A chance discovery has transformed an engine intended for speedboats into a powerful firefighting tool that douses flames with jets of water mist.

When used for boats, the engine works by injecting steam through a rear-facing, ring-shaped nozzle into a cylindrical chamber. As the steam emerges at three times the speed of sound, it rapidly condenses, generating a shock wave that pulls in water through an intake and expels it from the rear, generating thrust.

The new application emerged when engineers at its manufacturer, Pursuit Dynamics in Royston, Hertfordshire, UK, were testing the limits of the engine’s capabilities out of the water.

During the tests, a technician squirted water into it with a garden hose “purely out of curiosity”, says John Heathcote, Pursuit’s CEO. To everyone’s surprise, the water emerged as a jet of fine droplets that drenched anyone standing within 20 metres of it.

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