화학공학소재연구정보센터
Fuel, Vol.103, 334-346, 2013
Variation of hydrocarbon compositions and ignition locations on the radiative flame initiation characteristics through multi-dimensional DFCD incorporated image analysis
The experimental investigation of impinging diffusion methane (CH4) and propane (C3H8) ignition-to-combustion process under varying fuel flow rates and ignition positions have been characterised through multi-dimensional Digital Flame Colour Discrimination (DFCD) incorporated image processing methods. The DFCD post-processed digital flame images revealed that a 2D bluish-green flame kernel feature, similar to the common chemiluminescence-induced colour perception associated with premixed hydrocarbon flames, dominates the initial flame kernel propagation after the onset of ignition. The nominal yellowish soot colour feature typically associated with diffusion hydrocarbon flames was observed to trail the initial flame chemiluminescence emission entity by a time delay. The truncated 1D DFCD-processed colour signals illustrated discrepancies between the CH4 and C3H8 diffusion flame establishment process. It was found that under equivalent volumetric flow conditions, changes in the ignition position do not affect the typical C3H8 flame establishment procedure within the first 0.4 s of the ignition-to-combustion event. Diffusion CH4 flame, on the other hand, can be significantly influenced by ignition position; where the increase in ignition distance downstream resulted in the increase of chemiluminescence bluish-green flame distribution. This can be attributed to the enhanced local air entrainment and mixing in the downstream ignition location which effectively promotes partial mixing of reactants, and consequently reduce the local equivalence ratio states. With near-plate ignition, the diffusion CH4 flame colouration becomes completely bluish-green, which provides further credence to the elevation of local fuel/air partial premixing along with increase in downstream ignition distance. The propagation velocity of the DFCD-derived chemiluminescence-induced flame kernel for both CH4 and C3H8 ignition matched well with the propagation velocity of the initial combustion-induced density disturbance observed from the schlieren images. A constant C3H8/CH4 velocity ratio of 1.1 was observed from both the DFCD-processed and schlieren-derived results under different fuel flow rates. In addition, the DFCD processing was incorporated with stereoscopic 3D flame reconstruction technique to provide a feasible multidimensional data processing scope for quantifying the temporal evolution of different flame colour entities into comparable diagnostic parameters. The mapping of spatial DFCD-processed colour signal ratio onto the reconstructed 3D flame structure provided another step towards the development of a practical analytical platform for abstract local fuel/air monitoring and diagnosis. (C) 2012 Elsevier Ltd. All rights reserved.