Lena Voigt

Bio: Lena Voigt is an academic researcher from German Aerospace Center. The author has contributed to research in topics: Combustion chamber & Combustion. The author has an hindex of 3, co-authored 5 publications receiving 18 citations.

Planar measurements of CO concentrations in flames at atmospheric and elevated pressure by laser-induced fluorescence

Abstract: The article describes the development and application of a laser-optical technique for the quantitative measurement of carbon monoxide (CO) in combustion environments of elevated pressures relevant of gas turbine environments. Planar CO measurements can provide important information for the understanding of several aspects of the combustion process, such as localized lean blowout conditions or quenching effects of effusion cooling on the combustor flow. While laser-induced fluorescence is a sensitive non-intrusive measuring technique suitable for planar detection, the CO molecule cannot be excited directly in the visible or near UV. For the present implementation, a two-photon excitation scheme with resulting fluorescence in the visible range is utilized. To qualify the technique, planar measurements in a laminar premixed atmospheric flame are performed in a first step; this flame is later on used for calibration of CO concentrations in a laminar premixed flame at elevated pressure up to 5 bar and in a generic turbulent combustor with a swirl-stabilized flame operated at atmospheric pressure. Pressure effects on spectral structures and the calibration procedure are discussed, as well as potential interference by cross-sensitivity with other species. Based on this optimization strategies are defined for the respective experimental arrangements.

Time-resolved temperature profile measurements in the exhaust of a single sector gas turbine combustor at realistic operating conditions

Abstract: Records of the time-varying temperature profile at flight relevant operating conditions are acquired at the exit of a combustion chamber fitted with a staged, lean-burn fuel injector using high-speed laser induced fluorescence (LIF) at a sample rate of 10 kHz. Temperatures are estimated from the concentration dependent fluorescence of the hydroxyl (OH) radical under the assumption of local equilibrium. Beyond the time-series analysis, the acquired data is correlated with simultaneously acquired OH chemiluminescence sampled in the primary zone near the fuel injector. These analyses reveal a strong influence from the precessing vortex core, originating in the primary zone, on oscillations in the temperature profiles measured at the exit of the combustor.

Turbulent Flame Shape Switching at Conditions Relevant for Gas Turbines

Abstract: A numerical investigation is conducted in this work to shed light on the reasons leading to different flame configurations in gas turbine combustion chambers of aeronautical interest. Large eddy simulations (LES) with a flamelet-based combustion closure are employed for this purpose to simulate the DLR-AT Big Optical Single Sector (BOSS) rig fitted with a Rolls-Royce developmental lean burn injector. The reacting flow field downstream this injector is sensitive to the intricate turbulent-combustion interaction and exhibits two different configurations: (i) a penetrating central jet leading to an M-shape lifted flame; or (ii) a diverging jet leading to a V-shaped flame. First, the LES results are validated using available BOSS rig measurements, and comparisons show that the numerical approach used is consistent and works well. The turbulent-combustion interaction model terms and parameters are then varied systematically to assess the flame behavior. The influences observed are discussed in the paper from physical and modelling perspectives to develop physical understanding on the flame behavior in practical combustors for both scientific and design purposes.

Optische Messung von Geschwindigkeit und Temperatur am Austritt einer Magerbrennkammer unter realistischen Betriebsbedingungen

Abstract: Es werden Messungen von Geschwindigkeit und Temperatur am Austritt eines Magerbrennkammer-Sektors vorgestellt, der in Teillast ungestuft bei realistischen Bedingungen betrieben wird. Die eingesetzten Verfahren sind die Particle Image Velocimetrie und die Laser-induzierte OH Fluoreszenz. Das Geschwindigkeitsfeld weist am Austritt noch die Drehbewegung auf, die von den Drallerzeugern der Magerbrenner induziert wird. Durch die Warmefreisetzung des Pilotbrenners wird diese im Vergleich zur isothermen Stromung noch verstarkt, wahrend der Turbulenzgrad im Gegensatz dazu kleiner wird. Die turbulenten Langenmase, die aus den momentanen Geschwindigkeitsfeldern abgeleitet wurden, deuten auf eine Prazessionsbewegung des Brennerwirbels hin. Die Temperaturmessungen zeigen eine Temperaturerhohung im gesamten Querschnitt und demonstrieren so die turbulente Durchmischung des Rauchgases der Pilotverbrennung. Jedoch verbleibt ein heiser Kern im Zentrum des Sektors. Diese Informationen dienen dem verbesserten Verstandnis des hochenergetischen Ubergangs zwischen Brennkammer und Turbine und bilden somit auch einen Beitrag zur Vermeidung von Effizienzverlusten von Triebwerken mit Magerbrennkammern.

The Quantum Theory of Light

Abstract: (b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

Applied Combustion Diagnostics

Abstract: The editors have assembled a world-class group of contributors who address the questions the combustion diagnostic community faces. They are chemists who identify the species to be measured and the interfering substances that may be present; physicists, who push the limits of laser spectroscopy and laser devices and who conceive suitable measuremen

Rapid communication Planar laser-induced fluorescence imaging of carbon monoxide using vibrational (infrared) transitions

Abstract: We report a new imaging diagnostic suitable for measurements of infrared-active molecules, namely infrared planar laser-induced fluorescence (IR PLIF), in which a tun- able infrared source is used to excite vibrational transitions in molecules and vibrational fluorescence is collected by an infrared camera. A nanosecond-pulse Nd:YAG-pumped KTP=KTA OPO=OPA system is used to generate 12 mJ of tunable output near 2:35 mm which excites the 2 band of carbon monoxide (CO); fluorescence resulting from excited CO is collected at 4:7 mm by using an InSb focal plane ar- ray. Quantitative, high-SNR PLIF imaging of gas-phase CO is demonstrated at a 10-Hz acquisition rate with a minimum detection limit of 1350 ppm at 300 K. PACS: 32.50.+d; 34.50.Ez; 39.30.+w