H2Aircraft - CRYOPLANE and the future of flight
Driven by the foreseeable exhaustion of petroleum reserves and tightening environmental controls, the EU-funded CRYOPLANE project has developed a conceptual basis for a new generation of aircraft, preparing the way for a future without fossil fuels and where hydrogen rules.
Greenhouse gas emissions from air transport are increasing more than other modes of transport such as rail or road. If nothing is done, then these emissions will get considerably worse before the oil runs out. Between 1985 and 2000, annual carbon dioxide emissions from aircraft in the 15 EU member states more than doubled, in contrast to road transport that showed a mere 50% increase.
No quick fix
In part, this reflects the lack of easy alternatives available to the air transport sector; electrification can help reduce emissions from rail; financial measures such as road pricing can ameliorate the growth of car use - but these are not available or desirable options for aviation policy makers unless there is some alternative, cleaner fuel technology for the industry to adopt.
Aircraft manufacturers and their customers, the air carriers, take a long-term view. Aviation is a capital-intensive industry with investments in new aircrafts models and new fleets spread over decades. They see rising wealth in the developing world as a major driver for future demand for air travel.
In 1996 the USA, with only 4.6% of the world population generated 41% of world air traffic, while China and India, with 37% of world population, contributed only 3.4%. As these countries become richer there will be a huge increase in demand for air travel, accompanied by a correspondingly huge increase in carbon dioxide emissions if nothing is done. Demand is predicted to grow at 4-5% per year over the coming decades, but the increased carbon dioxide emissions are unlikely to be compensated by advances in energy efficiency. These scenarios are leading the aviation sector to look more closely at the hydrogen option.
The CRYOPLANE project, a European consortium of 35 partners from the aviation sector led by Airbus Deutschland, made an overall system analysis of hydrogen as an aviation fuel. It considered: applicability, safety and environmental compatibility issues; and also investigated medium and long-term scenarios for the switch from kerosene to hydrogen in aviation. A range of aircraft categories was considered from business jets to large long-range aircraft such as the Airbus A380.
A key issue was to model the liquid hydrogen fuel system architecture - per unit of energy, liquid hydrogen has four times the volume of kerosene - so fuel tanks four times as large needed to be fitted in, or on to, each aircraft category. Modelling showed that, owing to the larger exterior surface area needed to accommodate the fuel tanks; energy consumption would increase by 9% - 14%, as would the maximum take-off weight. Overall operating costs would increase by 4% to 5% due to the fuel alone.
The technical assessment concluded that hydrogen-fuelled engines will be as energy efficient as kerosene engines, and that conventional turbo engines can be converted to run on hydrogen, although some further research is needed. An aviation-specific safety assessment further concluded that hydrogen fuelled aircraft will not be less safe than current aircraft; although regulations for airworthiness, ground handling and servicing would require adapting.
No barriers to implementation
With regard to environmental compatibility, the assessment identified great long-term benefits from the switch to hydrogen. As hydrogen can be produced from water, and produces water on burning in air, then the greenhouse gas emissions are substantially less than with kerosene. However, there are minor emissions of oxides of nitrogen, and the water in the aircraft’s contrail is also a greenhouse gas at high altitudes. However the residency time of water vapour in the upper atmosphere is 6 months, whereas carbon dioxide remains in place for around 100 years.
The CRYOPLANE analysis concludes that hydrogen could be a suitable alternative fuel for future aviation. Based on renewable energy sources it offers the chance to continue the long-term growth of aviation without damaging the atmosphere. Importantly no critical barriers to implementation were identified in the study. Further research is needed, but implementation could take place within 15 to 20 years.