An Experimental Study of the Time Scales and Controlling Factors Affecting Drastic Blow-by Increases during Transient Load Changes in SI Engines

This paper presents the follow up to previous work done by Przesmitzki and Tian [1] studying large increases in blow-by in a spark ignition engine during transient load changes. This study examines the sensitivity of such blow-by spikes to differing intake pressures, and the time spent under both high and low intake pressure. The study consisted of experiments with a single cylinder test engine utilizing 2D LIF (Two Dimensional Laser Induced Fluorescence) techniques to view real time oil transport and exchange, along with computer modeling to explain certain phenomenon observed during the experiments.

The previous work found that a very large blow-by spike could occur upon a transition from low engine load to a high engine load. The hypothesis was the top ring groove was being filled with oil during low engine load. Thereafter, it was hypothesized a transition to high load resulted in radial collapse of the top ring, and the subsequent blow by spike.

The results of this study confirm through visual observation that the blow-by spikes were indeed the result of top ring radial collapse in the tested engine. They also show top ring radial collapse and the subsequent blow-by spike is ultimately the result of oil transport between the piston and top ring groove. There is a clear coupling between oil transport and gas transport. The results also suggest ring rotation may be a primary source of spreading oil in the top ring groove in the circumferential direction.