Fuel Cells for Aircraft Applications

Fuel Cells for Aircraft Applications

Several aircraft manufacturing companies, such as Boeing, Cessna, Sky Spark, and others are planning to utilize fuel cell-based electric propulsion systems to operate short-range all-electric aircraft [9]. All-electric technology provides a small, lightweight, virtually noiseless and highly maneuverable aircraft. The all-electric aircraft is considered a good military stealth aircraft for battlefield surveillance, reconnaissance and intelligence gathering missions. Various aircraft designers have considered hybrid technologies including lithium polymer batteries and hydrogen fuel cells for electric vehicles.

  1. Performance and limitations of an all-electric aircraft or vehicle

The use of hybrid technology in the design of an all-electric vehicle is an absolute necessity to ensure continued propulsion and reliable flight performance. Some aircraft designers have opted for 20kW PEM-structured hydrogen-based fuel cells and 20kW lithium polymer batteries to guarantee replacement or supplemental power capacity during takeoff and initial climb operations [9]. Hydrogen-based PEM fuel cells are capable of delivering current levels in excess of 100 A and output voltages ranging from 200 to 240 V [9]. This type of fuel cell converts hydrogen directly into electricity with the highest efficiency and does not convert heat through combustion.

In addition, the fuel cell is emission-free and quieter than a hydrocarbon fuel-powered engine. The air and water vapor that these cells emit at ambient temperature do not pose an environmental problem. The SkyPark is a fixed-wing all-electric aircraft that uses hydrogen fuel cells capable of delivering more than 65kW of electrical power, enough to power the aircraft, with lithium polymer batteries for additional power if needed in an emergency. This all-electric aircraft using fuel cells can fly at a speed of 100 mile/h for 1 to 3 hours. In March 2008, the European Boeing Research and Technology Agency verified these performances. As mentioned earlier, fuel cells provide flight power for all cruise phases. During takeoff and climb, more power is required, which can be supplemented by a lightweight lithium-ion battery. The key to deploying all-electric aircraft in the future is battery technology. Development of batteries must focus on increasing storage density and improving lifespan while reducing charging time. The possibility of high energy storage density (per unit volume and per unit mass) battery technology will clearly demonstrate its use in small all-electric aircraft.

Research by engineers designing an all-electric aircraft shows that a solar system consisting of 12,000 solar cells can turn on four electric motors, each rated at 7.5 kW. There are 4 pods, each with a set of lithium polymer batteries, a 10hp (1hp = 745.700 w) electric motor and a two-blade propeller. The all-electric aircraft successfully demonstrated a 26-hour flight, including a 9-hour night flight on July 7-8, 2010. Scientists believe that planes using regenerative solar energy have the potential to remain aloft at high altitudes indefinitely if the solar energy harvested from vertical atmospheric motion exceeds that of solar power by a factor of 10 or more.

  1. Fuel Cells for Electric Vehicles and Hybrid Electric Vehicles
Figure 1 - Thermodynamic efficiency of a heat engine (Carnot cycle efficiency) compared to that of an ideal H2-O2 fuel cell
Figure 1 – Thermodynamic efficiency of a heat engine (Carnot cycle efficiency) compared to that of an ideal H2-O2 fuel cell

Not every fuel cell is suitable for electric vehicles (EVs) and hybrid electric vehicles (HEVs), and a technical article published in the journal IEEE Spectrum in June 2001 suggests that metal-based fuel cells would be the most suitable for high reliability and Long-life backup and emergency power. Research conducted on metal-based fuel cells suggests they are best suited to power cars, trucks and electric motorcycles that work to reduce pollution in crowded cities. These fuel cells are especially found to be most cost-effective in third world countries, where scooters and motorcycles are powered by low-cost, two-stroke engines that run on cheap fuel. Noise-free, pollution-free, low-cost operation is only possible with metal-based fuels (see Figure 1).

Read more: Reasons to use flow batteries