Download or read book Large eddy Simulation Modeling of Diesel Sprays written by Chi-Wei Tsang and published by . This book was released on 2017 with total page 422 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this study is to develop/improve physical models for large-eddy simulations of Diesel sprays. The stochastic Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) atomization and breakup model, the synthetic eddy injection model, the droplet rotation model, and the sub-grid scale (SGS) dispersion model were developed and tested. Using the classical KH-RT model, it was found that simulation results are sensitive to several model parameters such as length and time scales of instability waves. The idea of the stochastic KH-RT model is to determine these parameters stochastically and dynamically. This is an attempt to reduce the sensitivity of the model parameters partly resulting from the incapability of predicting breakup mechanisms other than wave instabilities in the classical KH-RT model. The synthetic eddy injection model predicts fluctuations of the Lagrangian parcel initial velocity. The model attempts to simulate turbulence at the nozzle exit without the need of internal nozzle flow simulations, by superimposing a number of virtual coherent structures. The performance of these two newly developed models was compared to the original ones, namely the classical KH-RT and the cone angle injection models. Two experimental databases, the Engine Combustion Network (ECN) constant-volume sprays and the Engine Research Center optical engine sprays were used to validate the models. A number of simulated quantities such as liquid projected mass density, liquid and vapor penetrations, fuel vapor profiles, ignition delays, and lift-off lengths, were compared against the data. The stochastic KH-RT model improved the prediction of the projected mass density downstream and liquid penetrations in a range of operating conditions (errors within 5 %) without tuning the model constants case by case. The synthetic eddy injection model improved the prediction of vapor penetrations at early stage of injection since the development of instability modes and turbulent transport in the near-nozzle region were better resolved. The model also shows less grid sensitivity. Overall, using these two new models overcomes some limitations in the original models and makes LES as a more predictive tool for Diesel sprays. The droplet rotation model considers droplet force and torque due to relative rotational motions between droplets and gas. Simulation results of the ECN non-vaporizing and vaporizing sprays with and without using the rotation model were compared. It was found that the droplet rotation has negligible effect. This is because the droplet response time scale to the rotational motion is much smaller than that to the translational motion. That is, slip angular velocity approaches to zero much faster, resulting in much smaller rotational force than the drag force. The SGS dispersion model considers the effect of sub-grid motions on Diesel spray dispersion. The model assumes that the SGS dispersion velocity is decomposed into the deterministic and the stochastic parts. The deterministic part is modeled by the approximate deconvolution method and the stochastic part is assumed to be isotropic and Gaussian distributed. It was found that the two model parameters, variance of the Gaussian distribution and turbulence correlation time, have a critical effect on the spatial distribution of droplets with small inertia downstream of the spray. Larger variance or longer turbulence correlation time predicts wider liquid spray angle. However, they have small effect on predicting resolved gas-phase statistics. The primary reason for this is that the motion of high-momentum liquid blobs in the near-nozzle region leading to air entrainment and subsequent gas jet development is little influenced by the SGS dispersion. Moving further downstream a quasi-equilibrium is established between the two phases, resulting in relatively small slip velocities. Therefore, it was found that the spray momentum source term in the gas momentum equation is much smaller than the other terms in the downstream region.

Download or read book Large Eddy Simulation of Diesel Spray Combustion with Eddy Dissipation Model and CIP Methods by Use of KIVALES written by and published by . This book was released on 2007 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Large eddy Simulation of Non reacting Diesel Sprays written by Chi-Wei Tsang and published by . This book was released on 2014 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theoretical and Numerical Combustion written by Thierry Poinsot and published by R.T. Edwards, Inc.. This book was released on 2005 with total page 544 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introducing numerical techniques for combustion, this textbook describes both laminar and turbulent flames, addresses the problem of flame-wall interaction, and presents a series of theoretical tools used to study the coupling phenomena between combustion and acoustics. The second edition incorporates recent advances in unsteady simulation methods,

