mechanism ◽  
Gas Turbines ◽  
Carbon Number ◽  
Data Consistency ◽  
Estimation Methods ◽  
Experimental Measurements ◽  
Experimental Conditions ◽  
The Core ◽  
Wide Range ◽  
Core Reaction

Simulation of the combustion of fuels used in transportation and energy applications requires accurate chemistry representation of the fuel. Surrogate fuels are typically used to represent liquid fuels, such as gasoline, diesel or jet fuel, where the surrogate contains a handful of components. For gaseous fuels, surrogates are effectively used as well, where methane may be used to represent natural gas, for example. An accurate chemistry model of a surrogate fuel means a detailed reaction mechanism that contains the kinetics of all the molecular components of the fuel model. Since large hydrocarbons break down to smaller molecules during combustion, the core chemistry of C0 to C4 carbon number is critical to all such fuel models, whether gaseous or liquid. The usual method of assessing how accurate the fuel chemistry is involves modeling of fundamental combustion experiments, where the experimental conditions are well enough defined and well enough represented by the reacting-flow model to isolate the kinetics in comparisons between predictions and data. In the work reported here, we have been focused on developing a more comprehensive and accurate core (C0−C4) mechanism. Recently, we revisited the core mechanism to improve predictions of the pure saturated components (J Eng. Gas Turbines Power (2012) 134; doi:10.1115/1.4004388). In the current work, we focused on combustion of unsaturated C0−C4 fuel components and on the blends of C0−C4 fuels, including saturated components. The aim has been to improve predictions for the widest range of fundamental experiments as possible, while maintaining the accuracy achieved by the existing mechanism and the previous study of saturated components. In the validation, we considered experimental measurements of ignition delay, flame speed and extinction strain rate, as well as species composition in stirred reactors, flames and flow reactors. These experiments cover a wide range of temperatures, fuel-air ratios, and pressures. As in the previous work for saturated compounds, we examined uncertainties in the core reaction mechanism; including thermochemical parameters derived from a wide variety of sources, including experimental measurements, ab initio calculations, estimation methods and systematic optimization studies. Using sensitivity analysis, reaction-path analysis, consideration of recent focused studies of individual reactions, and an enforcement of data consistency, we have identified key updates required for the core mechanism. These updates resulted in improvements to predictions of results, as validated through comparison with experiments, for all the fuels considered, while maintaining the accuracy previously reported for the saturated C0−C4 components. Rate constants that were modified to improve predictions for a small number of reactions remain within expected uncertainty bounds.

An Improved Core Reaction Mechanism for Saturated C0–C4 Fuels

2011 ◽  
Author(s):  
Chitralkumar V. Naik ◽  
Karthik V. Puduppakkam ◽  
Ellen Meeks
Keyword(s):  
Reaction Mechanism ◽  
Validation Studies ◽  
Reaction Rate ◽  
High Pressures ◽  
Laminar Flame ◽  
Estimation Methods ◽  
Reaction Paths ◽  
The Core ◽  
Wide Range ◽  
Core Reaction

Accurate chemistry models are required to predict the combustion behavior of different fuels, such as synthetic gaseous fuels and liquid jet fuels. A detailed reaction mechanism contains chemistry for all the molecular components in the fuel or its surrogates. Validation studies that compare model predictions with the data from fundamental combustion experiments under well defined conditions. Such fundamental experiments are least affected by the effect of transport on chemistry. Therefore they are the most reliable means for determining a reaction mechanism’s predictive capabilities. Following extensive validation studies and analysis of detailed reaction mechanisms for a wide range of hydrocarbon components reported in our previously published work [1–5], we identified some common issues in the predictive nature of the mechanisms that are associated with inadequacies of the core (C0–C4) mechanism. For example predictions of laminar flame speeds and autoignition delay times for several fuels were inaccurate beyond the level of uncertainty in the data. This core mechanism is shared by all of the mechanisms for the larger hydrocarbon components. Unlike the reaction paths for larger hydrocarbon fuels, however, reaction paths for the core chemistry do not follow prescribed reaction rate-rules. In this work, we revisit our core reaction mechanism for saturated C0–C4 fuels, with the goal of improving predictions for the widest range of fundamental experiments as possible. To evaluate and validate the mechanism improvements, we performed a broad set of simulations of fundamental experiments. These experiments include measurements of ignition delay, flame speed and extinction strain rate, as well as species composition in stirred reactors, flames and flow reactors. The range of conditions covers low to high temperatures, very lean to very rich fuel-air ratios, and low to high pressures. Our core reaction mechanism contains thermochemical parameters derived from a wide variety of sources, including experimental measurements, ab initio calculations, estimation methods and systematic optimization studies. Each technique has its uncertainties and potential inaccuracies. Using a systematic approach that includes sensitivity analysis, reaction-path analysis, consideration of recent literature studies, and an attention to data consistency, we have identified key updates required for the core mechanism. These updates resulted in accurate predictions for various saturated fuels when compared to the data over a broad range of conditions. All reaction rate constants and species thermodynamics and transport parameters remain within known uncertainties and within physically reasonable bounds. Unlike most mechanisms in the literature, the mechanism developed in this work is self-consistent and contains chemistry of all saturated C0–C4 fuels.

