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GM Receives $2.7M ARPA-E Award to Explore Thermomechanical Waste Heat Recovery Using SMA Heat Engine

Concept diagram of an SMA heat engine for power generation from waste engine heat. Source: GM. Click to enlarge.

As one of 37 projects selected by the US Department of Energy’s ARPA-E (earlier post), General Motors R&D will receive $2.7 million (subject to final negotiation with DOE) to support building a prototype thermomechanical waste heat recovery system using a Shape Memory Alloy (SMA) heat engine to generate electricity from the heat in automotive exhaust. GM was the only automaker to receive an ARPA-E award in the first round of funding.

According to Jan Aase, Director of the Vehicle Development Research Laboratory at GM R&D in Warren, Michigan, the team calculates that they might be able to deliver up to a 15% improvement in fuel economy using as little as a 15-20 °C differential between hot and cold in the system. (Prior to joining GM R&D, Aase was at GE Global Research.)

GM will work with HRL Laboratories (co-owned by GM and Boeing); Dynalloy, Inc., a Tustin, CA manufacturer of shape memory alloys (Flexinol) specially made to be used as actuators; and the GM/University of Michigan Smart Materials Collaborative Research Lab to develop new low-hysteresis SMA materials and the prototype system.

When a stretched SMA wire is heated, it shrinks back to its pre-stretched length, and when it cools back down, it becomes less stiff and can revert to the original shape. This behavior can theoretically be used to enable a heat engine: a mechanism that is capable of converting heat energy to mechanical or electrical energy.

There was a surge of interest in the potential for SMA heat engines beginning in the 1970s, but the few devices that have been built were too large and too inefficient to make them worthwhile, Aase said.

SMA materials instead have been used as actuators (Dynalloy’s specialty). GM researchers have published a series of papers on using SMA in applications such as latches. The SMA heat engine for waste heat recovery is something the researchers have been talking about for less than a year, Aase said.

We have not written a paper on this particular idea. It had been sort of talked about, but when the ARPA-E solicitation came out [in February], it crystallized our thinking. We should go after this. It’s the kind of thing that is a little bit far out, and since we have so many short term actuator-type projects available to us where we would have a quick return on investment for the company, it’s harder to divert resources to a project that is much higher risk and longer term.

We did some calculations to estimate what we could get out of it. Whether it was theoretically viable, whether we can heat and cool it in an effective manner to cause this two-way action is yet to be proven. This is the kind of high-risk, high-reward activity we thought fit very well with the ARPA-E kind of missions.

—Jan Aase

Key to the success of the project will be developing a material for the particular temperature range of the application, and also to develop a low hysteresis material. SMAs tend to exhibit hysteresis, which would not be good in this application, Aase noted. “It is tolerable as an actuator, but not as a heat engine application.”

From a strictly thermodynamic point of view the SMA thermomechanical waste heat recovery system would not be as efficient as a thermoelectric generator such as the one GM is also developing, Aase said. However, he noted:

Per unit mass, we believe it will be very effective. And in a transportation application, the mass efficiency is very important.

The project at this point is fairly wide open. The team has not yet determined the cooling mechanism. While the simplest thing to do would be to tunnel air past the device, the researchers may also consider taking part of the engine coolant, because liquid has better heat transfer characteristics than air does. “The cooling is the tricky part of the heat cycle,” Aase says.

The material trick is to get the low hysteresis material, and the packaging and design is what we [the collaborative team] will work on together. We assume there will be durability and other issues that come up. We have to go over rollers [in our concept]..bending stresses tend to be rather high. Up to now, all the applications I know of have been with straight pieces of wire. And of course there is also the designing of the heat exchanger portion of it and the mechanical packaging.

—Jan Aase

The pay-off for a successful development could be significant. In a hybrid system, the electrical energy could be used to charge the battery. In a conventional engine, this could perhaps even replace the alternator without any load on the engine, Aase said.

This award is significant for the gains in energy efficiency it could bring, and because it signifies how GM is doing business though collaboration and partnership.

The days are gone when we would do this kind of ground breaking work on our own. We need to continue to find ways to combine our deep technical knowledge with others who can help take our ideas from concept to commercialization.

—Alan Taub, GM vice president of global R&D



Just $2.7 million for this research...with some significant, highly marketable gains? Why then can't GM finance this on its own? Why even more tax dollars going to that company? Something smells here....


“The researchers have been talking about this for less than a year” and have written no papers but decided “We should go after this” – ummm.

“.. the SMA … system would not be as efficient as a thermoelectric generator ..”

“ .. the pay-off .. could be significant .. : .. this could perhaps even replace the alternator ..”
Really? Wow.

OK - Never mind - it’s "Only" $2.7 million.

But I’m having second thoughts about being so hard on Scuderi – The honesty's too much.


Speaking of GM needing money, I found this today;

So now you know the real reason Detroit needed a baitout.


This McManus guy from GM that you refer to sounds like he suffers from delusions of grandeur.

He says he did the original study - says he changed the results and claims that it is his fault that (all of) Detroit had the wrong vehicles until now. Sure.

He says his NEW study (he was lead analyst) shows the new CAFE - will benefit the US auto industry more than foreign because the US makes so few small cars now.
That is too simplistic to bother with.

Now he says that once the market offers a wider selection of more fuel-efficient vehicles, consumers will come to realize that they want them.

There is no shortage of small cars.

He still hasn’t learned that what is in GMs showrooms, does not determine what people buy.

People already know they want fuel-efficient vehicles – Duh. But they want them from Asia – same as for the last 25 years.

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