Driving Cummins ISX-EGR, Pete 379 with Flex Air
STEVE STURGESS
SENIOR EDITOR
Our coverage of the hurry-up of the October '02 emissions deadline has been extensive. The implications for the end users of the new engines demanded it. So it came as a revelation that many fleets and individual owner-operators are still in the dark about how equipment changes will affect them.
We have devoted many stories and editorials to this issue, yet there apparently still is a huge lack of understanding about the implications of the Environmental Protection Agency's acceleration by 15 months of what was originally a 2004 deadline.
To return to the topic, to restate the issues and to drive one of the new engines for an extended period was the object of this test drive. How appropriate that we should depart Peterbilt's Denton plant with a Cummins ISX-EGR under the extended hood of a Pete 379 on Oct. 1, 2002, the EPA deadline day.
The Issue
EPA decided back in 1998 that North American heavy duty engine manufacturers were cheating in their emissions performance. At issue: engines were clean on the EPA test cycle, a "transient" cycle similar to driving typical urban freeways or delivery routes. But to maintain over-the-road fuel economy, where most of the time the engines are operated at a "steady state," the manufacturers gave the controlling electronics a different set of calibrations that minimized fuel consumption at the expense of emissions. The result: Engines met the EPA test requirements. And they met the users' need for economy.
But those seemingly incompatible aims opened up a debate about whether these engines met the spirit of the regulation, or just the letter. In the end, EPA with the Department of Justice in the background as the heavy prevailed. To stay in business, engine manufacturers signed consent decrees that said they would meet a new set of emissions regs written for 1999 that included steady-state testing. Furthermore they would agree to be penalized for their excess production of emissions specifically nitrogen oxides (NOx) by agreeing to a pull-forward of the January 2004 deadline for the next major emissions hurdle to October of 2002.
For most of us, 15 months is not a big deal. But in the development of new technologies to meet the most stringent emissions levels ever set, a 15-month shortening of the development process required deployment of huge and expensive resources.
Hardware
For all that, most of the engine makers have met the target. Only Caterpillar will not have a conforming engine until later in 2003. Its head-to-head competitor, Cummins, was one the first to say that it could and would meet the Oct. 1, '02 deadline. And it does so with cooled exhaust-gas recirculation (C-EGR) handled by a subsystem that is at the same time fully integrated into the engine, while mounting completely external to it.
On the ISX 15-liter powering the Peterbilt we were driving, the system consists of a very special Holset variable geometry turbocharger (VGT), an EGR valve to vary the amount of exhaust that is fed back into the engine, a cooler that transfers the exhaust heat to the cooling system, and a mixer that is mounted between the charge air cooler and the engine's charge inlet port.
The critical part of the Cummins EGR solution is the VGT, which is in the system to maintain exhaust pressure and hence push the recirculated exhaust into the high pressure inlet stream. Obviously, there is some pretty sophisticated control in the engine electronics that manages the EGR flow, fuel and boost.
The reason for the exhaust gas in the inlet stream is that the burnt fuel products and the low oxygen level mean that the incoming stream is basically inert. As such, it allows for the peak combustion temperature inside the combustion chambers to be lowered, reducing the formation of nitrogen oxides, which are the target of this emissions regulation.
The downside, and one that is played up by non-EGR Caterpillar, is that the engine is seeing a steady stream of combustion products that includes acids and soot not a healthy diet, you could suppose.
And therein lies some of the concern about C-EGR technology: What will be the reliability and durability?
In fact, because of the shortening of the development period due to EPA's hurry-up deadline, few EGR engines have been run beyond 200,000 miles. To date, reliability has been good and Cummins can point to the proof of its Holset VGT, which is working nicely, thank you, on more than 50,000 Iveco engines in Europe. Concerns about maintenance intervals and oil condition have been addressed by the new category CI-4 oils.
The Truck
The 127-inch BBC Pete 379 was similar in many ways to the truck we drove about a year ago and liked so well. That truck was also ISX-powered, a 600 Signature in that case. This time we were running a 475, though we are talking pre- and post-'02 and there are differences in the responsiveness of the engines that make the 475 seem bigger than the ratings suggest.
Up front, there's a new cooling system to deal with the heat rejected in the EGR cooling process. The grille opening in the 379 hood is very generous, so there was plenty of airflow already. But to maximize the heat transfer to the air there is a new over/under charge-air cooler/radiator setup. Also, there's more air shifted by the ISX's fan and modified fan shrouding to get the best performance possible. Peterbilt has avoided going to a fan ring, as the engineers say this has the potential for problems in service.
Backing up the ISX was an Eaton-Fuller 18-speed, and drive axles were Dana DSP40, running 3.70 ratios.
