HyChem - A Physics-based Approach to Modeling Real-fuel Combustion Chemistry PDF Download

Author: Rui Xu (Mechanical engineer)
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Real fuels usually contain hundreds to thousands of hydrocarbon components. Over a wide range of combustion conditions, large hydrocarbon molecules undergo thermal decomposition first to form a small set (usually less than 10 species) of low molecular weight products, followed by the oxidation of those products, which is usually rate limiting. Hence, the composition of the decomposed products determines the overall global combustion properties. For conventional distillate fuels, the pyrolysis products comprise ethylene (C2H4), hydrogen (H2), methane (CH4), propene (C3H6), 1-butene (1-C4H8), iso-butene (i-C4H8), benzene (C6H6) and toluene (C7H8). From a joint consideration of thermodynamics and chemical kinetics, it is shown that the composition of the thermal decomposition products is a weak function of the thermodynamic condition, the equivalence ratio and the fuel composition within the range of temperatures relevant to high temperature combustion phenomena. In this dissertation study, I demonstrate a hybrid chemistry (HyChem) approach to modeling the high-temperature oxidation of real, liquid fuels. In this approach, the kinetics of fuel pyrolysis is modeled using experimentally derived, lumped reaction steps, while the oxidation of the pyrolysis fragments is described by a detailed foundational fuel chemistry model. A wide range of modeling results are provided to support the approach, including three conventional aviation fuels (JP-8 POSF10264, Jet A POSF10325, JP-5 POSF10289), two rocket fuels (RP2-1 POSF7688, RP2-2 POSF5433), and a bio-derived alternative jet fuel (Gevo alcohol-to-jet fuel, C1 POSF11498). The HyChem models of those fuels were developed using advanced speciation data obtained from shock tubes and a flow reactor, and the models were subsequently tested against global combustion properties, including ignition delay time, laminar flame speed, and flame extinction strain rates across a wide range of pressure, temperature and reactant mixture conditions. Sensitivity analysis of the model predictions with respect to the measurement uncertainties and rate parameter uncertainties of foundational fuel chemistry model is assessed. In this dissertation, the HyChem modeling approach was also extended to three key aspects critical to modeling fuel combustion over an even wider range of condition. First, a modified HyChem model was formulated for capturing the physics in negative temperature coefficient (NTC) and low-temperature oxidation regimes. Sensitivity test and suggestions on future NTC enabled HyChem model development are presented. Second, the HyChem approach was applied to modeling the blend of a conventional Jet A fuel and an alternative, alcohol-to-jet synthetic fuel. The pyrolysis as well as the combustion properties of several blended fuels were predicted by a simple combination of the HyChem models of the two individual fuels, thus demonstrating that the HyChem models for two jet fuels of very different compositions can be "additive" as far as high-temperature properties are concerned. Lastly, I will discuss a case study in which the HyChem model of Jet A is extended to NOx prediction after combining it with a recently updated reaction model of nitrogen chemistry. The combined reaction model is shown to predict NOx formation in premixed stretched-stabilized Jet A flames satisfactorily.

