Lights, Camera, Ignition! 

‘Photo-ignition’ was discovered accidentally when scientists photographed carbon-metal tubes, known as carbon nanotubes (CNTs) during an experiment. CNTs are cylinders made from sheets of carbon atoms arranged in a hexagonal pattern. They possess exceptional strength and conductivity. In the experiment, photographic flashes caused the CNTs to spontaneously ignite. 

CNTs can fit one inside another, like a Russian nesting doll. If a cylinder contains multiple nested tubes, then it is referred to as a multi-wall carbon nanotube (MWCNT). Researchers tested MWCNTs modified by the addition of an iron-based molecule called ferrocene. These tiny metal impurities are what triggered the combustion; without them, the light flashes would have had no explosive effect.

This photo-ignition phenomenon has widespread applications, both inside the automotive field and beyond. The inclusion of MWCNTs makes the fuel combustion process more stable, which can dramatically decrease the chances of engine failure. This technology is great for satellites too, because it’s lightweight, spatially compact, and requires low energy to trigger ignition. It not only works in the vacuum of space but is useful on Earth, too. Carbon-metal tubes can trigger material explosions (e.g., the firing of bolts on aircraft exit doors) and control the burning of explosives (e.g. energy-efficient motors). 

Researchers found that, for all types of fuel and for all concentrations of MWCNTs, ‘photo-ignition’ was superior to spark plug use. A variety of measurements all contributed to this conclusion: peak pressure in the fuel chamber, duration of fuel combustion, and time from light flash to ignition. With the use of the nano-structures, there was higher pressure (so more heat), faster combustion, and a shorter ignition delay. Increasing the amount of MWCNTs in the fuel mixture caused even higher pressure and didn’t significantly affect timing.