ADVANCES IN COMBUSTION MODELING IN STAR-CD: VALIDATION OF ECFM CLE-H MODEL TO ENGINE ANALYSIS

New engine combustion regimes, like HCCI are in continuous development and considered as potential methods to reach the future emission and performance targets. Unfortunately, HCCI combustion can’t be used for all engine operation conditions. Therefore, a mix between conventional Diesel combustion and HCCI is a very promising solution. At present, the combustion mode of such engines is not well understood and CFD are now an essential tool in the conception loop of advanced engines. ECFM CLE-H is a new approach developed by CORIA [1][2] to simulate the different phases of Diesel combustion; auto-ignition, premixed and diffusion flame burning. The original proposal was based on two modeling for the two flame structures: premixed and diffusion flame. Particular emphasis was put on improving modeling for the diffusion combustion. The combustion model split the flame front in three zones: non-reactive zone, premixed zone and unpremixed zone. For each zone, a specific combustion model is attached based on flame structure analysis. CLE-H stands for Combustion Limited by Equilibrium Enthalpy; model uses an equilibrium fuel mass fraction to compute the average heat release rate. This equilibrium fuel mass fraction has been calculated a priori from complex chemistry calculations for fuel to limit burning rates. A presumed Beta-shape PDF is adopted to average the equilibrium at equilibrium. Auto-ignition is modeled from tabulated fully detailed chemistry. The tabulation strategy TKI proposed by IFP [3] is used. This model was implemented in STAR-CD and has been the object of a wide range of academic validations on test cases to check that fundamental dynamics are well captured. To evaluate the model, results were compared with extensive data from DI Engines in production at full and part load. The results show that the models give realistic Heat Release History, Indicated Power, as well as NOx emissions.