Author: Rishav Choudhary
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
The diversity of reactivities, intermediates, and pathways associated with the low-temperature oxidation of various component classes that constitute real fuels is perhaps the most challenging aspect of modeling combustion chemistry of these fuels. Unlike high-temperature oxidation (T > 1000 K), where the law of large numbers renders global combustion properties of real, multicomponent fuels weakly sensitive to compositional variability, reactions controlling low-temperature oxidation are very sensitive to fuel composition. Despite this fuel specificity, the formation of intermediates during low-temperature oxidation exhibits certain commonalities which can be observed in carefully designed shock tube experiments. Combining these observations with elemental balance, chemical kinetic considerations, and with the already mature Hybrid Chemistry (HyChem) approach for high-temperature oxidation of real fuels, I first propose an approach to develop simplified, physics-based chemical kinetic models for low-temperature oxidation of real fuels. In this approach, the low-temperature oxidation is described by lumped, fuel-specific reactions whose rate constants and stoichiometric parameters are determined using shock tube species time history measurements. These reactions augment the already developed high-temperature HyChem models which encompass fuel-specific reactions describing thermal and oxidative pyrolysis at high temperatures, and a detailed model describing kinetics of small hydrocarbons. Detailed arguments in support of the model formulation are presented. The model is then exercised to identify species to be targeted for measurements in shock tubes. Carbon monoxide (CO), and formaldehyde (CH2O) were identified as the most important species for determining the model parameters followed by OH, and HO2. Laser absorption spectroscopy based diagnostics for measuring some of these species were also developed in parallel with this work. The feasibility of the targeted speciation studies is first demonstrated during oxidation of five neat hydrocarbons, i.e., n-decane, n-octane, n-heptane, and its two branched isomers, 2-methyl hexane, and 3,3-dimethyl pentane. These studies not only demonstrated the feasibility of the diagnostics, but also highlighted the deficiency in the existing detailed models for low-temperature oxidation of heavy hydrocarbons. They also provided further evidence supporting some of the assumptions made while formulating the LT-HyChem approach. With the speciation strategy developed, and target experimental conditions verified, the application of the LT-HyChem approach to three classes of fuels is presented: a) A simple, three-component hydrocarbon mixture (TPRF-60), b) A jet fuel, c) Two high-performance gasoline fuels. Validation of the model against a range of ignition delay time (IDT) measurements conducted across a range of facilities worldwide is presented. The model predictions for all fuels show excellent agreement with the IDTs reported in the literature over a wide range of conditions. Moreover, the constraints imposed on the model parameters by the species time history measurements conducted in shock tubes result in a significant reduction in the uncertainty in the model's predictions. A detailed uncertainty analysis is presented and is supplemented with sensitivity analysis to identify the dominant contributing factors to the uncertainty in model predictions. The success of the LT-HyChem approach is encouraging as this approach can be extended to the sustainable fuels that will drive the engines of tomorrow. This will enable a rapid screening of candidates for the sustainable fuels of tomorrow.

Author: Jürgen Warnatz
Publisher: Springer Science & Business Media
ISBN: 3642980279
Category : Science
Languages : en
Pages : 309

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Book Description
Combustion is an old technology, which at present provides about 90% of our worldwide energy support. Combustion research in the past used fluid mechanics with global heat release by chemical reactions described with thermodynamics, assuming infinitely fast reactions. This approach was useful for stationary combustion processes, but it is not sufficient for transient processes like ignition and quenching or for pollutant formation. Yet pollutant formation during combustion of fossil fuels is a central topic and will continue to be so in future. This book provides a detailed and rigorous treatment of the coupling of chemical reactions and fluid flow. Also, combustion-specific topics of chemistry and fluid mechanics are considered, and tools described for the simulation of combustion processes. For the 2nd edition, the parts dealing with experiments, spray combustion, and soot were thoroughly revised.

Author: Kenneth Brezinsky
Publisher: Elsevier
ISBN: 0323993109
Category : Science
Languages : en
Pages : 666

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Book Description
As the demands for cleaner, more efficient, reduced and zero carbon emitting transportation increase, the traditional focus of Combustion Chemistry research is stretching and adapting to help provide solutions to these contemporary issues. Combustion Chemistry and the Carbon Neutral Future: What will the Next 25 Years of Research Require? presents a guide to current research in the field and an exploration of possible future steps as we move towards cleaner, greener and reduced carbon combustion chemistry. Beginning with a discussion of engine emissions and soot, the book goes on to discuss a range of alternative fuels, including hydrogen, ammonia, small alcohols and other bio-oxygenates, natural gas, syngas and synthesized hydrocarbon fuels. Methods for predicting and improving efficiency and sustainability, such as low temperature and catalytic combustion, chemical looping, supercritical fluid combustion, and diagnostic monitoring even at high pressure, are then explored. Some novel aspects of biomass derived aviation fuels and combustion synthesis are also covered. Combining the knowledge and experience of an interdisciplinary team of experts in the field, Combustion Chemistry and the Carbon Neutral Future: What will the Next 25 Years of Research Require? is an insightful guide to current and future focus areas for combustion chemistry researchers in line with the transition to greener, cleaner technologies. Provides insight on current developments in combustion chemistry as a tool for supporting a reduced-carbon future Reviews modeling and diagnostic tools, in addition to key approaches and alternative fuels Includes projections for the future from leaders in the field, pointing current and prospective researchers to potentially fruitful areas for exploration

