SAE AIR8466

The purpose of this AIR is to establish a baseline for hydrogen fueling protocol and process limits for both gaseous and liquid hydrogen fueling of aircraft (eCTOL, eRotor, eVTOL, LTA) at the airport from small aircraft to wide-body. A further goal is to harmonize and establish common aircraft fueling safety definitions wherever possible with other SAE and EUROCAE standards and NFPA codes alike. Hydrogen fueling process limits (including the fuel temperature, the maximum flow rate, time required, etc.) are affected by factors such as ambient temperature, fuel delivery temperature, and initial pressure in the hydrogen storage system. The further goal is to establish basic fueling protocols within these limits as a starting point while evaluating minimum criteria, including evaluation of fueling with or without communications. AIR8466 establishes the protocol and process limits for hydrogen fueling of aircraft and plans to establish fueling protocols starting with small aircraft. Optionally, communications may be used, and a general description will be included. Gaseous hydrogen fueling and liquid hydrogen fueling at cryogenic temperatures are two very different types of fuel stored in different types of vessels with safety mitigations. The goal is to start with an all-encompassing AIR for hydrogen fueling, both gaseous and liquid, and, after publishing, establish a family of documents covering categories of fueling as determined by the SAE AE-5CH team. To minimize storage volumes, compressed hydrogen gas stored under pressure up to 700 bar (70 MPa) achieves 39.5 kg per m3, or as a cryogenic liquid 20 K achieves 71 kg per m3. Other methodologies of liquified hydrogen, such as subcooled liquid or cryo-compressed, offer the potential for higher storage densities (the latter is not covered in this document). Figure 1 compares the volumetric and gravimetric densities of hydrocarbon fuels as well as the most common hydrogen storage methods in liquid and gaseous hydrogen and three types of hydrogen storage with different hydrogen density versus phases, pressure, and temperature (gaseous hydrogen, liquid hydrogen, and cryo-compressed). Presently, there are established codes and standards for ground vehicles at SAE, ISO, NFPA, etc., that could also be applicable to some applications for hydrogen at the airport. While there are some existing fuel cell and hydrogen standards for aerospace (such as SAE/EUROCAE information reports), there is a need to create new fueling station standardization efforts, which are outlined herein. The volume of hydrogen required will depend on the pressure and phase (ambient gaseous or cryogenic liquid) and the size of aircraft. Therefore, a series of ground standards will be required to cover the phase, thermal, and pressure variables. Hydrogen, produced from low-carbon sources, is one of the most promising decarbonization technologies for aviation. Adoption of hydrogen is supported by the International Civil Aviation Organization (A41-WP/514 EX/246), the International Air Transport Association (IATA Factsheet 7, August 2019), and numerous aerospace manufacturers. Hydrogen is considered to be an important technological pathway to achieve low-carbon commercial aircraft. Today, aviation accounts for around 2.5% of global CO2 emissions. Although aviation represents a relatively small percentage of global emissions today, that could rise to 22% by 20501 as more people fly and other sectors decarbonize quicker. This SAE Aerospace Information Report (AIR) provides guidance for development of fueling stations in preparation for hydrogen becoming a standard fuel type. Presently, there are established codes and standards for ground vehicles at SAE, ISO, NFPA, etc., that could also be applicable to some applications for hydrogen at the airport. While there are some existing fuel cell and hydrogen standards for aerospace (such as SAE/EUROCAE information reports), there is a need to create new fueling station standardization efforts, which are outlined herein. For one, the ambient conditions are significantly different related to expected temperatures on the airfield apron and tanks that could be exposed to direct sunlight. Large aircraft such as a regional, narrow body, or a wide-body require up to 100x to 1000x more hydrogen storage (e.g., 1000 to over 10000 kg) than light to heavy-duty ground vehicle fueling (5 to over 120 kg). With this larger amount for aircraft fueling, there will be an exponentially larger need for hydrogen supply and fueling on site. Gaseous hydrogen fueling and liquid hydrogen fueling at cryogenic temperatures are two different types of fuel stored in different types of vessels with safety mitigations. Similar to CNG and LNG at the same location, the objective of AIR8466 is to start with an overarching AIR for both gaseous and liquid hydrogen fueling stations and, after publishing, establish a family of documents covering these categories of hydrogen as a fuel as determined by the SAE AE-5CH team. AIR8466 is to provide hydrogen fueling station guidelines and process for both gaseous and liquid hydrogen fueling (eCTOL, eRotor, eVTOL, LTA, etc.) at the airport from small aircraft to wide-body. The hydrogen fueling process described herein (including fuel temperature, the maximum flow rate, time required, etc.) are affected by factors such as ambient temperature, fuel delivery temperature, and initial pressure in the hydrogen storage system. At the airport, similar to conventional hydrocarbon fuels, there will be both mobile fueling trailers and stationary hydrogen fueling stations that are planned to be within the scope of AIR8466 and EUROCAE DP007. A further goal is to harmonize and establish common aircraft fueling safety definitions wherever possible with other SAE and EUROCAE standards and NFPA codes alike. Gaseous hydrogen fueling and liquid hydrogen fueling at cryogenic temperatures are two very different types of fuel stored in different types of vessels with safety mitigations. The goal is to start with an all-encompassing AIR for hydrogen fueling and, after publishing, establish a family of documents covering categories of fueling as determined by the SAE AE-5CH task group.