Transportation Engineering (Dec 2020)
Modelling of combustion and knock onset risk in a high-performance turbulent jet ignition engine
Abstract
The reduction of CO2 emissions, and hence of fuel consumption, is currently a key driver for the development of innovative SI engines for passenger car applications. In recent years, motorsport technical regulations in the highest categories have seen the introduction of limits concerning the fuel flow rate and the total amount of fuel per race, thus driving engine development toward further reduction of specific fuel consumption. Among the different techniques that can be shared between conventional and high-performance SI engines, turbocharging, compression ratio increase and Turbulent Jet Ignition (TJI) have shown a significant potential for fuel consumption reduction. The combination of turbocharging and compression ratio increase, however, can promote the onset of knocking combustion, with detrimental effects on engine's efficiency and durability. Additionally, engines equipped with TJI systems show unusual combustion development and knock onset.In this study a methodology for the 3D-CFD modelling of combustion and knock onset risk was developed for a high-performance turbocharged engine featuring a passive TJI system. First, a comprehensive numerical study was carried out in a commercially available software, CONVERGE 2.4, in order to develop a 3D-CFD model able to reproduce the available experimental data. The resulting 3D-CFD model was then validated on different working conditions featuring different spark advances. Lastly, a methodology for the assessment of knock onset risk was developed, which led to the definition of two novel knock-risk indexes based on the progress of chemical reactions within the combustion chamber. The proposed knock-risk indexes showed good agreement with the experimental data.
