Energy Supply Device Aviation Rulemaking Committee

DOT/FAA/TC-19/16 Energy Supply Device Aviation Federal Aviation Administration William J. Hughes Technical Center Rulemaking Committee Aviation Research Division Atlantic City International Airport New Jersey 08405 April 2019 Final Report This document is available to the U.S. public through the National Technical Information Services (NTIS), Springfield, Virginia 22161. This document is also available from the Federal Aviation Administration William J. Hughes Technical Center at actlibrary.tc.faa.gov. U.S. Department of Transportation Federal Aviation Administration NOTICE This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the contents or use thereof. The U.S. Government does not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the objective of this report. The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the funding agency. This document does not constitute FAA policy. Consult the FAA sponsoring organization listed on the Technical Documentation page as to its use. This report is available at the Federal Aviation Administration William J. Hughes Technical Center’s Full-Text Technical Reports page: actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). Energy Supply Device Aviation Rulemaking Committee Final Report to: Federal Aviation Administration Executive Director, Aircraft Certification Service and Executive Director, Office of Rulemaking December 8, 2017 ii Executive Summary This report contains the findings and recommendations of the Energy Supply Device Aviation Rulemaking Committee (ESD ARC). The ESD ARC (the Committee) was charted by the Federal Aviation Administration (FAA) on April 15, 2015 to provide recommendations that may be used to develop appropriate airworthiness standards and guidance material for energy supply device installations on transport airplanes and other types of aircraft, with a focus on hydrogen fuel cells. Hydrogen fuel cells1 are electrochemical devices that convert chemical energy of a fuel (typically hydrogen) and an oxidant (oxygen) directly into electrical energy. This electrical energy can then be conditioned and used for multiple purposes. Below is a typical simplified fuel cell (FC) diagram. Each fuel cell produces approximately 0.6 volts of direct current. Placing each individual fuel cell with other individual fuel cells makes a fuel cell stack and this increases the amount of voltage produced. The more fuel cells in a stack, the higher the voltage output. The surface area of each individual cell controls the amount of current (i.e., amperage) available. Larger surface area equal higher current levels. A mock-up of a 46-cell fuel cell stack is shown in Figure 2. The reactants, product water and cooling water are fed though the manifold fittings on the end. Current is tapped off the two tabs just under the end plates. Figure 1. Simplified Fuel Cell Diagram (Typical) 1 “Hydrogen fuel cells” in this report are herein afterwards referred to as “fuel cells.” iii Figure 2. Mock-Up of a Fuel Cell Stack Composed of 46 Individual Fuel Cells Fuel cells have become increasingly important as alternative sources of power, offering the potential for a reduction in emissions in particulate matter, nitrogen oxides, and carbon dioxide. In addition, they offer quieter operation than a combustion engine, more efficient use of the fuel energy compared to combustion engines, and offer more flexible energy storage density compared to batteries. Apart from emissions reduction and thermal efficiency, fuel cell technology can constitute distributed power systems; enabling locating the power near the point of use and also reducing the power draw from the engines. The main by-products of a fuel cell are water and heat. Both of these by-products can be discarded; however, they also have the potential to provide potable water and heat for use by other airplane systems. Another by-product is oxygen depleted air that could be used for fuel tank inerting. Thus, potentially negating the need for a nitrogen inerting system. The main body of the report summarizes the findings and recommendations of the committee. Details of those findings and recommendations are contained in the report’s appendices. The appendices are presented in a logical order that begins with a comparison of fuel cells with other energy supply devices technologies. It discusses fuel cell benefits and compares FCs to batteries and combustion systems. The appendices then progress by presenting various FC technology options (i.e., different types of FCs), and then focuses on the technology options that are best suited for use in an aviation environment. Next is a discussion about all of the components that are required to enable the FC to produce electricity, deliver it to a load (e.g., galley power), and dispose of the by-products. The FC itself, along with these components, iv comprise a fuel cell system (FCS). A detailed discussion of the FCS is presented, as is a discussion of various sources and storage options for hydrogen and oxygen. For example, pure hydrogen can be stored in various forms, including a pressurized gaseous state. However, it can also be derived from jet fuel through a process known as reforming. Various reforming methods are discussed as well. Then airborne applications for fuel cells are discussed. Applications discussed are galley power, stand-alone power, medivac system power, auxiliary power, emergency power systems, and unmanned aerial system propulsion. These applications are the ones most likely to take advantage of the benefits that a fuel cell can offer using today’s fuel cell technology. The installation and use of a FCS for one of these applications requires some level of integration with other airplane systems. While some FC applications will require minimal modifications to install (e.g., self-contained medevac), others will require extensive modifications (e.g., emergency power system, auxiliary power). A discussion of fuel cell integration with aircraft systems is therefore provided in the application appendix as well. Following the applications discussion, fuel cell systems hazards are discussed. Fuel cell use as a source of power is becoming more common for ground based solutions. As examples; fuel cell powered forklifts are used in warehouses, fuel cell powered city busses are in use many countries, and Toyota sells a fuel cell powered passenger sedan. However, fuel cell use in airborne applications is in its infancy (the exception is the use of fuel cells in NASA’s Gemini and Space Shuttle programs). While hazards associated with hydrogen, whether used in ground based or in airborne applications, might not be new in themselves, they are not currently well addressed in the airworthiness requirements. Use in an airborne environment demands that potential hazards associated with fuel cell systems be fully understood. Therefore, the hazards appendix discusses a multitude of potential hazards and their mitigation means. This includes hydrogen fire and explosion hazards, mechanical and material hazards, physiological hazards, cryogenic hazards, non-hydrogen fuel and oxygen hazards, and electrical hazards. Following the discussion on hazards, the next appendix presents recommendations for regulatory standards and advisory material. After developing the information on various types of fuel cell technologies, their possible aircraft applications, their potential hazards, and the review of existing part 25 and operational regulatory requirements, it was decided to: 1) recommend the development of one new part 25 regulation, known as the fuel cell system safety baseline regulation; 2) recommend revisions to existing part 25 regulatory standards to accommodate fuel cell systems; 3) identify existing part 25 regulations that are applicable to fuel cell systems, but do not require any revision; and 4) identify operational regulations in parts 43, 91, 121, 125, and 129 that are applicable to fuel cell systems. With the exception of the operational requirements, the recommendations apply to both 14 CFR part 25 and EASA’s CS 25. Any differences between the two sets of standards is noted in the recommendation’s appendix. Although the committee does not provide recommendations for regulatory requirements for CFR / CS parts 23, 27, and 29 airworthiness standards, the same concerns would apply with the typical differences between the different product types. The committee therefore recommends v when a rulemaking group is created, this group will amend the different airworthiness standards based on the conclusions presented in this report. Also included in the recommendation’s appendix is a recommendation for more general regulation that would be applicable to most any type of energy storage device, independent of technology. The regulation would replace the existing 14 CFR § 25.1353(b) / EASA CS 25.1353(c). This regulation currently contains requirements for storage batteries, but does not contain adequate requirements for lithium based batteries or other types of ESDs, such as fuel cells or supercapacitors. Therefore, in the case of lithium batteries, the FAA, EASA, and other authorities must issue special conditions that are in lieu of the requirements contained in § 25.1353(b) / 25.1353(c). The recommended regulation is more performance

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