Numerical procedure for prechamber transfer from a single-cylinder engine to a rapid compression machine

Abstract

This paper presents a method for transferring a prechamber from a single-cylinder engine (SCE) to a rapid compression machine (RCM) as a pre-step for carrying out optical experiments. The overall objective of the transfer procedure is to achieve similar flow field conditions in the prechamber which is mounted on an RCM as compared to the same prechamber mounted on an SCE. Computational fluid dynamics (CFD) simulations of a large-bore natural gas SCE were carried out up to ignition timing which serve as the basis for the transfer procedure. The mass-flow rate in the prechamber neck, pressure difference between the main chamber and prechamber, prechamber pressure and mass in the prechamber were defined as the governing thermodynamic quantities which affect the evolution of the flow field in the prechamber during the compression stroke. All of these quantities in an RCM are largely influenced by operating piston speed and compression ratio for given initial conditions. The RCM operation parameters for each governing quantity were estimated with the help of 0D simulations. CFD simulations of RCM were performed for the determined RCM operation parameters, and the evolution of the velocity field and turbulent quantities in the prechamber were evaluated. The procedure has been applied to two prechambers of different shape and size and a good agreement between the RCM and corresponding SCE CFD simulations was achieved for the flow field conditions in both of the prechambers near the ignition timing. It was found that mass-flow rate in the prechamber neck is the most important quantity which influences the prechamber flow field. Overall this numerical procedure provided a flexible and computationally feasible approach to adjusting RCM operation parameters for transferring a prechamber from the SCE to RCM.