A startup company has developed a new type of engine that could generate electricity with the efficiency of a fuel cell, but which costs only about as much as an internal combustion engine.
Etalim, based in Vancouver, Canada, says its engine, roughly the size of a basketball, could improve the economics of electricity production for the cogeneration of power and heat in homes, and as a way to harness the heat produced at concentrating solar collectors. The company has created a prototype, but has yet to achieve the kind of efficiencies—in excess of 40 percent—that its computer models indicate are within reach.
The device shares some principles of a Stirling engine, in which an external heat source is used to expand a fixed amount of working gas (usually helium), which then contracts when it is pushed into a cooler space. This expansion-contraction cycle repeats itself, turning heat into mechanical work by driving a piston.
Etalim’s CEO Ron Klopfer says a fundamental problem with Stirling engines is that they need to run at very high temperatures and pressures to be efficient, making it difficult to keep the gas sealed inside the cylinder that encases the piston. “At these temperatures, you can’t use traditional methods of sealing,” he says. “You can’t use rubber, lubricants. It must be dry metal on metal, and those are very expensive, high-precision parts that lead to high costs.”
Etalim’s founder and chief scientist, Thomas Steiner, saw an opportunity to eliminate all the rubbing parts and seals that are prone to wear and leakage by using a design based on thermoacoustics—which employs heat to control the intensity of sound waves within a sealed cavity.
Encased within the core of Etalim’s engine is a plate of metal that replaces the function of a piston in a conventional Stirling engine. When pressurized helium on the top side of the metal plate is heated, sound waves traveling through the gas are amplified, causing the plate to vibrate, and a metal diaphragm below (separated by a cooler layer of helium) to push down on a shaft. All mechanical friction is eliminated. The shaft is attached to an alternator that produces electricity.