Author: Tarek Echekki
Publisher: Springer Science & Business Media
ISBN: 9400704127
Category : Technology & Engineering
Languages : en
Pages : 496

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Book Description
Turbulent combustion sits at the interface of two important nonlinear, multiscale phenomena: chemistry and turbulence. Its study is extremely timely in view of the need to develop new combustion technologies in order to address challenges associated with climate change, energy source uncertainty, and air pollution. Despite the fact that modeling of turbulent combustion is a subject that has been researched for a number of years, its complexity implies that key issues are still eluding, and a theoretical description that is accurate enough to make turbulent combustion models rigorous and quantitative for industrial use is still lacking. In this book, prominent experts review most of the available approaches in modeling turbulent combustion, with particular focus on the exploding increase in computational resources that has allowed the simulation of increasingly detailed phenomena. The relevant algorithms are presented, the theoretical methods are explained, and various application examples are given. The book is intended for a relatively broad audience, including seasoned researchers and graduate students in engineering, applied mathematics and computational science, engine designers and computational fluid dynamics (CFD) practitioners, scientists at funding agencies, and anyone wishing to understand the state-of-the-art and the future directions of this scientifically challenging and practically important field.

Author: Yujie Tao
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Due to the hierarchical nature of high-temperature hydrocarbon oxidation, modeling the combustion chemistry of higher hydrocarbon fuels typically requires a fuel-specific reaction model that describes the fragmentation of the fuel to small species, and a foundational fuel chemistry model that describes the oxidation of these species. Shared by the combustion of large hydrocarbons, the foundational fuel chemistry is also the rate-limiting step and therefore a crucial part for constructing reliable combustion models for any higher hydrocarbons. The dissertation studies the aforementioned problems from both ends. A detailed reaction kinetic model of the foundational fuel combustion is comprised of elementary chemical reactions and their associated rate coefficients. Each of the rate coefficients comes with some uncertainty. The inherent uncertainties of the rate parameters propagate into model predictions and need to be properly quantified. Without characterizing the uncertainty, a reaction model merely represents a feasible combination of rate parameters within a high-dimensional uncertainty space. The Foundational Fuel Chemistry Model (FFCM) is an effort directed at developing a reliable combustion model for the foundational fuels with rate parameters optimized and uncertainty minimized. The first version, FFCM-1, optimized for H2, H2/CO, CH2O and CH4 combustion was constrained with carefully evaluated fundamental combustion data that includes laminar flame speeds, shock tube ignition delay times, shock tube species profiles, and flow reactor species profiles. It has been shown that the model reconciles all the experimental targets chosen and has significantly reduced prediction uncertainties. The remaining kinetic uncertainties in FFCM-1 were further analyzed with extinction and ignition residence time predictions in perfectly-stirred reactor conditions. The reactions that were responsible for the remaining prediction uncertainties were studied with an impact factor analysis over a wide range of temperature, pressure and equivalence ratio. The optimization and uncertainty quantification procedure was then extended to also include temperature dependency by considering the joint optimization of pre-exponential factors and activation energies. An effective temperature was defined for every target and utilized in the response surface derivation. The resulting temperature-dependent uncertainties of key reactions in H2/CO flames in a test problem were discussed. JP10 was studied as a single-component large-fuel example, using the Hybrid Chemistry (HyChem) approach. The HyChem approach assumes a decoupled fuel pyrolysis and oxidation of pyrolysis products. The pyrolysis model is described with highly-lumped steps and optimized against experimental data from shock tube and flow reactor species profiles and shock tube ignition delay. Special attention was paid to the unique molecular structure of the fuel in the lumped pyrolysis reactions, and the overall performance of the model is shown to be satisfactory.

