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Designing trucks for 'platooning'
'Platooning' can improve fuel economy by at least 10% on large commercial vehicles. Exa Corporation explains the challenges and benefits of pursuing such an idea
Kevin Golsch, technical director at Exa Corporation
If Tesla wants its planned electric truck to come with enough range acceptable to haulage fleets, it might need to accelerate research into platooning. Platooning is when smart trucks connect digitally to travel in close convoy, in order to improve overall fuel economy.
The benefits of drafting in this manner have already been proven. In April this year a fleet of trucks, from all of the major European manufacturers linked via Wi-Fi, took part in a Dutch-organized transcontinental drive. They cut following distances from around 160ft to 50ft and saved around 10% on fuel. Exa has partnered with OEMs as well to investigate the platooning effect through simulation. Two papers, presented at SAE International conferences, (2014-01-2436 with Peterbilt and 2015-01-2896 with Volvo) have shown how multi-vehicle platooning impacts aerodynamics and leads to fuel economy improvement.
The saving comes from the decrease in drag on the trailing trucks, which are traveling in the wake of the lead vehicle. This effect is furthered by the trailing trucks ‘pushing’ the leading vehicle by increasing the base pressure on the rear of the trailer at close enough distances. But to get trucks following really closely, the design of the trucks themselves needs to be modified.
The simulations have shown that roughly 30ft is the optimum distance to maintain between platooning trucks, without triggering the engine cooling fans of any of the following vehicles. Any closer and additional cooling to replace the air that’s being blocked by the truck in front is required, which in turn negates some of the fuel saving.
You can get around this by focusing on active cooling. The best solution would be to design cooling ducts that open fully when in the middle of the platoon to keep the engine cool, but close again if driving solo or leading the platoon. Electric trucks, such as the one Tesla is planning, won’t need quite as much cooling so it could close the gap even further to the truck in front.
Such will be the benefit of being the truck in the middle of the platoon that we think it’ll trigger a whole new economy around booking the best slot. Our simulations show that the middle tractor-trailer gets the most benefit in terms of economy from platooning, so we’d expect that would be the most expensive position.
An alternative option could be to take turns at the front of the platoon by sequentially swapping positions, just like cyclists do in long-distance races. However that would be logistically more difficult to organize and require more fuel and road space for maneuvering.
The overall cost benefits of platooning to fleet users are obvious. Trucks designed to run in the middle of platoons won’t need the same horsepower to operate at highway speeds, and those fleets running more conventional trucks designed to lead would be paid by those further back in the convoy.
Thanks to aerodynamic advances and smart connectivity, road haulage costs could drop significantly as these trucks get smarter and forward-thinking fleet users feed the marketplace.