The lift-off of jet diffusion flames of a liquid fuel in coflowing streams of air was established experimentally for a range of jet discharge and stream velocities. The improvement in the lift-off stability of the flame due to the presence of a small concentration of an auxiliary gaseous fuel in the surrounding air was established. Liquid n-heptane was the jet fuel while methane, ethylene, propane, and hydrogen were employed individually in small concentrations as the auxiliary fuels. It is shown that the lift-off distance and the corresponding ignition delay of the jet flame can be correlated for all the observations made in terms of derived dimensionless grouping of the main parameters varied, which included the jet discharge velocity, the surrounding stream velocity, and the concentration of the fuel added to the surroundings of the flame.

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