The effect of poly(oxymethylene) dimethyl ethers (PODE3) on soot formation in ethylene/PODE3 laminar coflow diffusion flames

This paper investigates the effect of poly(oxymethylene) dimethyl ether(PODE3) on soot formation in ethylene/PODE3 laminar coflow diffusion flames. The flames were fuelled using ethylene/PODE3 mixtures, where up to 20% of the total carbon in the mixture was substituted with PODE3. Flame temperature measurements suggest that differences in the soot formation in the flames are more likely due to a chemical effect rather than a temperature effect. Colour ratio pyrometry and differential mobility spectrometry were used to measure the soot volume fraction and the particle size distribution of the flames. PODE3 was observed to be effective in reducing soot formation in previous engine studies. However, for the laboratory flames studied in this work, it was observed that introducing low levels of PODE3 actually increased the amount of soot. When PODE3 was blended with ethylene at 5%, there was an increase of about 10% in the soot volume fraction and about 6% in average particle size compared to the pure ethylene flame. Consideration of the chemical pathways suggests that this interaction is specific to C2 chemistry. Only when the amount of PODE3 was increased to 10% and 20% did the soot volume fraction and average particle size decrease compared to the pure ethylene flame. The results suggest that blending sufficient amounts of PODE3 with fuels could reduce soot formation, but that the use of too little PODE3 could increase soot formation in the cases of fuels that produce a substantial amount of C2 species in fuel-rich regions of an engine.