Fuel Cell Technology in Boeing and Airbus - Essay Example

My My (i.e. English 101) 14 Mar 2009 Fuel Cell Technology in Boeing and Airbus Aircraft This paper examines the new fuel cell technology that may in the near future be used to replace the Auxiliary Power Unit (APU) within the Boeing 737 and the Airbus A320. The paper presents research into the new fuel cell technology; the advantages of the fuel cell; the eco-friendliness of the fuel cell; and calculations showing reduction in cost and weight of the aircraft using fuel cells. Finally, some of the implications of developing fuel cell technology for aviation are considered. The Boeing 737 APU (see Appendix, Fig.4) is a gas turbine engine in the tail of the aircraft (Ludovic, 2009). It is monitored and controlled by the Electronic Controller. There are actually many different kinds of APUs used in the Boeing 737, created by a few different manufacturers. The AlliedSignal APU has the highest power rating at 90kVA up to 31,000 ft. (Brady, 1999); this power rating drops at higher altitude. Fuel cell technology is currently able to match this 90 kilo-Volt-Ampere power rating, in order to replace this APU. This has been demonstrated in test flights of hydrogen-powered aircraft, as described below. The future of the Boeing 737 APU may include a Solid Oxide Fuel Cell (SOFC) APU. According to Brady, (1999): ‘The SOFC uses jet fuel as the reformer in the proton exchange membrane to give a 440kW APU that is 75% efficient compared to the conventional 40-45% efficient APUs. This would give a typical fuel saving of 1,360t for a 737 over a year. It is actually a hybrid gas turbine / fuel cell due to the sudden surges in demand eg engine starts and gear retraction etc. The SOFC will use air from a compressor passed through a heat exchanger for its gas turbine section. A potential drawback is that it has a 40min start-up time, so it would have to remain on for the whole day and depending upon its noise levels this could be a problem at airports which require the APU to be shutdown during the turnaround. ‘ The efficiency of SOFCs over conventional APUs is large; although the long start-up time might be prohibitable. The technology needed for a SOFC APU to replace the current Boeing APU may be available by 2010, but it could take much longer. Boeing was working in conjunction with Airbus to develop the necessary technologies to replace the APUs with fuel cell technology, since they essentially share the same supplier pool, but they were ready to split when it came to time to develop competitive finished products. The technology for building hydrogen-fueled aircraft has already been demonstrated. The Airbus A320 Fuel Cell Demonstrator was first publicly presented in Berlin in 2008. The fuel cell system provides 20kW of electrical power (AsiaTravelTips 2009). Boeing modified an aircraft with a proton exchange membrane (PEM) fuel cell, lithium-ion battery hybrid system (Safer, 2008) for test flights in February and March of 2008. There have also been other aircraft that have demonstrated the feasibility of hydrogen-powered flight. Fig.1 shows the flyH2 aircraft, promoted by Mark van Wyck, which is using a 75 kW fuel cell to power a small two-seater aircraft. There have been many more test flights than this, and these test flights make the goal of designing aircraft run solely on hydrogen fuel a realistic plan of the near future. Hydrogen fuel cells were first designed as a reverse electrolysis process. In electrolysis, hydrogen and oxygen are split when an electric current is run through water. This process produces a separate supply of hydrogen gas and oxygen gas. In hydrogen fuel cells, the reverse process occurs: the hydrogen and oxygen gases are combined to produce electricity and water as a byproduct (see fig.2). This happens by using a catalyst, typically a metal or alloy. The hydrogen fuel is separated into its electrons and protons; the electrons are made to traverse a circuit, and the protons are recombined with the electrons and an oxidant to create waste water. There are many different kinds of fuel cells, usually classified by the electrolyte they use. The most promising for transportation include the polymer exchange membrane (PEM) fuel cell and the solid oxide fuel cell (SOFC). PEM fuel cells have high power density and low operating temperature, so it warms up and starts generating electricity relatively faster. The SOFC operates at very high temperatures; reliability becomes an issue unless in continuous use. The high temperature of the SOFCs can produce steam that can be channeled into turbines. It is also possible a different kind of fuel cell will be developed for aircraft. Figure 2- How PEM fuel cells work. From http://www.fueleconomy.gov/feg/fcv_pem.shtml.  