UAVs have evolved into increasingly capable platforms deployed for a wide variety of applications. The capability to fight effectively in urban areas against widely dispersed forces, while minimizing collateral damage and achieving information superiority has enabled the UAVs to play a greater role in critical missions. The UAVs have become one of the essential constituents of all militaries to perform intelligence, surveillance, and reconnaissance missions. Their roles have expanded to areas including electronic attack, suppression or destruction of enemy air defense, network node or communications relay, combat search and rescue and many others. The increasing demand and reliance on UAV in warfighting and peacekeeping operations has doubled the pace of UAV-related R&D in recent years.
The propulsion system provide UAV’s the necessary power to propel the aircraft for forward flight or hover. The endurance of a UAV is influenced by the propulsion technology used and is dependent on the aerodynamic design and amount of fuel carried. To fulfil the energy requirements of a large variety of UAVs, several variants of piston-engines and electric motors have been designed by the market players. The potential benefits of a propulsion system are measured by their impact on the costs of the whole UAV. Lightweight, more fuel-efficient engines permit usage of expensive payload for a given mission without significantly affecting the size and cost of the UAV.
Fuel Cell Power Systems (FCPS) and the many advantages that this technology, first proposed in 1838 by William Grove, bring to the table.The main advantage of fuel cells is the fact that they produce energy as required. That’s different from batteries, which simply store energy and release it on demand. Every fuel cell requires two components. One is the main body of the power-generating unit and the other is the fuel tank, being hydrogen or any other gas or liquid. However, since fuel cells use oxygen from the air for half the reaction, the energy density is much improved over batteries.
Hydrogen fuel cells provide quiet, reliable, low-maintenance operation, as well as being a clean energy solution with zero emissions. Batteries are heavy with a low relative energy density, providing only enough power for short-endurance drone missions with a typical recharge time that is much longer than the provided flight duration. The use of hydrogen fuel cells can boost UAV mission length and distance by up to three times, with quick and easy refuelling that can be accomplished in less than five minutes. Safe and readily available fuel source
It provides extended mission range and endurance, enabling BVLOS UAV missions for greater efficiency. Another advnatge is Quiet and reliable low-maintenance operation with zero emissions. One key element of the advantage of fuel cells over internal combustion engines is the lack of moving parts and therefore complete absence of lubricants and a dramatic decrease in maintenance costs and unit replacement. More efficient operation at higher altitudes than internal combustion engines. The technology is Scalable can be connected in parallel to provide required power.
Today, restrictions imposed on small commercially available drones of flying times of 25 minutes or less (depending on number of rotors and/or load) are being challenged by a number of manufacturers both here in the USA, Europe and China using fuel cells.
However fuel cells are also being challenged by batteries improvements in lithium batteries, which are possible with new materials, will make these batteries more efficient and comparable to fuel cells. Another problem with some fuel cells is that they generate a lot of heat, approximately equivalent to the electricity produced up to 1,000o C in some cases. Removal of the heat is an integration challenge in an industry where plastic is a large component of every small UAV. The use of delicate thermal or infrared sensors might be affected by this close source of temperature interference.
Hydrogen Fuel Cell Drone Sets World Record, Flies Uninterrupted For 331 Minutes
In March 2020, FuelCellWorks reported that according to various Chinese media sources, a research drone powered by hydrogen fuel cells set a world record by flying for 331 minutes uninterrupted. The news was first reported by the Science and Technology Daily report, that Beijing Xinyan Chuangneng Technology Co., Ltd. developed a six-rotor hydrogen fuel cell drone that flew for 331 minutes. This was a joint project between Xinyan Chuangneng and China National Airways.
The long flight time is made possible due to the core technology, which is hydrogen fuel cells. The drone is equipped with a high-pressure hydrogen storage bottle that provides hydrogen to the fuel cells to generate electricity. Apparently, Xinyan Chuangneng had only been working on implementing the hydrogen for one year. In that time, they successfully developed a 2kW metal plate fuel cell that has an air-cooled stack and system.
Keeping the size compact, its lightweight and the high power density provides excellent performance even at high altitudes. Speaking of high altitudes the long flight time in low oxygen, low temperature, high wind extremes proves the hydrogen fuel cells can hold up under harsh conditions.
Originally scheduled to fly for just 240 minutes, the team exceeded their own expectations by 91 minutes. Proving just how valuable hydrogen fuel cells are, while only emitting water vapor. A similar large-scale all-weather lithium battery drone has a flight time of less than one hour, and oil-powered drones have more vibration that requires shock absorbers for shooting high-quality images or videos.
Fuel Cell: Proton Exchange Membrane (PEM)
Fuel cells, as an advanced power generation technology, are regarded as alternative power sources in electrical systems because they offer higher energy density to extend the duration of flight. For the same energy capacity, the weight of fuel cells is 3.5 times lower than that of lithium-ion batteries, resulting in much preferable specific energy.
A fuel cell derives usable power from supplied chemical reactants in the form of an electric current. There are a wide variety of fuel cells, including proton exchange membrane, phosphoric acid, molten carbon, solid oxide, methanol, and alkaline.
The proton exchange membrane fuel cell (PEMFC) is the most promising technology for use in UAS propulsion systems. The molecular hydrogen is exposed to a platinum catalyst. The catalyst causes the hydrogen to ionize into its constituent protons and electrons. The electrolytic membrane separating the anode and cathode allows only the protons (hydrogen stripped of its electron shell) to pass through. At the cathode, oxygen combines with the protons in an electrochemical oxidation process, requiring electrons. This draws the electrons liberated in the anode across a load; the current produced can be used as a source of power.
