Validation of a laser-induced fluorescence (LIF) model for mole-fraction imaging

The successful development of a supersonic combustion ramjet (scramjet) engine depends critically on finding ways to mix fuel and air efficiently at supersonic speeds. A planar laser-induced fluorescence (PLIF) method for visualising fuel mole-fraction has recently been developed by Fox et al. (1998). This method is used in a turbulent environment to obtain instantaneous images of fuel mole-fraction. These images can then be analysed to determine the efficiency of mixing, allowing quantitative comparison between different fuel-injector designs. However, to obtain the maximum useful amount of information from the images it is necessary to establish the limitations of the LIF model. The paper presents a partial validation of the theoretical modelling used in the fuel mole-fraction imaging method. In particular, we investigate the collisional quenching dependence and the pressure dependence of the LIF intensity.