An Engine's Definition of Unleaded Gasoline

With unleaded and low-lead gasolines being introduced into the marketplace in increased numbers, definition of what is meant by the terms unleaded and low-lead is becoming important. What quantity of lead can a gasoline contain before effects normally associated with the use of gasolines leaded to current levels are encountered?

An engine program designed to investigate the effect of varying gasoline lead levels upon changes in hydrocarbon exhaust emissions levels resulting from combustion chamber deposits and valve recession was extended to very low lead levels. The results of this program define the amount of lead a fuel may contain before lead deposit effects on emissions are observed and valve recession problems are eliminated as falling between 0.04-0.07 gm/gal.

The usefulness of these parameters to define unleaded gasoline is discussed, together with other parameters that must also be investigated before a complete definition of unleaded gasoline can be established.