Road Antiknock Properties of Gasolines in Correlation with their Volatility Characteristics (II)

Abstract

Out of samples taken up in the previous report, four samples were selected for further studies. One sample of premium grade is representative of a gasoline, the road octane rating of which is comparable to its research octane rating, while two other samples of premium grade indicate significant road depreciations and the fourth sample of regular grade shows little depreciation in road octane rating. The latter three gasolines were found to be composed of very poor antiknock constituents concentrated in the lighter fraction.Effective volatility of these gasolines under the condition of a full throttle acceleration as used when testing road octane number was estimated from their ASTM distillation curves.The composition of the vapor and the liquid residue in the carburetter system was calculated by the flash vaporization method from the fractional distillation data and the effective volatility. The research octane numbers of the vapor and the residue were also calculated.The air-fuel mixture entering the cylinder must contain the residual liquid in the form of entrainment. The weight of entrainment per 100 weights of intake air is defined as "entrainment ratio", and the role of the entrainment was established by the theoretical calculation. The entrainment plays important roles in two ways. As the heavy ends of these gasolines have very high octane values, they contribute to the antiknock property of the cylinder mixture, and as a greater part of TEL is calculated to be concentrated in the residual liquid, the entrainment should act as a carrier of the antiknock compound.Rise of the experimental road octane number with engine speed by modified borderline method is attributed to the increase of entrainment ratio rather than the effect of aromaticity of the sample gasoline.