Fuel wall film effects on premixed flame propagation, quenching and emission

摘要

A fuel wall film has been a primary cause for emissions of unburnt hydrocarbons and soot in modern internal combustion engines, especially considering the more and more stringent emission regulations. When a premixed flame propagates towards a wall film with liquid fuel, the fuel vaporization flux and the concentration stratifications upstream of the flame will fundamentally affect the flame structure and propagation speed. More importantly, it is expected that the premixed flame might be more difficult to quench due to the increased amount of fuel entrainment entering the flame zone, which further affects the amount of unburned hydrocarbon emissions. In this work, investigation of a laminar premixed flame propagating toward fuel wall films in a constant volume reactor has been conducted using software CONVERGE. User defined functions describing the heat and mass transfer at the fuel wall film surface have been implemented as the boundary condition. Parametric studies have been further conducted to demonstrate the effect of initial chamber temperature and pressure. The results lead to useful insights on the interaction of flame propagation and wall film in relevant engine combustion conditions, and shed light on potential wall functions to be applied in 3D in-cylinder combustion for the prediction of soot and unburnt hydrocarbon emissions in the existence of fuel wall film.