Impacts of Hydrotreated Vegetable Oil as Renewable Diesel Fuel on Engine Performance and Emissions in a Heavy-Duty Diesel Engine

As the pressure increases to move to renewable carbon-neutral fuel sources, especially in heavy-duty diesel engine applications, hydrotreated vegetable oil (HVO) has shown to be an attractive alternative fuel to fossil diesel. Therefore, this study investigated the impacts of HVO used as a drop-in fuel on performance and emissions of a nonroad heavy-duty diesel engine by running back-to-back D2 ISO 8178 cycles with ultra-low sulfur diesel (ULSD) and HVO. The measurement results showed that brake specific fuel consumption with respect to mass reduced by 1.1%–3.6% switching from ULSD to HVO due to greater heating values of HVO, which is supported by 0.7%–3.5% lower CO₂ emissions recorded with HVO. Conversely, brake specific fuel consumption with respect to volume increased by 0.3%–2.9% with HVO because of its smaller density. Combustion analysis revealed that combustion of both fuels is comparable at high loads while HVO ignites earlier at low power. Thus, lesser reductions in NO_x emissions (0%–6%) were observed at high loads, which can be attributed to lower combustion temperatures of HVO. On the other hand, higher cetane number of HVO at low loads resulted in notable reductions in NO_x (36%–39%). Advanced start of HVO combustion at low power caused an increase in PM, soot, and smoke. At high to mid loads, PM, soot, and smoke decreased by 18%–55% because HVO is fully paraffinic, has higher H/C ratio compared to ULSD, and contains no sulfur or other mineral impurities. With greater reduction at low loads, HC and CO were lower for HVO due to its non-aromatic content, high cetane number, lower distillation curve, lower density, and smaller viscosity. Overall, it is concluded that HVO can play an important role as a sustainable fuel source for transportation and power production in the coming decades.