Although I am an electrochemist and spend most of my time working on batteries, supercapacitors and fuel cells, occasionally I raise my head and look at the alternatives for reducing emissions. The array, I must say, is impressive, and although I believe that the electrification of the powertrain is both inevitable and necessary, I am not blind to the fact that other technologies are competing and will find niches and even mainstream applications.
Flywheels, such as those developed by Flybrid and Williams Hybrid Power, originally created for Formula 1 KERS, are already finding their way into mainstream applications, such as hybrid buses and other heavy-duty vehicles. These are the natural competitors for supercapacitors and high power-density cells, with the technology able to provide a real kick of power very quickly and reliably with good all-round trip efficiency. The problem is that flywheels can’t store the energy for very long, with high self-discharge rates.
Compressed air engines seem to be another idea that has come around again – a notion first realized by the Liquid Air Company in London in 1903. Honda explored this powertrain area more recently, showcasing its Air concept a few years ago. However, probably a more practical solution is the use
of liquefied air, which is being pioneered by the Dearman Engine Company and promises zero emissions, similar (or better) range compared with battery electric vehicles, similar cost to an IC engine, and fast refueling with a liquid fuel. If this is demonstrable in practice, this technology could take the industry by storm and compete with both battery electric and fuel-cell vehicles head-to-head. However, supporters of this technology, like Dearman, need to take note and be quick. History teaches us that a technology that gets to market first can be very hard to dislodge – even by something superior.
One of the craziest notions, however, is actually electrochemical based, and involves the recent excitement over metal-air batteries, kicked off by Tesla filing a number of patents earlier this year. This seems to have generated a lot of discussion among Tesla observers, and others are understandably jumping on the bandwagon. However, the practical problems around implementing a refueling network for metal-air batteries are not trivial, and the potential round trip efficiency is even more than problematic. There is also the point that if, for example, coal-fired electricity were used to recycle spent aluminum, this technology would actually end up being one of the worst emitting forms of transport ever invented. The performance and reliability of metal-air cells is also an issue, meaning that they are still a long way from being commercially viable. Therefore, until practical solutions to these issues are found, this technology is far more likely to find a niche in military applications where the unique selling points will outweigh the costs.
With so much innovation ongoing, the next decade or so promises much powertrain fun to be had.