There is a lot of talk about the need to cut emissions and meet stricter governmental mandates, which understandably is why more OEMs are taking a more serious look at hydrogen options. Although much of the market is still focused on the potential of battery-powered vehicles, hydrogen fuel cell vehicles offer a viable supplement that is, at least for now, better suited for longer ranges and faster refuelling.
However, hydrogen presents its own set of challenges, and manufacturers need to think carefully about necessary design changes to their onboard fuel systems to meet the added demands of hydrogen. Here are some of the more important considerations when deciding to convert your fuel source.
More green options
Today there are more green power source options than ever before to fuel transportation fleets. Every OEM and fleet operator needs to determine which option works best for a specific application. This means deciding whether to go the route of natural gas (methane) or hydrogen. For the purposes of this article, we are focusing on compressed (not liquid) hydrogen since more manufacturers currently use compressed natural gas (CNG) rather than liquid. To date, there has been more market demand for compressed hydrogen than hydrogen in a liquid form.
Both CNG and hydrogen are gases. They can be used in an internal combustion engine (ICE), and are cleaner than diesel. However, while CNG is cleaner than diesel, it still contains some carbon. Only hydrogen represents the truly zero-carbon solution. On the downside, hydrogen is not as energy dense, so you need to store more of it, and it must be stored at a much higher pressure to achieve the same range. Whereas CNG vehicles typically keep natural gas at pressures of around 250 bar, hydrogen vehicles store their fuel at pressures of 350 up to 700 bar. This higher pressure presents safety and operational challenges.
Increasingly stricter standards
Many components found on a hydrogen vehicle can be validated through HGV3.1 or ISO 19887.S, which is soon to be released. EC-79, which is being phased out and replaced by ISO 19887, is an EU-created certification that ensures the safety and performance of hydrogen equipment under different pressures and electric, mechanical, and thermal conditions. It addresses the pressure containment, performance and safety characteristics of newly produced compressed hydrogen gas fuel system components intended for use on hydrogen-powered vehicles.
Components that have not met these higher standards may not be able to withstand the higher pressures associated with hydrogen-fuelled vehicles.
Hydrogen embrittlement is a reduction in the ductility of a metal due to absorbed hydrogen. Since hydrogen atoms are small and are under tremendous pressure, they can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement.
Lessons from the past
If you are considering converting your fleet to hydrogen, or at least part of it, this may at first seem like an overwhelming task because of all the changes needed in system design and concerns regarding component material compatibility.
However, take comfort in knowing that you do not need to start from scratch in addressing various challenges because, if you are already using CNG to some degree, you have already likely solved some of the challenges you’ll face in using hydrogen. For example, there are already sealing solutions on the market that have been designed to handle higher pressures.
Seal-Lok fittings and adaptors from Parker, for example, were specially created for onboard hydrogen and CNG fuel systems. The Seal-Lok fitting design is approved for 700 bar hydrogen service, and CNG service up to 250 bar. Seal-Lok fittings feature an enhanced flat-face sealing surface and approved O-ring compounds that meet the demands of high-pressure gaseous service. O-rings overall have proven more effective than metal-to-metal connections in maintaining a leak-free seal, despite the challenges of added vibration in over-the-road travel.
Whether you are using natural gas or hydrogen, you need the right filtration system to filter out particulates, oil, water or other contaminants that could otherwise damage the engine or fuel cell. In the more than 20 years that CNG has been used on refuse vehicles, we have learned how to convey fuel effectively, control it, and filter it. In addition, we have learned how to store fuel safely on the vehicle at high pressures, often using specialty hoses and seamless stainless steel tube assemblies that have proved effective for the task.
Advantages of fuel cells
A key difference is in the number of nitrous oxides released as part of the reaction when burning fuel in an internal combustion engine (ICE). Fuel cells convert the chemical energy in hydrogen directly into electricity, with pure water and useful heat as the only byproducts. With a fuel cell, you are not burning anything. Rather, the chemical reaction generates electricity that charges the onboard battery, so the only emission is water. Hydrogen fuel cells can act as effective range extenders, because they operate more efficiently than an ICE, possessing more than two times the efficiency of traditional combustion technologies.
Powering the transition to zero emissions
Renewable energy technologies have reached a level of maturity that allows competitive renewable electricity generation all around the world, a prerequisite for competitive green hydrogen production. However, hydrogen engines and hydrogen fuel cell technologies have various levels of maturity. From the perspective of OEM and fleet operators, the switch to a hydrogen-fuelled internal combustion engine (ICE) provides a common base line of parts and technology. This level of familiarity will provide a lower initial cost to convert to hydrogen. A hydrogen fuel cell electric vehicle (FCEV) has the added cost and complexity of an on-board battery and thermal management system.
However, FCEVs and hydrogen ICEs are not competing with one another. The development of one supports that of the other since both require a common hydrogen infrastructure. They are complementary technologies that are part of a gradual transition to reducing vehicle emissions. “When the green era finally takes hold, the hydrogen ICE will provide a bridge to the future use of emission-free FCEVs, taking full advantage of the hydrogen infrastructure created along the way,” says Steve Duricky, global platform manager of Parker Hannifin Fluid Connectors Group.
The right partner makes all the difference
Committing to convert on-board fuel systems to hydrogen is not a decision to be taken lightly. There will need to be system design changes and also component upgrades. In some cases, you may also need to retrain your teams on maintenance protocols and procedures.
By choosing the right partner, these challenges can be minimised. Make sure your suppliers have experience working specifically with hydrogen. Parker, for example, has been working with hydrogen applications for more than 60 years. We have an entire portfolio of products that have gained EC-79 certification, and soon many of these products will be approved according to the newer standards. In fact, our people have been actively involved in developing the new standards. That means greater confidence for you as you move forward in designing an efficient, safe and leak-free green fuel system with Parker at your side.
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