Impact of Flame Lifting on Nitrogen Oxide Emissions from Premixed Reacting Jets in a Vitiated Crossflow

This paper describes measurements of nitrogen oxide (NOx) emissions from reacting jets in crossflow (RJICF). Primary factors that influence RJICF NOx emissions are: jet stoichiometry, mixing between jet and crossflow before combustion, and mixing of the remainder of the crossflow with the combustion products of the secondary combustion region. The aforementioned mixing is controlled by shear layer vortices and the counter-rotating vortex pair, as well as flame lifting. The coupled effects of bulk averaged temperature rise as a result of the RJICF (Delta T), jet stoichiometry (phi(Jet)), and momentum flux ratio (J) present a challenge in understanding critical factors controlling NOx production as it is difficult to vary them independently. Therefore, significant attention was paid to designing a test matrix that differentiated these effects. The data reported herein were obtained from the injection of premixed ethane/air or ethane/methane/air mixtures into a vitiated crossflow at one of two temperatures (1350K and 1410K). Varying the ethane/methane ratio allowed for systematic variation of flame lifting independent of phi(jet) and J. The jets contained sufficient fuel to create an adiabatic bulk temperature rises from 75K - 350K, with J values from 8 - 40, and phi(jet) values from 0.8 - 8.0. The reported measurements confirm that NOx emissions increase monotonically with Delta T, as discussed in literature, but also indicates that the lifting of the flame significantly impacts NOx production. Lifting itself is a function of the variables described above and was quantified with chemiluminescence imaging. In fact, flame lifting is the dominant factor influencing NOx emissions, including Delta T.