Review of Biofuel Effect on Emissions of Various Types of Marine Propulsion and Auxiliary Engines

Abstract

The International Maritime Organization aims to reduce the maritime industry’s carbon emissions by 40% in the next two decades and has introduced measures to control CO2 emissions. These have significantly increased interest regarding biofuels, which can be used immediately on existing vessels, reducing their carbon footprint. The most common variant is B30, a blend of 70% crude oil and 30% biodiesel. Concerns exist for the potential effect on engine performance and NOx emissions. Scientific works on the subject are limited for two-stroke marine engines, while some studies are available for four-stroke ones, usually auxiliaries. To increase information availability on the subject, in this work, we review the results of testing on multiple marine engine types, two-stroke propulsion and four-stroke auxiliary units using B30 and conventional fuels. The effect on emissions and fuel efficiency is examined and cross-referenced with the available literature. A small increase in specific fuel consumption was observed for B30 use that varied with engine type. The increase was on average 1% for two-stroke and 2.5% for four-stroke engines. The effect of B30 on NOx emissions was low but varied between engines. For low-speed two-stroke engines, NOx increase was on average 4% compared to crude oil, and 2.4% for four-stroke auxiliary units, albeit with higher variance. For some four-stroke units, a decrease in emissions was found. All previous results were in line with other published studies. Overall, it was found that while biofuel effect can vary considerably between applications, 30% biodiesel blends can be used with no concerns regarding emissions and fuel efficiency.