Emissions, performance, and vibro-acoustic analysis of a compression-ignition engine running on hydrotreated vegetable oil (HVO)

To meet future energy sustainability and carbon neutrality requirements, disruptive changes to the current energy mix are expected. Renewable fuels, such as hydrotreated vegetable oil (HVO), could play an important role in this context. To assess the potential of HVO, further quantitative research analyses are still required in order to emphasize the benefits (and drawbacks, if any) from a global perspective, rather than limiting the investigation to a single topic (e.g., emissions). For this purpose, HVO and conventional diesel were compared, in this study, running initially the engine with the same (diesel-oriented) calibration, before being optimized using purposely developed fuel-specific calibrations. In terms of exhaust pollutant emissions, HVO showed the potential to substantially reduce engine-out emissions of soot, HC and CO at low loads, while differences in exhaust emissions at higher loads proved to be mainly determined by the amount of oxygen available in the combustion chamber, rather than the specific characteristics of the fuels. HVO also demonstrated reductions in tank-to-wheel CO2 emissions, due to lower fuel consumption, even though the primary benefit of renewable fuels should be highlighted in a larger well-to-wheel analysis. In addition to emission analyses, since extensive investigations on the area of vibroacoustic behavior of engines running on renewable fuels are rare in the literature, a thorough comparison between regular diesel and HVO was carried out on this aspect. In this preliminary activity, the acoustic analysis focused solely on combustion noise, which was extracted by using dedicated signal processing techniques. This approach allowed the authors to focus on the noise contribution that is specifically influenced by the fuel characteristics. Furthermore, the vibrations of the engine block were evaluated. The results showed slightly lower levels of HVO in terms of both noise and vibrations.