A one-dimensional model for the motor oil-fuel dilution under gasoline engine boundary conditions

Alma Mater Studiorum, University of Bologna, Department of Industrial Engineering, Italy

^* Corresponding author: valerio.mariani4@unibo.it

Abstract

Nowadays the climate change caused by the green-house effect increasing is a world-wide issue with which scientists have to face. Being the passenger vehicles filled with fossil fuels, the emission of the carbon dioxide green-house gas is unavoidable. In order to slowdown both the global warming and the fossil fuels wasting, lower fuel consumptions, thus high efficiency engines, are required. Currently, the coupled use of downsizing and direct injection in spark ignited engines meets both high efficiency and power-demand requirements. Being downsized engines more compact, the distance between the injector and the engine walls are shorter. Thus, depending on the engine operating condition, the fuel spray wall impingement may occur leading to the formation of a liquid fuel film. If the wall impingement occurs against the cylinder liner wall, which is wetted by a thin oil layer, the motor oil and the landed fuel dilute until the piston arrival. At this time, the mass transport by diffusion have promoted the creation of an oil-fuel mixture. Thus, while thicker part of the mixture layer is scraped into the piston top land crevice, the thinner, whose properties are degraded by the fuel contamination, remains on the cylinder liner. The mixture accumulated inside the crevice may be scattered due to the piston inertia leading to the oil detachment and transport in the combustion chamber. The latter may cause both abnormal combustions named preignitions at high loads and increased particulate emissions at low loads, cold states, and cat-heating. This paper reports the implementation of a onedimensional numerical model for the dilution between fuel and motor oil in a stroke of a gasoline engine. The model aims to give the composition of the oil-fuel mixture both on the cylinder liner after the piston arrival and in the piston top land crevice.