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RADIOACTIVE TRACERS have been used to study the fuel distribution among individual cylinders in two modern V-8 engines. Individual fuel components (both hydrocarbons and fuel additives) were “tagged” with radioactive hydrogen (tritium) or carbon-14. These “tagged” components were blended into a commercial-type fuel, and their distribution to engine cylinders was determined by measurements of exhaust-gas radioactivity. The quantity of fuel distributed to the cylinders was measured by an exhaust-gas analyzer of the catalytic-cell type. The results reported include the effect of various fuel factors, operating factors, and engine design factors on the distribution of both whole fuel and its components. A study of octane placement within the boiling range of the fuel revealed differences among fuels when rated under accelerating conditions (with “manifold lag”) and when rated at constant-speed conditions with poor fuel distribution.

RUMBLE is a type of abnormal combustion which may impose a limit on usable compression ratios if proper attention is not paid to fuel and lubricant factors. It is characterized by a low-frequency noise. This noise is much more likely to be present in engines which have been operated on light-duty schedules than in those which have been used in heavy-duty operation. Once deposits are present, rumble generally occurs at wide-open throttle and high engine speeds. Rumble does not appear to be confined to any particular type of combustion chamber, and increasing engine rigidity does not show promise of reducing the problem. Fuels with low deposit-forming tendencies help alleviate the problem. While not a complete cure, phosphorus fuel additives do a good job in reducing the incidence of rumble. This paper presents the results of work aimed at defining the problem, together with data illustrating the influence of various fuel factors.