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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 production SI engine originally designed at Fiat Auto to operate with unleaded gasoline was converted to run on natural gas. To that end, in addition to designing and building the CNG fuel plant, it was necessary to replace the multipoint electronic module for injection-duration and ignition-timing control with an ECM designed to obtain multipoint sequential injection. The engine was modified so as to work either with gasoline or natural gas. For the present investigation, however, the engine configuration was not optimized for running on methane, in order to compare the performance of the engine operated by the two different fuels with the same compression ratio. In fact, the engine is also interesting as a dual-fuel engine because of its relatively high compression ratio ≈10.5 that is almost suitable for CNG operation. The engine had the main features of being a multivalve, fast-burn pent-roof chamber engine with a variable intake-system geometry.