Volume and Not Weight Rule out Hydrogen Combustion for Passenger Cars

Hydrogen internal combustion engines (H2ICE) promise (almost) zero emissions transport without relying on expensive, slow-to-recharge batteries. As hydrogen is a carbon-neutral fuel, H2ICE offers an opportunity to retain the combustion engine in an increasingly zero-emissions world. The attraction for the automotive industry is clear. OEMs and suppliers can apply minor modifications to existing engine and vehicle production lines and produce carbon-neutral vehicles that retain many characteristics of existing ICEs. This contrasts with developing an entirely new production and supply chain for batteries and motors, requiring new minerals and metals. The grid must also be upgraded to accommodate the rollout of charging infrastructure.

 

Even as battery production scales up, energy density and recharging times remain pain points, as do slow recharging times. So, does the hydrogen combustion engine offer a viable route to continuing ICE vehicle production? According to IDTechEx's new "Hydrogen Internal Combustion Engines 2025-2045: Applications, Technologies, Market Status and Forecasts" report, the answer is, at least for cars, no. But why?

 

 

 

Hydrogen is the most abundant element in the universe, and it is also the lightest. When combusted in the presence of oxygen, hydrogen releases a huge amount of energy -around 39.3kWh per kg. Compared with this, a kilogram of diesel contains 12.6kWh, or 3 times less. This might suggest that hydrogen is a wonder fuel, able to store huge quantities of energy and enable hydrogen-powered vehicles to travel enormous distances without needing large storage tanks. This is only half true, and the reality is that weight is only half of the problem. The big issue is volume.

 

 

While hydrogen has a high gravimetric energy density, it has a very low volumetric energy density, about 3,000 times less than diesel at atmospheric pressure. To get useful amounts of energy, hydrogen must be stored as a compressed gas, typically at 350- or 700-times atmospheric pressure. It can also be stored as a liquid, which further increases its volumetric energy content, but this is a more complex process that requires cooling down to -250 degrees centigrade. Even when in its most dense form (liquid), hydrogen contains just 26% of the energy per volume as diesel.

 

The volume of energy contained is only part of the story; the driveable range also factors in the energy efficiency of a vehicle. This is where H2ICE falters compared with its hydrogen counterpart, the fuel cell electric vehicle (FCEV). FCEVs are an alternative method of using hydrogen in a vehicle, but instead of burning the hydrogen, it is combined with oxygen in a fuel cell to produce electricity and water. This electricity then powers a motor, much like in a BEV. The resulting drivetrain is of a higher efficiency, meaning a vehicle can travel further on less fuel. In the case of hydrogen, which is difficult to store, this represents a huge advantage for FCEVs over H2ICE. H2ICE vehicles are thermodynamically limited in their efficiency, as there are losses to heat and friction at various points along the drivetrain. The upshot is that FCEVs travel further on the same amount of hydrogen than an H2ICE vehicle.

 

 

 

IDTechEx has analyzed the real-world performance of various H2ICE and FCEV vehicles to assess fuel consumption, and the results clearly show that FCEVs are more fuel-efficient. The catch is that fuel cells are most efficient at low loads, so there is an argument that FC and H2ICE efficiencies would converge at a very high system load, but for a passenger vehicle, the amount of time spent at maximum engine load is extremely limited.

 

 

This means that for a passenger car to run on hydrogen combustion and achieve a range comparable to a petrol/diesel ICE, it would need an enormous storage vessel. In 2022, Toyota produced a modified prototype of the GR Corolla, which ran on liquid hydrogen. The regular GR Corolla has a tank size of 50L and the GR Corolla H2 required a tank of 148L. Yet despite this tank being 3x larger (without even considering the extra cooling equipment required for the tank), it only contained 80% of the energy that the petrol tank contained. So to contain the same energy content (and assuming a roughly equal energy efficiency between the ICEs), an enormous tank of 201 liters (or 3.5x larger) would be required.

 

 

This is not even the end of the problem. Petrol tanks and even Li-ion batteries can be geometrically oriented to fit the car's body most efficiently. Li-ion battery packs are often rectangular and integrated into the car's floor. This is not possible with liquid or compressed hydrogen. The physics involved in compression/ liquefication requires the vessel to have a minimized surface area. The shape that most storage containers, therefore, take is cylindrical, which is not an efficient shape to pack. The bottom line is that for cars, H2ICE requires large, bulky, and awkwardly shaped storage tanks to achieve comparable ranges with current ICE vehicles. FCEVs can get away with much less hydrogen due to their increased tank-to-wheel efficiencies. IDTechEx's report explores some of the sectors where these challenges are less pronounced, and the case for H2ICE is much stronger. For passenger cars, however, the future seems set to be electric.

 

To find out more about the new IDTechEx report, "Hydrogen Internal Combustion Engines 2025-2045: Applications, Technologies, Market Status and Forecasts", please visit www.IDTechEx.com/H2ICE. Downloadable sample pages are available.

 

For the full portfolio of hydrogen market research available from IDTechEx, please see www.IDTechEx.com/Research/Hydrogen.

 

 

Mika Takahashi, Technology Analyst at IDTechEx and author of this article, will be presenting a free-to-attend webinar on the topic onThursday 3 October 2024 - Can Hydrogen Reignite the Combustion Engine?

 

This webinar explores the key concepts and questions surrounding hydrogen internal combustion engines (H2ICE) including:

 

We will be holding exactly the same webinar three times in one day. Please click here to register for the session most convenient for you.

 

If you are unable to make the date, please register anyway to receive the links to the on-demand recording (available for a limited time) and webinar slides as soon as they are available.

IDTechEx provides trusted independent research on emerging technologies and their markets. Since 1999, we have been helping our clients to understand new technologies, their supply chains, market requirements, opportunities and forecasts. For more information, contact research@IDTechEx.com or visit www.IDTechEx.com.