|EPA-Certified Engines Covered by the 1998 Consent-Decree|
|C151||435, 435/500, 475, 500, 550, 560|
|C7||190, 210, 210AT, 230, 250, 275, 300, 330|
|ISX||400, 450, 475, 500, 530, 565|
|ISX SmartTorque||400, 450, 475, 500|
|ISX Vocational||435, 465|
|ISM||280, 310, 330, 350, 370|
|ISM SmartTorque||330, 350|
|ISM Vocational||285, 320, 350, 385|
|ISB||145, 170, 185, 190, 205, 210, 225, 240, 245, 260|
|12.7L ECON||350, 375, 375/350|
|12.7L STD||375, 375/430, 400, 430|
|14.0L PREM||435, 435/475, 435/500, 475, 500|
|VT 365||175, 195, 215, 230|
|DT 466||195, 215, 230|
|DT 530||275, 200, 330|
|HT 530||280, 300, 320, 340|
|ASET Highway (CEGR)|
|MaxiCruise||310/330, 330/350, 355/380, 380/410|
|Econodyne||350, 400, 427, 460|
|ASET Vocational (I-EGR)|
|Maxidyne||300, 335, 370|
|Econodyne||350, 400, 427, 460|
|VED12||365, 395, 435, 465|
| Engines certified by EPA as of June 15, 2003, as fully compliant with current emissions requirements
Ratings cover only commercial applications.
1 The C15 will be available in October.
While early perceptions of new, lower-exhaust-emissions engines were steeped in fears of poor fuel economy and questionable reliability, it looks like the anticipation was at least a little greater than the event.
The engines do cost more than their pre-’02 counterparts, but most users report somewhat better fuel economy than early experience indicated, and there are no serious maintenance or durability issues on the horizon.
The federal Environmental Protection Agency declared that as of October 2002, oxides of nitrogen (NOx) exhaust emissions from diesel engines had to be cut in half, without increasing particulate-matter (PM) emissions. Technically, that rule takes effect in January 2004, but a consent decree in 1998 accelerated that date for the major heavy-duty diesel suppliers at the time.
Meeting EPA’s mandate proved challenging, since traditional methods of reducing one pollutant tend to increase the other. For example, advancing injection timing creates higher peak cylinder temperatures and burns off PM, which consists largely of unburned fuel. But higher cylinder temperatures are what cause NOx. Retarding timing reduces temperatures and NOx, but those reduced temperatures make for less efficient combustion and increase PM.
With the exception of Caterpillar, over-the-road diesel engine manufacturers turned to cooled exhaust-gas recirculation (EGR) as a solution. This is a process by which a percentage of the exhaust gases are drawn, cooled, forced back into the intake and mixed with the fresh air and fuel in the cylinders. EGR reduces NOx by lowering the peak flame temperatures inside the combustion chambers.
EGR, especially combined with retarded injection timing, makes for less efficient combustion, which triggered concerns about reduced fuel economy. Also, EGR adds some cost and complexity to engines, so maintenance and durability concerns were raised early on. Finally, since EGR reduces peak cylinder temperatures, it increases condensation of water and acids in the engines, and many feared that it would also increase oil sooting. Therefore, a new API CI-4 oil standard has been established specifically for EGR diesels, and those oils must be used in them. All major lubricant suppliers have met the new standard with their latest engine oils.
Caterpillar opted to pursue a new combustion system called “ACERT,” or Advanced Combustion Emissions Reduction Technology, which will be available across Cat’s product line by the end of the year.
The engines feature a double turbo system, an air management system designed for better combustion efficiency, a new fuel system and new electronics. It also employs an exhaust aftertreatment system already in use on other Cat engines. In addition to meeting the new API CI-4 oil standard, oils used in ACERT engines must meet Cat’s new Engine Crankcase Fluids (ECF-1) specification. (See page 30 for more on ACERT.)
What users are saying
When we last reported on ’02 engine performance in Class 8 on-highway trucks, some fleet users were disappointed with the new engines’ fuel economy and were uncertain about long-term maintenance and durability issues (see “Technically Speaking,” CCJ, May 2003). While long-term maintenance and durability may still be under some scrutiny, most users are experiencing better fuel economy than they had originally projected.
Caterpillar wasn’t prepared to roll out ACERT when the new emissions requirements kicked in, so the company offered customers a “bridge” engine – a model that offered reduced emissions but not enough to avoid any non-compliance penalties. Cat is offering those engines to heavy-duty customers until October, when the company begins production of its C13 and C15 ACERT engines. EPA certified the C15 in June.
