Research On The Cycle-to-cycle Variation Of In-cylinder Cold Flow Of A Two Stoke Engine With The Method Of LES

CCV (cycle-to-cycle variation) has a decisive influence on theefficiency of combustion and it is a must to improve the efficiency of theengine by understanding and controlling CCV. LES (large eddysimulation) method shows its value in CCV issues by calculatingmulti-cycle process.A LES approach was used to study the in-cylinder turbulent flows ofa two stoke engine. The variation of the in-cylinder flow characteristicswas explored and compared with PIV measurement data. It shows thatLES simulation could reflect the pressure change and the transformationof turbulence. This article makes detailed analysis on the CCV level andturbulence scale of the spark plug gap, the transversal sections and thelongitudinal sections.The main conclusions are as follows: The integral scales which thesimulation got match the experimental ones well and detailed analysiscould be made with the LES method used in this research. The CCV ofvelocity is obvious while the CCVs of pressure, temperature and densityare not. With the piston moving to TDC, CCV and turbulent fluctuationintensity have similar changes, and for a certain section, the CCV intensity and velocity magnitude will come down, and so is to the swirlscale and tumble scale. Near the spark plug gap and17°CA BTDC, thecloser to the cylinder head, the stronger the CCV of transversal velocitieswill be, while the CCV of longitudinal velocities come weaker, the scaleof the swirls come bigger. The changing disciplines of the velocities ondifferent sections are alike. The COV of velocity magnitude on atransversal section varies within a limited area and the distribution on thesection is relatively stable which is only determined by factors such as theengine geometry, the initial conditions, the engine speed and so on.