Ignition measurement of non-premixed propane with varying co-flowing AIR through high-speed schlieren stereoscopic colour imaging

The flame kernel propagation characteristics stemmed from the spark ignition of low -Re, non-premixed propane (C3H8) under varying air co-flow conditions were studied using DFCD (Digital Flame Colour Discrimination) incorporated stereoscopic image processing technique. The current work focused on the viability of obtaining the combustion initiating kernel propagation speed (S-P), equivalence ratio (phi) and kernel depth (z) characteristics simultaneously as these parameters are important in the fundamental combustion theories and highly desired in the field of practical burner monitoring and diagnostics. Through the superimposition of schlieren and DFCD- enhanced colour images, the observed spatial location of kernel spearhead was found to conform to the disturbance front observed from the schlieren visualisation. Flame stretch principle was applied to experimentally determine the un-stretched kernel propagation speeds (SP,O). Concurrently, the estimation of the temporal state of reactant mixture equivalence ratio (phi(e)) variation was made using DFCD-segregated spatial colour signal characteristics. Further comparison were made against the CHEMKIN simulated results of un-stretched laminar flame speed (SL,O) at different phi. The experimentally determined SP,O values were found to overlap the SL,O range corresponding to the measured phi(e). The steady occurrence of digital colour fidelity observed for all considered cases suggest that the most reactive mixture fraction (xi(MR)) path followed by the kernel occurred in the fuel-rich premixed phi condition (approximately phi(e) = 1.34 to 1.40). Furthermore, stereoscopic reconstruction of DFCD- enhanced flame colour images provided additional dimensional linkage to correlate the dimensional-spectral variation along with changes in combustion flow conditions. The dimensional-spectral property, through the computation of local colour ratio and stereoscopically reconstructed z, illustrated linearity in both the time domain and in temporal cross-correlation with phi(e). The observed shift of the cross-correlated cluster towards the fuel-richer phi(e) condition is coherent to the corresponding increase in Re and exemplifies the observed conformance of the derived SL,O and phi(e) to properties of premixed combustion along the propagation front potentially denoting the path of xi(MR).

Automated summary

This study investigated the flame kernel propagation characteristics of low-Re, non-premixed propane under different air co-flow conditions. The study focused on obtaining important parameters such as combustion initiating speed, equivalence ratio, and kernel depth, and compared them with simulation results. The study also analyzed changes in combustion flow conditions using color signal characteristics and stereoscopic image reconstruction.