Apex Seals Research Articles

Third Paper: Lubricant Development for the Wankel-Type Rotary Engine

A review has been made of the factors which may influence the development of lubricants suitable for the Wankel-type engines. The lubricant requirements of the Audi-NSU Ro80 engine are discussed in comparison with the performance level of lubricants currently in use with conventional reciprocating piston engines. In Europe, high-speed pre-ignition has been one of the main causes for concern, but at the other end of the performance scale, cold wear of cast-iron apex seals under ‘stop and go’ driving conditions, created conflicting performance requirements for the lubricant under development. A compromise lubricant formulation has given complete freedom from pre-ignition and a marked decrease in the ‘cold wear’ rates, whilst maintaining the other desirable properties necessary for satisfactory Wankel-engine performance.

Second Paper: Recent Studies on Rotary-Engine Lubrication

Rotary-engine lubrication studies have been conducted on four engines covering the two types of rotary engine now in production. Metallic or carbon-metallic apex seals were used.Results presented have been obtained with 13 different oil formulations, including passenger-car-engine oils corresponding to API SC, SD or SE categories, automatic-transmission fluids of the Dexron II type, and oils for two-stroke engines. Seven different test procedures have been used in these investigations, employing either engine bench test stands or vehicles on chassis dynamometers.Satisfactory rotary-engine performance has been obtained with oils containing from 0 to 1·2 per cent by weight of sulphated ash. The ability of the base stock to provide good film thickness has also been found of benefit in reducing rotary-engine wear. Passenger-car-engine oils can be excellent rotary-engine lubricants and those oils corresponding to the latest API SE classification exhibit better performance than previous API SC or SD oils. Automatic-transmission fluids have also given promising results.