In this study a 5-step reduced chemical kinetic mechanism involving 9 species is developed for combustion of Blast Furnace Gas (BFG), a multi-component fuel containing CO/H 2 /CH 4 /CO 2 , typically with low hydrogen, methane and high water fractions, for conditions relevant for stationary gas-turbine combustion. This reduced mechanism is obtained from a 49-reaction skeletal mechanism which is a modified subset of GRI Mech 3.0. These skeletal and reduced mechanisms are validated for laminar flame speeds, ignition delay times and flame structure with available experimental data, and using computational results with a comprehensive set of elementary reactions. Overall, both the skeletal and reduced mechanisms show a very good agreement over a wide range of pressure, reactant temperature and fuel mixture composition.

a b s t r a c tThe validity of the commonly used flame marker for heat release rate (HRR) visualization, namely the rate of the reaction OH + CH 2 O , HCO + H 2 O is re-examined. This is done both for methane-air and multicomponent fuel-air mixtures for lean and stoichiometric conditions. Two different methods are used to identify HRR correlations, and it is found that HRR correlations vary strongly with stoichiometry. For the methane mixture there exist alternative HRR markers, while for the multi-component fuel flame the above correlation is found to be inadequate. Alternative markers for the HRR visualization are thus proposed and their performance under turbulent conditions is evaluated using DNS data.

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Direct numerical simulation (DNS) of freely-propagating premixed flames of a multicomponent fuel is performed using a skeletal chemical mechanism with 49 reactions and 15 species. The fuel consists of CO, H 2 , H 2 O, CH 4 , and CO 2 in proportions akin to blast furnace gas or a low calorific value syngas. The simulations include low and high turbulence levels to elucidate the effect of turbulence on realistic chemistry flames. The multi-component fuel flame is found to have a more complex structure than most common flames, with individual species' reaction zones not necessarily overlapping with each other and with a wide heat releasing zone. The species mass fractions and heat release rate show significant scatter, with their conditional average however remaining close to the laminar flame result. Probability density functions of displacement speed, stretch rate, and curvature are near-Gaussian. Five different mean reaction rate closures are evaluated in the RANS context using these DNS data, presenting perhaps the most stringent test to date of the combustion models. Significant quantitative differences are observed in the performance of the models tested, especially for the higher turbulence level case.

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In the context of Large Eddy Simulations, deconvolution is an attractive alternative for modelling the un-closed terms appearing in the filtered governing equations. Such methods have been used in a number of studies for non-reacting and incompressible flows, however their application in reacting flows is limited in comparison. Deconvolution methods

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