COMPUTATIONAL STUDY ON THE EFFECTS OF NON-PERIODIC FLOW PERTURBATIONS ON THE EMISSIONS OF SOOT AND NO_X IN A CONFINED TURBULENT METHANE/AIR DIFFUSION FLAME

Abstract

A computational investigation on the effects of fuel inlet perturbations in a confined turbulent CH₄/air flame has been performed. Non-periodic fluctuations were characterised at the fuel inlet via a pair of sinusoidal harmonics of incommensurate periods with identical amplitude and frequency. Harmonic amplitudes of 2.5%, 7.5%, and 12.5% with respect to the time-averaged fuel inlet velocity have been simulated and their results weighted against the predictions in a steady fuel delivery. The results showed a decrease in soot emissions as the amplitude of the perturbation increased; nonetheless, a logarithmic behaviour was observed, suggesting that soot reduction will stabilise after certain pulse amplitude for a given frequency. The results from the 12.5% incommensurate pulse were also compared with its simple harmonic equivalent. Localized reductions in NO emissions were also observed in the incommensurate flame with respect to the sinusoidal pulse. The case study was based on a 2-dimensional axi-symmetric piloted methane flame with a time-averaged jet Reynolds number of about 7000. Realizable k − ε and Eddy Dissipation were employed to solve turbulence transport and chemistry respectively. Magnussen's soot model has been employed to simulate the formation of particulates and the thermal and prompt NO_x sources have been considered.

Keywords:

• Computational
• Emissions
• IC Engines
• Incommensurate
• NO_x
• Pulsed Flames
• Soot

Notes

p = 1 atm, T_fu = 290 K, T_air = 300 K.