PNNL

Abstract

The Coordinating Research Council (CRC) is actively involved in achieving long-term goals in the fight against climate change. Among others, goals include developing and applying new advanced analytical techniques useful in the chemical characterization of transportation fuels used in advanced combustion studies. This paper supplements a 2017 project funded by the CRC to identify and compare the effects of a commercially available renewable diesel fuel (hydrotreated vegetable oil (HVO)) and ultra-low sulfur diesel (ULSD) fuel on engine-out gaseous and particulate matter (PM) emissions from a light-duty vehicle. Results showed that the combustion of HVO fuel had an advantage over ULSD in terms of lowering engine-out emissions (level of THC, CO, NOx, etc.). Furthermore, this advantage is strongly related to the fuel composition. This paper summarizes the analytical results of advanced and comprehensive analytical tests on ULSD and HVO fuels and attempts to make connections to some of the engine-out emissions results. Such data can be leveraged to estimate the effect of chemistry on fuel combustion behavior. A variety of test methods, generally unavailable in combination, were employed in this study, such as one-dimensional and two-dimensional gas chromatography equipped with bench-top detectors, nuclear magnetic resonance spectroscopy, and high-pressure solid-liquid phase transition experiments. In summary, the ULSD sample was found to have representation across the expected set of hydrocarbon classes typical for the sample type. Interestingly, a high content of cycloparaffins (>50 wt%) and a very low content of diaromatics (~2 wt%) were present. In contrast, HVO was found to consist of only two hydrocarbon classes: n-paraffins (~ 10 wt%) and isoparaffins(~ 90 wt%), both predominantly in a narrow carbon atom number range (i.e., C14-C18). Both positive and negative engine-out emissions results for HVO can be tracked to the narrow carbon atom number range of the n-paraffins and isoparaffins, which result in a high cetane number fuel that is delivered with a narrow distillation range. Additionally, while low-temperature operability of HVO has been a concern, both HVO and ULSD were evaluated at pressures up to ~275 MPa and found to have comparable solid-liquid equilibria, despite significant compositional differences.