Jet A Explosions - Field Test Plan: 1/4-Scale Experiments

Abstract

The TWA 800 crash investigation is focusing on the explosion of Jet A-air mixtures in the ullage of the center-wing tank (CWT) as the key event in the accident. Laboratory tests are being carried out on Jet A-air mixtures in the 1.2-m^3 HYJET facility at Caltech (Shepherd et al. 1997), and preparations are being made for larger-scale field testing. This document is a proposal for the first phase of the field testing. At the present time, one of the main goals of the investigation into TWA 800 is to determine the location and source of ignition in the CWT. The experimental test program has been designed to develop basic information that will aid the investigators in reaching this goal. Laboratory experiments have so far examined issues relating to fuel chemical properties, flammability limits and pressure histories during controlled laboratory explosions of Jet A vapor and air. Laboratory testing to determine ignition energies and flame speeds is in progress. All the laboratory testing has been carried out in simple test facilities consisting of a single, unvented chamber that is relatively small compared to the CWT, which has an approximate volume (not including the dry bay) of 50 m^3. Field testing is needed to address the effect of size, compartmentalization, and other factors such as vents in the center wing tank. The CWT is divided into six wet bays and one dry bay. There are passageways between the bays and vents to the outside of the airplane in four of the bays. The sequence analysis of the CWT failure indicates that the front spar (FS), the spanwise beam 3 (SWB3) and the manufacturing panel in spanwise beam 2 (SWB2) all failed and were ejected from the airplane early in the event. The construction of the tank and accident sequence analysis indicate that it is important to understand the phenomena associated with flame propagation in a multicompartment, vented tank and to also consider the coupling between the flame propagation and structural failure. A program of field tests has been developed to examine these issues. The experimental testing will proceed in conjunction with numerical simulations while maintaining constant feedback between the two programs in order to optimize the experimental conditions and minimize the number of tests to be conducted. The field testing has been divided into three phases. 1. 1/4-scale tests in a CWT-like geometry. 2. Full-scale tests of actual CWT or mockups. 3. Full-scale tests using actual aircraft. The general objective of the Phase 1 tests is to obtain information about combustion in a multicompartment, vented enclosure geometrically similar to the CWT. Phase 2 full-scale tests will be carried out to examine the effects of scale and more realistic structural failure on combustion. The airplane tests in phase 3 are intended to simulate as realistically as possible an explosion of a Jet A-air mixture within the ullage of the CWT in a 747-100 with a pressurized fuselage. This document focuses exclusively on the 1/4-scale tests. Subsequent documents will describe the test program in Phases 2 and 3. The program is proceeding sequentially, with information developed in the earlier phases being used to define the test program in subsequent phases.

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