Effects of diethyl ether addition on sooting transition in iso-octane counterflow diffusion flames

Abstract

This study studied the effects of the addition of diethyl ether (DEE) in the fuel stream on sooting transition process in iso-octane counterflow diffusion flames with optical and chemical diagnostics. Compared with the baseline iso-octane flame, two fuel/oxygen/nitrogen flames were studied with a 20 % DEE/iso-octane and a 40 % DEE/iso-octane mixture as the fuel, while holding constant fuel mole fraction. Optical diagnosis was used for the investigation of the effect of DEE addition on macroscopic sooting transition point with a high-resolution digital camera based on image processing and transition point extraction methods. Online gas chromatograph (GC) was used for all flames to investigate the flame structure and measure quantitative mole fraction profiles of stable and reactive species formed in the sooting transition process, especially the changes caused by partial substitution of iso-octane by DEE. Meanwhile, the experimental results were compared with predictions from a model suitable for both iso-octane and DEE. Sooting transition point was delayed with the increase of DEE addition. Although the overall flame chemical structure did not change significantly with the addition of DEE, it was found that some primary decomposition products and precursors had more significant effects. In most cases, experimental trends could be predicted and explained well by the model. It was noted that the dilution of carbon flow caused by partial substitution was the main reason for the inhibition of soot formation and the delay of sooting transition point. Secondly, on the chemical effect, DEE addition could produce a large amount of C2H2 which could contribute to the production of C3H3 and the formation of large PAHs.