The Power And The Glory
Engine manufacturers are on fast track to meet 2002 emissions deadline.
STEVE STURGESS
SENIOR EDITOR
The deadline is almost upon us. From October this year, over-the-road heavy duty diesel engines will be meeting an accelerated EPA requirement for reductions in emissions.
Legal wranglings have compressed the time allowed to develop engines that meet lower NOx requirements. Consequently, vehicle manufacturers have been deflected from other development programs in a crash effort to meet the new deadline.
For the engine OEMs, it has meant furious co-engineering efforts with the truck OEMs to ensure the technologies will fit into their chassis, and everyone has had to scramble.
For end users, the acceleration of the deadline poses some difficult questions: how much will this cost at a time when the economic situation is the worst it's been for a decade? How reliable and durable will the new engines be? And what about maintenance costs of the more complex diesel engines?
For the truck manufacturers and dealers, this deadline could not have hit at a worse time. Many are saddled with thousands of low-mileage used trucks either through buy-back programs or through the attrition of carriers hurt in the economic slowdown.
The general wisdom is that new truck sales will stall after the emissions deadline passes. It's predicted many potential buyers will take a wait-and-see position — instead of buying new trucks with EGR engines, they will add capacity by buying used trucks.
The New Engines
Cummins, Detroit Diesel, Mack and Volvo will roll out cooled exhaust-gas recirculation (EGR) technology to halve the levels of NOx in truck diesel exhaust.
In a controversial move, Caterpillar has said it does not intend to meet the deadline and that its technology — labeled ACERT for Advanced Combustion Emissions Research Technology — will be ready for adoption in October 2003.
Caterpillar has everyone dumbfounded with its announcement, since the Environmental Protection Agency has been adamant, insisting on the 2002 deadline.
Nobody knows how EPA will handle the Caterpillar situation. But Cat's stand is a bone of contention with the other heavy duty engine manufacturers who have struggled to accelerate enormously expensive development programs to meet the October 2002 cutoff.
And if predictions that new truck sales will stall with the new engine technology introductions, it may be that Caterpillar will be right on schedule to sell ACERT engines as the market picks up again in late 2003.
The Time Line
The timing for the lowered NOx requirements has actually been pulled forward from its original deadline of January 2004. This 15-month hurry-up was included in consent decrees between the engine makers and EPA /Department of Justice. It was in settlement of allegations that the engine manufacturers had been cheating on emissions prior to 1999.
EPA claimed engines were actually producing excess NOx through use of "defeat devices" built into the electronic controls. The deadline pull-ahead is to compensate for this NOx.
New Engine Technologies
Oxides of nitrogen — NOx — are formed in the heat of the combustion chamber. To reduce these oxides, the flame temperature during the combustion process must be lowered; this can be achieved through retarded injection timing or by substituting exhaust as an inert gas into the combustion mixture.
It is this exhaust gas recirculation (EGR) that all but Caterpillar will use to meet the upcoming requirement for the 2.0 g/hp-hr NOx limit. But the process is a little more involved than just bleeding off exhaust and injecting it into the inlet side of an engine.
For one thing, the exhaust is hot as it exits the combustion chamber. To reduce NOx as far as possible, the temperature in the combustion chamber has to be minimized so the recycled exhaust must be cooled.
Also, with a turbocharged engine, the inlet side downstream of the turbo is at a higher pressure than the exhaust, especially with today's high efficiency turbochargers.
To get the exhaust gas to mingle with the inlet stream is a bit like getting water to flow uphill. Fortunately, several technologies have been developed to achieve this remarkable trick. Three of the mainstream manufacturers are turning to variable geometry turbochargers (VGT), where exhaust back pressure can be increased to flow the exhaust gas into the inlet stream without losing turbocharger efficiency.
Volvo, though, is sticking with a conventional wastegated turbo but will use a technology it calls V-Pulse that relies on pressure pulses created by the opening of exhaust valves to push the exhaust into the inlet stream. The Volvo solution relies on a split exhaust with the odd and even cylinder numbers each with their own manifold.
According to Frank Bio, Volvo's senior director of marketing for engines, this avoids the complication of the variable geometry turbocharger.
