Untersuchungen zur Chemie-Turbulenz-Wechselwirkung an by Keck O.

By Keck O.

Swirling flows enable a quick and effective blending of fiiel and oxidizer and are. hence, frequently utilized in useful combustion platforms. nevertheless, a few difficulties come up within the numerical simulation of those flames and the development of Computional Fluid Dynamics (CFD) codes is a problem in modem combustion learn. the most aim of this paintings has been a qualitative and quantitative experimental characterisation of limited swirling usual gas/air diffusion flames (with a thermal load of 150kW) utilizing varied laser innovations so as to generate a database for the validation of CFD codes and for a greater realizing of swirl stabilized flames. with a view to visualize the constitution of the flames, qualitative two-dimensional laser-induced fluorescence (LIF) was once used. The single-pulse second LIF photos of OH exhibit powerful corrugations of alternative zones hello the flames, i.e., an internal and outer recirculation area and a blending quarter. The gasoline distribution and fuel/air blending have been investigated by means of 2nd LIF of NO. which was once seeded to the average gasoline. The mam a part of the research involved quantitative single-pulse laser measurements of spontaneous Raman scattering to figure out concurrently the temperature T. the combination fraction f. and the species concentrations of CO2, O2, CO, N2, CH4, H2O, and H2. The mam difficulties in adapting the measuring strategy to the flames and combustion chamber are defined and solved during this paintings, i.e., the mfluence of the correction of sign history because of laser-induced fluorescence from polycyclic hydrocarbons and the warmth move to the encircling optics. the consequences include the joint likelihood density capabilities (PDFs) of the measured amounts. The spatial distributions of the suggest values and rms fluctuations replicate the flame behaviour within the various zones: the internal recirculation region is characterised by way of sizzling, neat stoichiometric combustion items, the region of combining and response by means of powerful turbulent fluctuations of T and f. and the outer recirculation sector by means of a homogeneous mix of exhaust gasoline at chemical equilibrium yet diminished temperature. A deeper perception into the turbulence-chemistry interplay and the thermochemical nation of the flames used to be gamed from the correlations among quite a few amounts. The scatterplots of temperature as opposed to mix fraction printed, for example, the coexistence of unreacted gasoline and oxidizer, even for stoichiometric combinations. additionally, the temperature aid as a result of radiation, flame stretch, and wall touch can be quantified from those correlations.

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By Keck O.

Swirling flows enable a quick and effective blending of fiiel and oxidizer and are. hence, frequently utilized in useful combustion platforms. nevertheless, a few difficulties come up within the numerical simulation of those flames and the development of Computional Fluid Dynamics (CFD) codes is a problem in modem combustion learn. the most aim of this paintings has been a qualitative and quantitative experimental characterisation of limited swirling usual gas/air diffusion flames (with a thermal load of 150kW) utilizing varied laser innovations so as to generate a database for the validation of CFD codes and for a greater realizing of swirl stabilized flames. with a view to visualize the constitution of the flames, qualitative two-dimensional laser-induced fluorescence (LIF) was once used. The single-pulse second LIF photos of OH exhibit powerful corrugations of alternative zones hello the flames, i.e., an internal and outer recirculation area and a blending quarter. The gasoline distribution and fuel/air blending have been investigated by means of 2nd LIF of NO. which was once seeded to the average gasoline. The mam a part of the research involved quantitative single-pulse laser measurements of spontaneous Raman scattering to figure out concurrently the temperature T. the combination fraction f. and the species concentrations of CO2, O2, CO, N2, CH4, H2O, and H2. The mam difficulties in adapting the measuring strategy to the flames and combustion chamber are defined and solved during this paintings, i.e., the mfluence of the correction of sign history because of laser-induced fluorescence from polycyclic hydrocarbons and the warmth move to the encircling optics. the consequences include the joint likelihood density capabilities (PDFs) of the measured amounts. The spatial distributions of the suggest values and rms fluctuations replicate the flame behaviour within the various zones: the internal recirculation region is characterised by way of sizzling, neat stoichiometric combustion items, the region of combining and response by means of powerful turbulent fluctuations of T and f. and the outer recirculation sector by means of a homogeneous mix of exhaust gasoline at chemical equilibrium yet diminished temperature. A deeper perception into the turbulence-chemistry interplay and the thermochemical nation of the flames used to be gamed from the correlations among quite a few amounts. The scatterplots of temperature as opposed to mix fraction printed, for example, the coexistence of unreacted gasoline and oxidizer, even for stoichiometric combinations. additionally, the temperature aid as a result of radiation, flame stretch, and wall touch can be quantified from those correlations.

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Der Mischungsbruch ist nahezu konstant und liegt zwischen 0,045 und 0,052 (0,047 entspricht λ=1,2). 8 zeigt, wie im gesamten Mischungsbruchbereich, eine gute Übereinstimmung mit den berechneten Kurven. Stickstoff ist an den Hauptreaktionen der Verbrennung nicht beteiligt, sodass hier selbst die Rechnungen für die Gegenstromdiffusionsflamme und für die reine Mischung relativ eng beieinander liegen. Der N2-Molenbruch lässt in dieser Flamme keine Rückschlüsse auf den thermochemischen Zustand der Flammen zu und wird im Folgenden nicht weiter berücksichtigt.

5. h. dass die Gemische entweder noch nicht reagiert haben oder ausreagiert sind. Ab h=40mm wird die Verteilung breiter, es treten Temperaturen von 300K bis 2300K in den Messungen auf. Allerdings ist bei h=60mm und h=90mm eine verminderte Häufigkeit für Messungen mit 1200K bis 1600K zu erkennen. Dieses lokale Minimum kann auf die bereits angesprochenen Zündverzugszeiten zurückgeführt werden. Mischt sich heißes Abgas mit kalten Frischgasen zu einem zündfähigen Gas, so beeinflusst die aus der Mischung resultierende Temperatur entscheidend die Zündverzugszeit.

5. Ergebnisse der Raman-Messungen Temperatur [K] 2500 0,2 0,4 0,6 87 0,8 2500 2500 h=40mm 2000 0,15 0,20 0,25 2500 2000 2000 h=150mm -1 1500 1500 1500 -1 a = 400s 1000 1000 1000 1000 -1 a = 1s -1 500 0,0 2500 Temperatur [K] 0,10 2000 a = 1s 1500 0,05 0,2 0,2 0,4 0,4 0,6 0,6 0,8 0,8 1,0 0,05 0,10 0,05 0,10 0,15 0,20 0,15 0,20 500 0,25 0,30 0,25 2500 2000 2000 a = 1s 1500 0,00 2500 2500 h=20mm 2000 a = 400s 500 500 2000 h=90mm -1 1500 1500 1500 -1 a = 400s 1000 1000 -1 1000 1000 a = 1s -1 500 0,0 500 0,2 0,4 0,6 0,8 1,0 Temperatur [K] 2500 h=10mm 2000 a = 400s 500 0,00 2500 0,05 0,10 0,15 0,20 0,25 500 0,30 2000 h=60mm -1 a = 1s 1500 1500 -1 a = 400 s 1000 1000 500 0,0 0,2 0,4 0,6 0,8 1,0 -1 a = 400s 500 Mischungsbruch Abb.

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