Download or read book Modelling Diesel Combustion written by P. A. Lakshminarayanan and published by Springer Science & Business Media. This book was released on 2010-03-03 with total page 313 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phenomenology of Diesel Combustion and Modeling Diesel is the most efficient combustion engine today and it plays an important role in transport of goods and passengers on land and on high seas. The emissions must be controlled as stipulated by the society without sacrificing the legendary fuel economy of the diesel engines. These important drivers caused innovations in diesel engineering like re-entrant combustion chambers in the piston, lower swirl support and high pressure injection, in turn reducing the ignition delay and hence the nitric oxides. The limits on emissions are being continually reduced. The- fore, the required accuracy of the models to predict the emissions and efficiency of the engines is high. The phenomenological combustion models based on physical and chemical description of the processes in the engine are practical to describe diesel engine combustion and to carry out parametric studies. This is because the injection process, which can be relatively well predicted, has the dominant effect on mixture formation and subsequent course of combustion. The need for improving these models by incorporating new developments in engine designs is explained in Chapter 2. With “model based control programs” used in the Electronic Control Units of the engines, phenomenological models are assuming more importance now because the detailed CFD based models are too slow to be handled by the Electronic Control Units. Experimental work is necessary to develop the basic understanding of the pr- esses.

Download or read book Solving Ordinary Differential Equations II written by Ernst Hairer and published by Springer Science & Business Media. This book was released on 2013-03-14 with total page 615 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Whatever regrets may be, we have done our best." (Sir Ernest Shackleton, turning back on 9 January 1909 at 88°23' South.) Brahms struggled for 20 years to write his first symphony. Compared to this, the 10 years we have been working on these two volumes may even appear short. This second volume treats stiff differential equations and differential alge braic equations. It contains three chapters: Chapter IV on one-step (Runge Kutta) methods for stiff problems, Chapter Von multistep methods for stiff problems, and Chapter VI on singular perturbation and differential-algebraic equations. Each chapter is divided into sections. Usually the first sections of a chapter are of an introductory nature, explain numerical phenomena and exhibit numerical results. Investigations of a more theoretieal nature are presented in the later sections of each chapter. As in Volume I, the formulas, theorems, tables and figures are numbered consecutively in each section and indicate, in addition, the section num ber. In cross references to other chapters the (latin) chapter number is put first. References to the bibliography are again by "author" plus "year" in parentheses. The bibliography again contains only those papers which are discussed in the text and is in no way meant to be complete.

Download or read book Modelling Diesel Combustion written by P. A. Lakshminarayanan and published by Springer Nature. This book was released on 2022-01-21 with total page 419 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book comprehensively discusses diesel combustion phenomena like ignition delay, fuel-air mixing, rate of heat release, and emissions of smoke, particulate and nitric oxide. It enables quantitative evaluation of these important phenomena and parameters. Most importantly, it attempts to model them with constants that are independent of engine types and hence they could be applied by the engineers and researchers for a general engine. This book emphasizes the importance of the spray at the wall in precisely describing the heat release and emissions for most of the engines on and off-road. It gives models for heat release and emissions. Every model is thoroughly validated by detailed experiments using a broad range of engines. The book describes an elegant quasi-one-dimensional model for heat release in diesel engines with single as well as multiple injections. The book describes how the two aspects, namely, fuel injection rate and the diameter of the combustion bowl in the piston, have enabled meeting advanced emission, noise, and performance standards. The book also discusses the topics of computational fluid dynamics encompassing RANS and LES models of turbulence. Given the contents, this book will be useful for students, researchers and professionals working in the area of vehicle engineering and engine technology. This book will also be a good professional book for practising engineers in the field of combustion engines and automotive engineering.

