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Hydrogen – Future Fuel or Folly

By autotech-nath on June 15, 2024

In his previous article, Andy Crook of GotBoost explored Zero Emission vehicles and the role of electrification. Here, he examines the various uses of Hydrogen as a fuel and an energy carrier for transportation.

The UK Government Hydrogen Road map suggests that the demand for Hydrogen in the transport sector is likely to increase rapidly in the late 2020s and mid-2030s.

Hydrogen demand for the transport sector is predicted to be via derivative fuels for maritime and aviation; HGV, rail, and light vehicles are not expected to drive significant demand. However, should the HGV sector decide that electrification is not the only option then the transport energy landscape could look very different to the Government’s roadmap.

The Government’s decision to push back the deadline of the sale of new internal combustion vehicles to 2035 is an indication that alignment with our European neighbours is necessary for the survival of the UK Automotive industry. Meanwhile, the EU is under pressure to consider alternative strategies to electrification due to environmental, economic, and social concerns.

What are the alternatives to battery vehicles?

Battery Electric Vehicles (BEVs) are currently the dominant Zero Emissions Vehicle (ZEV) technology, but the percentage of new BEVs registered reduced in 2023 – due, in part, to the Government ICE sales push back but also the economics of EV ownership and the lack of charging infrastructure.

But there are growing concerns over the green credentials of BEVs due to the use of rare earth materials, lithium mining practices and the extra weight of the batteries.

In my previous article, Life Cycle Assessments (LCAs) were used to compare the CO2 impact of the various fuels from manufacture (cradle), in-use period and recycling (grave), see Figure 1. The results suggest that Plug-in Hybrid Vehicles (PHEVs) have a similar CO2 impact to BEVs, and that you need to drive around 90,000 or 120,000 kms before BEVs produce less CO2 than fossil fuel (petrol & diesel combustion) equivalents.

Figure 1

These assessments and other economic and environmental factors have resulted in some German Automotive manufacturers investing in E-Fuel technologies (synthetic fuels), while Korean and Japanese OEM’s have extensive R&D projects in the use of Fuel Cells and Hydrogen Internal Combustion. Suggesting that Zero Emissions Vehicle (ZEV) is far from a one-horse race.

Alternatives to electrification are available, but none are yet in widespread use. Sectors where batteries are not a viable solution, such as maritime and aviation, are considering the use of alternative fuels such as ammonia and Sustainable Aviation Fuel (SAF).

E-Fuels…

E-Fuels, also known as synthetic fuels or electro-fuels, are created in a unique way. Hydrogen is combined with CO2, which can be captured from the air or from industrial processes, using a process developed in the 1930’s called Fischer Tropsch Synthesis to produce a liquid Hydrocarbon fuel. This liquid fuel is chemically similar to petrol or diesel and is therefore a drop-in solution. Although burning E-Fuels releases CO2, if the CO2 was taken from the atmosphere to make the fuel, the process can be close to carbon-neutral if the electricity used comes from renewable sources.

E-Fuels and SAF are a way to keep existing technologies and infrastructure while reducing the harm to the environment. However, E-Fuels still produce particulate emissions which means they are only seen as a bridge to a cleaner transport future.

Fuel Cells…

A Fuel Cell Electric Vehicle (FCEV) doesn’t burn hydrogen; instead, it uses a device called a fuel cell to convert hydrogen into electricity. This electricity then powers the electric motor that drives the car. A FCEV is a hybrid vehicle, that still uses a battery to store energy recovered during braking (regenerative braking) and to provide extra power during high-demand situations, like acceleration.

The fuel cell consists of an anode, a cathode, and an electrolyte membrane. Inside the fuel cell, hydrogen molecules are split into electrons and protons. The key to this process is that the fuel cell only allows protons to pass through the electrolyte membrane. Electrons can’t pass through this membrane and are forced to flow through an external circuit. The electricity generated in this external circuit is what powers the vehicle’s electric motor.

