Come in, emission control

by Jim Park and Rolf Lockwood

It’s been one full year since most makers of heavy-duty diesel engines have had to comply with tougher standards on nitrous oxide and other harmful emissions. The October 2002 deadline–outlined in the infamous consent decree between the U.S. Environmental Protection Agency and Caterpillar, Cummins, Detroit Diesel, International, Mack, and Volvo–accelerated the development of emission controls and radically altered long-established trade cycles for truck buyers, who feared a fall-off in performance and a hike in up-front prices. While these new engines do pass pollution tests, can they pass muster in the real world? Does the new technology inhibit performance on the road? Or save fuel dollars? Our testers put two newcomers through their paces: Caterpiller’s ACERT-equipped C15, and Mack’s versatile ASET engine.Gear fast, run slow. It’s a universally accepted principle of linking engine and drivetrain to balance performance and fuel economy. But how about spec’ing to run 105 km/h at 1,325 rpm? Caterpillar suggests just that with some of its new ACERT (Advanced Combustion Emissions Reduction Technology) powerplants. It won’t help you battle mountain passes or haul fish around the Maritimes, but if you want to sip fuel–with surprisingly good performance and drivability–in a rig that plies open highways and at 80,000 gross weight, Cat has some ideas.

For example, you can mate a C15 ACERT Multi-Torque 435 (435 horsepower with 1,550 pounds-feet of torque, rising to 1,750 in the top two gears) with an Eaton Fuller RTOC-16909A Top 2 transmission. That’s a 9-speed but essentially a 13-holer with the splitter mechanism removed (though convertible to a normal 13) with close steps and overdriven top ratios of .86 and .73. Out back you’d need a fast axle ratio giving you 90 km/h at 1,121 rpm and 105 at 1,325.

I recently drove that spec in a Kenworth T2000 grossing 80,000 pounds out of Cat’s Technical Center in Mossville, Ill. The key to Cat’s recommendation of the convertible transmission–conceived partly to answer the American fleet manager’s penchant for 9-speed transmissions–is the very close 17-per-cent step between those two overdriven top ratios of .86 and .73. You can get those same top ratios in the Eaton Fuller 13-speed box (a more common sight here) or the 18-speed, for that matter. While ZF Meritor has yet to mate its FreedomLine transmission with the C15, the 16-speed model would offer an 18-per-cent step between 14th and 15th gears, and 20 per cent between 15th and 16th–a promising option for a low-rpm spec. There’s 29 per cent between the top cogs on the 12-speed version.

My drive of the 1,325-rpm Kenworth involved three hours of cruising, including several long 3- to 5-per-cent grades. The transmission made just two downshifts from top gear. Being a Top 2 transmission, shifts between the highest two gears are automated, and Cat lowers the torque peak from 1,250 rpm to 1,150 so the driver has a little room to manoeuvre. The electronics also limit vehicle speed and activate gear-down protection so drivers aren’t tempted to run on a lower rung.

Cat knows it’ll be a challenge getting drivers to buy into this low-revs thing, but I found no driveability issues at all. The test-rig’s full-load upshift point into top gear was 1,400 rpm, and it shifted down from the top at 1,150. That downshift point is programmed to be 1,225 rpm if the engine load is 100 per cent and the deceleration rate is more than 10 rpm per second. Heading into a long grade at cruising speed, and with cruise control on, the revs would fall but I could feel that extra 200 pounds-feet of grunt. The two times where a downshift happened I didn’t have to make another as the rig crested the hill with the tach at 1,100 or so. The engine didn’t mind, and in fact that’s now the lower end of its operating range.

Many owner-operators cruise at low rpm anyway to cut fuel costs. After all, fuel economy–and driver satisfaction–is largely a matter of the number of times you shift. And with such a narrow gap between cruise speed and maximum torque output, I had visions of using that gear lever a lot. In practice, no sweat.

There’s another C15 MT model, the 475, with 1,650 and 1,850 pounds-feet, and two C13 MTs: a 410-horse version (1,450/1,550 pounds-feet) and a 430 (1,550/1,750 pounds-feet). With non-Multi-Torque C15 models pulling 80,000 pounds or less, you can still spec for 1,325 rpm at 105 km/h provided you have an engine producing 1,750 pounds-feet of torque or more. Otherwise, gear it to cruise at 1,400 rpm. Non-MT C13s should be spec’d for 1,450 rpm at 105 km/h. For higher weights, spec a C15 of any type to cruise at between 1,500 and 1,650 rpm as you’ve been doing all along.

