I recently heard Roy Horton, alternative fuel and driveline marketing product manager for Mack Trucks, discussing the alternative fuel plans for Mack, and something new came up: dimethyl ether (DME). DME is a gas made from natural gas, coal, or biomass, converted under modest pressure (about 5 bar, or 75 psi) into a liquid. DME has been around for several years, often used to mix with liquid petroleum gas (LPG) to reduce LPG supply deficiencies in many Asian markets. DuPont Fluorochemicals markets DME under the product name “Dymel A” as a propellant for aerosols.
DME is attractive for a few reasons: it’s easy to handle with low pressure tanks (75 psi vs. 3,600 psi for compressed natural gas, or CNG); it produces no particulate matter (but does produce carbon monoxide and nitrogen oxide); it can be produced from multiple feedstocks; it is non-toxic and non-carcinogenic if ingested; and it has a cetane rating of about 60. The higher the level of cetane, a hydrocarbon, the lower the temperature at which the fuel auto-ignites and the quicker it vaporizes. Lower cetane numbers mean slower ignition in the cylinder. Slower ignition produces more particulate matter and reduces the fuel economy. DME’s high cetane number means that, like diesel, the fuel can be used with direct injection and auto-ignite. Diesel has a cetane number of between 45 and 55, depending on its grade (biodiesel has a cetane number of about 55).
The Infrastructure Question
Volvo, which owns Mack Trucks, became interested in DME after a review of seven different carbon-neutral fuels in Sweden in 2007, in which DME led the pack. Volvo began customer testing of bio-stock-produced, DME-fueled trucks in 2010 in Europe, which ultimately led to the announcement this year of retail sales of MY 2015 Volvo and Mack trucks running on DME. In conversations, rival large truck companies, such as PACCAR and Daimler Trucks, have mentioned that they are also watching DME developments; whether that means a truck brought to market could largely depend on infrastructure.
Similar to other alternative fuels, infrastructure for DME remains a key issue yet to be worked out. Oberon Fuels in California is the first to produce DME as a vehicle fuel in the United States, using natural gas from the gas grid. The price for DME as a truck fuel remains high, roughly comparable to diesel. The high cost comes, in part, because production for vehicles, distribution, and retail operations is still in the early stages.
Cost, Cost, Cost
So, are fleet managers willing to pay extra for a renewable fuel that has a significantly better environmental position? I’m skeptical because DME will compete with CNG and LNG for alternative fuel budgets in heavy duty trucks, where ultimately cost trumps everything else. In the near term, the incremental cost for DME trucks is not likely to be recovered by the cost of fuel since DME is similarly priced to diesel. Since CNG and LNG are both positioned as environmental fuels with fast payback on the investment, DME will be at an economic disadvantage (and that position has not worked out for hybrids in the heavy duty market). Whether DME can gain ground as a truck fuel in the long term will ultimately depend on improving the economics of the fuel and the trucks, and how good Volvo is at convincing its competitors to jump into the market.
Tags: Alternative Fuel Vehicles, Clean Transportation, Renewable Energy, Smart Transportation Program
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