Abstract
Physical simulations of tribo contacts in internal combustion engines can act as a supporting tool to match upcoming guidelines and emission restrictions. In particular, the scuffing resistance of the contact between the piston ring and cylinder liner suffers under decreasing oil viscosity and limitation of antiwear additives. This paper aims to provide an experimental method to simulate the scuffing of the piston ring/cylinder liner-contact and to validate this method with real engine parts and the literature from engine tests. The experimental methodology uses a linear tribometer TE77 to test specimens from original piston rings and liners under reciprocating motion. Additionally, the ring specimen is given the opportunity to perform secondary movements (ring twisting, ring turning) and to run under deficient lubrication conditions similar to the engine. A specially designed test strategy enables the reproducible creation of seizure of the tribosystem. The seizure resistance of two engine oils, tested for validation, correlates with the known engine performance. Therefore, the model test system can be seen as a reproducible tool for simulating seizure of a ring/liner-system, showing similar trends and wear mechanisms as in an engine. Surface analysis depicts similarities between the scuffed surfaces of an engine and the model and discusses the origin of seizure based on the model specimens together with the relevant literature.
Highlights
Because of the continuing trend towards a reduction in lubricant viscosity [1,2] and a reduction in crucial antiwear additive ingredients, piston groups in future engines are facing a higher risk of seizure and failure during operation
When the speed increases to 15 Hz, a drop in coefficient of friction (COF) together with a rise in the contact temperature takes place
The tests stop with a sudden seizure event, showing a COF and a contact temperature peak
Summary
Because of the continuing trend towards a reduction in lubricant viscosity [1,2] and a reduction in crucial antiwear additive ingredients, piston groups in future engines are facing a higher risk of seizure and failure during operation. Simulating the conditions in such future engines with new lubricants and material combinations and providing a low-cost alternative to engine tests can be done via laboratory model tests. Ring on liner model tests are known tools for benchmarking materials and lubricants in terms of friction assessment [3,4] and seizure resistance [5,6,7]. Basic investigations about chemical interaction of lubricants and sliding materials can be carried out by model tests with simple geometries [8,9]. These test configurations have a limited potential to depict the application’s damage mechanisms and tribosystem rankings. Manufacturing specimens out of original parts and using the original running surface is the closest to a real application [11,12,13,14,15], but can be difficult in terms of manufacturing
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