Assessment of Hydrotreated Vegetable Oil (HVO) Applicability as an Alternative Marine Fuel Based on Its Performance and Emissions Characteristics

In current study, the combustion and emission characteristics of hydrotreated vegetable oil (HVO) were studied and compared to those of conventional marine gas oil (MGO). The main goal was to verify its applicability as an alternative marine fuel. All experiments were performed using generator set and propeller-law test cycles, i.e., standardized E2 and E3 cycles respectively. Additional emphasis was paid to the particulate matter (PM) emissions combining gravimetric and particle number measurements. The obtained results indicate average 10-15 % reduction in nitrogen oxides (NOx) emissions, while total unburned hydrocarbons (THC) emissions were reduced by 50-55 %. It is believed that a much higher cetane number of HVO together with its superior chemical composition (overall higher H/C ratio, absence of aromatics and heavy-boiling compounds) plays a vital role here. This may also explain the observed around 30 % PM mass reduction, which however showed a strong dependence on load (fuel-air ratio) and speed (time available for combustion) settings. Measured particle size distributions showed a clearly unimodal nature for both the tested fuels with pronounced accumulation (soot) mode found at around 60-80 nm. The total particle concentration in the measured size range of 14-750 nm was almost 30 % higher for HVO than for MGO. This increase is mainly associated with an increase in the number of produced nanoparticles. The main reason for that is most likely the less-optimal injection (shorter penetration length with larger cone angle due to lower density and longer injection duration related to lower volumetric energy content of HVO). The latter negative factors were however counterweighted by the advantages in terms of better chemical composition/structure resulting in an overall better combustion of HVO.