Learning from the beetles

An amazing insect, which sprays its predators with toxic steam, has inspired research into a new generation of technology at Leeds University.

The research has resulted in the development of a new system called µMist which has the potential to become the platform for the next generation of more effective and eco-friendly mist carrier systems.

It has multiple potential applications – such as new nebulisers, needle-free injections, fire extinguishers and powerful fuel injection systems – all more efficient and environmentally-friendly than existing technologies.

The research funded initially by the Engineering and Physical Sciences Research Council, and subsequently by Swedish Biomimetics 3000, enabled the Leeds team, led by Professor of Thermodynamics and Combustion Theory Andy McIntosh to examine the mechanisms at work in the bombardier beetle.

Just 2cm long, the beetle defends itself against frogs, spiders, birds and insects with a cocktail of steam and stinging chemicals which it can blast for distances of up to 20cm.

The chemical and physical characteristics of the spray and the insect’s physiology have been simulated using a scaled-up experimental rig in Prof McIntosh’s laboratory at Leeds and built by Novid Beheshti and Andreas Prongidis with the expertise of technician Steve Caddick. The rig uses heating and flash evaporation techniques to propel a variety of liquids, and its 2cm chamber can blast the fluid for up to 4m.

The µMist spray system enables droplet size, temperature and velocity to be closely controlled, allowing advancements in a variety of areas where the properties of the mist is 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.

In the medical field, the technology could provide a water-based carrier for propelling substances such as drugs, replacing conventional propellants which are potential pollutants. Used with fuels, the system offers the potential to substantially increase fuel burning efficiency, improving fuel consumption and minimising exhaust pollution.

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. 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.

Prof McIntosh likens the beetle’s defence mechanism to a pressure cooker controlled by a complicated system of valves: '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,' he said.

'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.'

Swedish Biomimetics 3000 has signed a worldwide exclusive licensing agreement for the development and commercialisation of the µMist technology.

Swedish Biomimetics 3000 is an organisation which funds research of biomimetics concepts to the point where they are commercially viable, when corporate partners are sought for the technology’s further development. It was founded 2004 in Sweden and has established an affiliated company in the UK.