Wide differences of opinion are expressed by automobile builders regarding crankcase-oil dilution. The theories advanced in explanation of dilution fail to elucidate some important facts and must therefore be regarded as unsatisfactory. From a theoretical investigation, the author determines the conditions under which the vapors of various fuels condense during the compression stroke of the engine and, as a result of such analysis, presents the theory that “surface condensation,” or the aggregation of the liquid fuel-particles on the cylinder-walls, is chiefly responsible for crankcase-oil dilution.
First, suggested explanations of the dilution are presented, references to previous experiments by several authorities are stated and these are discussed. The effect of jacket-water temperature is analyzed, and whether any condensation of fuel takes place during the compression stroke of a carbureter engine is debated.
A procedure is developed that should show the effect of compression upon a fuel-air mixture with a reasonable degree of accuracy, its details being explained and supplemented by empirical data and charts that refer to alcohol, benzene, pentane, hexane, heptane, and octane, as well as by a cautionary discussion regarding the application of thermodynamic principles to the operation of the internal-combustion engine. Varied compression-conditions are treated, and the conclusion is reached that most of the fuel particles that become “condensed” are particles that never have been evaporated. Several remedies for crankcase-oil dilution are then suggested.


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