Knock and Antiknock Properties

IP 119) weak mixture performance is also determined (ASTM D 2700, IP 236). 

The higher grades of fuel are thus classified by their specified antiknock ratings under both sets of test conditions. For example, 100/130 grade fuel has an antiknock quality of 100 minimum by the weak mixture test procedure and 130 minimum by the rich mixture procedure. Octane numbers are used to specify ratings of 100 and below, whereas performance numbers are used above 100. 

The pour point of a petroleum product is an index of the lowest temperature at which the product will flow under specified conditions. Pour point data can be used to supplement other measurements of cold flow behavior (such as the freezing point). 

In the original (and still widely used) test for pour point (ASTM D-97, IP 15), a sample is cooled at a specified rate and examined at intervals of 3°C (5.4°F) for flow characteristics. The lowest temperature at which the movement of the oil is observed is recorded as the pour point. A later test method (ASTM D-5853) covers two procedures for the determination of the pour point of crude oils down to -36°C. One method provides a measure of the maximum (upper) pour point temperature. The second method measures the minimum (lower) pour point temperature. In these methods, the test specimen is cooled (after preliminary heating) at a specified rate and examined at intervals of 3°C (5.4°F) for flow characteristics. Again, the lowest temperature at which movement of the test specimen is observed is recorded as the pour point. 

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