Researchers at the University of Twente in Enschede, Netherlands, have created an internal combustion engine of just five cubic microns that burns both hydrogen and oxygen.
Getting an engine that small isn’t easy, the researchers led by Vitaly Svetovoy, explained in their ‘Nature’ paper, amidst speculation about the mechanism by which they managed to get the combustion processes happening.
As scientists have built ever smaller devices, the need for ever smaller microengines has grown; unfortunately, the science for tiny engines hasn’t kept pace. Those based on electrostatic forces aren’t able to produce enough power and traditional combustion engines become less and less efficient as they are made smaller. In this new effort, the researchers built a tiny combustion engine in a new way that overcomes the problems of others before it, though they can’t say for sure how it works.
“It is not obvious that the reaction in nanobubbles and performance of the microscopic actuator are related. Nevertheless, we speculate that the gas combustion in the chamber happens via combustion in transitional nanobubbles,” they write.
The search for a Liliputian V8 might sound silly, but the researchers say “a fast and strong actuator can be applied in microfluidics, micro/nano positioning, or in compact sound/ultrasound emitters.”
The 100 x 100 micron microengine is fabricated on silicon, with a 530 nm layer of silicon rich nitride (SiRN), and platinum electrodes. The SiRN layer was etched to create the actuator membrane, and the membrane was filled with Na2SO4 in de-ionized water.
Applying a voltage to the chamber produced hydrogen and oxygen by electrolysis, and as the paper puts it, “termination of the gases happens very fast due to spontaneous combustion.” That reaction causes pressure of around 3.6 bar, enough to deflect the actuator by 1.4 microns.
Frequency of the motor is controlled by oscillating the voltage applied to the chamber. The researchers say the actuator was able to operate at frequencies from 5 kHz up to 20 kHz, and 100 kHz is possible, albeit at a lower pressure.
The microengine produces a lot of torque for its size, and thus could very well serve as the basis for very tiny devices that need to either perform physical work, or move around. At the same time, it’s a certainty that the original team and others will set to work trying to nail down exactly why the engine works and to determine just how small such an engine could be.