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Author:
John I. Kurtanidze
Abstract:

With a rising interest in hydrogen-fueled aircraft comes many design and safety concerns. There are many problems to be solved and safety standards and precautions established if aircrafts are going to be equipped with hydrogen. To that end, the objective of this project is to understand the fundamental characteristics of hydrogen flames. More specifically, small hydrogen flames resulting from leaks in diameter of less than 2mm will be studied and their flame characteristics recorded. To simulate leak conditions, a small-scale, horizontal custom hydrogen burner was made with five interchangeable nozzles, each representing a different leak. The nozzles varied in shape between circular and slot orifices, varied in size under 2mm, and the standard leakage flow rate varied was between 1SLPM (Standard Liters Per Minute) and 5SLPM. Nozzle exit-sensor spacing was an additional parameter which was varied between 1in (25mm), 2in (50mm), and 4in (100mm). A water-cooled gardon gauge was utilized to record impinging flame heat flux and K-type thermocouples were used to record cross-sectional flame temperature. Additionally, a flame tracking software was used to estimate the horizontal flame length from the nozzle exit up to the furthest horizontal reach of the flame. Results show that the most influential parameters for leakage flames are the leak size and the flow rate of hydrogen, while the leak shape (whether a crack or a pore) has little influence on the flame characteristics. Generally, increasing standard flow rate (SFR) of hydrogen while keeping leak size constant resulted in an increase in flame heat flux and flame temperature, while increasing the leak size for a given flow resulted in a decrease in flame heat flux and flame temperature. Additionally, reducing the nozzle exit-sensor spacing generally resulted in an increase in flame heat flux while a decrease in flame temperature.

Report:
Pages:
67
Size:
2.4 MB
Author:
Dan Keslar, Steven Rehn
Abstract:

Additive manufacturing (AM), commonly referred to as three-dimensional (3D) printing, is a modern manufacturing technology that can be applied within many different areas of the aerospace industry due to its ability to produce light and durable parts with complex geometries. Aircraft manufacturers and airlines have expressed interest in the use of AM produced parts in aircraft cabins. However, AM presents new safety challenges that must be examined, including the flammability of the 3D printed part used in the aircraft cabin. Due to the different parameters used during the production process compared to traditional manufacturing methods, it was necessary to determine the effect that variations in print parameters have on the flammability of a 3D printed part. In order to accomplish this, the following print parameters were evaluated; material type, sample thickness (number of inner layers), infill percentage, infill pattern, raster width, raster angle, and print orientation. The scope of this report only includes samples produced from the Fused Filament Fabrication (FFF) AM method, a type of extrusion-based AM process.

Testing was conducted using the Vertical Bunsen Burner (VBB) test methodology outlined in Chapter 1 of the Aircraft Materials Fire Test Handbook (FAA, 2023). In the first phase of testing, only a few variables in the samples were altered and the remaining variables were kept constant so that accurate comparisons between fire data could be made. Subsequently, a Design of Experiments (DOE) analysis was conducted to determine the interaction among multiple print variable combinations.

Results indicate that all evaluated variables had an impact on the flammability of a 3D printed part. The three variables that were observed to have the most significant effect on data were material type, sample thickness, and infill percentage. Other factors such as raster width, raster angle, print orientation, and infill pattern were observed to produce only interaction effects in conjunction with the other print variables listed.

Report:
Pages:
85
Size:
4.5 MB
Author:
Steven Rehn
Abstract:

This report summarizes a short test conducted by the Federal Aviation Administration (FAA) to determine the effectiveness of a trained canine to detect lithium batteries hidden inside of boxes. Fifteen identical cardboard boxes that either contained different types of lithium batteries, or were empty, were spread out around a building for the canine to inspect. On the initial quick scan, the dog was correct on 11 out of the 15 boxes, with more accurate results on lithium-ion batteries than lithium metal. On a second more thorough inspection, the canine was 100% accurate on all the boxes. The effectiveness of this dog in detecting lithium batteries shows that this could potentially be a reasonably accurate and practical method for future detection of non-compliant lithium battery shipments on passenger and cargo aircraft.

