Oil Transport Phenomena during extreme load transients inside the power cylinder unit as investigated by HS-2DLIF (High-Speed 2D Laser-Induced Fluorescence) 2019-01-2363

This paper presents findings of optical investigations conducted via the HS-2DLIF (high-speed two-dimensional laser-induced fluorescence) technique under extreme transient conditions. These extreme conditions are a transition from WOT to closed throttle and vice versa. The goal is to gain a better understanding of oil transport magnitudes and timescales for transitions to and from extreme throttled conditions. These conditions are similar to the boundary conditions found during cylinder deactivation.

The transients were conducted under motored conditions with injection and spark disabled in a speed range from 650 rpm to 3000 rpm. The load was transitioned from WOT to different low load conditions (closed, 150 mbar and 200 mbar), held at that low load for a variety of durations (10 sec - 600 sec), before going back to WOT. The experiments showed a strong dependence of oil transport on speed and load. The higher the speed, the faster the oil transport.

When transitioning to WOT in cases with a lot of oil in the ring pack, a drastic blow-by increase could be measured. The cause of the phenomena could be explained in detail with HS-2DLIF. Previous hypotheses were able to be verified and extended. It was found that, during the time spent at low engine load, oil was transported towards the combustion chamber and into the top ring groove. When a sufficient amount accumulated, the introduction of the transient allowed flow past the top ring, since its sealing capability was lost due to oil blocking its path towards its ID (inner diameter). Additionally, a large amount of oil was pushed through the top ring gap due to reverse flow in collapsing cycles. The top ring collapse ended when enough oil was suddenly released, allowing the ring to regain sealing capabilities.