The smallest working engine in the world is a Wankel type rotary engine, it was created at The College of Engineering, University of California, Berkeley, CA, USA. It is made from solid steel, with all steel working parts such as the piston and bearings. Below is an image of the engine with the side plate removed to show the rotary piston.

The engine runs on butane or propane and delivers power to light up a 2.5 watt light bulb, but the engineers at Berkeley Labs are working on a 'tuned-up' version to deliver an estimated 30 watts of electrical power. This would be ample to run moderate electrical appliances like a laptop computer.

This “mini engine” is also a prototype for a Berkeley labs proposal to create a microscopic engine chemically etched from silicon.

“We are at the frontier of research into how to generate power using the smallest of components,” said Carlos Fernandez-Pello, a mechanical engineering professor who developed the engine with the help of Kenji Miyaska of Fukui University in Japan, Berkeley post-doctoral researcher David Walther and graduate students Kelvin Fu, Aaron Knobloch and Fabian Martinez.

The worlds smallest steam engine is built with nano technology or the ability to create objects at the atomic scale. The image above shows a steam engine built with nano technology, the engine is about 5 microns across. A human hair is about 100 microns across, so this engine is very miniscule.

This steam engine was developed by Dr. Jeff Sniegowski at Sandia National Laboratories in Albuquerque, New Mexico, USA.

It classes as the worlds smallest steam engine as it works like a full size one. There are three pistons that are run by steam created by water from a tiny reservoir. A tiny electrical current boils the water in its tiny boiler to create steam which is then fed under pressure through the array of pistons which in turn push the pistons out. When the electrical current is stopped the steam condenses back to its original state of water and the pistons retract. Repeating this process makes the engine run continually.

The engine has been built with the same technology that is used to build silicon chips and micro-processor components. This is basically done by photographing an image and etching the image onto photo sensitive material which is then reduced to a very small size on a silicon wafer.  The information on the photo-stat of course is still there, similar to micro-dots that the spies used to hide secret information.  These etchings are then done in layers to build up the device as a dimensional object.

When this is complete, the engine is a three dimensional working unit.  Its the appliance of science, but you need an electron microscope to see it !