Joe Stianche, fleet manager, Sanderson Farms, Laurel, Miss., was expecting a 3 percent to 5 percent fuel economy penalty with his ’02 Caterpillar bridge engines. Now, after five months experience with those 12 engines, Stianche is still crunching numbers. He says that, while fuel economy still isn’t as good as with his pre- ’02 engines, “it appears to be moving in the right direction. It’s getting closer to what the engine guys have been telling us.”
Clayton, Ala.-based Boyd Bros. Transportation has seen some degradation in fuel economy, but the company knows that can – and often does – change. “Our ’02 Cats’ fuel economy is a little low right now,” says David Baker, vice president of maintenance for Boyd Bros. “But we’ve only been running them for a few months. We know these engines improve after about 40,000 to 50,000 miles – once they’re fully broken-in.
“In fact, if you go back and look at the fuel economy of our pre- ’02 Cats before break-in, it’s about the same,” Baker says. “We’ve had no shocks – we’re pleased.”
For Dependable Auto Shipping in Mesquite, Texas, the bridge engines are working without a hitch. “We’ve been running 20 Cat bridge engines since April,” says Earl Daniel, maintenance manager, “and we’ve had no problems so far. The drivers like them, and we haven’t had to change any maintenance practices.
“We don’t get very good fuel economy to begin with, since our trucks have no aerodynamic devices,” Daniel continues. “These engines are giving us 4.8 to 5 mpg which, for us, is normal for a new engine.”
One area in which many of the new engines get high marks is driveability, which translates into driver satisfaction. That experience is common among Cummins ISX users.
“Generally, drivers seem to like them,” says James Hall, owner of Charleston, Mo.-based J. Hall Transport. “They did notice that engine temperatures run 10 to 15 degrees hotter than they were used to, but we’re told that’s normal. And we haven’t changed any maintenance practices. We still sample oil and change it at 50,000 miles. We’re going to keep a close eye on that.”
J. Hall Transport is running 20 Cummins ISX EGR engines, some of which have been in service since February and have logged about 70,000 miles – ample time to judge fuel economy. Hall has seen some decline in fuel economy. “We usually run with fairly light loads, and see about a 0.2-mpg decrease from our old N14s. At full load, the worst we’ve seen is a 0.5-mpg difference.”
One concern Hall has centers around EGR valves. “That valve is constantly moving,” he says. “And anything that moves is going to wear and need service. But it’s like anything new – there are going to be some problems.”
Charlotte-based Lance Inc., which has six ISXs in service, reports no engine-related failures in the 30,000 to 50,000 miles each engine has run. Grainger Smith, Lance’s transportation manager, doesn’t yet have numbers he’s comfortable with reporting, but he says early data suggests that mpg is “close to” that of the fleet’s N14s. Overall, Lance’s drivers are satisfied with the ISX, although they report that the N14s “pull better,” Smith says.
Truckload carrier Highway Express, Richmond, Va., has had 10 Cummins ISXs in service for about 40,000 miles. “Our drivers have commented very favorably about the improved throttle response,” reports fleet manager Dennis McCurry.
So far, Highway Express has had no problems or maintenance issues, and “Our pre-’02 engines were getting 6.1 to 6.5 mpg, while the new ones are getting 5.9 to 6.3,” says McCurry. “That’s not too bad, and you have to remember that these engines are still pretty new. We’ll have to run them longer and get them good and broken-in. Then we’ll see what they’ll do.”
From a fuel economy perspective, user experience with the Detroit Diesel Series 60 EGR engines is in line with – or better than – initial projections.
“The initial cost is higher than we had projected, and we’re looking at a 3 to 5 percent fuel-economy reduction,” says Steve Duley, director of equipment purchasing and disposal for Green Bay, Wis.-based Schneider National. “We project that will cost us about $1,000 per year, per truck, in added fuel costs.” Schneider is running 55 EGR-equipped Series 60 engines, the oldest of which are 250,000-mile pre-production units.
But despite the additional acquisition and fuel cost, Duley views the Series 60 favorably in other areas. “Reliability has been good, and drivers favor them slightly over the pre-’02 units,” he says. “They’re running well so far – I hope they keep on going.”
Reading, Pa.-based Penske Truck Leasing’s 1,150 EGR-equipped Series 60 Detroit Diesels “have been a pleasant surprise,” says Bob Douglas, vice president of maintenance operations. Four of Penske’s units are pre-production engines with up to 200,000 miles on them. The rest have logged up to 65,000 miles.
Penske has seen about a 0.2 mpg drop in fuel economy for lighter loads and about a 0.3 drop for heavy loads, Douglas says. “We’ve done oil sampling and found soot levels to be normal, so we’re not changing maintenance intervals. And drivers report that the engines are more responsive and quieter.”
