Clearing last hurdles

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Like other engine manufacturers, Detroit Diesel insists its products are ready for 2007 emissions regulations, having performed dynamometer, durability and reliability testing, and having embarked on fleet testing and a customer demonstration program.

Of DDC’s four development stages – A. Concept; B. Prototype; C. Issue identification; and D. Production intent with limited changes – the company is somewhere between C and D, according to Tim Tindall, director of the manufacturer’s Series 60 2007 program. The engines are out gathering real-world miles, he says, and whenever there is an incident, it’s assigned to a specific engineer to resolve. And it’s that mileage that makes him and DDC confident that the switch to ’07 engines will go more smoothly than the ’02 experience.

While DDC performed 2.8 million miles of testing on its ’02 engines, the plan is for 14.8 million test miles to squeeze as many gremlins to the surface as possible before line production begins on its ’07 powerplants.

Working with ultra-low-sulfur fuel and prototype CJ-4 engine oil, DDC faces a few last challenges – for example, finalizing a diesel particulate filter (DPF) regeneration strategy.

As a recap, a DPF, sometimes called a soot or particulate trap, contains a porous substrate made of ceramic cordierite, which traps particulate matter from exhaust gas flowing through it. Since the accumulating particles eventually will impede exhaust flow, causing excess backpressure – which hurts fuel economy and performance – the particulates continually are burned off by exhaust heat in a process called passive regeneration.

When a vehicle’s duty cycle is such that the exhaust gas is not hot enough to burn the particulates, but hot enough to ignite fuel, a small amount of diesel is injected into the DPF to raise the temperature and burn them off. This is called active regeneration, and there has been industry debate as to whether the process should be totally automatic or require driver involvement after notification via a dash light that regeneration is necessary. A manual disabling feature also could be included to prevent regeneration heat from being expelled from the exhaust pipe when not desired, as in a shop environment.

At any rate, I recently experienced an active regeneration event during a ride and drive for trucking media from Freightliner headquarters in Portland, Ore., to a place called Camp 18, some 65 miles west, and back. Maybe “experienced” isn’t the right word, since when Todd Price, Detroit Diesel’s resident electronic applications engineer, initiated the regeneration, I neither felt nor heard anything out of the ordinary.

But I did keep an eye on the screen of Price’s laptop, which was set up to monitor regeneration status, DPF soot level, exhaust temperature and pressure, and other parameters. And since the road included lots of hills, those parameters changed frequently. For example, on level stretches and when pulling a hill, regeneration remained active, and the DPF soot level dropped steadily – which is the whole idea. But when going downhill, exhaust temperature dropped like a rock, and regeneration was interrupted.

According to Price, that’s because the exhaust wasn’t hot enough to fully light off the fuel. And, since passing partially burned fuel through the DPF only would add soot, the electronic control unit halted the process.

Finalizing exhaust-temperature thresholds is one of the tasks remaining for DDC, but the company seems sure that this time around, time and testing will prove more than adequate to ensure a smooth transition in ’07. “The testing program enables DDC and Freightliner to gain valuable test miles, from both a component and systems perspective,” says Tindall, “so they can continue refining the engine well before the start of production.”