Modeling and simulations of evaporating spray, turbulent flow, and combustion in internal combustion engines

A multicomponent droplet evaporation model, which discretizes the one-dimensional mass and temperature profiles inside a droplet with a finite volume method and treats the liquid phase as thermodynamically real, has been developed and implemented into a large-eddy simulation (LES) code for evaporating and reacting spray simulations. Single drop evaporation results obtained by the variable property multicomponent model are shown to match with the constant property model in the limiting conditions. The LES code with the multicomponent model is used along with the Kelvin-Helmholtz - Rayleigh-Taylor (KH-RT) droplet breakup model to simulate realistic fuel sprays in a closed vessel and is found to reasonably well predict the experimentally observed non-linear behavior of spray penetration lengths with changing ambient conditions for n-hexadecane and 4 different multicomponent surrogate diesel fuels with 2-8 components. The effects of various modeling assumptions and gas and liquid parameters on the drop and spray evolution and evaporation are investigated in details. A previously studied single piston Rapid Compression Machine (RCM), extended to a twin-piston RCM, is simulated by LES for different stroke ratios of the two pistons, as a precursor to the study of opposed piston two-stroke engines. Opposed piston engines, which have recently generated interest due to their high power density and fuel economy, are mechanically simpler compared to conventional four-stroke engines but involve highly unsteady, turbulent and cycle-variant flows. LES of turbulent spray combustion in a generic single cylinder, opposed-piston, two-stroke engine configuration has been conducted with the two-phase filtered mass density function (FMDF) model, which is an Eulerian-Lagrangian-Lagrangian subgrid-scale probability density function (PDF) model for LES of two-phase turbulent reacting flows. The effects of various geometric parameters, operating conditions and spray parameters on the flow evolution, turbulence, spray and combustion in the engine are studied. The cycle-to-cycle variations in the flow variables like swirl and tumble are found to be significant while those in thermodynamic variables like temperature are negligible. The hybrid LES/FMDF methodology has been applied to simulate non-reacting turbulent spray for single-component and multi-component fuels and the consistency of the method has been established. The effects of spray parameters like nozzle hole diameter, injection pressure and injected fuel temperature on the spray penetration length are found to qualitatively follow experimental trends. Combustion simulations of n-dodecane fuel sprays are carried out for the opposed piston engine with a global kinetics mechanism and the consistency of the LES and FMDF components is demonstrated.