Direct observation of oil consumption mechanisms in a production spark ignition engine using fluorescence techniques
Lusted, Roderick M.
Wong, Victor W.
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The oil consumption characteristics of a four cylinder, normally aspirated spark-ignition engine were investigated for different piston ring end-gap configurations. A radiotracer was used to perform direct measurement of the oil consumption while Laser-induced Fluorescence (LIF) was used to perform the oil film thickness measurements for consumption predictions using the "Puddle Theory of Oil Consumption, " which relates oil consumption to second land film thickness and reverse flow through top ring gap. The consumption data was evaluated to determine the impact of top ring end-gap azimuthal location on oil consumption. The film thickness data was used to evaluate the extent to which the Oil Puddle Theory predicts variations seen in the actual oil consumption. A tritium radiotracer oil consumption measurement system with an accuracy of 94.6% was designed and constructed. This was used to perform direct measurements of the test engine oil consumption in two different test matrices. The first evaluated a piston ring configuration with the rings free to rotate. The second evaluated configurations with the top ring and second piston rings pinned to fix the azimuthal location of the end-gap; the azimuth of the top ring was varied. In the second test matrix, the oil film thickness on the piston's second land was measured, and predictions were made on the basis of that measurement . The first test matrix results indicated only a weak speed dependence and a large amount of variability in the oil consumption measurements. The second test matrix results showed an oil consumption speed dependence that was a function of top gap azimuth. Speed normalized results showed that the oil consumption was larger when the end-gap was on the thrust side of the test engine than when on the anti-thrust side. Measured oil consumption differed substantially from that predicted. This was found to be due to difficulties in determining effective ring gap flow areas and due to a previously un-documented azimuthal variation in second land oil film thickness. However, analysis of the results also indicates that the Puddle Theory is still a plausible oil consumption mechanism.
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