The tires were 22.5 Bridgestones, R227 up front and M726 on the drives, giving us an overall engine speed in top gear of 60 mph at a shade under 1,400 rpms. For states that permit it, it also means a comfortable cruise at 1,600 rpm and 70 mph.
A feature we were keen to experience and that was absent from the other Pete was the new Flex Air suspension.
It's not so very new, since it was introduced at the Mid-America show 18 months ago, but this was the first time we were to ride on this unique tandem air-ride. It is quite unlike any other air suspension, in that the forward end of the spring beam is allowed to move on an almost semicircular tapered spring. According to Peterbilt, this provides the optimum ride in a suspension that offers significant weight savings.
On The Road
We wanted to run much the same loop as the previous year, although we had to shorten it, running only as far south as Waco before striking west on Hwy 6 to Abilene. By the time we had made the return to Peterbilt's Denton plant, we had covered 550 miles.
But within the first few miles we had already noticed the strong performance of the 475, pulling hard with minimal rpms.
We have enjoyed a number of drives during the development of the ISX C-EGR engine and have been impressed with the throttle response that comes from the new Holset turbo. With its variable geometry, it can spool up the turbo more quickly than a conventional unit. And the controller for the EGR system also interacts, often anticipating a need to apply fuel so that the turbo is already up and running when you tromp down on the pedal.
On the road, this adds up to a very responsive engine, and one that feels like it is making substantially more horsepower than is advertised. So this 475 felt more like a 550. Also, the turbo makes substantial boost. Bringing the engine up through 1,400 rpms on a climb, we saw the gauge hit 41 psi. And as you come over the top of the grade and back down on the throttle, the VGT will keep the turbo spinning, sometimes even accelerating it. If you are balked on a climb, then traffic opens up, this gives you a significant edge as you get back on the throttle again.
Maybe it doesn't sound like much of a change, but it makes a big difference in driving. The instant you drive your first EGR engine with a VGT, you'll feel it and love it.
One concern expressed in the early stages of EGR development was the amount of fan-on time the new engines would exhibit. One of the issues, of course, is noise. The other is fuel consumption. On this drive, though, with temperatures in the 90s, we experienced only minimal fan time, probably little more than a previous generation engine. And when it did cut it, it was quite unobtrusive, a tribute not only to the fan design, but also to the exceptional sealing of the 379's cab.
Running down 35W from Denton towards Ft. Worth, there are the usual abrupt steps up onto bridge decks and plunges off them. Added was a lot of road construction where new asphalt started and stopped. The first time we encountered a bridge, the front suspension announced it and we braced for the jolt from the tandem. But nothing happened. I caught myself looking in the mirror to see what had happened. Nothing. The Flex Air had done what it was supposed to and soaked up the step.
It was the same running through the road works: on and off the asphalt and through the rough where the road had been stripped off. The good news is that this enhanced ride doesn't seem to have compromised the overall handling. There's a little turn-in on initial steering but no more so than with an Air Leaf suspension. If there's any downside, the front suspension becomes more noticeable. That's odd. On the previous test of the 379, I had noted that the front suspension was very supple and rode extremely well, especially for an axle-forward setting.
When we ran across a Cat scale, we found that the front axle was loaded to 10,700 pounds and the tandem was about 900 pounds over. The fifth wheel was all the way forward, so there was no way to load up the steer axle any more. A full load of fuel might have improved the weight distribution and added load to the front end, but it likely would still be short of the full 12,000 pounds. For maximum loading, the 379 might need a spread-tandem trailer.
Interestingly, one of the concerns about EGR has been the additional weight of the engines. And it's not just the EGR add-ons, but the weight of the cooling system as well. Our experience with the 379 shows that, especially with the relatively light ISX, those fears are unfounded.
Missing from the otherwise full complement of gauges was any kind of driver display, so we were not able to quickly assess fuel mileages. Cummins -- along with all engine producers -- is predicting a slight fuel penalty from EGR. Currently, the range is in the 2% to 5% region, with some of the testing showing it is toward the higher percentage. However, one of the consequences of the rush to meet the accelerated deadline is that there has been less time to refine the economy. Despite this, Cummins maintains that for anyone switching from an N14 to an ISX, there will likely be an equal fuel usage or even an improvement in mileage.
As for durability and reliability, time will tell. To date Cummins EGR engines have had more testing than any other product the company has launched previously. And Cummins has announced its confidence in the engines with an uptime warranty.
That, and some generous rebates and offers from Peterbilt, might mean stepping up to EGR isn't such a bad idea. Especially in a Pete 379.
Sidebar
Pete's Flex Air Suspension
