Building Trailers To Save Fuel

Many operators talk about building trailers to save fuel, but not so many put their money where their mouth is and really drive fuel savings from the top to the bottom in a fleet, Diesel News talked to one such fleet in the UK which is trying gas power and designing its own trailers.


Waitrose is an upmarket supermarket, concentrating on quality of produce and not driven solely by price. The company talks about its customers being the middle class upper market consumers. There are 3,367 vehicles in the fleet, this includes around 1,000 trailers, over 500 prime movers, 80 heavy rigid trucks, 237 light rigid trucks, plus nearly 1,000 vans.


Building Trailers To Save Fuel

Simon Gray


“We’ve always spent extra on our trailers,” said Simon Gray, Waitrose Vehicle Engineering Manager. “We’ve used large radius capping on the sides and other things. When we did some testing a long time ago, Kuhne and Nagel, who handle 50 per cent of our deliveries, used off the shelf trailers. We found our trailers were already four per cent more fuel efficient in testing at the Millbrook Group, who provide vehicle test, validation and engineering services to customers in the transport industry.”


Some government funding became available for 13 projects, three of which were successful. One combination achieved a seven per cent improvement with a three per cent saving on the prime mover by lowering the ride height. However, this made it problematic when delivering to a number of retail sites, and has been dropped.


Building Trailers To Save Fuel


The side skirts remain as does the trailer design. The rear end has a slight taper to reduce air vortices at the rear door, mimicking the boat tail favoured by some operators. Underneath the trailer the components have been arranged along the same line to improve airflow. There is also a gap above the rear underrun bar to improve airflow.


Building Trailers To Save Fuel


The initial design led to a model running in a wind tunnel and this was followed by a larger scale model running through a water tank at high speed. In this test millions of silver particles float in the liquid and by shining a laser though the tank as the trailer passes through it, a picture of the air flow can be achieved. The trailer height is 3.8 metres, as low as is practical, but this still involved customisation of the fridge units. This developed a four per cent decrease in the drag coefficient for the semi.


Further fuel usage improvement are expected to come from a new strategy in fridge unit use. In fact, 20 per cent of Waitrose’s diesel usage is in fridges. There is a trial running, in which the fridge units are powered directly from the truck. An alternator is driven off the gearbox PTO in some while others use an engine mounted alternator coupled to an inverter to power the refrigeration unit. The fridge will be powered by the truck when coupled and from shore power when parked in the yard.


“If everything is done as it should be, which it normally is,” said Gray. “It will be put on a bay, plugged in and brought down to temperature. Then it will be loaded, before the truck couples up. Then the alternator drive will connect up.


“If the fridge is loaded at the right temperature, it’s only 20 per cent of the time when the engine is actually powering the fridge. All it is doing is maintaining the temperature, not pulling it down.”


The use of quiet and clean CNG engines with quiet clean fridges is a bargaining chip being used by Waitrose to try and get access to certain urban areas at night, which are currently off limits. Some Waitrose outlets are in residential areas where loading at night or early in the morning is prohibited.


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Author: Tim Giles

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