Download or read book Development of a General Diesel Combustion Model in the Context of Large Eddy Simulation written by Bing Hu and published by . This book was released on 2008 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Using Large Eddy Simulations to Study Diesel DI HCCI Engine Flow Structure Mixing and Combustion written by Rahul Jhavar and published by . This book was released on 2007 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book MILD Combustion Modelling Challenges Experimental Configurations and Diagnostic Tools written by Alessandro Parente and published by Frontiers Media SA. This book was released on 2021-11-26 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Large eddy Spray Simulation Under Direct injection Spark ignition Engine like Conditions written by Hongjiang Li and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this dissertation is on the development and improvement of spray models for large-eddy simulation (LES) of turbulent two-phase flows in direct-injection spark-ignition (DISI) engines. The work can be regarded as a continuation of the development of LES framework at the Engine Research Center (ERC). The LES two-phase governing equations are solved using the Lagrangian-Eulerian (LE) approach in a variation of the OpenFOAM-2.3.x code developed by the OpenFOAM Foundation. A mixed-type one-equation dynamic structure turbulence model is used as the basis for turbulence modeling. LES models are developed for DISI spray breakup, Sub-grid scale (SGS) turbulent dispersion, and SGS energy dissipation rate. The spray breakup model builds on top of the hybrid Kelvin-Helmholtz (KH)/Rayleigh-Taylor (RT) model by incorporating the bag/bag-stamen breakup regimes. A concept of RT breakup length is introduced to account for the plume-interactions and the effective nozzle diameter of DISI spray. The SGS models are developed in the context of LES and require the SGS kinetic energy, which is obtained by solving its transport equation in the turbulence model. The performance of the new models is evaluated against a wide range of DISI spray experiments covering both early and late injection engine-like conditions. Examination of spray characteristics is performed for both global and local quantities such as penetration length, Sauter mean diameter (SMD), droplet velocity, liquid-phase concentrations, and spray envelop. The discussion focuses primarily on the DISI spray breakup, followed by \textit{a posteriori} test results of the SGS models. An uncertainty quantification (UQ) study is also performed to analyze the impact of spray boundary conditions and breakup model parameters on LES of DISI sprays. LES results show that the addition of models for bag/bag-stamen breakup regimes results in more accurate predictions of spray characteristics. The modified breakup length concept also predicts more realistic penetration curves across a range of ambient temperature and density conditions without tuning the model parameters. The improved SGS dispersion model correctly predicts local liquid-phase characteristics such as velocity and projected liquid volume fraction. A preliminary study of SGS dissipation rate modeling also shows that the SGS model is able to accurately predict the energy balance between the resolved and the SGS fields across various mesh resolutions.

Download or read book Fundamentals of Combustion Processes written by Sara McAllister and published by Springer Science & Business Media. This book was released on 2011-05-10 with total page 315 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamentals of Combustion Processes is designed as a textbook for an upper-division undergraduate and graduate level combustion course in mechanical engineering. The authors focus on the fundamental theory of combustion and provide a simplified discussion of basic combustion parameters and processes such as thermodynamics, chemical kinetics, ignition, diffusion and pre-mixed flames. The text includes exploration of applications, example exercises, suggested homework problems and videos of laboratory demonstrations

Download or read book Fluid Dynamics and Transport of Droplets and Sprays written by W. A. Sirignano and published by Cambridge University Press. This book was released on 2010-01-11 with total page 481 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses the theoretical foundations of spray and droplet applications relevant to the technology for active control of sprays applied to new products and applications, improved product performance, cost reductions, and improved environmental outcomes. It also covers theory related to power and propulsion; materials processing and manufacturing technologies including droplet-based net form processing, coating, and painting; medication; pesticides and insecticides; and other consumer uses.

Download or read book Large Eddy Simulation of a Reacting Spray Flame with Multiple Realizations Under Compression Ignition Engine Conditions written by and published by . This book was released on 2015 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: An n-dodecane spray flame (Spray A from Engine Combustion Network) was simulated using a [delta] function combustion model along with a dynamic structure large eddy simulation (LES) model to evaluate its performance at engine-relevant conditions and to understand the transient behavior of this turbulent flame. The liquid spray was treated with a traditional Lagrangian method and the gas-phase reaction was modeled using a [delta] function combustion model. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. Significantly different flame structures and ignition processes are observed for the LES compared to those of Reynolds-averaged Navier--Stokes (RANS) predictions. The LES data suggests that the first ignition initiates in a lean mixture and propagates to a rich mixture, and the main ignition happens in the rich mixture, preferably less than 0.14 in mixture fraction space. LES was observed to have multiple ignition spots in the mixing layer simultaneously while the main ignition initiates in a clearly asymmetric fashion. The temporal flame development also indicates the flame stabilization mechanism is auto-ignition controlled. Soot predictions by LES present much better agreement with experiments compared to RANS, both qualitatively and quantitatively. Multiple realizations for LES were performed to understand the realization to realization variation and to establish best practices for ensemble-averaging diesel spray flames. The relevance index analysis suggests that an average of 5 and 6 realizations can reach 99% of similarity to the target average of 16 realizations on the mixture fraction and temperature fields, respectively. In conclusion, more realizations are necessary for the hydroxide (OH) and soot mass fractions due to their high fluctuations.

