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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.

A systematic experimental investigation was undertaken to compare the fuel consumption and exhaust emissions of a production SI engine fueled by either gasoline or compressed natural gas (CNG). The investigation was carried out on a two-liter four-cylinder engine featuring a fast-burn pent-roof chamber, one centrally located spark plug, four valves per cylinder and variable intake-system geometry. The engine was originally designed at Fiat to operate with unleaded gasoline and was then converted at Politecnico di Torino to run on CNG. A Magneti Marelli IAW electronic module for injection-duration and spark-advance setting was used to obtain a carefully controlled multipoint sequential injection for both fuels.