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PARTING OF THE WAYS

13th April 2006, Page 63
13th April 2006
Page 63
Page 63, 13th April 2006 — PARTING OF THE WAYS
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Which of the following most accurately describes the problem?

Opinions are sharply divided in the EGR vs SCR debate. Steve

Banner discovers who supports which system — and why.

Advocates of Exhaust Gas Recirculation (EGR) as the most effective route to achieve Euro-4 may be in the minority, but they believe rigid operators would do well to heed their arguments.

Clive Burnet,Scania's UK technical manager, contends that EGR makes a lot more sense than Selective Catalytic Reduction (SCR) for the sort of stop-start urban delivery work rigids are often engaged in. SCR involves injecting a solution of urea and water,commonly referred to asAdBlue, into the exhaust gases.

"The trouble with SCR is that the catalyst fitted has to work at a temperature of at least 25°C to be effective," he says."It won't always achieve that on city centre runs unless the back pressure is increased, and that's not something truck manufacturers usually want to do."

Dave Cussans, sales and marketing director at EGR cheerleader MAN ERF, says: -EG R works 100% of the time,but SCR does not. Let an SCR catalyst go below 25°C, and you're down to Euro-1 levels.

That's not to say SCR systems don't generate heat.They do, says Burnet,but enough space has to be allowed for it to dissipate. "That's what we've found in cases where we've fitted Euro-4 V8 engines to rigid chassis, usually elsewhere in Europe, and it's something that body builders will have to bear in mind."

Scania is using SCR to allow the V8 to reach Euro-4, but is employing EGR on its sixcylinder diesels. We'll have EGR on everything for Euro-5," says Burnet.

However. SCR-supporting Daf UK marketing director Tony Pain rejects the argument that SCR catalysts are ineffective in big city traffic. Pointing out that all SCR systems have been type-approved, he argues that SCR has the big advantage of reduced diesel consumption.

Fuel economy "It will give you 5% and possibly 10% better fuel economy than an equivalent Euro-4 EGR engine," he says. While that may not bring the financial benefits to a 7.5-tonner covering a low annual mileage on urban work that it does to a high-mileage tractor unit, he believes those returns are worth having given the high cost of diesel."The SCR 7.5-tormer will also enjoy longer service intervals," he adds.

In response, Cussans claims the highpressure common-rail fuel injection systems fitted to the diesels that MAN uses in its rigids puts them ahead of the competition so far as fuel consumption is concerned at Euro-3.He believes the efficiency of this platform means the economy gap between MAN engines and the SCR engines fitted by most of its rivals at Euro-4 will be almost non-existent.

SCR imposes a typical weight penalty of around 120kg; not critical at 44 tonnes, but more of an issue on lighter vehicles."Remember. EGR generally adds about 70kg to the vehicle's weight. so with SCR the true weight penalty is around only 50kg," says Brian Smith,Volvo's UK and Ireland truck manager.

"If weight remains a concern then it's always possible to reduce it by, for example, fitting alloy air tanks rather than steel ones," says Bruce Allison,marketing director at Renault Trucks UK. Renault is exclusively wedded to SCR, as is Iveco.

While Volvo is prepared to offer EGR for certain niche applications, the vast majority of its rigids and tractor units will be equipped with SCR,says Smith.

"While SCR obviously relies on an AdBlue tank, there are no real problems when


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