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The work presented is a comparative analysis between Reynold’s Averaged Navier Stokes (RANS) and Large Eddy simulation (LES) description of turbulence to capture the in-cylinder flow structures. Simulations are performed using RNG k - € RANS model and LES one equation eddy viscosity model with Werner and Wengle wall model. ECFM combustion model has been used to achieve the desired rate of heat release when compared against the experiments. KH-RT spray model has been used to define the primary and secondary breakup of parcels. A Renault engine operating on Miller cycle has been chosen for this study. Consecutive perturbation method (CPM) available in Converge has been used to take the advantage of availability of higher number of cores to reduce the effective CPU time. Results of RANS simulation indicates that increase in valve overlap results in faster tumble decay compared to LES.

The increasing use of downsized turbocharged gasoline engines for passengers cars and the new European homologation cycles (WLTC and RDE) both impose an optimization of the whole engine map. More weight is given to mid and high loads, thus enhancing knock and overfueling limitations. At low and moderate engine speeds, knock mitigation is one of the main issues, generally addressed by retarding spark advance thereby penalizing the combustion efficiency. At high engine speeds, knock still occurs but is less problematic. However, in order to comply with thermo-mechanical properties of the turbine, excess fuel is injected to limit the exhaust gas temperature while maximizing engine power, even with cooled exhaust manifolds. This also implies a decrease of the combustion efficiency and an increase in pollutant emissions. Water injection is one way to overcome both limitations.

This paper is focused on the experimental and numerical investigation of tumble motion on a single cylinder optical engine on three important parameters like engine load conditions, engine speed and level of tumble. Experiments are conducted in an optical engine and the velocity fields are measured with the aid of advanced particle image velocimetry (PIV) measurement technique. For simulation, multiple cases were considered to develop the numerical process for transient in-cylinder aerodynamics to capture the tumble motion and turbulence level in a Spark Ignited (SI) engine. The simulation results, velocity fields of each case were directly compared with the corresponding test results for different crank positions of the engine. On comparison, a good agreement between the measurement and the simulation is obtained for different configurations.