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20th May 1993, Page 44
20th May 1993
Page 44
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Page 44, 20th May 1993 — SMOOTH INC
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Which of the following most accurately describes the problem?

Following the success of a DoE-backed project to produce a streamlined 17tonner, aerodynamics experts have now applied similar technology for the benefit of artic operators. The effect on fuel bills can be dramatic.

F, 4 ngine development has improved vehicle efficiency steadily over recent

years. But as pressure builds to clean up emissions still further, the engine manufacturers will have their work cut out to simply maintain pre-Euro-1 fuel consumption levels. Any reduction in fuel consumption is likely to come from one of three areas that help to resist momentum: in the transmission, at the wheels or through the air.

Wind resistance has the greatest potential of the three and we have already reported on the improved aerodynamics achieved on a 17tonne rigid operated by Exel Logistics ((.M 12 April 1990). That project, carried out under a contract to the Energy Technology Support Unit (ETSU), showed that a 50% reduction in drag could result in a 20% saving in fuel. Now that research has been extended to cover articulated vehicles.

Following a similar procedure to the 17tonner project, under the direction of Val Dare Bryan, Ricardo Consulting Engineers first set out to establish the drag coefficient of the unmodified vehicles using 40% scale models in wind-tunnel tests. TNT Express agreed to be the host company, so the models were based on its MAN 17.322 4x2 tractive units and Cartwright GRP box-bodied, tandem-axle semi -trailers.

The tractive units come with underbumper air dams as standard, and TNT fleet engineer Alan Parker had already introduced a degree of aerodynamic styling to the trailer design, so the original target of a 50% fuel saving was unrealistic — but the actual gain of 42 (1.0 was far from disappointing.

Adding and retrimming components reduced the wind-averaged drag coefficient of the control vehicle from 0.824 to 0.474.

By far the greatest improvement came from adding aerodynamic equipment to the tractive unit. A three-dimensional roof f-airing guides air up from the cab to blend in smoothly with the roof line of the box trailer. Vertical panels at the rear of the cab increase the effectiveness of the roof spoiler but experiments with side skirts showed little advantage.

Things were different on the trailer, where side skirts, with a large leading radius in front of the landing legs, closed the gap beneath the body. A modification to the front corners of the box encourages the air flow to cling to the trailer sides and roof, while rounded corners along the length of the roof line help to prevent separation in cross winds. A sloping roof section and angled, tapering quarter panels behind the trailer wheels reduce the Vow-pressure area at the rear of the vehicle.

Establishing benefits in a wind tunnel is one thing repeating those results in everyday operation is quite another.

For 10 months TNT ran two modified artics alongside two standard control vehicles in its normal operational programme. They ran over two mutes from its base at Atherstone: one route consists largely of motorway-class roads; the other has a much larger dual-carriageway content.

Next-day delivery means that TNT vehicles run mainly through the night so traffic was not a problem, but to contain the variables the drivers were given maximum engine and road speeds for each gear: overall speed was restricted by Lucas Kienzle speed limiters. While TNT's articulated vehicles are plated at 32.5 tonnes, a typical gross running weight is closer to 24 tonnes. The aerodynamic kit adds about 190kg to the unladen weight, of which about 70kg is on the tractive unit, but height, width and length remain unchanged, s(_, load space and ease of maintenana are not compromised.

Throughout -.he test day-to-day variations in fuel consumption were small compared with the differences between the standard and modified types of vehicle. On the road the modified combination gave an average fuel savings of 1625% on largely nonmotorway routes, and 15.1% over largely motorway routes.

Not surprisingly, steady-state testing on the track gave even more impressive results.

Track tests at between 80 and 96km/h (50 and 60mph) show that the weight of the payload has a bigger effect on the fuel consumption for the streamlined vehicle than for the unmodified vehicle. At 32 tonnes it is calculated that consumption will increase by 24% and 21" o respectively over that of an unloaded vehicle.

But speed is the real fuel guzzler. Running at 10km/h over the legal limit with the full kit uses the same amount of fuel as running without the streamlining at 961m/h.

At the time of the trials in 1991, it cost

£1,000 to equip the tractive unit in 85% of the savings: spending the s amount to equip a trailer contribut 15% of the fuel saving. As it is usu two trailers with each tractor the t. was 0,000 per rig.

For TNT vehicles covering aim 200,1000km a year this amount can back in less than 10 months — ant tractive unit is modified payback down to less than four months. Fol standard UK fleet artic averaging 85,000km a year, the predicted pay period is increased to two years fo or 11 months for the tractive unit up to four years if only the two tra modified and used with a standar(

Since completing the trials, TN modified its entire Atherstone flee E Copies of the report Fuel SavinA Articulated Vehicles Through Aeri Styling can be obtained from the E Efficiency Enquiry Bureau, Energ Technology Support Unit, Buildin Harwell, Oxon.

D by Bill Brock


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