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ONE OF the most promising sustainable fuels is appearing first in heavy trucks. Volvo believes it has found a winner in DME, dimethyl ether.
Among DME benefits are simple conversion for diesel powerplants, cost-effective control of engine emissions and a straightforward infrastructure for refueling.
SAE International’s Automotive Engineering International magazine, September 3, 2013, offers details. Also, many thanks to Bill Urban for his informative communications, including drawing my attention to Volvo and DME.
DME is a colorless gas derived from wastewater treatment, animal waste and any other source that contains methane. Ordinary natural gas, the sort delivered in pipelines across the country, is another feedstock.
DME is stored and distributed in a manner similar to other gaseous fuels. However, it doesn’t require the cryogenic storage of liquefied natural gas, LNG, nor the high tank pressures of compressed natural gas, CNG.
As with these other fuels, its energy density is considerably less than diesel’s, thus requiring larger fuel tanks. However, DME tanks are lighter and less expensive than those supplying CNG or LNG. And range is greater; 600 miles is possible with a typical heavy-duty truck.
The supply infrastructure can be based on regional feedstocks. San Diego-based Oberon Fuels has developed on-site refueling stations costing only a tenth that of a typical CNG or LNG installation.
Volvo examined eight options for replacing diesel fuel.
In order of their perceived benefits, least to best, these are ethanol, biodiesel, hydrogen + biogas, CNG, LNG, synthetic diesel, methanol and DME.
Modern truck diesels are increasingly challenged by clean-air regulations, even with their precise ultra-high injection pressures and costly exhaust treatment. By contrast, because of DME’s molecular structure, it burns with no soot, thus eliminating the particulate problem.
This translates into less costly emissions controls, both upstream and downstream, elimination of exhaust gas recirculation and less complex turbocharging.
Volvo truck engines using DME have the same 17.0:1 compression ratio as their diesel counterparts. Power ratings with DME are unchanged.
Volvo has conducted more than 650,000 miles of DME testing, primarily in Europe.
In the U.S., several fleets have been on the road. As an example, the company is partnering with Oberon Fuels and with Safeway Inc., one of the country’s largest food and drug retailers. A pair of Volvo VNL models are fueled by DME produced from biomass.
The project received $500,000 from California’s San Joaquin Valley Air Pollution Control District. The process first converts agriculturally derived methane-rich feedstock to syngas, a mixture of carbon monoxide and hydrogen. Then this syngas is transformed to methanol which in turn is converted to DME.
Based on a diesel gallon equivalent—and even absent subsidies—DME is considered cost-competitive with diesel fuel. What’s more, on a well-to-wheel basis, compared with diesel it’s said that biomass-derived DME can provide up to a 95-percent reduction in CO2.
As an added benefit, there’s the potential for exploiting organic waste. To produce DME at a rate of 4500 gal./day, the president of Oberon Fuels, Rebecca Boudreaux, says, “If you think about it in terms of food waste, that’s about 100 tons of waste.”
That this is sustainable sounds depressing—and yet very promising. ds
© Dennis Simanaitis, SimanaitisSays.com, 2013
Dennis, thanks for the shout-out. Volvo first became interested in DME formulated from “black liquor”, a by-product of the Swedish pulp industry. They see the potential for DME to replace 50% of EU heavy truck diesel by 2030, if a distribution infrastructure is built. Also, they predict five times better utilization of land area than, for instance, biodiesel.
The one problem that I see with most of these alternate fuels is supply infrastructure. It will take quite a while to get supply to all corners of our countries, and understandably with multiple alternate fuel types being explored this gets even more complex.
Taking just conventional diesel alone, a fuel that has been part of our infrastructure for years now, is still less readily available than gasoline. This summer, while my old Audi S4 was in for some work that kept it in the shop for several days, I was loaned a new 2014 TDI Q5. I was very impressed with the vehicle and seriously considered getting one, but while thinking about making the decision I noted that out of all the gas stations that I regularly use near home or work, about ½ don’t carry diesel. And of those that did, there was usually only 1 bank of pumps that had a diesel pump (and also gasoline pumps too) making refuelling a challenge waiting to get to that one tank in competition with non-diesel cars, often in a forecourt that didn’t make it easy to “get in line” without blocking access for other vehicles to the other pumps. I experienced this the day that I had to return the loaner topped up.
In the end I bought a Q5 with the TFSI 3L gas V6.
Indeed, the problem of infrastructure is one of the biggest problems with the introduction of any alternative fuel, and more so with a gaseous one. However, hydrogen fuel cells seem to be the “future fuel” being pushed by auto and oil companies, at least in the US, and it presents the same problems and then some. DME sounds like a brilliant option. Sad to say, I will be very surprised if it gets any traction in the US. Here’s hoping so, though!
Check out this video on YouTube: