Due to the accumulation of deposits in the combustion chamber, the “appetite” of an engine for octane increases with mileage. Depending on the type of engine, driving conditions, and gasoline, this octane requirement increase (ORI) ranges from 3 to 10 octane numbers.
Because of ORI, national specifications for octane number of gasoline must be based on engines' octane requirement at equilibrium. Applying the incremental analysis technique to refining economics, F. Bernasconi calculated that the incremental cost of producing each extra octane number by refining ranges from $2 to $6 per ton. It is generally well accepted that an increase of one octane number will lead to a loss in refinery yield of 4 to 6%.
Octane requirement increase can be controlled with a new type of ashless, non-metallic additive. An ORI reduction of 50 to 80% has been observed, opening the route to decreasing national gasoline octane specifications. Savings of millions of dollars and up to 20% of crude are possible. Emissions are reduced.