The Effect of the Random Inflow Conditions and Initial Conditions to Cycle-to-Cycle Variations Using Detachment Eddy Simulation

The overall goal of all engine researchers is to enhance fuel economy and reduce emissions. To achieve this objective, one should reduce the cycle-to-cycle variations in the combustion process. It is well known that cycle to cycle variations in combustion significantly influence the performance of spark engines. Traditionally, it has been explained as being the result of random fluctuations in equivalence ratio and fluid flow conditions due to the unsteady nature of turbulent flow in the engine.

This paper presents a numerical study of the effect of the random inflow conditions and initial conditions to cycle-to-cycle variations in-cylinder flow. This study has been performed with the commercial CFD (computational fluid dynamic) code (FLUENT) coupled with our own development based on UDF facilities given by FLUENT. Detached Eddy Simulation Shear-Stress Transport (DES SST) model, which is a hybrid Reynolds Averaged Navier-Stokes (RANS) and Large Eddy simulation, appear to be a promising way to simulate cycle to cycle variations in-cylinder flow. Measured data obtained by literature are used for the validation of computations. The case considered is a geometrically simplified engine. In this study, non-reacting DES is undertaken with a single cycle (SC) strategy for the generation tumbling motion. The general flow structure is analyzed first and cycle to cycle variations of the velocity field are analyzed. The results showed significant effect of random initial conditions and inflow conditions on the features of flow Tumble.