Similarity Issues of Kerosene and Methane Confined Flames Stabilized by Swirl in Regard to the Weak Extinction Limit

Abstract

One of the most promising methods for reducing NO x emissions of jet engines is the lean combustion process. For realization of this concept the percentage of air flowing through the combustor dome has to be drastically increased, which implies high volume fluxes in the primary zone of the combustion chamber and represents a substantial challenge in regard to the flame stabilization. Swirl motion is thus applied to the air flux by the swirl generator and decisively contributes to the flame stabilization. The current paper reviews an atmospheric investigation of a burner configuration in regard to the weak extinction limit, comprising a confined nonpremixed swirl-stabilized flame. The burner can be supplied with either kerosene or after a small adaption with natural gas (methane). Therefore, a comparison of a kerosene-fuelled flame (spray flame) to a natural gas fuelled one (methane flame) can be performed. Both are realized by almost identical burner configuration and at identical conditions. The main idea of this work is to align the stability characteristics of both flames by means of similarity. However, fundamental differences regarding the flame structures of the flames are detected through in-flame measurements. This determines the limits of the current approach and motivates an appropriate choice of flame modeling. Flow Turbulence Combust (2012) 89:73-95 A Area [m 2 ] AFR Air-Fuel Ratio [-] α Thermal diffusivity C Reaction progress [-] Da Damköhler-number [-] Da t turbulent Damköhler-number [-] D Diameter of comb. chamber [m] D/d Flow expansion ratio [-] d Nozzle throat diameter [m] D Angular momentum [kg·m 2 /s] IRZ Inner Recirculation Zonė I Axial momentum [kg·m/s] k turbulent kinetic energy, mass specific Ka Karlowitz-number [-] L t integral length scale [m] L length of contact zone [m] LBO Lean blowout LDA Laser Doppler Anemometrẏ M Mass flow rate [kg/s] ORZ Outer Recirculation Zone PDA Particle Dynamics Analysis PERM Partially Evaporated, Rapidly Mixed Pe Peclet-number [-] p Pressure in the chamber [bar] r radial position [m] R 0 Nozzle exit radius [m] Re t turbulent Reynolds-number S Swirl Number [-] S t turbulent flame velocity [m/s] S lam laminar flame velocity [m/s] SMD Sauter Mean Diameter [m] T Temperature [K] U 0 Nozzle exit volumetric velocity at referenced condition [m/s] U lim Nozzle exit volumetric velocity at LBO [m/s] UHC Unburned hydrocarbons [-] u mean axial velocity [m/s] u', v', w' velocity fluctuations [m/s] u 2 , v 2 , w 2 normal Reynolds stresses [m 2 /s 2 ] x Axial position [m] p/p normalized pressure loss [%] 3D Three dimensional Flow Turbulence Combust (2012) 89:73-95 75 2D Two dimensional χ, Mass flow rate split [-] φ Equivalence ratio [-] ν kinematic viscosity [m 2 /s] λ 1/φ τ time scale [s]

Numerical and experimental investigation on droplet dynamics and dispersion of a jet engine injector

“…in cooperation with the Karlsruhe Institute of Technology in (Marinov et al, 2012), is based on the prefilming air-blast atomization technology (Lefebvre, 1989). It produces a polydispersed spray with a large dilute spray zone.…”

“…This rig was unconfined to allow easier optical access and to avoid deflection of droplets at chamber walls (Marinov et al, 2012). The operating conditions, including the relative pressure drop as the pressure loss across the injector system, are summarized in Tab.…”

Influence of Single-Component Fuels on Gas-Turbine Model Combustor Lean Blowout

“…There is general interest in understanding lean blowout as modern combustors are operated under lean conditions to reduce emissions [13--15]. In their reviews Cavaliere et al [16] and Marinov et al [14] show that a significant body of work regarding lean blowout of gaseous fueled swirling flames exists. However, lean blowout of spray flames has been studied in much less detail.…”

“…More recently, Marinov et al [14] used an approach to study lean kerosene and methane flames and their lean limit in one single burner without significantly changing the hardware environment.…”

Review of laboratory swirl burners and experiments for model validation

“…This paper focuses on "laboratory swirl burners" which are, by design, more amenable to fundamental studies and the long term objective of model development and validation. Moreover, and for simplicity, the swirl stabilized burners covered in this paper are only concerned with gaseous fuels and do not extend to those operated on sprays [35,36] or pre-vaporised fuels [37][38][39].…”