Simulation and Modeling of Direct Gas Injection through Poppet-type Outwardly-opening Injectors in Internal Combustion Engines

Abstract

The obligation for the development of highly efficient and low-emission combustion engines has renewed interest in compressed natural gas (CNG) engines using a direct injection (DI) system. CNG has high knock resistance, and with the use of DI, the volumetric efficiency can be increased compared to port-injected CNG engines. Additionally, carbon dioxide and particulate emissions are lower due to a high hydrogen-to-carbon ratio. Therefore, the DI-CNG technology has the potential to surpass the thermal efficiency of conventional gasoline spark-ignition engines while producing lower emissions. However, the design of DI-CNG engines is challenging because of gaseous and, hence, highly compressible fuel running through small injector passages, which results in complex supersonic flows with shocks. The supersonic gas jets emerging from the injector outlet interact with the in-cylinder flow field, which has an impact on fuel–air mixing and combustion. Therefore, it is essential to understand the fundamental physics of the injection process to develop modeling strategies for DI-CNG systems and further study the influence of direct gas injection on the in-cylinder flow field and mixing. To this end, the current chapter is dedicated to the fundamental understanding of the gas injection process through poppet-type outwardly-opening injectors. The DI modeling strategies are discussed for the application in engine simulations. Furthermore, the impact of gas injection on the in-cylinder flow field and fuel–air mixing is analyzed for centrally-mounted injector configurations.