This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: "Ammonia was first used as a fuel during World War II, when gasoline was hard to get hold of," explains David Emberson, associate professor at NTNU's Department of Marine Technology. "It was actually quite a crazy idea because ammonia is a very poisonous, toxic gas." Necessity, however, is the mother of invention.
Where fuel shortages drove the development of ammonia engines in the 1940s, the need for carbon-free propulsion is inspiring a new era today. Ammonia is abundant and common, and it can be produced using renewable energy. It is a zero-carbon fuel that produces no carbon dioxide emissions during its use.
But ammonia has poor ignition characteristics and will not burn well on its own. To power an engine, ammonia is usually used alongside another fuel to help ignition. These are known as dual-fuel engines.
Coal gas, biofuels and diesel are examples of ignition fuels—they are used to "spark" ammonia into action. Diesel shortages during World War II prompted the first real-world use of ammonia as a fuel. A fleet of Belgian buses was retrofitted to run on ammonia, but the engines required a fuel mixture containing up to 40% coal gas to achieve stable combustion.
Ignition fuels reintroduce carbon emissions into the equation, which weakens the case for ammonia engines in today's market. Engineers are researching carbon-free alternatives and investigating how to use them as efficiently as possible. Emberson has previously investigated how to minimize the amount of ignition fuel required in a dual-fuel system.
Using similar techniques, he and his team have now investigated using hydrogen as the ignition fuel in an ammonia engine. Hydrogen is also a zero-carbon fuel and can be created from the ammonia itself. Its use would require additional hydrogen storage or onboard equipment to separate the hydrogen from the ammonia as needed.
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