Chemical Kinetics Modelling Study Of Naturally Aspirated And Boosted Si Engine Flame Propagation And Knock
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Chemical Kinetics Modelling Study Of Naturally Aspirated And Boosted Si Engine Flame Propagation And Knock
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Author : Jiayi Gu
language : en
Publisher:
Release Date : 2015
Chemical Kinetics Modelling Study Of Naturally Aspirated And Boosted Si Engine Flame Propagation And Knock written by Jiayi Gu and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
Journal Of Engineering For Gas Turbines And Power
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Author :
language : en
Publisher:
Release Date : 2008
Journal Of Engineering For Gas Turbines And Power written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Gas-turbines categories.
Cumulative Index Of The Sae Papers
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Author : Society of Automotive Engineers
language : en
Publisher:
Release Date : 1965
Cumulative Index Of The Sae Papers written by Society of Automotive Engineers and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1965 with Engineering categories.
A Study Of The Physics And Chemistry Of Knock In Modern Si Engines And Their Relationship To The Octane Tests
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Author : Vikram Mittal
language : en
Publisher:
Release Date : 2009
A Study Of The Physics And Chemistry Of Knock In Modern Si Engines And Their Relationship To The Octane Tests written by Vikram Mittal and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
Avoiding knock is the major design constraint for spark ignition engines because of the unacceptable noise and engine damage associated with it. Hence, the Research and Motor Octane Number (RON and MON) tests were established in 1928 such that a fuel with a higher RON and MON is less likely to knock than a fuel with a lower value. However, engine and fuel technology has evolved since 1928, and thus the relevancy of these tests for modem engines needed to be evaluated. First, the study compared knock onset, knock metrics, reference fuels, and test conditions for the octane tests to those in modem engines. The results showed that in modem engines, for a given RON, fuels with lower MON values performed better than fuels with higher values, and this trend becomes stronger when engines are boosted and intercooled. Second, detailed chemical kinetics models were used to study fuel autoignition phenomena leading to knocking conditions. These models showed that the fuel autoignition chemistry in modem engine is different from that in the RON and MON tests. Based on these results, it was concluded that the RON and MON tests no longer represent modem engine operating conditions; therefore, modifications are suggested and evaluated to improve the tests' applicability.
Multidimensional Modeling Of Combustion And Knock In Spark Ignition Engines With Detailed Chemical Kinetics
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Author : Long Liang
language : en
Publisher:
Release Date : 2006
Multidimensional Modeling Of Combustion And Knock In Spark Ignition Engines With Detailed Chemical Kinetics written by Long Liang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Chemical Kinetic Modelling Of Autoignition Under Conditions Relevant To Knock In Spark Ignition Engines
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Author : Hakan Serhad Soyhan
language : en
Publisher:
Release Date : 2000
Chemical Kinetic Modelling Of Autoignition Under Conditions Relevant To Knock In Spark Ignition Engines written by Hakan Serhad Soyhan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2000 with categories.
The phenomenon called the ''engine knock'' is an abnonnal combustion mode inspark ignition (SI) engines. it might lead to very high peak pressure in the cylinderand serious damages in engines. Knock limits the compression ratio of the ~ngine. The higher compression ratiomeans the higher fuel conversion efficiency of the engine. it also means highercylinder pressure and thereby higher gas temperature which can cause knock becauseof shorter ignition delay time. Increasing compression ratio is the simplest strategyfor increasing the efficiency of combustion, so a more detailed understanding of theprocesses goveming knock is important.it is generally accepted that knock is initiated by autoignition in the unbumed gasmixture as a result of compression due to the f1ame front propagation and the piston movement. Auto ignition can be defined as spontaneous ignition of some part of thecharge in the cylinder. The autoignition is may cause an extremely rapid chemicalenergy release. it causes a high local pressure and propagation of pressure waveswith high amplitude across the combustion chamber. The rapid rise in pressure andthe vibration of the resultant pressure wave across the combustion chamber cause erosion of the piston, piston rings and head gaskets. Known measures to avoid theoccurrence of engine knock cause either environmental problems, for example theusage of MTBE or reduce the engine thennal efficiency , for example lowcompression ratio, high swirl or early ignition timing. Because of this, the occurrenceof knock was subject of continuous public and industrial research.A detailed investigation of the combustion processes in intemal combustion engines is necessary for the improvement of engine technology .Chemical kinetic model ofthe combustion process implemented