Sensitivity of Flamelet Combustion Model to Flame Curvature for IC Engine Application

Paper #:
  • 2017-24-0038

  • 2017-09-04
Engines with reduced emissions and improved efficiency are of high interest for road transport. However, achieving these two goals is challenging and various concepts such as PFI/DI/HCCI/PCCI are explored by engine manufacturers. Three dimensional computational fluid dynamics is becoming an integral part in analysing engine in cylinder processes, since it provides access to in-cylinder flow and thermo-chemical processes which gives a closer understanding to the tumble and swirling motions in order to construct clean engines. The combustion modelling, its accuracy and robustness play a vital role in this. Flamelet based methods are quite attractive for SI engine application. In this study, an unstrained flamelet model is used to simulate premixed combustion inside a GPFI single-cylinder, four-stroke SI engine. This model involves scalar dissipation rate of a reaction progress variable fluctuation as an important quantity, which is modelled using a physically consistent closure developed recently. This closure includes a parameter,$\beta_{c}$, representing the effects of flame curvature on the burning rate and this parameter is obtained in past studies using direct numerical simulation data of constant pressure combustion. Since the reactant temperature and pressure inside the cylinder are continually varying with time, the mutual influence of flame curvature and thermo-chemical activities are expected to be stronger in IC engines and thus the parameter$\beta_{c}$ may not be constant. To better understand this, the above combustion model is implemented in STAR-CD/es-ICE package for RANS calculations and the predicted pressure variation with CAD are compared to measured values for the above full-metal engine operating at 3500 rpm close to full load (10 bar of BMEP) at stoichiometric conditions. The predicted pressure curve is sensitive to the flame-curvature parameter and the paper will explore this sensitivity for a range of engine operating conditions.
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