I have a story in MIT Technology Review today that looks at a very cool engine design from a Vancouver-based startup called Etalim. The story gives a somewhat technical explanation of how the engine works, but basically its a hybrid of a thermoacoustic engine and a Stirling engine. What’s impressive about this technology is that — according to the company, at least — it’s compact, made of non-toxic and recyclable materials, easy and inexpensive to manufacture, can use any source of high-grade heat (biogas, biomass, natural gas, solar, fossil fuels), and is not subject internally to mechanical friction, meaning the product is highly reliable and has a long life with very little need for maintenance.
Stirling engines, to put it simply, use heat to drive a piston as a fixed volume of gas, such as helium, heats, expands, then cools and contracts. This cycle of expansion and contraction repeats itself, and the higher the heat the higher the power. Problem is, there is a lot of mechanical friction and all of this has to operate within a sealed vessel under high temperature and high pressure. Leakage of gas is a big challenge. Rubber seals and lubricants don’t cut it, so parts have to be machined precisely to achieve metal-on-metal fittings and this adds a lot of cost, and even then, long-term reliability can be an issue. Etalim founder and chief scientist Thomas Steiner, a former chief physicist at Creo (where he worked side-by-side with Michel Laberge, founder of nuclear fusion startup General Fusion), decided to turn to thermoacoustics to solve the problem.
Research into thermoacoustics has been around for years, but it’s still a relatively new area. I’m not qualified to say too much about it, suffice to say it involves the bizarre interaction of thermodynamics and acoustics — i.e. heat can be used to stimulate the creation of intense sound waves that can be used to achieve mechanical work. Dr. Greg Swift, a thermoacoustics expert at Los Alamos National Laboratory and someone I quote in the article, has a great little essay here that describes what thermoacoustics is all about.
In a nutshell, Steiner designed an engine core that eliminates all rubbing parts (i.e. mechanical friction). The piston is replaced with a thick steel plate fixed to the engine wall. Helium gas on the top side of the plate is heated, triggering intense sound waves that cause the plate to vibrate. Below the plate and separated by a thin layer of helium is another metal plate — a diaphragm — attached to a shaft. As the first plate vibrates it causes the diaphragm (and the shaft) to move rapidly up and down. And I mean rapidly — 30,000 cycles per minute. The shaft is connected to a linear alternator that induces an electric current as it moves up and down. That movement is very minimal at only 200 microns so Etalim has had to cleverly configure its alternator to capture such small movement. (See video with this post to get a visual of how this all works).
The end result is a highly efficient and durable compact engine that moves less gas per cycle than a conventional Stirling engine but compensates by achieving dramatically more cycles per minute. Etalim is aiming to manufacture engines that can supply 1.6 to 3 kilowatts and it believes it can get the cost down to a stunning 15 cents per watt, which is more than competitive with internal combustion engines and leaves fuel cells in the dust. It if can deliver, this would change the economics of microCHP (combined heat and power) for the home, biogas/landfill generation, solar thermal power generation and a whole host of distributed generation applications in need of a small, efficient and affordable engine that’s agnostic to fuel or energy source, as long as it supplies heat.
Etalim has a long way to go. It made its first prototype last year and proved that the design works as expected, but efficiency was low — just 10 per cent. The second prototype will come this spring and will aim for up to 30 per cent efficiency, with hopes of achieving 40 per cent by the time Etalim comes out with its first commercial product in 2012. That puts it in the territory of fuel-cell efficiency, but at a fraction of the cost. Etalim’s goal is to reach 50 per cent, but it has to figure out how to design the engine to handle temperatures exceeding 1,000 degrees C, meaning some use of ceramic materials will be necessary.
This is a great emerging story. So far the company has raised about $4.7 million, roughly half private equity (no VC) and the rest a grant from Sustainable Development Technology Canada for a demonstration project. It will likely be seeking $6 to $8 million in a first round of VC financing this summer.