Effect of dimethyl ether (DME) addition on sooting limits in counterflow diffusion flames of ethylene at elevated pressures

Abstract

The effects of dimethyl ether (DME) addition to ethylene fuel on sooting tendencies with varying pressure were investigated in counterflow diffusion flames by using a laser scattering technique. Sooting limit maps were determined in the fuel (XF) and oxygen (XO) mole fraction plane, separating sooting and non-sooting regions. The results showed that when DME is mixed to ethylene, the sooting region was appreciably shrank, especially in the cases of soot formation/oxidation (SFO) flames as compared with the cases of soot formation (SF) flames. This indicated an inhibiting role of DME on sooting. An interesting observation was that the critical XO required for sooting initially decreased and then increased with the DME mixing ratio to ethylene β for the cases of SF flames, exhibiting a non-monotonic behavior. This implied a promoting role of DME on sooting when small amount of DME is mixed to ethylene. As the pressure increased, the sooting region generally expanded. Specifically, the range of β in promoting soot formation extended with pressure. This implies that a strategy in reducing soot by adding DME to ethylene at high pressures required a large amount of DME addition. To interpret the observed phenomena, kinetic simulations including reaction pathway and sensitivity analyses were conducted with the opposed-flow flames model using the KAUST-Aramco PAH Mech. The results showed that the thermal effect of DME addition on sooting tendency monotonically decreases with . The chemical effect was found to be the main contributor to the DME addition effect on sooting tendency, resulting in the non-monotonic sooting limt behavior. The pathway analysis showed the role of methyl radicals generated from DME promoted incipient benzene ring formtion when small amount of DME was added, which can be attributed to the soot promoting role of DME addition for small β.

Investigation of Thermal Radiation from Soot Particles and Gases in Oxy-Combustion Counter-Flow Flames

“…Therefore, the incipient soot formation was studied by varying the mole fraction of oxygen in the oxidant stream for a given mole fraction of fuel in the fuel stream, similar to the definition of Z st . Incipient soot formation is generally referred to as the sooting limit, which has been studied by many scholars, especially in diffusion flames [32][33][34]. Figure 4 shows the three calculated iso-T ad (solid lines) and six calculated iso-Z st (dotted lines) curves in the O 2 /CO 2 atmosphere, highlighting that flames with a lower T ad have larger ranges of Z st , corresponding to more varied flame structures.…”

Morphology and Nanostructure Transitions of Soot with Various Dimethyl Ether Additions in Nonpremixed Ethylene Flames at Different Scales

“…19−22 Among them, DME has been regarded as a promising renewable bioenergy with many favorable properties such as the low C/H ratio and particulate emission. 15,23,24 Due to the merits above, DME was extensively adopted as alternative fuel or fuel additions to enhance combustion performance and reduce soot emissions in various flame configurations such as inverse diffusion flames, 14,18 counterflow diffusion flames, 15,23,25 jet diffusion flames, and premixed flames. 17,26,27 For example, Wu et al 26 experimentally and numerically investigated the effect of DME addition (5 and 10%) on PAH and soot formation in premixed plat flames.…”

A comparative study of the sooting tendencies of various C5–C8 alkanes, alkenes and cycloalkanes in counterflow diffusion flames

“…Although not abundant, several sooting tendency studies have been performed in CDFs, through the measurement of either peak soot volume fraction [48] , [49] , [50] or critical sooting condition (i.e. sooting limit) [ 51 , 52 ]. In a previous study [19] , we also investigated the sooting tendencies of various C 1 –C 4 gaseous fuels in CDFs, and proposed an alternative sooting index for rating sooting tendency of different fuels, i.e.…”