The bombardier beetle (Brachinus Carabidae) must be the most unlikely collaborative partner ever to become involved in an advanced automotive technology research project. However, this amazing little insect’s ability to spray a stinging 100°C (212°F) cocktail from its internal “combustion chamber” over a distance 10 times its own length has concentrated the minds of a team at a leading British university.
The 2 cm (0.8 in) long beetle uses its toxic irritant exothermic spray as a protection against ants. The insect creates the spray by reacting hydroquinone with hydrogen peroxide, stored in its fuel glands, to produce a blast of steam. It is an ability that may contribute to greater fuel efficiency, and subsequently to reducing emissions in the fuel-injection systems of production automobile engines.
Andy McIntosh, Professor of Thermodynamics and Combustion Theory at Leeds University, explained: “The beetle’s capability has direct applicability to fuel injectors due to its ability to tune the size of the droplets down to as little as 2 µm. This greatly increases the burning efficiency of the fuel, since the surface area (with respect to volume) increases greatly and consequently, less fuel is burned, and thus pollution is reduced.”
The bombardier beetle’s capability was revealed in AEI’s sister magazine, Aerospace Engineering, four years ago. At that time, work by a research team under McIntosh had just begun at Leeds, with the project title, “Learning from controlled explosion in nature—modeling the catalytic explosion device of the bombardier beetle.” At that time, the team focused on the extrapolation of the beetle’s spray “technology” to support research into the re-light procedure for aircraft gas turbine engines at high altitudes.
Now, the list of potential applications of the beetle’s forceful personality has expanded to include automotive fuel-injection systems. Said McIntosh: “We have built a rig which simulates the physics of the bombardier beetle. It has the capacity to eject a very fine mist with 2 µm droplets as well as large droplets up to 100 µm. The maximum throw ratio (distance thrown divided by chamber dimension) is 200—the same as that of the beetle itself—striking confirmation that we had got the physics right!”
The beetle’s 1-cm (0.4-in) diameter “combustion chamber” works rather like a pressure cooker. As the liquid in the chamber is held under pressure, a valve is opened, and flash evaporation occurs. The valve closes, the chamber refills, and heating brings the liquid to above atmospheric boiling point again—although this is not achieved until the chamber valve is opened once more. The beetle does this at 400 to 500 cycles/s. “Essentially, it is a high-force steam cavitation explosion,” said McIntosh.
The experimental rig built by the McIntosh team (Novid Beheshti, Andreas Prongidis, and Steve Caddick) generates a slower frequency of 10 to 20 cycles/s, and rather than heating by catalytic chemistry like the beetle, achieves heating electrically. “But the principle is the same,” explained McIntosh. “The great advantage of such a device is that the delivery is not through a high-pressure atomizer, but the small droplets are achieved with minimal damage to the environment. This has direct applicability to automotive fuel injectors due to the ability to tune the droplet size down to less than 10 µm.”
The beetle-based technology developed at Leeds has been given the trademark name, µMist. The research work was funded originally by the U.K.’s Engineering and Physical Sciences Research Council (EPSRC) and subsequently by Swedish Biomimetics 3000, a virtual venture philanthropic intersectional organization founded in Sweden in 2004 by Lars Uno Larssen to fund translational research of biomimetics concepts to the point where they are considered commercially viable. At that point, corporate partners are sought for the technology’s further development.
The µMist spray technology enables droplet size, temperature, and velocity to be closely controlled. The dynamic electronic tuning capability of the mist’s properties presents what McIntosh regards as “the unique potential to sense the optimal mist characteristics required and then adjust accordingly, in real time”. He added: “Nobody had studied the bombardier beetle from a physics and engineering perspective as we did—and at first, we did not appreciate how much we would learn from it.”
The work at Leeds was inspired by entymologist Tom Eisner of Cornell University in the U.S. Swedish Biomimetics 3000 has signed a worldwide exclusive licensing agreements for the development and commercialization of µMist technology and potential application opportunities arising from the work have been filed for intellectual property rights, stated the EPSRC.