Appropriate structural parameters of biogas SI engine converted from diesel engine

A simulation of effects of combustion chamber shape, compression ratio, and spark timing advance to the performance of a biogas spark-ignition (SI) engine converted from a diesel engine is presented. It is a comparative research which uses computational fluid dynamics (CFD) software FLUENT for identifying basic structural parameters of the diesel engine that could be modified in order to obtain a high performance biogas engine. The presence of CO₂ in biogas fuel slows down the burning velocity of the mixture, thus any mechanisms speeding up the combustion would be desirable. Under the same operating conditions of biogas engine, an increase of indicated cycle work is observed as replacing flat combustion chamber shape by omega combustion chamber shape. Optimal spark timing advance of a biogas engine is greater than that of a gasoline engine and it depends on engine speed and/or on CH₄ fraction in the biogas. At rated regime of engine fueled with normal biogas, the results pointed out an optimal value of compression ratio. The research is successfully applied to convert a typical ZH1115 diesel engine to a biogas SI engine. The evidence developed from this research can be applied to any other diesel engine.