Carbonaceous Deposit Formation from Advanced Fuels Under Supercritical Conditions

Abstract : Methods for measuring speed of sound and heat transfer coefficients in supercritical reacting fluids were developed and tested. These measurements were used to show that relationships for predicting supercritical fuel properties near the critical point are not valid and that in-situ measurement is important. Measurement of reaction products from the thermal stressing of MCH over a wide range of pressures and temperatures with and without oxygen contamination shows that (1) dissolved oxygen is important in the formation of products in the bulk phase (2) insoluble residues from hydrocarbons at temperatures less than 850K are likely caused by the presence of the oxygen and/or an active surface (3) the only aromatic species observed at low temperatures was toluene and naphthalene production can proceed through reactions of the benzyl radical (4) the coating of the wall of the supercritical fuel reactor with catalytically inactive titanium nitride prevented significant surface activity. Deoxygenation and passivation of metallic surfaces can be used in actual aircraft systems to reduce deposit formation. Prevention of hot-spots is also critical as rupture of the MCH ring can quickly produce benzene and higher mass aromatics.