STUDIES OF JET FUEL THERMAL-STABILITY IN A FLOWING SYSTEM

A flowing, single-pass heat exchanger test rig, with a fuel capacity o f 189 liters, has been developed to evaluate jet fuel thermal stabilit y. This ''Phoenix Rig'' is capable of supplying jet fuel to a 2.15 mm i.d. tube at a pressure up to 3.45 MPa, fuel temperature up to 900 K, and a fuel-tube Reynolds number in the range 300-11,000. Using this te st rig, fuel thermal stability (carbon deposition rate), dissolved oxy gen consumption, and methane production were measured for three baseli ne jet fuels and three fuels blended with additives. Such measurement were performed under oxygen-saturation or oxygen-starved conditions. T ests with all of the blended fuel samples showed a noticeable improvem ent in fuel thermal stability. Both block temperature and test duratio n increased the total carbon deposits in a nonlinear fashion. Interest ingly, those fuels that need a higher threshold temperature to force t he consumption of oxygen exhibited greater carbon deposits than those that consume oxygen at a lower temperature. These observations suggest ed a complicated relationship between the formation of carbon deposits and the temperature-driven consumption of oxygen. A simple analysis, based on a bimolecular reaction rate, correctly accounted for the shap e of the oxygen consumption curve for various fuels. This analysis yie lded estimates of global bulk parameters of oxygen consumption. The te st rig yielded quantitative results, which will be very useful in eval uating fuels additives, understanding the chemistry of deposit formati on, and eventually developing a global chemistry model.