TS-138
Developments in Two-Stroke Engine Cylinder Lubrication
Robert W. Allen and Shigebisa Yura
ABSTRACT
This paper examines the trends in engine performance from the perspective of the cylinder lubricant. Boundary layer lubrication and the mechanisms involved with thin oil films and metal to metal contact are examined and current research into this field is discussed. Broad proposals are made on the type and nature of cylinder lubricants for future higher pressure engines.
: Key Words: Two-stroke engines, Cylinder Lubrication, Adnesive wear, Tribology
1. INTRODUCTION
The development of the two-stroke engine has seen a greater rate of change over the last fifteen years than at any other time in its 100 history. The improvements made in the thermal efficiency of these engines has required higher pressures which in turn means higher temperatures and higher thermal loading. Whereas a decade ago standard cylinder lubricants provided sufficient protection against liner and ring wear the same lubricant today will not adequately lubricate and protect the most modern engine. The trend towards engines of even higher specific output is likely to continue.
Cylinder lubricants have been relatively simple in their chemical composition. Tradition has been to provide an oil of sufficient viscosity for lubrication purposes added to which are alkaline detergents to provide some protection against the sulphur acids arising from combustion. In the modern high pressure engine increases in contact pressure between ring and liner and lower viscosity due to higher liner temperatures means that the resultant thinner oil film is no longer capable of preventing metal to metal contact. In addition the higher liner temperatures are now well above the acid dew point such that the corrosive wear is no longer a problem.
Definitions
A distinction is made between lubrication and lubricant and the following definitions are widely recognised as meaningful and practical.
Lubrication is concerned with the reduction of friction and wear between load bearing surfaces, in relative motion, by the application of a lubricant. Lubrication embraces parts of mechanical engineering, chemistry, physic's, and metallurgy. There are three main types of lubrication these being --- Hydrostatic. Hydrodynamic, and Boundary.
Lubricants are products to be introduced between interacting surfaces to form thin films that can reduce friction and protect against wear. Lubricant design and performance becomes critical during boundary layer lubrication.
Affiliations: Castrol Marine
R.W. Allen Castrol Marine, Swindon, SN3 1RE, UK
S Yura Castrol Marine, 46-1, honcho 2 chome, Nakano-ku, Tokyo 164-0012, Japan.