The argument is sometimes made that a lot of energy has to go into making the hydrogen gas needed by the fuel cell. It is true that some energy has to be expended to separate hydrogen from oxygen, in order to supply the fuel cell with hydrogen gas, as illustrated in the PEM fuel cell of fig. 2. However, companies such as the flyH2 company advocate producing this hydrogen gas by utilizing solar energy and wind energy, and storing it for future use in fuel cells. In that way clean renewable resources are also used in order to create the entire fuel cell system. Hydrogen fuel cells are the most eco-friendly fuel alternative. Fuel cells use hydrogen and oxygen to make electricity, with water and heat the only waste products. There is zero pollution. This makes hydrogen fuel cells in compliance with zero-emissions goals. Since the aviation industry contributes 5% of the global carbon emissions that contribute to global warming (flyH2, 2009), this would be a significant environmental improvement. Making aircraft run cleaner will also have a positive impact on the airline personnel work closely with the aircraft and may be breathing in harmful exhaust. In addition, hydrogen fuel cells circumvent the need for loud internal combustion engine technology or gas turbine engines of the aircraft industry, which currently make noise pollution such a problem at airports. Instead of the gas turbine engines, the electric motors run by the fuel cells are relatively very quiet, some would even say silent. This makes hydrogen fuel cells a quieter technology, and could potentially change airports into a more pleasant work environment. The aircraft will not have to carry extra water since it can reuse this waste water in its water and waste system, thereby saving weight, reducing fuel consumption, and reducing emissions over combustion engines. Weight is also saved because less jet fuel is needed to power onboard electrical generators. How much weight would the water produced by hydrogen fuel cells save? During a flight test in February 2008, Airbus fuel cells produced 10 litres of water (Airbus 2008). How much jet fuel would typically be burned to carry this extra weight, if instead of using fuel cells, the extra water had to be stored? According to Fig.3, there would be a net reduction in fuel of 5.1 times less fuel by weight if hydrogen was used instead of gasoline. This is assuming that the gas turbine engines used in aircrafts have a similar range of efficiencies as the ICE technology, and taking into account the lower heating values of gasoline and hydrogen. Heating Content (Lower Heating Value) LHV Density LHV   MBTU/gallon kg/gallon MBTU/kg Gasoline 0.115 3.22 0.035714 Hydrogen     0.1136 Specific energy H2/specific energy gasoline     3.18         Fuel Cell Efficiency 52%     Internal Combustion Engine Efficiency 32%     Ratio H2/ICE efficiency     1.63         Net reduction in fuel weight     5.17 What would be the total savings in weight for Airbus A320 or Boeing 737 if they took onboard 5.17 times less gasoline? The 737-900ER has a maximum fuel capacity of 7, 837 US gallons (Wikipedia). Multiplying this by the weight of gasoline, 3.22 kg/gallon, this would be 30, 116 kg of gasoline. Dividing this by a net reduction of 5.17, there would be a need for only 5,815 kg of hydrogen fuel in a comparable aircraft, saving 24,290 kg of weight on each flight. Less weight is a great advantage of hydrogen compared to aviation fuel for aircraft. Hydrogen is much lighter, which allows either greater payload or longer range.  It turns out that the weight of hydrogen can be five times less than the weight of the gasoline or diesel fuel (fig. 3).  This is a combination of the higher specific energy of hydrogen (BTU/kg) and the higher efficiency of fuel cell.  The same principal as discussed above holds for all the demonstrated hydrogen-power flights: you need 5 times less fuel weight for a given mechanical purpose, whether it is propelling the aircraft or running a motor/generator APU system.  