Tackling Liner Erosion

News from AVL’s Virtual ICE Development

Losing an engine to liner erosion is a headache for everyone involved. For vehicle owners, it means forced downtime, a potential loss of income and costly repairs. For engine manufacturers, it means covering expensive warranties and suffering a blow to their reputation. To avoid liner erosion, engineers need to carefully investigate its root causes and design appropriate counter measures.

Engineers know that when an engine’s piston changes its direction of movement in top dead center (TDC) and bottom dead center (BDC), the “piston secondary motion” phenomenon induces contact between the piston crown and piston skirt and the liner. In turn, this creates high frequency vibrations that cause adjacent coolant volume to increase locally and decrease alternately. As the volume expands, the local pressure in the coolant jacket drops, leading to cavitation.

When cavitation occurs, the coolant changes its phase from liquid to gas, which creates vapor bubbles. When the vibrating wall moves in the opposite direction, the local pressure in the cooling jacket rises and the bubbles implode. Liquid coolant quickly fills the space previously occupied by the bubbles, causing high speed jet flows. If the implosion of a bubble happens close to the liner surface, the energy released can be so high that material is torn off from the liner surface, leading to erosion.

AVL has developed a simulation solution based on numerical models that lets engineers compute the interaction of piston slap and cavitation, which helps them identify erosion areas and create strategies to avoid critical conditions. This virtual development solution consists of simulation tools and a methodology, allowing engineers to determine the impact of design parameters on liner cavitation and erosion. The unique cavitation/erosion model in AVL FIRE™ M also takes fluid properties into consideration and is sensitive to changes in fluid temperate and pressure. Realistic boundary conditions for piston primary and secondary motion and liner displacement are acquired from AVL EXCITE™ simulations, making use of its superior elastic-hydrodynamic modelling capabilities.

Deploying AVL’s simulation method lets engineers efficiently and effectively test design proposals to avoid liner erosion and its consequences. With our solution, this can be done in a virtual environment during the early product development phrase, well before prototypes are available. This reduces the risk of having to perform expensive, last-minute design adaptations in the preproduction phase.