Conditional Moment Closure Model for Ignition of Homogeneous Fuel/air Mixtures in Internal Combustion Engines PDF Download
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Author: Wei Wang
Publisher:
ISBN:
Category : Internal combustion engines
Languages : en
Pages : 145
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Book Description
To improve the fuel economy and to reduce the emission in internal combustion (IC) engines, advanced engine technologies such as the homogeneous charge compression ignition (HCCI), further increasing the compression ratio, and gasoline engine downsizing with charge boosting need to be further developed. The development of these technologies is restricted by the prediction and control of the ignition of premixed fuel/air mixtures. The ignition of the premixed mixtures in IC engines is governed by complex chemical kinetics. The in-cylinder flow turbulence, temperature inhomogeneity, and other mixture conditions affect the ignition processes by influencing the chemical reaction rates.
Author: Wei Wang
Publisher:
ISBN:
Category : Internal combustion engines
Languages : en
Pages : 145
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Book Description
To improve the fuel economy and to reduce the emission in internal combustion (IC) engines, advanced engine technologies such as the homogeneous charge compression ignition (HCCI), further increasing the compression ratio, and gasoline engine downsizing with charge boosting need to be further developed. The development of these technologies is restricted by the prediction and control of the ignition of premixed fuel/air mixtures. The ignition of the premixed mixtures in IC engines is governed by complex chemical kinetics. The in-cylinder flow turbulence, temperature inhomogeneity, and other mixture conditions affect the ignition processes by influencing the chemical reaction rates.
Author: Adrian Milford
Publisher:
ISBN:
Category :
Languages : en
Pages : 129
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Book Description
Autoignition of high pressure methane jets at engine relveant conditions within a shock tube is investigated using Conditional Moment Closure (CMC). The impact of two commonly used approximations applied in previous work is examined, the assumption of homogeneous turbulence in the closure of the micro-mixing term and the assumption of negligible radial variation of terms within the CMC equations. In the present work two formulations of an inhomogeneous mixing model are implemented, both utilizing the [beta] -PDF, but differing in the respective conditional velocity closure that is applied. The common linear model for conditional velocity is considered, in addition to the gradient diffusion model. The validity of cross-stream averaging the CMC equations is examined by comparing results from two-dimensional (axial and radial) solution of the CMC equations with cross-stream averaged results. The CMC equations are presented and all terms requiring closure are discussed. So- lution of the CMC equations is decoupled from the flow field solution using the frozen mixing assumption. Detailed chemical kinetics are implemented. The CMC equations are discretized using finite differences and solved using a fractional step method. To maintain consistency between the mixing model and the mixture fraction variance equation, the scalar dissipation rate from both implementations of the inhomogeneous model are scaled. The autoignition results for five air temperatures are compared with results obtained using homogeneous mixing models and experimental data. The gradient diffusion conditional velocity model is shown to produce diverging be- haviour in low probability regions. The corresponding profiles of conditional scalar dis- sipation rate are negatively impacted with the use of the gradient model, as unphysical behaviour at lean mixtures within the core of the fuel jet is observed. The predictions of ignition delay and location from the Inhomogeneous-Linear model are very close to the homogeneous mixing model results. The Inhomogeneous-Gradient model yields longer ignition delays and ignition locations further downstream. This is influenced by the higher scalar dissipation rates at lean mixtures resulting from the divergent behaviour of the gradient conditional velocity model. The ignition delays obtained by solving the CMC equations in two dimensions are in excellent agreement with the cross-stream averaged values, but the ignition locations are predicted closer to the injector.
Author:
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 138
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Book Description
Author: Santanu De
Publisher: Springer
ISBN: 9811074100
Category : Science
Languages : en
Pages : 663
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Book Description
This book presents a comprehensive review of state-of-the-art models for turbulent combustion, with special emphasis on the theory, development and applications of combustion models in practical combustion systems. It simplifies the complex multi-scale and nonlinear interaction between chemistry and turbulence to allow a broader audience to understand the modeling and numerical simulations of turbulent combustion, which remains at the forefront of research due to its industrial relevance. Further, the book provides a holistic view by covering a diverse range of basic and advanced topics—from the fundamentals of turbulence–chemistry interactions, role of high-performance computing in combustion simulations, and optimization and reduction techniques for chemical kinetics, to state-of-the-art modeling strategies for turbulent premixed and nonpremixed combustion and their applications in engineering contexts.
Author: Ahmad El Sayed
Publisher:
ISBN:
Category :
Languages : en
Pages : 280
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Book Description
This thesis describes the application of the first-order Conditional Moment Closure (CMC) to the autoignition of high-pressure fuel jets, and to piloted and lifted turbulent jet flames using classical and advanced CMC submodels. A Doubly-Conditional Moment Closure (DCMC) formulation is further proposed.
Author: Alessandro Parente
Publisher: Frontiers Media SA
ISBN: 2889717003
Category : Technology & Engineering
Languages : en
Pages : 160
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Book Description
Author: Anthony Jefferies
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Zhichao Tan
Publisher:
ISBN:
Category :
Languages : en
Pages : 240
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Book Description
Author: Norbert Peters
Publisher: Cambridge University Press
ISBN: 1139428063
Category : Science
Languages : en
Pages : 322
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Book Description
The combustion of fossil fuels remains a key technology for the foreseeable future. It is therefore important that we understand the mechanisms of combustion and, in particular, the role of turbulence within this process. Combustion always takes place within a turbulent flow field for two reasons: turbulence increases the mixing process and enhances combustion, but at the same time combustion releases heat which generates flow instability through buoyancy, thus enhancing the transition to turbulence. The four chapters of this book present a thorough introduction to the field of turbulent combustion. After an overview of modeling approaches, the three remaining chapters consider the three distinct cases of premixed, non-premixed, and partially premixed combustion, respectively. This book will be of value to researchers and students of engineering and applied mathematics by demonstrating the current theories of turbulent combustion within a unified presentation of the field.
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.