Mike Jeffress is unconvinced that the change in engine technology will impact fuel economy. “We still find that fuel economy is driver related,” says Jeffress, vice president of maintenance for Little Rock, Ark.-based Maverick Transportation. The fleet has had 120 new-technology Detroit Diesel engines in service since January, with the highest-mileage ones at about 60,000.
“I have one group of drivers who were getting 6.8 to 7 mpg with pre-’02 engines, jumped into the new tractors, and continued to get 6.8 to 7,” Jeffress says. “Then I have another group who used to get 6.5 to 6.8, and can’t do better than 6 with the new equipment.
“Overall, drivers are very satisfied with the engines, but they note that the engine fan on-time has increased,” Jeffress adds. “Maintenance wise, we’re being very conservative right now, with a 15,000-mile oil drain interval, which is down from 30,000 miles. But we’re doing oil analysis and seeing outstanding results. We’ll eventually try to stretch that interval back out.”
Mack’s solution to the emissions challenge was separate technologies for vocational and on-highway applications. Like the other engine makers except Caterpillar, Mack’s highway engine, the ASET CEGR, is based on cooled EGR.
Driver satisfaction with the CEGR engine is high, reports Hagerstown, Md.-based D.M. Bowman Transportation. The carrier is operating four new engines, two of which have passed 150,000 miles.
“It’s unusual to give a driver something new and find they can’t think of a single thing bad to say about them,” says Sam Kennedy, D.M. Bowman’s chief maintenance officer.
“The noise level inside the cab is 100 percent lower,” adds Charles Buffington, a driver/trainer for D.M. Bowman. “I’ve driven them to Chicago, through New England, and to Florida.” Buffington also says that the engines warm up much more quickly than the pre-’02 engines.
D.M. Bowman did experience one turbocharger compressor failure, which was repaired in short order. That turbo had the previous aluminum compressor wheel, rather than the improved design.
While initial results showed a 4 percent reduction in fuel economy as compared with pre-’02 engines, recent results with the engines more fully broken-in indicate an improvement, Kennedy says. The largest variables are the driver and the types of runs rather than the engine itself, he adds.
Oil analysis shows a similar pattern at D.M. Bowman, with soot levels showing “mixed results.” Oil change intervals have been shortened to 25,000 miles. “It’s what you do with the truck that matters,” Kennedy says.
Okeechobee, Fla.-based Walpole Inc. also has shortened its oil drain interval – from 25,000 to 10,000 – and samples at each change, says Robert Orr the carrier’s maintenance director. Walpole had some problems with the older units among the 13 CEGR engines it runs. Those trucks have been in service from one month to a year, and the oldest are at 100,000 miles. Orr reports that the older units experienced some hard-part failures, such as rocker arms, cams and turbos.
“The more recent engines seem to be doing a lot better,” Orr says. Walpole hopes to increase its oil-drain interval at least to 15,000 miles. Despite some of the problems with the early units, Orr is confident that reliability won’t be a long-term issue. “Mack has been around a long time. I’m sure they’ll get it right.”
Fuel economy isn’t an issue for Walpole, Orr says. “We pull a lot of open-top trailers.” With such a non-aerodynamic load in tow, “our fuel economy wasn’t that great to begin with – about 5.5 to 5.6 mpg. With our new Mack engines, the numbers are pretty close.”
At Pittsburgh-based Pitt Ohio Express, a true comparison on fuel economy between the old-technology engines and the CEGR engines is difficult because the specs have changed. “I can’t give you meaningful feedback yet, because when we got our 15 Mack ’02 engines, we bumped our horsepower spec from 400 to 427 to compensate for any perceived power loss due to the EGR,” says Denny Martin, the carrier’s director of fleet maintenance. “We lost between 0.5 and 0.8 mpg, but I can’t tell you how much of that is attributable to EGR.”
Martin can speak to performance in other areas. “Our drivers have accepted the new engines very well, and we haven’t had any maintenance issues, except that, at Mack’s recommendation, we reduced our oil drain interval from 30,000 miles to 25,000.” Martin is also pleased with the support Pitt Ohio Express is getting. “Mack has been very helpful. They’ve made programming changes, and we actually pulled two of the new engines back to 400 hp. On those engines, preliminary data indicates that fuel economy will be in line with what we used to get.”
For Volvo users, comparing the old and new engines isn’t necessarily a simple matter because Volvo rolled out new versions of its engines and its tractors simultaneously. The company chose to introduce its long-planned redesign of the VN series as it made changes necessarily in the engine compartment to accommodate the V-Pulse EGR engines.
Burley, Idaho-based Idaho Milk Transport has had 12 Volvo V-Pulse engines in service for 30,000 to 50,000 miles. “Drivers like them a lot, and fuel economy is at least equal to that of our previous Volvo engines,” says Gene Brice, the carrier’s president and owner.
