Peugeot’s air-brained idea
An engine that runs on air?
You’ve probably heard the rumours . . . maybe even seen a story on the Internet. The car that runs on air. It’s an intriguing idea.
No more gasoline or diesel fuel to pump; not even an electrical cord to plug in. And an unlimited supply of fuel, free for the taking.
If only it weren’t suppressed by Big Oil or Big Auto or . . . name your own conspiracy theory. Just like the 100 mile-per-gallon carburetor of days gone by.
Intriguing, but unrealistic. Or is it? In theory, the idea is sound. After all, a piston engine is, in essence, just an air pump that powers itself by igniting a combustible fuel mixture in each cylinder to apply downward pressure on the piston at the appropriate time.
That pressure could just as plausibly be applied by compressed air from an external source. In fact, compressed-air engines have been around for a long time — turbines and rotaries as well as piston-type configurations. They’re used today in pneumatic hand tools. And they have been successfully employed in applications as big as train locomotives and underground mining equipment.
So why can’t they be used in cars? The short answer is they can.
In fact, there is documentation suggesting that at least one airpowered vehicle was built even before the construction of the first internal-combustion-engined automobile. And several recent prototypes have been built and demonstrated in locales as far flung as Australia, France, India, Japan, Korea and South Africa. But . . . there’s always a “but.” The key word in the description of a compressed-air engine is “compressed.” And compressing air, wherever and however it’s done, requires energy.
Air compressors are typically powered by electricity or by some form of internal-combustion engine that is fuelled by gasoline, diesel fuel or natural gas.
To power an automobile engine, air would have to be compressed to a much higher pressure than is required for blowing up tires — as much as 30 MPA (4500 psi).
So, as well as the energy cost to compress the air, there would also be a financial cost. Contrary to the signs that used to adorn service stations in the pre-self-serve days, there’s no such thing as “free air.”
Just as you have to pay for the compressed air in a scuba-diving tank, you’d have to pay for the compressed air to power an automobile engine. A lot of compressed air. To provide any significant driving range would require a huge on-board storage tank, much larger than a conventional gasoline tank. But what if the air could be compressed on-board the car and stored in containers just large enough for immediate needs? And what if it could be compressed using energy that is otherwise wasted? More specifically, what if a compressed air system could be substituted for the hybrid-electric system in a hybrid car?
Those are questions that engineers at the French automaker PSA Peugeot Citroën asked. And they answered them with a technology called Hybrid Air, which was revealed at the 2013 Geneva auto show in March.
Fitted to an existing Peugeot 2008 subcompact urban crossover vehicle, the Hybrid Air system comprises a high-pressure air storage tank in the central tunnel, a low-pressure expansion tank in the rear and a hydraulic motor/ pump connected to an Electronic Gearbox Control that replace the conventional transmission.
Those components work in conjunction with a 1.2-litre, threecylinder gasoline engine.
In effect, they perform the same functions as a battery storage system and electric motor/generator in a hybrid-electric vehicle.
In Air mode, only the energy contained in the compressed air tank is used to drive the vehicle, providing zero-emissions operation. Air mode is employed primarily when driving in urban areas.
In gasoline mode, used primarily at steady speeds in highway operation, only the gasoline engine powers the vehicle. In Combined mode, both the gasoline and air engines work simultaneously to provide additional power for acceleration or hill-climbing and to achieve optimum fuel economy for the given conditions. The air tank can be replenished in two ways. On deceleration, speed is reduced via resistance to the compression of the air. Alternatively, some of the energy produced by the gasoline engine is used to compress the air. In either case, maximum capacity can be reached in just 10 seconds. Whether or not the Hybrid Air system will prove to be a feasible alternative to a more-conventional hybrid-electric system remains to be seen. But rumours say that PSA is considering a production version for 2016. wheels@thestar.ca