Experimental investigation of equivalence ratio fluctuations in a lean premixed kerosene combustor

Abstract

In this study a measurement technique for determination of equivalence ratio fluctuations from flame chemiluminescence in a kerosene-fuelled lean premixed combustor under atmospheric conditions is presented. Firstly, fundamental investigations into the relationship between the ratio of different chemiluminescence signals and the equivalence ratio are carried out using an imaging spectrometer. The chemiluminescence intensity is recorded for a wide range of equivalence ratios and fuel mass flows during steady state operation. The spectra show that the CH*/OH* ratio depends linearly on the equivalence ratio and is independent of the mass flow in the investigated range. Moreover, the background radiation has no influence on the monotonous trend of the CH*/OH* ratio for kerosene combustion. This interesting finding opens up new possibilities for passive optical measurement of the equivalence ratio in kerosene flames. Bandpass-filtered phase-correlated images of OH* and CH* chemiluminescence of an acoustically excited flame are taken simultaneously on one camera chip using an image doubler. After distortion correction, the image pair is used to calculate the global equivalence ratio from the CH*/OH* ratio. Based on the calibration chart derived in stationary operation, phase-resolved equivalence ratio perturbations are determined during acoustic excitation. The presented technique allows a quantitative measurement of equivalence ratio fluctuations in spray combustion and can therefore provide a better understanding of the fundamental mechanisms of thermoacoustic instabilities triggered by equivalence ratio fluctuations. Graphic abstract

Optical Equivalence Ratio Measurement of a Dual Fuel Burner for Natural Gas and Kerosene

“…The CH*/OH* ratio with background correction exhibits a linear correlation to the equivalence ratio, whereas the ratio without background correction can be approximated better by a power law. This correlation for the CH*/OH* chemiluminescence ratio can also be found in previous work [36]. The CH*/CO 2 * ratio both with and without background correction is approximated by a first-order polynomial.…”

“…The Reynolds number varied from 26,000 to 42,000 referring to the burner outlet diameter of 32 mm. A detailed description of the test rig can be found in previous work [36,40,41].…”

“…The global mean ratio was then calculated as the average of the local ratios for each operating point. A detailed description of the post-processing procedure can be found in previous work [36].…”

“…The objective is to analyse the influence of background radiation on the relationship between these ratios and the equivalence ratio. Secondly, simultaneously acquired images of CH* and CO 2 * chemiluminescence are depicted using the bandpassfiltered chemiluminescence technique developed in previous works [35,36]. Here, the focus is on providing the local relationship between the different chemiluminescence signals and the equivalence ratio.…”

Comparison of the flame dynamics of a premixed dual fuel burner for kerosene and natural gas

“…In order to additionally allow liquid operation, the burner is equipped with a two-fluid nozzle which is mounted on the centre axis at the head air port 16 in the dual fuel burner configuration. The lance is fed with kerosene and atomizing air, which are brought into contact at the nozzle exit where the high momentum air flow atomizes the liquid flow.…”