[EN] The mixing of isothermal liquid sprays in engine-like conditions has been investigated by applying the structured planar laser imaging technique to remove multiple light scattering. The intensity of the illumination plane has been recovered by removing multiply scattered light and mapping the spray three-dimensionally via discrete tomography. Based on the extinction of light within the illumination plane, the number density has been extracted. Coupled with 2-D maps of droplet diameters obtained through LIF/Mie ratio, the number density allowed to calculate the fuel concentration in the sprays. The mixture fraction of DI Diesel sprays injected into an inert environment held at room temperature has been evaluated and compared to a 2-D model based on gas-jet theory. The experimental results showed good agreement with the predictions when a Gaussian radial distribution is assumed and the Schmidt number is correctly tuned. Differences in the radial distribution has been observed and related to incomplete momentum transfer between the liquid spray and the surrounding gases. For different testing conditions, while the influence of ambient density on mixing was expected, the effect of injection pressure has been found to provide additional information concerning the global mixing of liquid sprays. © 2012. This research has been funded in the frame of the project FLEXIFUEL reference TRA2010–17564 from Ministerio de Ciencia e Innovacin (Spanish Ministry of Sciences) The authors thank José Enrique del Rey (from CMT-Motores Térmicos, Universidad Polité- cnica de Valencia) for his collaboration during the experimental setup Payri, R.; Gimeno, J.; Marti-Aldaravi, P.; Manin, J. (2012). Fuel concentration in isothermal Diesel sprays through structured planar laser imaging measurements. International Journal of Heat and Fluid Flow. 34:98-106. https://doi.org/10.1016/j.ijheatfluidflow.2011.12.007