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Clean Diesel Engines

Posted in How To: Engine on May 1, 2006
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Dodge Cummins 610

You don't often see the words "clean" and "diesel" put together like that, but get ready for some big changes to the diesel landscape. Starting in October 2006, gas stations and truck stops will sell a whole new kind of diesel, one that burns far cleaner than the diesel we're using today. And when that fuel is run through the next generation of diesel engines and emissions-control systems (which will begin to show up in model year 2007), they'll be in some ways cleaner than gasoline engines.

That's all well and good if you're planning to buy a brand-new diesel truck next year. But what about the thousands of you driving older diesels? Will this new fuel work in your rigs too?

Since we hate surprises as much as the next guy, we won't leave you hanging. The short answer is yes, though you may need to keep an eye on your fuel system for leaks. Keep reading to learn more about this new clean diesel and how it will run in current and older diesel engines.

Starting this summer, refineries are going to change the way they produce diesel, and by doing so will reduce the amount of sulfur in the fuel. Current standards allow a sulfur content of 500 parts per million (ppm) by weight; the new rule hacks that standard down to 15 ppm. By itself, this ultralow sulfur diesel (ULSD) will have a significant effect on diesel engine emissions, reducing sulfur oxides by 88 percent and particulate matter by 4 percent, reports the California Air Resources Board.

This diesel gets really clean when it's paired with new emissions control equipment that will be added to diesel trucks starting in 2007. Traps in the exhaust system will capture particulate matter, cutting those emissions by 80 to 90 percent, according to the Diesel Technology Forum. Catalytic converters will focus on nitrogen oxides (NOx), reducing those emissions by 25 to 50 percent. The net result is that when these systems take effect, "clean diesel trucks and buses will have reduced both particulate matter and NOx by 98 percent from 1988 levels-a virtual elimination of these emissions from on-highway engines," says the Forum.

Jeep 2.8L Common Rail Diesel

This dramatic decrease in diesel's sulfur content has some side effects, as you may imagine. "Among the ways diesel is different from gasoline is that fuel is used to lubricate the fuel pump, not oil," said Loren Beard, senior manager of environmental and energy planning for DaimlerChrysler. "When you take out all the sulfur compounds, the hydro-treating process also takes out compounds that give diesel its natural lubricity, which protects the fuel pump and injectors." To prevent any lubricating problems with the new fuel, the American Society for Testing and Materials added a lubricity specification for all diesel fuels in 2005. "That additive will actually make diesel's lubricity better than it was before," said Beard.

The sulfur-reducing process also lowers the "aromatics content and density of diesel fuel, resulting in a reduction in energy content," said a report from Chevron, a reduction that could affect power production and energy efficiency. However, Chevron and other refiners peg this energy content loss at approximately 1 percent, so unless you own an over-the-road trucking company that tracks its fuel economy very carefully, any loss of mpg or power most likely won't be felt.

On the upside, the sulfur reduction causes an increase in diesel fuel's cetane rating, which is sort of like gasoline's octane. The cetane rating is a measure of the fuel's ignitability; increasing it improves the fuel's efficiency and also reduces its black, smoky emissions.

Clean diesel may still be months away, but Jeep demonstrated the technology's potential by unveiling the Bluetec Grand Cherokee concept at the North American International Auto Show in Detroit. Bluetec is the name DaimlerChrysler is giving to a number of diesel-related technologies, including new-generation, clean-burning engines (like the Euro-spec 3.0L common-rail diesel in the concept SUV); a diesel particulate filter; and a selective catalytic reduction (SCR) system for reducing nitrogen-oxide emissions.

Our upcoming ULSD has been compared to the diesel fuel currently used in Europe, but the two aren't identical. While Europe's diesel has a sulfur content that's even lower than our new fuel-at 10 ppm-its cetane rating is in the mid-50s, much higher than the low-40s ratings for U.S. diesel. Plus, according to Andrew Buczynsky, a senior fuels engineer for General Motors, European emissions laws are more lax than ours regarding NOx. "Those engines will have to be tweaked before they can be used in the U.S." That tweaking may have already begun, as you'll see later in this story.

