A modeling study on the combustion characteristics of alcohol/diesel dual fuel counterflow flame

This study combines a 0D Well Stirred Reactor (WSR), 1D counterflow flame, experimental data, and a 1D gas dynamic model to create an integrated modeling tool to study the dual fuel combustion behavior in engine-relevant conditions, fueled with E85 and diesel fuels. First, the performance of a reduced chemical kinetic mechanism is studied, and the most important reactions are identified. Subsequently, the validated mechanism is utilized to investigate ignition and flame propagation characteristics, and to analyze the combustion mode in different thermal and compositional stratification levels. The results reveal that under the studied operating conditions, auto-ignition of the background mixture was unlikely due to long ignition delay times compared to experimental combustion durations. Instead, the combustion mode is more of a partially premixed flame and diffusive combustion influenced by reactivity and thermal stratification. The effects of thermal stratification revealed that at higher temperatures of the background mixture, the location of the most reactive mixture fractions moves to the richer sides. Notably, low-temperature ignition behavior reflects the existence of cool flame chemistry near the stoichiometric zone, where intermediate species like formaldehyde form before full heat release occurs. When the oxidizer temperature increases further, a secondary, most reactive mixture fraction can be observed on the oxidizer (lean) side. Temperature and heat release rate profiles also revealed that at lower oxidizer temperatures, the heat release rate shows more traditional diffusive combustion behavior. However, at elevated temperatures, the secondary heat release rate, which corresponds to flame propagation, becomes more prominent. Increasing the ratio of E85 to diesel also influences the partially premixed flame propagation and its heat release. When the oxidizer temperature or E85 content is increased, the location of the secondary heat release moves further away to the oxidizer side, away from the stoichiometric region.