It’s becoming increasingly likely that the internal combustion engine (ICE), which has served the transport industry so well for 100-plus years, will continue to be a key enabler in the industry’s pursuit of decarbonization.

However, the fuels burned within an ICE engine will need to become fossil-free, and hydrogen is a leading candidate to meet this requirement. Hydrogen is often associated with fuel cells, but hydrogen ICE (H2-ICE), brings some inherent advantages over the complexity of fuel cells.

The base engine design offers parts commonality with today’s diesel and natural gas engines for OEMs, and the associated familiarity for end users.

The cost to upgrade therefore is more palatable to customers and offers more diesel-like performance attributes related to power and range. H2-burning engines also can withstand higher levels of hydrogen impurities than can fuel cells, adding reliability and peace of mind, especially in dirty environments.

These and other considerations related to H2-ICE were discussed during a webinar and related white paper produced by the Engine Technology Forum.

“Today, we find ourselves in the midst of an energy transition,” noted Engine Technology Forum executive director Allen Schaeffer. “One the one hand, we have an energy system that relies heavily on fossil fuels. On the other hand, we are working toward a system of reduced carbon emissions and energy systems reliant wholly on renewable energy. Internal combustion engines uniquely have one foot in both of those worlds.”

Dr. Ameya Joshi authored the white paper and addressed webinar attendees, acknowledging hydrogen will play a key role in the decarbonization of trucking.

“There’s room for a role for all fuels to participate in decarbonizing the transport sector,” he said. “It’s a hard problem, and we certainly need new fuels to address decarbonization. We’re not going to have one technology that solves the problem.”

H2-ICE stacks up well against fuel cells and other zero-emission alternatives such as battery-electric powertrains, but has some challenges to overcome. For one, it’s not a purely zero-emission solution, at least not according to the U.S. EPA. While H2-ICE produces no carbon or soot emissions, it does create traces of NOx and relies on a small dose of pilot fuel – normally diesel – during ignition.

The associated NOx emissions can largely be addressed through exhaust aftertreatment systems not unlike those found on diesel-fueled trucks today, albeit simpler such systems, since soot is non-existent and NOx levels already low.

Dmitri Konson, vice-president, global engineering at Tenneco said, “We will have an aftertreatment system that will be similar to many of the systems that are on the road today, but will be tailored to the temperature ranges, the duty cycles, and the flow rates that we will see from these new engines.”

This will drive down tailpipe emissions to extremely low levels, Konson said, adding “We’re talking the fourth decimal place here.”

In Europe, the standards for zero-emission vehicles have been recently redefined to levels that would allow H2-ICE engines to qualify as such. The U.S. EPA, however, doesn’t currently consider H2-ICE technology to meet the ZEV designation that would allow it to meet future ZEV requirements or the related incentives granted to battery-electric or fuel cell vehicles.

Another challenge remains the cost and availability of hydrogen, particularly of the green variety.

Fueling stations lacking

“If the energy used to create the fuel is renewable, it’s a well-to-wheel story of zero and a tailpipe story of zero – so, zero carbon at the tailpipe and zero carbon well-to-wheel,” said Jim Nebergall, general manager of the hydrogen engine business with Cummins.

But, about 99% of hydrogen produced today is derived from fossil fuels – usually natural gas and coal. There’s also a lack of fueling stations that can accommodate heavy trucks, meaning hydrogen may initially have to be transported long distances, which is expensive and carbon intensive.

The Engine Technology Forum white paper notes that of 1,000 hydrogen fueling stations that exist today, nearly 60% are in China, Japan and South Korea. There are only 59 retail stations in the U.S., mostly in California and most designed for passenger vehicles and unable to meet the dispensing requirements of heavy trucks.

Hydrogen is significantly more expensive to produce than diesel. The U.S. Department of Energy has set a target of making it available for US$1 per kg by the end of this decade, the white paper reports, and to that end has offered incentive programs to subsidize the production of green hydrogen through electrolysis.

Hydrogen cost estimates range

The EPA, however, is less optimistic, estimating the cost of hydrogen production, distribution, storage and dispensing will likely be more like US$4-$7 per kg by 2030.

“There is large uncertainty in these estimates and there are other research groups who have provided much lower and much higher estimates of the cost,” the white paper suggests.

While the industry does not yet have widespread access to affordable green hydrogen, Louise Arnold, product line director at chemical producer Johnson Matthey, notes H2-ICE’s ability to withstand impurities that fuel cells cannot, mean those engines can be fueled by any form of hydrogen while production of green hydrogen ramps up.

“The great thing about a hydrogen combustion engine is it can use any of them,” she said, referring to the spectrum of colors available today (see sidebar). “So, as we progress to getting the maximum green hydrogen – the one that’s made from renewable electricity – we can enable the investment in the infrastructure and the market that’s going to drive that demand [for hydrogen].”

While hydrogen fuel cells will continue to be an answer in some applications going forward, Cummins’ Nebergall said H2-ICE will offer a “complementary solution.” He added, “A lot of people view this as competition between a fuel cell and an engine, but they’re quite complementary.”

“There is no silver bullet solution to decarbonize all segments,” the white paper concluded, and “H2-ICE will play a key role in the transition away from fossil fuels.”