Report:
Pages:
14
Size:
376 KB
Author:
Michael Burns, Francis Hahn, Brian Conover
Abstract:

A study was conducted to determine the feasibility of adding the capability of measuring material smoke emissions to the Federal Aviation Administration (FAA) rate of heat release test method, which is performed in a specially developed test device that iscommonly referred to as the Heat Release Rate 2 Apparatus (HR2). A laser/sensor means of measuring cumulative smoke release, analogous to specific optical density Ds as measured in the FAA smoke emission test, was devised by using a continuous wave 670-nanometer wavelength laser and a thermopile power sensor. Tests performed in the FAA smoke emission chamber compared the output obtained from the legacy smoke chamber photometric system and the newly devised laser/sensor assembly measurement system. Neutral density light filters with varying percentage of light transmission were placed in the light paths, and specific optical density was determined for each value of percentage light transmission, which found both measurement systems to be in good agreement over the entire range of filters tested. Material smoke tests using both measurement systems wereperformed to compare the material smoke emission. In general, peak smoke-density measurements obtained with the laser/sensor system were lower than those obtained with the photometric system, though test-to-test repeatability was similar for both measurement methods. Material smoke emission tests were performed in the HR2 apparatus with the laser/sensor assembly attached horizontally such that the laser light path spanned the width of the vertical exhaust gas stream. Cumulative smoke release data obtained during the HR2 tests were affected by the conditions at the exhaust stack of the HR2. The elevated temperature at the exhaust opening was found to increase the thermopile sensor output reading; though this was compensated for by setting the sensor baseline after the HR2 has reached a stable operating temperature. In materials that produce large flames from the HR2 exhaust, thermopile sensor readings were observed to be significantly impacted, as the luminosity of the flames resulted in increased thermopile sensor output. Overall, this study demonstrated the feasibility of measuring smoke density during a heat release test in the HR2 apparatus, with mitigations employed to compensate for the elevated temperatures and possibility of visible flames at the HR2 exhaust opening.

Report:
Pages:
24
Size:
516 KB
Author:
Dan Keslar, Tim Marker
Abstract:

The transport of oxidizers and compressed oxygen within aircraft is heavily regulated, largely as a result of the fatal 1996 ValuJet accident. Past Federal Aviation Administration (FAA) studies have found that released oxidizers can exacerbate burning within a halonsuppressed cargo compartment fire, potentially overwhelming the fire suppression system within an aircraft.

Recently, a request was submitted to ship medical devices containing small quantities of gaseous nitrous oxide (N2O). As part of the certification process, the manufacturer of this device completed the PHMSA-required thermal resistance and flame penetration tests; however, the packaging was unable to pass the thermal resistance portion of the required tests and small quantities of N2O were able to escape. As a result of these initial tests, the manufacturer requested an exemption from this requirement.

PHMSA requested assistance from the FAA Fire Safety Branch to determine if quantities of released N2O would significantly impact a cargo compartment fire. Although N2O is not flammable, it is an oxidizing agent that could exacerbate an otherwise controlled cargo compartment fire, and ultimately overwhelm the integrity of the suppression and containment capabilities of the system. Tests were conducted within an aircraft lower deck (LD-3) sized steel test chamber using a fire load of eighteen cardboard boxes filled with shredded paper. During each test, the shredded paper was ignited and the ensuing fire was allowed to develop. Two baseline tests were first conducted, in which the fire within the test chamber was allowed to burn unabated, without introducing N2O. Three subsequent tests were conducted in which various quantities of N2O gas (5.8 oz, 11.6 oz, and 17.4 oz) were released into the testchamber once the fire was fully developed.

Results indicated that released quantities of N2O less than or equal to 11.6 oz did not produce a significant reaction within the fire in the test chamber. However, it was observed that as the quantity of released N2O increased, more significant combustion reactions occurred. Therefore, until further data is acquired, it is recommended that the amount of N2O be limited to no more than 11.6 oz per Unit Load Device (ULD) for air transport.

Report:
Pages:
29
Size:
1.3 MB
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