ASTM Primary reference fuels used for octane knock test engine, isooctane, n-heptane, volumetrically proportioned mixtures of isooctane with n-heptane, or blends of tetraethyllead in isooctane that define the octane number scale.
Primary reference fuel blends below 100 octane number, the volume % of isooctane in a blend with n-heptane that defines the octane number of the blend. Isooctane being assigned as 100 and n-heptane as 0 octane number.
For example, a blend by volume of 80% isooctane and 20% n-heptane would have an octane number of 80.0.
O.N. = O.N. (isooctane) × percent isooctane + O.N. (n-heptane) × percent n-heptane
Primary reference fuel blends above 100 octane number, the milliliters per U.S. gallon of tetraethyllead in isooctane that define octane numbers above 100 in accordance with the ASTM specifications.
PRF, isooctane and n-heptane classified as ASTM reference fuels grade and meeting the specifications that follow:
Isooctane shall be no less than 99.75 % by volume pure, contain no more than 0.10 % by volume n-heptane, and contain no more than 0.5 mg ⁄L (0.002 g ⁄U.S. gal).
n-heptane shall be no less than 99.75 % by volume pure, contain no more than 0.10 % by volume isooctane and contain no more than 0.5 mg ⁄L (0.002 g ⁄U.S. gal).
80 octane PRF blend, prepared using ASTM reference fuel grade isooctane and n-heptane shall contain 80 % +/- 0.1 % by volume isooctane.
Dilute Tetraethyllead (Commonly referred to as TEL Dilute Volume Basis) is a prepared solution of aviation mix tetraethyllead antiknock compound in a hydrocarbon diluent of 70 % (V/V) xylene, 30 % (V/V) n-heptane. (Warning—Dilute tetraethyllead is poisonous and flammable. It may be harmful or fatal if inhaled, swallowed, or absorbed through the skin. May cause flash fire.)
TSF volumetrically proportioned blends of two or more of the following: ASTM Reference fuel grade toluene, n-heptane, and isooctane that have prescribed rating tolerances for O.N. ARV (accepted reference value) determined by round-robin testing under reproducibility conditions.
Toluene, ASTM Reference Fuel Grade shall be no less than 99.5 % by volume pure. Peroxide number shall not exceed 5 mg per kg (ppm). Water content shall not exceed 200 mg per kg. (Warning—Toluene is flammable and its vapors are harmful. Vapors may cause flash fire.)
The specifications for ASTM reference fuels are given in ASTM D2699 and ASTM D 2700.
Automatic Reference Fuel Blending System Unit is used for the automated preparation of cetane and octane ASTM reference fuels and standardization fuels for Octane/Cetane Knock Test Engine.