By 2014, the Environmental Protection Agency’s Tier 4 Final regulations will call for particulate matter (PM) and nitrogen oxide (NOx) levels to be reduced by more than 90% from Tier 3 levels. To meet these stringent standards, engine manufacturers anticipate employing a combination of advanced engine technology and exhaust aftertreatment. Their more immediate concern, however, is meeting Tier 4 Interim standards. Although less stringent than the Final regulations, the standards are still impressive from a clean-air viewpoint, requiring major reductions in both PM and NOx.
For diesel engines above the 173 hp range, the deadline to meet Tier 4 Interim is Jan. 1, 2011; a year later for those between 75 and 173 hp.
The technology
“To meet 2011 and 2012 Interim standards, most engine manufacturers are banking on two approaches,” says Illinois-based engine consultant John Fischer. “They will likely take the exhaust gas recirculation (EGR) path to reduce NOx. This technology essentially sends exhaust gas back into the engine where it works to lower heat and NOx production. A diesel particulate filter (DPF) will be added to control PM.”
The approach will combine with other engine technology that evolved over the years, including the use of turbochargers and electronic fuel delivery. What most manufacturers will avoid, at least for the time being, says Fisher, is selective catalytic reduction (SCR) technology that calls for injecting urea into the exhaust. “This technology, although quite popular in Europe, is more cumbersome since it involves an external tank to store the fluid.”
Announcements made by Cummins and John Deere Power Systems support his conclusions. Both have indicated that their Tier 4 Interim solution will include EGR and a particulate filter, along with proven engine technology enhancements. They have elected not to use a SCR system to meet Tier 4 Interim regulations.
Equipment impact
In April 2009, Cummins announced four-cylinder engines that would join its six-cylinder counterparts in meeting EPA Tier 4 Interim standards.
Hugh Foden, executive director, Cummins Off-Highway Business, explains: “Our four-cylinder development program for Interim Tier 4 was driven by the need to avoid the complexity of increasing displacement or overloading the engines with complications such as dual turbochargers. We have instead focused on minimizing the installation impact for our OEM customers with space-saving solutions such as the Cummins Direct Flow air filtration system, and we’ve scaled down the EGR and aftertreatment technology for these compact engines.”
He says the particulate filter for these engines replaces the OEM muffler and that the direct flow air filter represents up to 35% space savings compared to today’s radial filter. “Cummins is deeply involved with our OEM partners with our internal machine integration process and testing of Tier 4 engines and aftertreatment in off-highway equipment,” says Foden. “Pilot and field test equipment is being evaluated years in advance of the dates when EPA Tier 4 regulations take effect.”
As more sophisticated emissions-control technologies are added to diesel engines, upfront planning by OEMs is more important than ever. “Engine manufacturers will need to integrate Interim Tier 4 engines and aftertreatment into equipment designs,” says Geoff Stigler, manager of product marketing, John Deere Power Systems. The company, along with its distributors, have “increased resources dedicated to application integration reviews to ensure Interim Tier 4 products are applied efficiently and in conjunction with application guidelines.”
Stigler encourages OEMs to provide more operational transparency with appropriate guidance on equipment that uses Tier 4 Interim engines. “Clearly identifying components with labels and providing work instructions will help make users more comfortable with the adoption and implementation of technology.
“End users should also be aware of operational considerations that will affect regeneration, a process that cleans trapped particulates from the diesel particulate filters. Extreme cold and light-duty use can increase the frequency of regeneration, so John Deere Power Systems recommends users run equipment harder—under higher loads—in these situations to encourage passive regeneration.”
Are engine manufacturers sacrificing performance for cleaner air? Not really. In fact, both report that their Tier 4 Interim engines will be as fuel efficient, if not more, than their predecessors. Cummins explains it like this: “Any additional maintenance required for Interim Tier 4 products will be more than offset by fuel efficiency improvements of up to 5%, depending on the rating and duty cycle.”
