One Dimensional Modeling of a Turbogenerating Spark Ignition Engine Operating on Biogas

Turbocompounding is generally regarded as the process of recovering a proportion of the exhaust gas energy from a reciprocating engine and applying it to the output power of the crankshaft. In conventional turbocompounding, the power turbine has been mechanically connected to the crankshaft but now a new method has emerged. Recent advances in high speed electrical machines have enabled the power turbine to be coupled to an electric generator. Decoupling the power turbine from the crankshaft and coupling it to a generator allows the power electronics to control the turbine speed independently in order to optimize the turbine efficiency for different engine operating conditions. Some renewable electricity is presently being generated from compression ignition engines fuelled primarily on biogas using a small proportion of injected palm oil to initiate combustion. Spark ignition engines are being considered as an alternative lower cost option. This paper considers the challenges of implementing turbogenerating on a spark ignition engine operating on biogas. The 1D engine simulation work reported in the paper shows the required air/fuel ratio, compression ratio, ignition timing, valve timing and turbomachinery specifications in order for the engine to operate at maximum efficiency. The predicted performance of the turbogenerated spark ignition engine is compared with that of an equivalent turbocharged spark ignition engine also operating on biogas.