Emission reduction potential of hydrotreated vegetable oil (HVO) in a dual-loop EGR diesel engine with fuel-specific optimized calibration

In the pursuit of carbon neutrality, biofuels offer a viable alternative to reduce net CO2 emissions, as their production absorbs CO2. Hydrotreated vegetable oil (HVO), a second-generation biodiesel, offers several advantages with respect to fatty acid methyl esters (FAME). In particular, HVO can be also utilized pure without significant modifications to current diesel technology. This paper shows the potentialities of using pure HVO in a prototype dual-loop EGR diesel engine derived from a modern Euro 6 latest-generation version. Preliminary experimental tests show appreciable advantages when HVO is used as a drop-in fuel, that is, without any modification to the original diesel-oriented engine calibration. Substantial reductions in HC, CO and soot engine-out emissions are obtained, with variations in NOx primarily depending on the specific engine operating conditions. Nevertheless, the paper shows that even greater benefits can be achieved with dedicated HVO-specific calibrations, optimized using statistical techniques of Design of Experiments (DoE). For instance, a tailored HVO-specific calibration that maximizes NOx reductions could decrease NOx engine-out emissions by approximately 30% at medium-to-high load and as much as 60% at low load, if compared to a diesel-oriented calibration targeting the same objectives. The study also compares other engine-out emissions and noise levels by implementing alternative dedicated calibrations aimed at minimizing CO or brake specific fuel consumption, depending on the operating point considered.