A rapid and precise oil consumption measurement in an automotive engine can be made in 5-7 minutes by a radiometric method. Several hours are usually required for conventional methods. The radiometric method consists of tagging the engine oil with a radioactive tracer, 1,2-dibromo-octadecane containing bromine-82. This material undergoes combustion with the oil, and the radioactive hydrogen bromide is extracted from the exhaust gas with one molar sodium hydroxide. Scintillation counting is employed to determine the amount of radioactivity recovered, which in turn is proportional to oil consumption.
Oil consumption measurements were determined over a speed range of 1500-3000 rpm and over manifold vacuum ranges of 22-2 in. Hg. It was found that the presence of lead, either as engine deposits or in the gasoline, interfered with the recovery of hydrogen bromide. Therefore, this method is restricted to nonleaded engines. In addition it was necessary to add some bromine derivative to the gasoline to act as a carrier for the tracer. A fuel consisting of isooctane with 4 cc/gal ethylene bromide proved satisfactory.
The method is capable of 10% precision determined from pairs of duplicate measurements. When compared to conventional methods, the agreement is better than ± 12%.
Typical oil consumption data obtained at various speeds as a function of manifold vacuum are given. Oil consumption data measured during engine break-in, unobtainable by conventional methods, are discussed.