Figure 1 (above) – A concept aircraft using ammonia as a fuel

In our pursuit of exciting stories about Green Aviation, we found two interesting stories that pointed in the same direction – that of using ammonia to fuel jet engines.

The first part of this story comes from:

“Compared to hydrogen, ammonia is far easier and cheaper to transport and store, even though it can only carry roughly 20% of the energy that hydrogen does by weight. But on the flip side, it can carry roughly 70% more energy than liquid H2 in volume, according to the report. Typically, the problem of weight usually rules out ammonia when it comes to new aviation technologies. It has less than half the specific energy of jet fuel; it appears less appealing than hydrogen. But hydrogen has issues with volume: modern airliners are made for jet fuel, which makes the idea of retro-fitting large-volume and long-range hydrogen tanks (challenging).”

A U.K. company, Reaction Engines, is preparing for this potential industrial shift by joining with other partners, some of whom are funded by the U.K. government. Their technology proposal aims to employ a heat exchanger technology which captures heat from the jet engine’s exhaust and then uses it to generate power for the onboard cracking reactor. This reactor catalytically converts pure ammonia into a blend of ammonia and hydrogen, which are then combusted. The combustion products of this new engine will be nitrogen and water.

Burning ammonia and hydrogen creates nitrous oxides. NOx emissions are known to harm humans and animals, as well as making smog and acid rain. Ammonia-based aircraft engines could provide a viable alternative to hydrogen in budding companies that are pursuing cleaner attempts at commercial aviation and space ventures.

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The second part of this story comes from New Atlas

Two innovators from Australia are proposing to deploy ammonia as the fuel source for a Falcon 50 business jet and they plan to fly by mid-2023.

Figure 2: Aviation H2 directors, brothers Christof (left) and Helmut Mayer, with a Falcon 50 business jet, propose to be flying on ammonia by mid-2023

Source: New Atlas

To these innovators, ammonia is a promising energy carrier and future fuel with exciting potential for decarbonizing other sectors such as shipping and rail. And they feel that it has potential for aviation as well. Ammonia is the second-most produced chemical globally and is primarily used as a fertilizer. However, aerospace innovators are considering its usefulness as a source of green hydrogen.

Aviation H2 has zeroed in on the potential of ammonia as a combustion fuel. With a few modifications, a regular jet engine can be converted to operate on ammonia which will does not produce carbon dioxide. It is posited that using ammonia will be much faster and cheaper than a hydrogen fuel cell conversion. Fuel cell conversions require replacing jet engines with electric motors, as well as changing out the entire fuel storage system. This is a sharp contrast to only modifying aircraft systems that will use ammonia.

Figure 3: The fuel system schematics of an ammonia-based jet engine

Source: New Atlas

The fuel system will require some ammonia to be cracked into hydrogen before being fed into the turbofan engine. Engine exhaust heat will then be routed into the ammonia cracker.

The two innovators recognize that it will be necessary to modify the fuel storage system into something similar to an LPG tank. Additionally, the fuel storage, the engine control, and the engine itself are the big-ticket items that need to be developed.

The company’s initial target is to get a small regional nine-seat jet built, and flight tested. After three months of feasibility studies, the company has signed an agreement giving Aviation H2 access to hangars, facilities and operating licenses.

As far as range goes, the initial plan is to build an aircraft capable of hour-long flights, with the same engine thrust and performance characteristics as using Jet-A fuel.

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