None of the refiners we spoke to wanted to make specific estimates of what the new diesel will cost at the pump, but expect an increase. "As an industry, we've invested $8 billion to make the change," said John Leon, who works in fuels marketing for Shell.

Some of the rise in the pump price will be to offset the new diesel's refining process, which is more expensive than the current system. There will be additional transportation costs too, especially at the fuel's introduction. Diesel fuel is very susceptible to sulfur gain, said Leon. Any exposure to the old, 500-ppm fuel-in pipes, tanks or transport trucks-could cause the new fuel's sulfur content to rise out of spec. So the refiners will be taking a lot of care to clean their transport means and keep the new fuel away from the old.

The closest we could get to a cost estimate was from a study of ULSD by Washington State University, which found that areas already using the fuel were paying anywhere from 11 to 15 cents per gallon over the cost of conventional diesel.

Daimler Chrysler's Beard looked at it another way: "It's hard to predict changes in retail price. If people believe there will be a shortage and rush to stations to fill up, there will be shortages. Shortages will cause prices to spike. But the actual cost to produce this new fuel is low, pennies per gallon, which is less than seasonal price fluctuations we experience now."

Keep in mind, too, that diesel engines are inherently 20 to 40 percent more efficient than gasoline, and should return a comparable increase in fuel efficiency, which should help offset the higher per-gallon price.

When we asked about coming applications for the new diesel fuel, the automakers were, as usual, somewhat vague in their answers. Tom Read, a P.R. rep for GM, said his company is "always looking for opportunities" to make use of the new fuel. "We'll drop it in where we see the opportunities, and where the market is right. If the market is right, we'll make it work." He went on to say that Duramax applications in 2500- and 3500-series trucks will likely be among the first prospects for the new technology, as will medium-duty trucks.

A recent article in trade journal Automotive News stated that several makers have new diesel applications on the drawing boards, including Toyota and Nissan for their fullsize trucks. Honda, too, has a four-cylinder diesel in the works for light-duty trucks, says the magazine.

GM's medium-duty trucks will likely be among the General's first recipients of clean-diesel technology. Shown here is a concept version of Chevrolet's Kodiak C4500 4x4, modified by Monroe Truck Equipment, that was shown at the auto show in Detroit.

Daimler-Chrysler proved it's already in the hunt by demonstrating a whole system of clean diesel technologies-called Bluetec-on a Jeep Grand Cherokee concept SUV at this year's North American International Auto Show in Detroit. The Jeep's European 3.0L common-rail diesel engine was just the start of the Bluetec system, which also included a diesel particulate filter and a catalytic converter that transformed NOx into nitrogen and water vapor. At the Detroit show, Dieter Zetsche, Daimler Chrysler's CEO, said Bluetec is "ready for all 50 states, and can even meet 2009 emissions standards."

It's these kinds of particulate traps and catalytic converters that'll make the '07-and-newer trucks clean enough to sell in smog-bound places. Yet they don't exactly sound like performance-enhancing devices, do they? If anything, they conjure up memories of the days when gasoline switched from leaded to unleaded, and we were warned of how leaded gas would destroy the new smog equipment. Well, guess what. The same thing is happening again.

PhotosView Slideshow

The emissions controls on the '07-and-newer diesel trucks will be damaged-"poisoned" is the word used by a couple of our sources-if subjected to the old, higher-sulfur diesel. "Two tankfuls of high-sulfur and the catalyst will be shot," predicted Shell's Leon. So these vehicles will be stickered, most likely on the dashboard and at the fuel filler, warning the owner to pump only ULSD into the tank. Gas pumps, too, will be well marked with signs indicating that the new fuel is in the storage tank. Chevron is already calling its new diesel S15; BP calls it ECD, for Emissions Control Diesel.

