D2700-24 – Standard Test Method Technical Guide

🔬 Test Engine Configuration and Fuel Scope

ASTM D2700-24c specifies a standardized laboratory test method for determining the Motor Octane Number (MON) of liquid spark-ignition engine fuels. The test is conducted using a standardized single cylinder, four-stroke cycle, variable compression ratio, carbureted, CFR engine run in accordance with a defined set of operating conditions. The method is applicable to liquid fuels, including those containing up to 25 % v/v of ethanol, though it may not be applicable to fuel and fuel components that are primarily oxygenates.

The octane number scale is defined by the volumetric composition of primary reference fuel blends. The sample fuel knock intensity is compared to that of one or more primary reference fuel blends to establish the Motor octane number.

⚙️ Test Procedure and Knock Rating

The procedure involves running the sample fuel in the standardized CFR engine under the specific Motor method conditions. The knock intensity of the sample is directly compared to the knock intensity of primary reference fuel blends. The octane number of the primary reference fuel blend that matches the knock intensity of the sample fuel establishes the Motor octane number. For purposes of determining conformance with all specified limits in this standard, an observed value or a calculated value shall be rounded “to the nearest unit” in the last right-hand digit in accordance with the rounding method of Practice E29.

📊 Key Specifications and Octane Number Scale

The Motor octane number scale covers the range from 0 to 120 octane number. This test method has a validated working range from 40 to 120 octane number. Typical commercial fuels produced for automotive spark-ignition engines rate in the 80 to 90 Motor octane number