Interim Tier 4 (IT4)/Stage III B off-highway emissions regulations that begin in 2011 for engines 130 kW (174 hp) and above will require a 90% reduction in PM and a 50% reduction in NOx from previous Tier 3/Stage lll A requirements.
“The key technologies we’re carrying forward from Tier 3 engines include cooled exhaust gas recirculation (EGR), a variable-geometry turbocharger (VGT), high-pressure fuel systems, air-to-air aftercooling, and four-valve cylinder heads,” said Tom Withers, Marketing Communications Manager, John Deere Power Systems. “We increased the flow of exhaust gases by almost double what they were with Tier 3, and that’s how we will achieve the 50% reduction in NOx gases that needs to take place in our engines to meet the new regulations.”
While the PowerTech Plus engine platform that JDPS will continue to use for IT4 could handle double the flow, the cooler needed to be increased in size to be able to cool the extra exhaust gas; a bigger valve was also designed into the system to address the increased flow.
JDPS claims to be the first engine manufacturer to widely commercialize cooled EGR and variable-geometry turbocharger (VGT) technologies in off-highway applications, introducing them in 2005 with the start of Tier 3 regulations.
“We adopted cooled EGR for Tier 3 to drive improvements in our performance and in our fuel economy,” said Withers. “Our customers have asked for better fuel economy, and we delivered that by adopting cooled EGR and VGT with our Tier 3 engines. What you’re going to see is that a lot of the other engine manufacturers are going to finally adopt cooled EGR. The benefit that we have is we’ve already applied that technology off-highway. Off-highway and on-highway engines are quite different in their applications, and we have a lot of experience making these technologies more rugged and durable for tough off-highway conditions. We’ve already been through that learning curve.”
JDPS says that its Tier 3 PowerTech Plus 9.0-L engine consumed nearly 9% less fuel than its Tier 2 counterpart, and 17% less fuel than one competitor’s comparable Tier 3 engine. Because JDPS IT4 engines continue to use essentially the same technologies, the expectation is they will maintain similar fuel-economy advantages.
For IT4, the PowerTech Plus cylinder head, fuel system, cooled EGR, VGT, and air-to-air aftercooling system were all updated, but are similar to Tier 3 configurations. The engine control unit, developed and manufactured by Phoenix International, a business unit of John Deere’s Intelligent Mobile Equipment Technologies, will change substantially to provide twice the RAM, double the processing speed, and four times the program memory of the previous version to handle requirements of added sensor and control logic. The pressure of the high-pressure common-rail fuel system on the 6.8- and 9.0-L has been increased from 26 to over 30 ksi (1790 to 2070 bar). The pressure in the 13.5-L engine’s electronic unit injector fuel system has been increased from 29 to over 33 ksi (2000 to 2275 bar)
Another major change is the use of aftertreatment.
“Our aftertreatment device has to be robust enough to withstand harsh off-highway conditions like vibration and extreme temperatures,” said Withers.
While JDPS has been conducting research on aftertreatment systems for over 15 years, it recently formed a dedicated aftertreatment business/technology group within its Waterloo-based Product Engineering Center to provide the necessary focus to not only develop and validate technologies, but also to do the necessary sourcing logistics, marketing, and service planning to support the new technology.
JDPS developed its DOC/DPF (diesel oxidation catalyst/diesel particulate filter) unit specifically for off-highway applications. The DOC component reduces carbon monoxide, hydrocarbons, and some PM. The downstream cordierite DPF traps and holds particulates remaining in the exhaust stream. Trapped particles are eventually incinerated within the DPF through a process known as regeneration. In most cases, passive and active regeneration will not have an impact on machine operation and will not be noticeable to the operator.
JDPS engineers designed into the system three phases of regeneration: passive, active and forced.
“When equipment is operating at about 70% or greater load factor, enough heat is available during normal operation to regenerate the DPF passively,” said Withers. “When operating in cold temperatures, under lighter loads or lower speeds, there may not be enough heat to regenerate passively.”
During active regeneration, fuel is injected into the exhaust stream flowing to the aftertreatment device. The mixture creates temperatures high enough to burn away trapped particles.
Sensors monitor the flow through the aftertreatment device. When the pressure through the device starts to drop, thus signifying an accumulation of trapped particles, a signal will be sent to the cab alerting the operator. A scale will show the operator how full the device is getting. The system will warn the operator a short time before active regeneration starts.
“If you’re in the middle of an operation when its not convenient or in a location you don’t want to generate high temperatures and you don’t want to regenerate, you can push a button to override active regeneration,” said Withers. “You might be able to do that two or three times, but at some point a level will be reached when the filter becomes saturated and efficiency is going to go way down.”
When the filter reaches a critical level, an alert will inform the operator that a forced regeneration is required and power to the equipment will be derated. To return to full power, the operator will need to initiate an activate regeneration. The equipment remains static during forced regeneration.
To maintain compliance with regulations, the filter needs to be periodically cleaned. Where there is fire, as there is during regeneration, there is ash. Based on U.S. EPA rules, filters must have at least a 4500-h interval before cleaning out the ash, which involves the actual removal of the filter.
“Most manufacturers will probably follow that guideline and at a minimum design the filter to 4500 hours,” said Withers, adding that every dealer will most likely have a service process that they go through to clean it.
“We are also investigating having an exchange program,” he said. “The customer buys a remanufactured aftertreatment device, and when equipment gets to the 4500 hour mark, he pulls it off, puts the other one on, and minutes later he’s back in the field again. Aftertreatment devices contain precious metal and should be returned for credit.”
One thing JDPS (and just about everyone else) will not be using for IT4 is spelled S-C-R. An SCR (selective catalytic reduction) system injects liquid urea into the exhaust stream to reduce NOx. While it is effective, it also requires that the vehicle or machine be fitted with a separate tank, a sophisticated urea-injection system, and an EPA/EU-required tamper-proof diagnostic system.
Since urea freezes at about 18°F (-8°C), heating systems for the tank and delivery lines are required. Also, urea is not conveniently available in most parts of the world at the present time, which creates access and storage concerns. SCR may be an appropriate technology for Final Tier 4/Stage IV regulations, and is of course already taking hold in
While SCR may not be on anyone’s agenda for IT4 (at least as standard; some may offer it as a secondary option), some studies have shown that the use of urea results in reduced overall life-cycle costs of a vehicle.
“We are not ruling out the future use of urea by any means,” said Withers. “We may find that to meet Final Tier 4, we have to use urea. We’re hoping that between now and then , technologies will be unveiled that will allow engineers to reduce the amount of urea we have to use, and thus the size of the urea tank. We’d like it ‘out of sight, out of mind,’ so that an operator may only have to fill up when he gets an oil change, and then have another 250 to 500 hours.”