Polyoxymethylene dimethyl ethers as clean diesel additives: Fuel freezing and prediction

Polyoxymethylene dimethyl ethers are promising additives for tailoring clean diesel fuels and have attracted wide interests. Cold-flow properties are also so important because diesel fuels would freeze at temperatures lower than freezing point leading to engine-attack of internal combustion engines. In this work, the freezing behaviors of DMMn mixtures and DMMn-diesel blends were investigated experimentally by a modified standard test method and theoretically by an improved prediction model. Results showed a heavy component do not necessarily lead to increase of freezing point. A minimal point may exist in the freezing diagram. DMM3.5 mixture with composition of Schulz-Flory distribution would be qualified for application at temperatures below - 19.9 degrees C when growth factor was less than 0.7 and even heavier components of DMMn > 5 below a certain limit also could be acceptable as diesel additives for different utilizing temperature grades. Results also indicated that DMMn would have strong ability of depression of freezing point in the diesel blend with low n-alkane contents, but have relatively weak ability for high n-alkane diesel. The intermolecular interactions played an important role on the freezing behavior.