A Chemical-Kinetic Approach to the Definition of the Laminar Flame Speed for the Simulation of the Combustion of Spark-Ignition Engines

Paper #:
  • 2017-24-0035

Published:
  • 2017-09-04
Abstract:
The laminar burning speed is an important intrinsic property of a air-fuel mixture determining key combustion characteristics such as ignition delay and flame propagation, turbulent flame propagation and knock tendency. The laminar burning speed is a function of the fuel, equivalent ratio and mass fraction of the residual gases in the fresh mixture (EGR). It also depend on the unburned mixture temperature and pressure. Due to experimental limitations the laminar flame speeds over the full range of pressures and temperatures of an internal combustion engine, temperature can be as high as 1000 K and the pressure up to 35 bar with different value of EGR, are not available. The most widespread models used to extrapolate the experimental data to the engine conditions are derived from the model of Metghalchi and Keck. This family of models usually fail to correctly predict value really outside of the experimental space. Thanks to the development of accurate chemical kinetic models, capable of predict the laminar flame speed and the autoignition time not only for a wide range of conditions but also for arbitrary fuel mixtures for which the experimental data are not available, the numerical approach can be used to overcome some of the limitation of the Metghalchi and Keck model. The motivation for this study arises from the necessity to define the laminar burning speed for different fuel blend required for the simulation of high-performance spark ignition engines. Using the open source chemical solver Cantera, the laminar flame speed is evaluated in a design space that encompass the characteristic engine value for unburned pressure, temperature, equivalence ratio and EGR, in order to define a corrected interpolation of the Metghalchi and Keck equation for fast evaluation and a library of tabulated of laminar flame speed and autoignition time for the CFD evaluation.
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