September 24, 2023
By Oraan Marc

Hydrogen Internal Combustion Engines Seem To Be Regaining Momentum

Some agree that batteries are the clear winner in the race against hydrogen technologies, while others think the opposite. There's no such debate among internal combustion engine proponents. Almost all of them believe that replacing fossil-fuel-based fuels with H2 is feasible. However, there are some significant caveats to H2ICEs.

The Latin phrase "Inter duos combatentes, tertius vincit" translates to "between two combatants, the third wins." I always feared the fierce debate between battery-electric propulsion enthusiasts and hydrogen-powered systems supporters would benefit the internal combustion engine devotees.

And I was not wrong, as recently, e-fuels seduced many to believe that phasing out of an almost obsolete technology is not necessary anymore. Moreover, these people believe that internal combustion engines deserve not only a top spot in history but also a bright future, along with new high-tech-green technologies.

That's because many in the transport industry and policymakers believe more and more in the potential of combining hydrogen and ICEs.
The fuel-cell sand castle
Currently, Toyota is the most stubborn carmaker willing to keep on investing big money in hydrogen technology for passenger cars. Besides small evolutions in fuel-cell technology – which are marketed as giant leaps, but analysts agree it's not the case – the Japanese also make efforts to use hydrogen for internal combustion engines.

BMW and Hyundai are still in the game, but the new iX5 Hydrogen demonstration vehicles failed to impress, while Hyundai Nexo's future is uncertain. Honda took everyone by surprise when the main rival of Toyota in the fuel cell realm announced it put the hydrogen program on hold to prioritize hybrids and EVs.

As for Volkswagen, their conclusion is sharp: "In the case of the passenger car, everything speaks in favor of the battery, and practically nothing speaks in favor of hydrogen." Mercedes-Benz also joined the "ditch the fuel-cell" bandwagon after 30 years of pursuing the H2 dream.

But you'd be wrong to think EV fanboys were right and batteries prevailed. For now, this is the case regarding passenger cars and light-duty vehicles: electric propulsion is more feasible thanks to fast improvements in the battery sector, while hydrogen fuel cell propulsion is still far from an economically viable option.

But road transportation is not all about the more than 1.3 billion cars worldwide. There is also heavy road transport consisting of millions of big trucks and lorries, buses and coaches, and all sorts of other heavy vehicles used in agriculture, construction, mining, and so on.

What do these heavy road vehicles all have in common? Big diesel engines. At least one-quarter of the transportation pollution and emissions are attributable to them. If only there would be a solution to convert them almost overnight into close-to-zero-polluting vehicles…
The caveats of using H2 in an ICE
The fuel cell is a "magical" device that combines hydrogen stored in tanks aboard the vehicle and oxygen in the air, resulting in electricity and water vapor. The electricity is used to power one or several electric motors, and that's your zero-emissions vehicle.

However, fuel cells must be fed with pure hydrogen, which is very expensive. It will most likely remain a costly fuel despite the expected drop in costs when economy of scale will apply. Fuel cell systems are also costly and require more complex manufacturing processes and expensive raw materials like batteries.

In other words, fuel cells for heavy-duty applications still require a lot of research and investments to become feasible. At this point, batteries have a clear edge but also many downsides for being a compelling alternative to diesel engines in heavy vehicles.

Is there a third option to decarbonize heavy road transport? Yes, in theory. We could replace diesel fuel with hydrogen. It's not a new idea, as the first internal combustion engine fueled by a mixture of hydrogen and oxygen was invented more than 200 years ago. But let's get back to our times.

While H2 has over 2.5 times more specific energy than fossil-fuel-based fuels, it also requires four times more volume to store as liquid and up to 19 times more as gas. Using H2 in a heavy-duty engine would lead to an achievable efficiency of 20-25%, almost half that using diesel fuel.

Then, there's the problem of the hydrogen-air mixture ratio in the combustion chamber, as hydrogen ignites much easier than gasoline or diesel fuel. Also, twice as much air must be supplied to the cylinder to keep NOx emissions lower, while the combustion process temperature must not be too high.

All of these require a specific design for the direct injection system and the combustion system, as well as exhaust treatment solutions. Remember that an ICE needs lubricants, which also burn in small amounts in the cylinder.

In the end, burning H2 in an ICE doesn't make the vehicle a zero-emissions one, but it supposedly can slash emissions by a large margin. You could say it's the same "near to 90%" reduction the e-fuels promise.
The investment-benefits ratio is more and more interesting
In the last decades, hydrogen was mainly used as a mixture additive for traditional fossil fuels. CO2 emissions were somewhat reduced, justifying the cost increase for technical modifications. But now, the need to slash emissions is much more stringent.

In light of recent evolutions, the European Commission decided to modify the CO2 emissions standards for heavy-duty vehicles this year. Even though H2ICE is not zero-emission, heavy-duty vehicles using this engine type will be considered zero-emissions.

On one condition: the hydrogen used by H2ICE heavy-duty vehicles must be genuinely a carbon-free fuel. It means it can't be sourced from fossil fuels. As a reminder, more than 95% of the hydrogen used today in the industry comes from natural gas, so it's carbon-intensive "black hydrogen."

Of course, there's nothing more but a huge coincidence that the EU accepted to allow European carmakers to manufacture ICE cars beyond 2035 if e-fuels fuel them. But let's stay optimistic about H2ICE, shall we?

Following the EU-funded H2Engine project, between 2020 and 2022, the German company KEYOU developed a solution to convert conventional diesel engines into much cleaner hydrogen. Earlier this year, such a converted engine was used by Mercedes-Benz Special Trucks in a Unimog prototype.

In September, KEYOU started the first deliveries of their 18-tonne truck equipped with a hydrogen engine, based on the Mercedes Benz Actros. The six-cylinder converted diesel engine has a fuel consumption of 7.5 kg H2 / 100 km, and the fuel is supplied via port fuel injection, designed specifically for using hydrogen.

KEYOU claims that efficient lean-burn combustion keeps the NOx levels well below limits, and the converted engine meets Euro VI standards and the new EU's CO2 requirements. As a result, the truck is exempt from truck tolls, saving fleet operators "up to €15,000 in tolls per year."

American corporation Cummins is also providing heavy-duty vehicles with hydrogen internal combustion engines. Their latest product is the X15H hydrogen engine designed to fit heavy-duty trucks up to 44 tonnes, providing an impressive peak torque of 2,600 Nm.
New paradigm: H2ICE vs. fuel cell?
Because passenger cars (and especially SUVs) gather public attention, it's only normal that ICE vs. batteries or batteries vs. fuel cell subjects spark so many fierce debates. In the meantime, the real problem we face is achieving transport decarbonization faster.

Using hydrogen as a fuel in big engines for heavy-duty vehicles suddenly became a top priority. It requires far less money than replacing those vehicles with electric ones or powered by fuel cells. Converting their diesel engines into hydrogen-fueled ones takes much less time than developing similar vehicles using cutting-edge green technologies.

H2ICE really seems like the best solution for the short and medium term to slash emissions in heavy-duty road transport. Of course, we should also avoid sourcing hydrogen from fossil fuels. Still, I believe the industry will require that compromise – hopefully for a short time until green hydrogen infrastructure is more developed.

I only wish we understood that H2ICE must be perceived only as a transitory solution. Just as e-fuels ICEs should be perceived. H2ICE must pave the way for fuel cells, not become an alternative in the long run.

The internal combustion engine's time is up. It had a tremendous role in our technological evolution, just like fossil fuels did. But it's time to acknowledge that ICE is obsolete technology, just like burning fossil fuels hugely damages our environment.