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Abstract Combustion processes operating under fuel lean conditions can reach very low emissions and extremely high efficiency. However, ultra-lean combustion is more prone to thermos-acoustic instabilities and the flame can even get extinguished by the blowing out of the combustion chamber. Hence the Lean Blow-Out (LBO) limit plays a critical role in the stable performance of gas turbine combustors since it represents the boundary between the flame extinction and the stable flame region. The occurrence of LBO in real engines can significantly reduce the engine availability and operating reliability. Therefore, early detection of LBO is a key performance parameter that needs to be investigated. In this way, the engine can be guided through precautionary actions using a control system, like setting the max air-to-fuel ratio, changing the split among fuel lines, etc. From a numerical perspective, the unsteady phenomena of LBO are indeed challenging to be captured as the flame is marching towards to the quenching conditions from a stable point. The present work leverages the capabilities of a tabulated chemistry approach in predicting the process of a lean blowout occurring in a swirled technically-premixed flame. One of the experimental events conducted at high pressure and high temperature to understand the LBO event for a given geometry/fuel composition is considered as benchmark condition for the numerical investigation. The paper will presents the validation of the numerical model/approach against the experimental measurements. More in detail, an Extended Turbulent Flame Speed Closure (ETFC) model was implemented to introduce the effect of stretch and heat loss on the partially premixed flame. The exploitation of the numerical results is carried out through the analysis of the main fields like the heat-release rate, the pressure fluctuation and the temperature. The extinction equivalence ratio is predicted quite accurately, showing that the ETFC is suitable for the study of the blow-off for the partially premixed flames, without an increase in computational cost. The presented methodology would serve as the primary benchmark for assessing the models’ effectiveness in capturing the flame dynamics: the approach can be extended/repeated to other operating conditions of the combustor to define the LBO map for a finite TCD range and different fuel split.
Rajesh et al. (Mon,) studied this question.