Beetles toxic steam inspires researchers

Researchers are using an insect that sprays its predators with toxic steam to inspire new types of nebulisers, needle-free injections, fire extinguishers and powerful fuel injection systems.

The deadly defence system of the Bombardier Beetle has inspired a new type of delivery system

The bombardier beetle defends itself with a cocktail of steam and stinging chemicals which it can blast for distances of up to 20cm - and after scaling up this deadly defence, researchers at Leeds University say it could make an ideal delivery system.

Professor of Thermodynamics and Combustion Theory at Leeds, Andy McIntosh said: “Essentially it’s a high-force steam cavitation explosion. Using a chamber less than one millimetre long, this amazing creature has the ability to change the rapidity of what comes out, its direction and its consistency. Nobody had studied the beetle from a physics and engineering perspective as we did – and we didn't appreciate how much we would learn from it.”

The scaled-up rig uses heating and flash evaporation techniques to propel a variety of liquids and its 2cm chamber can blast the fluid for up to 4 metres or at the other extreme produce a soft mist with droplets as small as 2μm.
Called “µMist” spray technology, the team hope say it can enable droplet size, temperature and velocity to be closely controlled, allowing advancements in a variety of areas where the properties of the mist are critical. Such applications include fuel injection, medical drug delivery systems, fire extinguishers and fire suppression, all of which face major challenges relating to the demands of greater performance and reduced environmental impact.

Prof McIntosh’s research was inspired by entomologist Prof Tom Eisner of Cornell University who has worked for a number of years on the bombardier beetle. Ultra slow motion pictures shot by Eisner showed how the bombardier beetle expels fluid through a series of rapid pulses - the pressure in the insect's fluid chamber causing the liquid to be ejected, followed by a drop in pressure, which allows more fluid to enter and the pressure to build up once more.

There are 500 species of bombardier beetle, mostly found in hotter areas of the world - Africa, Asia and South America - though there are some small colonies in the UK. Their tiny fluid chambers typically react hydroquinone with hydrogen peroxide to produce a fiery blast of steam, though different species use slightly different combinations of exhaust nozzle arrangements.