DRIVE AGAINST DRAG
Much of the advanced world is seeking savings by reducing trailer drag and an opportunity to do more exists here. Rob McKay writes
Much of the advanced world is seeking savings by reducing trailer drag; the opportunity to do more exists here
AUSTRALIA IS ONE OF THE WORLD’S great trucking success stories, with trailer innovations, particularly as related to Performance-Based Standards, one area the country is recognised as a global leader. Road trains are also seen as a heavy-duty productivity marvel that would be picked up elsewhere if nations that would gain from them could get past their own red tape and vested interest. Much of this progress has arrived through creativity driven by need and bright minds, and much more could still be done if our own inertia and bureaucracy could be shifted out of the way.
Indeed, and perhaps unsurprisingly, Australia is home to an international trailer aerodynamics equipment manufacturer and innovator in Aerotrans Australia, based in Rowville, Victoria.
Mostly the industry players have been keen to take on ideas that allow them to steal a march on competitors and make them attractive to existing and potential customers, often braving the sometimes bizarre and surreal world of vehicle and road compliance for years before being able to hit the road with new concepts. So it is something of a conundrum for some industry observers that trailer aerodynamics struggles as a popular avenue to running efficiency and cost savings.
It’s not as if extensive research on the subject over decades has not been undertaken for trailers and even the most casual observer of the truck manufacturer’s art will struggle hard to avoid descriptions of tapering and wind-resistance reduction strategies even for something as blunt as a cab-over.
Nor is the northern hemisphere without significant interest and investment among fleet owners in trailers designed to be as dragless as possible. The AirFlow Starship shows the latest US thinking on the concept.
Two years ago, Owner//Driver reported on British supermarket chain Waitrose, a fleet-owner in its own right, and its work on efficiency performance of its trailing equipment. This had got to the point that it could justify the cost of fitting less cargo into lower-roofed trailers with drag-lowering design aspects, given on savings enjoyed in the rest of the driving and distribution task.
Research by the US Environmental Protection Agency (EPA)-
backed SmartWay partnership, with its list of verified body technology, includes results for skirts, tails, gap reducers, under trailer design and splash guards.
This is not to say nothing has been done. Aerotrans Australia has seen progress its business through an ongoing focus on innovative aerodynamic solutions. Through its brandline business, AerozProducts, it offers Fuelscoop and NoseCone to all sectors of the market.
It has found that many fleets, which in the past specified NoseCone, have developed to now use roofmounted Fuelscoop, and Full Aerodynamic Kits.
Further to standard roof mounted Fuelscoop, the Aeroz-Products range now includes new roof mounted products for rigid refrigerated trucks. Recent trials by PFD confirmed a 12.2 per cent fuel saving from Fridgescoop 4 Small Trucks, and they now have added this to their standard truck specification.
Fuel-Skirts have been available within the AerozProducts range since development for a successful trial with Toll and Woolworths, where Fuel-Skirts were combined with our longer cab extender kit for Mercedes Benz Actros. Recorded results of this trial were 7.8 per cent fuel savings in addition to the performance gained from the standard Mercedes Benz OEM aerodynamics that was replaced with the Fuelscoop Full Aero Kit.
“The market seems to have developed over our 29-year history from nothing with NoseCone as an option, to NoseCone being the base requirement, with those more aware of aerodynamics moving to Fuelscoop,” Aerotrans Australia MD Nigel Fletcher tells Owner//Driver. “Beyond this, increased awareness leads operators to fit Full Aerodynamic Kits, including cab extenders.
“Aerotrans Australia continues to develop its standard products and is working on a range of new initiatives to offer local and overseas fleets with additional ways to reduce fuel consumption.
“In Australia, the ‘slippery’ nature challenge for the trailer starts at the cab due to the size of gap between truck and trailer [in cab-over applications]. Trials of a combination of products have confirmed filling the gap goes ‘hand in hand’ with developing the trailer aerodynamics.
“We have conceptual proposals based on our 29 years of IP that will provide huge savings by means of more ‘slippery’ trailer. To become a reality, it will require forward thinking within the industry and small changes in trailer design.’’
But despite having what appears a compelling story to tell the local industry, the company is facing a certain inertia, notwithstanding having just completed its best year financially. But Fletcher is not deterred.
“We believe in the product category and continue to develop the product and are currently developing openings in export markets,” he tells Owner//Driver.
“A couple of trailer manufacturers are working on preparing trailers to more easily offer the Fuel-Skirts option for clients. Further to this, Aerotrans Australia has much broader trailer initiatives with potential savings well beyond Fuel-Skirts alone.”
Australian interest in trailer aerodynamics has been around for decades but mostly in academic circles, and much research has centred on Melbourne institutions. It is possible to go back to 1986 to find Royal Melbourne Institute of Technology (RMIT) researchers taking to wind tunnels to prove points and discuss the merits of the approach as related to on-road testing.
So, 30 years ago, RMIT researchers concluded that wind tunnel testing often significantly over-predicts the drag reduction of add-on aerodynamic devices on trucks and that over prediction is a function of the type of device and the yaw angles involved.
Lack of turbulence simulation was suggested to be a significant factor in the discrepancies between wind tunnel and on-road results and the former should be a first-estimate design tool only, with final conclusions to be in real-world testing. That said, they also concluded that basic tipper truck configurations are aerodynamically very inefficient with a wind average drag coefficient of about 1.6, with significant savings possible with add-on devices.
