A study of alternative diesel fuel lubricity, deposit formation, and material compatibility: Dimethyl ether, biodiesel and ultra low sulfur diesel fuels.

摘要

As emissions restrictions on the diesel engine community continue to tighten, the search for alternative fuels with reduced tailpipe exhaust has become critical. Problems with utilizing alternative fuels are holding back their entrance into mass markets. This work focuses on three types of diesel fuels; ultra low sulfur diesel, biodiesel and dimethyl ether, and explores several critical operational issues.; Viscosities of ultra low sulfur diesel (ULSDF), biodiesel, and dimethyl ether (DME) blended and with additives were explored using a new high pressure capillary viscometer. It was found that existing additives are not capable of improving the viscosity of a 25 wt % DME-ULSDF or biodiesel blend unless used at very high concentrations. Existing blending theory is capable of predicting the response of low viscosity components. The effect of pressure on viscosity was explored and determined to be minimal.; Data from a Cameron-Plint wear testing machine, modified to mimic fuel injector operation, showed that increasing the concentration of DME in fuel blends resulted in increased wear of the components. A profilometer for wear scar measurement was employed to quantify wear.; Elastomer durability in alternative fuels is critical to engine operation. Currently used elastomer types are not robust in the harsh chemical environment provided by DME. Highly fluorinated polymers resisted breakdown, while non-fluorinated types degraded readily.; ULSDF deposits formed at engine operating temperatures were caused by the fuel's molecular makeup. Severe refining to remove trace quantities of sulfur causes significant shifts in the molecular weight distribution and functional groupings. High aromatic and unsaturates content were responsible for this shift, and when removed, deposits were significantly reduced. Deposit characterization revealed the formation mechanism was both metal catalyzed and bulk fuel polycondensation, resulting in little or no distinct layer formation.