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High performance Spark Ignition (SI) Port-Fuel Injected (PFI) internal combustion engines are usually optimized to deliver high power output at high speed in Wide Open Throttle (WOT) conditions. However, they also have to run consistently at idle, possibly with stoichiometric Air-Fuel Ratio (AFR), in order to limit tailpipe emissions. The two requirements are sometimes conflicting, as it is difficult to match high-speed volumetric efficiency with low-speed turbulence: the intake runner size and shape are often designed for performance, meaning that usually they do not guarantee a satisfying air-fuel mixing at idle. The consequence of poor mixture formation may be high cycle-to-cycle variation or misfiring, with obvious consequences on pollutant emissions and driveability. In the worst cases, however, the consequence could be even more serious: stalling phenomena have been observed on the test bench.

Modern internal combustion engine control systems require on-board evaluation of a large number of quantities, in order to perform an efficient combustion control. The importance of optimal combustion control is mainly related to the requests for pollutant emissions reduction, but it is also crucial for noise, vibrations and harshness reduction. Engine system aging can cause significant differences between each cylinder combustion process and, consequently, an increase in vibrations and pollutant emissions. Another aspect worth mentioning is that newly developed low temperature combustion strategies (such as HCCI combustion) deliver the advantage of low engine-out NOx emissions, however, they show a high cylinder-to-cylinder variation. For these reasons, non uniformity in torque produced by the cylinders in an internal combustion engine is a very important parameter to be evaluated on board.

The paper presents the development and real-time implementation of a combustion control system based on optimal management of multiple spark discharge events, in order to increase combustion stability, reduce pollutant emissions and fuel consumption, and avoid partial or missing combustion cycles. The proposed approach has been developed as a cost-effective solution to several combustion-related issues that affect Gasoline Direct Injection (GDI) engines during cold start and part load operation. The problem of optimizing combustion efficiency and improving its stability during such operating modes is even more critical for high performance engines, which are designed to maximize charge efficiency especially at medium-high engine speeds.