Laser-induced incandescence for soot measurements in an aero-engine combustor at pressures up to 20 bar

Abstract

Soot is one of the most discussed pollutants in ground and air traffic. Moreover, its effect as source of intense radiation is significant as soon as locally rich mixtures occur, especially at increased pressure. This motivates the need to better understand soot formation and oxidation in turbulent, pressurised environment in order to prevent its emission as much as possible. A detailed understanding of the underlying processes can be gained when correlating sophisticated CFD modelling with well-defined validation experiments at technical conditions. LII has proven to be a valuable diagnostic to quantitatively monitor soot distributions inside combustion processes. However, application to pressurized gas turbine combustors has rarely been published for several reasons. Here, we present trends for soot distributions inside at technical combustor operated between 4 and 20 bar at realistic geometries and flow rates. Considerations on tackling typical challenges at technical conditions are presented. The resulting time-averaged soot distributions serve to determine positions of soot formation and oxidation as well as quantification of soot concentrations under the highly challenging technical conditions of the study. In general, soot concentrations were found to be relatively low. In combination with data derived independently from the present work, involving application of other diagnostics (OH and kerosene distributions as well as temperatures), a good validation data set is available to support soot modellers.

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

“…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).…”

Effects of pressure on soot production in piloted turbulent non-premixed jet flames

“…An Nd:YAG 165 laser (same laser as for the LII but with higher energy for ignition) was used to ignite the pilot flames by sparking off the central fuel tube. transfer of the LII calibration from ambient conditions to higher pressures [18].…”

“…Multiple diagnostics have been used to characterize a number of flames in this gas turbine model combustor, including: laser-induced incandescence and OH chemiluminescence [14]; 55 LII, laser-induced fluorescence of OH, and coherent anti-Stokes Raman scattering [15]; LII with laser-induced fluorescence of polycyclic aromatic hydrocarbons [16]; and high-speed stereoscopic particle image velocimetry with laser-induced fluorescence of OH [17]. More recently, LII was performed on a few conditions up to 20 bar using kerosene as the fuel [18]. Because of the complexity of this 60 configuration, including differences in global equivalence ratio and the addition of oxidation air through a secondary inlet in some cases, it is difficult to isolate the effect of pressure on a representative soot volume fraction parameter.…”

A comparison between fossil and synthetic kerosene flames from the perspective of soot emissions in a swirl spray RQL burner

“…This study highlights the importance of testing with liquid fuels as these dynamics may not be captured properly in flames with gaseous fuels [15]. Measurements of soot volume fraction (f 𝑣 ) on an aero-engine combustor operating with a kerosene spray at elevated pressures were performed by Geigle et al [16] simulating various stages of the engine's operations during flight. Instantaneous images of 𝑓 𝑣 showed relatively small, point-wise soot filaments that vary greatly both spatially and temporally with many images not containing any detected signal.…”