Mercedes' 'green' diesel meets tough air standards

It seemed silly to be carrying cloth grocery bags as I locked up the $62,000 Mercedes-Benz and headed into the market. But then I was driving a "green" diesel.

Mercedes' E320 Bluetec sedan is the only new diesel passenger car currently available in California. And there's a catch. It is available only as a two-year/24,000-mile lease and at the end of the term it goes back to Mercedes.
It seems ironic that the mileage is limited to 24,000 when a tank of diesel will propel this car close to 700 miles. But there is a reason.

The E320 Bluetec lease is a bridge until 2009 when the E-class will be redesigned and the new diesel engine will be 50-state compliant for emissions standards. The new engine will have a particulate filter, as does the E320 Bluetec, but it also will have urea-injection to further control oxides of nitrogen, which is the crud in smog.

Mercedes-Benz was able to cut a deal with the California Air Resources Board that the Bluetec E-class will meet the state's air standards for the lease period. And to further allay concern by the board, the cars will be shipped out of state afterward.

New diesel engines - passenger truck or car - have to burn as cleanly as a gasoline engine. And while Mercedes' 3.0 liter V-6 diesel is likely to remain clean-burning after two years, Mercedes acknowledges that the exhaust system won't be as clean as the vehicle ages.

This fall, Mercedes-Benz will begin selling diesel-powered versions of its ML- and GL-class SUVs and the R-class crossover. These also will use the so-called AdBlue injection, which adds a urea-based solution into the exhaust stream.

Urea injection has been a stumbling block for the advancement of diesels in the United States. Without urea, the engine won't pass stringent emission standards. But how to keep the engines burning clean with 8 gallons of urea onboard that will need to be refilled about every 10,000 miles? For some drivers that could be once a year, for others it will mean more trips to the dealer or learning to make refills at home. The tank is hidden in the trunk.

When the urea needs to be refilled, the car's onboard computer will initiate a series of alerts, just as a gasoline-engine E-class will alert with a dashboard warning that a service interval is approaching.

Ignore the urea warnings, and the vehicle will begin a countdown of remaining starts, beginning at 20. Miss that deadline and the driver will have to add at least a gallon of urea to get the car restarted.

Diesels have always had different maintenance needs, but the pluses generally outweigh the negatives.

Diesel engines are heavier than gasoline engines to handle the much higher ignition pressure in the cylinders. Fuel is combusted by squeezing air to extremely high pressure inside the cylinders, then injecting fuel to ignite in the hot air.

Modern engines, such as this one, use high-pressure direct fuel injection. Piezo-electric injectors spray atomized diesel fuel directly into the center of the combustion chamber. The injectors are placed similar to spark plugs in a gasoline engine. Putting them deeper into the cylinder has taken away much of the diesel clatter that so identifies older diesels.

And with more complete combustion and fuel distribution, there is no smoke or smelly exhaust. Even the ultra-low-sulfur fuel is less pungent if a drop gets on clothing or skin while refueling.

The ignition process is as simple now as a gasoline-powered vehicle: turn the key and go. There's no waiting for "glow" plugs to heat up to be able to detonate fuel. And after the initial warm-up the diesel noise mellows into good engine sound, even on full-bore acceleration.

The turbocharger gives good boost at all rpm levels so there is little to object about modern diesels. Except finding your neighborhood station that carries diesel.

There's more energy in diesel fuel than gasoline - the pistons don't have to work as hard and the engine revs are lower. You're hard pressed to get one to go over 4,500 rpm, when many gasoline engines hit the peak horsepower at 5,000 to 6,500 rpm.

The E320 Bluetec has a horsepower rating of just 210 at 3,800 rpm, but there are 400 foot-pounds of torque at 1,600 to 2,400 rpm. That's high-performance launch force.

Compared to the gasoline E-class, the diesel is a tenth of a second slower from zero to 60 mph. But between 50 to 70 mph the diesel has more punch.

And the Bluetec's fuel-mileage ratings of 23 mpg city and 32 highway are definitely of interest.

In the early 1980s, 79 percent of Mercedes' sales were diesels. And for the E320 Bluetec, Mercedes came back to market with a more traditional type of luxury car. The Bluetec has 16-inch tires and alloy wheels, versus 17s on the gasoline E350. The suspension is set for comfort, not sport, but it handles confidently under pressure.

The driving experience is lovely and lush. The optional wood and leather steering wheel glides through the fingers. The brakes apply with refined and robust stopping power and the cabin is luxuriously quiet. Steering force is light but precise. In tight parking situations, this car seems to pivot into place.

The only aspect I found too traditional were the seat bottoms, which felt hard, after not much time on the road.

The 2009 Bluetec will offer more Sport features, Mercedes said.

Standard equipment includes all the expected amenities, but I did appreciate the optional trunk closer ($530). I also liked the Keyless Go starting, which allows unlocking and starting without having to pull the key pod from purse or pocket. It is part of the $4,320 Premium II package, which also includes a navigation system (that isn't too difficult to use), Sirius satellite radio, bi-xenon headlights that turn with the steering wheel, cornering fog lights and more.

The E320 is a desirable package that costs about the same as the E350 gasoline version. But with diesel now costing more than $4 a gallon, the key to Bluetec is in its extended range, but that's out of reach with the current lease.

This car is one more choice as more people try to place a smaller carbon footprint on the planet.

Mercedes-Benz will offer a hybrid S400 sedan by the fourth quarter of next year. It will be a mild hybrid with lithium-ion batteries and an electric motor to assist the gasoline engine under acceleration. Also with start-stop mode and regenerative braking.

Then it will offer the ML450 SUV as a dual-mode hybrid and, ultimately, a diesel hybrid.

Emission targets will only get stricter.

"We are trying to come out with solutions that are viable without compromise," spokesman Rob Moran said. "Being first to market is a big deal for us."

Mark Maynard is driving in cyberspace at mark.maynard@uniontrib.com.

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