Experimental research on the wall-wetting effects on the frictional property of the cylinder liner–piston ring pair

The application of novel injection strategies (high-pressure injection, early injection, retarded injection, etc.) in combustion engines has made the wall-wetting problem severer. As the splashed fuel dilutes the lubricating oil, the tribological performance of the cylinder liner–piston ring pair will be affected. In this research, the viscosity and wettability tests were conducted firstly by mixing diesel into lubrication oil. It was found that the dynamic viscosity of the mixture drops with more fuel diluting the oil, and a small quantity of diesel mixed will cause a remarkable decline in lubricant viscosity; also, the contact angle shows a downward trend with the increasing diluting ratio. Then based on several typical diluting ratios, the reciprocating friction tests were carried out to measure the instantaneous friction force of the production ring/liner pair. The experimental results showed that under a mixed lubrication state, the peak friction force of the ring/liner pair occurs around the dead centers, while the minimum force occurs at the middle position of the reciprocating stroke; with more fuel diluting the oil, the bearing capacity of oil film degrades, resulting in the increase of friction force. In addition, the average friction coefficient of the ring/liner pair shows an upward trend with the increasing diluting ratio, and the Stribeck curve moves toward the upper-left, which means the lubrication condition of this pair tends to transit from mixed lubrication to boundary lubrication, causing negative effects on the frictional property of the cylinder liner–piston ring pair. Therefore, the diluting ratio should be controlled under 20%.

Experimental research on the frictional performance of real laser-textured cylinder liner under different lubrication conditions

Laser surface texturing technology including the steps of surface pre-processing, laser texturing, and surface post-polishing was utilized to process typical micro-dimples(diameter 50 μm, depth 8 μm, and area ratio 10%) on the cylinder liner surface in a production engine. By conducting the reciprocating friction tests on a friction-wear tester, the instantaneous friction force of the real cylinder liner-piston ring pair was measured for comparing the tribological performance of plateau-honed cylinder liner and laser-textured cylinder liner. The testing results showed that under different lubrication conditions, laser texturing cylinder liner could effectively reduce the friction force, especially the peak force around the reciprocating stroke ends of ring/liner pair. Within a reciprocating stroke, the average friction coefficients of the laser-textured cylinder liner-piston ring pair decrease by approximately 18.6%–37.6% under low temperature oil bath condition dominated by hydrodynamic lubrication, while the friction coefficients decrease by approximately 1.8%–6.1% under high temperature oil bath condition dominated by mixed lubrication compared with these of the plateau-honed cylinder liner-piston ring pair. This indicates that laser texturing cylinder liner with appropriate micro structures could enhance the hydrodynamic effects and reduce the friction of ring/liner system, which is conducive to improving the engine mechanical efficiency and the application of low-friction design on production engine.

On almost valuation ring pairs

If [Formula: see text] are (commutative) rings, [Formula: see text] denotes the set of intermediate rings and [Formula: see text] is called an almost valuation (AV)-ring pair if each element of [Formula: see text] is an AV-ring. Many results on AV-domains and their pairs are generalized to the ring-theoretic setting. Let [Formula: see text] be rings, with [Formula: see text] denoting the integral closure of [Formula: see text] in [Formula: see text]. Then [Formula: see text] is an AV-ring pair if and only if both [Formula: see text] and [Formula: see text] are AV-ring pairs. Characterizations are given for the AV-ring pairs arising from integrally closed (respectively, integral; respectively, minimal) ring extensions [Formula: see text]. If [Formula: see text] is an AV-ring pair, then [Formula: see text] is a P-extension. The AV-ring pairs [Formula: see text] arising from root extensions are studied extensively. Transfer results for the “AV-ring” property are obtained for pullbacks of [Formula: see text] type, with applications to pseudo-valuation domains, integral minimal ring extensions, and integrally closed maximal non-AV subrings. Several sufficient conditions are given for [Formula: see text] being an AV-ring pair to entail that [Formula: see text] is an overring of [Formula: see text], but there exist domain-theoretic counter-examples to such a conclusion in general. If [Formula: see text] is an AV-ring pair and [Formula: see text] satisfies FCP, then each intermediate ring either contains or is contained in [Formula: see text]. While all AV-rings are quasi-local going-down rings, examples in positive characteristic show that an AV-domain need not be a divided domain or a universally going-down domain.