Effect of compression ring elastodynamics behaviour upon blowby and power loss

The automotive industry is subject to increasing pressure to reduce the CO emissions and improve fuel efficiency in internal combustion engines. Improvements may be achieved in a number of ways. The parasitic losses throughout the engine cycle emanate from friction in all engine contact conjunctions in addition to pumping losses. In particular one main contributory conjunction is the piston ring pack assembly. At low engine speeds, the contribution of friction to the total losses within the engine is increased significantly compared with the thermodynamic losses. Additionally, the sealing capability of the ring is crucial in determining the power output of the engine with any loss of sealing contributing to power loss, as well as blowby. Most reported studies on compression ring-cylinder conjunction do not take into account complex ring in-plane and out-of-plane elastodynamics. Hitherto, there has not been a numerical methodology which integrates tribology of an elastic compression ring, subject to modal behaviour in a coupled solution. This paper discusses the inclusion of transient ring elastodynamics of the top compression ring, interacting with blowby effects within the ring pack. The ring dynamics methodology is briefly highlighted for both in-plane and out-of-plane motions. In addition, a one-dimensional gas flow model that captures blowby behaviour is included. A case study is presented, using measured engine data. Gas flow and frictional losses at various engine speeds are predicted. The effect of gas blowby on the ring's tribological response can be ascertained, as well as the ring's dynamic motion within its retaining groove. Copyright © 2014 SAE International.