Dimethyl ether (DME) is a synthetically produced alternative to diesel for use in specially designed compression ignition diesel engines. Under normal atmospheric conditions, DME is a colorless gas. It is used extensively in the chemical industry and as an aerosol propellant. Dimethyl ether requires about 75 pounds per square inch (psi) of pressure to be in liquid form. Because of this, DME's handling requirements are similar to those of propane—both must be kept in pressurized storage tanks at ambient temperature.
The use of DME in vehicles requires a compression ignition engine with a fuel system specifically developed to operate on DME. There have been a number of DME vehicle demonstrations in Europe and North America, including one in which a customer operated 10 vehicles for 750,000 miles.
Although dimethyl ether can be produced from biomass, methanol, and fossil fuels, the likely feedstock of choice for large-scale DME production in the United States is natural gas. DME can be produced directly from synthesis gas produced from natural gas, coal, or biomass. It can also be produced indirectly from methanol via a dehydration reaction. DME is not commercially available in the United States.
Dimethyl ether has several fuel properties that make it attractive for use in diesel engines. It has a very high cetane number, which is a measure of the fuel's ignitibility in compression ignition engines. The energy efficiency and power ratings of DME and diesel engines are virtually the same.
Because of its lack of carbon-to-carbon bonds, using DME as an alternative to diesel can virtually eliminate particulate emissions and potentially negate the need for costly diesel particulate filters. However, DME has half the energy density of diesel fuel, requiring a fuel tank twice as large as that needed for diesel.
Research and Development
In 2013, Pennsylvania State University, Volvo, and Oak Ridge National Laboratory completed field testing of a prototype DME truck. The heavy-duty truck performed well under real-world driving conditions, achieving comparable efficiency to a conventional diesel truck. Test results indicated that particulate matter emission standards could be met without the use of a diesel particulate filter. As with conventional diesel vehicles, oxides of nitrogen (NOx) emissions reductions can be handled with standard NOx after-treatment systems. Alternatively, the engine can be calibrated to negate the need for such a system, but this reduces efficiency.
Learn more about dimethyl ether from the links below. The Alternative Fuels Data Center (AFDC) and U.S. Department of Energy do not necessarily recommend or endorse these companies (see disclaimer).
- Process Design and Economics for the Conversion of Lignocellulosic Biomass to Hydrocarbons via Indirect Liquefaction: Thermochemical Research Pathway to High-Octane Gasoline Blendstock Through Methanol/Dimethyl Ether Intermediates
- Emissions and Performance Benchmarking of a Prototype Dimethyl Ether-Fueled Heavy-Duty Truck
- California Dimethyl Ether Multimedia Evaluation: Final Tier I Report
The AFDC also provides a publications search for more information.