A methodology to formulate multicomponent fuel surrogates to model flame propagation and ignition delay

Abstract

Nowadays, the leading driver for the development of internal combustion engines is the search for increased fuel efficiency and reduced emissions. To develop and optimize new combustion systems, a high degree of accuracy is needed in 3D-CFD simulations. In particular, detailed chemical kinetics models and fuel surrogates able to represent the main physical and chemical properties of the real commercial fuels are needed. A series of fuel surrogate formulation methodologies were presented in the recent past with the aim of matching fuel properties and combustion-related characteristics using a set of well-known compounds. While most of the gasoline-targeted available studies mainly focused on the possibility to simultaneously match the gross fuel properties, the evaporating characteristics and the auto-ignition behaviour of the fuel, none of them explicitly targeted the flame propagation characteristics. In this work, a novel methodology is introduced to formulate gasoline fuel surrogates able to match the main chemical and physical properties, the auto-ignition and the flame propagation characteristics of a commercial gasoline. Due to the increasing presence of oxygenated fuels in the market share, an average gasoline fuel named ULG95, representative of a European oxygenated gasoline with Research Octane Number RON = 95, is targeted to validate the presented methodology. Three fuel surrogates of increasing complexity are formulated and validated against laminar flame speed, shock-tube and rapid compression machine experiments available in literature for oxygenated gasolines. The results suggest that a unique gasoline fuel surrogate can be used, together with validated chemical kinetics mechanisms, to model auto-ignition and flame propagation characteristics.