This paper presents the results of a study cooperatively undertaken by The Standard Oil Company (Ohio) and Ethyl Corporation to determine the feasibility of a “road blending number” for a gasoline component. Volumetric averaging of such blending numbers would permit direct calculation of the road octane number of a gasoline blend. The prediction system based on road blending values is designed to provide refiners with a method more accurate and convenient than those presently used for blending gasoline to meet road octane specifications.
For this investigation, 80 blends were formulated from 4 components typical of those used in premium gasoline. Three of the components - alkylate, light reformate, and light catalytic distillate - were combined in various proportions to yield 16 base fuels. Heavy reformate was added to each of these base fuels in five concentrations to provide a broad range for examining its blending behavior. All finished blends contained 2.0 ml TEL per gallon, plus other additives commonly used in premium fuel.
The blends were road rated in two 1959-model test cars selected to represent basically different designs of engines and transmissions. Ratings were obtained under maximum-knock operating conditions by both the Modified Uniontown and Modified Borderline techniques.
The data from this program were evaluated by regression analysis to correlate various fuel properties with component blending behavior and, hence, the road octane number of finished blends. Two distinct methods of correlation were examined. In the first method, road antiknock quality was predicted on the basis of common laboratory tests. The second method entailed substitution of road octane ratings of components for their laboratory ratings in prediction equations.
The results of this study show that accurate road octane predictions based on component blending numbers are feasible. One such blending number system utilizes laboratory properties to predict the resultant road antiknock quality when combining a component with a base gasoline. A knowledge of the percentage of the component and the Research and Motor octane numbers of the base gasoline is required. This system could be especially useful in process-planning operations, where rapid assessment of the road antiknock effects of component concentration and base-fuel properties is of prime interest.
Road blending numbers also were derived for individual gasoline components based directly on their road octane ratings and hydrocarbon types. Road octane prediction is achieved by volumetrically averaging the blending value of each component in a blend. In addition to its utility in process planning, this system appears to offer the most direct approach to the refinery control of finished blends on a road octane basis. However, these correlations require the use of test cars to evaluate component antiknock performance. This is admittedly a radical departure from current methods of laboratory octane control of blending. The prime advantages of such a system appear to be increased accuracy and precision in direct prediction of road octane quality. The technical problems connected with such road testing probably could be solved to permit the application of component road ratings. At the same time, economics would require each refiner to balance the possible benefits from direct octane control against the added cost of extensive road rating.
During the course of this work, two interesting methods of correlating fuel antiknock behavior at various engine conditions were studied. A single equation was derived to predict the road octane rating of a blend at any Modified Borderline engine speed in a given car. In addition, we found that the Modified Uniontown rating of a blend can be predicted from the low-speed and high-speed Modified Borderline ratings of its components.


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