For a representative truck speed of 80km/h and a total mass of 26 tonnes the following fuel saving reductions to within 2 per cent accuracy were predicted:
• Tarp over trailer 7.6 per cent
• Tarp with trailer faring 9.7 per cent
• Light porous rap with trailer faring 4.9 per cent
• Trailer fairing with tailgate fairing 4.8 per cent.
A few decades later, technology advances meant changed perceptions. RMIT researchers found that even simple modifications such as a fairing on the front of the truck are capable of reducing drag by as much as 20 per cent at a zero-degree yaw angle. Additionally under small cross winds, as little as five-degree yaw angle, with the addition of a full skirting along the truck, aerodynamic drag can be reduced by over 35 per cent.
“These findings indicate that there is high potential for aerodynamic drag reductions in existing heavy commercial vehicles,” they said in a 2012 report,
A Computational Simulation of Aerodynamic Drag Reductions for Heavy Commercial Vehicles.
“These drag reductions could be capable of leading to sizable reductions in fuel costs and CO2 emissions.
“With trucks being the result of around 20 per cent of global warming emissions, a reduction of even 20 per cent in aerodynamic drag is sizable. There is clear potential for drag reductions in heavy commercial vehicles.”
Like alternative fuels, it seems few things focus industry’s attention on innovation more than a rise in fuel prices. It should come as no surprise that the latest bout of advice from industry experts and organisations should coincide with the price spike in the first half of this decade.
The Victorian Transport Association (VTA), in its fuel efficiency advisory document of the time, made the case for aerodynamics.
‘’At highway speeds, over half the energy used by your truck is required to overcome aerodynamic drag,” its Transport Safety Pack Fuel Efficiency Guide says. “You can reduce your fuel bill by reducing aerodynamic drag and minimising mechanical and rolling resistance. Choose to have a roof fairing with van trailers, chassis fairings, cab extenders and aerodynamic mirrors.
“Fitting aerodynamic cab deflectors can improve fuel efficiency by at least six per cent and in some cases more than 20 per cent (depending on the body fitted and the load carried).
“Close coupling – minimising the gap between the rear of the prime mover and trailer/body – also dramatically reduces drag. A reduction of aerodynamic drag of 25 per cent will reduce highway fuel consumption by 10-15 per cent.”
In the vortex
Around the same time, the New South Wales Green Truck initiative took time amongst other technologies to test vortex generation in semi-trailers. Aerodynamic drag is created as air resists the movement of a vehicle. The vehicle engine must work harder to overcome this resistance and therefore consumes more fuel.
At high speeds, up to half of the truck’s fuel burn can be for overcoming aerodynamic drag. “Aerodynamic devices redirect air flow more efficiently, reducing drag and improving fuel efficiency,” its case study states of the technology that does have its critics.
This trial involved a vortex generator device. The device was fitted to the trailing edges of both the prime mover and trailer, to reduce drag in areas where it is most significant: usually at the truck-trailer gap and at the rear of the vehicle.
These devices work by breaking up the air flow into counter rotating vortices, thereby dispersing the energy more evenly. They are easily attached – essentially glued to the vehicle in a strip along the trailing vertical and horizontal edges of the truck cab and trailer. The literature also suggests that various kinds of aerodynamic devices can achieve fuel savings of two to three per cent individually and up to 15-20 per cent in combination
The findings of this trial suggest that vortex generators can provide a measurable improvement in fuel efficiency and greenhouse gas (GHG) benefit in a curtain-sided semi-trailer linehaul application. The truck in this trial showed a 2.7-4.1 per cent improvement after the devices were fitted.
Though the improvement may seem small, it is a statistically significant improvement and highly unlikely to be a random result.
Similarly, the variation in improvement using different analysis techniques simply shows different analytical viewpoints, none of which are necessarily more right than others. Further, the analytical techniques were applied to two different sets of data logging systems, and both data sets returned relatively consistent figures of improvement.
In financial terms, this would represent a $1.40 per 100 kilometres saving (or 1.4 cents per kilometre) on the truck used in this trial (using net diesel costs at the time of the trial of $1.20 per litre). Over an annual mileage of 150,000 kilometres in a regional line haul application, this could translate to a fuel saving of over $2,100 per annum.
Taking into account the purchase and installation cost at the time of the trial, this would result in a payback period of around one year (less with a higher diesel price). In addition, the device is low maintenance and relatively easy to install.
Previous studies on vortex generators, along with preliminary analysis of unpublished studies, suggest that the benefit may be sensitive to the configuration of the truck and trailer. In other words, different types of trailers may not achieve the same saving. Despite such findings, progress seems glacially slow in Australia, despite the magnitude of the task.
To some, the seemingly inescapable equation of greater distance travelled leading to greater savings still awaits general industry acceptance.
“There is high potential for aerodynamic drag reductions in existing heavy commercial vehicles.”
Below: The AirFlow Starship has a slippery trailer profile
Above: One of Waitrose’s specifically designed trailersOpposite top: The current generation of Aerotrans skirts as incorporated on a Krueger TrailerOpposite middle: Aerotrans skirts fitted to a MaxiTrans Freighter trailerOpposite below: Skirts on a Cheetah trailer in the UK