CleanMarch 7th, 2012 | Posted by in T2W
During a normal working day, operators of Atlas Copco water well rigs might not have time to reflect on the fact they are driving the world’s cleanest trucks. It is no exaggeration: in some ofAmerica’s larger municipalities, Atlas Copco engines are actually cleaning the city air as they drive through town.
These engineering marvels have been designed to meet the 2010 U.S. Environmental Protection Agency (EPA 2010) over the road diesel exhaust emission standards. And if they happen to be driving the newest generation Atlas Copco T2W, they might not notice anything different at all.
It was purposely designed so that operators would not experience anything different than in a pre EPA 2010 rig: the T2W features Advanced Exhaust Gas Recirculation (EGR) technology.
Both Advanced EGR and the more common Selective Catalyst Reduction (SCR) are effective methods for meeting the new standards. Atlas Copco is offering water well rigs in both technologies because contractors have a wide range of needs that can be better met by one or the other.
It just so happens that one of their long time mobility partners, International Trucks, is the only manufacturer who has 100 percent EGR based diesel engine designs. The first new generation T2Ws off the line feature International carriers with Maxxforce EPA 2010 compliant EGR diesel engines.
Case for EGR
Several other manufacturers had attempted EGR before announcing SCR as their EPA 2010 solution.
International focused on EGR, believing it to be a permanent solution, one that was user-friendly. Lyndell Pannell, a sales representative ofTexasbased Southwest International Trucks said, “Our goal was to build an engine no different to operate than pre EPA 2010 rigs.”
He noted that among the most significant values of owning a solely EGR based rig are that it meets the EPA 2010 standard without requiring additional operator training or action and that it allows companies to travel to remote areas without having concerns for diesel exhaust fluid (DEF) sources. Liberation from DEF also means no concerns about performance rating as the DEF tank runs low, or restarts if it has run out.
Additional benefits are that there is no mixture to monitor and no additional fluid to maintain records for. Nor is there any additional equipment to maintain, such as a DEF doser and DEF container. There simply are no externally visible clues that an EGR rig is meeting EPA 2010 standards.
Atlas Copco partners with only the most trusted manufacturers. Performance is guaranteed by either system. To know whether to choose a rig built on an SCR engine, such as a Peterbilt, or an EGR based International, you will want to know more about how the systems differ.
Much of the information on the Web is conflicting, though, and most of it seems biased in preference of one system or the other. Atlas Copco does not manufacture diesel engines and provides information only for the benefit of customers making a choice based on their unique requirements.
Keith Estes, the Altas Copco product marketing engineer for water well rigs, said that although Atlas Copco has chosen International for its newest T2W and offers an
International T3W, customers may request either rig be installed on a Peterbilt carrier as well. Atlas Copco has some Peterbilts currently in stock.
As of June 1, 2006, Pannell said, the U.S. EPA has required that all highway diesel fuel be Ultra Low Sulfur Diesel (ULSD). ULSD’s sulfur content is 15 parts per million (ppm) or less. This was one step toward meeting the EPA’s Clean Air Act target.
American diesel engine manufacturers took it from there, designing engines that would burn ULSD and emit no more than 0.01 grams of particulate matter per brake horsepower from their exhaust. Brake horsepower is the total horsepower before subtracting the loss in power consumed by things such as the alternator, power steering pump, and part friction.
To do this they had to overcome the problem of nitrogen oxides (NOx) and particulate matter, or soot, that are produced during combustion at high temperatures. Engineers chose between two effective solutions.
External vs. Internal Treatment
Selective Catalytic Reduction (SCR) reduces NOx externally, post combustion, by introducing a Diesel Exhaust Fluid (DEF) into the exhaust system. DEF consists of about 30 percent synthetic urea or ammonia and is commonly purchased under the name Ad Blue. It combines with NOx in the exhaust, converting it to harmless by products, such as water and carbon dioxide.
The technique requires the purchase and continuous onboard storage of DEF, with requisite maintenance of associated DEF storage and mixing equipment. In normal conditions, the rate of DEF consumption means operators only need to refill the DEF container about every other time they fill their fuel tanks. The fluid is widely available for purchase at dealerships and many diesel refueling stations.
International’s Exhaust Gas Recirculation (EGR) systems treat NOx internally, “in cylinder,” two ways. First, combustion takes place at lower temperatures, so less NOx is produced. Second, exhaust is re-circulated back to the cylinders, where it replaces excess oxygen in the mixture. Drivers operate an EGR rigs no differently than they drive pre EPA 2010 rigs. All of the technology is built into the engine with no need for additional operator action.
In addition to these NOx reducing systems, both methods also incorporate catalytic converters and diesel particulate filters and to deal with soot and other particulate contamination. The particulate filters require a periodic regeneration cycle that raises exhaust temperatures to burn off any accumulated matter.
International’s advanced EGR
While some early EGR competitors were unable to avoid horsepower loss due to lower combustion temperatures, International completely redesigned their EGR engines to increase performance while lowering the overall cost of operation specifically for the EPA 2010 standard.
International diesel engines for theU.S.market feature new injectors and a high pressure, common rail fuel system that increases injection pressure to effectively atomize diesel for combustion at the lower temperatures. They also have matched duel turbochargers for low end and high end boost and an optimized piston bowl design.
Pannell said ultimately it’s the customer who pays for the cost manufacturers invested in designing EPA 2010-compliant engines over the past few years. An EGR system means the customer does not continue paying for that investment with the additional operating costs of the urea after-treatment. Pannell commended Atlas Copco for offering water well rigs in such a complete array of 2010 compliant packages for customers to choose from.