The world might be breathing easier, but a lot of diesel engineers are hyperventilating in their efforts to reach the new Tier 4 Interim standards for 2011. The new standards for agricultural diesel engines will require a 90 percent reduction in particulate matter (PM) and a 50 percent drop in nitrous oxide (N2O) compared to Tier 3 regulations. The standards are part of the US Environmental Protection Agency’s (EPA) emission policy for diesel engines, and Canadian farmers have no choice but to follow along because agricultural engines are primarily made in the US or Europe, where the same standards are being applied.
Until 1994, farm diesel engines were unregulated for vehicle exhaust emissions. That changed, though, in 1994 when the first of the EPA’s emission standards was implemented. The EPA’s initiative to lower diesel engine emissions goes back to the Clean Air Act of 1970 in the US, passed just after the first Earth Day. First to be regulated were automobiles and then on-highway trucks.
For the past 16 years, the emission standards for off-road diesel engines have steadily become more stringent. The first Tier 1 standard was phased in from 1996 to 2000, and more stringent standards for Tier 2 and Tier 3 were phased in from 2000 to 2008. Tier 4 Interim standards will be in place in January 2011, with full Tier 4 Final standards implemented by 2015. At that point, an additional 80 percent reduction in N2O will be required compared to Tier 4 Interim, while maintaining PM emissions at Tier 4 Interim levels.
Roger Hoy, director of the Nebraska Tractor Test Laboratory (NTTL) at the University of Nebraska at Lincoln, has been following the development of the Tier 4 technology closely. The NTTL is the officially designated tractor testing station for the United States and tests tractors according to the international codes of the Organization for Economic Co-operation and Development (OECD). He has had a chance to preview some of the new emissions reduction technology, and while pleased with the performances, he has some concerns about the impact on engine efficiencies. “So far, the EPA will tell you that reduction in emissions will increase fuel economy. That is sort of true, and sort of false. Applying emissions reductions alone will reduce fuel economy, naturally, but some of the things that manufacturers have introduced at the same time to reduce emissions have improved fuel economy,” says Hoy. “Electronic fuel injection to control emissions has improved fuel economy. We’ve seen two valve heads go to four. When John Deere went from the 8020 series to the 8030 series, they got a huge increase in fuel economy because they redesigned their engine to give it more air. My personal opinion is that going to Tier 4 Interim might be a wash, but going from Tier 4 Interim to Tier 4 final is probably going to lose some fuel economy.”
Hoy explains that there are several technologies currently being used for Tier 3 reductions that will be used in Tier 4 Interim reductions. Two that have helped achieve Tier 3 reductions include the Internal Exhaust Gas Re-circulation (IEGR) and the Cooled External Gas Re-circulation (CEGR) system.
The IEGR is primarily used at engine start-up to reduce emissions by recirculating exhaust gases back into the engine for more complete combustion. The CEGR technology cools the gas through a heat exchanger to allow a greater mass of exhaust gases to be recirculated back into the engine.
Selective Catalytic Reduction technology
Two other key technologies will help manufacturers meet Tier 4 Interim reductions. They take divergent approaches.
The first is Selective Catalytic Reduction (SCR) that operates like a catalytic converter on a car. AGCO is one of the companies using this technology, and SCR has been introduced already on some of the Fendt tractor models. In this case, a 32 percent urea solution is sprayed into the exhaust gases as they leave the engine and just before they enter the catalytic converter. Inside the SCR, the exhaust heat turns the urea into ammonia, which reacts with N2O to produce water vapour and harmless nitrogen gas. “What they have done is say that they aren’t going to worry about some of the emissions within the engines. They will let the N2O go back to a Tier 2 setting, and they are going to take out the N2O with a separate component like the SCR,” explains Hoy.
The urea solution is commonly called diesel exhaust fluid (DEF). It is stored in a separate, refillable tank. AGCO calls their urea solution AdBlue/DEF. “The DEF is a consumable quantity. These tractors have a separate tank where you might put five or 10 gallons of DEF, and if you try to put water in, or don’t fill it, the tractor won’t run, or it de-rates to a point that is so obnoxious that you put the right stuff in,” says Hoy.
Hoy had the opportunity to test the performance of an AGCO engine equipped with SCR technology. He used a normal PTO test and measured the consumption of the DEF urea solution. He found that, depending on the operation of the tractor, DEF consumption was between two and four percent of diesel fuel consumption.
