Can Hydrogen Save the Internal Combustion Engine? Yes, According to These Engineers

Motor Trend

3 days ago

Tesla Semi updates and autonomous trucks might have garnered headlines at this year's Advanced Clean Transportation (ACT) Expo, but behind such electrification a hydrogen-powered future was on full display. Honda unveiled a hydrogen fuel-cell concept big-rig, Hyundai announced the latest evolution of its fuel-cell-powered Xcient Semi, and Toyota revealed plans to run its own fleet of hydrogen fuel-cell trucks in Southern California. However, amidst all the fuel-cell news, we spotted a trend that, if it develops, could save the powerplants traditional car enthusiasts love: internal combustion engines.
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During a seminar focused on hydrogen-powered internal combustion engines (H2 ICE), Volvo, Bosch, Cummins, and Cespira executives highlighted the work their companies are doing to advance H2 ICE development and why the trucking industry in particular is interested in the technology. The arguments in favor of H2 ICE, as far as the trucking world is concerned, center on a few key points: existing mechanical know-how, higher efficiency than fuel cells or EVs in high-speed, high-load, long-haul situations, and less tailpipe emissions than existing diesel- and natural-gas-powered trucks. These efforts mirror those of manufacturers like Toyota, which is developing hydrogen internal combustion engines for passenger vehicles and race cars.
The 'Fuel of the Future,' Today?
More than a few people are familiar with these promises. Many of a certain age grew up reading about hydrogen as the 'fuel of the future.' The most common element in our galaxy, this incredibly combustible fuel was showcased under the hoods of concepts like 1966's GM Electrovan and roadgoing demonstrators like the BMW Hydrogen 7, Mazda RX-8 Premacy, and Toyota Highlander FCHV, all from the 2000s. While the Electrovan and Highlander used hydrogen fuel-cell technology not unlike what's found in today's Toyota Mirai or Hyundai Nexo, the BMW and Mazda were unique because they were powered by internal combustion engines modified to run on hydrogen. In an era when electric cars were far from a sure thing, hydrogen-powered cars seemed like a safe bet.
Theoretically, the conversion from petroleum-based engines to hydrogen ones is easy. Hydrogen engines effectively work the same way as gas or diesel engines do: Hydrogen in either its gaseous or liquid form is injected into a cylinder head via port, direct, or high-pressure direct injection. It's then ignited, with the resulting explosion turning chemical energy into mechanical energy, helping move the vehicle. Suck, squeeze, bang, and blow—the same principle that's propelled cars and trucks for a century.
This is indeed one of the main benefits of H2 ICE that Bosch, Cummins, and Cespira—a joint venture between Volvo Trucks and Westport Fuel Systems—cite.
'One of the big advantages of H2 ICE is technology commonality,' said Cummins fuel delivery system engineering and integration leader, Chad Fohne. 'These engines can be integrated internally in a chassis with minimal modification, so they're shareable with diesel and natural gas engines.… The similarities between H2 ICE and diesel and natural gas products enable repair locations to quickly adapt to supporting H2 ICE vehicles.'
Brett Keppy, a manager/engineer in Bosch's power solutions department, agreed during the seminar. 'When we talk about the different aspects of technology that need to be addressed, calibrated, and refined with a hydrogen engine, you notice all of those different topics are exactly the same as any of us old engine guys have been working on for years,' he said.
There are other advantages besides existing institutional knowledge. From a regulatory standpoint, juridistictions such as the European Union consider H2 ICE vehicles to be 'zero emissions,' while logistically hydrogen fuel can be transported by truck. The latter makes it theoretically easier to supply to some regions where electrical infrastructure is nonexistent and EVs aren't viable, such as large parts of Africa.
The biggest plus as far as drivers are concerned is that the experience of H2 ICE is largely the same as gasoline and diesel internal combustion. Because hydrogen combusts quicker than gasoline, Toyota touts H2 ICE's responsiveness and its ability to 'relay the fun of driving, including through sounds and vibrations' as one of the technology's chief benefits. Cummins' Fohne reports 'diesel-like torque curves' from his company's hydrogen engines. Cespira promises more than just matching the characteristics of existing engines with its high-pressure direct-injection technology, which is used to convert diesel engines into hydrogen ones. The HPDI system—it injects a small amount of diesel as a pilot fuel along with hydrogen—boosted the power output of Scania's CBE1 12.7-liter turbocharged inline-six from 560 hp and 2,065 lb-ft of torque to 600 hp and 2,213 lb-ft while improving engine responsiveness, said David Mumford, the company's senior director. (Of course, this approach does not qualify as zero-emissions.)
