Conventional wisdom says people wealthy enough to buy luxury cars don’t care about the cost of fuel.

Conventional wisdom is wrong. Nowadays, even members of the One Percent are counting miles per gallon.

Luxury car manufacturers, as a result, are trying to deliver better fuel economy without harming the essential nature of their exotic machines. That essence is excess — more power, performance, better handling, superior build quality, better safety technology and more standard amenities than can be found in less-expensive automobiles.

It is a contradictory pursuit that makes perfect sense in today’s marketplace. Buyers of luxury cars aren’t asking for less power, according to engineers and sales executives at Mercedes-Benz, Lamborghini, McLaren Automotive and Bentley — four companies I spoke to for this week’s column.

Those buyers instead are demanding oomph absent penalty — especially desirable in a time of rising fuel prices and globally increasing taxes on mobile-source pollution.

(Photo Courtesy of Mercedes-Benz)

Manufacturers are using a variety of technologies to solve the power-economy paradox. Among them are a growing reliance on aluminum, high-strength but lightweight steels, and carbon fiber and other composite materials. The aim is to reduce weight and thereby limit the work and fuel consumed in moving a load.

Older technologies, such as turbocharging, using exhaust driven impellers to pull more air into combustion chambers to get a bigger bang per unit of fuel burned, are being revisited with remarkable results. Consider this week’s subject, the 2012 Mercedes-Benz S350 BlueTEC 4Matic sedan, a born-again diesel member of Mercedes-Benz’s premium S-Class line.

There have been Mercedes-Benz turbo-diesels before, first introduced by the company in 1977. But none like this.

Diesel engines generally get 30 percent more miles per gallon than their gasoline counterparts. Turbocharged diesel engines, such as the one in the S350 4Matic, improve on that performance by directly injecting diesel mist into the combustion chamber for a better air-fuel mixture.

The results will impress anyone who loves driving. Here is a large, fully dressed, all-wheel-drive luxury sedan that moves from 0 to 60 mph in seven seconds, yet delivers 17 to 25 miles per gallon in the city and 25 to 37 miles per gallon on the highway.

Mileage is affected by multiple factors, including driving styles and road conditions. But those are fairly decent numbers for a large, high-performance luxury sedan.

You fall in love with the sheer movement of this one. All of that torque, most easily described as engine’s twisting power, gives you a powerful launch from “start.” Once you’re underway, cruising is a breeze with a seven-speed automatic transmission deftly managing the gear changes.

The S350 4Matic is luxury defined. It has every imaginable amenity and safety technology, including automatic distance monitoring between your car and the one in front of you and Mercedes-Benz’s patented “Pre-SAFE” predictive protection system to hold you in your seat and otherwise cushion you in the event of a crash.

The S350 4Matic has a healthy exhaust note, the way the tailpipes sound when pushing on the accelerator. But more pleasing is the constant purr of its turbo-diesel 3-liter V-6 engine (240 horsepower, 455 foot-pounds of torque) when moving along the highway.

It’s a stink-free drive, too. There’s no smoke, no discernible discharge of diesel particulate matter. The car requires ultra-low-sulfur diesel fuel, which translates to a sulfur content of 15 parts per million. The fuel is now available at most service stations nationwide.

The kicker is what Mercedes-Benz does with burned fuel gases in the S350 4Matic’s exhaust stream before those gases reach the car’s catalytic converter. From a compact container near the spare-wheel well, a urea formula (Mercedes-Benz calls it “AdBlue”) is automatically injected into the outflowing gases, turning them into ammonia, which is then converted to harmless nitrogen and oxygen after passing through the catalytic converter into the atmosphere.

It is a complicated business. It’s expensive. But no one who makes and sells cars for a living truly believed that providing a high-performance luxury sedan with maximum fuel economy and ultra-low emissions would be easy — or cheap.