At an average three percent consumption, if a grower using 1000 gallons of fuel could expect to use 30 gallons of DEF. “We realize this is an operating cost that should be tracked, just like you do with diesel fuel,” says Hoy.
Overall, though, Hoy explains that the fuel economy with the AGCO SCR technology was excellent; the engine was allowed to use more fuel-efficient operating modes because it did not have to deal with N2O emissions within the engine.
Regenerating Particulate Filter technology
The other main technology that will be employed to reach Tier 4 Interim standards is the Regenerating Particulate Filter (RPF). In many cases, the RPF replaces the muffler, trapping and holding particulates remaining in the exhaust system. Trapped particles are eventually oxidized within the RPF in a process called regeneration. “In this case, the N2O emissions are controlled within the engine without worrying about particulates,” explains Hoy. “What it does with the particulate matter (PM) is to replace the muffler with a particulate filter trap. That all sounds nice, but eventually the PM builds up and periodically the tractor may have to inject diesel fuel into the exhaust system to raise the exhaust gas temperatures up to burn off the particulate that has been trapped.”
“When the filter starts building up soot (PM), the back pressure in the system starts to go up, and if exhaust gas temperatures aren’t high enough, or not in the right range, this soot won’t convert to ash on its own, so something has to be done to bring it up, so diesel fuel is injected,” explains Hoy. “You might see a change in fuel consumption as these things burn.”
The PM is converted to ash during regeneration, and remains inside the filter. The amount of ash accumulated during a period of use will eventually mean the RPF will need replacing after about 3500 or 4000 hours.
John Deere is combining a Diesel Oxidation Catalyst (DOC) with RPF (Deere calls it a Diesel Particulate Filter (DPF). The company’s Tier 4 Interim information says that under normal operating conditions, the DOC reacts with exhaust gases to reduce carbon monoxide, hydrocarbons and some PM. The downstream RPF forces exhaust gases to flow through porous channel walls, trapping and holding the remaining PM. Trapped particles are eventually oxidized within the RPF through a self-cleaning process called passive regeneration, utilizing exhaust heat created under normal operating conditions. But when the exhaust temperature is incapable of oxidizing the PM, the RPF filter reverts to active regeneration with the injection of diesel fuel to help burn off the PM.
Hoy had an opportunity to observe a John Deere Tier 4 Interim engine at a John Deere test facility. There, he observed that engine torque was within 3/10ths of a percent between soot load and fully cleaned after regeneration with the RPF system. OECD requires test measurement tolerances to be within 0.5 to one percent so the Deere result is within the measurement requirements. “I do have the conclusion that Deere has a very well designed system here. There is no guarantee that similar systems from other manufacturers will be well designed, so we are going to ask that that this type of performance information be recorded and supplied to us,” says Hoy.
For the time being, the Nebraska Tractor Test Lab will not be conducting these additional tests related to the Tier 4 Interim technology, but will be recording manufacturer results on the NTTL reports. They are currently working at developing those standard tests. The reports will also require mention of any special conditions for regeneration of the RPF. Hoy explains that the Deere system does not require any, and an operator might not even know it is going on, but says, “It is possible, due to a system design, or the operating conditions, that the tractor might force you to stop what you are doing and let the system regenerate. If that is the case, we want it to be identified.”
Buy now or later?
With the two main Tier 4 Interim technologies now firmly entrenched in most manufacturers’ programs, the choice will be either an SRC or RPF system as the main component. And they will likely be seen on virtually every Tier 4 Final engine by 2014, unless something else appears in the next few years.
For growers in the market for a new farm implement powered with a diesel engine, the question might be whether to buy a Tier 3 or Tier 4 Interim. One issue may be cost. Research and development costs are high. The EPA admits there will be an additional cost to equipment, anticipated in the range of one to three percent of the total purchase price for most non-road diesel equipment categories. On a $200,000 tractor, that could add up to $6000.
Hoy says Tier 4 Interim regulations were implemented three years earlier for on-road diesel engines, and that there was a large pre-buy of diesel trucks in the transport industry. And some bugs certainly had to be worked out of the new technology. However, the agricultural sector had three additional years to fine-tune the technology. Whether a grower wants to wait to purchase the new technology (and some 2010 models may already have the technology), may be a matter of personal preference. There are pros and cons to pre-purchase, as there are for the new Tier IV Interim technology.