Too Good to Be True?
Despite near uniform optimism from industry leaders, many of the issues that have stymied hydrogen development remain in place.
There's a laundry list of roadblocks in H2 ICE's way, beginning with hydrogen on the molecular level. Hydrogen might be abundant, but it has a pesky tendency to attach itself to other elements. That's why you never find a singular 'H' in nature; it's sometimes 'H2,' but hydrogen prefers to be paired with other elements—especially oxygen, forming H2O (water). Or, if we can tap into that final bit of high school chemistry we retained, carbon and another three hydrogens forming the natural gas methane (CH4).
Separating the H molecule from its carbon buddies is incredibly energy intensive and expensive. Today this occurs most commonly via a process called steam-methane reforming, which applies a high amount of heat to natural gas to produce steam that runs through a catalyst to separate it into hydrogen, carbon monoxide, and carbon dioxide. The carbon monoxide and dioxide are then separated from the hydrogen and either released into the atmosphere or stored via carbon-capture technology (though the former is more likely), while the hydrogen remains. Hydrogen produced in this method is called gray hydrogen when the excess carbon is released into the atmosphere along with steam, and blue hydrogen when it's stored via carbon capture.
Like electricity produced via natural gas or coal, neither can truly be considered 'zero emissions.' According to MIT's Climate Portal, about 12 kilograms of CO2-equivelant emissions are released into the atmosphere for every kilogram of gray hydrogen produced, while blue hydrogen emits about 3 to 5 kg of CO2-equivelant emissions for every kilogram of hydrogen.
It is now possible to process hydrogen from water via renewable sources like solar or wind power (green hydrogen) using electrolysis. Electrolysis uses electricity to split hydrogen atoms from oxygen in water, but the process is costly and not done on a significant scale. Producing green hydrogen typically results in about 1 kg of CO2-equivalent emissions for every kilogram of hydrogen produced.
That's Not All
And those are just the hurdles with hydrogen production—there are plenty on the vehicle side of the equation, too, no matter what grade of hydrogen is used. The challenges begin with the form hydrogen fuel takes and continue all the way into the cylinder-head level. Let's start with the tank: Hydrogen fuel comes in two forms, gaseous or liquid. Gaseous hydrogen fuel is relatively easy to plumb directly from tank to engine, but it must be stored in a pressurized cylindrical tank that's difficult to package in a car. It's also the least energy-dense form of hydrogen fuel—liquid hydrogen is 1.7 times denser than gaseous hydrogen, allowing for longer vehicle range (though neither is as energy-dense as gasoline). Liquid H2, however, has problems of its own.
Liquid hydrogen must be kept at a constantly cooled –423.4 degrees Fahrenheit (–253 degrees Celsius) or it will boil off and turn into a gas—that's just shy of the ambient temperature of space, which is approximately –455 degrees F. This presents a few problems: Gaseous hydrogen takes up more space than liquid hydrogen, so without a place to go it'll increase the pressure inside the fuel tank and explode. This is why early liquid hydrogen cars like the BMW Hydrogen 7 couldn't use more than 80 percent of their fuel tanks for fuel and why they incorporated an elaborate pressure release mechanism that vented gaseous hydrogen into the atmosphere from the roof if the tank started boiling off.
The need to keep liquid hydrogen cooled efficiently requires the use of an oval cross-section fuel tank, somewhat negating the fuel's density advantages versus gaseous hydrogen; Toyota says it can fit 1.5 times more liquid hydrogen in an oval tank than it can gaseous hydrogen in a cylindrical tank in automotive applications.
Liquid hydrogen's journey into a cylinder head is also somewhat more complex than gaseous hydrogen's. Fuel pumps are a particularly thorny issue: Hydrogen's small molecular size and the extreme cold combine to make pumping liquid hydrogen incredibly difficult. The pump's piston must be made to extremely tight tolerances and forgo any lubricating oil as it would otherwise foul the fuel. Even then, H2 has a pesky tendency to slip past the pump's piston and eventually break the pump. During its first 24-hour race with the liquid-fueled version of its GR Corolla H2, Toyota had to replace its race car's fuel pump twice.
