How steam injection in gas turbines could help green aviation

By adapting steam-injection technology, long used in industrial power, for flight, the company claims it can unlock dramatic efficiency gains while tackling both CO₂ and overlooked non-CO₂ emissions.

From its new base in Toulouse-Blagnac, at the heart of Europe’s aerospace ecosystem, French startup Viraj Aero is positioning its first engine, Eyja, as a scalable breakthrough. 

Enlit asked the company’s founder, Joseph Risson, about the engineering challenge, the role of hydrogen, and why aviation’s biggest climate impacts remain underappreciated.

How does your steam-injection technology work, and why is it a breakthrough?

Steam injection in gas turbines isn't new; it has been used in industrial power plants since the 1980s because it simultaneously increases thrust, improves thermodynamic efficiency, and significantly reduces NOₓ emissions. 

What we've done at Viraj Aero is something no one has achieved before: engineer this process specifically for aeronautical use.

The core challenge is the water source. Water tanks are too heavy to be viable aboard an aircraft. Instead, we condense the water naturally present in the exhaust gases and reinject it. This creates a closed-loop cycle: all the water we inject, we recover, effectively an unlimited water supply with no tanks required.

The result is a fundamentally more efficient engine that reconciles environmental and economic constraints, making it viable at scale, and all this without requiring a complete architectural reinvention of either propulsion systems or aircraft.

How does Eyja overcome the efficiency plateau in aviation propulsion?

The aviation industry has squeezed out marginal gains through incremental improvements in blade geometry, materials, and combustion chambers but we've largely hit a wall on thermodynamic efficiency with conventional approaches.

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Eyja, our first product, attacks the problem from a different angle: by injecting steam into the cycle, we increase the working fluid mass in the turbine without burning more fuel. This unlocks efficiency gains that conventional combustion optimisation simply can't reach. 

We're talking up to 30% fuel savings compared to today's turboprops: that's not a marginal improvement; that's a step change.

How do steam injection and hydrogen operation complement each other?

They're almost made for each other. 

Hydrogen combustion produces roughly 2.5 times more water vapour than kerosene and, in our architecture, that water is exactly what feeds the steam injection system. So, the more hydrogen you burn, the more steam you can inject, and the more efficient the cycle becomes. 

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It's a virtuous loop. In the near term, steam injection delivers immediate gains on conventional or SAF-powered aircraft. In the long term, hydrogen takes those gains even further. One technology roadmap, two fuel strategies both pointing in the same direction.

How does your move to Toulouse-Blagnac accelerate development?

Being at the epicentre of European aerospace means direct proximity to Airbus, ATR, tier-1 suppliers, certification bodies, and an incredibly dense talent pool. We went from testing in lab environments to operating in a real airport hangar, on actual runway infrastructure. 

That proximity to the industrial ecosystem compresses timelines considerably.

How critical is it to address non-CO₂ effects like NOₓ and contrails?

It is absolutely critical, and it's one of the most underappreciated issues in aviation decarbonisation. 

CO₂ gets all the headlines, but the scientific consensus is that non-CO₂ effects, NOₓ, contrail formation, and associated cirrus cloud formation account for roughly two-thirds of aviation's total warming impact. If you only fix CO₂, you've addressed maybe a third of the problem. 

Our 50% total climate impact reduction figure specifically accounts for these non-CO₂ effects. Steam injection inherently lowers combustion hotspots, which directly reduces NOₓ formation. 

We didn't engineer this as a side benefit; it was a core design objective from day one.

What inspired you to start Viraj Aero, and what advice would you give to other engineers building climate-tech ventures?

Aviation is the hardest sector to decarbonise, and that's exactly what drew me to it. 

During my work in fluid dynamics, I kept coming back to steam injection as this elegant, under-explored solution sitting right in front of the industry. Nobody had seriously pursued it for aeronautical applications, and I couldn't understand why. 

So, I decided to do it myself. 

My advice to engineers wanting to build in climate tech: Find something economically compelling that also happens to be great for the planet. That's how you'll have a real impact.