Potential of oxymethylenether-diesel blends for ultra-low emission engines

In the race to counteract global warming, fossil fuel dependency and urban air pollution, it is clear that vehicle emissions have to be reduced considerably. A pathway out of today's limitations in engine technology is synthetic fuel. In particular, oxymethylenether (OME) is an attractive candidate due to its soot free combustion. In this work, OME1-diesel blends are considered aiming to outline their potential as a near future alternative fuel. Various blends ranging from 0% to 80% vol OME1 in diesel fuel were investigated in a single cylinder research engine. Results show that tradeoffs of NOx-soot and NOx-HC/CO are in general retarded with increasing OME1 content in the fuel. With 50% (vol) OME1 in diesel, the NOx-soot tradeoff is completely eliminated up to the higher end of moderate loads similar to 10 bar. Furthermore, with increasing content of OME1 in the blend, exhaust gas temperatures reduce down to -7% (degrees K) and indicated thermodynamic efficiency increases up to +2% with respect to pure diesel. Due to the lower cetane number (CN) of blends containing OME1, the combustion noise level increase at lower loads compared to diesel combustion. At higher loads, the lower heating value of the OME1-containing blends results in a reduction of combustion noise. To identify an optimal blending range for OME1 in diesel, the soot reduction potential is systematically analyzed by a Gaussian process regression analysis at the higher load points. From the analysis an optimal blend ratio of 35% OME1 in diesel is suggested, being the best compromise between soot reduction (similar to 90%) and the deterioration of fuel properties like heating value (-15%) and cetane number. With a CN of 51, the 35% OME1-diesel blend still complies with the CN lower limit in the current EN590 Norm. Finally, we conclude that from the combustion and emission point of view, OME1 is a superior diesel fuel substitutive, in particular when higher blending ratios (20-40%) are considered.