Prime Mover Magazine

Fuel for thought

Fuel for thought

Aerodynamic trucks are not new and manufacturers and operators have been smoothing out the sides of trucks since the 1930s. For a long time Volvo Trucks has been involved in the development of improved aerodynamics in Europe and now the Australian division is making some serious engineering and aerodynamic efforts to explore fuel savings.

The Volvo Fuel Super Truck is a mostly Australian project, headed up by Alistair Burnett, who has been a senior design engineer at Volvo’s Wacol facility for the past 15 years and Matt Wood, who has a background as both a driver and journalist.

Matt came on board with Volvo earlier this year in the newly created role of Fuel Efficiency Manager.

The annual Volvo Drivers’ Fuel Challenge, for which Matt has some involvement, is a focus for efficient driving and is another reason for Volvo’s appropriate involvement in such a project.

Rather than pursue the radical engineering of some of the concept vehicles in Europe and North America that may employ secretive hybrid drivelines and high technology energy convertors, the Australians have wanted to work with a ‘real world’ project in which it was possible to utilise technology and components that are readily available now.

Other than finessing the driveline, the project has mainly been about reducing drag both through the air and along the road surface.

The strongest aerodynamic evidence is the use of side skirts that give the combination the appearance of a hovercraft and the overall visual impact has polarised opinions with comments in online ranging from ‘slippery and sexy’ to ‘that’s so ugly’.

Regardless of the opinions concerning the aesthetics, the proof already is that the efforts have been successful to the tune of up to 20 per cent improvement in fuel efficiency.

The Fuel Super Truck uses a basic trailer set and the undercarriage has not received any modifications such as relocating brake boosters and fitting round instead of square axles and cross members that could further reduce turbulence.

To this point in time the project has concentrated on reducing drag and hasn’t ventured into affecting downforce or even lift.

Trailer manufacturer MaxiTRANS is closely involved in the development of the aerodynamics for the trailers with the most obvious addition being the fairing skirts that serve to significantly reduce turbulence.

Access to the tyres is straightforward. The hinged panels have been raised and are supported by gas struts.

Michelin co-operated with the tyre selection and super singles are utilised to both reduce weight and significantly reduce drag.

After experimenting with several alternatives the steer tyres are currently Michelin XFE 385/65R22.5 sourced from Europe with the drive wheels using Michelin X ONE LINE ENERGY 445/50R22.5, sourced from the USA.

Trailer brakes and hub bearings are cooled by more exposure to airflow due to the use of offset wheels and the onboard tyre management system that constantly monitors pressure and temperature. It also delivers an alert if the parameters indicate that a tyre is about to blow out.

Volvo’s own initial results from local testing are encouraging. Using another FH16 prime mover with a ‘standard’ B-double set as the base line the Volvo Fuel Super Truck achieved an impressive 20 per cent improvement in fuel consumption over the conventional rig.

The loads were the same and both trucks operated on the same route travelling approximately five minutes apart so that weather, road and traffic conditions were much the same.

The time gap between the two trucks meant that there could be no slip streaming advantage for either.

Fuel consumption was measured by weighing the fuel, which is more accurate than using flow meters and also negated any volume changes due to temperature.

The I-Shift automated manual transmission features a crawler gear which permits the use of a much taller final drive than normal and the 3.09:1 differential ratio in conjunction with the diameter of the drive tyres translates to 1,260rpm at 100 km/h in top overdrive gear and that just happens to be right in the middle of the engine’s ‘sweet spot’.

The addition of the crawler gear is great for B-double slow speed maneuvering and greatly reduces the stress on the driveline particularly the clutch.

The addition of the crawler gear also results in multiple low ratio reverse gears becoming available that further enhance the prime mover’s flexibility.
The manual over-ride that allows the driver to select and hold gears is disengaged in the interest of maximising fuel efficiency and a press of the ‘D’ button is all that is required as far as forward gear selection is concerned.

A button on the end of the engine brake wand does activate down-shifting when deaccelerating so that in the interests of safety the effect of the engine retardation is increased.

The engine used is a 16-litre that in normal circumstances would be rated at either 600 or 700 horsepower but for the Volvo Fuel Super Truck it has been de-rated to 540hp.

Despite that same rating being available from the 13-litre Volvo engine there are sound engineering principles behind using the larger capacity engine in the Fuel Super Truck project.

At 2,650 Nm of torque it produces only marginally more than the smaller engine yet retains similar torque characteristics to the higher rated versions of the 16-litre with the maximum output available from 1,000rpm to 1,500 rpm.

To offset the extra weight of the skirts and fairings the prime mover is fitted with a smaller muffler than standard and also smaller fuel tanks with a total capacity of 1,005 litres.

Overall, the combination is around 400kgs lighter than a similar regular truck and trailers. Removing the front bumper also saved some weight although the front under run protection system is still in place behind the lower front panel.

The prime mover sits 50mm lower than its standard equivalent.
Significant aerodynamic improvements have been achieved from smoothing and filling gaps to reduce turbulence around the front door areas.

This includes the steps as well as enlargements made to the front fenders to close the gap between the body and wheels.

The gap between each of the two trailers has been closed up as far as practicable and the distance between the rear of the cab and the front of the lead trailer has also been reduced in addition to having extended cab fairings.

A practical consideration is that the cab still has to be able to tilt for service access.

The relocation of the air and electrical connectors from the centre to the driver’s side improves the access and has a secondary safety bonus because the driver doesn’t have to climb up into the area behind the cab to access the connections.

On this test trip from Brisbane to Sydney the Fuel Super Truck is tracked on Volvo’s Dynafleet telematics system and the results of the 905km trip show an average fuel burn of 2.2 kilometres per litre and a driver’s fuel efficiency score of 95 per cent thanks to some coaching input from Matt Wood himself.
Grossing 62.5 tonnes, the truck is only slightly different to drive from a standard FH.

The combination of the low rolling resistance tyres and the slippery body panels mean the combination cuts through the air and has reduced friction between truck and pavement and it is definitely noticeable.

The I-Shift’s transmission’s EcoRoll coasting feature can lead to situations where the truck can tend to build speed very quickly on steeper downhill sections to a greater extent than just running off the bottom of a hill in a regular truck.

The driver needs to be aware of this although the situation is easily countered by the integrated braking that brings on the engine brake when the brake pedal is depressed to quickly ensure that we are doing the legal speed.

When following in convoy with other trucks on the highway it’s interesting to observe the wattle bushes at the roadside swaying in the turbulence created. Looking in our mirrors there is a discernible reduction in the wash from this trailer set and prime mover.

The Volvo Fuel Super Truck project is still in its infancy and most of the gains to date are from the trailer modifications but the tweaks to the prime mover have contributed as well.

Future innovations may not produce the same big steps in efficiency as found with this initial package but areas offering further worthwhile improvements have already been identified and will continue to be tested in practical rather than theoretical manners.

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