Compression rings for heavy duty diesel engines are traditionally made of ductile cast iron material. These rings, in general, have conservative standard dimensions limited by the strength of their base material. More recently, however, the market for heavy duty diesel engines demanded products able to cope with high levels of power density and, at the same time, lower levels of oil consumption, friction, and emissions.
This paper discusses the advantages of some radical changes made on the design of compression rings in order to take advantage of steel as the base material. The superior mechanical properties of steel allow the use of rings with smaller cross sections which minimizes the friction losses caused by the combustion gas pressure pushing the ring against the liner. It also allows the use of compression rings with a free gap significantly larger than usual. The larger free gap and subsequent higher ring diametral loading greatly improve the ability of the ring to conform to frequently distorted cylinder bores thus enhancing its ability for scraping oil.
Results from analytical tools such as finite element analysis and performance simulation programs are presented and discussed in an effort to validate and quantify the impact of the new design on engine performance. Oil consumption and blowby levels of a heavy duty diesel engine were reduced when steel compression rings with smaller cross section and larger than usual free gap were used. Comparative bench fatigue tests with the steel top ring also showed higher fatigue strength than that of the current cast iron ring.