BIOCLEAN: Using renewable fuels to reduce emissions of climate-relevant gases and particulates in large diesel engines

The results of the study demonstrate that from a climate perspective, low sulphur fossil fuels and biofuels offer a viable alternative to heavy fuel oil with a high sulphur content used in large diesel engines. No technical adjustments to the engines are required for biofuels. However the cultivation of the biomass must be sustainable so as to achieve positive climate impacts.

So far there has been little research on the emission characteristics of medium-speed large-bore diesel engines pertaining to COâ‚‚ and other greenhouse active gases as well as particulates. Prior to the project it was also unclear whether any technical modifications would be required when using biofuels.
The objective of the BIOCLEAN project, therefore, was to quantify all climate-impacting components in heavy oil, marine gas oil (MGO), palm oil, soybean oil, sunflower oil and waste oil when used to run medium-speed large-bore diesel engines for power plants and maritime applications. The aim was to determine whether the substitution of heavy oil with low sulphur fuels, such as MGO (a fossil fuel) or biofuels, is viable from a climate perspective.
All climate-impacting components were analysed to prevent the occurrence of side effects, such as an increase in one radiative forcing agent caused by a decrease in another. 
Results:

• The studied biofuels demonstrated good combustion properties overall. No significant levels of corrosion were determined. Thus there are no restrictions on the use of biofuels as regards engine parameters.
• The use of low sulphur fuels (MGO, biofuels) results in significantly lower emissions of particulates, such as sulphate and carbon black, as compared to heavy oil.
• NO_x and CO emissions are at similar levels for all fuels. Emissions of gaseous hydrocarbons, however, are lower for low sulphur fuels as compared to heavy oil.
• CO₂ emissions are lower for biofuels than for heavy oil provided there are no major changes in land use in the process of fuel production. However, emission levels are considerably higher if tropical rain forests or savannahs are cleared for fuel production.
• Palm oil has the lowest greenhouse gas emissions if sourced from sustainable cultivation. Significant emission reductions can also be achieved with soybean oil and waste oil, although since waste oil is available only in limited quantities, it is more useful for regional power generation.

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