Diesel Fuels Research

 

Emissions Performance of Oxygenate-in-Diesel Blends and Fischer-Tropsch Diesel in a Compression Ignition Engine

Engine fuel tests were conducted with two oxygenates blended with conventional diesel and a synthetic Fisher-Tropsch (F-T) diesel to determine their emissions reduction potential. The oxygenated additives evaluated were dimethoxy methane (DMM) (also known as methylal) and diethyl ether (DEE). Blends of 5, 10, 20 and 30% by volume were investigated. The test engine was a 1993 Cummins B5.9 diesel, and data was collected for steady state operation at nine engine speed-load conditions.

Experimental results show that all of the test fuels reduce PM when data is averaged across the nine engine operating modes. The largest reductions in PM were observed with a blend of 30% DMM in diesel, which yielded a 35% reduction compared to the baseline diesel fuel. Lower DMM blend levels also resulted in PM reductions, but to a lesser extent. On a modal averaged basis, F-T diesel reduced PM emissions by 29%, and DEE in concentrations of 10 to 30% reduced PM emissions by between 13 and 24%.

On a modal averaged basis, NOx emissions for F-T diesel and the DMM and DEE blends were reduced by between 1 and 10%. Corresponding increases in fuel consumption (beyond that necessary to compensate for the differences in energy densities) were also observed. Modal averaged emissions of THC and CO were in most cases higher for the test fuels, but their overall levels remained low.

Investigation of individual modal data revealed large differences in the effect of the DMM and DEE blends on PM emissions. In general, measured PM levels were drastically (as much as 76%) lower for the higher engine power test modes. For the lower power modes, however, PM emissions were often unchanged or even increased.

Isotopic Tracing of Particulate Matter from a Compression Ignition Engine Fueled with Ethanol-in-Diesel Blends

Accelerator Mass Spectrometry (AMS) was used to investigate the relative contribution to diesel engine particulate matter (PM) from the ethanol and diesel fractions of blended fuels. Four test fuels along with a diesel fuel baseline were investigated. The test fuels were comprised of 14C depleted diesel fuel mixed with contemporary grain ethanol (>400 the 14C concentration of diesel). An emulsifier (Span 85) or cosolvent (butyl alcohol) was used to facilitate mixing. The experimental test engine was a 1993 Cummins B5.9 diesel rated at 175 hp at 2500 rpm. Test fuels were run at steady-state conditions of 1600 rpm and 210 ft-lbs, and PM samples were collected on quartz filters following dilution of engine exhaust in a mini-dilution tunnel. AMS analysis of the filter samples showed that the ethanol contributed less to PM relative to its fraction in the fuel blend. For the emulsified blends, 6.4% and 10.3% contributions to PM were observed for 11.5% and 23.0% ethanol fuels, respectively. For the cosolvent blends, even lower contributions were observed (3.8% and 6.3% contributions to PM for 12.5% and 25.0% ethanol fuels, respectively).