Quasi-dimensional analysis of combustion, emissions and knocking in a homogeneous GDI engine

Abstract

A quasi-dimensional model is developed with the surrogate mechanism of isooctane and n-heptane to predict knock and emissions of a homogeneous GDI engine. It is composed of unburned and burned zone with the latter divided into multiple zones of equal mass to resolve temperature stratification. Combustion is based on turbulent entrainment and burning in a spherically propagating flame with the entrainment rate interpolated between laminar and turbulent flame speed. Validation is performed against measured pressure traces, NOx and CO emissions at different load and rpm conditions. Comparison is made between predictions by the empirical knock model and the chemistry model in this work. There is good agreement for pressure, NOx, CO and knock for the test engine. Promising results are obtained through parametric study with respect to octane number and engine load by the chemistry knock model.