Experimental study on the effect of different CO2 concentrations on soot and gas products from ethylene thermal decomposition

This research work reports a laboratory study of the influence of environments with different CO2 levels, representative of conditions in which exhaust gas recirculation is used in combustion systems, on soot and gas products formed in the thermal decomposition of ethylene–CO2 mixtures. The investigation includes experiments, in a flow reactor, with 30,000 ppm of ethylene at different experimental conditions of temperature (975–1475 K) and CO2 concentrations (25%, 50% and 78.5%), using nitrogen as bulk gas. The analysis is performed by comparison with the data obtained during the pyrolysis of ethylene in a N2 atmosphere. esent results highlight the importance of the CO2 level in the system, since the presence of 25% CO2 tends to promote the formation of soot, whereas an increased CO2 addition of 78.5% leads to a diminution in the production of soot, compared to the pyrolysis of pure ethylene in N2. The different evolution in soot formation tendencies can be attributed to competing reactions that gain importance depending on the different CO2 levels, boosting or suppressing soot formation as function of the composition of both the O/H radical pool and the reacting species. The outlet concentrations of H2, CO and C2H2, as well as the formation of H2O, are directly related to the different soot-forming tendency found as function of different CO2 environments.