A fundamental study of injection and combustion characteristics of neat Hydrotreated Vegetable Oil (HVO) as a fuel for light-duty diesel engines

Renewable fuels are essential for decarbonization because they can significantly reduce greenhouse gas emissions compared to fossil fuels. Among the renewable fuels capable to be mass produced, Hydrotreated Vegetable Oil (HVO) is attracting major attention thanks to its noticeable physical and chemical properties, which make it a viable and effective diesel substitute. In this work, the fundamental injection and combustion characteristics of neat Hydrotreated Vegetable Oil (HVO) as an alternative fuel for light-duty diesel engines have been analysed by means of an extensive experimental campaign based on a single injection strategy in both spray and engine laboratory tests. A Euro 6 light-duty diesel engine was selected as a case study for the research activity, comparing the neat HVO injection, combustion, and emission characteristics with those of a B5 diesel fuel. Differences were firstly scrutinized in terms of injection rate and main spray characteristics, these latter by means of both spray imaging and Phase Doppler Anemometry (PDA) techniques. Then, engine tests were performed for three different operating conditions (at low, medium, and medium–high load, respectively) to investigate the combustion properties and emissions. Furthermore, the sensitivity of neat HVO and B5 diesel to different Exhaust Gas Recirculation (EGR), Start of Injection (SOI), and injection pressure levels was also explored. In conclusion, HVO showed an excellent adaptability to nowadays automotive diesel engines also as a neat fuel without the necessity of a specific engine recalibration, allowing to achieve an impressive 85% reduction in terms of CO emissions on a WTW basis, with a limited increase (lower than 4%) in volumetric fuel consumption and with impressive reductions in terms of CO and HC emissions (more than 40 and 50 %, respectively).