The use of a PEMFC has advantages over a strictly battery-based system, such as better endurance and better replenishing characteristics (refill hydrogen tanks as opposed to recharging the battery); They are quiet, low-moving parts; zero-emission signature; higher-energy density than battery; reversible reaction has regenerative properties; uses electric motor as the prime mover that has advantages, including reliability, maintenance, control, and high-altitude operational benefits.
The disadvantages of the PEMFC-based systems are: expensive (platinum catalyst); pressurized components (inside fuel cell and liquid hydrogen); complexity as compared to a battery system; catalyst sensitivity; and humidity/water management.
Two innovators in the field of fuel cells are Protonex, a wholly owned subsidiary of Ballard Power Systems (BLDP) that is based in Massachusetts, and MMC, headquartered in the province of Shenzhen, PR China. Both of these private companies are making significant inroads in the development and commercialization of FCPS for regular use in UAVs with missions which require longer time in the air. FCPS come in many forms. Some are more suitable for the world of light, small drones. Others are specifically designed and manufactured for large, industrial or military uses.
Protonex 550 Watt FC System
Protonex has focused on the use of Proton Exchange Membrane (PEM) technology for small, light UAV applications weighing less than 20 lbs. For this category they offer the SBH UAV Power System which is a PEM fuel cell operating at relatively low temperatures of 60o to 80o C (140ºF to 175ºF). This alternative offer quick start-up times, generating 350 W at full capacity. The hydrogen is stored in a chemical hydride cartridge and liberated as the system requires, while the oxygen comes from the air. The fuel cell is hybridized with a battery to provide peak power required for launch or climbing. The system features power generation 2 to 3 times the specific energy of LiPo batteries.
For applications that require high payloads and are not heat sensitive Protonex offers PEM fuel cells running on compressed hydrogen with systems providing up to 1.4 kW of electricity. When properly integrated into a small fixed wing UAV, improvements over 5 times LiPo batteries have been demonstrated, including the 26 hour flight of the Ion Tiger by the Navy Research Laboratory (35 lbs including a 5 lbs payload). This technology is now making its way out of military systems and into commercial UAS.
Similarly, MMC has focused on the use of hydrogen as the main source of fuel for their power cells. MMC is currently manufacturing and distributing two models of fuel cells, HyDrone 1800 & HyDrone 1550 with endurances (TITA) of 4.5 hours and 2.5 hours respectively. Their hydrogen fuel cells are designed for a wide range of popular commercial drones, both fixed-wing and multi-rotors, such as DJI M600, DJI M600 Pro and other heavy-payload drones.
Ballard Subsidiary Protonex Receives Orders from U.S. Navy for Fuel Cell Systems to Power UAV Field Trails
Ballard Power Systems announced in June 2018 that the Company’s subsidiary, Protonex, has received purchase orders from the U.S. Navy for a total of 13 fuel cell propulsion systems for unmanned aerial vehicle (UAV) or drone platforms. Protonex has supplied proton exchange membrane (PEM) fuel cell propulsion systems for the successful Ion Tiger fuel cell powered UAV program, and is now providing a variant of its 600 watt PEM fuel cell propulsion system for the subsequent Hybrid Tiger UAV program.
Phil Robinson, Protonex Vice President of Unmanned Systems said, “We have been working with the U.S. Navy for a decade to optimize our fuel cell propulsion system and deliver key benefits, including long range, quiet operation, high reliability, minimal vibration and low maintenance. It is exciting to put our innovative design to the ultimate test in rigorous operating conditions with an important customer.”
The Hybrid Tiger UAV was designed by the U.S. Naval Research Laboratory (NRL) to explore new power system technologies for UAV propulsion. High efficiency fuel cells from Protonex, in combination with other technologies, are expected to enable greater endurance than the 26 hours demonstrated by Ion Tiger in 2009. Through this program, Protonex is providing a key technology to advance the Navy’s unmanned system performance goals.
Protonex fuel cell UAV propulsion systems are used by the U.S. Department of Defense to enhance flight duration and range, while minimizing audible noise. The rugged and reliable systems are designed to operate in all types of environments and at high altitudes, enabling deployments in exacting missions worldwide. The Protonex FCair™ line of commercial UAV power systems builds on this defense heritage for applications in such areas as agriculture, asset inspection, surveillance, and search & rescue.
Malaysian firms partner for hydrogen-powered UAVs
In August 2020 it was reported, NanoCommerce Sdn Bhd (NCSB), a subsidiary of NanoMalaysia Bhd, and Pulsar UAV Sdn Bhd (PUSB), have signed a partnership agreement to commercialise a hydrogen-powered drone also known as the High Endurance Fuel Cell Powered Unmanned Aerial Vehicle (UAV). The agreement will see NCSB taking a 20 percent stake in PUSB, a Malaysian company that manufactures UAVs. PUSB CEO, Izmir Yamin, said that partnering with NanoMalaysia assists the company to validate the requirements of drone services in various different sectors.
“The market validation gives us reason to further improve our drone services by developing an on-board hydrogen generator,” said Yamin. “Now, with our in-house hydrogen technology, we’re not only improving the services, but are also able to venture into other sectors like energy and transportation.”
A hydrogen-powered drone allows it to fly for a longer time than a normal battery charge. The longer flight is made possible by the hydrogen fuel cell, known for its longer endurance. The differentiating factor, in this case, is that the drone is equipped with a nanotechnology enhanced hydrogen reactor that produces hydrogen on-demand to the fuel cells. This generates electricity to power the rotors for flight without the need for heavy compressed gas storage thereby, improving the power-to-weight ratio.
NCSB and NanoMalaysia CEO, Dr Rezal Khairi Ahmad, explained NanoMalaysia places an intrinsic value on the project via a variety of project investments, intellectual properties, and market validation and access. Dr Rezal Ahmad commented, “The on-board hydrogen powered drone has already been sandboxed for precision agriculture with a level of success.”
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