DIMETHYL ETHER (DME)

9.0 DIMETHYL ETHER (DME)

Dimethyl Ether (DME) is an ether compound having a molecular structure in which one oxygen atom and two methyl groups are bonded. It is chemically synthesized from natural gas, coal-associated, etc. DME is a gas looking colourless and smelling etheric at room temperature and under normal pressure. Like LPG, DME is liquefied by applying a pressure of approximately 0.5 Mpa.

9.1 Emissions:

Table 13 and 14 show a comparison of engine performance and emissions between diesel and DME buses. The table indicates that a DME engine, although having an equal energy efficiency level to that of a diesel engine, emits extremely low NOx and particulate matters. From Table-14 it is clear that DME bus easily meets the Euro-IV diesel standards. A DME vehicle outperforms diesel vehicles for regulated emissions like NOx, total hydrocarbons and particulate matters. Peak acceleration smoke of a DME vehicle is almost nil and it also performs better with regard to combustion noise when compared to that of a diesel vehicle. DME is now being tried in USA and Japan to achieve severe emission reduction targets of as low as 50% of the proposed Euro-IV levels. Fuel economy of a DME vehicle is also found to be comparable to that of conventional diesel vehicle. Volvo is working on to further reduce emissions from their DME buses, which at present easily meets the equivalent Euro-IV standards.

9.2 Advantage of DME:

The greatest advantage of DME when used as an automobile fuel is that its high cetane number makes it applicable to a diesel engine and being an oxygen containing fuel, it prevents a diesel engine from emitting soot and particulate matter to a greater extent than diesel fuel does.

9.3 Disadvantage of DME:

Some of the disadvantages of DME are:

- DME has a viscosity lower than that of diesel.
- Lubricity is also low causing wearing of engine parts.
- It is found to react with some rubber components

9.4 Technology Development Trend of DME Vehicles:

DME vehicles are under developmental stage in many countries of the world. Several developmental projects are being promoted for commercializing this fuel. The Danish Government in cooperation with petroleum and automobile manufacturers is pushing ahead the Scandinavian Bus Project. This is the demonstration project aiming to introduce low-emission DME buses to public transportation. Specifications of the VOLVO DME bus used in this project are given in Table-15.

Another project, the PNGV project is a research programme of the US Federal Government and USCAR (United States Council for Automotive Research). The researcher of this project concludes that in the short term, synthetic diesel fuel like DME is not commercially very viable but it holds promise for the future. Renaut, TNO, Peugeot PSA and IFP has launched a project in 2000 called the "European DME Passenger Car Demonstration Programme" with the objective to achieve emission targets of 50% of Euro-IV limit values for regulated emissions and LPG/CNG levels for non-regulated components. Some projects on DME are also going on in Japan.

9.5 Comparison of CNG/LPG/DME:

Compressed Natural Gas (CNG), Liquified Petroleum Gas (LPG) and Dimethyl Ether (DME) are the three prominent gaseous alternatives to conventional fuels. CNG and LPG have already penetrated as automotive fuels in many parts of the world and DME is also fast emerging as a promising alternative. Comparisons of some of the properties of these fuels with diesel are given in Table-16. Figures-2 & 3 show the comparison of CO2 emissions and energy density of the fuels respectively.

9.6 Indian Initiative on DME:

Recognizing that DME can be a new economical fuel for the 21st century, India's Ministry of Petroleum & Natural Gas invited British Petroleum (BP) in 1997 to develop DME supplies in an exclusive partnership with India's leading energy marketers and research organizations. In July 1998, a collaboration agreement was signed between BP, IOCL, GAIL and IIP for development, production and marketing of DME as a multi-purpose fuel for India. DME will be produced through Gas-to-Liquid (GTL) technology and for this gas will be sourced from the Middle East. Intention of this project was to establish DME as a multi-purpose fuel for India but in the initial stages the project identified some southern Indian states to supply DME as a feedstock for power plants.