Soot Formation and Flame Characterization of an Aero-Engine Model Combustor Burning Ethylene at Elevated Pressure

Abstract

Swirl-stabilized, nonpremixed ethylenelair fiâmes were investigated at pressures up to 5 bar to study the effect of different operating parameters on soot formation and oxidation. Focus of the experiments was the establishment of a database describing well-defined fiâmes, serving for validation of numerical simulation. Good optical access via pressure chamber windows and combustion chamber windows enables application of laserinduced incandescence to derive soot volume fractions after suitable calibration. This results in ensemble averaged, as well as instantaneous soot distributions. Beyond pressure, parameters under study were the equivalence ratio, thermal power, and amount of oxidation air. The latter could be injected radially into the combustor downstream of the main reaction zone through holes in the combustion chamber posts. Combustion air was introduced through a dual swirl injector whose two fiow rates were controlled separately. The split of those air fiows provided an additional parameter variation. Nominal power of the operating points was approximately 10 kWI bar leading to a maximum power of roughly 50 kW, not including oxidation air.

Experimental Investigation of Soot Production and Oxidation in a Lab-Scale Rich–Quench–Lean (RQL) Burner

“…The goal here is to understand better how the quenching section of the RQL burner affects the flame front and soot formation and oxidation by systematically varying the amount and location of dilution air and investigating their effects through a series of optical and laser diagnostics. This variation of jet location and flow split will extend the understanding presently available on the effect of dilution on soot levels reported in Stöhr et al (2019), Geigle et al (2011Geigle et al ( , 2013Geigle et al ( , 2015aGeigle et al ( , b, 2017. These results will also serve to validate numerical investigations such as those presented in Giusti et al (2018).…”

“…However, ex situ diagnostics are extractive processes that perturb the flow, and the method of extraction can alter the physical and chemical properties of the soot particles so that they are no longer representative of combustion environments. Additionally, probes are most widely used with laminar flames, and while they can be used to measure size distributions in turbulent flames (Boyette et al 2017), they cannot measure the high levels of spatial and temporal intermittency of soot formation in turbulent flames identified in many studies (Wang et al 2019a, b;Lammel et al 2007;Geigle et al 2019;Stöhr et al 2019;Geigle et al 2011Geigle et al , 2013Geigle et al , 2017Bartos et al 2017;Qamar et al 2005Qamar et al , 2009Mahmoud et al 2017Mahmoud et al , 2018Köhler et al 2011;Narayanaswamy and Clemens 2013). These techniques can be used as an accompaniment to in situ laser diagnostics that are currently the main diagnostic techniques used to characterize sooting behavior in turbulent flames.…”

“…Turbulent flames exhibit spatial and temporal fluctuations not present in laminar flames, as well as shorter residence times that add a level of complexity to soot studies (Wang et al 2019a, b;Lammel et al 2007;Geigle et al 2011Geigle et al , 2013Geigle et al , 2017Geigle et al , 2019Stöhr et al 2019;Bartos et al 2017;Qamar et al 2005Qamar et al , 2009Mahmoud et al 2017Mahmoud et al , 2018Köhler et al 2011;Narayanaswamy and Clemens 2013). Qamar et al (2005) investigated soot volume fraction in simple jets (SJ), precessing jets (PJ), and bluff body flames (BB).…”

“…Swirling flows provide benefits such as flame stabilization and increased mixing, and understanding soot formation in these systems is of the utmost importance. Extensive work using laser diagnostics has been done on swirl stabilized, turbulent flames, premixed and non-premixed, using mostly gaseous fuels with some more recent work looking at liquid fuels (Wang et al 2019a, b;Stöhr et al 2019;Geigle et al 2011Geigle et al , 2013Geigle et al , 2015aGeigle et al , b, 2017Roussillo et al 2018). Geigle and coworkers have looked at the effect of equivalence ratio, thermal power, pressure, and secondary air injection on soot formation in swirl stabilized, turbulent non-premixed ethylene-air flames (Stöhr et al 2019;Geigle et al 2011Geigle et al , 2013Geigle et al , 2015aGeigle et al , b, 2017.…”

“…Their work focused on characterizing the flame and understanding soot formation and mitigation through the use of dilution air. They used instantaneous imaging to focus on the intermittent nature of soot and its sensitivity to gas composition, pressure, temperature, equivalence ratio, amount of oxidation air, and flow field effects such as strain and dilution (Geigle et al 2013). Simultaneous measurements revealed that the distribution of soot and OH changes with the addition of dilution air.…”