BIOCLEAN is a German government-sponsored, predominantly technologically oriented joint project with the German Aerospace Centre (DLR) dealing with the various emissions of large-bore four-stroke engines run on fossil and renewable fuels. It focuses on investigating the overall balance of emissions of climate-relevant gases (carbon dioxide, nitric oxides, sulphur dioxide) and particles. The whole fuel cycle from production to consumption is explored in this context. The engines can be used in both ships and power plants.
The engine experiments were conducted between July 2007 and June 2008 on a one-cylinder experimental engine of type 32/40 at MAN Diesel & Turbo in Augsburg, and on a MAN complete engine operating in a waste grease combustion plant in Fritzens in Austria. During long-term trials, the following renewable fuels were tested:
• Palm oil
• Soya oil
• Rapeseed oil
• Sunflower oil
• Waste grease
Heavy fuel oil was used as a reference fossil fuel.
In order to make an overall assessment of the climatic effects of the fuels, a climate response model was used and the radiative forcing for the greenhouse gases ozone, methane and CO2 and for particle and SO2 emissions calculated. With regard to the production of biogenic fuels in particular, diverse parameters must be taken into account such as land use, cultivation, processing and transport of biomass, use of fossil energies and upstream process chains such as fertiliser production.
The BIOCLEAN studies on the test engine show that the bio-fuels investigated are in principle suitable for efficient combustion in large-bore diesel engines. Sulphurous emissions are negligible compared to heavy fuel oil. Emissions of nitric oxides do not vary significantly from those of fossil fuels. The question as to what extent the use of these fuels will lead to a reduction in CO2 emissions and therefore reduce the climatic impact of ships’ emissions cannot yet be conclusively answered. Although the CO2 released during the combustion of bio-fuels is offset by the CO2 absorbed from the atmosphere during the plants’ growth phase, it becomes questionable to assume that using these fuels is CO2 neutral when the greenhouse gas balance during their production is taken into account.
Only by combining all the factors in a climate response model it is possible to conclusively evaluate how to use bio-fuels sensibly in shipping and energy generation.