This cat's out of the bag

| January 03, 2006

Cat’s ’07 C-15 prowled up and down some serious grades with nothing more than a purr.

Truckers who rely on their big, yellow diesels won’t see much difference between the 2007 lower-emission engines and previous models.

That’s what Caterpillar claims. To find out for myself if this is so, I took one on a test drive up and down some serious Illinois grades.

“The ’07 engines have the same reliability and performance that our customers expect and have always got from us,” says CAT spokesman Jason Phelps.

And what about fuel economy?

“Fuel mileage is expected to be the same, depending on the fuel’s British thermal unit content, application, proper gearing and other factors,” says Caterpillar Customer Service Manager Robert Keene.

Caterpillar invited me to its Mossville, Ill. plant, just north of Peoria, in October. After a morning lecture and plant tour, Phelps, Keene and I went to the test vehicle – a 2000 Kenworth T2000 with a 550-horsepower 2007 C-15 boasting 1850 pounds-feet of torque at about 1,200 rpm, a nine-speed Eaton-Fuller transmission, 3.25 rears and 22.5 LP tires. The T2000 was hooked to a 53-foot dry van partially loaded with gravel. Gross weight was 76,800 pounds.

My guides explained that the T2000 had held several different engines, and some fit its frame better than others. But when building their ’07 models, truck OEMs will spec’ the frame to fit the engine, and each OEM will mount the exhaust system’s diesel particulate filter differently.

The ’07 C-15 was a snug fit in the test truck’s frame, and Cat technicians had mounted the DPF on the passenger side just aft of the door. The exhaust stacks were not new and showed some corrosion inside.

I rubbed a finger inside one stack. On any other truck my finger would’ve come out black with soot, but this time it came out clean. That’s because the ’07 power units comply with the EPA’s emissions law for on-highway diesel engines: 1.2 grams nitric oxide/nitrogen dioxide (NOx) and .01 grams particulate matter (PM) per braking horsepower, and sulfur at 15 ppm.

NOx is formed by diesel fuel’s combustion at the high temperatures and pressures typical of pre-’07 diesel engines. Cat addresses this with its proprietary, pre-’07 ACERT technology fuel system and by cooling the intake air and replacing part of its oxygen with non-combustible gas from the engine’s clean gas induction system.

“More oxygen means higher combustion temperature,” Keene says. “The CGI takes PM-free, non-combustible gas from the exhaust down-flow of the diesel particulate filter, cools it in a water jacket and sends it through the turbo chargers and air cooler and into the engine.”

Cat’s hydraulic variable valve actuation also addresses NOx. “It reduces NOx and improves fuel economy on the inlet side and provides optimal compression brake horsepower on the outlet side,” Keene says, adding that the C-15 has 600 braking horsepower at 2,000 rpm.

Cat’s self-regenerating DPF, about the size and weight of the muffler it replaces, handles the particulate matter pollution. “Particulate matter is all hydrocarbons from incompletely combusted fuel and engine oil that gets past the rings,” Keene says. Cat’s DPF absorbs all PM. At maximum absorption, the DPF oxidizes the diesel fuel PM via a high-heat chemical reaction so only carbon dioxide and water exit the exhaust. Harder-working engines make enough heat to cause the reaction. In cooler-running engines the DPF automatically oxidizes diesel PM buildup with a small injection of diesel fuel: a few ounces “at most maybe every other week,” Keene says. “Either way, the driver will never know it’s happening,” he says, and the amount of fuel used is negligible.

The same reaction that oxidizes diesel fuel PM reduces engine oil PM to ash, which gathers in the DPF. “That has to be cleaned out,” Keene says. The EPA requires 150,000 miles between cleanings. Cat’s target is 300,000 miles. “It’s about two hours of shop labor, with the DPF either on or off the vehicle, once every two or three years,” Keene says.

The DPF weighs about 125 pounds and replaces the muffler. It will be used with different exhaust configurations, so Cat can’t say how it will affect a truck’s weight.

The sulfur issue is addressed primarily with low-sulfur fuel. “We had to get low-sulfur diesel fuel for this test drive,” Phelps says.

