2004-01-2574 Jet Fuel Vapor Ignition within a Duct Thermal Insulation Guilherme Araújo Lima da Silva Ricardo José Barbosa Embraer S.A. – Empresa Brasileira de Aeronáutica Euryale Jorge Godoy de Jesus Zerbini Integral Engenharia, Estudos e Projetos Escola Politécnica da Universidade de São Paulo Copyright © 2004 SAE International ABSTRACT A test setup was built to identify the ignition of jet fuel vapor-air mixtures within an insulation media and induced by a hot duct surface. The external diameter of the duct was 76.2 mm (3 inches) and covered with a 12.7 mm (0.5 inch) layer of ceramic fiber insulation, which had its pores completely filled with fuel vapor and air mixtures. The ignition was detected by thermocouples installed in insulation media and confirmed by chromatography and mass spectrometry. In order to design the experimental apparatus and allow behavior investigation in other operational conditions, a mathematical model was developed. INTRODUCTION A combustible mixture can be ignited spontaneously and almost simultaneously through its volume if it is heated to a certain temperature. According to ASTM E 659-78 definition, autoignition is the lowest temperature to which a combustible mixture must be raised so that the rate of heat generated by the exothermic oxidation reactions will over-balance the rate of heat transfer to surroundings and cause ignition 1 . On the other hand, external agents like electrical discharge; heat transfer from hot surfaces to the combustible mixture and pilot flames can induce a forced or non-spontaneous ignition. In aircraft environmental control system installations, the hot and compressed engine bleed air is delivered to the pneumatic users, such as environmental control unit packs and airfoil ice protection systems, by a duct network that extends along aircraft. Some system installations may have bleed ducting passing through zones in the neighborhood of a fuel tank that can have fuel vapor in some concentration. A jet fuel vapor ignition process will be initiated by a hot surface of a bleed system ducting, or component, if the heat transfer from the hot surface cause enough increase of fuel vapor-air mixture temperature. Several factors can influence a hot-surface ignition such as geometry, heat transfer by radiation, convection and conduction, properties of the fluid near the wall, chemical kinetics. The threshold ignition temperatures can be compared only when considering similar installations, operational and environmental conditions 1, 2 . In the 60´s, the Royal Aircraft Establishment (RAE) performed an original and extensive research program to investigate the ignition of aircraft fuels. Cansdale and Macdonald 3 continued and extended the research work covering the fuel liquid and vapor ignition developed at RAE. In previous researches, Macdonald and White 4 tested kerosene fuel vapor ignition inside uniformly heated vessels and Macdonald 5 investigated ignition promoted by hot ducts. In the last reference, the ducts were placed horizontally into a spherical enclosure with controlled wall temperatures and filled with fuel and air mixtures. Botteri et al edited a comprehensive review of aircraft fire safety issues, including fuel vapor ignition 6 , as result of NATO´s AGARD Propulsion and Energetics Panel Working Group 11 tasks. OBJECTIVE The main objective was to investigate the jet fuel vapor- air mixture ignition phenomena induced by a hot surface within a duct thermal insulation. The ignition occurrence characterization was performed with the measurement of temperature profile distortion promoted by the reaction processes in the duct insulation media. Therefore, the intention was to start exploring the subject in order to provide insights for future works, indicate trends, and discuss practices but not to define any criteria for design.