Abstract
The liftoff and blowout characteristics of laminar flames in a partially premixed jet are studied for propane and n-butane fuels mixed with air. As the flow rate increases, flame lifts off from a nozzle attached flame and liftoff height increases highly nonlinearly with flow rate, and then blowout occurs. The jet velocities at liftoff and at blowout decrease linearly with the increase in air dilution and are independent of nozzle diameter. The liftoff height at blowout is proportional to the square of nozzle diameter and to the square of fuel mass fraction. Correlations for the liftoff heights and blowout conditions are derived by using a cold jet theory for velocity and species concentrations, based on the tribrachial nature of lifted flames. That is, at the flame anchoring point, the flame has the characteristics of a stoichiometric flame and its propagation speed balances axial flow velocity. The experimental findings of liftoff and blowout are successfully predicted.