The weather was clear, dry and breezy. Keene had found some grades nearby steep enough to test the ’07 C-15’s power. The first grade was a mile-long, 3-to-4 percent grade on Peoria’s I-474 by-pass. Nodding to Illinois’ big truck speed limit, I set the cruise control at 60 mph at 1,270 rpm. I didn’t touch the throttle or gears. The C-15 held at 60 mph for the climb: neither lugged nor strained, but went stoically about its business. It’s my guess that if the hill had been 1,000 miles long, the C-15 would have maintained 60 mph at 1,270 rpm under the 77,000-pound load.

The scuttlebutt was that Cat’s ACERT engines perform well only at higher rpm for cruising and before shifting. To clarify this, I asked Keene if there was a certain engine speed at which the C-15 ran best. “Between 1,200 and 1,300,” he replied, adding, “I don’t like to run them above 1,500.”

After ascending the grade on I-274, we U-turned and headed back down. I engaged the engine brake and coasted in ninth gear. The C-15 once again performed well, slowing the rig below our 60 mph cruising speed, and I disengaged the brake before we obstructed traffic. The DPF seems to do a better job of quieting the C-15 than the old muffler, as even with engine brake on the exhaust was either inaudible or nearly so.

We drove back to I-74 and headed west. Between I-274 and exit 54 just east of Galesburg were two more grades much like the first: about a mile long, although the second was clearly steeper, a four percent grade. The C-15 climbed both hills without hesitation or strain while Keene, occupying the passenger seat, explained how Cat is already putting into place its service network for its ’07 engines. Before one upgrade I slowed to 55 mph and re-engaged the cruise control for the climb. The C-15 brought the 381/2-ton rig back up to 60 mph and 1,270 rpm up the hill.

For the drive back I chose U.S. 150 with its steeper hills, sharper curves and small towns: no place for cruise control, and I’d get an idea of the C-15’s performance in a non-interstate environment.

Observing the narrower, bumpier, two-lane road and cross traffic, I reduced cruising speed to 55 mph at about 1,225 rpm. The highway dipped steeply down and up through several ravines. Maintaining speed, I braked gently going down and dropped to eighth gear climbing, as I’d expect to with any engine. I started in second gear from each traffic stop, evaluating the C-15’s performance up through the gears, mindful to shift below 1,500 rpm. The engine smoothly brought the truck to speed each time, perhaps more quickly and easily than most engines: 550 horsepower and 1,850 pounds-feet of torque handling 77,000 pounds exactly as any driver would expect.

Phelps says a common complaint from fleets and OEMs after 2002 was that there was insufficient time to evaluate the engines before law required them to be used. “We responded to that by getting as many ’07 engines out to our customers over the summer, so they have 18 months with the engines before Jan. 1, 2007,” Phelps says. “They needed supplies of low-sulfur fuel,” Phelps says. “We helped them with that, too, although it was hard to get.”

Phelps says Cat benefits from this attention to detail. “It gives us more accurate return data,” he says. “We want to hear about our products from our customers.

So far, all return data has been good. “We’re getting all positive reports from fleets and OEMs,” Keene says.

I asked about costs. “That varies from engine to engine, from OEM to OEM,” says Keene. “There’s no relationship between our cost increase and the end user’s.”

Our return to the Cat plant was like the entire 100-mile, two-hour test drive: remarkable only in that it was unremarkable. In other words, Cat’s ’07 on-highway ACERT engines, even spec’d with flatlander gears and a nine-speed transmission and pulling heavy loads up long inclines, will perform as well as earlier model Cat engines. If spec’d to its maximum 625 horsepower and 2,050 pounds-feet of torque and matched with the right transmission, rear end and tires, Cat’s ’07 C-15 will likely provide enough pulling power to handle even the heaviest applications over the long term.

The biggest difference is that Cat’s ’07 ACERT engines exceed EPA emissions requirements, so long as low-sulfur fuel is available. There’s no loss of power, weakness or strain. Cat’s modified fuel/air injection and exhaust systems will not decrease their ’07 engines’ performance.


Vital Specs as Tested
Engine: 2007 Caterpillar ACERT C-15
Displacement: 15 Liters
Horsepower/Torque: 550/1,850 pounds-feet
Transmission: Eaton-Fuller Nine Speed
Rear Axle Ratio: 3:25
Tires: 22.5 LP
Truck: 2000 Kenworth T2000
GVW: 76,900 pounds
Test Drive Length: 100 Miles
RPM at MPH as Spec’d: 1,270 at 60; 1,325 at 65

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