Photo: Mercedes-Benz

• Power Plant: 1.8-L four-cylinder 190-kW (255 hp) turbocharged homogeneous charge compression ignition engine • Transmission: 7-speed automatic with integrated electric motor assist • Claimed Fuel Efficiency: 5.3 L/100 km (44 mpg) during cruising • Claimed CO2 Emissions: 127 g/km • More: The way Germans pronounce “DiesOtto” (the company's name for the engine design) sounds just like “DeSoto.” Daimler sold Chrysler (which owned DeSoto) this year, so shouldn't Mercedes-Benz pick another name?

A new type of engine in a radical reinterpretation of the big benz

Low and sleek, the styling of this highly conceptual study for a future full‑size S-Class Mercedes-Benz is almost as striking as its tiny power plant: a 1.8‑liter four-cylinder engine that combines the advantages of diesel and spark-ignition engines while avoiding the disadvantages peculiar to each.

First let's review: spark-ignition engines use a spark plug to ignite a vapor of gasoline and air, compressed at a ratio of perhaps 10:1, so that the burn starts at one end of the combustion chamber and propagates to the other. Diesel engines compress the vapor to a much higher ratio—say, 25:1—so that it combusts spontaneously, beginning at the edges and propagating inward.

The Mercedes design gets the best of both worlds by exploiting a formerly wasted product: the exhaust gas left over from the previous combustion cycle. That gas prewarms the incoming fuel-air mixture so that it needs less compression to reach ignition temperature. There are two such injections per cycle, and both require a very fine control of temperature and pressure.

When the piston reaches the top of its compression stroke, at a ratio closer to a spark-ignition engine's than a diesel's, the ignition begins spontaneously, not only at the edges of the chamber but at many points throughout. The result is a complete, efficient burn at temperatures too low for the formation of nitrous oxides—the diesel engine's Achilles' heel. Although the new engine's combustion produces less torque than you'd get from either a diesel or a spark-ignition engine, you'll never notice the lack under partial load—when you're at cruising speed, for instance. When you do need that torque, the engine operates just like its spark-ignition counterpart.

This design is known in the industry as homogeneous charge-compression ignition (HCCI), although Mercedes calls it DiesOtto, in homage to Rudolph Diesel and Nikolaus Otto, who invented the diesel and spark-ignition engines, respectively, in the 19th century. For many years the idea was shelved because practical engine controls were lacking. Relentless improvement in processing power, as quantified by Moore's Law, has now solved that problem.

The F700's engine includes two turbos—a small one for lower engine speeds, a large one for higher speeds—plus additional torque on launch from an electric motor integrated into the transmission. There's also a modification to the crankshaft, which the manufacturer doesn't spell out, that makes it possible to vary the engine's compression ratio. (Other manufacturers experimenting with HCCI engines, notably General Motors, make no such modification.)

The results are fairly startling. The carmaker claims 190 kilowatts (255 horsepower) at maximum load from a mere 1.8-liter four-cylinder engine while using only 5.3 liters per 100 kilometers (44 miles per gallon) at cruising speeds—in a vehicle weighing 1700 kilograms (3748 pounds).

The drawbacks? First, each cylinder needs its own pressure transducer so that the engine controller can fine-tune the combustion cycle, and those transducers are still very expensive. Second, the torrent of data from those transducers and other sensors makes the logic in the engine controller far more challenging.

In time, HCCI engines might be cheaper than diesels to build because they don't need the structural reinforcement that makes high-compression diesels heavier than conventional engines of equal power. They can also dispense with the complex emissions-control systems (such as Mercedes's Bluetec) that diesels need in order to meet California standards.

The F700 concept has a slew of other fascinating features, from rear-hinged rear doors to its Pre‑Scan hydraulic active suspension, which continuously processes optical data from the road ahead to change its settings proactively.

The industry expects HCCI engines to make it into production sometime between 2015 and 2020. This concept car could be the basis of perhaps the least conservative model ever seen in the S-Class, the most prestigious Mercedes line. Even in a world of rising oil prices and legislated limits on carbon emissions, this daring vehicle shows that there's life left in the combustion engine.

Photo: BMW

• Power Plant: 298-kW (400 hp) 4.4-L twin-turbocharged direct-injection V8 • Transmission: 6-speed automatic; steering wheel–mounted paddle shifters • Claimed Fuel Efficiency: Information not available • Claimed CO2 Emissions: Information not available • More: The X6 lineup is likely to include both hybrid-electric and 197-kW 3.0-L six-cylinder diesel variants in the near future; the BMW X5 sport utility, to which it is closely related, will offer that diesel in 2009.

Meet FlexRay, the new high-speed automotive data bus

Remember how magical the first antilock brakes seemed, back in the 1980s, when they stopped your car smoothly with half the wheels on ice and the other half on dry pavement? Those systems processed sensor data a few times per second, feeding the information to a dedicated brake controller. Compare that with today's cars, which process data from scores of in-car sensors—and even include external factors, like vehicle proximity—and instantly crunch the numbers with up to a dozen control systems, integrated by a vehicle controller. Now consider tomorrow's car, which will be nothing less than a local area network on wheels. For it, the relevant metric will be bandwidth.

The BMW X6 is the first production vehicle to build in the next order of bandwidth, using a scheme called FlexRay, a high-speed data bus developed by a consortium of carmakers and component suppliers. FlexRay offers two communication channels, each with a data rate of 10 megabits per second, a 10- to 40-fold increase over current in-car communications protocols, depending on how the system is implemented.

FlexRay ferries data among the components of adaptive drive, a vastly enhanced descendant of yesteryear's automatic braking. Instead of just detecting a wheel's traction, adaptive drive uses a central controller to interpret sensor data on speed, steering angle, longitudinal and lateral acceleration, body and wheel velocity, damper position, and other criteria. The system controls body roll and adjusts the dampers to keep the vehicle stable during virtually any maneuver.

The all-wheel-drive X6—which BMW calls a sports activity coupe—doesn't stint on horsepower, either. It's offered with a 4.4-liter aluminum V8 that puts its twin turbochargers in a novel position. They nestle between the V‑shaped banks of the engine instead of hanging off the exhaust manifolds outside the V. The scheme works because BMW has switched the position of the manifolds and the air intakes, so that the exhaust gases flow inside the V‑formation and therefore need to travel just a few centimeters to reach the vanes of the charger's turbine. This way, the exhaust can spin the turbine up with less delay between stamping on the accelerator and getting that extra turbo goodness.

To make that process possible, the company developed turbochargers from materials that could operate in the hotter environment between the banks, a virtual oven that continuously bakes the turbo system at hundreds of degrees.

Another innovation is what BMW calls Dynamic Performance Control, or DPC—one entry in an alphabet soup of electronic traction, suspension, and engine control systems. The DPC controls the effects of a rear differential that includes two planetary gear sets, each containing a central gear (the “sun”) spun by engine torque. This sun is surrounded by planet gears that are in turn housed in a ring gear that drives the individual wheel through two clutch packs, allowing the controller to reduce or multiply torque to each rear wheel individually to enhance steering, stability, and traction.