A few weeks ago, I wrote an article titled "Ammonia as an engine fuel?" It mentioned plans by a South Korean shipyard to build a major container vessel powered by ammonia, as opposed to fuel oil, diesel or natural gas, and speculated on the future use of ammonia in other engines.
A recent article at the BBC examines ammonia's potential for more widespread use, particularly due to environmental factors.
The International Maritime Organization (IMO) wants to halve emissions by 2050, from 2008 levels. That requires a substantial shift to green technology.
Brian Soerensen, a research and development chief at Man Energy Solutions, says several fuels are being explored: "One of the options we believe will be ammonia. Methanol could be another one, biofuel could be a third."
Ammonia has an advantage as it contains no carbon, so can burn in an engine without emitting carbon dioxide.
While it is less energy-rich than today's marine fuels, liquid ammonia is more energy-dense than hydrogen, another zero-emission fuel ... "Ammonia sits very nicely in the middle," says Dr Tristan Smith, an expert in low carbon shipping from University College London. "It's not too expensive to store and not too expensive to produce."
There's more at the link. It makes interesting reading from a mechanical and technical perspective.
Thinking about it, that makes a lot of sense. If emissions control is a priority, it makes sense to use the "greenest" fuel available; and ammonia, while not nearly as efficient as fossil fuels, is nevertheless more energy efficient (and therefore more economical in practice) that other "green" fuels.
Like almost everything else in engineering, it's a trade-off. You'll use more ammonia than bunker fuel or diesel or natural gas, thus costing more money; but you'll give off less carbon-based pollution, which is costly from an environmental standpoint (and possibly in carbon taxes as well). You pays your money and you takes your choice.
However, I'm not sure how well this will translate to smaller engines, particularly in close proximity to people. Ammonia fumes are toxic. The less we have of them around us every day, the better! Out at sea, that's not necessarily much of a problem, particularly given ship-scale scrubber technology to filter them. In a big city . . . not so much.