Spark Advance and Octane Number - A Road-Test Technique 380171
THE road-test technique outlined in this paper, the authors explain, was developed to find a method that would give a broader picture of the car-fuel relationship. Although conceding that the general method employed - using the knock die-out point as a datum in the study of fuels in road cars - is not new, they claim that their technique increases the speed and precision in the method of obtaining borderline advance, and offers data over a wider field than hitherto presented.
A fully manually controlled distributor, a spark-advance indicator, and thermocouples for indicating the necessary operating temperatures comprise the apparatus used, the paper reports. The authors suggest that a more accurate and dead-beat means of indicating car speed than the car speedometer be employed, such as a fifth-wheel electric tachometer.
The general procedure consists in accelerating the car in high gear from approximately 10 m.p.h. and noting the speed and the spark advance at which audible knock disappears, thus locating one point on the curve. The spark advance is then altered by about 2 deg. and the acceleration repeated to locate another point, and so on until enough points are located to complete the curve.
The paper follows with notes on testing; correlation of borderline knock data with data obtained on a knock-intensity basis; a discussion of octane requirement and road rating of fuels; and concludes by pointing out the usefulness of this technique in evaluating car variables.