into the computational f1uid dynamic sapplications for the prediction of gas f1ow in the combustion chamber provides anefficient tool in tenns of time and cost for the investigation and improvement of the combustion process.The software tools for the modeling of combustion processes in combustion devicesrequire the reduction of the kinetic model to a limited number of species. Since the engine geometry is very complex, the performnnance of commercial software productsfor combustion device optimization decreases considerably if the number of species exceeds about 10. Consequently, a variety of methods in chemical kinetic modelingare needed to construct a reaction mechanism for a complex fuel such as PRF and toreduce it to a low number of capable species without a loss of information that mightbe important for the accuracy of the calculations. One method having the following steps is The generation of a ''detailed reaction mechanism'',The construction of the ''skeletal mechanism'',The final reduction of the reaction mechanism using Quasi Steady State Approximations (QSSA).This study concentrates on the construction of the problem oriented reduced mechanism. A method for automatic reduction of detailed kinetic to reduced mechanisms for complex fuels is proposed. The method is based on the simultaneoususe of sensitivity, reaction-f1ow and lifetime analyses. The sensitivity analysis detects species that the overall combustion process is sensitive on. Small in accuracies, in calculating these species, result in large errors in the characteristic behavior of the chernical scheme. Species, not relevant for the occurrence of autoignition in the end-gas, are defined as redundant. The automatic detection of there dundant species is done by means of an analysis of the reaction f1ows from and towards the most sensitive species, the fuel, the oxidizer and the final products. Theyare identified and eliminated for different pre-set levels of minimum reaction flow and sensitivity to generate a skeletal mechanism. The resulting skeletal mechanism is investigated with lifetime analysis to get the final reduced mechanism. A measure ofspecies lifetimes is taken from the diagonal elements of the Jacobian matrix of the chernical source terms. The species with the lifetime shorter than and mass-fractionIess than specified limits are assumed to be in steady state and selected for removalfrom the skeletal mechanism. The reduced mechanism is valid for the parameter range of initial and boundary values that the analysis has been performed for.The proposed reduction method is exemplified on a detailed reaction mechanism foriso-octane/n-heptane rnixtures. The gas-phase chernistry is analyzed in the end gas of an SI engine, using a two-zone model with conditions chosen relevant for engine knock. Comparing results obtained from the skeletal and the reduced mechanism swith results from the detailed mechanism shows the accuracy of the resulting mechanisms. it is shown that the error in the mechanisms increase with increasingpre-set Ievels of reduction. This is visualized by the help of the predicted crank angle degree at which auto ignition in the end gas of the engine occurs.The reduced mechanism is used for investigation of the modeling of the auto ignitionin the SI engines. The effects of engine operator parameters such as compression ratio, spark advance, fuel equivalence ratio and engine speed on autoignition onsettime have been studied.This work shows that it is possible to achieve a simplified reaction mechanism withgood agreement to the original mechanism by the reduction method. Fundamental knowledge about the detailed mechanism is not necessary to apply the method. Theprocedure used for reduction is fully automatic and provides a fast technique togenerate the problem oriented reduced mechanisms.
Modeling And Simulation Of Knock And Nitric Oxide Emissions In Turbocharged Direct Injection Spark Ignition Engines
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Author : Dirk Linse
language : en
Publisher: Cuvillier Verlag
Release Date : 2013-11-13
Modeling And Simulation Of Knock And Nitric Oxide Emissions In Turbocharged Direct Injection Spark Ignition Engines written by Dirk Linse and has been published by Cuvillier Verlag this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-11-13 with Technology & Engineering categories.
Im Rahmen dieser Arbeit wurden neue Modelle entwickelt, um Stickoxidemissionen und Klopfen in turboaufgeladenen Ottomotoren mit Direkteinspritzung abbilden zu können. Das Klopfmodell basiert auf einer Zündfortschrittsvariable für das Transportgleichungen für den Favre-Mittelwert und die - Varianz hergeleitet worden sind. Die in diesen Gleichungen auftretenden mittleren chemischen Quellterme werden mittels einem „presumed PDF“ Ansatz für Temperatur und Mischungsbruch in Kombination mit tabellierter detaillierter Reaktionskinetik bestimmt. Mit diesem Klopfmodell lässt sich an jedem Ort im Brennraum die Selbstzündungswahrscheinlichkeit bestimmen. Zur Bestimmung der Stickoxidemissionen wurde ein neues Multizonenmodell hergeleitet. Damit lassen sich die Zonen auf das verbranntes Gemisch konditionieren, um dort die Stickoxidbildung mittels detaillierter Reaktionskinetik zu berechnen. Durch den Abgleich mit experimentellen Ergebnisse konnte gezeigt werden, dass das Klopf- und NOx-Modell in der Lage sind den mittleren Klopfzeitpunkt und Anzahl klopfender Arbeitsspiele bzw. die Stickoxidemissionen mit hinreichender Genauigkeit zu bestimmen.
