Hydrogen Internal Combustion Engines and Hydrogen Fuel Cells

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January 31, 2023

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by Jim Nebergall (Cummins) ... (B)oth hydrogen engines and hydrogen fuel cells are receiving an increasing interest. Given medium and heavy-duty trucks are a major source of CO₂ emissions, the transportation sector’s journey to destination zero features both technologies.

As more truck makers join the ranks of auto companies developing CO₂-free or CO₂-neutral alternative to gasoline and diesel vehicles, let’s look at the similarities and differences between hydrogen engines and fuel cells.

Hydrogen engines and fuel cells: Similarities and differences in how they work?

Both hydrogen internal combustion engines and hydrogen fuel cells can power vehicles using hydrogen, a zero-carbon fuel.

Hydrogen engines burn hydrogen in an internal combustion engine, in just the same way gasoline is used in an engine. Hydrogen internal combustion engines (Hydrogen ICE) are nearly identical to traditional spark-ignition engines. You can read more about how hydrogen engines work if interested.

Fuel cell hydrogen vehicles (FCEVs) generate electricity from hydrogen in a device known as a fuel cell, and use that electricity in an electric motor much like an electric vehicle.

Hydrogen engines and fuel cells: Complementary use-cases

Hydrogen engines and hydrogen fuel cells offer complementary use cases.

Internal combustion engines tend to be most efficient under high load—which is to say, when they work harder. FCEVs, in contrast, are most efficient at lower loads. You can read more examples of hydrogen engines in mobility and transportation. These range from heavy-duty trucking to construction.

So, for heavy trucks that tend to spend most of their time hauling the biggest load they can pull, internal combustion engines are usually the ideal and efficient choice. On the other hand, vehicles that frequently operate without any load—tow trucks or concrete mixer trucks, for example, may be more efficient with a fuel cell. Fuel cell electric vehicles can also capture energy through regenerative braking in very transient duty cycles, improving their overall efficiency.

Hydrogen engines can also operate as standalone powertrain solutions and handle transient response demand without the need for a battery pack. Fuel cells combined with battery packs can also accomplish the same.

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Hydrogen engines and fuel cells: Similarities in emissions

Hydrogen engines and hydrogen fuel cells also have similar emissions profiles.

FCEVs, actually, produce no emissions at all besides water vapor. This is a very attractive feature for vehicles operating in closed spaces or spaces with limited ventilation.

Hydrogen engines release near zero, trace amounts of CO₂ (from ambient air and lubrication oil), but can produce nitrogen oxides, or NOx. As a result, they are not ideal for indoor use and require exhaust aftertreatments to reduce NOx emissions.

Hydrogen engines and fuel cells: Hydrogen fuel considerations

Yes, both hydrogen engines and fuel cells use hydrogen fuel; but there is more to this story.

Hydrogen engines often are able to operate with lower grade hydrogen. This becomes handy for specific use cases. For example, you might have a site where hydrogen can be produced on site using steam methane reforming and carbon capture and storing (CCS). This hydrogen then can be used in hydrogen engines without the need for purification.

The hydrogen engine’s robustness to impurities is also handy for a transportation industry where the transition to high quality green hydrogen will take time.

Hydrogen engines and fuel cells: Varying maturity levels

Finally, hydrogen engines and hydrogen fuel cell technologies have different levels of maturity.

Internal combustion engines have been universally used for decades and are supported by extensive service networks. Rugged engines that can operate in dusty environments or that can be subjected to heavy vibrations are available in all sizes and configurations.

From the perspective of vehicle manufacturers and fleet operators, the switch to hydrogen engine drivetrains involves familiar parts and technology. Risk-averse end-users will find comfort in the tried-and-tested, reliable nature of internal combustion engines.

So it is not really the case that FCEVs and hydrogen ICEs are competing with one another. On the contrary, the development of one supports that of the other, since both drive the development of a common hydrogen production, transportation, and distribution infrastructure. Both also involve the same vehicle storage tanks. They are complementary technologies that are part of reducing vehicle and transportation emissions towards destination zero, now. READ MORE

How do hydrogen engines work? (Cummins)

Hydrogen Internal Combustion Mobility is Here (Advanced Clean Tech News/Westport Fuel Systems)

Excerpt from Cummins: In fact, one of the very first internal combustion engines ran on a mixture of hydrogen and oxygen—and featured an electric spark ignition mechanism. Its inventor, a former Swiss artillery officer named François Isaac de Rivaz, used it to build a vehicle that could carry heavy loads over short distances.

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Four-stroke hydrogen internal combustion engines (Hydrogen ICE) operate on the same cycle as regular natural gas engines and have almost the same components—engine block, crank, cylinder heads, ignition system, installation parts, and so on.

