Large eddy simulation of an ignition sequence and the resulting steady combustion in a swirl-stabilized combustor using FGM-based tabulated chemistry

Purpose This study aims to deal with the large eddy simulation (LES) of an ignition sequence and the resulting steady combustion in a swirl-stabilized liquid-fueled combustor. Particular attention is paid to the ease of handling the numerical tool, the accuracy of the results and the reasonable computational cost involved. The primary aim of the study is to appraise the ability of the newly developed computational fluid dynamics (CFD) methodology to retrieve the spark-based flame kernel initiation, its propagation until the full ignition of the combustion chamber, the flame stabilization and the combustion processes governing the steady combustion regime. Design/methodology/approach The CFD model consists of an LES-based spray module coupled to a subgrid-scale ignition model to capture the flame kernel initiation and the early stage of the flame kernel growth, and a combustion model based on the mixture fraction-progress variable formulation in the line of the flamelet generated manifold (FGM) method to retrieve the subsequent flame propagation and combustion properties. The LES-spray module is based on an Eulerian-Lagrangian approach and includes a fully two-way coupling at each time step to account for the interactions between the liquid and the gaseous phases. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for the flow field while the eddy diffusivity model is used for the scalar fluxes. The fuel is liquid kerosene, injected in the form of a polydisperse spray of droplets. The spray dynamics are tracked using the Lagrangian procedure, and the phase transition of droplets is calculated using a non-equilibrium evaporation model. The oxidation mechanism of the Jet A-1 surrogate is described through a reduced reaction mechanism derived from a detailed mechanism using a species sensitivity method. Findings By comparing the numerical results with a set of published data for a swirl-stabilized spray flame, the proposed CFD methodology is found capable of capturing the whole spark-based ignition sequence in a liquid-fueled combustion chamber and the main flame characteristics in the steady combustion regime with reasonable computing costs. Research limitations/implications The proposed CFD methodology simulates the whole ignition sequence, namely, the flame kernel initiation, its propagation to fully ignite the combustion chamber, and the global flame stabilization. Due to the lack of experimental ignition data on this liquid-fueled configuration, the ability of the proposed CFD methodology to accurately predict ignition timing was not quantitatively assessed. It would, therefore, be interesting to apply this CFD methodology to other configurations that have experimental ignition data, to quantitatively assess its ability to predict the ignition timing and the flame characteristics during the ignition sequence. Such further investigations will not only provide further validation of the proposed methodology but also will potentially identify its shortfalls for better improvement. Practical implications This CFD methodology is developed by customizing a commercial CFD code widely used in the industry. It is, therefore, directly applicable to practical configurations, and provides not only a relatively straightforward approach to predict an ignition sequence in liquid-fueled combustion chambers but also a robust way to predict the flame characteristics in the steady combustion regime as significant improvements are noticed on the prediction of slow species. Originality/value The incorporation of the subgrid ignition model paired with a combustion model based on tabulated chemistry allows reducing computational costs involved in the simulation of the ignition phase. The incorporation of the FGM-based tabulated chemistry provides a drastic reduction of computing resources with reasonable accuracy. The CFD methodology is developed using the platform of a commercial CFD code widely used in the industry for relatively straightforward applicability.

SIMULATION OF THE AIR-METHANE COAL DUST MIXTURE COMBUSTION IN THE SWISS-ROLL BURNER

One of the ways to utilize coalmine methane containing coal particles is to use it as a fuel for recuperative type burners that allow sustaining combustion of a lean methane-air mixture. The aim of the work is to study the steady combustion modes of a methane-air mixture containing coal particles in a Swiss-roll burner depending on the feed rate of the mixture and the parameters of the supplied coal-methane-air mixture. The paper considers numerical simulation of the combustion process of the methane-air mixture containing coal dust in a Swiss-roll burner of the recuperative type.

Ignition and Self-Supporting Burning of Gas-Air Mixtures with Hydrogen Admixtures on Platinum Wire

The proposed work describes analytical identification of hydrogen admixture concentration and catalyst temperatures limit values beyond which catalytic flameless steady combustion of gas-air mixtures at ambient temperature at platinum wires is observed. The effect of gas-air slip velocity upon considered values is shown. Initial platinum wire preheating temperatures required for catalytic ignition are determined.

Combustion Characteristic of Flow Through a Low Swirl Injector

An experimental study was carried out in order to provide a better understanding of the combustion characteristics of a low swirl injector (LSI). The swirl vanes angles are respectively 37°, 42° and 50°, and the swirl numbers are varied in a wide range. The fuel gases used in the experiment include propane, methane and methane with hydrogen. The results show: (1) the lean premixed propane, methane, methane with hydrogen and air flow through the LSI can sustain steady combustion at a lower swirl number; (2) the LSIs can generate a blue lift-off “W” type flames surrounding a long yellow pulsating flame and the blue flame consists of four clusters blue flames connected together along circumferential direction; (3) the flame structure converts the “W” type flame into the “broom” type flame with the pulsating yellow flame, and the distance between the front of the flame and the nozzle shortens with increasing swirl number in the same vane angle case; (4) the spectroscopic of the flame shows the yellow flames are emitted by diatomic carbon.