Additives are essential ingredients of today’s motor gasolines. They enhance fuel quality by supplementing its natural characteristics or by providing new properties. As a result of additive use and modern refining methods, today’s inexpensive motor gasolines give excellent service performance and long storage life. This has permitted engine and equipment manufacturers to build more powerful and efficient equipment which operates with a minimum of service difficulties.
In spite of the broad well-established use of additives by the petroleum industry, the average mechanical engineer engaged in engine or equipment development has little opportunity to become more than casually acquainted with them. Thus, he is unlikely to have more than a hazy idea of their functions. Nor is he likely to fully appreciate the extensive and thorough chemical and engineering development that usually precedes their marketing.
A frequent misconception among engineers is that gasoline additives are primarily for passenger car usage. This is far from true. Additives are also of utmost importance in gasolines used in trucks and in farm and industrial equipment to insure the improved performance and reliability of modern engines used in these types of service.
In this paper the intention of the authors is to furnish the engine and equipment development engineer with a review of modern gasoline additives in a convenient form. The authors discuss the types of problems which additives are asked to solve, the types and concentrations of compounds used, and the mechanisms by which these additives accomplish their objectives. The similarity between additive and engine development is brought to light. The discussion is confined to applications of additives in so-called “motor gasolines,” which include all gasoline engine fuels with the exception of those used for aviation.
A gasoline additive must meet many stringent requirements by passing many tests before it can become a commercial product. The evaluation of additives is extremely complex because of the great variability of engines, equipment, fuels, lubricants, and operating conditions. Moreover, the evaluation of “side effects” on engines and equipment may be more costly and time-consuming than tests for effectiveness.
To illustrate the size and complexity of an additive evaluation program, Ethyl Corporation’s investigation of the effects of increasing the TEL content of gasolines from 3.0 to 4.0 ml per gallon is described. In this program, over 2 million truck miles, 21,000 farm tractor hours, 2.1 million passenger car miles, and 2000 dynamometer hours were accumulated in investigating side effects alone. This amount of testing was necessary to be sure that the higher TEL concentration would result in no significant problems during engine, vehicle, and equipment utilization.


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