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Hydrogen & Ammonia: Dual Fuels Leading the Clean Energy Revolution
Hydrogen and ammonia are emerging as powerful partners in decarbonizing aviation, shipping, and heavy industry—reshaping the future of global energy.
The Carbon Conundrum
For over a century, hydrocarbon fuels (CₓHᵧ) have formed the backbone of global energy systems—powering turbines, propelling aircraft, and generating electricity. But this convenience has come at a steep environmental cost. Each year, combustion of fossil fuels releases more than 38 billion tonnes of CO₂, accelerating the climate crisis. While the rise of renewables like wind and solar is transforming electric power grids, applications requiring high energy density—aviation, shipping, and industrial turbines—remain tethered to combustion.
In these hard-to-electrify sectors, eliminating carbon emissions calls for a new breed of fuels. Hydrogen (H₂) and ammonia (NH₃), both devoid of carbon atoms, are emerging as the most promising alternatives. Rather than displacing combustion altogether, these fuels aim to reinvent it—cleaner, safer, and free from the legacy of carbon.
Why Hydrogen and Ammonia? The Zero-Carbon Duo
Hydrogen is celebrated for its extraordinarily high energy density by mass, combusting cleanly into water vapor. However, its handling presents formidable challenges. Storage requires cryogenic temperatures near -253°C, leading to significant daily losses due to boil-off. Hydrogen molecules are so small they seep through metal, degrading pipelines and tanks. And turning hydrogen into a usable liquid or compressed gas consumes up to 40% of its energy, which undermines its overall efficiency.
Ammonia, on the other hand, provides a more practical pathway for zero-carbon combustion. Created by combining nitrogen from the air with hydrogen via the Haber-Bosch process, ammonia is a liquid at -33°C and can be transported and stored using infrastructure already in place for propane and other industrial chemicals. With nearly twice the energy density by volume compared to liquid hydrogen, ammonia offers compelling logistics and scalability advantages. According to the International Energy Agency, ammonia stands out as the only carbon-free hydrogen carrier with a global distribution network already in operation.
The Combustion Challenge: Taming Flames Without Carbon
Despite their promise, both hydrogen and ammonia introduce unique challenges when used in combustion. Hydrogen burns quickly and across a wide range of fuel-to-air ratios, which is advantageous for turbines but increases the risk of flashback—where flames travel back into fuel lines. Engineers are addressing this through design adaptations like porous flame arrestors and controlled blending with natural gas, allowing existing systems to operate more cleanly without full-scale retrofits.
Ammonia’s issues lie in its slower flame speed and the tendency to produce large amounts of nitrogen oxides (NOₓ) during combustion. However, recent advances show promise. Injecting ammonia in stratified layers within turbines can significantly reduce NOₓ emissions. Meanwhile, mixing small amounts of hydrogen with ammonia not only improves flame propagation but also reduces the amount of unburnt ammonia in the exhaust. Techniques like plasma-assisted ignition are also emerging, enabling cleaner breakdown of ammonia molecules without producing thermal NOₓ.
The emissions profiles of these fuels reflect their strengths and limitations. Hydrogen generates no carbon emissions and negligible pollutants, while pure ammonia, though CO₂-free, risks releasing harmful nitrogen compounds. Blending ammonia with hydrogen appears to strike a favorable balance between performance and pollution.
Green Synthesis: Building the Ammonia-Hydrogen Ecosystem
Currently, most ammonia production is carbon-intensive, accounting for about 1.8% of global CO₂ emissions. This “gray” ammonia is synthesized using fossil fuels. Transitioning to “green” ammonia involves using renewable electricity to power electrolyzers that produce hydrogen from water, which is then combined with atmospheric nitrogen using cleaner Haber-Bosch processes. Advanced catalysts and electric compressors have already demonstrated energy savings compared to conventional methods.
Real-world examples are beginning to demonstrate feasibility. In Kenya, a solar-powered fertilizer facility is producing one ton of green ammonia daily, helping decarbonize agriculture. In Australia, the Nel-Yara plant is exporting green ammonia to Japan, capitalizing on existing marine infrastructure.
To convert ammonia back into usable hydrogen at the point of use, ammonia crackers are being developed. Conventional catalytic systems can achieve high conversion rates at elevated temperatures but consume significant energy. Electrochemical crackers, still in their infancy, show promise for lower-temperature, more efficient hydrogen release—especially when integrated with fuel cell systems.
