Thermal Stability Test, JFTOT

Products which were evaluated in JFTOT and thermal stability tests were distilled and stored in glass. Petroleum- or coal-derived fuels which have been distilled or stored in metal equipment sometimes fail these tests due to contamination by metals. 

The most common technique for estimating thermal stability is called the Jet Fuel Thermal Oxidation Test (JFTOT). It shows the tendency of the fuel to form deposits on a metallic surface brought to high temperature. The sample passes under a pressure of 34.5 bar through a heated aluminum tube (260°C for Jet Al). After two and one-half hours, the pressure drop across a 17-micron filter placed at the outlet of the heater is measured (ASTM D 3241). 

For jet fuels, a visual rating of No. 1 or No. 2 is required at 260°C in the jet fuel thermal oxidation stability test (JFTOT-ASTM D 3241). Also, a pressure drop of less than 25 mm Hg is required in this test, As shown in Table XI, the 250°F+ product from hydrotreated Illinois H-Coal syncrude passes both parts of the JFTOT test, even when the jet fuel is not refined enough to pass three other specifications aromatic content, smoke point, and gum content. When jet fuels are prepared from coal-derived syncrudes, the smoke point appears to be the limiting specification. The gum content and end point specifications are met when the jet fuels are distilled at 600°F. 

This test method for measuring the high temperature stability of gas turbine fuels uses the Jet Fuel Thermal Oxidation Tester (JFTOT) that subjects the test fuel to conditions that can be related to those occurring in gas turbine engine fuel systems. The fuel is pumped at a fixed volumetric flow rate through a beater after which it enters a precision stainless steel filter where fuel d radation products may become trapped. 

A2.1.1 The instrument described in this annex is the Jet Fuel Thermal Oxidation Tester, or JFTOT, that is used to test the thermal oxidation stability of turbine fuel. There are five models of JFTOT which will be described. All provide a means to pump the sample once through the test system across the metal test coupon and through a test filter. There are means to control and measure coupon temperature, system pressure, and pressure drop across the filter, and methods of control and measurement vary with each model of JFTOT. Mechanism for pumping is positive displacement using a gear pump or piston pump. 

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