TY  - GEN
AV  - public
Y1  - 2007///
TI  - CFD Simulation of Combustion Using Automatically Reduced Reaction Mechanisms : A Case for Diesel Engine
KW  - Verbrennung 
KW  -  Intrinsische niedrigdimensionale Mannigfaltigkeit 
KW  -  Numerische StrömungssimulationTurbulent Combustion 
KW  -  Reduced Reaction Mechanism 
KW  -  ILDM 
KW  -  CFD
ID  - heidok7251
A1  - Aglave, Ravindra
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/7251/
N2  - The intrinsic low-dimensional manifold (ILDM) method is a technique for automatic reduction of a detailed chemical mechanism based on a local time scale analysis. Chemical processes faster in comparison to the turbulent mixing time scale are assumed to be in a dynamic equilibrium, allowing the chemistry to be expressed only in terms of a few progress variables. It allows the prediction of intermediate and minor species in order to accurately capture the flame propagation and predict pollutant formation. In current work, using n-heptane as a model Diesel fuel, a one- and two-dimensional ILDM with the CO2 and H2O as the progress variable is created. It is combined with a presumed probability density function (PDF) method in order to enable turbulence-chemistry interactions. Scalar dissipation rate is calculated to compare the mechanical and chemistry time scales and to choose the appropriate numerical cells for chemistry calculations. NOx and soot, which are considered as the main pollutants in a Diesel engine are predicted using a Zeldovich model and a phenomenological two-equation model respectively, with the NO and soot precursors obtained from the ILDM chemistry. Low-temperature reactions lead to the slow formation of a radical pool after the fuel is injected in the engine. The concentration of this radical pool increases during the ignition-delay period due to chain reactions. After a critical mass of radicals is formed, rapid reactions start, indicating the occurrence of ignition. It is impractical to use hundreds of reacting species and thousands of reactions in the ignition simulation. Turbulence-chemistry interactions are accounted for by integrating the reaction rate over a presumed probability density function (PDF). Therefore, ignition-delay can be calculated and location of ignition can be identified precisely. Both parameters play a critical role in further flame propagation and ultimately pollutant formation. Radiation is an important mode of heat transfer in soot-rich Diesel engines. The six-dimensional radiative transfer equation (RTE) is solved for the radiative intensity. Models describing the variation of the radiative properties (e.g., absorption coefficients) with wavelength are incorporated. The radiative properties of the gases (CO2 and H2O) are described with a weighted sum of gray gases model (WSGGM). A Caterpillar Diesel engine, for which experimental data were available, is simulated for several injection timings. Ignition is observed to occur at the edge of the spray, in the lean-to-stoichiometric region, where the temperatures are higher. This work establishes the suitability of ILDM in simulating turbulence-chemistry interactions using a presumed PDF approach, with greater accuracy in predicting kinetically controlled processes, without the computational burdens of using detail kinetic reaction mechanisms. 
ER  -