Revolutionizing the Diesel Industry: The New Hydrogen Engine from Aquarius Engines

Aquarius Engines announced in 2021 that it had tested a lightweight free-piston linear engine running on hydrogen. Worth stating plainly up front: the performance, lifespan, and maintenance figures attached to it are the company’s own claims about a prototype, not independently verified results, and we’re repeating them here as claims rather than as facts.

As a shop that has been working in the diesel repair industry for years, we pay attention to this kind of announcement — while keeping in mind how many promising engine technologies have been announced and never reached production.

The interesting part of the pitch is genuinely interesting: hydrogen used in combustion rather than in a fuel cell sidesteps some of the cost and materials problems that have held fuel cells back.

But the design is frequently described wrong, including in an earlier version of this page. It is not hydrogen injected into a conventional diesel engine’s intake and burned alongside diesel fuel. It’s a free-piston linear engine — no crankshaft, a piston moving between opposed combustion chambers and generating electricity directly — running on hydrogen as its fuel. That architecture is what makes it light and simple, and it’s also what makes it a very different machine from anything in a truck today.

Which points at the honest caveat: a small linear generator is not a drop-in replacement for a 15-liter diesel in a Class 8 truck. Even if every claim holds up, the nearest applications are range-extender and stationary-power roles, not repowering the fleet.

We will be keeping a close eye on the progress and development of this technology, and we are excited to see how it could potentially change the diesel industry for the better.