ASTM D6812 tandard Practice for Ground-Based Octane Rating Procedures for Turbocharged/Supercharged Spark Ignition Aircraft Engines
4. Summary of Practice
4.1 A recently overhauled, remanufactured, or new, turbocharged/supercharged aircraft engine is octane rated to determine the minimum ground-based octane requirement. Minimum octane requirement is defined as one number above the highest MON orAN where knock was detected. The engine is tested at three or more of the worst power points subject to knock behavior while operating under harsh and repeatable environmental conditions. These points usually involve high manifold pressures. At the very least, takeoff power, a maximum continuous or climb power, and a cruise configuration shall be tested. Takeoff power and climb power are tested under full-rich mixture conditions, and cruise power is tested under full-rich and lean mixture configurations in 5 % increment reductions from full-rich fuel flow to peak exhaust gas temperature. Engine operating temperatures and oil temperatures are kept at maximum allowable limits.
4.2 Octane ratings are determined under stable engine conditions using known PRFs and RFs.
4.3 Knock sensor installation and knock quantification are described in Annex A1.
5. Significance and Use
5.1 This practice is used as a basis for determining the minimum ground-based octane requirement of turbocharged/supercharged aircraft engines by use of PRFs and RFs.
5.2 Results from standardized octane ratings will play an important role in defining the octane requirement of a given aircraft engine, which can be applied in an effort to determine a fleet requirement.
