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Turbulent flows in a model engine having a square piston were analyzed in detail by using a numerical simulation method with higher-order accuracy to perform simulations on an orthogonal homogeneous grid without grid motions. Calculations were performed during several continuous engine cycles. A better understanding of the cycle-by-cycle differences, i.e., cyclic variations, in flow fields may lead to more effective ways of stabilizing combustion.

Fluid-dynamic principle for obtaining relatively stable combustion is found by performing cycle-resolved computations of turbulent flows in engines. Cycle-resolved computations are performed by using the implicit large eddy simulation (ILES) code, which we have proposed earlier. Calculations over continuous cycles show us the existence of “silent domain” in the engine cylinder, having weak cyclic-variations of flow. Time-dependent velocities averaged over six cycles, mean velocities, are also small in the silent domain. Moreover, we examine further on why cyclic variations of flow is weaker in the silent domain. This brings us a way for controlling cyclic variations for several engines.

Instability of the Initial flame propagation is examined after computing the flows during three continuous cycles of an engine. Cycle-resolved large eddy simulation (CLES) is employed for these computations. First, we calculated the compressible turbulent flows during three continuous cycles in a model engine having square piston. Then, the initial flame propagation processes are calculated by using G-equation at the flow condition of TDC. Grid system of 1,000,000 points is employed. Relation between cyclic-resolved turbulence and initial flame is qualitatively examined by the computational results.