Aircraft

Reaction Engines testing ammonia as carbon-free aviation fuel

Reaction Engines testing ammon...
The new ammonia propulsion system uses heat exchanger technology originally developed for Reaction Engines' Skylon spaceplane
The new ammonia propulsion system uses heat exchanger technology originally developed for Reaction Engines' Skylon spaceplane
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The new ammonia propulsion system uses heat exchanger technology originally developed for Reaction Engines' Skylon spaceplane
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The new ammonia propulsion system uses heat exchanger technology originally developed for Reaction Engines' Skylon spaceplane

Reaction Engines and Britain's Science and Technology Facilities Council (STFC) have completed a concept study into the practicality of using ammonia as a jet aviation fuel. By teaming Reaction Engines's heat exchanger technology with STFC's advanced catalysts, they hope to produce a sustainable, low-emission propulsion system for tomorrow's aircraft.

Modern jet engines use a variety of fuels based on kerosene that have a very high energy density that can propel aircraft well beyond the speed of sound and carry passengers and cargoes across the globe. Unfortunately, such fuels are also derived from fossil fuels and produce significant carbon dioxide emissions, which the airline industry and many governments have pledged to reduce radically by 2050.

One way of achieving these cuts is to look at alternatives to conventional jet fuels to power airliners. The problem is that most of these alternatives have much lower energy densities than standard aviation fuels and suffer from other drawbacks. For example, present-day battery technology would require future aircraft to be very small, short-range, and with little payload capacity. Meanwhile, liquid hydrogen could be a viable alternative, but so much of it would need to be carried that planes would have to be completely redesigned and new infrastructure built.

The idea of using ammonia as aviation fuel isn't new. Though it only has a third of the energy density of diesel, it's relatively easy to liquefy and store, and was already used by the famous X-15 rocket-plane, propelling it into space on a series of suborbital missions in the 1950s and '60s. In addition, it's carbon-free.

The tricky bit is finding an economically viable way to use it in aviation. To solve this problem, Reaction Engines produced a new propulsion system based on the heat exchanger technology it developed for its SABRE hypersonic engine, which was then evaluated by STFC’s Rutherford Appleton Laboratory near Didcot in Oxfordshire.

In this new system, the ammonia is stored as a chilled, pressurized liquid in the wings of the airplane just as kerosene-based fuel is today. Heat harvested from the engine by the heat exchanger would warm the ammonia as it is pumped out and fed into a chemical reactor where a catalyst breaks down some of the ammonia into hydrogen. The ammonia/hydrogen mixture is then fed into the jet engine where it burns like conventional fuel, though the emissions consist mainly of nitrogen and water vapor.

According to Reaction Engines, the energy density of ammonia is high enough that the aircraft wouldn't need significant modifications and the engine could be retrofitted in a relatively short time. A ground-based test is in the works with a first flight possible in a few years.

"The combination of Reaction Engines’ transformative heat exchanger technology and the STFC’s innovative catalysts will enable development of a game-changing class of green ammonia-based aviation propulsion systems," says Dr. James Barth, engineering lead at Reaction Engines. "Our study showed that an ammonia-fueled jet engine could be adapted from currently available engines, and ammonia as a fuel doesn’t require a complete re-think of the design of civil aircraft as we know them today. This means a fast transition to a sustainable aviation future is possible at low cost; ammonia-powered aircraft could be serving the world’s short-haul routes well in advance of 2050."

Source: Reaction Engines

22 comments
C Alvin Scott
Hello, this is not so good, there is the case that the Nitrogen content on Ammonia when combusted joins with oxygen easier than nitrogen in Air as when kerosene is used in a gas turbine so in terms of NOx this is worse option to cut CO2
windykites
Ammonia has been used in road vehicles successfully. I believe it was used in Belgium in WW2 in trams.
It is a noxious gas, but disperses quickly. The article implies that more energy is obtained by separating hydrogen by catalysis, than by burning ammonia (NH3) directly. Is this correct?
Worzel
Why waste so much time and effort, when CO2 is not a pollutant, except in the myths of the mainstream media?
Brian M
The logical way forward is to invest in trying to efficiently create a kerosene substitute that can be used in the current fleet of aircraft from a green processes that fixes as much carbon as is burnt during its use, with energy for the production process coming from renewable/non-carbon source.

nd , i.e fixing the components from th eatmosphere and usign green
Nobody
I wonder if seeding the atmosphere with nitrogen oxides will affect the weather? No one seems to worry about acid rain anymore.
FB36
"Though it only has a third of the energy density of diesel"

Nobody here ever heard of a fuel called "bio-diesel"?
(Which can be easily/cheaply produced from a very wide range of bio-mass & can be also used for all trucks & ships as well as aircraft & would require almost no infrastructure/design changes?)
piperTom
There is a hugely important factor missing from the analysis, so far: cost. Ammonia is already commercially available, so it shouldn't be hard to guess the base cost. But carrying three times (?) more fuel and it being pressurized means increased cost for each flight, even after paying for upgraded tanks and engines.
Food4Thought
I would think that Bio-fuels would offer a better alternative...as a drop-in replacement for Kerosene. As I try to unpack this statement: "In this new system, the ammonia is stored as a chilled, pressurized liquid in the wings of the airplane just as kerosene-based fuel is today." I did not think modern airplanes can store chilled and pressurized fuels. To me this seems like an engineering re-design that would be no small feat...
TechGazer
I hope someone bothers to check the exhaust gasses for the various reactive molecules (NOx and others) and how they would react with the upper atmosphere, before bringing this to market. Remember: CFCs were the wonderful solution to the problems of their time. For that matter, fossil fuels were the answer to the problems of their time.
Expanded Viewpoint
Oh good grief, here we go again!! Ammonia, (NH3) doesn't grow in nature, it's a chemical compound that is created by people in factories. Therefore, it has a "bad Carbon footprint" attached to it. Carbon based fuels are used to generate the electricity that makes the Ammonia. Is everybody following along here? Then, you need trucks that run on Carbon based fuel to haul it hither and yon, unless you have a vast network of piping to deliver it, and again, lots and lots of carbon based fuels are involved, leaving their footprints all over the landscape.
Then, we move on to Oxides of Nitrogen, possibly, as we're not told just how any energy that is invested into the production of the Ammonia is pulled back out of it, nor at what level of efficiency. In short, it's just another boondoggle that will never "get off the ground" no matter how many pretty pictures of it are painted for us to gaze upon and marvel at.

Randy