A new optical technique for measuring Sauter Mean Diameter changes of a fuel spray under an electrostatic field was checked, calibrated, and implemented. The optical technique is based on measuring scattered light at two angles using a variable focal length apparatus. Special attention was given to improving the electrical control loop parameters in order to minimize measurement errors. In order to measure more realistically the effects of the electrostatic probe inside a gas turbine combustor, a pressure chamber was added to the outlet of the present combustion simulation device. Hot tests were carried out with diesel fuel DF-2. Pressure chamber, combustor's temperatures, fuel, and air mass flow rates, were recorded together with the voltage applied at the electrode. Results of the cold tests with the new optical device show a Sauter Mean Diameter of 50.0 micron at fuel pressure (DF-2) of 100 psi, 51.7 micron at 125 psi and 47.8 micron at 80 psi. The device could not resolve changes while the high voltage field was exerted. Combustion temperatures with the pressure chamber are presented. Preliminary designs for improvements of the various devices are also described. Keywords: Particle measurement; Sauter mean diameter, T56 jet engine combustors; Electrostatic atomization; Alternative fuels; Optical radiometers.