OCR Text |
Show air into the fuel boundary dominates the initial fuel-air mixing zone. Once the gas velocity becomes sufficiently high, the entrainment and mixing of air creates boundary conditions where velocity of the combustible mixture exceeds its maximum rate of flame propagation. The flame, then, detaches from the end of the open pipe. Such detachment is the inception of stability concerns. The question of interest for turbulent jet diffusion flame is, "how fast can a gas mixture of a certain composition be exited before flame lift-off and ignition stability problems occur?" With transverse wind velocity the initial fuel-air mixing dynamics are altered, but the gas exit velocity remains the controllable variable of importance. COMBUSTIBILITY CONSIDERATIONS For stability of a turbulent jet diffusion flame, the air en-trainment- mixing of the turbulent jet discharge is limited by the combustibility of the fuel. It is known from practical flare and burner observations that a pure hydrocarbon fuel can be discharged at a much higher velocity than can the same hydrocarbon fuel vitiated with inerts. The inerts alter the flammability limits, raise the ignition temperature and slow the flame speed. Figure 2 lists some of the combustion characteristics normally available for hydrocarbon fuels. Research of the combustion science literature, for a given gas, illuminates significant variations in the flammability limit, ignition temperature and flame speeds^). Figure 2 also lists some 5.2.4 |