By Paul Abelson
Senior Technical Editor
Remember the trauma that trucking experienced in October 2002?
That’s when new engine management strategies were required to meet new, stringent emissions requirements. Exhaust gas recirculation and ACERT entered our vocabulary.
Uncertainty about new hardware, potential maintenance problems and durability issues caused a swell of pre-buying by fleets and wise owner-operators seeking to avoid any potential problems.
Those who bought before October 2002 were proven correct.
Given the time that has passed and the lessons learned, engine makers are optimistic as they gear up to meet the 2007 emissions standards. Engine makers are confident that by addressing the problems that plagued the 10/02 engine platforms early on, the 2007 engines will not only meet the emissions standards, but will also return to days of better fuel efficiency and engine performance – but with a price tag.
Push forward fallout
Early 10/02 engines had problems with EGR coolers and valves. Fuel economy suffered, often by more than 10 percent. Higher than expected under-hood temperatures affected belts, hoses, alternators and accessories. Glycol coolants underwent chemical changes as they literally cooked in the EGR coolers.
Even Caterpillar’s engines, using their non-EGR based ACERT – short for advanced combustion emissions reduction technology – were not exempt from high under-hood temperatures and lower mpg. All the 10/02 engines experienced reductions in reliability.
The new technology was required to meet a mandated 50 percent reduction in nitrogen oxide. In 1990, NOx limits were set at 6 grams per horsepower per hour. The next year, they went to 5 grams, and in 1998 they dropped to 4 grams. Those were relatively gradual and attainable by improving combustion without adding external components. The drop to 2 grams per horsepower per hour was the first to require additional hardware.
NOx, which is instrumental in the formation of smog, is just one of the environmental contaminants in exhaust. Another is particulate matter, which includes soot, partially burned and unburned hydrocarbons, sulfur from fuel and ash from lubricating oils.
Since 1994, particulate matter has been limited to 0.1 grams per horsepower per hour. That did not change with the 10/02 engines – engine makers and truck operators had enough to worry about meeting NOx standards that were reduced by half.
Strategies to control particulate matter and NOx differ greatly. NOx is formed when nitrogen and oxygen, the primary components of air, are subjected to high heat and pressure, as in an engine’s combustion chamber. But that same high heat that creates NOx helps hydrocarbon fuel to burn more completely, minimizing soot and unburned hydrocarbons.
Because particulate matter regulations were unchanged for the 10/02 engines, manufacturers were free to concentrate on reducing NOx. Even though there was a trade-off with particulate matter formation, the effect on particulate matter was not that significant.
Most engine makers chose to dilute the incoming air charge with an inert gas. The most readily available non-combustible gas is the engine’s own exhaust. EGR mechanisms divert a portion of the exhaust back into the intake to mix with incoming combustion air. The flow is controlled by the EGR valve. Because it is too hot to be used effectively, the exhaust must be cooled by engine coolant in a high-temperature stainless steel heat exchanger – the EGR cooler.
Cummins, Detroit Diesel and Mack on-highway engines rely on cooled EGR controlled by a stainless valve. Volvo engines currently use the pulses of the exhaust for their metering.
All engine makers use improved air intake systems and better-controlled fuel injection than in pre-10/02 engine designs. Caterpillar ACERT engines have two turbochargers, one feeding into the other. The other engine makers use variable geometry turbochargers.
A side benefit with either system is that turbo lag, that hesitation when you press the accelerator while waiting for the turbocharger to get up to speed, has been eliminated. All the new engines respond instantly. Fuel injection is electronically timed, with some engines getting as many as seven separately timed and metered squirts of fuel per stroke.
During the first 15 to 18 months after introduction, many new engines experienced durability and reliability problems.
The deadline for the emissions reduction was pushed forward 15 months from the original January 2004 schedule. Had the deadline stayed at January 2004, that 15 months would have allowed truck OEMs time to engineer changes into their vehicles. Instead, engines were shipped for installation in production trucks almost as soon as EPA certified them.
Hot under the hood
Problems arose related to the high heat encountered by EGR valves and coolers. High under-hood heat affected accessories and components. Engine makers have acknowledged these problems.
For example, Cummins officials said that their newer engines meeting the 10/02 engine standards had virtually all issues addressed. The 10/02 engine technology will be the foundation for engines designed to meet 2007 emissions regulations, but there will be more exhaust gas recirculated, and under-hood temperatures could get even higher.
While excessive engine heat is the cause of many problems, it will take the efforts of engine manufacturers, truck OEMs, component suppliers and lubricant makers to solve them.
Engine builders have already placed 2007 engines with truck OEMs, so they could work on installation, airflow and component and accessory placement to manage underhood heat and related problems. Those problems range from washer fluid boiling off and containers melting, to deteriorating serpentine fan belts and belt tensioners.
