A Model for Predicting Turbulent Burning Velocity with Low-Temperature Oxidation Reactions in Unburned Mixtures

Improving turbulent burning velocity under exhaust gas recirculation (EGR) conditions can increase thermal efficiency of spark-ignition (SI) engines. In the one-dimensional (1D) model-based development approach, the turbulent combustion under EGR conditions should consider the influences of enhanced turbulent intensity, dilution-induced flame stretch, and low-temperature oxidation reactions. In this work, the authors have developed a model to predict turbulent burning velocity with low-temperature oxidation reactions in unburned mixtures. Low-temperature oxidation reactions are calculated using a zero-dimensional detailed kinetics simulation. The model considers the effects of turbulent intensity, unstretched laminar burning velocity, Markstein number, and Karlovitz number. Markstein number is calculated using a detailed kinetics simulation by Opposed-Flow flame model, while Karlovitz number is predicted using three-dimensional computational fluid dynamics with detailed kinetics. Boundary conditions and model inputs are taken from experiments under various engine loads, speeds, and EGR rates of a single-cylinder gasoline engine equipped with a high tumble-port. The model also accounts for the effects of partial oxidation and low-temperature heat release on the flame stretch. The developed model is then implemented into a 1D engine model to predict the SI combustion characteristics under EGR conditions. As a result, the measured combustion data from the SI engine are reproducible using the developed model.