Effects of Oxygenated Fuels on DI Diesel Combustion and Emissions

Experiments to study the effects of oxygenated fuels on emissions and combustion were performed in a single-cylinder direct-injection (DI) diesel engine. A matrix of oxygen containing fuels assessed the impact of weight percent oxygen content, oxygenate chemical structure, and oxygenate volatility on emissions. Several oxygenated chemicals were blended with an ultra-low sulfur diesel fuel and evaluated at an equivalent energy release and combustion phasing. Additional experiments investigated the effectiveness of oxygenated fuels at a different engine load, a matched fuel/air equivalence ratio, and blended with a diesel fuel from the Fischer-Tropsch process. Interactions between emissions and critical engine operating parameters were also quantified. A scanning mobility particle sizer (SMPS) was used to evaluate particle size distributions, in addition to particulate matter (PM) filter and oxides of nitrogen (NO_x) measurements.

The oxygenated diesel fuels were found to decrease the volume fraction of particles, but did not alter the total number of particles emitted. The reduction was a function of the fuel's weight percent oxygen content and oxygen containing functional group. Agreement was achieved between the relative trends observed with the integrated SMPS particle volume fraction and filter based mass measurement. Preliminary physical and chemical characterization of particulate matter from the reference and oxygenated fuels did not reveal any significant morphological or compositional differences.