The H966 is Liebherr’s 6-cylinder motor with port fuel injection. (Liebherr)

Liebherr goes all in on hydrogen fuel

Liebherr has invested heavily in the development of hydrogen-fueled engines to decarbonize the off-highway sector.

At the Bauma conference in late October, Liebherr displayed two prototype H2-fueled engines, the H964 and H966, to showcase its hydrogen-engine technology. Each prototype employed a different hydrogen injection technology, direct injection (DI) and port fuel injection (PFI). Liebherr states that it has made “significant investment” into the development of its hydrogen engines and test facilities and has been testing these engines since 2020.

The first machine to be powered by one of these engines was the Liebherr R 9XX H2 crawler excavator, which is fitted with the H966 6-cylinder motor with PFI. The 4-cylinder engine prototype, the H964, is equipped with a DI system, which offers increased performance in combustion efficiency and power density.

SAE Media was granted an interview at Bauma with Liebherr’s Ulrich Weiss, managing director for the construction and development of combustion engines, to discuss the company’s investment and development of hydrogen ICEs, their advantages over other forms of alternative propulsion, and the challenges that lay ahead for industry-wide adaptation of this technology.

What is Liebherr’s view on where hydrogen fuel is going and its potential applications?

We believe that especially in off-highway applications that the combustion engine will have a future. We do not believe that all machines can be electrified or powered by fuel cells due to reasons such as NVH and load factors. So, the question then becomes how can you bring a combustion engine to zero emissions? From our point of view, we have a lot of simulations that show H2 is a possibility to accomplish this. Especially with green hydrogen, we are directly zero-emissions. We also have an advantage at high load factor compared to a fuel cell. If you have a high load factor requiring high torque, we think that the combustion engine has an advantage.

What are the biggest advantages of hydrogen ICE in off-highway applications?

For off-highway, one of the biggest benefits is the robustness of the engine. The fuel cell is sensitive to vibrations, which is something that a combustion engine is not as susceptible to. Additionally, the fuel cell has a need for very clean air, which means the question of filtering is very important, and in our environment, not always a given. Fuel cells also need very clean hydrogen. In H2 you have different levels of cleanliness from one to five, and a fuel cell needs a minimum of class four. Therefore, due to the operating environment, we think the fuel cell is not robust enough for off-highway machines. Also from the cost side, a hydrogen combustion engine will be cheaper compared to a fuel cell.

Why have other OEMs followed the fuel-cell path towards decarbonization with hydrogen fuel?

It depends on what size of machines you’re talking about. Liebherr’s machines are focused on the higher (larger) range and work in very rough and harsh environments. So, we believe that based on our tests that there are limits for the fuel cell. We are also following this technology, but with smaller machines. Today the big challenge is that there is not a clear tendency to indicate what will bring the future. We have no direction from the government and there is no clear picture about what the infrastructure will look like. So, you have to produce or develop a machine for use around the world because this is the market you have to cover. Otherwise, you will never get the volume. So, you have to develop a complete powertrain for global use.

Do you think its simpler from a scalability perspective to have an ICE hydrogen engine or a hydrogen fuel cell?

Absolutely a combustion engine, because the combustion engine is much more flexible and can cover a lot of load cases. You can start with a machine that is running at low load with a lot of idling but can also cover a lot of high torque applications. Our current machines are all more or less using the same engines. But they are operating in different strategies.

A mobile crane, for example, spends a lot of time idling, waiting to do the work, and only when they have to lift a load does the engine have to reach its highest level of performance. Conversely, a dumper is always running at high torque because they are always operating with a high load factor. The fuel cell has a big advantage in efficiency when you are able to run it at lower loads. But as you request more power from the fuel cell, the efficiency drops significantly and then the combustion engine crosses the efficiency line.

Also, due to polarization curve, a fuel cell has to be adapted for each application and load factor. That means you have to design your fuel cell specifically for the machine and how you want to use it. So, you are creating a lot of variants, which is why we are convinced that the combustion engine has a much wider range of uses.

How many different displacements of hydrogen-powered engines do you think you would have to offer to cover all your current applications?

If you compare an H2 engine to a diesel engine in the same engine size, you always have a little less power with the H2 engine. This means you tend to have to develop a bigger engine to cover the same range that you are covering today. That said, we expect that from around 9 liters, which is our four-cylinder engine, up to a 25-liter V12 engine should satisfy what we are looking for.

What have you found is the best injection system for your applications?

Today, its port injection because this is the easiest to control. But to increase the efficiency and power output, you have to move in the direction of direct injection. We have started to develop a DI system as well as high pressure injection (up to 300 bar). That said, when you move to this system you will get some surprises because H2 is not behaving like diesel if you want to mix it inside the chamber. We think there is a limit today of around 60 bar that you can control if you want to do so from the nozzle in the chamber or if you use a pre-chamber. We are developing our own combustion system and will not have DI in the traditional way but will have something in between.

What is the challenge with getting to the point where DI is stable enough for this application? Do you see enough benefit to moving to that right now or is PI meeting your standards for performance?

The port injection is on our demonstrator today because it is our quickest way to show that this type of engine could run and fulfill our applications and requests of our customers. Our real target in two years’ time is to go into series production with our engine. By then [2025] we will be on our next generation of this hydrogen engine, which will be not only port injected, but there will be something else paired with our special combustion system.

Do you have customers who are specifically asking for H2 engines right now? If so, what are the various industries requesting from these engines?

Yes, several industries. The rail and mining industries are requesting this kind of powertrain, and now earthmoving has high interest as well. From the engine side, the desires are nearly the same. It’s more a question of the infrastructure and also the size of the tanks because this is a completely different fuel. On the rail side this isn’t as much of a challenge because you have more space and a clear timetable of how the train is running, so the refueling can be better planned. An earthmoving machine which moves around constantly makes it difficult to forecast fueling locations, so you need a different kind of infrastructure.

What are some of the big hurdles of H2 acceptance in terms infrastructure adaptation?

The hurdle is getting the energy companies to start thinking about hydrogen as one of the possible energies of the future. What we’ve seen in the past few years indicates that its coming. A lot of oil companies are getting into contact with us about building infrastructure, but we also see it from the other side with companies which are creating electrical power that are interested in increasing their product portfolio with hydrogen, because they are also starting to question their future. But we are only at the beginning, and what we need is companies that are willing to follow and support us so that we can guarantee to our customer that not only do they have the machine but also the energy they need.

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