Identification and early prediction of lean blowout in premixed flames
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Ó Indian Academy of Sciences
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Identification and early prediction of lean blowout in premixed flames SOMNATH DE1,* , ARIJIT BHATTACHARYA1, SIRSHENDU MONDAL2, ACHINTYA MUKHOPADHYAY1 and SWARNENDU SEN1 1
Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India Department of Mechanical Engineering, National Institute of Technology, Durgapur 713209, India e-mail: [email protected]
2
MS received 15 April 2018; revised 5 February 2019; accepted 11 April 2019 Abstract. Lean premixed combustion is a state-of-the-art technology to meet the stringent emission norms, especially to reduce the NOx emission. In the present study, we focus on the transition to lean blowout of premixed flames. The main objective of the study is to explore some important measures for prediction of lean blowout as the existing methods are not always suitable in early detection of blowout in case of premixed flames. We further consider different cases through which lean condition can be attained. For such cases, we first discuss the flame dynamics prior to blowout. Among different statistical measures, mean, median, root mean square and coefficient of variance of heat release rate fluctuations are found to be useful in blowout prediction. On the other hand, skewness and excess of kurtosis do not show any predictive quality. We also observe that the flickering frequency defined in a specific manner also shows a significant variation near lean blowout. Further, the mean frequency evaluated using Hilbert transform is found to show indication of LBO well before its occurrence. Therefore, the frequency analysis along with statistical analysis of the heat release rate oscillations is found to be very relevant in the context of blowout prediction and can be applied in the practical combustors. Keywords. frequency.
Premixed flame; heat release rate oscillation; lean blowout; statistics; flickering frequency; Hilbert
1. Introduction Lean premixed (LPM) combustion has been found to be one of the suitable technologies in gas turbine combustors for reducing NOx emission while ensuring an improved fuel economy and efficiency. Although diffusion flame provide excellent stability characteristics and reliable performance, NOx emission is much higher than for lean premixed combustors. Therefore, research on the performance and dynamics of the gas turbine combustors operated with lean premixed air-fuel mixture is of prime importance today [1]. In lean premixed prevaporized (LPP) combustors, liquid fuels are employed after being vaporized. Keeping this in mind, we study precursory events of lean blowout with a premixed flame. Furthermore, the lower temperature of the flame and combustion gases during lean combustion further increases the life time of the engine components, especially the turbine blades [2]. However, lean mixture results in a reduction of chemical reaction rate, thereby, make the This paper is a revised and expanded version of an article presented in ‘‘First Interna
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