In every case, you’ll have to look carefully at your specific startability and gradeability needs.

So what about ACERT? Cat is the only engine maker to use something other than exhaust-gas recirculation (EGR) to meet last fall’s stringent new emissions regulations. ACERT is a combination of new electronics, variable valve actuation, combustion-chamber changes like higher cylinder pressure and compression ratio, higher fuel-injection pressure and multiple injections per combustion stroke, twin turbochargers linked in series with electronic wastegates, and an oxidation catalyst incorporated in the exhaust system.

Two other key changes are in bore and stroke: the C15’s displacement is now 15.2 litres, up from 14.6, and the C13 is at 12.5 litres, up from 11.9 on its predecessor, the C-12 (the hyphen has been dropped). The twin-turbos on the C15 and C13 meet ACERT’s demand for high air flow and give a lot more overall boost (up to a whopping 42 psi). The two turbos actually loaf along, the one on the high-pressure side turning shaft speeds about 80 per cent of normal, and its mate turning slower still at 60 per cent.

Aside from the unique cruise rpm, this C15 delivered the solid throttle response and smooth, pleasing torque flow I expect from a Cat. I like multiple or changing torque output partly because they let you spec a less expensive drivetrain. You spec for the lower torque figure because the higher output only happens in higher gears where its stress on driveshaft and U-joints and axle is light.

C15s are available in horsepower ranges from 435 to 550, with up to 1,850 pounds-feet of torque. Next year Caterpillar will offer 600 horses with models offering both 1,850 and 2,050 pounds-feet of torque. Displacement is not yet decided, but my own horsepower preference is. Forgetting the health of my bank account, and failing to be a responsible commentator, I’ll take 600 ponies any day.The engineers at Mack Trucks decided that a single solution to last October’s emission challenge just wouldn’t work. They knew they wanted to use exhaust-gas recirculation (EGR), but how could it best serve Mack’s two distinctly different markets: vocational use, which the company has dominated for a rock’s age, and on-highway, in which Mack has been making in-roads on the strength of its Vision tractor?

The answer: Mack offers two different types of EGR–“internal” and “cooled,” and hence the “ASET” brand name for Mack’s E7 engine (the acronym stands for Application Specific Emissions Technology).

Internal EGR is for the vocational crowd–dump truckers, refuse haulers, concrete mixers, etc. Used on Mack’s new “AI” Series engines, I-EGR is less complex and less expensive than cooled EGR, but also less fuel-efficient. AI engines can be spec’d in the Granite series as well as the RD6, RB, DM, MR, and LE chassis. Seven engines are available: three Maxidynes (a 300-horsepower engine plus new 335- and 370-hp versions) and four Econodynes (at 350, 400, 427, and 460 hp). For the Vision and the CH chassis, Mack uses cooled EGR (C-EGR) on its “AC” Series engines, available in in both Econodyne and MaxiCruise models. Five Econodyne ratings range from 350 to 460 hp, while the four MaxiCruise models go from 310 to 380 hp.

Internal EGR is deceptively simple, relying on managed airflow through the engine with an extra lobe on the exhaust cam to bleed the right amounts of uncooled exhaust gas back into the cylinder. The design of the cylinder head, coupled with the speed of the flow-through of the exhaust, adjusts the amount of exhaust gases being recirculated without the need for EGR valves or cooling of the hot gas.

It comes at a price: fuel economy. It’s less a consequence for vocational users in a stop-and-go short-haul world. That said, the point of peak torque in Mack’s vocational engines has risen from 100 to 180 rpm up to 1,300, and torque values have dropped by about 225 pounds-feet to 1,200 on the Maxidyne 300 (it’s 1,340 and 1,480 pounds-feet on the new 335 and 370 respectively). Mack also changed the old operating range from 1,000 to 1,750 rpm: now it’s 1,300 to 2,100 rpm on all three Maxidynes, for example. All of this necessitated an extra transmission gear for Maxidyne motors and a change from the very tall 0.60:1 overdrive gear to a more ordinary 0.71:1.

Cooled EGR can only achieve decent fuel economy running in a steady-state situation, such as cruising down the highway. That’s why it’s being used for highway applications. The most visible aspect of a C-EGR engine is the transfer tubing and the heat-exchanger unit needed to get the hot exhaust gas from the manifold, cool it, and get it back into the engine. Since the degree of recirculation varies with engine speed and load, Mack has installed a new and separate control loop in the fuel-cooled V-MAC engine control module to manage the amount of gas diverted from the normal exhaust stream. The oil-actuated EGR control valve diverts exhaust gas first through the liquid-cooled EGR cooler, then over top of the engine and into the venturi mixer where it’s re-introduced to the intake manifold, along with the clean air drawn through the intake system.

