Friday, 22 November 2013

Scania breaks new ground in ISB6.7 purchase

For the first time in its long history, Swedish truck and bus maker Scania has had to resort to using another manufacturer’s diesel engines in its vehicles.

Scania’s top brass have elected to equip the company’s Citywide single deck bus with the Euro 6 version of Cummins 6.7-litre six-cylinder ISB6.7 diesel engine.

This has not been an easy decision to make and could be a sign of the times. Could this be the precursor for further use of the US company’s engines in Scania’s product line-up? And why didn't Scania use an engine from MAN, for example? MAN has a 6.9-litre I6 diesel engine which is used in mid-range trucks. The MAN engine could be heavier and maybe more costly than the Cummins ISB6.7 - the latter aspect of cost may depend on whether the comparison is made between MAN engines made in Germany and Cummins units engines made in Darlington, or Cummins engines made in Darlington and the US

One answer certainly could lie in the matter of weight. The kerb weight of the Citywide bus could be cut by as much as 500kg simply by replacing Scania’s DCO9 engine with the Cummins ISB6.7 when the new arrangement begin next year. That is probably the equivalent of seven additional fare-paying passengers.

Now if that is possible with a city bus, then surely it is possible also to increase the payload capacity of a truck by 500kg, possibly making way for a new generation of lighter-weight Scania trucks which might presumably compete with those built by MAN.

Last month, at the Busworld show in Kortrijk, Belgium, it was announced that Cummins would be supplying Scania with the ISB6.7 engines.

Scania and Cummins are no strangers to one another. The two companies have a long-established and successful joint venture that stretches back some 15 years and led to the development and subsequently manufacture of high pressure fuel injection systems in the shape of the XPI common rail system currently used in Scania’s truck and bus engines.

At present, the Citywide is offered with diesel/biodiesel five-cylinder DCO9 engines with a maximum power rating of 230bhp, 280bhp or even 320bhp. Alternatively, power ratings of 270bhp or 305bhp are possible from the Scania nine-litre engine running on bioethanol or compressed natural gas (CNG).

The Euro 6 version of the ISB6.7 engine has a maximum power output of 225bhp to 310bhp for trucks or 220bhp to 280bhp for buses.  

Unlike Scania, which adopts SCR (selective catalytic reduction)-only versions of its Euro 6 9.3-litre (DC09) and 12.7-litre (DC13) engines, the ISB6.7 uses a combination of exhaust gas recirculation and SCR to meet the tough Euro 6 limits on emissions of oxides of nitrogen. The exhaust after-treatment system used on all Euro 6 B-Series engines has been developed in-house at Darlington by Cummins Emissions Solutions.

In passing it should be noted that two Scania engines – the DC13 and DC16 – in some versions, have adopted compacted graphite iron (CGI) cylinder blocks, a technology that Cummins Inc. in the US is just beginning to adopt for the new ISB5.0 vee engines that will be built at its Columbus Engine Plant.

The Cummins ISB6.7 (in Scania form known as the DC07 to fit in conveniently with the Swedish company’s terminology) also has the latest sliding-vane variable geometry turbocharger from Huddersfield-based Cummins Turbo Technologies (formerly Holset) and a closed crankcase ventilation system.

Some observers have noted that the new DC07 would make an ideal alternative to the DC09 unit – and not just in buses.

It remains to be seen just how far this replacement programme goes. Certainly it has to be assumed that the DC07 engines purchased from Cummins are probably cheaper to buy than Scania’s in-house made DC09, and lighter too.

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