This is the reason that they use hydrogen and oxygen for the main engines of the Space Shuttle: less fuel weight means more payload into orbit. Here they can only take advantage of the 3.2 times better specific energy for the main Shuttle engines, but they also use fuel cells on the Shuttle itself once in orbit, in which case they use 5 times less fuel weight to provide the electricity to run the Shuttle (and water for the astronauts to drink). These same principles of payload and reutilizing water apply to the passenger aircrafts, and there is an advantage when water is recycled through the system. It is possible that aircraft such as the Boeing 737 and Airbus A320 could become even more cost-effective by utilizing even further clean technologies on board and creating a more self-contained, recyclable system. These improvements could make the aircrafts able to travel for further distances without refueling. The other aspect of advantage of hydrogen over gasoline is cost.  Today, we can produce hydrogen for around $3/kg by reforming natural gas (this process is: CH4 + 2 H2O = 4H2 + CO2). This process of producing hydrogen is widely used today by the hydrogen community, however, it is less than ideal since it produces carbon dioxide, a greenhouse gas, as a byproduct.  One kilogram of hydrogen has approximately the same energy content as one gallon of gasoline. To be precise, the lower heating value (LHV) of hydrogen is 0.1136 MBTU/kg, while the LHV of gasoline is 0.115 MBTU/gallon.  So this would be somewhat equivalent to gasoline (or aviation fuel) selling at $3/gallon. This price of gasoline may go even higher during economic or politically unstable times, and the price of gasoline can be seen to be controlled to a great degree by Middle Eastern oil-producing countries and by OPEC. Whereas the price of hydrogen should be less tied to global political events, since it can be produced anywhere. For use on an airplane, however, the hydrogen would have to be compressed or liquefied.  The approximate cost of compressed hydrogen would be on the order of $4/kg, and that of liquid hydrogen $5 to $6/kg.  These calculations depend on the efficiency of the current APUs on a jet aircraft, and those figures will vary even within one aircraft designer, since they use multiple vendors.  Presuming that they run a generator off the jet engines, and the generator might have even higher efficiency than the fuel cell.  If so, the advantage of the fuel cell would diminish (compared to an ICE on a small plane). There would still be great advantages to using hydrogen, and these could be increased by developing the associated hydrogen fuel cell technologies further. When comparing costs between hydrogen and gasoline, the long-term costs may be very different than current costs. Airbus’ hydrogen fuel cell was developed with Michelin, Liebherr Aerospace, and the German Aerospace Center (DLR). The fuel cell serves as a power source for the A320’s backup hydraulic and electrical systems, and the aircraft’s ailerons. In the future, Airbus plans to use hydrogen fuel cells to replace emergency power systems and the APU. Replacing the APU will cut down on noise pollution and emission levels. Patrick Gavin, Executive Vice President of Engineering for Airbus (Hill, 2008) has recently commented on these plans. The APU is a mini-turbine engine that supports aircraft functions such as main engine start, electrical, heating and air conditioning. The APU runs aircraft functions on the ground and is usually left on during takeoff, in case of engine failure during takeoff. So replacing the APU with fuel cells would be a small step compared to replacing the two many engines of a large commercial passenger aircraft. The capabilities of current fuel cell technologies are not there, and it is a debatable question if hydrogen fuel cell technologies will ever be able to completely power the larger aircraft. Airbus is planning on deciding by 2015 whether the technology will be made available to replace the ram air turbine (RAT) with ‘a fuel cell housed in an airliner’s wing-body fairing…the first concrete step towards the European manufacturer’s long-term goal of eliminating an airliner’s gas-turbine auxiliary power unit’ (Doyle, 2008). The weight of the RAT and that of the fuel cell are similar: about 200 kg (440 lb). After replacing the RAT, there are three further steps that need to be taken to replace the APU. The first step would be a continuously running fuel cell producing oxygen-depleted exhaust gas for fuel-tank inerting, and reusable water. The second step would be operating an airplane on the ground without using kerosene: cabin air-conditioning and electrical systems would all be run on the fuel cell. The last step would be full replacement of the APU. According to Thomas Sherer, Airbus Vice President Environmental Controls, this will entail improvements in the fuel cell technology, which currently supplies only one fortieth of the power of current APUs. One other advantage of the fuel cell system for aircrafts is the greater reliability of the system’s mechanics. There is only one moving part in the fuel cell system: the electric motor that the fuel cell electricity drives.  