To overcome the loss of turbo boost created by shrinking the supply of exhaust to spin the turbo, all the engine makers using cooled EGR are employing a variable-geometry turbocharger (VGT) of some sort to make the best use of the available exhaust stream. The Borg Warner turbo on the ASET AC engine uses pivoting vanes on the drive turbine to grab more or less of the exhaust stream as needed, extracting better response from the turbo. This makes for better driving; arguably, it’s even better than pre-’02 engines on that front. Reliability and durability concerns surrounding the C-EGR engines shouldn’t be much of an issue. There were no changes required to the major components: the block, pistons, crank, etc., are all the same as the pre-’02 models.

Thanks to the variable turbo, Mack was able to redesign its proprietary engine brake, now called PowerLeash. Mack says the optional compression brake is 65 pounds lighter, simpler in design, and more efficient than other brakes.

The ASET engine carries a three-year, 300,000-mile base warranty, with five years, 500,000 miles on the hard components. Not incidentally, the ASET AC remains one of the lightest packages in the 12-litre class, tipping the scales at just 2,350 pounds dry. Its AI brother is lighter still at 2,210 pounds.

Mack cut the drain point for its ASET E7 engines to 25,000 miles, down from 40,000 on pre-’02 versions. Mack bumped the capacity of the E7’s oil sump from 32 to 40 quarts and increased the capacity of its CENTRI-MAX centrifugal oil filter in order to keep oil-drain intervals on the high side.

The ASET AC engine runs best at about 1,600 rpm–100 rpm higher than previous engines. Peak torque on the AC-427 comes 100 rpm higher, too (at 1,200 rpm), so the new engines will demand a different approach to gearing than before. One of the trade-offs with EGR has been a narrowing of the engine’s operating range and its “sweet spot.”

Mack’s current VIP (vehicle information profiler) driver display already has an engine sweet-spot indicator, in the form of a backlit “$” sign, but the company will offer a separate dash display to help drivers without a VIP keep the engine in the optimum operating range.

Drivers will have some adjustments to make with all EGR engines, not unlike the learning curve we all had to climb as we switched from mechanical to electronic controls. As we see with ASET, the trend to lower and lower engine speeds has shifted back to a slightly higher speed, and that’ll take some getting used to, as will managing the difficulties in reining them in while trying to shift progressively.

The VGT literally lights up the engine when you step on the throttle, so drivers will have to get used to going even easier on the pedal. And the EGR engines are quiet, which is good from an in-cab noise perspective, but as Carrie-Ann Baker, Mack’s director of key accounts points out, drivers will have to pay closer attention to gauges until they get used to the engine.

“Eventually they’ll be able to come back to driving by sound and feel, but it’ll take time,” she says.

After short drives with five different truck configurations, thrilling throttle response is clearly the biggest change in the way Mack’s C-EGR engines perform. I noticed the same thing with the Cummins ISX I drove in Texas several months earlier, but the Mack engine seemed a little less aggressive. The revs on the Mack engine rose and fell just a tad slower, making it easier to control–especially while progressive-shifting. There’s no turbo lag with the VGT, making it much easier to maintain power to the wheels after an upshift.

The AC-427 engine hits its peak torque of 1,550 pounds-feet at 1,200 rpm, 400 rpm below the recommended cruising rpm of 1,600, so there’s lots of twist to fall back on as you begin climbing a grade. On the high side of the pedal, the output flattens out noticeably as the rpms climb, encouraging drivers to shift low, before running out of punch in each gear. The power band was nicely mated to the 10-speed transmissions in the test trucks, especially to the Maxitorque T310 gearbox with its wide steps.

The engines run noticeably hotter than the non-EGR engines of the past (about 190 to 195 degrees on the gauge), but that’s about the only obvious difference on the dashboard. Intake manifold pressure and oil pressure are about what you’d expect. They’re really quiet, too, so much so that I had to resort to watching the tach to time my downshifts.

In a nutshell, Mack’s answer to EPA’s latest emissions standards are better performers–on the road–than their non-EGR counterparts of the past. We couldn’t judge fuel economy, reliability, or life expectancy, of course, but those performance factors will be revealed in the fullness of time.

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