Potential of Dimethylether as an alternative Diesel fuel for a CO₂ sustainable powertrain solution

Abstract

Worldwide, combustion engines will remain as major power unit for vehicle propulsion in long-term. Consequently, immediate measures are claimed to reduce the current CO₂ production from combustion engines which are accomplished by three approaches: (1) an increase of the thermal efficiency, (2) the application of fuels with low carbon content and (3) the production of fuels from renewable feedstocks. The first aspect clearly emphasizes compression ignition (CI) engines, the second aspect draws the attention to hydrogen and single C-bonded fuels and the third aspect has initiated sensitive discussions about renewable resources which lead to the commitments of first/ second/ third generation biofuels. In this context, the use of Ethers as neat or blended fuels for combustion engines has been discussed for more than 20 years. Among these, the simplest compound, Dimethylether CH3-O-CH3 (DME), has an exceptional position as a neat fuel for compression ignition (CI) engines due to its excellent ignition and combustion properties which have been well investigated published by many authors.

However, Diesel engines must be specifically adapted for use with DME and one fuel system cannot be used for both Diesel fuel and DME. Due to the lower density and heating value of DME compared to Diesel fuel a 1.8 times higher fuel volume must be injected into the combustion chamber for same power output. Furthermore, the high vapour pressure indicates that DME behaves more like a gas than a liquid which limits the nozzle flow. On the other hand, this characteristic leads to a fast fuel-air mixing at moderate injection pressures (<1000 bar). Due to these outstanding properties, it is appropriate to consider new approaches to accomplish the fuel injection and fuel-air mixing process.