An Improved Core Reaction Mechanism for Saturated C0-C4 Fuels

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Chitralkumar V. Naik ◽  
Karthik V. Puduppakkam ◽  
Ellen Meeks
Keyword(s):  
Reaction Mechanism ◽  
Validation Studies ◽  
Reaction Rate ◽  
High Pressures ◽  
Estimation Methods ◽  
Reaction Paths ◽  
Technical Paper ◽  
The Core ◽  
Wide Range ◽  
Core Reaction

Accurate chemistry models are required to predict the combustion behavior of different fuels, such as synthetic gaseous fuels and liquid jet fuels. A detailed reaction mechanism contains chemistry for all the molecular components in the fuel or its surrogates. Validation studies that compare model predictions with the data from fundamental combustion experiments under well-defined conditions are least affected by the effect of transport on chemistry. Therefore they are the most reliable means for determining a reaction mechanism’s predictive capabilities. Following extensive validation studies and analysis of detailed reaction mechanisms for a wide range of hydrocarbon components reported in our previously published work (Puduppakkam et al., 2010, “Validation Studies of a Master Kinetic Mechanism for Diesel and Gasoline Surrogate Fuels,” SAE Technical Paper No. 2010-01-0545; Naik et al., 2010, “Validated F-T Fuel Surrogate Model for Simulation of Jet-Engine Combustion,” Proc. ASME Turbo Expo, Paper No. GT2010-23709; Naik et al., 2010, “Applying Detailed Kinetics to Realistic Engine Simulation: The Surrogate Blend Optimizer and Mechanism Reduction Strategies,” SAE J. Engines 3(1), pp. 241–259; Naik et al., 2010, “Modeling the Detailed Chemical Kinetics of Mutual Sensitization in the Oxidation of a Model Fuel for Gasoline and Nitric Oxide,” SAE J. Fuels Lubr. 3(1), pp. 556–566; and Puduppakkam et al., 2009, “Combustion and Emissions Modeling of an HCCI Engine Using Model Fuels,” SAE Technical Paper No. 2009-01-0669), we identified some common issues in the predictive nature of the mechanisms that are associated with inadequacies of the core (C0-C4) mechanism, such as inaccurate predictions of laminar flame speeds and autoignition delay times for several fuels. This core mechanism is shared by all of the mechanisms for the larger hydrocarbon components. Unlike the reaction paths for larger hydrocarbon fuels; however, reaction paths for the core chemistry do not follow prescribed reaction rate-rules. In this work, we revisit our core reaction mechanism for saturated fuels, with the goal of improving predictions for the widest range of fundamental experiments. To evaluate and validate the mechanism improvements, we performed a broad set of simulations of fundamental experiments. These experiments include measurements of ignition delay, flame speed and extinction strain rate, as well as species composition in stirred reactors, flames and flow reactors. The range of conditions covers low to high temperatures, very lean to very rich fuel-air ratios, and low to high pressures. Our core reaction mechanism contains thermochemical parameters derived from a wide variety of sources, including experimental measurements, ab initio calculations, estimation methods and systematic optimization studies. Each technique has its uncertainties and potential inaccuracies. Using a systematic approach that includes sensitivity analysis, reaction-path analysis, consideration of recent literature studies, and an attention to data consistency, we have identified key updates required for the core mechanism. These updates resulted in accurate predictions for various saturated fuels when compared to the data over a broad range of conditions. All reaction rate constants and species thermodynamics and transport parameters remain within known uncertainties and within physically reasonable bounds. Unlike most mechanisms in the literature, the mechanism developed in this work is self-consistent and contains chemistry of all saturated fuels.

