Experimental methods to analyse crankcase aerodynamic losses and flow fields
Date of Award
Doctor of Philosophy
School of Engineering
The air flow inside the crankcase of an internal combustion engine and the resistance that the air inside the engine induces on the moving engine components results in a component of the parasitic power loss of the engine, reducing the power output and efficiency of the engine. While these air flows have been researched using computational fluid dynamics in previous studies, there was no significant research found which had investigated these flows experimentally. The aim of this research was to develop experimental equipment to visualise the air flows in the crankcase of an engine. Particle Image Velocimetry (PIV) was the method that was chosen to visualise these air flows because it enabled instantaneous flow fields to be measured on a cross section through the entire crankcase of the test engine without creating any disturbance to the flow being measured.
The experimental equipment that was developed in this research consisted of an electric motor driven 450 cc single cylinder engine. The crankcase of the engine consisted of a transparent box structure to enable visualisation of the flow inside the crankcase. The internal engine components were designed to run without a lubrication system to prevent contamination of the air inside the crankcase or the transparent sides of the crankcase. Planar PIV flow visualisation was carried out on 3 parallel planes in the crankcase perpendicular to the crankshaft’s axis of rotation. Sets of multiple crankshaft angle resolved PIV measurements were compiled at eight evenly spaced crankshaft angles over a full engine rotation. PIV flow visualisations were repeated for engine speeds of 500 rpm, 900 rpm, and 1500 rpm in clockwise and counter clockwise directions.
PIV results were post processed to produce two dimensional velocity vector, vorticity, temporal variability, and pressure maps of the flow field inside the crankcase on each of the planes where flow visualisation was captured. The results indicated that the most significant flows in the crankcase were driven by the reciprocating motion of the piston, which forced air to flow in and out of the crankcase through the breather ports. The interaction of the rotating crankshaft with the air in the crankcase only affected the air flow in the immediate vicinity of the crankshaft and had minimal effect on the bulk flow of air inside the crankcase, therefore reversal of the engine rotation only effected the air flow near the crankshaft. The velocity of the airflows in the crankcase increased proportionally with increasing engine speed in the range of engine speeds tested.
While the PIV observations made were not specific to any particular production engine, the general characteristics of the air flows observed may be applied to improve future engine designs. The results from this project may assist in the reduction of crankcase parasitic pumping losses and the aeration of lubrication oil in future engine designs.
Access to this thesis is embargoed until 24th August 2023.
Ayres, T. J. (2022). Experimental methods to analyse crankcase aerodynamic losses and flow fields. https://ro.ecu.edu.au/theses/2500