Standard Test Method for Motor Octane Number of Spark-Ignition Engine Fuel

This technical document establishes a standardized protocol for determining the research octane number of spark-ignition engine fuels. The procedure involves operating a single-cylinder variable compression ratio engine under precisely controlled conditions to measure the fuel's anti-knock characteristics relative to reference blends. By systematically varying the compression ratio, the method quantifies the fuel's resistance to abnormal combustion, which is critical for evaluating performance in typical automotive engines. The approach relies on specific test fuels, strict temperature control, and defined operating speeds to ensure consistent and reproducible results across different laboratories. Adherence to these detailed operational guidelines allows manufacturers and regulators to compare fuel quality accurately. The methodology covers sample preparation, engine setup, measurement techniques, and data calculation steps. It serves as a foundational reference for assessing fuel suitability and optimizing engine design for various markets.