Analysis of Oil Consumption Behavior during Ramp Transients in a Production Spark Ignition Engine

Engine oil consumption is recognized to be a significant source of pollutant emissions. Unburned or partially burned oil in the exhaust gases contributes directly to hydrocarbon and particulate emissions. In addition, chemical compounds present in oil additives poison catalytic converters and reduce their conversion efficiency. Oil consumption can increase significantly during critical non-steady operating conditions. This study analyzes the oil consumption behavior during ramp transients in load by combining oil consumption measurements, in-cylinder measurements, and computer-based modeling.

A sulfur based oil consumption method was used to measure real-time oil consumption during ramp transients in load at constant speed in a production spark ignition engine. Additionally in-cylinder liquid oil behavior along the piston was studied using a one-point Laser-Induced-Fluorescence (LIF) technique. Land pressure traces and engine blowby were measured to analyze oil transport along the piston and models that predict ring dynamics and gas flows were used to analyze the transient oil consumption behavior.

A sudden increase of oil consumption to a level significantly higher than the steady state values was observed during transient measurements from low load to higher load conditions. During these transients, oil consumption reached a peak and then gradually decreased to the steady state level of the final operating condition. This phenomenon occurred at all speed conditions investigated. LIF results showed significant decrease of accumulated oil on the piston after the transients. However, this difference of oil accumulated could not explain the total extra oil consumed during the transition. Further analysis with the ring dynamics and gas flow models suggested that the oil flow driven by the reverse gas flow through the top ring groove was the source for the excess of oil consumed. This hypothesis was supported using observations on a one cylinder research engine with the same ring-pack and engine design. Images acquired using 2-D LIF during the same load transients clearly show liquid oil outflow from the top ring groove.