Measurements and Modeling of Ingress in a New 1.5-Stage Turbine Research Facility

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Marios Patinios ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
Gary D. Lock
Keyword(s):  
Theoretical Model ◽  
Gas Turbines ◽  
Test Facility ◽  
Radial Clearance ◽  
Operating Life ◽  
The Core ◽  
Wide Range ◽  
Purge Flow ◽  
Rotor Disk ◽  
Engine Components

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor disks as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance, and integrity of highly stressed, vulnerable engine components. Rim seals, fitted at the periphery of the disks, are used to minimize ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the disks. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. The fluid-dynamically scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure, and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

Measurements and Modelling of Ingress in a New 1.5-Stage Turbine Research Facility

2016 ◽  
Author(s):  
Marios Patinios ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
Gary D. Lock
Keyword(s):  
Theoretical Model ◽  
Gas Turbines ◽  
Test Facility ◽  
Radial Clearance ◽  
Operating Life ◽  
The Core ◽  
Wide Range ◽  
Purge Flow ◽  
Engine Components ◽  
First Time

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor discs as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance and integrity of highly-stressed, vulnerable engine components. Rim seals, fitted at the periphery of the discs, are used to minimise ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the discs. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. The fluid-dynamically-scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing-flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary-layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

Arylation of enelactams using TIPSOTf: reaction scope and mechanistic insight

2021 ◽  
Author(s):  
Tomasz J. Idzik ◽  
Zofia M. Myk ◽  
Łukasz Struk ◽  
Magdalena Perużyńska ◽  
Gabriela Maciejewska ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Multinuclear Nmr ◽  
Mechanistic Insight ◽  
Nmr Study ◽  
Wide Range

Triisopropylsilyltrifluoromethanesulfonate can be effectively used for the arylation of a wide range of enelactams. The multinuclear NMR study provided deep insights into the reaction mechanism.

Ligand-Enabled γ-C(sp3)–H Olefination of Free Carboxylic Acids

2020 ◽  
Author(s):  
Kiron Kumar Ghosh ◽  
Alexander Uttry ◽  
Francesca Ghiringhelli ◽  
Arup Mondal ◽  
Manuel van Gemmeren
Keyword(s):  
Reaction Mechanism ◽  
Carboxylic Acids ◽  
Michael Addition ◽  
Kinetic Studies ◽  
Wide Range ◽  
Palladium Catalyzed

We report the ligand enabled C(sp3)–H activation/olefination of free carboxylic acids in the γ-position. Through an intramolecular Michael-addition, δ-lactones are obtained as products. Two distinct ligand classes are identified that enable the challenging palladium-catalyzed activation of free carboxylic acids in the γ-position. The developed protocol features a wide range of acid substrates and olefin reaction partners and is shown to be applicable on a preparatively useful scale. Insights into the underlying reaction mechanism obtained through kinetic studies are reported.<br>

Strongly Coupled Redox-Linked Conformational Switching at the Active Site of the Non-Heme Iron-Dependent Dioxygenase, TauD

2019 ◽  
Author(s):  
Christopher John ◽  
Greg M. Swain ◽  
Robert P. Hausinger ◽  
Denis A. Proshlyakov
Keyword(s):  
Active Site ◽  
Structural Model ◽  
Heme Iron ◽  
Chemical Transformations ◽  
Experimental Conditions ◽  
Strongly Coupled ◽  
Non Heme Iron ◽  
Reversible Redox ◽  
Wide Range ◽  
Complex Structural

2-Oxoglutarate (2OG)-dependent dioxygenases catalyze C-H activation while performing a wide range of chemical transformations. In contrast to their heme analogues, non-heme iron centers afford greater structural flexibility with important implications for their diverse catalytic mechanisms. We characterize an <i>in situ</i> structural model of the putative transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a combination of spectroelectrochemical and semi-empirical computational methods, demonstrating that the Fe (III/II) transition involves a substantial, fully reversible, redox-linked conformational change at the active site. This rearrangement alters the apparent redox potential of the active site between -127 mV for reduction of the ferric state and 171 mV for oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural perturbations exhibit limited sensitivity to mediator concentrations and potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD complexes, thus attributing the reorganization to the protein moiety rather than the cosubstrates. Redox difference infrared spectra indicate a reorganization of the protein backbone in addition to the involvement of carboxylate and histidine ligands. Quantitative modeling of the transient redox response using two alternative reaction schemes across a variety of experimental conditions strongly supports the proposal for intrinsic protein reorganization as the origin of the experimental observations.

