The effect of dimethyl ether addition on sooting limits in non-premixed counterflow flames

Regarded as one of the most promising alternative fuels, dimethyl ether (DME) plays a positive role in the reduction of combustion emissions, e.g., NOx, SOx, and soot particles. The effect of DME on the sooting limits was investigated systematically in counterflow diffusion flames of DME and ethylene mixtures. The primary technique conducted to rate sooting tendency was laser extinction and scattering. The critical fuel mole fraction (xf,cr) and critical oxygen mole fraction (xo,cr) at the point which soot started to appear in the elastic light scattering signal were recorded to evaluate sooting limits. In this work, the sooting limit map of ethylene/DME mixtures was developed based on the xf,cr and xo,cr. The highest sooting tendency appeared at around 6% of DME mixing ratio (β). When β>6%, the addition of DME decreases sooting propensity; to the contrary, when β< 6%, the addition of DME increases sooting propensity. Dilution conditions also affected the impact of DME addition. Additionally, sooting temperature index was introduced to rate sooting, where the limiting flame temperatures (Tf) were computed with Chemkin.