Shape-shifting trailer for fuel-saving future

Renault Trucks used its recent Alternative Fuels day to launch its diesel-powered Optifuel Lab 3 heavy-duty artic prototype, promising a 13 per cent fuel saving over existing designs thanks to a broad range of technical improvements which cover virtually everything from the exhaust system to the tyres.

It is part of the Falcon (flexible and aerodynamic truck for low consumption) project, which is a French government-funded initiative that brings together established players such as Renault Trucks, Fruehauf trailers, Total lubricants and Michelin tyres, with various academic institutions, innovators and start-up companies.

Visually, there are two main changes to the Renault Range T tractor and Fruehauf curtainside trailer that were the starting point for the project. The tractor has a new sloping front, which takes advantage of the extra length that the EU will allow for aerodynamic shaping from next year, and the trailer has a curved roofline, which is reminiscent of the Don-Bur Teardop.

But the key difference between the Optifuel Lab 3 trailer and other aerodynamic designs is that the profile of the trailer roof is adjustable via 10 electrical actuators: five on each side of the trailer. If a maximum cube load is carried, then the height of the rear of the trailer can be increased until the standard 4.2m high rectangle shape is achieved. If a denser, lower load is carried, and the full height not required throughout the trailer length, then the rear of the trailer can be lowered to create a more aerodynamic shape. This is an automated process governed by sensors and a built-in command and control system.

The rear of the tractor’s cab is blended into the trailer nose by fairings, and additional fairings designed by Styl’ Monde cover the trailer wheels.

At the front end, the cab has a redesigned A-pillar, chisel-shaped nose and extended doors and wheel-arches.

Traditional external mirrors have been ditched in favour of cameras, for reasons of both safety and aerodynamic efficiency. Unlike the latest Mirrorcam-equipped Mercedes-Actros, the main rear-view cameras are mounted at below door window level. According to project manager Georges de Turnay, this makes it easier for drivers to judge their width, so reducing the chance of damage, and makes them easier to keep clean. Also unlike the Actros, all mirrors, even the close-proximity ones, have been replaced with cameras.

All of these changes reduce wind resistance, and further fuel-savings will come from prototype low rolling resistance tyres being developed by Michelin, which were not fitted to the truck at the launch. Renault points out that tyre rolling resistance can account for 25 per cent of total fuel consumption.

Driveline efficiencies will save fuel at all speeds. Renault is working with Total to test a range of low-viscosity lubricants in the otherwise standard powertrain. Engine oils of 5W-30 and 0W-20 viscosities are being trialled to explore both the potential fuel savings from reduced pumping and churning losses, and also any impact that they may have on the durability of wearing parts such as bearings and piston rings.

The power of IT is being utilised to enable the truck to adapt to changing road conditions. Navigation and traffic information, weather data and even information gathered from the tyres will be used to control vehicle road speed, and the engine cooling system. For instance, the truck will reduce its speed if the road ahead is obstructed by slow-moving or stationary traffic even before the driver sees it, thanks to a so-called electronic horizon which harvests real-time traffic data.

Coolant circulation can be slowed if demands on the engine are low. The driver is kept informed by a comprehensive human-machine interface.

A similar approach is taken in ‘intelligent charging’ of the batteries with controlled alternator output to reduce parasitic loss. There are two separate battery systems: one for starting the vehicle, and the other for maintaining electrical functions, particularly for cab systems. Renault claims that this combination will save weight while ensuring reliable starting and extending battery lifetime.

Future developments include the introduction of an energy-recovery device into the exhaust system. While Volvo Trucks (like Renault, part of the Volvo Group) has returned to a mechanical turbo-compound system for this role, Renault Trucks is exploring heat recovery using the Rankine system. This uses exhaust heat to vaporise a non-flammable liquid, with the resultant hot vapour driving a turbine before being cooled and returned. The turbine could be used to ether return mechanical energy to the driveline, or generate electricity.

Georges de Turnay emphasised that that the Rankine technology was still at the experimental stage and was only being bench-tested, although road testing of the Optifuel Lab 3 artic combination had already commenced