Meanwhile, on the other side of the membrane (in the cathode), oxygen from the air is combined with the protons that have passed through the membrane and the electrons that have travelled through the external circuit. This reaction produces water and heat as byproducts. Therefore, the only emissions at the point of use are water vapor. The advantages of FCEVs over BEV are the quick refuelling time and the long driving range, similar to conventional cars.

Hydrogen Combustion…

Hydrogen is different from the usual fuels we use in internal combustion engines. These differences in physical and chemical properties make designing and operating hydrogen engines challenging.

The wide flammability range allows for efficient and clean combustion, especially if you use very lean mixtures. This cuts down on NOx emissions. The high ignition temperature means higher compression ratios can be utilised, making the engine more efficient. However, it means that using hydrogen in compression ignition engines (like diesel engines) requires unrealistically high compression ratios.

Hydrogen burns very quickly and at much higher temperatures than fossil fuels, which results in rapid energy release rates and higher thermal loads, which may damage pistons and deform the exhaust valves. Hydrogen is corrosive to various engine components, including some metals and plastics, making it tough on the engine’s fuel and lubricating systems, possibly resulting in premature wear.

Hydrogen has a low heating value on a volume basis, therefore there is a need to turbocharge the engine or increase the capacity by 40-60% to achieve the same power as an equivalent petrol/diesel engine. Because hydrogen is easy to ignite, it can cause engine problems like pre-ignition (burning too early), backfiring (burning outside the engine), and knocking (abnormal combustion). These issues happen because hydrogen can ignite from hot spots in the engine before the spark event, leading to damage and efficiency losses.

While there are engineering solutions for many of the challenges presented by Hydrogen, it is not a drop-in solution for internal combustion engines.

Ammonia…

Ammonia (NH3) has been considered as an alternative fuel for internal combustion engines for decades. In fact, using NH3 as a fuel in internal combustion engines can be traced back nearly a century, where it was used to run buses in Belgium during the 2nd World War.

It has many beneficial properties – high hydrogen content, ease of storage, and availability of infrastructure. However, ammonia also faces challenges when used in engines due to its high autoignition temperature, low flame speed, corrosiveness, and tendency to produce NOx emissions.

However, Ammonia seems well-suited for low-speed engines such as those used in maritime applications.

A glimpse into the future…

What technologies will be competing for market share of light vehicle transport in 2050?

I believe there will a mixture of fuel types used in the future, much as there are now.

Comparing these future technologies requires assumptions to be made.

In 2050, all hydrogen used for light vehicle transport will be produced from renewable sources, the energy mix of the national grid results in the minimum amount of CO2 possible. Liquid E-Fuel as a by-product of Sustainable Aviation Fuel (SAF) production offers motorists a low carbon alternative to fossil fuels (at a price – it is expected that duty on E-fuels will be high) therefore, ICE vehicles are still in use.

In this future scenario, BEVs are the most carbon intensive mode of transport (although this is almost half the current level of CO2 impact) due to the size of the batteries required for adequate range and the trend of ever-bigger vehicles, see Figure 2. FCEVs emit 52,000 tonnes of CO2 during a 200,000 km life cycle. Petrol E-Fuel and PHEV emit a similar amount of CO2 (44,000 & 46,000 tonnes) over their lifecycle, while diesel is shown, in reality, the Particle Matter (PM) emissions have resulted in diesel being legislated out of passenger car use and is now only used in commercial vehicles outside of town and city limits.

Figure 2

Hydrogen combustion and Ammonia are not yet in widespread use in passenger vehicles, they are used in HGV’s, off-road and maritime applications. Improved battery technologies have resulted in increased range but there is still concern over the rare earth materials used in the batteries and the motors. The next generation of EV’s promises to use a fraction of the Lithium of the current technologies however, they are not expected until 2075. Vehicle ownership is increasingly seen as unnecessary, and most young people use a Mobility on Demand Service, MODS.

In the next issue, Andy discusses the safety implications of working with Hydrogen.

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