SAE J2794_200702

The oil consumption of an internal combustion engine is a significant performance attribute. The loss of engine oil through the combustion chamber is critical because it impacts the emissions signature of the engine and potentially poisons any exhaust gas after treatment devices. In addition, oil consumption is an attribute that directly affects the operator of a vehicle. The durability of an engine is defined, in many cases, as the point at which oil consumption becomes excessive.

This document addresses the oil consumption transport mechanisms for the power cylinder. Other sources for oil consumption which will not be covered in this document are the turbocharger, the crankcase ventilation system, leaks, and the valve train. The material covered is appropriate for both spark ignition and compression ignition engines.

The intent of this document is not to be a comprehensive oil consumption handbook. It is an introduction to the oil consumption mechanisms. Since every engine is unique, this document handles oil consumption mechanisms in a general way, leaving the specific dimensions, surface finishes, end gaps, and angles to be detailed by the power cylinder engineer for each individual engine. Consequently, the document evaluates each feature in a qualitative manner. Each source of oil consumption is evaluated by the qualitative parameters of Major, Medium, and Minor. For example, the unit pressure of the oil ring is categorized as a major effect on in-cylinder oil consumption. In solving oil consumption problems, this feature should be explored before the piston skirt surface finish since skirt finish is categorized with a minor rating. In addition, if a new engine is being designed specifying the unit pressure of the oil ring will be a significant step in ensuring that a new engine design will have acceptable oil control.

This document does not emphasize the effect of wear on oil consumption. It applies to essentially new power cylinder components whose dimensions will change as the result of wear processes. Experience with each individual engine will determine how significant the power cylinder oil consumption is impacted by wear. This document is an introduction to understanding power cylinder oil transport mechanisms. The specific details of each individual engine will remain with the power cylinder development engineer.