Abstract

JAWUREK, H. H.; FRENZ, D.  and  MYERS, C.. Biogas in Small-scale Rural Electricity Generation. R&D j. (Matieland, Online) [online]. 1985, vol.1, pp.7-12. ISSN 2309-8988.

Small-scale anaerobic fermentation of organic wastes, particularly cattle manure, to yield both methane-rich fuel gas (biogas) and fertiliser is discussed and found to be potentially beneficial in rural African situations. An experimental study on the fuelling of a portable engine-alternator set with simulated biogases (mixtures of methane, CH₄, and carbon dioxide, C0₂) is then presented. The only modification required for gas-fuelling of the engine (a normally petrol-fuelled, side-valve machine rated at 5,2 kW mechanical output) is the fitting of a simple commercially available gas feed adaptor. The engine runs reasonably smoothly on gases containing up to 31% C0₂; at higher C0₂ concentrations simultaneous fuelling with a pilot quantity of petrol is necessary. Replacement of petrol with pure CH₄ is found to result in a 17% loss in maximum power output. Increasing C0₂ content of the gas leads to further losses of maximum power, with a 35% loss at 31% C0₂. Specific fuel consumption data are presented and the overall efficiency of the unit (electrical output divided by calorific input) is found to be higher with gas-fuelling than with petrol. The loss in power on fuelling with biogas, instead of petrol, can be partially offset by increasing the compression ratio of the engine.

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