Duoethnography: A Polytheoretical Approach to (Re)Storing, (Re)Storying the Meanings That One Gives

2020 ◽  
pp. 396-423
Author(s):  
John Joseph Norris ◽  
Richard D. Sawyer
Keyword(s):  
Social Justice ◽  
Critical Theory ◽  
Third Space ◽  
The Third ◽  
The Core ◽  
Wide Range ◽  
Core Elements ◽  
Feminist Inquiry

This chapter summarizes the advancement of duoethnography throughout its fifteen-year history, employing examples from a variety of topics in education and social justice to provide a wide range of approaches that one may take when conducting a duoethnography. A checklist articulates what its cofounders consider the core elements of duoethnographies, additional features that may or may not be employed and how some studies purporting to be duoethnographies may not be so. The chapter indicates connections between duoethnography and a number of methodological concepts including the third space, the problematics of representation, feminist inquiry, and critical theory using published examples by several duoethnographers.

scholarly journals Soft-drop grooming for hadronic event shapes

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Jeremy Baron ◽  
Daniel Reichelt ◽  
Steffen Schumann ◽  
Niklas Schwanemann ◽  
Vincent Theeuwes
Keyword(s):  
Event Generator ◽  
Experimental Measurements ◽  
Event Shape ◽  
Matrix Elements ◽  
Underlying Event ◽  
Hadronic Event ◽  
Wide Range ◽  
Event Shapes ◽  
The Impact ◽  
Perturbative Corrections

Abstract Soft-drop grooming of hadron-collision final states has the potential to significantly reduce the impact of non-perturbative corrections, and in particular the underlying-event contribution. This eventually will enable a more direct comparison of accurate perturbative predictions with experimental measurements. In this study we consider soft-drop groomed dijet event shapes. We derive general results needed to perform the resummation of suitable event-shape variables to next-to-leading logarithmic (NLL) accuracy matched to exact next-to-leading order (NLO) QCD matrix elements. We compile predictions for the transverse-thrust shape accurate to NLO + NLL′ using the implementation of the Caesar formalism in the Sherpa event generator framework. We complement this by state-of-the-art parton- and hadron-level predictions based on NLO QCD matrix elements matched with parton showers. We explore the potential to mitigate non-perturbative corrections for particle-level and track-based measurements of transverse thrust by considering a wide range of soft-drop parameters. We find that soft-drop grooming indeed is very efficient in removing the underlying event. This motivates future experimental measurements to be compared to precise QCD predictions and employed to constrain non-perturbative models in Monte-Carlo simulations.

scholarly journals Low-Energy Electron Damage to Condensed-Phase DNA and Its Constituents

2021 ◽  
Vol 22 (15) ◽  
pp. 7879
Author(s):  
Yingxia Gao ◽  
Yi Zheng ◽  
Léon Sanche
Keyword(s):  
Condensed Phase ◽  
Genetic Material ◽  
High Energy ◽  
Dna Lesions ◽  
Low Energy ◽  
Experimental Investigations ◽  
Experimental Conditions ◽  
Strand Breaks ◽  
Sequence Of Events ◽  
Wide Range

The complex physical and chemical reactions between the large number of low-energy (0–30 eV) electrons (LEEs) released by high energy radiation interacting with genetic material can lead to the formation of various DNA lesions such as crosslinks, single strand breaks, base modifications, and cleavage, as well as double strand breaks and other cluster damages. When crosslinks and cluster damages cannot be repaired by the cell, they can cause genetic loss of information, mutations, apoptosis, and promote genomic instability. Through the efforts of many research groups in the past two decades, the study of the interaction between LEEs and DNA under different experimental conditions has unveiled some of the main mechanisms responsible for these damages. In the present review, we focus on experimental investigations in the condensed phase that range from fundamental DNA constituents to oligonucleotides, synthetic duplex DNA, and bacterial (i.e., plasmid) DNA. These targets were irradiated either with LEEs from a monoenergetic-electron or photoelectron source, as sub-monolayer, monolayer, or multilayer films and within clusters or water solutions. Each type of experiment is briefly described, and the observed DNA damages are reported, along with the proposed mechanisms. Defining the role of LEEs within the sequence of events leading to radiobiological lesions contributes to our understanding of the action of radiation on living organisms, over a wide range of initial radiation energies. Applications of the interaction of LEEs with DNA to radiotherapy are briefly summarized.

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