Soot Formation in a Laminar Non-Premixed Planar Mixing Layer Flame (PMLF) Fueled by Ethylene Doped with Iso-Dodecane

CHRISTIAN P. BJORK, Evangelos K. Stefanidis, Mahmoud K. Ashour, Scott W. Wagnon, Chiara Saggese, Francesco Carbone, University of Connecticut

     Abstract Number: 250
     Working Group: Combustion

Abstract
Iso-dodecane isomers are pivotal components of any surrogate mixture of Sustainable Aviation Fuels (SAFs) whose usage would, therefore, be accelerated by developing a validated chemical kinetic model of their combustion. This development requires an experimental database unraveling the complex pyrolysis and oxidation chemistry of such long-chained and highly-branched alkanes. Hence, this study examines the doping of a slightly sooting laminar non-premixed, ethylene-fueled, Planar Mixing Layer Flame (PMLF) with 1500 ppm of 2,2,4,6,6-pentamethyl-heptane. The PMLF is unconfined and stabilized between adjacent slot jets of the fuel and oxidizer streams being sandwiched between annular shielding nitrogen. The flow is stabilized by exhausting the hot buoyant flame products through a slot in a plate onto which the remaining cold flow impinges. Importantly, any horizontal cross-section of the PMLF has the self-similar structure typical of a boundary layer that grows at increasing Height Above the Burner (HAB) and can be modeled as a 1D Counterflow Flame (CF) which is several millimeters thick and, hence, not accessible in CF experiments. Thanks to these characteristics, the PMLF is ideal for performing spatially resolved measurements with minimal effects of the sampling-induced perturbations, to develop and validate detailed chemical kinetic models. The horizontal profiles of C0-C18 gas species and soot are measured at HAB = 25 and 50 mm using capillary sampling followed by GC/MS analysis and Laser Induced Emission Spectroscopy (LIES), respectively. The comparative analysis of the results in the baseline PMLF fueled only by ethylene with those in the doped PMLF in which 1500ppm of ethylene with 2,2,4,6,6-pentamethyl-heptane demonstrates that the doping boosts the mole fraction of several aromatics and the soot volume fraction at both HABs by approximately 120% and 50%, respectively. The experimental results partially validate the tested state-of-the-art detailed kinetic model and also point toward the further improvement of its predictive capabilities.