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* Particulate traps work by trapping sooty particles in a

14th January 1999
Page 49
Page 49, 14th January 1999 — * Particulate traps work by trapping sooty particles in a
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ceramic honeycomb filter that has a catalytic coating. They are called continuously regenerating taps (CRTs) because once the temperature in the exhaust gets high enough (typically over 250°C) the particles are oxidised, clearing the filter. The catalytic coating can be contaminated by sulphate ash, so most CRTs need to be qsed with ultra-low-sulphur diesel (ULM), slvhich has a sulphur content below 5Oppm, clompared with standard diesel's 500ppm.

Best known of the CRT companies is Eminox which collaborated with catalyst expert Johnson Matthey to develop the Greencat CRT more than three years ago. Since then about 400 have been sold, mainly to bus operators.

Not surprisingly, company secretary Mike Galey expects the VED rebate scheme to tempt more truck operators to retrofit CRTs, despite the £3,500 cost.

A retrofit CRT exhaust that will run on standard diesel has been developed by Wasey and US based catalyst and PM filter manufacturer Engelhard. Wasey recommends using UL5D, but adds that standard diesel will not damage the filter, and it says that while emissions will be slightly higher with standard diesel, they will still be low enough to qualify for an RPC. Thatcham-based Engine Control Systems is a subsidiary of Canadian fuel-additive company Lubrizol. Tests by London Buses showed that its AZ oxidation catalysts gave cleaner emissions than a Euro-2 engine during an urban driving cycle, but ECS still predicts that operators will have to fit one of its DPF regenerative particulate filters to qualify for an RPC. Volvo is one of the first truck makers to offer a CRT as an option: it will fit the Erninox CRT on the new FM7. Volvo environmental manager Ray Cattley warns that operators must be sure of their fuel supply: "It only takes 1 00 litres of standard diesel to contaminate the filter," he explains "At best that cracks the filter unit; at worst, there's engine damage " Despite these reservations, Coley believes CRTs are preferable to gas engines. "You can buy 11 CRTs for two gas-powered trucks," he points out, "and if there's a problem with the exhaust at least it can be changed.'

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Locations: Thatcham

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