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Author: W. B. Bush Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
A rapid-compression machine is a laboratory apparatus to study aspects of the compression stroke, combustion event, and expansion stroke of an Otto cycle. As a simple model of such a machine, unsteady one-dimensional nonisobaric laminar flame propagation through a combustible premixture, enclosed in a variable volume, is examined in the asymptotic limit of Arrhenius activation temperature large relative to the conventional adiabatic flame temperature. In this limit, a thin propagating flame separates nondiffusive expanses of burned and unburned gas. The pressure through the enclosure is spatially homogeneous for smooth flame propagation. However, expansion of the hot burned gas results in compressional preheating of the remaining unburned gas, and in fact the spatially homogeneous gas may undergo autoconversion prior to arrival of the propagation flame. If such an explosion is too rapid for acoustic adjustment, large spatial differences in pressure arise and the resulting nonlinear waves produce audible knock. Here attention is concentrated on what fraction (if any) of the total charge may undergo autoconversion for a given operating condition, and what enhanced heat transfer from the end gas would preclude autoconversion--though too great heat transfer from the end gas could result in flame quenching (unburned residual fuel). (Author).
Author: W. B. Bush Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
A rapid-compression machine is a laboratory apparatus to study aspects of the compression stroke, combustion event, and expansion stroke of an Otto cycle. As a simple model of such a machine, unsteady one-dimensional nonisobaric laminar flame propagation through a combustible premixture, enclosed in a variable volume, is examined in the asymptotic limit of Arrhenius activation temperature large relative to the conventional adiabatic flame temperature. In this limit, a thin propagating flame separates nondiffusive expanses of burned and unburned gas. The pressure through the enclosure is spatially homogeneous for smooth flame propagation. However, expansion of the hot burned gas results in compressional preheating of the remaining unburned gas, and in fact the spatially homogeneous gas may undergo autoconversion prior to arrival of the propagation flame. If such an explosion is too rapid for acoustic adjustment, large spatial differences in pressure arise and the resulting nonlinear waves produce audible knock. Here attention is concentrated on what fraction (if any) of the total charge may undergo autoconversion for a given operating condition, and what enhanced heat transfer from the end gas would preclude autoconversion--though too great heat transfer from the end gas could result in flame quenching (unburned residual fuel). (Author).
Author: Andreas Manz Publisher: Logos Verlag Berlin GmbH ISBN: 3832542817 Category : Science Languages : en Pages : 263
Book Description
Downsizing of modern gasoline engines with direct injection is a key concept for achieving future CO22 emission targets. However, high power densities and optimum efficiency are limited by an uncontrolled autoignition of the unburned air-fuel mixture, the so-called spark knock phenomena. By a combination of three-dimensional Computational Fluid Dynamics (3D-CFD) and experiments incorporating optical diagnostics, this work presents an integral approach for predicting combustion and autoignition in Spark Ignition (SI) engines. The turbulent premixed combustion and flame front propagation in 3D-CFD is modeled with the G-equation combustion model, i.e. a laminar flamelet approach, in combination with the level set method. Autoignition in the unburned gas zone is modeled with the Shell model based on reduced chemical reactions using optimized reaction rate coefficients for different octane numbers (ON) as well as engine relevant pressures, temperatures and EGR rates. The basic functionality and sensitivities of improved sub-models, e.g. laminar flame speed, are proven in simplified test cases followed by adequate engine test cases. It is shown that the G-equation combustion model performs well even on unstructured grids with polyhedral cells and coarse grid resolution. The validation of the knock model with respect to temporal and spatial knock onset is done with fiber optical spark plug measurements and statistical evaluation of individual knocking cycles with a frequency based pressure analysis. The results show a good correlation with the Shell autoignition relevant species in the simulation. The combined model approach with G-equation and Shell autoignition in an active formulation enables a realistic representation of thin flame fronts and hence the thermodynamic conditions prior to knocking by taking into account the ignition chemistry in unburned gas, temperature fluctuations and self-acceleration effects due to pre-reactions. By the modeling approach and simulation methodology presented in this work the overall predictive capability for the virtual development of future knockproof SI engines is improved.
Author: United States. Army Research Office Publisher: ISBN: Category : Military research Languages : en Pages : 284
Book Description
Vols. for 1977- consist of two parts: Chemistry, biological sciences, engineering sciences, metallurgy and materials science (issued in the spring); and Physics, electronics, mathematics, geosciences (issued in the fall).
Author: Alexander Fandakov Publisher: Springer ISBN: 3658248750 Category : Technology & Engineering Languages : en Pages : 233
Book Description
The majority of 0D/1D knock models available today are known for their poor accuracy and the great effort needed for their calibration. Alexander Fandakov presents a novel, extensively validated phenomenological knock model for the development of future engine concepts within a 0D/1D simulation environment that has one engine-specific calibration parameter. Benchmarks against the models commonly used in the automotive industry reveal the huge gain in knock boundary prediction accuracy achieved with the approach proposed in this work. Thus, the new knock model contributes substantially to the efficient design of spark ignition engines employing technologies such as full-load exhaust gas recirculation, water injection, variable compression ratio or lean combustion. About the Author Alexander Fandakov holds a PhD in automotive powertrain engineering from the Institute of Internal Combustion Engines and Automotive Engineering (IVK) at the University of Stuttgart, Germany. Currently, he is working as an advanced powertrain development engineer in the automotive industry.
Author: Francesco Cupo Publisher: Springer Nature ISBN: 3658316284 Category : Technology & Engineering Languages : en Pages : 119
Book Description
To drastically reduce the emission of greenhouse gases, the development of future internal combustion engines will be strictly linked to the development of CO2 neutral fuels (e.g. biofuels and e-fuels). This evolution implies an increase in development complexity, which needs the support of engine 3D-CFD simulations. Francesco Cupo presents approaches to accurately describe fuel characteristics and knock occurrence in SI engines, thus improving the current simulation capability in investigating alternative fuels and innovative combustion processes. The developed models are successfully used to investigate the influence of ethanol-based fuels and water injection strategies on knock occurrence and to conduct a virtual fuel design for and engine operating with the innovative SACI combustion strategy.
Author: G. S. S. Ludford Publisher: American Mathematical Soc. ISBN: 9780821896914 Category : Mathematics Languages : en Pages : 542
Book Description
These two volumes represent the culmination of the Special Year `84-'85 in Reacting Flows held at Cornell University. As the proceedings of the 1985 AMS/SIAM Summer Seminar in Applied Mathematics, the volumes focus on both mathematical and computational questions in combustion and chemical reactors. They are addressed to researchers and graduate students in the theory of reacting flows. Together they provide a sound basis and many incentives for future research, especially in computational aspects of reacting flows. Although the theory of reacting flows has developed rapidly, researchers in the two subareas of combustion and chemical reactors have not communicated. The main goal of this seminar was to synthesize the mathematical theory and bring it to the interface with large-scale computing. All of the papers have high research value, but the first five introductory lectures should be especially noted.
Author: W. B. Bush
Author: W. B. Bush
Author: Andreas Manz
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Author: United States. Army Research Office
Author: Alexander Fandakov
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Author: 
Author: Francesco Cupo
Author: G. S. S. Ludford
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