The numerical simulation of combustion processes in internal combustion engines, including also the formation of pollutants, has become increasingly important in the recent years, and today the ...simulation of those processes has already become an indispensable tool when - veloping new combustion concepts. While pure thermodynamic models are well-established tools that are in use for the simulation of the transient behavior of complex systems for a long time, the phenomenological models have become more important in the recent years and have also been implemented in these simulation programs. In contrast to this, the thr- dimensional simulation of in-cylinder combustion, i. e. the detailed, integrated and continuous simulation of the process chain injection, mixture formation, ignition, heat release due to combustion and formation of pollutants, has been significantly improved, but there is still a number of challenging problems to solve, regarding for example the exact description of s- processes like the structure of turbulence during combustion as well as the appropriate choice of the numerical grid. While chapter 2 includes a short introduction of functionality and operating modes of internal combustion engines, the basics of kinetic reactions are presented in chapter 3. In chapter 4 the physical and chemical processes taking place in the combustion chamber are described. Ch- ter 5 is about phenomenological multi-zone models, and in chapter 6 the formation of poll- ants is described.
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Due to the increasing number of engine setting parameters to be optimized, model based calibration techniques have been introduced to medium speed engine testing to keep the number of engine tests ...low. Polynomials in combination with d-optimal test plans have been proven to be a good choice for modeling the stationary behavior of selected engine outputs. Model approaches like artificial neural networks (ANNs) have been rarely used for medium speed purposes since they require quite high amounts of testing data for model training. To evaluate the potential of these model approaches radial basis function networks, a subclass of neural networks, as well as Gaussian processes have been investigated as alternatives to polynomials. A manageable amount of tests according to an adapted d-optimal test plan was carried out at a test bench. Based on the test results polynomials, radial basis function networks (RBFs) as well as Gaussian process models (GPMs) have been fitted for selected engine outputs. Furthermore, an extensive appraisal and comparison of these model approaches, using statistical criteria for regression evaluation, was executed.
The results show that radial basis function networks or Gaussian processes are promising alternatives to polynomials even if the amount of testing data is limited. The quality of the approximation results of the model types is on a comparable level. However, an advantage of radial basis function networks and Gaussian processes is the higher flexibility allowing a better representation of local nonlinear behavior of modeled engine outputs in comparison to polynomials.
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Thesis (M.S.)--University of Wisconsin--Madison, 1994.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves ...140-143).
Reaction Kinetics Stiesch, Gunnar; Eckert, Peter
Combustion Engines Development
Book Chapter
A chemical reaction between reactants Aa, Ab, etc., which form the products Ac, Ad, etc. can be described in the following form5.1\documentclass12pt{minimal}
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$$ {\nu_a} {A_a} + {\nu_b}{A_b}{ + } \ldots \to {\nu_c}{A_c} + {\nu_d}{A_d}{ + } \ldots. $$
\end{document}The νi thereby designate the so-called stoichiometric coefficients of the reaction. Since every chemical reaction can in principle run both forwards as well as backwards, the reaction arrow in (5.1) can be replaced with an equal sign. We thereby obtain the general form of the reaction equation5.2\documentclass12pt{minimal}
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$$ \sum\limits_i {{\nu_i}{A_i} = 0,} $$
\end{document}whereby the stoichiometric coefficients are conventionally negative for all educts and positive for all products.
For the calculation of engine combustion processes, various model categories can be employed, which are quite diverse in their level of detail, but also in their calculation time requirements, see ...Stiesch (2003). Calculation models are customarily designated as phenomenological models that can calculate combustion and pollutant formation contingent upon important physical and chemical phenomena like spray dispersion, mixture formation, ignition, reaction kinetics, etc. Because a spatial subdivision of the combustion space into zones of varying temperature and composition is often necessary, the models are also referred to as quasidimensional models. Phenomenological (or quasidimensional) models differ on the one hand from zero-dimensional (or simplified thermodynamic) models, which simplify the combustion chamber as being ideally mixed at every point in time and are based on empirical approaches for the combustion rate. On the other hand, phenomenological combustion models differ from the CFD codes (CFD = computational fluid dynamics, see Chap. 12 ff.), in that we consciously do without an explicit solution of the turbulent three-dimensional flow field, which reduce the calculation time considerably (Fig. 11.1). The calculation time for one engine revolution lies in the region of seconds in phenomenological models, while in CFD codes it takes hours (Fig. 11.2).
A spray model for pressure-swirl atomizers that is based on a linearized instability analysis of liquid sheets has been combined with an ignition and combustion model for stratified charge spark ...ignition engines. The ignition model has been advanced, such that the presence of dual spark plugs can now be accounted for. Independent validation of the spray model is achieved by investigating a pressure-swirl injector inside a pressure bomb containing air at ambient temperature. In a second step, the complete model is used to estimate the performance of a small marine DISI Two-Stroke engine operating in stratified charge mode. Simulation results and experimental data are compared for several different injection timings and the agreement is generally good such that there is confidence in the predictive quality of the combustion model. Finally the model is applied in a conceptual study to investigate possible benefits of split injections. The simulation results suggest that both fuel economy and NOx-emissions can be improved when a two-pulse injection is used such that the late injected, stratified fuel ensures stable ignition at the spark plug whereas the early injected, diluted fuel reduces the maximum combustion temperature and controls NOx-formation.
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