You're invited to attend
(Advisor: Prof. Wenting Sun)
"Investigation of Ozone Initiated Ethylene Oxidation at
Room Temperature: Chemistry and Flame Dynamics"
Friday, August 6
Being one of the most promising new concepts, ozone (O3) addition has been proved efficient in combustion enhancement and control. For saturated fuels, it is recognized that the O3 decomposition at elevated temperatures dominantly contributes to the improvement. However, for unsaturated fuels, the knowledge is still quite limited, due to the much more complicated kinetic pathways induced by direct reaction between fuel and O3, i.e., the ozonolysis reaction.
In this work, the O3 initiated ethylene (C2H4) oxidation is experimentally investigated at T = 298 K using multiple diagnostic methods. To accommodate the nearly immediate reaction between C2H4 and O3, a novel flow reactor system with online fast-mixing feature is designed, manufactured, and applied. By coupling the flow reactor system to 255 nm UV LED absorption technique, the global reaction rate constant of C2H4+O3 is re-evaluated at current experimental conditions. Being supplementary to former studies, abundant new products and intermediates are successfully identified using both gas chromatography and tunable photoionization mass spectrometry. Based on determined molecular structures, the detected species can be mainly categorized into alcohol, aldehyde, and peroxide, while many of them have been widely considered key intermediates in low-temperature oxidation chemistry. Moreover, direct probing and characterization of multiple highly reactive organic peroxy radicals are succeeded in this work, which are proposed to be generated via either classic low-temperature oxidation mechanism or possible bimolecular reaction between radicals and stabilized Criegee Intermediate.
Additionally, the effect of ozonolysis reaction on laminar flame dynamics is studied. Stable C2H4 lifted flames are established with oxygen/nitrogen co-flow at reduced oxygen content conditions. By adding certain amounts of O3 into the oxidizer co-flow, inconsistent flame dynamic behaviors are recorded. Depending on the initial value of the flame liftoff height before O3 is added, it is observed that the lifted flame could either ascend or descend. Formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) measurement shows that prompt ozonolysis reaction between C2H4 and O3 produces large amounts of CH2O upstream of the flame. In contrast to previous studies of O3 addition on lifted flames—with saturated fuels in which O3 decomposition dominates—the ozonolysis reaction between C2H4 and O3 considerably changes the chemical composition of flow even at room temperature. Such chemical reaction causes the simultaneous increase of both the triple flame propagation speed of lifted flame and the axial jet velocity along the stoichiometric contour, which also therefore changes the dynamic balance between these two values to stabilize the flame. While the increase of triple flame propagation speed tends to decrease the flame liftoff height, the increase of axial jet velocity along the stoichiometric contour tends to have the opposite effect. A competing kinetic-dynamic process forms, and the final location of the flame depends on the degree of ozonolysis reaction, which is determined by the initial flame liftoff height before O3 is added.
- Prof. Wenting Sun – AE, Georgia Institute of Technology (advisor)
- Prof. Jechiel Jagoda– AE, Georgia Institute of Technology
- Prof. Lakshmi Sankar – AE, Georgia Institute of Technology
- Prof. Ellen Yi Chen Mazumdar – ME, Georgia Institute of Technology
- Prof. Adam Steinberg – AE, Georgia Institute of Technology
- Dr. Timothy Ombrello – Senior Research Aerospace Engineer, Air Force Research Laboratory, Wright-Patterson AFB, OH