A comparative study of the port geometrical effects on sharp corners' jet triple flames

The performance of sharp corners' jet triple flames was modulated by compromising the increase in both the number of sharp corners between 3 and 16 and the overall perimeter up to 218% with the reduction in vertex angle to 30°. While the turbulent kinetic energy peak value correlated with the vertex angle and its average value depended on the number of corners, the entrainment rate gain was pronounced in accordance with the perimeter. By having each port stabilizing the inner flame wing such that the sharp corners lay on the diffusion flame envelope at its base, the flow strain due to corners increased the triple flame stability limit to a maximum of 9.2 m/s and minimized the NOx emissions to 14 ppm. Upon incorporating the swirl impact, the highest firing rate was reached at a jet velocity of 26.3 m/s at which excessive entrainment of reactants into corners provided a compact flame with a firing intensity of 50.3 MJ/m3. While the flame length was related to the extent of jet deformation from the circular shape, a flame shortening by 67% was verified by an enhancement of 192% over the circular port entrainment rate. Improved combustion efficiencies with respective decrease in CO and HC emissions to 61 ppm and 0.04% were reported by maximizing the effect of sharp edged appendices. The swirl introduced a favorable advection transport, whereby the turbulence peaks at corners merged to provide a relative increase of 11.8 times in the average turbulence energy. By effectively combining the active and passive control techniques via providing swirl and modulating the port geometry, the lean operation limit extended by 19% from that of the circular port whereby NOx emissions for triple flames case II had a minimum of 4 ppm.