SCR In 2010?
2007 diesel exhaust will be further cleansed with 'heavy' egr and particulate filters. What next?
Tom Berg
Equipment Editor
It's May of 2010, and you're scratching your head about the trucks you've just taken delivery of. They've got more piping than you can shake a wrench at and more wiring than even a nerd can comprehend. More junk than just three years ago when those confounded '07 models came out with their increased rates of exhaust-gas recirculation and the new particulate filters.
Those engines have been working OK, but they sure were a chore to get sorted out, and your ears are still ringing from what the financial people said about the price hikes.
Now these '10 models! The bean counters again can't believe the prices. You can't believe the complexity. How will you keep them running? How can the company afford the extra fuel, now at more than three bucks a gallon?
Then you wake up, and you know the nightmare isn't true - at least not yet. You're doubly relieved because you've heard that there might be hope for 2010 diesels in the form of selective catalytic reduction, or SCR, the comparatively simple emissions-reduction method slated for use in Europe starting this fall.
If engine makers had their way, SCR would be used to lower nitrous oxides for U.S. 2007 regulations. Exhaust systems would still need particulate filters to catch "nanoparticles" of soot, but they could get by with less EGR and other combustion complications to reduce NOx. SCR does that by injecting a special fluid into the exhaust stream. The fluid contains a catalyst - urea - which converts NOx into nitrogen and water. These are expelled out the stack.
SCR could be especially helpful in 2010, when NOx must be cut further, but there's stubborn opposition from the federal Environmental Protection Agency. EPA officials worry that SCR's urea-based fluid will not be widely available by the time it's needed. And even if it is, truckers will try to cheat by simply not filling up their urea tanks, and exhaust will revert to being dirty.
In panel sessions at industry meetings and press events, industry engineers scoff at these objections. They note that SCR fluid will be used in small quantities -5% to 6% of diesel fuel burned in European diesels, and only 3% and perhaps as little as 1% on 2010-model diesels in America. So the "infrastructure" that EPA dreams of won't be necessary.
At 3%, only six gallons of urea fluid would be required for every 200 gallons of diesel. Filling 'er up with urea won't be much at all. Fleet terminals and truckstops won't need big underground storage tanks and special pumps to dispense it, and chemical companies won't need fleets of tanker trucks to deliver it. They'd sell it in jugs, like antifreeze, and it would cost about the same as diesel.
One slight complication is that the fluid is about two-thirds deionized water, so it would have to be kept above its freezing temperature. "AdBlue," as European engineers call the fluid for its color and the fact that it's an additive, freezes at 12 degrees Fahrenheit. If jugs of the stuff were stocked near fuel pumps in cold climates, they'd probably have to be kept in heated cabinets.
On the truck, the fluid tank as well as hoses and couplings would also have to be heated. Many trucks running in northern climes already have heated fuel lines, and similar devices could be employed for the AdBlue lines. Meanwhile, winter tests in Finland show that SCR equipment aboard trucks works just fine.
As for cheating, sensors in the truck's AdBlue tank could detect low levels and signal the engine controls to reduce power, then shut down completely when the tank runs dry. This is already done when controls sense other problems, and builders say it would be easy to add this function.
It appears that EPA is beginning to come around. Chet France, director of EPA's standards division, told attendees at a recent Clean Heavy Duty Vehicle Conference that his agency recognizes SCR as one of the ways to meet '07 and '10 emissions limits. However, the industry must demonstrate that it can distribute and stock the fluid, and how it would thwart any attempts at operating engines without it.
"There is no question that the challenges can be overcome," France remarked. "I personally think they can be."
