Powered flight has relied on fossil fuels for 120 years. Changing to renewable energy is not easy…but possible
Aircraft have been a vital part of our lives and economy for decades. Because of climate change many of the things we have come to take for granted in the last 60 years are up for grabs. While aviation is not the largest contributor to the atmospheric carbon load, it is growing as demand for air travel increases.
Applying renewable power sources to aircraft is tricky. Consequently, there needs to be considerably further development and more variety in the types of drive used to get an aircraft into the sky.
One solution would be electricity provided by batteries. The catch is that any aircraft must be weight conscious, but batteries are, and remain, heavy. Nor do they last long enough to send an aircraft more than a few hundred miles. For short range flights of up to 500 miles, with nine to 15 seats per plane, this is all that is required. Such an aircraft powered by battery and electric motors would require a battery weighing anything up to five tonnes.
Longer haul flights are beyond the reach of batteries and there are several potential methods that could fill the gap. One (albeit temporary) solution might be a sustainable aviation fuel, such as synthetic kerosene, although this is carbon-neutral not carbon-zero
Hybrid aircraft, as with hybrid cars, would use a mix of energy sources. For example, a kerosene powered engine driving a generator could power electric motors. The conventional engine could be used on take-off and landing, two key moments requiring a lot of power. Cruising at high altitude would then be powered electrically. Possibly with batteries or another form of electrical power.
Alternatively, hydrogen (a by-product of refining oil) could in some form be a fuel of the future. So-called ‘green’ hydrogen, perhaps sourced from offshore wind power to hydrolyse water, would be needed in large quantities. The ‘H’ in H2O could then be used to generate electricity to power an aircraft over a much greater range than possible with batteries. Alternatively, the hydrogen could be burned in an engine.
The Hydrogen in Aviation (HIA) alliance is attempting to do just this. It is a grouping of companies from the UK aviation and renewable energy sectors, including easyJet, Rolls-Royce, Airbus, Ørsted, GKN Aerospace and Bristol Airport. Their goal is to press for the UK to develop the infrastructure, policy, regulatory and safety frameworks required for when the first hydrogen-powered aircraft takes its maiden flight.
The alliance has made hydrogen its clean fuel source of choice for airplanes. This is something the British public supports, with 91% of people saying the UK government should invest in hydrogen production for use in the aviation sector.
For some perspective, the UK aviation sector currently consumes 12.3 million tonnes of jet fuel a year, producing 8% of the country’s greenhouse gas emissions. Air transport is a hard-to-abate sector, lacking technologically mature alternatives to jet-fuelled engines.
However, hydrogen has been long been held as a potential source of clean fuel for the aviation sector, possibly boosting the UK economy by £34bn a year by 2050.
A HIA report, due at the end of the year, will mark the milestones to be met over the next 10 years to make hydrogen-flying a reality. There are three main areas: supporting delivery of the infrastructure necessary to make the UK a global leader; ensuring the aviation regulatory regime is hydrogen ready; converting the funding model to support hydrogen aviation R&D into a 10-year programme.
Some of HIA’s member companies have already made large investments into hydrogen research, with a focus on powering short-haul flights. Airbus aims to have a new hydrogen-powered aircraft entering commercial service from 2035. In 2020, ZeroAvia staged a test flight at its Cranfield Airport R&D facility to demonstrate a commercially available aircraft powered by hydrogen fuel cells. The six seater flew for just 20 minutes. Similarly, Rolls-Royce has proven that hydrogen could power a jet engine following successful ground tests in 2022.
Staying with Rolls-Royce, the engine maker says it has reached a key milestone in developing a hydrogen-powered engine. It is working with easyJet to develop hydrogen combustion engine technology to power a range of aircraft from the mid-2030s onwards. Last year, easyJet and Rolls-Royce ran a modern aero engine, an AE2100, on green hydrogen at Boscombe Down, UK.
RR says it has completed tests on a full annular combustor of a Pearl 700 engine, which was running solely on hydrogen fuel. The test proves the fuel can be burned in conditions needed to achieve maximum take-off thrust.
The secret is in a newly developed fuel spray nozzle that allows precise control over the combustion process.
The nozzles (tested at Loughborough University’s National Centre for Combustion and Aerothermal Technology (NCCAT)), were able to control the flame position using a new system that progressively mixes air with the hydrogen to manage the fuel’s reactivity.
These tests have improved engineers’ understanding of the combustion element of the hydrogen programme, while work continues on systems to deliver the fuel to the engine and integrate them with an engine.
Switching the fuel source for aviation from fossils to renewables is both difficult and exciting. It also asks us to answer some awkward questions. What do you think of the issues raised in this blog?
What does the future of powered flight hold? What value is there in promoting carbon-neutral solutions while we develop the technology / systems to finally go net-zero carbon?
Would you be willing to fly in an aircraft powered by hydrogen? What would you like to know before you do it?
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