Optical Characterization of a Diesel Spray at High Temperature and Pressure

The analysis of diesel sprays in engine-like conditions is of fundamental importance for the study and development of diesel engines. Laser diffraction techniques were used in this work to study droplet size distribution of a diesel spray injected into a constant-volume combustion vessel with line-of-sight optical access. The experiments were conducted using a common rail injector electronically controlled to inject after the combustion of a stoichiometric air-methane mixture. This allowed to reach temperature of around 1000 K and pressure of more than 10 bar. In the first stage of the work back-light technique was employed to measure spray characteristics such as penetration and cone angle. The liquid phase behavior was highlighted by means of a high-speed digital camera for different values of injection duration and pressure. In the second phase particle size distribution and pertinent attributes of the distribution were measured on the spray axis at 10 mm from the injector orifice. The obtained results were finally discussed putting in evidence the main sources of disturbance encountered during the measurements and illustrating their effects on the measurement accuracy