Lubricant and seal suppliers are testing new formulations for the tensioners. The engine makers have addressed most EGR-related engine problems, including EGR valve durability and cooler integrity. But the inherent designs of EGR systems and Cat’s two-stage turbocharging create more under-hood heat.
With more EGR needed for the 2007 models and more heat to be managed, it will be up to truck OEMs to design for airflow and cooling, and to relocate under-hood components such as power steering pumps. Look for increased use of electrically driven fans to remove fan clutches and drive mechanisms from engines.
Belt and hose manufacturers are working with truck makers on new formulations. Two major alternator makers, Prestolite and Delco Remy, already introduced high temperature models. Freightliner redesigned its Columbia and Century Class front ends for better under-hood airflow. Others will likely do the same. Volvo’s new VT 880 has enlarged front openings. It may be the prototype for airflow modifications.
This summer, fleets will start putting engines into service. Unlike 10/02 experiences, when engines were rushed into production, there will be more time to de-bug problems, fewer of which are expected.
Paring out particulate matter
On Jan. 1, 2007, diesel engines must emit no more than 0.01 grams per horsepower per hour of particulate matter, a 90 percent reduction. Over the course of the next three years, NOx must trend toward the 2010 standard of 0.2 grams, averaging 1.2 grams for all
engines produced in the period. The phase-in provision will allow engine makers to concentrate on reducing particulate matter now, while working toward the 2010 NOx limit.
All engine makers will use exhaust after-treatment to remove soot and other particles. Caterpillar has been using proprietary after-treatment as part of ACERT since their engines were certified.
The others will be incorporating diesel particulate filters – or DPFs, also called particulate traps. These are porous filters, usually made of a high-temperature ceramic structure, or densely packed ceramic and metal fibers. They catch particulate matter within their structure, while allowing gases to escape. DPFs may also be used in combination with catalytic converters similar to those found in automobiles. Some converters may use platinum or other temperature-stable precious metals. The catalysts aid regeneration of the traps.
To keep DPFs from clogging, they will need to be cleaned out periodically. Regeneration involves injecting high-energy fuel into the filters and burning the soot completely, then taking any remaining residue and ash and blowing it against the normal exhaust flow and into a container for disposal.
Outboard diagnostics will monitor the trap’s condition and manage regeneration. On-board fuel reformers that convert diesel to a more hydrogen-rich, hotter-burning fuel will facilitate the development of on-board regeneration capability. An alternative to on-board regeneration would be cleaning at a maintenance facility. This would require costly equipment, and would likely be done at a dealership, truckstop or fleet shop.
The EPA requires that DPFs go at least 150,000 miles before needing cleaning. Early models will likely require regeneration at a maintenance facility.
Really, really low sulfur
Today’s low sulfur diesel, with 500 parts-per-million sulfur, is not suitable for use with emissions controls, just as leaded gasoline was not compatible with automobile emissions controls.
Ultra low sulfur diesel for the 2007 engines will be readily available by June 2006, according to the EPA. Ultra low sulfur diesel will eventually be limited to 15-ppm sulfur. With 97 percent of the sulfur removed, sulfur compounds will not contribute significantly to particulate matter or acid formation. Refiners and pipeline operators have concerns about co-mingling diesel with other higher sulfur fuels in the pipelines, but the EPA is adamant that the fuel will be available on target.
A new API oil classification (see related article on Page 70) is being developed for 2007 engines. Oils will leave less than 1 percent ash residue. Engines have already been modified to keep oil out of the combustion chamber. With sulfur and ash no longer significant contributors to particulate matter, emissions control technology can realize their full potential.
What’s it gonna cost?
DPFs and related hardware are projected to add as much as $6,000 to the price of a new truck, although some industry insiders believe that with all related NOx reducing equipment, that may grow closer to $10,000.
The downside to all this is the cost. DPFs and related hardware are projected to add as much as $6,000 to the price of a new truck, although some industry insiders believe that with all related NOx reducing equipment, that may grow closer to $10,000. DPF service every 150,000 miles is expected to cost $150 or less each time. ULSD fuel may add 5 cents to 15 cents per gallon, in an era when fuel is already oppressively high.
Offsetting these added costs, oil drain intervals should be comparable to today’s engines. They may even be able to be extended. Although more soot will enter the oil, the reduction in sulfur will allow the new oils to suspend the soot in finer sizes, and acid formation will be less of a problem.
Fuel economy is expected to be back to 2001 levels in the 2007 engines. Cummins recently reported overall thermal efficiency of 45 percent, up from 41 percent in current engines. Improved thermal efficiency translates to improved fuel economy.
Engine makers expect the new engines should last longer, surpassing 1 million miles. All this, and our air will be cleaner, too.
Paul Abelson may be reached at firstname.lastname@example.org.