The first U.S. emissions regulations for on-highway diesels arrived in 1973. The first U.S. emissions regulations for mobile off-highway diesels arrived in 1996, a lag of 23 years. The gap between on- and off-highway implementation has now narrowed to three or four years. The goal is to have all diesel applications coordinated by 2015 or so. At the same time, there is a movement to harmonize standards among industrial countries, particularly the United States, Japan and those in the European Union.
Engine manufacturers know this unity is coming, and they’ve worked hard to create engines that will perform across all these platforms. Differences in duty cycles and operating conditions have made this a challenge, but the OEMs are succeeding. Here’s what Cummins is doing.
On highway: Something old…
Cummins has been using exhaust gas recirculation (EGR) with on-highway engines since October 2002 and will continue to do so. EGR reduces nitrogen oxides, one of the emissions targeted by EPA and California Air Resource Board standards. With EGR, a measured amount of exhaust gas is cooled and then routed back through the engine. This gas displaces oxygen that would otherwise be available for the combustion process, which reduces combustion temperatures. Since NOx increases exponentially as combustion temperature rises, even a little cooling yields a big drop in NOx.
The 2007 Cummins ISB, ISC and ISL engines will keep high-pressure, common-rail fuel injection. This method of injection breaks the bond between engine speed and injector pressure so that high pressure injection is available at all engine speeds. The benefits are especially clear at idle and just off idle. With high-pressure, common-rail injection, engineers have much greater control over the number and duration of injections and the volume of fuel delivered in each combustion cycle.
Other technologies carried forward are the use of a variable geometry turbocharger, the CELECT fuel system found on the ISM, and the HPI fuel system on the ISX. For 2007, the VG turbo gets an electronic actuator for its patented sliding-nozzle architecture, which replaces the mechanical actuator of earlier designs.
…And something new
Starting in 2007, on-highway diesel engines can no longer vent their crankcases to the atmosphere without some kind of emissions control. Cummins’ answer is to add a coalescing filter to the vent. Crankcase gases are routed back into the intake. Oil scavenged from those gases is returned to the crankcase. “The filter will be monitored for back pressure so that the driver is alerted when it’s due to be changed,” says Chuck Goode, director of national accounts at Cummins. “Duty cycle will determine change intervals, but we’re looking at once a year or every third or fourth oil change as typical.”
Exhaust aftertreatment will debut on the ’07 engines as well. The Cummins particulate filter consists of a diesel oxidation catalyst (DOC) and a catalyzed particulate matter filter (DPF or PM trap). The two parts work together to reduce particulate matter.
For typical line haul applications, exhaust temperatures remain high enough to ensure regeneration of the particulate matter filter. But under other conditions, such as pick up and delivery service in frigid weather, the exhaust temperature may not be high enough to keep the filter clean. By heating the DOC when needed, Cummins can manage regeneration and keep the filter functioning.
Even with regeneration, the particulate matter filter must be periodically serviced. The two components are housed in a single unit that replaces the muffler. The DOC/DPF assembly is held together with band clamps so that it can be disassembled easily for cleaning and the removal of accumulated ash.
Goode estimates service intervals for the DPF to be 6,000 hours or every one to three years. The cleaning process takes about 30 minutes. All Cummins-certified warranty repair locations will have the equipment needed to perform the cleaning. Larger fleets may want to own the equipment, which is expected to cost in the range of $5,000 to $6,000, or they may keep spare filters on hand and simply swap out clean filters for dirty ones. The DOC itself will require no servicing.
Off Highway: Something borrowed
Tim Meyer, marketing product leader for mid-range off-highway products at Cummins, says most on-highway technology is unnecessary for off-highway applications. “Our engine lineup meets current off-highway emissions standards with no EGR, no PM traps, no oxidation catalyst and no aftertreatment of any type,” he says.
What has crossed the aisle from on- to off-highway is rigorous control of the combustion cycle. Advanced turbocharger design and precise control of fuel injection are two of the technologies that made the leap.
One of the earliest improvements to combustion was a reconfigured combustion chamber. Top rings were higher on the piston to reduce crevice volume. Piston crowns were reshaped to encourage more complete combustion. Valves were added, or existing valves were repositioned to improve flow.
Such internal tinkering is likely to continue, says Bruce Farrar, manager of off-highway communications at Cummins. “There will be continuous, ongoing improvements for in-cylinder design,” Farrar says. “Whether it’s piston ring location and materials or piston crown designs that improve swirl, those technologies will keep engineers busy for many, many years.”
Avoiding the blues
Keeping the new engines running as OEMs intended will require the use of the right fuel and oil. Ultra-low-sulfur diesel fuel, which has no more than 15 parts per million sulfur, will be required, as will CJ-4 (formerly designated PC-10) engine oil, which contains less ash. The reduction in sulfur and ash will prevent premature plugging of DPF units.
Service intervals and procedures will remain unchanged from those required for earlier engines.
Plans for the future
After 2007, the next big crunch in on-highway emissions arrives in 2010. What technologies will be required? “Nobody really knows the answer,” says Goode. “We’re engaged in the technology development for NOx adsorber systems and also selective catalytic reduction. SCR is what we use in production European automotive engines today.” Both adsorbers and SCR have a host of issues that must be resolved, says Goode, “and we’re also evaluating the total cost of ownership with those technologies.”
Meyer says the off-highway and on-highway standards start to merge in 2010 and 2011. “We expect ultra-low-sulfur fuel to be mandated for off-highway in the 2010-2014 time frame,” he says. (Ultra-low-sulfur fuel must be available to on-highway fleets starting in 2007.)