Rheology and engine performance of very low sulfur fuel oil blended with 10% fast pyrolysis and hydrothermal liquefaction oils in a 2-stroke crosshead engine

• VLSFO viscosity was lowered by adding fast pyrolysis (FP) and hydrothermal liquefaction (HTL) oils. • Thermal efficiency of VLSFO was improved with 10% FP and HTL oils. • BSFC of VLSFO was improved with 10% FP and HTL oils. • NOx emissions were unaffected by the added FP and HTL oils. The performance and emissions for a single-cylinder 2-stroke crosshead engine were determined for a very low sulfur fuel oil (VLSFO) containing partially upgraded 10 wt% fast pyrolysis (FP) or hydrothermal liquefaction (HTL) bio-intermediates. The FP and HTL oils were derived from biomass and hydroprocessed to reduce oxygen and nitrogen. The addition of either biofuel reduced the overall viscosity of the VLSFO. Aging tests at 50, 90, and 120 °C showed that the viscosity of VLSFO increased with exposure time up to two weeks. Similar trends were observed for the FP and HTL blends, but a pronounced spike in viscosity occurred for these fuels during the early period of exposure. None of the viscosity increases exceeded the operational limits of fuel system pumps. Engine performance studies were conducted under low, medium, and high load operational settings. In general, the engine results for the three test fuels were similar, but modest improvements in brake thermal efficiency and brake specific fuel consumption were observed, which may be attributed to the heightened reactivity of the low molecular weight fraction of the FP and HTL oils.