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This work presents a series of simulations of the light-round process in a premixed annular combustor, consisting of 18 individual swirl bluff body burners, using improvements to the previously-published stochastic low-order model SPINTHIR that mimics flame propagation with a Langevin particle model and continuous new particle generation. The improvements presented include the effect of dilatation and a stochastic component to the quenching criterion, resulting in capturing reasonably well the bending behaviour of the turbulent flame speed with turbulent intensity. The results showed that the light-round mechanism was well reproduced compared to experiments. The various versions of the model captured the trend of light-round time τLR as a function of the mixture's laminar flame speed with different degrees of accuracy. Overall, the results here reported improve our low-order capability to model the ignition transient in complex multi-burner configurations, which can help the design process of gas turbine combustors. ; European Union Marie-Curie project ANNULIGHT (Grant Agreement No. 765998), and Clean Sky 2 project PROTEUS (Grant Agreement No 785349).

Laser Induced Breakdown Spectroscopy (LIBS) was applied to homogenous methane–air mixtures of a wide range of compositions ranging from only air to only fuel in order to establish a new calibration scheme suitable for LIBS measurement of mixture fraction in turbulent non-premixed flames. Both a portable low resolution spectrometer equipped with a CCD detector with wide temporal detection window and a monochromator with a fast gated ICCD camera were employed to monitor the plasma emission. The results obtained using the two detection systems were fully consistent, suggesting that LIBS can be used successfully with the CCD detector that is more suitable for industrial applications. From the spectroscopic analysis, it was shown that the ratio of the intensities of Hα (656.3 nm) over O (777.3 nm) (Hα/Ο) and of C2 (Δυ = 0, d3Πg –#x03B1;3Πu) over CN (Δυ = 0, Β2Σ+ – Χ2Σ+) (C2/CN) depend monotonically on the mole fraction of methane in the ranges of 0.0–0.3 and 0.3–1.0 respectively, therefore providing a new scheme for measurement of mixture fraction in non-premixed systems spanning the complete range of equivalence ratios. The technique was also applied to a swirling recirculating premixed flame and it was found that the equivalence ratio is successfully measured in both reactants and products. Based on the above, LIBS experiments were then carried out in turbulent axisymmetric non-reacting and reacting jets, and the mean mixture fraction determined by the aforementioned calibration curves was in good agreement with empirical correlations, while the rms measurement showed the expected trends, demonstrating hence the usefulness of the technique. ; At Patras, this research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) – Research Funding Program: Heracleitus II. Investing in knowledge society through the European Social Fund. MK acknowledges the Heracleitus II Program for a Ph.D fellowship and ERASMUS placement program that made possible a visit to the University of Cambridge in 2013. At Cambridge, RY has been funded by the Dorothy Hodgkin studentship program of the EPSRC. ; This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.combustflame.2016.02.025

There is a need to better understand particle size distributions (PSDs) from turbulent flames from a theoretical, practical and even regulatory perspective. Experiments were conducted on a sooting turbulent non-premixed swirled ethylene flame with secondary (dilution) air injection to investigate exhaust and in-burner PSDs measured with a Scanning Mobility Particle Sizer (SMPS) and soot volume fractions (fv) using extinction measurements. The focus was to understand the effect of systematically changing the amount and location of dilution air injection on the PSDs and fv inside the burner and at the exhaust. The PSDs were also compared with planar Laser Induced Incandescence (LII) calibrated against the average fv. LII provides some supplemental information on the relative soot amounts and spatial distribution among the various flow conditions that helps interpret the results. For the flame with no air dilution, fv drops gradually along the centreline of the burner towards the exhaust and the PSD shows a shift from larger particles to smaller. However, with dilution air fv reduces sharply where the dilution jets meet the burner axis. Downstream of the dilution jets fv reduces gradually and the PSDs remain unchanged until the exhaust. At the exhaust, the flame with no air dilution shows significantly more particles with an fv one to two orders of magnitude greater compared to the Cases with dilution. This dataset provides insights into soot spatial and particle size distributions within turbulent flames of relevance to gas turbine combustion with differing dilution parameters and the effect dilution has on the particle size. Additionally, this work measures fv using both ex situ and in situ techniques, and highlights the difficulties associated with comparing results across the two. The results are useful for validating advanced models for turbulent combustion. ; European Union (EU), Horizon 2020 (H2020), Clean Sky 2 Joint Undertaking, Industrial Leadership (IL) (Project LEAFINNOX, grant number 831804)