Abstract
Large bore natural gas engines with pre-chamber combustion systems are increasingly gaining popularity for marine and rail propulsion due to their high power density potential combined with high efficiency. Moreover, these engines have the ability to fulfill very demanding emission targets without costly after-treatment systems. A challenge in the layout of high powered gas engines is the narrow operating window at high loads and high efficiency with respect to the mechanical, knocking and emission limits. Therefore, the application of advanced CAE tools is an appropriate method to efficiently optimize the operation parameters as well as the geometry of the pre-chamber and the main combustion chamber. This publication presents a fast and efficient 3-D CFD combustion, NOx and an auto-ignition model to be used in the combustion layout of scavenged pre-chamber natural gas engines. A detailed 3-D CFD gas exchange and combustion model of a single cylinder research engine was set up. The model included the gas injection and mixture formation in the intake port as well as in the pre-chamber. A prescribed burn rate combustion model was chosen for the CFD simulations. A NOx formation model based on the extended Zeldovich mechanism was programmed with reduced number of scalars in the CFD model. A fast running integral based model, which was calibrated to detailed chemistry, was implemented in 3-D CFD to model the auto-ignition in the unburnt gas. The presented models have been calibrated to experimental results.