Can Heavy-Duty Diesel Engines Fueled with DME Meet US 2007/2010 Emissions Standard with A Simplified Aftertreatment System?

Emissions from CI engines fueled with dimethyl ether (DME) were discussed in this paper. Thanks to its high content of fuel oxygen, DME combustion is virtually soot free. This characteristic of DME combustion indicates that the particulate filter will not be needed in the aftertreatment system for engines fueled with DME. NO_x emissions from a CI engine fueled with DME can meet the US 2007 regulation with a high EGR rate. Because 49% more fuel mass must be delivered in each DME injection than the corresponding diesel-fuel injection, and the DME injection pressure is lower than 500 bar under the current fuel-system technology, the DME injection duration is generally longer than that of diesel-fuel injection. This is unfavorable to further NO_x reduction. A multiple-injection strategy with timing for the primary injection determined by the cylinder temperature was proposed. It is believed that employing the Miller cycle for the low load operations and the multiple injection strategy for high load operations, plus a high EGR rate, NO_x emissions from DME engines could possibly meet the US 2010 standard. In the case that the aftertreatment for NO_x is needed, the reformed DME - a product of the DME-water partial reaction, may be used as a NO_x reductant for the lean NO_x trap (LNT). The reformed DME has higher NO_x conversion efficiency than hydrocarbon fuels, which reduces the fuel penalty for the LNT regeneration.