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Tue, May 29th 2012, 13:35 by Indresh Mathur

Primary Reference Fuels (PRF) for Octane Number Determinations

Dr. Indresh Mathur

PRFs are required to determine the combustion quality of gasoline and diesel fuels. The key combustion parameter for gasoline is measured by determination of the octane number of the fuel in a Cooperative Fuel Research (CFR) engine.

Octane Number Fuels

Pure isooctane (2, 2, 4-trimethylpentane) has been assigned an octane number of 100 because of its excellent antiknock properties and n-heptane is assigned an octane number of zero because of its propensity to pre-ignite easily. Therefore, an 80:20 mixture of isooctane and n-heptane has an octane number of 80. In certain circumstances pure toluene is also used as a PRF because it has an octane number >100. ASTM test method D2700 and D2699 describe the methods; Motor Octane Number (MON) and Research Octane Number (RON), respectively. In these test methods, a candidate fuel is combusted in Waukesha CFR engines and its knock characteristics are compared with a fuel composed of PRF grade isooctane and n-heptane. The isooctane specified by ASTM for use in D2700 and D2699 must have a minimum content of 99.75% of 2,2,4-trimethylpentane  and the n-heptane must be minimum 99.75% pure. ASTM requires that PRF toluene specified for use in D2700 and D2699 must have a minimum purity of 99.5%.

In the past, Haltermann supplied Primary Reference Fuels to the North American market but exited the market after being acquired by Monument Chemicals. Effective immediately, Haltermann Solutions is now pleased to again offer PRF fuels to its customers. Haltermann is introducing PRF fuels in stages starting with isooctane and toluene. During our introduction, we wanted to ensure that ASTM members were confident that Haltermann PRF fuels met all the ASTM requirements. To assure compliance to ASTM specification requirements, Haltermann contracted numerous third part labs to analyze our octane PRF fuels for purity. Samples were sent out to the certified contract analytical laboratories listed in Table 1. To-date, test results have confirmed that Haltermann’s PRF grade isooctane and toluene comply with the exacting purity and performance requirements of ASTM and can be used with confidence. The numerical average of the test results and standard deviations are given in Table 2 and Table 3 for isooctane and toluene. These ASTM compliant PRF fuels are now available from Haltermann in 55 gallon drums and 5 gallon pails. The PRF grade toluene is stabilized to prevent excessive peroxide formation.

PRF grade n-heptane and PRF grade 80 octane fuels will be the next additions to our PRF family of products. We expect these high purity products to be available during the 3rd quarter of 2012 after the certification data has been filed with the ASTM.

For more information on Haltermann PRF fuels, please contact Josh Petersen, Haltermann Manager of National Accounts at 615-812-7063  (





































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