There are also some hurdles under the hood regardless of which form of this fuel is being used. Hydrogen can be combusted using either port injection or direct injection. The former is easier to implement in existing engines, but hydrogen's higher combustibility and lower density versus gasoline makes backfiring a problem and power output significantly less than comparable gasoline engines. Direct injection requires hydrogen to be pressurized nearly three times higher than port injection, making it more difficult to engineer and eventually homogenize. The benefit, however, is near gasoline-like power output. Most companies working on H2 ICE appear to be focusing their efforts on further developing direct-injection hydrogen engines.
Passing Gas
Then there are emissions, the other hurdle for those looking to hydrogen ICE as an eco-friendly alternative to gasoline.
On the engine side, Cespira says its hydrogen powerplants have been shown to have up to 52 percent thermal efficiency in lab settings without parasitic losses, meaning 48 percent of the hydrogen fuel the engine consumes is turned into waste heat. The company says as a point of comparison that the same engine running diesel can be up to 50 percent thermally efficient. Gas engines are about 25 percent thermally efficient in the real world, while hydrogen fuel cells come in at about 60 percent thermal efficiency (for references, EVs are closer to 91 percent).
There are also tailpipe emissions. Hydrogen engines primarily produce water and oxides of nitrogen (NOx), the former a refreshing drink and the latter a major pollutant. Though produced at a lower level than petrochemical-powered engines, the latter still requires hydrogen engines to be fitted with an exhaust aftertreatment system like diesel exhaust fluid to reduce the amount of NOx emitted. And, annoyingly, trace amounts of carbon pollution are still emitted from hydrogen engines, too, due to their need for lubricating oil.
Fueling is another hurdle for hydrogen's future. While EVs have benefitted greatly yet still not enough from existing electrical infrastructure, hydrogen infrastructure is nearly nonexistent in the U.S. There are just 54 public hydrogen stations in the U.S., with 53 of them in California and one in Hawaii. As a point of comparison, there are 55,568 DC fast-charging stations throughout the country, and more public hydrogen stations have closed than have recently opened. Hyundai is building hydrogen fueling stations for its own use in factory trucks in Georgia, and Toyota has committed to building some for its own fleet of trucks in Southern California, but beyond that, there's been no real movement in making the fuel of the future attainable to average consumers.
Why Now and What's Next?
While H2 ICE supporters face many challenges in front of them, they're also making steady progress with some of the largest technological hurdles.
Toyota, which has competed in numerous races with its GR Corolla H2, introduced a new technology last year it says could solve liquid hydrogen's boil-off problem. It fit the GR Corolla H2 with a self-pressurizing system that collects boiled-off hydrogen in a pressurized tank that's powered by a small hydrogen fuel cell, converting a portion of the hydrogen back into a liquid fuel. The fuel cell is fed by the hydrogen that doesn't get converted, turning that gaseous hydrogen into electricity that powers the pumps needed for the system. The excess is then run through a catalyzer that releases it outside the car as water. Toyota hasn't said how efficient its novel system is and says it is actively seeking partners to help it commercialize and develop its tech.
Aside from racing, Toyota is also trialing a liquid-hydrogen Corolla Cross and gaseous-hydrogen HiAce on roads in Europe and Australia, respectively.
Back in its home country of Japan, Toyota, Mazda, Subaru, Kawasaki, and Yamaha have announced a partnership to collaborate further on H2 ICE development. The first result of that collaboration will be a new 5.0-liter V-8 hydrogen engine developed by Toyota and Yamaha.
Truck makers and suppliers are bullish, too. Some look at H2 ICE as the optimal solution for long-haul interstate freight trucking, and as the needed push to help speed development of hydrogen infrastructure for fuel-cell trucks, which industry experts agree is the more mature technology. Others look at it as just a way of leveraging existing expertise and surviving in a 'decarbonized' future.
Absent governmental regulations, fleet owners we spoke with at the ACT Expo expressed ambivalence about H2 ICE; their primary concerns are operational costs and vehicles' ability to do the job at hand. For many of them, electric, natural gas, and existing diesel trucks appear to be their preference. As for enthusiasts dreaming of hanging onto the emotionally satisfying experience of an internal combustion engine while lessening their environmental impact, H2 ICE could have the potential to scratch that primal itch, but it's going to take serious investment in advancing the technology, commercializing green hydrogen production, and figuring out hydrogen infrastructure to have a chance of overcoming the inertia of electrified vehicles.