Download or read book Large eddy Simulations of Direct injection Spark ignition Engine Spray and Flow Variability written by and published by . This book was released on 2015 with total page 396 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cycle-to-cycle variations (CCVs) in engines limit the ability of engine designers to reach the theoretical limits of engine efficiency. This study investigates CCVs in Direct-injection Spark-ignition (DISI) engines through Large-eddy Simulations (LES). Multi-cycle simulations of motored engine flow and spray simulations with variable boundary conditions were performed. The Dynamic Structure turbulence model, which is an advanced 1-equation non-viscosity turbulence model, was used to enable coarser, engineering type meshes and reasonable computational requirements. Multi-cycle motored engine simulations were run for an optical engine at several different engine operating conditions. Comparisons included both pressure and velocity measurements using Particle Image Velocimetry (PIV). Simulations were run using computational domains that either did or did not include intake and exhaust mixing plenums. Results from runners-only and full-domain simulations were overall similar, but there were differences in specific flow structures at certain times. Changes to engine speed or manifold pressure increased flow magnitudes, even after adjusting for different mean piston speeds, but had relatively minor effects on the flow structure. A spray model adapted from diesel spray simulations is presented. The adapted models were unable to match experimental trends with changing ambient density in both liquid and vapor phases simultaneously. Two spray break-up model parameters were changed to vary as functions of ambient density, which greatly improved the vapor predictions but worsened liquid predictions. Two methods from Uncertainty Quantification (UQ) were used to test the response of the spray models to prescribed uncertainty in spray boundary conditions. The effects of having uncertainty in two numerical model parameters and two physical boundary conditions was examined. Overall simulation uncertainty was much larger than the experimental uncertainty. Further tests showed the uncertainty in the simulation response variables was due primarily to uncertainty in the numerical modeling parameters. When examining the effects of uncertainty in the physical boundary conditions alone, the resulting variability in the response variables was approximately equal to the variability in the spray measurements.

Download or read book Large Eddy Simulations of Diesel Combustion Chambers written by and published by . This book was released on 1999 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents findings of a systematic study of turbulence predictions for diesel combustion chambers. Particular topics covered include (1) turbulence models for Reynolds averaged Navier-Stokes solutions, (2) turbulence scale analysis, (3) efficiency and accuracy improvements of the KIVA codes, (4) large eddy simulations(LES) of in-cylinder turbulence with and without combustion, (5) sub-grid scale models for LES, and (6) combustion models for diffusion flames. The generation of the turbulence during the intake stroke and its subsequent decay during the compression stroke was predicted successfully. The turbulence induced by the piston-bowl geometry alone was investigated. It was found that significant turbulence can be generated during the compression stroke from the re-entry flow in the squish area. Simulations with spray combustion indicated an augmentation of the turbulence intensity corresponding to start of ignition. These findings are in good qualitative agreement with experimental observation. A quantitative analysis of the results in comparison with experiments will require simulations of many cycles to account for cycle-to-cycle variations. This could be possible with use of computers with parallel processors. To this end a successful attempt was made to transform KIVA to run on several parallel platforms including a locally built Beowulf Workstation cluster. initial runs with fixed grids could handle up to four million nodes. This holds promising prospects for future LES of in-cylinder combustion/turbulence in internal combustion engines.

Download or read book Large Eddy Simulation Turbulence Modeling of Spray Flows written by Nidheesh Bharadwaj and published by . This book was released on 2010 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: