Burner Platform for the Investigation of Ozonolysis-Assisted Flame Speeds

This study presents a new coinjected reactor-assisted Bunsen (CRAB) burner for the experimental investigation of ozonolysis-assisted flame speeds at atmospheric pressure and room temperature. The CRAB burner's capacity to modify the residence time of the ethylene/air/ozone mixture prior to the flame front is crucial for controlling the extent of ozonolysis reactions and ozone consumption. The experimental measurements reveal that, with ozone addition and the subsequent ozonolysis reactions, longer residence times result in higher pre-flame temperatures, which lead to an increase in the flame speed. The flame speed enhancement by ozone is the largest for high ozone concentrations and off-stoichiometric mixtures. One-dimensional numerical simulations employing detailed chemical kinetic models are able to capture the enhancement of the flame speed quite accurately through the use of a plug flow reactor in combination with a freely-propagating laminar flame. However, the absolute flame speeds predicted by the simulations are not always in agreement with the experimental measurements, particularly for mixtures with lean equivalence ratios. Further analysis of the results shows that the adiabaticity of the upstream flow reactor has an enormous influence on the flame speed enhancement by ozone; in fact, the temperature rise is the dominant mechanism for the increase in the flame speed. The kinetic effects of ozonolysis reactions, which are much less impactful that the thermal effects, can lead to a decrease in the flame speed at extended residence times due to radical recombination. © 2021 American Chemical Society.