Experimental study on the interaction between flame propagation and wall film in a confined vessel

With applying the direct injection strategy, it is inevitable to develop a liquid fuel wall film, which would significantly affect the combustion process afterward. In this work, the interactions between the premixed flame propagation and wall film in a confined vessel were investigated thoroughly. The methane-air premixed mixture was used to generate the flame, while the wall films were prepared by directly placing liquid fuel onto a plate surface that attached inside of the combustion chamber. Besides laminar flame, a turbulent premixed flame was also induced by putting a cluster of columnar obstacles on the path of the flame propagation to study the effects of turbulent flame on film consumption. The flame propagation processes, as well as the pressure variations, were captured and recorded by a high-speed Schlieren photographic system and a pressure transducer, respectively. The flame morphology, propagation speed, and pressure characteristics were compared to each other under dry and film walls by varying initial conditions. The impact of different types of wall films and chamber structures (e. g., with and without narrow channels of different widths) on the flame propagation was also examined. Results indicated that the flame propagation process was accelerated because the high reactivity species within the film get vaporized and well mixed into the methane-air combustion mixture. Under turbulent combustion conditions, the vaporization and loss of the film were enhanced by the strong heat transfer as indicated by the Schlieren images observations. Furthermore, different fuel/oil films have different mass loss rates under combustion conditions due to the vaporization property. N-dodecane fuel film has the highest film loss rate, followed by diesel and lube oil film. In addition, the turbulent flame leads to higher film loss as well by increasing the heat transfer.

Automated summary

This study thoroughly investigated the interactions between premixed flame propagation and wall film in a confined vessel, showing that high reactivity species within the film vaporized and mixed into the combustion mixture, accelerating flame propagation. Under turbulent combustion conditions, the vaporization and loss of the film were enhanced.