Everyone we spoke to said the new fuel should work just fine in current and older diesel engines. Its lubricity won't be a factor, and the slightly lower energy content will be felt only by the most sensitive of drivers. The only issue that did arise had to do with rubber and other elastomers in a truck's fuel system.

Ford's Mighty F-350 Tonka concept truck-Power Stroke powered-looks as good today as it did at its debut four years ago. If this is the face of Ford's clean diesel, bring it on!

Said John Leon, "In 1993, diesel changed from high (2,500 ppm) sulfur to the low sulfur we have now, and at that time I'm told there was some leaking in O-rings and fuel systems. Vehicles made before 1993 used to use nitrile rubber-based seals which would shrink when exposed to high temperatures or changes in the sulfur content of the fuel. Since 1993 all manufacturers have changed to synthetic materials in their O-rings."

Because the change in sulfur content from 500 ppm to 15 ppm isn't as drastic a drop as the one in 1993, Leon said he doesn't anticipate seeing the same kind of impact. "But people with vehicles older than 1993 may want to check with the vehicle's manufacturer to see if they recommend any course of action because of the new diesel."

Everyone we spoke to was bullish on diesel's future. "Shell as a company thinks diesel will get bigger in the U.S.," said Leon. "Maybe not as big as in Europe, but certainly bigger." It certainly has a leg up on that other alternate fuel on the horizon, hydrogen. "The nice thing about diesel is that the infrastructure is already there," Leon said. "Hydrogen will require completely new infrastructure. But with diesel, you get your fuel at the same place you've always come to, just at a different pump."

Every Jeep Liberty fitted with the 2.8L common-rail diesel rolls off the Toledo assembly line running on B5 biodiesel, made from soybeans grown in Ohio. It's Chrysler's way of encouraging the use of renewable fuels.

Bio Willie sounds like a drug for male enhancement, but it's actually a biodiesel fuel made by a company co-owned by country singer Willie Nelson. Bio Willie may be the best known, but it's just one of several biodiesel fuels that have become available recently.

Biodiesel is an alternative form of diesel fuel that's made from vegetable oil, cooking oil, or animal fat-resources that are easily found in this big, bread-basket nation of ours. It's not a new idea; when Rudolf Diesel demonstrated his namesake engine at a Paris fair in 1898, it ran on peanut oil. It was Diesel's hope that his engine would be a viable power source for farmers, small business owners, and others for whom a steam engine just wasn't practical or affordable.

Today, biodiesel is sold pure (also called "neat") or blended with petroleum-based diesel. Bio Willie, for example, is a B20 fuel, meaning it contains 20 percent pure biodiesel and 80 percent petro-diesel. B5-5 percent bio, 95 petro-is the other commonly found blend and is the percentage most often suggested by OE manufacturers of heavy-duty diesel engines, including Ford and Cummins.

This map, from the National Biodiesel Board, indicates areas of the country where biodiesel was sold as of late 2004. We're sure you can add a few more pins to the map by now. Biodiesel fuel is primarily available in areas with significant soybean farming.

Beyond its non-petroleum origins, biodiesel's main advantage is emissions reduction. According to statistics provided by Cummins, using a B20 diesel fuel can decrease particulate emissions by 16 to 33 percent, carbon monoxide emissions by 11 to 25 percent, and hydrocarbon emissions by 19 to 32 percent. Because of biodiesel's high oxygen content, though, B20 actually increases NOx emissions by 2 percent, cites Cummins. (As a side note, we can tell you of another "emissions" benefit from firsthand experience: An engine running on biodiesel smells like french fries, not your typical smoke-spewing semi.)

What's the downside of biodiesel? It has less energy content compared with petro-diesel, so mileage may be affected, depending on the blend ratio. It also has a higher viscosity than conventional diesel, so flow problems may develop, particularly in cold weather. And the methyl esters in the fuel have been known to attack rubber and composites in fuel systems, creating the potential for leakage.

Despite those issues, biodiesel is growing in popularity, as does our motivation to find non-petroleum-based energy resources. Thanks to visible spokes-folks like Willie Nelson, it'll probably continue to do so. More info:

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