| Size distributions were obtained after dilution tunnel sampling from a 1988 Cummins L10 engine using a conventional sulfur fuel (CS, 0.32 wt.%), a low sulfur fuel (LS, 0.01 wt.%) and the same low sulfur fuel doped to 0.29 wt.% (DS). Data were also obtained from a 1991 Cummins LTA 10 diesel engine using the same LS fuel with and without an oxidation catalytic converter (OCC).; The particle size distribution results from the 1988 engine revealed that the accumulation mode particles (0.04-1.0 {dollar}mu{dollar}m in diameter) for all the fuels were similar, but, the number of nuclei mode particles (0.0075-0.04 {dollar}mu{dollar}m in diameter) with both the CS and DS fuels were more than two orders of magnitude greater than with the LS fuel. Hetero-molecular nucleation theory for H{dollar}sb2{dollar}SO{dollar}sb4{dollar} and H{dollar}sb2{dollar}O vapor revealed that for the CS and DS fuels, the dilution tunnel's H{dollar}sb2{dollar}O and H{dollar}sb2{dollar}SO{dollar}sb4{dollar} vapor pressures were favorable for H{dollar}sb2{dollar}SO{dollar}sb4{dollar}-H{dollar}sb2{dollar}O particle nucleation and growth. The theory indicated that particle formation is a function of fuel sulfur level, % fuel sulfur converted to SO{dollar}sb4{dollar}, fuel/air ratios, dilution tunnel relative humidity, and dilution tunnel temperatures.; Data from the 1991 engine using the LS fuel indicated that there was a distinct nuclei mode for all conditions tested with and without the OCC. The OCC is designed to remove the hydrocarbons and because there were no differences in the nuclei mode with and without the OCC, it was concluded that the nuclei mode particles were primary carbon spherules that formed during combustion. Compared to the 1988 engine using LS fuel, the 1991 engine's carbon fractions were reduced 81% or more depending on the engine condition. The overall carbon reductions were due to decreases in the accumulation mode even though the nuclei mode increased more than two orders of magnitude by number.; The particle size distributions from both engines were used to develop empirical models to estimate the composition of the individual size particles. The model indicates that with the 1988 engine and CS fuel, the nuclei mode particles are mainly H{dollar}sb2{dollar}SO{dollar}sb4{dollar}-H{dollar}sb2{dollar}O particles while with the 1991 engine, the nuclei mode consists of primary carbon spherules with adsorbed HCs. This shift in nuclei mode composition is important when designing new engines and exhaust control technology. |
