Alternatives in Aviation After Peak Oil
|By Harry Valentine|
October 9, 2006
What will happen to the aviation industry after the world's supply of fossil oil begins to diminish? Harry Valentine offers a review of some of the alternatives that need to be discussed and considered now, so that the industry can be prepared to change and thrive in the future.
Commercial aviation is an essential component of the global economy. The cost of aviation fuel is directly determined by the prevailing world price of oil, and it accounts for a major proportion of airplane operating costs. Several airline companies now add a fuel surcharge to the ticket cost of a commercial flight to compensate for the recent rapid rise in fuel costs. World oil prices are expected to remain high for several years. The prospect of sustained high aviation fuel prices could propel airline companies to seek alternative aviation fuels. Seeking alternative fuel could become paramount for the airline industry should the peak-oil phenomenon actually occur. Short-haul/Commuter Aircraft:
The cost of liquid combustible fuel would likely escalate during the post peak-oil period. Synthetic fuel that is processed from natural gas and coal could become an important alternative fuel. The market demand for and prices of coal, natural gas and biofuels such as ethanol and biodiesel would also escalate. Municipal transit systems would likely be using more electrically powered vehicles as the number of (lithium) battery powered cars in service increases. The commercial aviation industry would likely compete for fuel and energy in a market of scarcity and escalating fuel prices.
Aircraft turbine engines are very flexible in the kind of fuel that they can burn. Short-haul and commuter airline companies that operate routes of under 500-miles would be the most likely candidates to use alternative aviation fuel. Their fleets are mainly powered by turbo-prop or by turbofan engines and may likely have sufficient capacity in the fuel tanks to carry a cheaper fuel with a lower energy content. They may use such fuel if its cost per BTU undersells fossil aviation fuel.
Ground-effect aircraft use a specialized wing design that generated a cushion of air between the wing and the surface over which it flies. Large and heavy versions of such aircraft could be flown at moderate speed over water and carry passengers and freight between coastal centers up to 500 miles apart. Eliminating the need for take-off to at least 10,000-feet would cut fuel costs. The performance of such craft can be enhanced by a recent development from Britain that has been successfully tested in a scale model aircraft. Aeronautical "paddle wheels" are mounted transversely on the topside of aircraft wings to provide propulsion and increase lift at very low flight speeds.
Such craft may to be powered by unconventional engines including external-combustion air turbines that burn competitively priced (per BTU) unconventional fuels such as coal-water fuel that is unsuitable for use in internal-combustion engines. Large versions of such craft may use electrical transmissions and be driven by electrically powered propellers that are the size of helicopter rotors. Such units can move a large mass of air at lower velocity to deliver high thrust (200,000-lbf per propeller) at higher propulsive efficiency. An alternative system could drive the propellers by ducting hot combustion gases through thick rotor blades to adjustable jets that are built into the tips of the rotors.
Breakthroughs and Research:
It may become possible for supercooled liquid hydrogen to eventually be used as an alternative fuel for some types of commercial airline service. Extensive research will be needed to resolve the numerous logistical problems that are related to its use as an alternative aviation fuel in supersonic and hypersonic aircraft. Other alternative fuels may include high-density energy-storage technologies that result from breakthroughs in research in the areas of nanotechnology and in high-temperature superconductivity.
Sporadic and significant breakthroughs periodically occur in both fields. High-temperature superconductivity holds great promise for use in high-density energy-storage technology. A coil formed into a torus and made from "high-temperature" superconductive material could theoretically store enough energy to enable a full-sized commercial airliner to undertake an extended trans-oceanic or trans-continental flight. Advances in nanotechnology could enable superconductive materials to eventually be manufactured at a cost that could justify their application in airliner propulsion.
Electrical Storage and Propulsion:
Energy stored in a superconductive storage technology could power electric motors that drive the identical propulsion fans that are found at the front-end of modern, "high-bypass" turbo-fan aircraft engines. Such fans provide up to 90% of the propulsive thrust of the turbo-fan engine. Each electrically powered propulsion fan may be driven by multiple (induction) lightweight electric motors during take-off. Some electric motors would "cut-out" under reduced power demand at cruising altitude so that the remaining motors will operate at higher efficiency (electric motors have poor part-load efficiency).