Cummins' chief technical officer John Wall both differs and agrees on the issue of VGT complexity. Cummins is using a unique Holset VGT turbo that might be described as a variable-area turbocharger. The patented design moves one wall of the turbocharger exhaust chamber to squeeze down or open up the exhaust passages between the vanes, varying the speed of the exhaust as it impinges on the turbine wheel. This varies the backpressure without loss of efficiency and makes the device elegantly simple. Wall points out that this turbo design has been in use on a European Iveco engine for several years with excellent results and no durability issues.
Competing VGT designs are anything but simple, Wall says. Because of the Holset patent, other VGTs use variableŠvane turbos. In these, the vanes that direct the exhaust within the turbine housing swing to adjust the cross-sectional area that the exhaust must flow through and at the same time vary the angle that it impinges on the turbine wheel. They do a good job, but where the Holset design has a single moving member, these turbos have many and all in the hot exhaust flow.
It is a discussion that will be played out in the field, because the swing-vane VGT is being used in both the Detroit Diesel and Mack cooled EGR engines.
Whatever the relative complexity of the turbos, there is undoubtedly additional componentry on these engines in the shape of the control valves that vary the amount of exhaust gas according to the demands on the engine.
While the valves are relatively simple, they do add to the overall packaging of the EGR engines and their control adds to the demands on the engine electronic control unit. So all manufacturers of the new EGR engines have new-generation electronic controllers to handle the highly complex balancing act of air, fuel and EGR ratio over the engine speed and load range.
Cooling Demands
Undoubtedly, chassis OEMs have had to direct engineering talent away from other areas to satisfy installation needs for these new engines. A particular issue has been cooling and, in this respect, the vertically integrated Mack and Volvo have had something of an advantage in packaging their own power.
In the initial stages, the added load on the cooling system had many worried. In cooling the exhaust gas using an engine-coolant heat exchanger, a good proportion of the heat in the exhaust that previously escaped up the exhaust stack now has to be dissipated by the vehicle radiator. In general, this has been handled by upping the operating temperature of the engine, adding cooling capacity to the radiator and enlarging fans and fan drives.
Volvo already had a fan ring running very close clearances at the blade tips for maximum efficiency and Mack has brought over similar technology developed for the refuse-truck MR to a number of its on-highway, high-horsepower ratings, said Don Brugger, project director for Mack.
Mack 12-liter product director Steve Heffner also notes that the oil-pan capacity on the E-7 engine has been increased by a gallon, allowing Mack to stay with current oil drain intervals, a priority for all engine manufacturers. In this they will be helped by the new oil category CI-4 (see accompanying story on page 40), which includes specific testing in EGR engines to provide oil formulations that will handle the anticipated additional soot and acid products that EGR engines are likely to produce.
Cost Conscious
If the new engines are going to allow extended drains (though they are unlikely to go beyond 50,000 mile intervals, say the lubricants experts) the main discussion over price concerns the higher initial cost and any loss in fuel economy.
In general, the industry is expecting the installed on-cost to be between $2,500 and $4,000 by the time the added cost of the engine and the chassis modifications are factored in.
Caterpillar has been very guarded about its ACERT program, though it says that its technology will not change the interface between the engine with the chassis. This, Cat says, will mean it will be easier and less costly to fit into the chassis. However, it is widely anticipated that the Caterpillar solution will feature exhaust aftertreatment of some kind, meaning the need to add a catalytic converter and/or particulate trap, adding cost to the chassis.
As for fuel economy, each manufacturer says the goal is to introduce the new technologies with no fuel penalty.
On The Road
We have now driven, in various stages of development, the EGR versions of Detroit Diesel's 14-liter Series 60, Cummins' 15-liter ISX and Mack's 12-liter E-7 engines. In all cases — especially those in the later stages of their development — we have found that from a driver's perspective there is little difference from today's diesel.
According to the engineers, the adoption of the new turbo technology does improve throttle response so there is a barely detectable small positive trade-off in performance.
The jury is still out on fuel consumption. In each case as we tested the different engines, engineers said the performance and emissions objectives had been reached in all cases, but there was still fine tuning of electronic controls needed to bring consumption in line with objectives.
More Power 2002
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