Electric vehicle systems aren’t the only way to create a hybrid. Technically, a hybrid is any vehicle that uses more than one fuel source and propulsion system to operate. So a gasoline-electric hybrid is a car with a gasoline engine and an electric motor that can both either partially or fully move the car. The same goes for a hydraulic hybrid system, which uses an internal combustion engine and a hydraulic pressure system to move the car.
In this case, what some Swedish researchers are looking at is using an ICE engine and compressed air to move a car. Sound goofy? Don’t be confused by the hokey “compressed air cars” you might have seen in the past. This is very different and very plausible.
Well, it’s not as dumb as it seems at first glance. The idea is similar to how a hydraulic hybrid works. The energy from braking is stored as compressed air rather than pressurized hydraulics and then released into the drive train when the car accelerates. Hydraulic hybrids used in medium- and heavy-duty vehicles like garbage trucks have shown to reduce fuel use by 30% or more. There’s no reason to think the same (or better) couldn’t be achieved using compressed air as well.
The technology, according to the scientists researching this, would be targeted for urban commuter and other stop-and-go drivers. In a smaller car, such as a Honda Civic or similar, they theorize that fuel savings of up to 60% could be seen.
The stop-and-go part is critical and explains the huge benefit that might be possible here. When a car stops or slows down significantly, it loses a lot of kinetic energy – mostly through heat in the brakes. By capturing as much of that as possible, this form of regenerative braking would be utilizing that energy to compress air in small tanks at each wheel. When the car accelerates, say out of a stop light or while in gridlock, the energy would be returned to the drive train rather than gained by burning more fuel.
Unlike a similar system using electricity, this air-hybrid system would be able to store the compressed air (energy) almost indefinitely and would be much cheaper, simpler, and more cost-effective to implement.
So far, the research team has built a small 1-cylinder prototype test bed and proven the concept. Now they are ready to put it on a full-sized mockup. Eventually, the team wants to prove the technology on platforms ranging from small cars all the way up to city buses.