Nerva, J.; Genzale, CL.; Kook, S.; García Oliver, JM.; Pickett, LM. (2013) soy methyl-ester biodiesel is injected into a constant-volume combustion facility. A range of optical diagnostics is performed, comparing biodiesel to a conventional #2 diesel at the same injection and ambient conditions. Schlieren imaging shows virtually the same vapor-phase penetration for the two fuels, while simultaneous Mie-scatter imaging shows that the maximum liquid-phase penetration of biodiesel is higher than diesel due to their different boiling-point temperatures. But the different liquid-phase penetration does not affect overall mixing rate and downstream vapor-phase penetration because each fuel spray has similar momentum and spreading angle. The ignition delay and lift-off length are only slightly less for biodiesel compared to diesel, consistent with the CN. Because of the similarity in lift-off length, the differences in equivalence ratio distribution at the lift-off length are mainly affected by the fuels oxygen content. For biodiesel, the equivalence ratio is reduced, which, along with the fuel molecular structure and oxygen content, significantly affects soot formation downstream. Spatially-resolved soot volume fraction measurements obtained by combining laser extinction measurements with planar laser-induced incandescence imaging show that the soot concentration can be reduced by an order of magnitude for biodiesel. These integrated measurements of spray mixing, combustion, and quantitative soot concentration provide new validation data for the development of CFD spray, combustion, and soot formation models suitable for the latest biofuels. AbstractThough biodiesel has begun to penetrate the fuel market, its effect on injection processes, combustion, and emissions formation under diesel engine conditions remains somewhat unclear. Typical tailpipe measurements from engines running biodiesel indicate that PM, CO and UHC are decreased, whereas NO X emissions tend to be increased. However, these observations are the result of complex interactions between physical and chemical processes occurring in the combustion chamber, for which understanding is still needed.To characterize and decouple the physical and chemical influences of biodiesel on spray mixing, ignition, combustion and soot formation, a soy methyl-ester biodiesel is injected into a constant-volume combustion facility under diesel-like operating conditions. A range of optical diagnostics is performed, comparing biodiesel to a conventional #2 diesel at the same injection and ambient conditions.Schlieren high-speed imaging shows virtually the same vapor-phase penetration for the two fuels, while simultaneous Mie-scatter imaging shows that the maximum liquid-phase penetration of biodiesel is higher than diesel. Differences in the liquid-phase penetration are expected because of the different boiling-point temperatures of the two fuels. But the different liquid-phase penetration does not affect overall mixing rate and downstream vapor-phase penetration because each...

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For a better understanding of soot formation and oxidation processes in conventional diesel and biodiesel spray flames, the morphology, microstructure and sizes of soot particles directly sampled in spray flames fuelled with US#2 diesel and soy-methyl ester were investigated using transmission electron microscopy (TEM). The soot samples were taken at 50mm from the injector nozzle, which corresponds to the peak soot location in the spray flames. The spray flames were generated in a constant-volume combustion chamber under a diesel-like high pressure and high temperature condition (6.7MPa, 1000K). Direct sampling permits a more direct assessment of soot as it is formed and oxidized in the flame, as opposed to exhaust PM measurements. Density of sampled soot particles, diameter of primary particles, size (gyration radius) and compactness (fractal dimension) of soot aggregates were analyzed and compared. No analysis of the soot micro-structure was made. The overall morphology of the biodiesel soot bears similarity to that of #2 diesel, but the soot density, primary particle size, and fractal dimension are smaller for biodiesel.

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ElsevierPastor Soriano, JV.; García Oliver, JM.; Nerva, J.; Giménez, B. (2011). Fuel effect on the liquid-phase penetration of an evaporating spray under transient diesel-like conditions. Fuel. 90 (11) AbstractMeasurements of the maximum liquid-phase penetration have been performed injecting five different fuels through a single-hole nozzle in an optical engine under a large set of thermodynamic and injection conditions. The focus of this paper is twofold. First, it pretends to study fuel physical properties