This is much more reliable than an internal combustion engine with many dozens of moving parts (pistons, connecting roads, camshaft, valves, etc.) or the gas turbine engines and all of its moving parts. This has the potential to cut down on the types of incidents such as occur during engine failure during takeoff. In the long run, when fuel cell technology is fully developed, it will potentially be a more reliable aircraft technology than the engine technology in place now. Developing fuel cell technologies for aircraft will also potentially contribute to other areas of technological development within society. The demand for fuel cells to replace the APUs of Boeing 737 and the Airbus A320 will likely spur research into ways of making fuel cells atleast as powerful as today’s APUs. This in turn may create unforeseen technological spin-offs. This research may also drive down the cost of fuel cells, which then may be viewed as increasingly cost-effective enough to be placed in other vehicles such as cars and in many other modern appliances drawing on power, everything from cell phones to household appliances. In particular, when an industry begins to develop hydrogen fuel cells, the hydrogen economy may be able to get off the ground; the market may suddenly become available to build the hydrogen infrastructure that the fuel cells need to take off. These technological developments may spur even further economical growth across the world. In conclusion, the future of fuel cell technology being used to replace the APUs of aircraft, in particular within the new Boeing 737 and Airbus A320, is promising yet still years away. Fuel cell technology will have to be advanced to the point where it can produce the same power of aircraft APUs. This will likely occur when the demand for fuel cells increases. When this occurs, the advantages of the fuel cell are immense, and include greater cost-effectiveness; safer, cleaner, quieter, and more reliable aircraft technology; and environmental soundness due to the complete elimination of greenhouse gas emissions from aircraft. The greatest advantage of fuel cell powered aircraft may be in the way the research performed to achieve this goal may help to create a hydrogen economy that can drive and sustain our power hungry world, just as many developing countries with billions of people such as China are beginning to emulate the conspicuous consumption lifestyles of the west. Not to mention the security that will come from our aircraft industries relying on a renewable technology, instead of depending on limited, dwindling fossil fuel resources, the demand for which steadily increases the potential for global war. References Airbus (2008). Emission free power for civil aircraft: Airbus successfully demonstrates fuel cells in flight. http://www.airbus.com/en/presscentre/pressreleases/pressreleases_items/08_02_19_emission_free_power.html AsiaTravelTips.com (2009). First Public Demonstration of Airbus A320 Fuel Cell Demonstrator. http://www.asiatraveltips.com/news08/275-FuelCells.shtml Brady, C.(2006). The Boeing 737 Technical Guide. Tech Pilot Services Ltd. Brady, C.(1999).Auxiliary Power Unit. The Boeing 737 Technical Site. http://www.b737.org.uk/apu.htm Doyle, A. (2008, May 29). Fuel cell could replace ram air turbine on next Airbus narrowbody. FlightGlobal. http://www.flightglobal.com/articles/2008/05/29/224309/fuel-cell-could-replace-ram-air-turbine-on-next-airbus-narrowbody.html FlyH2 (2009). Welcome to flyH2 Aerospace. http://www.flyh2.com/ Hill, B. (2008). Airbus Develops Fuel Cells for In-Flight Power. DailyTech. http://www.dailytech.com/Airbus+Develops+Fuel+Cells+For+Inflight+Power/article10804.htm Ludovic, A. (2009) Boeing 737 Systems Review. smartcockpit.com. http://old.smartcockpit.com/b737/B737%20APU.PDF Safer, Will (2008, Apr. 4). Boeing’s Hydrogen-Powered Airplane Completes Test Flights. Switched. http://www.switched.com/2008/04/04/fuel-cell-airplane-completes-test-flights-in-spain Wikipedia (2009). Boeing 737. 14 Mar 2009. http://en.wikipedia.org/wiki/Boeing_737 Appendix – Additional figures Figure 4 - Boeing 737 APU. (Brady, 1999). Figure 5- Hybrid Air Berlin -Boeing 737-700. From http://en.wikipedia.org/wiki/Boeing_737. Fig. 6 - Swiss International Air Lines Airbus A320-200. From http://en.wikipedia.org/wiki/Airbus_A320_family Read More