Studies on the effects of methyl soyate (biodiesel) blends with #2 diesel fuel in conjunction with various high pressure injection schemes were conducted on a single cylinder version of the Caterpillar 3400 series heavy duty diesel engine. Engine operating conditions at both high and low loads were investigated. Experiments were performed over a range of injection timings allowing particulate versus NOx trade-off curves to be generated. Phillips 66 certified #2 diesel fuel was used as the baseline; mixtures of 20% and 40% by volume of methyl soyate with the baseline fuel were used as the biodiesel blends. A blend of 20% by volume octadecene (a hydrocarbon fuel that is representative of the biodiesel hydrocarbon's composition but without the oxygen) in #2 diesel fuel was also investigated to help determine the mechanisms of emissions reduction.
Under high load conditions, a large reduction in particulates with a slight increase in NOx was observed with the biodiesel blends; the largest particulate reduction was observed with the 40% biodiesel blend case. The 20% biodiesel blend reduced particulate emissions an additional 36% versus the 20% octadecene blend, thus, implying that the presence of oxygen in the biodiesel fuel was the dominant factor in reducing the particulates, as opposed to effects such as those due to the dilution of aromatics or sulfur in the baseline diesel fuel. With a split injection strategy, the particulates were further reduced for all fuel cases and a decrease in NOx emissions was observed. At low loads, the addition of biodiesel in the fuel increased the particulate and, overall, NOx decreased with multiple injections for the low load cases.
At both high and low engine loads, the percentage of soluble organic fraction (SOF) in the particulate matter increased when biodiesel was blended with the #2 diesel fuel. The majority of the particulate matter in all the low load cases was composed of soluble organic material; 60%-90% SOF in the particulate matter were observed, depending on the fuel and fuel injection timing.
In regards to combustion, shorter ignition delays were observed for the biodiesel blended fuels relative to the baseline #2 diesel fuel in the high load case; however, this trend was not observed at the low load cases. In general, the biodiesel blend cases exhibited similar combustion characteristics as compared to the #2 diesel fuel cases.