58622 - Synergistic Effect of Soot Formation in Ethylene/propane Co-Flow Diffusion Flames at Elevated Pressures 

The synergistic effect of soot formation refers to the interaction between different fuels during soot formation process, which results in higher soot than any individual fuels at certain mixture ratios. The present study experimentally investigates the synergistic effect of soot formation in co-flow diffusion flames of gaseous hydrocarbon fuel mixtures including methane/ethylene, ethane/ethylene, and propane/ethylene. The fuel carbon mass flow rate in the fuel stream was kept constant at 0.5 mg/s, and the volume flow rate of oxidizer stream was 15.75 L/min for all cases. The laser-induced incandescence (LII) technique was applied to measure the soot volume fractions at pressures of 1-5 atm. Argon was used to replace the nitrogen in the oxidizer stream to increase the flame temperature due to its lower specific heat capacity. Oxygen concentration in the oxidizer stream was also varied to study its effect on the soot formation. The results showed strong synergistic effects in the mixtures of propane/ethylene and ethane/ethylene at atmospheric conditions; meanwhile, it was interesting to find that the synergistic effect decreases with increasing pressure. On the contrary, synergistic effect of propane/ethylene mixture is slightly enhanced when using argon replacement, which was considered as the temperature effect. It was found that soot volume fraction of propane/ethylene mixture first increases and then decreases with increasing oxygen concentration, while the synergistic effect is insensitive to the variation of oxygen concentration. It should be noticed that the flame temperature has ever been found to be decreased when pressure increases in sooty co-flow diffusion flames. Therefore, the decreased flame temperature may partly contribute to the mitigated synergistic effect with increasing pressure.