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The simulation activity for the piston bowl development in a low compression ratio (CR) high-performance diesel engine is described, starting from the calibration of a 3-D CFD commercial code by pressure-based combustion diagnostics data. Calibration was made for the baseline engine built by GMPT-E, matching experimental pressure traces and heat release rates derived from these through the diagnostic tool. Measured pollutant emissions were also applied for calibration at this stage. The engine was susceptible to modifications, according to the outcomes of combined simulation and experimental investigations. The validated CFD model was used for the screening of three new piston bowls featuring a reduced compression ratio. The 3-D code has been integrated with a robustly calibrated 1-D hydraulic model for the injection system simulation and with a 1-D fluidynamic tool for modeling engine flow processes external to the cylinder to provide quite accurate boundary conditions.

The present work concerns the study of the potentialities of high-boost small-displacement C.R. (Common Rail) diesel engines where the compressor and the expander are mechanically disengaged for the purpose of power cogeneration from the exhaust gas. This objective can be achieved by means of advanced concept electrical devices capable of delivering the energy produced by the expander either to the drivetrain transmission or to the even more power-demanding auxiliary equipment of both the engine and the vehicle. The performance of a small-displacement boosted diesel engine with a common-rail injection system has been predicted by means of a computational code obtained by integrating different in-house non-commercial codes that simulate the intake, combustion and exhaust processes. The model validation has been carried out by means of the experimental data obtained at Fiat Research Center on a commercial small-displacement C.R. turbocharged diesel engine.

A comparative investigation of both fuel consumption and exhaust emissions has been carried out on a production SI engine operated by either gasoline or compressed natural gas (CNG). The engine had the main features of being a multivalve, fast-burn pent-roof chamber engine with a variable intake-system geometry. It was originally designed at Fiat Auto to operate with unleaded gasoline and was then converted at Politecnico di Torino to run on CNG. To that end, in addition to designing and building the CNG fuel plant, the multipoint Bosch Motronic M1.7 electronic module for injection-duration and spark-timing control was replaced with a Magneti-Marelli IAW ECM designed to obtain a multipoint sequential injection. With this new ECM, the engine was modified so as to work with either natural gas or gasoline.

An integrated theoretical and experimental investigation was carried out in order to evaluate the effects that the pump delivery-valve assembly can produce on the performance of a pump-line-nozzle fuel-injection system with a distributor-type pump for automotive diesel engines. Four distinct delivery valves, one constant-pressure valve, one reflux-hole and two relief-volume valves, were separately fitted to the pump and for each configuration of the delivery assembly the system behavior was analyzed under full-load steady-state operations in a wide pump angular-speed range. Fuel injection-rate as well as local pressure time-histories were investigated, paying specific attention to the occurrence and temporal evolution of cavitation phenomena in the pressure pipe and injector nozzle, after the valve closure. The flow across the delivery-valve assembly was theoretically examined in order to ascertain any instability sources as possible causes of cyclic fluctuations.