Effects of Atmospheric Variables on Passenger Car Octane Number Requirements 660544

Octane number requirement studies were made with eight late-model passenger cars to evaluate effects of temperature, humidity, and altitude. Primary reference fuels and 1965 CRC full-boiling reference fuels were used.
Temperature and humidity tests were made on a chassis dynamometer at sea level, while effect of barometric pressure was studied on the road at altitudes up to 6000 ft. Regression analysis was used to study the correlation between changes in octane number requirement and changes in temperature and humidity. These correlations were linear and varied among the cars. The average changes in ONR were somewhat smaller, but in fair agreement with those reported in the literature.
The altitude effect also varied among cars tested and was generally nonlinear. On the average, the effect of barometric pressure from sea level to 3000 ft was smaller than concluded from earlier studies; from 3000-6000 ft, the pressure effect was larger.
To supplement actual test work, several surveys were conducted to determine if engine modifications are made on vehicles distributed and operated in high altitude areas.


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