Determination of the Impact of Biogas on the Engine Oil Condition Using a Sensor Based on Corrosiveness

Fuels, in particular low refined fuels and biofuels, may undergo considerable changes upon storage and circulation in the fuel supply system. (Bondioli et al., 2003) The knowledge of the quality of such fuels is crucial to maintain system reliability. Besides rubbing contact to parts in the fuel supply system, fuels and biofuels have also an impact on parts of the combustion section of an engine including the engine oil. (De Castro, 2007; Demirbas, 2009) Biofuels of interest are bioethanol, biodiesel and biogas. Biofuels usually differ significantly in chemistry from fossil fuels expressed by undesired interactions with oil additives accelerating oil alteration and hence significantly shortening oil intervals. (Luther, 2008) The determination of the optimum oil change interval is increasingly important for both ecological and economical reasons. Therefore, different approaches exist to determine the right time for the oil change. For automotive applications, a common method is the forecast of the oil quality by algorithms based on indirect parameters such as the oil temperature, load profile or number of cold starts. (Fitch, 2004; Wang, 2001) For large engines or stationary machines, the current oil condition is determined by laboratory analysis of oil samples regularly taken. (Smolenski et al., 1994) The latter is the most accurate and reliable method for the determination of the current oil condition. But laboratory analysis suffers from the drawback of unacceptable time delays between sampling and analysis. Biogas combusted in stationary gas engines is considered as one challenging renewable resource of energy. (Deublein, 2010) Besides methane and carbon monoxide as combustible compounds, undesired trace compounds can be found in biogas, sometimes at considerable levels (Harasimowicz et al., 2007). Among others, hydrogen sulphide, mercaptans, and halogen compounds are formed from processing of biomass at landfill sites, sewage plants, fermentation sites and wood gasification facilities. These components in the biogas are able to form aggressive and potentially corrosive components during the combustion process (Abatzoglou et al., 2009; Agoston et al., 2005a). The uptake of these compounds in the lubricant results in a higher degree of oil acidification. Therefore, a higher potential for corrosion of engine parts is given and may result in engine breakdown. (Richard et al., 2010) The direct measurement of the resulting corrosiveness of the engine oil could be used as main indicator for an oil change.