IDTechEx: Could Hydrogen ICEs cut Scope 3 Emissions

The idea of hydrogen-powered internal combustion engines (ICEs) eliminating harmful emissions while maintaining familiar technology is appealing. While electrification is the leading method for decarbonising transportation, challenges such as slow adoption rates persist. According to Mika Takahashi, Technology Analyst at IDTechEx, only 11% of all car sales 2023 were fully electric.

"The IDTechEx report Hydrogen Internal Combustion Engines 2025-2045 explores whether hydrogen could be a disruptive technology with zero-emission potential," says Mika. This report offers critical insights into how hydrogen ICEs can reduce Scope 3 emissions across the automotive value chain by utilising existing manufacturing and supplier networks.

Understanding hydrogen combustion

Hydrogen combustion is different from traditional petrol or diesel. In a conventional ICE, fuel reacts with oxygen at high temperatures, producing carbon dioxide (CO2) and nitrous oxides (NOx). However, hydrogen combustion has no carbon in the fuel, effectively eliminating CO2 from the tailpipe.

As Mika explains, "No CO2 is formed when using hydrogen, but there's a caveat to this zero-emission claim." A small amount of motor oil is burned in the engine due to necessary lubrication. Most motor oils are hydrocarbon-based, leading to minimal CO2 emissions. Despite this, Mika points out, "Compared to conventional ICEs, this amount is negligible." Hydrogen ICE vehicles (H2ICE) produce less than 1kg of CO2 per 1,000 miles, whereas traditional engines emit 272 kilogrammes.

Nitrous oxides: A key challenge

While hydrogen eliminates CO2 emissions, it still generates high temperatures during combustion, leading to the formation of nitrous oxides (NOx). NOx are harmful greenhouse gases (GHGs) and air pollutants subject to increasing global regulations.

"For H2ICE to achieve credible emissions reductions, it must substantially reduce NOx emissions," Mika highlights. The report delves into thermal NOx formation, analysing factors such as:

• Air-fuel ratios and the trend toward lean burn spark ignition designs.
• The impact of engine speed on NOx formation.
• Existing exhaust gas treatments for hydrogen engines, including catalytic converters and exhaust gas recirculation (EGR).

The report includes real-world data from current H2ICE vehicles and compares NOx emissions with historical and current tailpipe limits in critical regions.

The importance of hydrogen's origin

Hydrogen's emissions reduction potential is directly tied to its production method. "Although hydrogen is carbon-free when burned, its lifecycle emissions depend heavily on its origin," Mika explains. Hydrogen is categorised by colour, indicating its source:

• Green hydrogen: Produced using renewable energy, this is the only truly carbon-free option.
• Yellow hydrogen: Solar-powered, though still expensive and difficult to scale.
• Blue hydrogen: Made from natural gas with carbon capture, yet still less eco-friendly than green hydrogen.
• Grey hydrogen: Derived from fossil fuels, resulting in high CO2 emissions.

The production, compression, and transportation of hydrogen require energy, and these processes can reduce overall energy efficiency. Mika notes, "3kWh of renewable electricity generates roughly 1kWh of usable hydrogen," adding significant energetic inefficiencies.

Comprehensive Lifecycle Emissions

The report assesses the lifecycle emissions of H2ICE vehicles by evaluating green, blue, and grey hydrogen. It compares these vehicles to fuel cell electric vehicles (FCEVs) and traditional petrol/diesel engines and benchmarks against battery-electric vehicles (BEVs) under different energy grid scenarios.

Challenges for reducing Scope 3 emissions

Despite hydrogen's potential, several factors complicate its ability to reduce Scope 3 emissions across the transportation sector significantly:

• Limited hydrogen refuelling infrastructure can increase emissions in the fuel supply chain.
• The large-scale production of green hydrogen remains challenging, which could lead to higher upstream emissions.
• Low adoption rates mean conventional vehicles will continue to dominate for some time, delaying widespread emission reductions.

Hydrogen engines show great promise in reducing CO2 emissions, but challenges relating to NOx pollution and the environmental impact of hydrogen production must be addressed. The report provides a detailed exploration of hydrogen's potential to become a zero-emission solution for the transportation industry, though significant hurdles remain before it can be widely adopted.

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