It's a diesel, a hybrid, a plug-in, a three-cylinder--and a tour de force, perhaps?

BMW's Vision EfficientDynamics concept has been the subject of rumor and innuendo for weeks, but now the German car company is setting the stage for its 2009 Frankfurt Auto Show display with new details of its concept.

Click here for PHOTOS

As the name implies, this concept car grafts fashionable green technology on the body of a 2+2 sports car. The promise: BMW M-car performance from a vehicle with a three-cylinder diesel plug-in hybrid powertrain.

To break down everything in that last clause takes some effort. The combination of fewer cylinders, plug-in hybrid technology, lithium-ion battery cells, and diesel combustion is a technological tour de force, should it ever reach production. It's a holy grail for green-car drivers that melds the state of the art in lower-consumption driving in ways that haven't made the step from engineering lab to the street quite yet.

The drivetrain marries a direct-injection, 1.5-liter, 163-hp, three-cylinder turbodiesel to two electric motors (one per axle), a set of lithium-ion batteries and a software controller that modulates and marries both powertrains to a combined total of 356 horsepower and 590 pound-feet of torque. Using only the diesel engine's power, a six-speed dual-clutch transmission sends power to the rear wheels. The hybrid powertrain is less conventional: it's actually two distinct applications, a hybrid system on the rear wheels and a hybrid motor on the front wheels. The rear-wheel hybrid system operates in tandem with the diesel engine, while the front system operates on battery power alone. With this arrangement--similar in concept to the Ferrari hybrid system announced earlier this year--the Vision EfficientDynamics could provide all-wheel drive in electric-only mode, with battery power twisting its front and rear axles simultaneously.

Performance is geared to please the toughest Bimmerphile. BMW claims a 155-mph top speed and a 0-60 mph time of less than 4.8 seconds, while providing fuel economy of almost 63 mpg, and for European enthusiasts, CO2 emissions of 99 grams per kilometer.

Because it's also a plug-in hybrid, those controversial CO2 emissions could be halved to 50 grams per kilometer, if the Vision EfficientDynamics were juiced up with electricity and driven on battery power alone. The plug-in technology used means the concept car would use a standard 220-volt household outlet to recharge its batteries. A 2.5-hour recharge time is predicted, though on a 380-volt line, BMW says a 44-minute full recharge is possible.

Driving range could pass 400 miles with fuel or 31 miles on electricity alone, BMW also adds.

A grand tourer in silhouette, the concept wears aerodynamically influenced cues for style and purpose. A low front end and active louvers cool the drivetrain when needed, and close to improve airflow when unnecessary. The racing-inspired details continue with well-managed airflow--so tightly tuned, the EfficientDynamics concept generates a coefficient of drag of 0.22, while today's best production cars sit at 0.24 (the Mercedes-Benz E-Class Coupe).

Dimensions place the EfficientDynamics concept in the middle of BMW's current coupe range. It measures 181.1 inches long, 74.8 inches wide, and 48.8 inches tall, and weighs 3076 pounds. The concept has 5.3 cubic feet of luggage space, enough for two golf bags.

The body of the Vision concept is lightweight in design and execution, its engineers say. The body shell and suspension are rendered in aluminum, the roof and door skins are formed from polycarbonate glass that darkens automatically in response to climate--like photochromic glasses. The cockpit of the Vision concept also uses lightweight materials. Kevlar frames the seats, and connects them to the center console, but elsewhere, sustainability is penned into the colors and materials chosen. LED lighting inside has ambient hues, while the headlights and taillights are linked to the ambient lighting to shift its color and intensity, depending on exterior conditions. A head-up display and night vision are configured into the gauges and driver displays.

Click here for PHOTOS

Sophisticated software underpins virtually every system of the concept. That software takes constant readings from the car's systems and interprets the data to enable more efficient operation. BMW says, for example, the navigation system's traffic data can cue the drivetrain to shut down the concept's cooling fans to prepare it for more efficient highway operation. Even the air conditioning and electric power-steering sensitivity are constantly tweaked in this way for optimum performance, BMW says.

Click here for more from TheCarConnection.com