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  • Getting to Green

    An administrator pushes, on a shoestring budget, to move his university and the world toward a more sustainable equilibrium.

Blowing cold air
February 6, 2009 - 6:17am

One of the tactics Greenback would like to use to decrease our carbon footprint in the short term is to replace our existing (largely unremarkable) fleet of campus vehicles with ones which are more fuel-efficient. Long-term, we'd like to get away from fossil-fueled vehicles entirely, but at the moment that's hardly practical.

As a result (and because I'm a car nut from way back), I try to keep up on the most promising automotive engine technologies. And one recent development has my attention piqued. Hybrid cars/truck/whatever. But not electric hybrid -- pneumatic hybrid. And no, I'm not talking about motors that run on compressed air (although, for some applications, those are potentially interesting).

Look, an internal combustion engine is basically an air pump. Air flows in through the filter, then fuel gets sprayed -- injected -- into it so that (in the presence of a well-timed spark) it will explode and force the air out the exhaust system. As a byproduct of all this airflow, pistons get pushed and cranks get turned and vehicles get moved; still, the principal process is about airflow.

As a result, anything that improves the flow into and through the pump makes the engine more efficient. Superchargers. Turbochargers. Now, pneumatic hybrids.

What a pneumatic hybrid does is to capture the kinetic energy of the car during the braking process, and use it to compress air. Your (or your neighbor's) Prius captures the same energy, and uses it to generate electricity. The Prius uses the captured electricity to run the whole vehicle for the first 20 or 25 miles of low-speed driving, and otherwise turns the job over to a gasoline engine. What a pneumatic hybrid does is to feed the compressed air into a small gasoline engine when it's needed most -- when the car is accelerating from a dead stop, for instance. Pressurized air flows very efficiently into that pump, so the engine generates more power, using less gasoline. Up to one-third less gasoline. By using a technology which is simple, relatively mature, and adds only about 20% to the manufacturing cost of the engine. (To put that in perspective, a Prius drive system costs about 200% more than the similar components of a Corolla.)

Minimal changes in technology (most of the car is unaffected). A small bump to purchase price, but a significant decrease in operating expense -- figure a payback period under two years, and most Americans are keeping their cars 8 years or so, these days. To a mechanical engineer, the virtues of the design are obvious, once the idea is even suggested. It's the idea that's been missing. (OK, and the software algorithm to control the air compression/release mechanism.)

The take-away on this story? That even the industries and technologies which are most mature and most settled can be reinvigorated by a few good ideas. And that, with new necessities, we can expect to spawn a bunch of new inventions. And (as I keep trying to convince the engineering department), the colleges and universities which will have to worry the least about the next economic downturn will be the ones which develop, encourage, and host the most creative (and lucky) idea-generators during the upcoming round of industrial re-engineering.



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