Anaerobic digestion is a popular method of treating sewage sludge. Biogas or sewage gas is a by-product of this process. Significant volumes of biogas are produced at many sewage treatment works and also at some landfill sites from the natural breakdown of municipal waste. This biogas can be used as a fuel for an engine and generating set, producing electrical power and heat.A multi-cylinder two-stroke cycle system, capable of being retrofitted to current production four-stroke cycle engines, is proposed, primarily for the combustion of biogas in combined heat and power applications. The engine incorporates features to give good tolerance to the corrosive agents associated with biogas. This paper describes the design and initial development of a purpose built single cylinder research engine to investigate this concept. A low pressure direct injection system which has been developed for use with the engine is also outlined. Finally, some results from the initial running of this engine on actual biogas are presented.