Knocking Gas

Last year U. S. motor cars consumed 15 billion gallons of gasoline--almost as much as the drinking water which passed down U. S. throats. About 15% of this total was "special" gasoline, a term which has little meaning to motorists, little more to oil refiners since each company has its own idea of what constitutes a "special" fuel. One's "special" is another's ordinary.

Equally "special" are low-boiling-point fuels which vaporize easily, facilitate quick starting in winter time (but which do not produce more power), and the knock-reducing fuels. Function of the latter is to eliminate the metallic clanks which old motors make when straining on hills. The puzzling question of what constitutes a knock-reducing fuel was perhaps solved by an announcement last week telling of the work of the co-operative steering committee.

Two years ago the Society of Automotive Engineers and the American Petroleum Institute joined forces and appointed this committee to find a uniform scale by which the knock-reducing quality of fuels could be expressed. At that time they explained that knocking is not directly caused by valves or carbon but by irregular and too rapid explosion of gasoline injected into cylinders overheated by any cause--insulating carbon deposits, lime coatings in the cooling system, faulty oiling.*

To control the high pressure explosion waves which pound against cylinder walls and produce the metallic sound, oilmen added to gasoline substances which raise the detonating point. Examples: aniline, tetraethyl lead.

To discover the exact influence of these materials on gasoline and to find a means of giving numerical values to specially treated fuels was the task of the committee. According to the announcement, the committee proceeded by selecting two chemicals, one knock-preventing (iso-octane), one knock-producing (normal heptane). Numerical rating was arrived at by noting the number of parts of non- knocking isooctane which must be added 1 to ten parts of heptane to duplicate exactly the fuel being rated. Thus, a fuel with a rating of 5 would be inordinately bad; fuel with a rating of 50, superlatively good. It remains now for the industry to accept the method; to decide that Number 30, say, is the standard commercial knock-reducer.

Most special gasolines are designated at filling stations by manufacturers' individual colors Only color not found: yellow. Reason: yellow has always been taken as an indication of poor refining. Coloring gasoline was started during the war when dyes were added to aviation fuels to distinguish them from motor car gasolines.

*Also suggested: when a cylinder becomes clogged with carbon its volume is reduced, fuel vapor is consequently subjected to greater pressures, which cause knocking explosions.

This file is automatically generated by a robot program, so reader's discretion is required.