Analysis of a Syngas HCCI Engine for CHP Biomass Gasification Facilities

The downdraft fixed-bed gasifier is well adapted to decentralized combined heat and power (CHP) facilities. It can use locally available biomass as well as polluted wastes. However, the use of conventional internal combustion engines requires cooling down the produced syngas to avoid knocking. This requires a specific filtering step to remove the condensable tars that could otherwise damage the engine. These complex cooling and scrubbing steps account for one third of the gasification facility costs and involve a great amount of maintenance. In this context, we investigate the use of the Homogeneous Charge Compression Ignition (HCCI) engine which can be directly operated with the hot gas and thus avoid condensing the tars. This paper first presents the validation of a Computational Fluid Dynamics (CFD) model that uses the Tabulation of Dynamic Adaptive Chemistry (TDAC) model to include a detailed combustion kinetic mechanism. This validation is performed with experiments on an HCCI engine operated with synthetic syngas at typical composition and inlet temperatures around 180°C. This model is then used to investigate the combustion characteristics at a higher inlet temperature which avoid the condensation of tars. It also gives the engine settings that keep the combustion timing near top dead center and maintain the maximum pressures and maximum pressure rise rates within the engine constraints. The engine settings are an important prerequisite to design the HCCI engine. Other parameters might affect the engine performance and durability and will therefore remain the focus of future work.