Reaction Based Knock Predictive Modeling And Model Based Stochastic Knock Limit Control Of Spark Ignition Engines
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Author : Ruixue Li
language : en
Publisher:
Release Date : 2020
Reaction Based Knock Predictive Modeling And Model Based Stochastic Knock Limit Control Of Spark Ignition Engines written by Ruixue Li and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with Electronic dissertations categories.
This dissertation studies the spark-ignition (SI) engine knock phenomenon, abnormal combustion due to the auto-ignition of end-gas ahead of the propagated flame front, resulting in the rapid chemical energy release with aggressive combustion, limiting the further improvement of thermal efficiency and even damaging the engine mechanically. A control-oriented combustion and pressure wave model with satisfactory accuracy and low computational effort is a necessity for the knock control strategy design. This dissertation develops a control-oriented knock predictive model that includes a two-zone reaction-based combustion model and a pressure wave model. This knock predictive model is capable of accurately describing the combustion process of a spark-ignited engine and predict the in-cylinder pressure oscillations under knocking combustion in real-time. Based on this model, a feedforward and feedback stochastic knock limit control strategy is developed to reduce the knock cyclic variability and control the knock mean-intensity below a desired up bound while keeping spark timing as close to engine maximum brake torque (MBT) timing as possible. A control-oriented two-zone reaction-based model to accurately describe the combustion process of a SI engine is first developed. Instead of using the conventional pre-determined Wiebe-based combustion model, a two-step chemical reaction model is utilized to predict the combustion process along with important thermodynamic parameters such as the mass-fraction-burned, in-cylinder pressure, temperatures and individual species mass changes in both zones. Sensitivities of model parameters are analyzed during the model calibration process. As a result, one set of calibration parameters are used to predict combustion characteristics over all engine operating conditions studied in this paper, which is the major advantage of the proposed method. Also, the proposed modeling approach is capable of modeling the combustion process for real-time simulations. As the by-product of the model, engine knock can also be predicted based on the Arrhenius integral in the unburned zone, which is valuable for model-based knock control. The proposed combustion model is intensively validated using the experimental data with a peak relative prediction error of 6.2% for the in-cylinder pressure. Based on this validated combustion model, a control-oriented pressure wave model for SI engines is further developed. This model is capable of predicting the in-cylinder pressure oscillations under knocking combustion in real-time and can be used for the model-based knock prediction and control. A pressure wave equation including the knock deadening behavior is proposed, simplified, and used to calculate the pressure perturbations generated by the knocking combustion. The boundary and initial conditions at knock onset are analyzed and the analytic solution of the pressure wave equation is obtained. The model is calibrated and validated over two different engine operating conditions at knock limit. The chemical kinetic-based Arrhenius integral (ARI) and the KI20 are used as the evaluation methods for knock onset and intensity prediction, and the knock frequency is studied with a fast Fourier transform of the filtered in-cylinder pressure oscillations. Especially, the knock characteristics associated with gas mixture properties at intake valve closing is analyzed based on the experimental data and their effect to knock cycle-to-cycle variation is also studied for the proposed model. In addition, this dissertation studies the correlation between in-cylinder mixture temperature at intake valve closing and the engine knock, along with knock cyclic variability based on the knock predictive model. A strong correlation between the intake temperature and knock intensity has been obtained and validated based on the simulation investigation and experiment data obtained at knock limit. Therefore, a model-based feedforward and feedback stochastic knock limit control strategy is developed to reduce the knock cycle-to-cycle variability and maintain the knock mean-intensity within a desired up bound by controlling the spark timing as close to MBT timing as possible. The control performance is validated with the simulation results to show the capability of the model-based feedforward and feedback stochastic knock limit control in significantly reducing the knock cyclic variability and improving the knock intensity distribution for the best fuel economy.
A Computational Study Of Auto Ignition And Flame Propagation In Stratified Mixtures Relevant To Modern Engines
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Author : Ramanan Sankaran
language : en
Publisher:
Release Date : 2004
A Computational Study Of Auto Ignition And Flame Propagation In Stratified Mixtures Relevant To Modern Engines written by Ramanan Sankaran and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004 with categories.
Modeling Of End Gas Autoignition For Knock Prediction In Gasoline Engines
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Author : Andreas Manz
language : en
Publisher: Logos Verlag Berlin GmbH
Release Date : 2016-08-18
Modeling Of End Gas Autoignition For Knock Prediction In Gasoline Engines written by Andreas Manz and has been published by Logos Verlag Berlin GmbH this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-08-18 with Science categories.
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.