Author: W.C., Jr. Gardiner
Publisher: Springer Science & Business Media
ISBN: 146121310X
Category : Science
Languages : en
Pages : 553

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Book Description
Superseding Gardiner's "Combustion Chemistry", this is an updated, comprehensive coverage of those aspects of combustion chemistry relevant to gas-phase combustion of hydrocarbons. The book includes an extended discussion of air pollutant chemistry and aspects of combustion, and reviews elementary reactions of nitrogen, sulfur and chlorine compounds that are relevant to combustion. Methods of combustion modeling and rate coefficient estimation are presented, as well as access to databases for combustion thermochemistry and modeling.

Author: J. Warnatz
Publisher: Springer Science & Business Media
ISBN: 3540259929
Category : Technology & Engineering
Languages : en
Pages : 389

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Book Description
This book provides a rigorous treatment of the coupling of chemical reactions and fluid flow. Combustion-specific topics of chemistry and fluid mechanics are considered and tools described for the simulation of combustion processes. This edition is completely restructured. Mathematical Formulae and derivations as well as the space-consuming reaction mechanisms have been replaced from the text to appendix. A new chapter discusses the impact of combustion processes on the atmosphere, the chapter on auto-ignition is extended to combustion in Otto- and Diesel-engines, and the chapters on heterogeneous combustion and on soot formation are heavily revised.

Author: Jürgen Warnatz
Publisher: Springer Science & Business Media
ISBN: 3642976689
Category : Science
Languages : en
Pages : 276

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Book Description
Combustion is an old technology, which at present provides about 90% of our worldwide energy support. Combustion research in the past used fluid mechanics with global heat release by chemical reactions described with thermodynamics, assuming infinitely fast reactions. This approach was useful for stationary combustion processes, but it is not sufficient for transient processes like ignition and quenching or for pollutant formation. Yet pollutant formation during combustion of fossil fuels is a central topic and will continue to be so in future. This book provides a detailed and rigorous treatment of the coupling of chemical reactions and fluid flow. Also, combustion-specific topics of chemistry and fluid mechanics are considered, and tools described for the simulation of combustion processes.

Author: Nedunchezhian Swaminathan
Publisher: Springer Nature
ISBN: 303116248X
Category : Technology & Engineering
Languages : en
Pages : 353

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Book Description
This open access book introduces and explains machine learning (ML) algorithms and techniques developed for statistical inferences on a complex process or system and their applications to simulations of chemically reacting turbulent flows. These two fields, ML and turbulent combustion, have large body of work and knowledge on their own, and this book brings them together and explain the complexities and challenges involved in applying ML techniques to simulate and study reacting flows. This is important as to the world’s total primary energy supply (TPES), since more than 90% of this supply is through combustion technologies and the non-negligible effects of combustion on environment. Although alternative technologies based on renewable energies are coming up, their shares for the TPES is are less than 5% currently and one needs a complete paradigm shift to replace combustion sources. Whether this is practical or not is entirely a different question, and an answer to this question depends on the respondent. However, a pragmatic analysis suggests that the combustion share to TPES is likely to be more than 70% even by 2070. Hence, it will be prudent to take advantage of ML techniques to improve combustion sciences and technologies so that efficient and “greener” combustion systems that are friendlier to the environment can be designed. The book covers the current state of the art in these two topics and outlines the challenges involved, merits and drawbacks of using ML for turbulent combustion simulations including avenues which can be explored to overcome the challenges. The required mathematical equations and backgrounds are discussed with ample references for readers to find further detail if they wish. This book is unique since there is not any book with similar coverage of topics, ranging from big data analysis and machine learning algorithm to their applications for combustion science and system design for energy generation.