Diesel engines and hydrogen engines also share similar components. These include an engine block, crank, and installation parts such as mounts and flywheel housings.

At Cummins Inc., we are leveraging our existing platforms and expertise in spark ignited technology to build hydrogen engines. Our hydrogen engine is a spark ignited engine variant with similar engine hardware to natural gas and gasoline engines.

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For example, differences in the physical properties of hydrogen impacts how fuel and air are metered and injected. Pre-ignition is a greater problem for hydrogen engines than for gasoline engines, because hydrogen is much easier to ignite. Direct injection is one way to overcome pre-ignition issues. Direct injection systems introduce fuel–hydrogen, in this case –directly into the cylinders, rather than into the intake manifold or ports. If the injection takes place at a time when the inlet valve is closed, backfire conditions are avoided. Another solution is to completely design the combustion system for hydrogen.

Another consideration is the formation of nitrogen oxides, or NOx. NOx is an atmospheric pollutant which can cause poor air quality and lead to the brown-orange haze that forms above some large cities in the summer.

When hydrogen burns in the presence of lots of oxygen, very little NOx is formed. However, when hydrogen burns with air fuel ratios that are near stoichiometric, a significant amount of NOx can be created. As a result, hydrogen engines are typically tuned to run lean with an excess air ratio of 2 or greater. This means that approximately twice as much air needs to be supplied to the cylinders than for a stoichiometric engine. Hydrogen engines often require an exhaust treatment system to remove this excess NOx.

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Hydrogen engines look, sound and work like the internal combustion engines that every mechanic in the world is used to. Their reliability and durability are equal to that of diesel engines.

Cummins is currently testing hydrogen engines to mitigate the risks of hydrogen embrittlement and erosion. We will share our findings as our tests progress.

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So, you might not know immediately that a vehicle is designed for hydrogen if you saw its engine, but if you saw its fuel tank, you would know right away. Storing hydrogen onboard motor vehicles is safe and becoming more economical and practical. Cummins has recently formed a joint venture with NPROXX, a leader in hydrogen storage and transportation for hydrogen storage tanks. This joint venture will provide customers with hydrogen and compressed natural gas storage products for both on-highway and rail applications. READ MORE

Excerpt from Advanced Clean Tech News/Westport Fuel Systems: There are many similarities between the internal combustion engine running diesel and the hydrogen ICE, making them a comfortable transition for OEMs and fleets alike.

An internal combustion engine burns hydrogen in much the same way it burns diesel
The range and refueling times are comparable
The ICE performs best at consistent high loads with either diesel or hydrogen making it the ideal solution for long-haul applications
Diesel and hydrogen engines share similar componentry creating scale benefits

The above outlines the viability of transitioning to hydrogen ICE from an operational and economic standpoint. Other key motivators include that for OEMs, hydrogen engines offer ease of adaptability in heavy-duty applications by utilizing existing vehicle architectures. For fleets, they are a known technology in operation, troubleshooting, maintenance, servicing and drivability, all offering a high level of familiarity. Moreover, for both OEMs and fleets, the existing and established ICE supply chain can be leveraged efficiently.

By leveraging existing technologies and supply chains, the commercial transportation industry at large can take comfort that the time-tested, reliable ICE can live on with new fuel and new purpose.

Big Solution. Small Change.

H₂ HPDI, or High Pressure Direct Injection, provides complete injector “tip-to-tank” OEM solutions that allow the same internal combustion engines that are in fleets now, the ability to shift the system to run on hydrogen instead of diesel. The system, when fueled with hydrogen, offers more power and torque than diesel while dramatically reducing emissions. Westport’s H₂HPDI fuel system provides the following benefits:

Up to 20% more power than diesel
Up to 18% more torque than diesel
Near zero CO₂ emissions
Preserves existing diesel engine architecture
Preserves existing engine manufacturing infrastructure and investment
Lowest cost to achieve CO₂ compliance

H₂ HPDI is the most cost-effective way to reduce CO₂ emissions in long-haul trucking and other high-load long-haul applications. The system can utilize existing manufacturing infrastructure, with reduced capital investments, thus expediting time to market. The rapid scaling of production means H₂ HPDI can quickly be deployed, further stimulating the demand for hydrogen and accelerating the reduction of cumulative GHG emissions.

Westport Fuel Systems is a leading supplier of advanced fuel delivery components and systems for clean, low-carbon fuels such as natural gas, renewable natural gas, propane, and hydrogen to the global transportation industry. To learn more about our technologies, visit www.westport.com. READ MORE