Hanwha Power Systems, a subsidiary of South Korea’s Hanwha Group, has taken a significant step toward maritime decarbonization by signing a non-binding MoU with GasLog to explore converting the Greek shipowner’s LNG carrier fleet to ammonia-powered gas turbines. This collaboration follows a joint feasibility study with Hanwha Ocean that assessed both technical and economic viability for retrofitting GasLog’s 21 vessels. The partners will now advance to demonstration planning, focusing on performance optimization, regulatory compliance, and commercial feasibility—marking a potential industry milestone in clean propulsion for large-scale shipping.
The initiative aligns with tightening emissions regulations, as Hanwha accelerates development of its proprietary ammonia combustion technology, including successful high-pressure system tests. CEO Justin Lee emphasized the transformative potential of the project, noting success could redefine global shipping’s shift to eco-friendly fuels. Hanwha is concurrently engaging multiple shipowners to expand the business case, positioning ammonia turbines as a scalable solution for maritime’s energy transition—a strategic move as the industry races toward IMO 2030/2050 targets.
From Labs to Oceans: Real-World Applications Taking Flight
Ammonia is gaining traction in maritime propulsion, where its high energy density and ease of storage align with the needs of large-scale shipping. MAN Energy Solutions is testing a 50 MW marine engine using a 70:30 ammonia-diesel mix, reducing CO₂ emissions by as much as 80%. Meanwhile, companies like Höegh Autoliners are committing to blending green ammonia and methanol into their shipping fuel portfolio by the end of the decade.
In aviation, ammonia may play a role in auxiliary systems before making its way into full propulsion. Rolls-Royce is exploring the use of ammonia in auxiliary power units (APUs), while other groups are investigating ammonia-to-hydrogen cracking systems that could power fuel cells to lighten battery loads. These hybrid solutions could serve as bridge technologies as aviation transitions to cleaner energy sources.
Thermal power generation is also embracing ammonia. Japan’s national utilities plan to co-fire ammonia with coal in existing power plants, with a target of consuming 3 million tons of ammonia annually by 2030. Stored in liquid form in geological formations like salt caverns, ammonia offers long-duration energy storage capacity—enabling backup power for months at a fraction of the cost of current battery technologies.
The Road Ahead: Synergies, Sensors, and Policy
Ammonia and hydrogen should not be seen as competitors, but rather as complementary players in a broader decarbonization strategy. Surplus renewable energy can be used to produce hydrogen, which is then converted into ammonia for transport and storage, before being cracked back into hydrogen where needed. This cycle leverages existing ammonia infrastructure, including thousands of kilometers of pipelines in the United States alone, avoiding the astronomical costs of building dedicated hydrogen networks from scratch.
Of course, challenges remain—particularly around ammonia’s toxicity and detectability. Researchers are exploring methods like nanobubble encapsulation to contain and control ammonia release, while AI-powered sensor arrays can detect even minute leaks in industrial settings, triggering automatic shutdowns and reducing risk.
Policy will play a critical role in supporting these technologies. A robust carbon pricing system can help close the cost gap between gray and green ammonia, while clear emissions standards for ammonia combustion are essential to ensure we don’t merely swap carbon pollution for nitrogen pollution. Regulating NOₓ and nitrous oxide (N₂O) emissions is key to a genuinely clean transition.
Conclusion: The Burnable Future
As we move beyond hydrocarbons, combustion technologies are not fading—they are transforming. Hydrogen and ammonia offer powerful tools for achieving zero-carbon power and propulsion without compromising on energy density. Hydrogen’s role may lie in lightweight, high-performance systems like aviation, while ammonia could dominate where logistics, storage, and infrastructure compatibility matter most, such as in maritime transport and grid backup.
These fuels are not silver bullets, but part of a strategic mix. Their successful adoption will depend on advances in combustion science, fuel synthesis, emissions control, and international regulation. As researchers and engineers tackle the challenges head-on, a future powered by carbon-free combustion is not only possible—it’s increasingly within reach.
Key Takeaway: The energy transition is not about choosing electrons or molecules. It’s about electrifying wherever we can—and molecularizing where we must. Ammonia and hydrogen are not just fuels of the future—they’re essential to building a sustainable, high-density energy world.
