Technologue: Air Apparent - The wackiest hybrid yet - the MDI Air Car - hails from France via India
Say you're a developing country with a billion or so poor, upwardly mobile, would-be drivers pining for personal transportation. You could tool up for a billion cheap two-stroke Tuk-tuks and hope your citizenry evolves a genetic ability to breathe blue air. Or you could hope to attract a billion tech-support phone-bank jobs so they can afford Priuses. Or maybe you could engineer a $9000 car that runs on air.
All three solutions sound equally unlikely, but indeed French R&D firm MDI has licensed technology for an air engine to India's largest car company, Tata. And indeed the engine runs on compressed air-and electricity and the combustible liquid fuel of your choice. This system omits the priciest bits of a typical gas/electric hybrid vehicle-the battery and power controller-in favor of a composite compressed-air tank and some valves. The air is metered into an ingenious piston engine using matched pairs of small and large pistons. A small one works with a conventional connecting rod, while the large one employs an intermediate rocker arm that allows it to pause at top-dead-center for 70 degrees of crankshaft rotation, building pressure during the small piston's power stroke. This allows each pair of cylinders (two-, four-, and six-cylinder variants are envisioned) to produce power over 270 degrees of crankshaft rotation, while sharing a common intake and exhaust valve. CLICK HERE for a video demonstration of how the engine works.
In a small-city car weighing 1100 pounds, two 100-liter (26.4-gallon) cylindrical tanks pressurized to 4350 psi provide 60 to 90 miles of city driving range. Refilling would take about two minutes at a compressed-air station. Plugging into a 220-volt electrical outlet at home or work, the tank fills in about four hours, while an on-board motor spins the engine as a compressor. This same starter/alternator is used to maneuver the car in reverse and to recharge the ordinary 12-volt battery that runs the lights and accessories when slowing or stopping the car. Running the engine as a compressor during braking is technically feasible, but expensive and trickier to integrate seamlessly than this electrical regeneration is. Reversing on electricity simplifies the design of the automated manual transmission, too.
The MDI Air Car compares favorably with the soon to be reborn Norwegian TH!NK electric city car. It weighs about half as much, costs less than a third as much (even before counting the lithium-ion battery pack, which TH!NK will make buyers lease), and recharges a couple hours quicker, though it travels just over half as far on a charge. Both accelerate slowly and top out around 60 mph.
