Cutting-edge technologies: Biofuel innovations in marine propulsion systems to lower black carbon emissions

Abstract

The marine sector is an important contributor to global black carbon (BC) emissions, which can negatively affect air quality and climate. Biofuel advancement provides a green substitute for traditional maritime fuels, which could help in meeting the almost unreasonable emission reduction targets laid down by International Maritime Organization (IMO). This study reviews some engineering-oriented biofuel applications that seem to effectively minimize BC emissions from marine propulsion systems without sacrifice of the operational performance metric. Biofuels (hydrotreated vegetable oil [HVO] and biodiesel from algae or other processing routes) show the potential to reduce BC emissions by 50–80 % under controlled conditions in medium-speed diesel engines. For example, a marine trial using 50:50 HVO-diesel demonstrated up to a 60 % reduction in BC emissions compared with fossil fuels but maintained engine performance. Qualitatively, enhanced combustion properties due to the relatively high cetane number and low aromatic content in biofuels compared with those of petroleum fuels result in lower soot emissions when burning biofuels. Lifecycle assessments show greenhouse gases (GHG) emission reductions of up to 75 % when biofuels displace heavy fuel oil (HFO) in terms of quantitative measurements. Increased biofuel scalability to marine fuel applications is due in part to technological advancements, such as catalytic cracking of lignocellulosic biomass and microbial fermentation of seaweed. Biofuels save less than a ton of CO₂ per cubic meter as they are hard to store and incorporate during the fuel production process, but they still represent an appropriate tool in decarbonizing shipping and complying with international climate goals. This review highlights the transformational function of biofuels in enabling sustainable marine propulsion.