Coanda fans may propel subsonic commercial aircraft that use high-density electrical storage technology. Such units were originally developed by physicist Henri Coanda and can operate at comparable efficiency and at comparable flight speeds as turbine-driven propulsion fans. Electrically powered aircraft that use either turbine propulsion fans or Coanda fans could be flown in thinner air at higher altitude (up to 65,000-feet) to reduce energy consumption (less drag on aircraft) on extended flights. The cooler air found at such altitudes could assist in keeping the superconductive energy storage systems functioning properly.
Superconductive energy storage systems used in future commercial aircraft would likely be cooled by liquid nitrogen. Both systems would need to be frequently recharged. Commercial aircraft that operate long-haul service usually undergo cleaning and servicing in hangars after long flights. It is during such service periods when the energy storage and cooling systems could be recharged, a process that would likely be both energy-intensive as well as time consuming.
It may be possible to design the energy storage systems along with their cooling systems to be removed and replaced during shorts layovers—such technology could help reduce the turn-around time of the aircraft. The introduction of superconductive energy storage systems in commercial aircraft in the long-term future would require that future airport terminals be equipped with power generation technology at or near the premises.
The number of electrically powered and hydrogen powered road and railway vehicles would likely increase during a post peak-oil period. Commuter aircraft that operate short-haul service could be powered by ethanol or by hydrogen while future supersonic aircraft could use liquid hydrogen as fuel. The commercial aviation industry of the future (post peak oil) could likely require vast amounts of electric power to recharge superconductive energy storage systems, recharge liquid nitrogen cooling systems as well as to generate, compress and supercool large amounts of hydrogen.
Modern commercial aircraft are energy intensive during take-off. Airports that serve metropolitan areas presently process continual processions of large long-distance aircraft during peak periods. Such aircraft could require between 300-Mw-hr and 1000-Mw-hr of power to undertake trans-oceanic flights at subsonic speed. The power requirements of a future electrically based commercial aviation industry could likely overwhelm the power generation industry of most developed nations.
Major international airports may eventually need to generate electric power on-site to meet the energy needs of future fleets of electrically powered and hydrogen-fueled commercial aircraft. Airport power stations may be nuclear; use hydrogen fusion or be based some other unconventional power generation technology that is still subject to research. The heat that will be rejected by these thermal power stations could be reclaimed and put to productive use, including:
- Heating buildings (district heating) during winter.
- Putting heat into geothermal storage during summer for use during.
- Powering absorption air-conditioning systems during summer.
- Energizing low-grade heat engines to generate electricity during winter.
The ability to store large amounts of energy at or near major airports could gain importance during a post peak-oil period. Electric power could be purchased from the grid during their off-peak periods and put into short-term storage. Airport power stations that encounter off-peak periods could replenish airport energy storage systems that may include superconductive storage, flow batteries, hydraulic storage in hydroelectric dams in nearby mountains (coastal airports) or off-site pneumatic storage (subterranean salt domes that were emptied). Air that is exhausted from pneumatic storage systems may be sufficiently cold to assist in "replenishing" liquid nitrogen supercooling systems.
Power Regulation (Airports):
Power stations that provide energy for air transportation use may have to be excluded from the regulatory framework. Most of the electrically powered airliners that will be recharged would be "foreign" owned, that is, the owners would be domiciled in a different jurisdiction to where the aircraft would be recharged. The idea of regulators in one jurisdiction looking after the interests of parties who live, do business and pay taxes in another jurisdiction is quite ludicrous. Power stations that supply a future airline industry with electric power would need to be regulatory-free despite the "foreign" airline owners being "captive" customers. It would be possible for power to be supplied to a single airport by several small providers who compete against each other. Power providers and airline companies could negotiate deals, perhaps even on a daily basis.
Future scientific breakthroughs are likely to occur in both nanotechnology and in superconductivity. High-density energy storage technologies could be the likely result and appear in the distant future. Electrically powered commercial aircraft that fly at subsonic speeds could appear in the future irrespective of whether or not peak-oil actually occurs. Alternative liquid fuels that are cost-competitive to fossil oil are also likely to appear and find applications in aviation. Large ground-effect aircraft that fly above water and that carry either passengers or freight between coastal cities are also likely appear in the future.
Harry Valentine holds a degree in engineering and has a backround in free-market economics. He has undertaken extensive research into the field of transportation energy over a period of 20 years and has published numerous technical articles on the subject. His economics commentaries have included several articles on issues that pertain to electric power generation. He lives in Canada and can be reached by e-mail at firstname.lastname@example.org.