Maintenance, oil, and fuel
Day-to-day maintenance between Tier 3 and Tier 4 Interim engines will remain basically unchanged, according to both manufacturers. Devices that may have been added to comply with Tier 4 legislation, e.g., a crankcase filter and an aftertreatment system, reportedly have maintenance intervals aligned with other major maintenance intervals on the current product. The exception would be the ash cleaning of the particulate filters. The EPA has set minimum intervals of 4,500 hours for above 173-hp engines and 3,000 hours for 173-hp engines and below.
“John Deere’s cooled EGR engines will integrate seamlessly into equipment markets,” notes Stigler. “Engines will perform as they have in past emissions tiers by achieving the same power levels and performance typically associated with diesel powered equipment. Maintenance intervals associated with Deere engines will be unchanged with the only added requirement being the infrequent servicing of the DPF. In most cases, DPF service will only be required once in the lifetime of the product.
“From a cost perspective, the addition of emissions technologies such as exhaust aftertreatment will incrementally increase up front purchase costs, but diesel engines will remain the preferred source of mobile power for the foreseeable future. Customers of rental companies will need to utilize ultra low sulfur diesel (ULSD) in Tier 4 equipment much like on-highway trucks have been using since 2006.”
Timeline
Engines under 74 hp manufactured by both John Deere and Cummins already meet the Tier 4 Interim standards, and the manufacturers indicate that production of compliant engines in the 173-hp range and below, and those above 173 hp will be in production several months prior to regulation dates. In the meantime, engine manufacturers will have approximately three years before Tier 4 Final goes into effect. The solution will likely build on current technology and incorporate ongoing advances in emissions controls to meet the near-zero NOx and PM standards.
Rod Dickens is senior editor of PRO Magazine, a sister publication to OEM Off-Highway.
Engine technology
Cleaner engines provide an efficient,durable source of diesel power.
The need to reduce emissions levels has spawned some interesting developments within the internal combustion engine. A “cleaner” combustion process means less work is needed to treat the exhaust, and the subsequent increased efficiencies have resulted in a more complete utilization of the energy available in the fuel.
Achieving a perfect combustion event requires that each fuel molecule is burned, a difficult goal because of the shape of the combustion chamber. To enhance combustion, engine manufacturers have made considerable advancements in the design of the piston and ring package. For example, moving the top ring as close to the top of the piston as possible has minimized the amount of fuel that fills the crevice volume above the ring—fuel that is typically not burned and then exits the exhaust as unburned hydrocarbons. The challenge has been to locate the ring precisely to minimize this volume, yet not too high so that it is harmed by the high combustion temperatures at the top of the piston.
The top of the piston has also received considerable attention. Engine manufacturers have spent countless computer and development hours optimizing the bowl into which the fuel is injected. The goal here is to enhance mixing and ensure a more complete combustion process and use of the energy available in each drop of fuel.
To maximize the vaporization of the fuel as it is injected into the engine, manufacturers have worked to improve injection systems. The common rail system used on many engines uses a separate pump to generate and store a common supply of fuel at high pressure. This fuel is then available at any engine speed. The benefit is that under any operating conditions—low speed, low load, etc.—a healthy shot of high pressure fuel is always available to promote good combustion and engine response. To further enhance combustion, injection pressures have steadily increased and now approach 30,000 psi, a level that was inconceivable not long ago. A higher pressure allows more fuel to be broken up into individual molecules that burn more readily, resulting in increased performance and lower emissions.
Manufactured to very close tolerances, today’s injectors are capable of handling these high pressures. In fact, the newest ones are so sophisticated that they can provide several injections for each combustion event. This improves combustion, and injecting a small amount of fuel before the “main event” has significantly reduced engine noise.
These are just a few examples of how engine manufacturers have met increasingly stringent emissions regulations while working to provide a more efficient—and durable—source of diesel power.
— John Fischer, engine consultant, Palatine, IL