In fact, using its Qualcomm mobile communications system to help keep extremely close tabs on fuel economy, Idaho Milk Transport noted “a couple of tenths” better mpg with the new engines, Brice says. However, with the tractor/engine change also came a tire-spec change and, “we haven’t isolated that benefit yet,” he says.
“We’ve had absolutely no problems with the engines, and we’ve made no changes to our 30,000-mile oil-change interval,” Brice adds.
Highland Park, Ill.-based Eagle Express reports similar experiences. “Our two new Volvo V-Pulse engines have only been in service for a month, so they’re barely broken-in,” says Jim Haan, maintenance manager. “But they’re already getting 7.3 mpg, which is right where we were with the older Volvos.”
So far, Eagle Express is planning to keep its oil-drain interval at 25,000 miles, Haan says. “But with EGR, we may need to adjust that.”
Driver acceptance is strong, Haan adds. “Our drivers like them just fine They say there’s plenty of power, and I haven’t heard any complaints. We’re ordering 40 more.”
For Phoenix-based Knight Transportation, which has had 10 V-Pulse engines in operation for six months, transition to the EGR engines seems to be mostly a non-event. “I’ve heard nothing negative from our drivers,” says David Williams, vice president of equipment maintenance.
“Fuel mileage is down a couple of tenths, but that’s not too bad, judging from some of the stories I’ve heard,” Williams says. “And we’ve been able to keep our 30,000-mile drain interval with no problems. There’s nothing in our experience to indicate that we should be afraid of these engines.”
If the experiences of these engine users hold, the 2002 technology shift may not be the catastrophe some doomsayers predicted. The question is: Will the same be said after 2007?
Is it Miller time for ACERT?
The new Cat C-13 and C-15 ACERT engines combine twin series turbochargers with hydraulically varied valve timing. Such technology hearkens back to a 1990 article in Automotive Engineering magazine, entitled “The Flexible Diesel Engine.” Authored by Southwest Research Institute’s Dr. Robert Thring, the article described something called a “Miller Cycle” diesel.
When it looks like a Miller, smells like a Miller, and quacks like a Miller, it’s probably a Miller. Presented with the theory that Caterpillar’s ACERT Technology essentially represents a Miller Cycle engine, Cat officials didn’t argue.
The Miller Cycle delivers what amounts to refrigerated intake air to the engine at the end of the intake stroke. With that in mind, here’s what’s likely going on inside ACERT engines:
Twin turbos increase boost pressure in the charge air cooler and intake manifold, significantly above what’s normally used even for EGR engines. The additional compression makes the air hotter than it otherwise would be, causing more heat than normal to be thrown off in the charge air cooling system. This system now includes jacket water cooling before the standard air-to-air unit. The engine generates extra boost only to throw it away by closing the intake valve early, rather than letting all the pressure into the cylinder. Instead of hitting the seat 15 degrees or more after Bottom Dead Center, the intake valve actually closes before the piston hits the bottom end of its stroke. This has the effect of throttling the intake air, creating a cooling effect, and supplying the same amount of air you would in traditional engines, in spite of the higher boost pressure.
Naturally, cooler air makes the engine produce less NOx because NOx forms only at the highest temperatures in the combustion chamber. Cooler conditions also have a positive effect on combustion by improving the way fuel and air mix, easing the NOx/PM tradeoff.
ACERT includes hydraulic actuators on both intake and exhaust valves. These likely allow a small amount of exhaust gas to be recirculated into the cylinder internally and mix with the chilled air at some point in the intake cycle when cylinder pressure is low.
There are other important aspects of the technology. The engines use pilot injection – a small shot of fuel injected during compression, and well before the main injection. This warms the air and gives instant ignition when the main injection starts. This removes the spike in pressure that results from ignition delay – the time between start of injection and start of combustion – which is a big source of high temperatures and NOx. The system also likely has very retarded timing of the main injection – meaning that the piston is on the way down throughout the combustion process. This means the energy of combustion is quickly being removed because of expansion, keeping temperatures low.
The only downside is a little bit of hydrocarbons and soot left over, probably mostly because of the very late timing. This is overcome with Cat’s catalytic exhaust treatment.
One of the most obvious characteristics of the Miller cycle, according to the article, was a reduced flow of heat into the cylinder liners and other parts exposed to combustion. Such reductions in cylinder heating usually show up as increased power for the amount of fuel burned, and the Miller Cycle did make the engine more efficient. Only road experience will tell, of course, but if this educated guess at Cat engines’ inner workings is correct, chances are very good that their technology will provide good fuel economy and take some stress off the cooling system.