Experimental and Numerical Investigation on Cavitating Flows in Diesel Injection Systems

The present study is concerned with the phase change during rapid depressurization of fluids: the role of vapor bubbles nucleation and growth and the effect on the system fluid dynamics were modeled and experimental measurements were made. Following a control-volume approach, averaged equations governing the motion of a one-dimensional, homogeneous, no-slip two-phase flow were used considering both thermal equilibrium (equal temperature) and non-equilibrium (non-equal temperature) between the liquid and vapor phases. In the non-equilibrium model, the heat transfer from the liquid to the vapor and the corresponding mass transfer velocity were modeled. Model results were compared with experimental data for a loss-of-coolant accident in nuclear power plants: the comparison of numerical vs. experimental data showed the role of nucleation velocity during the earliest phase of rapid depressurization. The experimental study of two-phase flow in a diesel engine injection system has been carried out using a rotative pump which is operated by using a purpose-developed test-bench; pressure measurements inside the system pipes were performed using pressure transducers; moreover, an ultrasonic technique was employed to study phase change phenomena. Several measurements were performed comparing the results obtained by different experimental techniques with the model outputs.Sommario.presente studio riguarda il fenomeno della cavitazione durante la depressurizzazione di fluidi. E'stata considerata la velocità di formazione e nucleazione delle bolle di vapore e le equazioni di conservazione sono state integrate con solutori al 1°e 2°ordine di tipo ENO. Sono stati utilizzati dati sperimentali ottenuti durante incidenti per perdita di refrigerante in centrali nucleari; per quanto riguarda gli apparati di iniezione, gli autori hanno sviluppato due differenti tecniche sperimentali, basate rispettivamente sulla pressione e sulla riflessione degli ultrasuoni. Il confronto dei risultati numerici con quelli sperimentali è stato soddisfacente.     

Injection characteristics simulation and analysis in diesel engines

By means of a purposely developed numerical code an investigation of injection systems in diesel engines has been carried out. Cavitation at low pressure was simulated. The experimental results obtained were compared with the numerical ones. Data on cavitation waves, in the pipe between pump and injector, were obtained during that simulation. In particular, the influence of the relief volume on cavitation volume and injected fuel rate were computed. Unstable working conditions, characterized by a large variation of the injected fuel, at the same operating point, have been experimentally investigated and simulated. Lecture delivered at the Workshop on Fluiddynamics, Combustion and Exposition in Reciprocating Engines, held at Capri in 1990.     

Design and demonstration of interferometric integrated-optic sensors in Ti:LiNbO3 waveguides

The design of an integrated optic Michelson interferometer sensor for stress, temperature, and microdisplacement measurements consisting of a semi-asymmetric X-junction made by Ti in-diffused LiNbO₃ waveguides is reported. The possibility of performing simultaneous measurements of strain and temperature is investigated, and different calibration schemes are proposed. Experimental results of displacement-only measurements show a 64% intensity modulation with 33-dB optical loss.