ALTERNATIVE FUEL DIMETHYL ETHER DME engines are to a truck
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near you Going for the burn A clean-burning fuel that has long been used in countries such as China and Egypt, DME could soon be available in Europe wares: wiver Dixon VOLVO is to commercialise production of dimethyl ether (DME)-powered trucks and will offer a DME variant of its D13 engine in 2015— initially in 425hp guise, with a 500hp option offered at a later date.
DME is a clean-burning fuel that produces no particulate matter and has been in use for decades in markets such as China, Japan, South Korea and Egypt. It has a cetane number between 55 and 60, and is comparable to diesel fuel.
Volvo began trialing DME as an alternative fuel in 1999 and, to date, has logged more than 650,000 test miles. As part of a comprehensive evaluation of a number of alternative fuel types — which included biodiesel, compressed natural gas (CNG) and liquefied natural gas (LNG) —Volvo's research scored DME as having the greatest long-term potential. "I believe that this is the one to bet on," says Goran Nyberg, president of north American sales and marketing at Volvo Trucks.
While DME addresses a number of issues that bedevil the adoption of natural gas by the trucking industry — it doesn't require significant enhancements to vehicles or service bays — it does suffer from the same primary restraint. Despite being used in numerous other industrial and domestic applications, its distribution infrastructure as a vehicle fuel is near non-existent.
Kick-starting acceptance To address this issue and hopefully kick-start wider availability — and thus acceptance — of DME as a road fuel, Volvo has partnered with Oberon Fuels, which has developed a modular, small-scale process to turn methane and carbon dioxide into DME using feedstock such as natural gas, animal waste or food scraps. These units produce 3,000 to 10,000 gallons of DME a day, and Oberon's business model sees such plants as functioning at the centre of a localised hub-and-spoke network, with regional demand being fed from local production.
The first of these plants came on-stream in California's San Joaquin Valley region, and supermarket operator Safeway is to trial two trucks using DME manufactured at Oberon's adjacent Brawley site.
Another issue that has concerned some is vehicle range. DME-equipped day-cabbed trucks have an effective range of at least 600 miles, according to Volvo, while sleeper cabbed models, owing to their extended wheelbase, boast significantly greater distance between fuel stops.
DME uses compression ignition and because there is effectively twice the fuel flow as with a diesel, the injection system had to be reworked. Injection pressures of 300-600 bar are significantly lower than in diesel equivalents. While the trucks will initially be launched with SCR after-treatment, there is, says Volvo, the potential to remove this should the fuel prove capable of being engineered down to the 0.2g/hp-hr NOx standard.
Because DME can be stored indefinitely at ambient temperatures and fills at low pressure, many of the handling issues that cause trouble with CNG and LNG are not relevant. Oberon points to the suitability and wide availability of propane storage tanks for its onsite storage, and the company has developed a 21-gallon/minute flow dispenser that sells at about $20,000 (£13,000).
As for the price of the truck, Volvo remains tightlipped, pointing to the fact that commercial production is some way off and a final specification has to be drawn up. That said, Nyberg is talking a tough game already. "We believe that, in terms of total cost of ownership, we will be competitive with a diesel-powered truck," he says. •