Tier 4 Report
| November 09, 2010 |
Tier 4 Interim engines
Reducing emissions with a whole arsenal of tools
By Tom Jackson
With a substantial engine business, not just for Deere-branded equipment but many other OEMs worldwide, John Deere Power Systems has a significant new lineup of engines for 2011.* And the company wasted no time getting certification for and fielding its first Tier 4 Interim (T4i) machine, the 744K wheel loader (at right) several months ahead of the emissions deadline.
To meet the new emissions standards, JDPS built on its five years of experience with EGR (exhaust gas recirculation) designs and added a number of new features to its engines, says Doug Laudick, manager of product planning. Here’s a rundown of the technology being used in Deere’s T4i engines, how it works and what it means to you:
When Tier 3 regs went into effect in 2005 some manufacturers turned to EGR to lower the oxygen content in the combustion chamber and reduce NOX (nitrogen oxide) in the exhaust. EGR got the job done, but brought more heat back into the cooling system. T4i, however, required an additional 50-percent reduction in NOX from T3 standards and in most cases that meant increasing EGR rates.
In Deere’s engines this meant increasing cooled EGR rates from about 10 to 15 percent to 20 to 30 percent, Laudick says. For T4i Deere was able to reduce combustion temperatures even further through cooled EGR technology, which enabled achieving the required reductions in NOX.
“We run the exhaust air through an EGR cooler on the engine to get the exhaust temperature back down closer to the engine coolant temperature, so we’re not dumping extremely hot air back into the air charge,” says Laudick. The EGR cooler is a small package, in most cases mounted next to the exhaust manifold, and uses the engine coolant to reduce the exhaust gas temp before routing it back into the air intake manifold where it is mixed with fresh air from the charge air cooler.
The big challenge for all T4i engines is to reduce the other targeted emission component, particulate matter, or PM. Compared to T3, T4i engines have to cut PM by 90 percent. This gets even more challenging since the EGR process mentioned above reduces combustion temperatures, which increases the amount of PM out of the engine.
The best way to deal with this PM downstream of the engine is to use an exhaust filter. These filters typically sit where the muffler would have gone and use various media to trap PM. The filters are bigger than the mufflers they replace but will have a minimal impact on the footprint of the engine or the size of the engine compartment and the sheet metal that encloses it, Laudick says. Soot accumulates in the filter, especially during idle or low rpm applications, but will be automatically burned off in a self-regulating process – known as automatic cleaning or passive regeneration – that will be transparent to the operator.
Over a long period of time, ash (a by-product of combustion that comes from inorganic solids found in engine oils) will also accumulate in the filter and unlike soot or PM, cannot be burned off and will need to be cleaned out. The EPA requires that diesel exhaust filters go at least 4,500 hours before a cleanout is needed on engines 175 horsepower and up and 3,000 hours on engines below 175 horsepower. In both cases, Deere’s engines will exceed that requirement, Laudick says.
The procedure for cleaning ash out of the exhaust filters will probably take one of two different paths. Some dealers will invest in the cleaning equipment and perform the maintenance themselves. Others may have an exchange program and remove the old filter and install a new one while giving the machine owner a core credit for the old, Laudick says.
High-pressure fuel injection
The more complete the combustion process, the fewer emissions created in the cylinders, and high-pressure fuel injection can burn fuel more completely. “The big advantage of a high-pressure common rail system is that it’s much easier to control fuel injection timing while providing precise control for the start, duration and end of injection,” Laudick says. “The pressure can be based on speed and load and the increased pressure also atomizes the fuel better. Ours is increasing from about 23,000 psi on T3 engines to about 29,000 psi on T4i, which is almost 21 percent.”
Almost every electronically controlled engine above 175 horsepower today will have four valves per cylinder, and Deere is no exception, Laudick says. The extra valves help control the combustion process for a more complete burn. To reduce costs below 175 horsepower, Deere has some platforms that are two-valve, electronically controlled. But going into T4 Final there will be more engine platforms using the four-valve design, he says.
Full authority electronics
Just about every aspect of the engine is managed by electronics on Deere’s T4i engines. “When electronic engine controls first came out, they only controlled certain aspects, such as the electronic governor of an engine,” Laudick says. As the technology evolved the electronics have taken over management of fuel system pressures, injection timing and a number of other functions. “It allows you to achieve more efficient combustion,” he says.
Three turbo designs
With some variations all the Deere T4i engines greater than 75 horsepower use the above mentioned technology. The big differences you’ll find within the T4i Deere engine family are the turbo designs. There are three different turbos, each one wedded to a particular engine sub-group.
• PWX. The W in the PWX engine group stands for a wastegated turbocharger. “Our PWX is a lower cost turbo design compared to a variable geometry turbo, says Laudick. “While wastegated turbos provide excellent performance across the entire operating range of an engine, they will give you a 2 percent hit on fuel economy, because you’re dumping off excess air flow under full load rated speed conditions – creating a lot of energy you don’t use.” For engines 75 to 122 horsepower (not due for T4i until 2012).
• PVX. The “V” stands for variable geometry turbo, which by virtue of altering the angle of the blades in the turbo more efficiently manages air flow than the wastegated design. This efficiency gives it a small fuel efficiency advantage. For engines 185 to 425 horsepower.
• PSX stands for a series turbo design, what Laudick calls the best of both worlds. “With the exhaust filters there’s a little more backpressure on the engine and you have to increase your airflow,” he says. “One way to do that, especially on the high horsepower engines is to use two turbos. You get more turbo boost pressure, which benefits performance and helps you maintain capabilities at high altitudes. You can speed up the low pressure turbo to feed the high pressure one without over-speeding either one, which gives you improved durability. For engines 225 to 600 horsepower.
By and large, the end users of Deere’s 2011 and 2012 engines should experience little if any changes in machine design or performance and there should even be a bit of an upside gain on fuel economy over an already fuel efficient T3 engine platform, says Laudick.
The things that change are outside the engine design. These include the need to use ultra low sulfur diesel fuel, but this fuel will be the only type of diesel sold by next year in regions of the world governed by the EPA and European Union emissions regulations. You’ll also want to use the new American Petroleum Institute CJ-4 standard engine lube oil. This is a low-ash oil that will enable your exhaust filters to go longer between cleanouts. And other than the ash cleanout mentioned earlier, service and preventive maintenance schedules don’t change.
Those are the impacts, and they’re pretty small, Laudick says. “Our customers won’t be able to tell it’s a T4i engine.” EW
*Editor’s note: 2011 is the deadline the Environmental Protection Agency gave off-road engine manufacturers to meet its strict new engine emission levels. Known as Tier 4 Interim (T4i), the regulations apply to engines from 175 to 750 horsepower next year and engines 75 to 175 horsepower in 2012. For more background on the regulations see the September issue, page 43 of Equipment World or go to www.equipmentworld.com.