At this point, if you are at all a fan of EngineLabs, you know we are fans of hydrogen combustion technology. We’ve brought you several different stories covering various iterations of the technology in different applications. So, when we ran across this Jason Fenske video covering Yamaha’s new hydrogen combustion outboard engine, our ears perked up.

If you aren’t familiar with hydrogen combustion, the first part of the Engineering Explained video covers the operational cycle and injection theory behind a hydrogen combustion engine. Then, once that is sorted he moves on to this awesome new technology demonstration project between Yamaha, Roush (yes, THAT Roush), and Regulator Marine.

For this particular project, the hydrogen will be stored in three 700 bar (10,152 psi) tanks plumbed in parallel, with the gas pressure regulated pre-injection to 100 bar (1,450 psi). From there, the system used direct injection to get the compressed hydrogen into the cylinders, in a similar fashion to gasoline direct injection, but sans fuel pumps.

The outboard engine itself is a 5.6-liter (341 ci) V8 engine that Yamaha has a gasoline variant of already, highlighting the adaptability of hydrogen compression to existing engine designs. In gasoline form, the engine produces about 450 horsepower from the factory. In theory, that same output is achievable with hydrogen, but the challenge is matching that performance, exactly, in an engine that was originally designed for gasoline.

Unfortunately, Yamaha has not released any performance figures, official or otherwise, on the hydrogen-powered concept boat. But, fortunately, that’s where Fenske comes in clutch, doing some of his trademark whiteboard math to make some educated guesses. Starting with the size of the tanks, Fenske starts running the numbers on fuel capacity, and hydrogen’s energy density (roughly one kilogram of hydrogen has the same energy as a gallon of gasoline), coming up with a range of the prototype at about a quarter of that of the production gasoline model.

Designed by Roush, the current fuel system configuration uses no pumps to transfer hydrogen from its 10,000psi storage tanks to the injectors (after being reduced to 1,450 psi). The problem with using pressure alone is that each tank is effectively “empty” with about 20 percent of the fuel remaining in the tank. Even with the three hydrogen tanks plumbed in parallel, once the system hits the 1,450 psi injector pressure, the remaining hydrogen is effectively unusable.

Where the issue lies, is the 700 bar storage pressure. The volume of gas at the storage pressure is such that the storage space required to get the same amount of energy as the 107-gallon gasoline tank, would be pretty significant, as you’d need 13.5 of the tanks being used in the boat currently, as opposed to the three that have been fit to the hull, currently.

As Fenske points out, this is early in the prototype phase, and there are a number of ways to increase the hydrogen capacity that are relatively easily implemented, ranging from bespoke tank design and configuration, to higher-pressure storage. While hydrogen as a fuel isn’t necessarily a difficult conversion, mechanically, the storage of the hydrogen has proven to be a considerable challenge. Fenske dives into that subject pretty deeply in the last few minutes of the video.

As the use of hydrogen as a combustible fuel continues to mature, it appears that the larger engineering issues right now are on the storage side, rather than the mechanical applications. The exciting part is that companies like Yamaha and Roush believe in hydrogen combustion enough to sink significant resources into research and development to advance the technology and solve engineering issues as they arise.

Just to accommodate the three hydrogen tanks being used, significant structural alterations to the vessel are required. These are off-the-shelf fuel tanks, so they are not optimized for this particular application. While this technology demonstrator will be able to make the same power as its gasoline-fed production counterpart, it would require 10.5 more of these tanks pictured to equal the range of the gasoline version with a 107-gallon gas tank. There are some creative ways to increase the volume of hydrogen storage, and that will likely be the focus of most of the engineering going forward.