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Juni 2014
eBook (PDF)
Wilfried Edelbauer
Numerical Simulations of the Lubricating Oil and Air Flows in the Crankcase of an Internal Combusion Engine
Due to the increasing demand for high efficiency of Internal Combustion (IC) engines, engineers are compelled to pay attention to the complex two-phase flow of oil and air in the crankcase. Reduction of the ventilation losses and limitation of the oil consumption due to oil droplets leaving the crankcase are the targets of optimization.
The aim of this thesis is to provide a better understanding of the complex flow phenomena in the crankcase and to model formation and transport processes of the two-phase flow. Therefore model correlations have been implemented into a multi-phase CFD code using the Eulerian-Eulerian approach. Due to the complexity of the moving crank drive and the multi-phase flow, CFD has been so far rarely used for the simulation of the lubricating oil and air flows in the crankcase. Up to now performed CFD simulations have dealt with very simple geometry conditions for the computational mesh. Either non-moving meshes have been used, or the movement has been strongly simplified, disregarding the whole crank drive and performing piston motion only.
In this work the time scales of the different flow phenomena are estimated to determine the most relevant processes. Oil disintegration at the crank drive and oil atomisation due to the blow-by at the piston rings are pointed out as the major sources for the oil droplets. Therefore existing models are combined and adapted for the application in crankcase simulations. Droplet formation due to condensation of evaporated oil components is a further source for the oil mist. But due to negligible contribution in the short time of a few engine cycles, it is not considered in the simulations. Separate simulations of the blow-by gas flow and the oil disintegration at the crankweb have been performed. The moments of droplet size distribution functions are transported to obtain the spatial Sauter mean diameter distribution of the oil droplets. To enable the simulation of several engine cycles, the blow-by flow simulation is performed on a simple crankcase geometry including the moving pistons and neglecting the crank drive. The simulation of the oil disintegration at the crankweb is done on an advanced computational mesh with a moving piston and a rotating crankshaft. Although the conrod is not modelled, the two-phase flow simulations on a mesh with a moving crank drive lead the way to further investigations in that field. Besides the oil droplet propagation in the three-dimensional gas flow field, the simulations show that blow-by generates small droplets with diameters of a few micrometers, while large droplets are generated by the oil disintegration at the crankweb.
The aim of this thesis is to provide a better understanding of the complex flow phenomena in the crankcase and to model formation and transport processes of the two-phase flow. Therefore model correlations have been implemented into a multi-phase CFD code using the Eulerian-Eulerian approach. Due to the complexity of the moving crank drive and the multi-phase flow, CFD has been so far rarely used for the simulation of the lubricating oil and air flows in the crankcase. Up to now performed CFD simulations have dealt with very simple geometry conditions for the computational mesh. Either non-moving meshes have been used, or the movement has been strongly simplified, disregarding the whole crank drive and performing piston motion only.
In this work the time scales of the different flow phenomena are estimated to determine the most relevant processes. Oil disintegration at the crank drive and oil atomisation due to the blow-by at the piston rings are pointed out as the major sources for the oil droplets. Therefore existing models are combined and adapted for the application in crankcase simulations. Droplet formation due to condensation of evaporated oil components is a further source for the oil mist. But due to negligible contribution in the short time of a few engine cycles, it is not considered in the simulations. Separate simulations of the blow-by gas flow and the oil disintegration at the crankweb have been performed. The moments of droplet size distribution functions are transported to obtain the spatial Sauter mean diameter distribution of the oil droplets. To enable the simulation of several engine cycles, the blow-by flow simulation is performed on a simple crankcase geometry including the moving pistons and neglecting the crank drive. The simulation of the oil disintegration at the crankweb is done on an advanced computational mesh with a moving piston and a rotating crankshaft. Although the conrod is not modelled, the two-phase flow simulations on a mesh with a moving crank drive lead the way to further investigations in that field. Besides the oil droplet propagation in the three-dimensional gas flow field, the simulations show that blow-by generates small droplets with diameters of a few micrometers, while large droplets are generated by the oil disintegration at the crankweb.
Schlagwörter: simulation; blow-by; CFD; crankcase; droplet size distribution; engine oil; liquid disintegration; multi-phase flow; rotary atomisation
DOI 10.2370/OND000000000168
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