Development of a Multi-Spark Ignition System for Reducing Fuel Consumption and Exhaust Emissions of a High Performance GDI Engine

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 costeffective 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. The main benefits that have been achieved by introducing and optimizing a multi-spark ignition mode can be summarized as follows: missing and partial burn combustions elimination, combustion variability minimization, HC emissions reduction (also due to absence of misfiring events), NOx emissions reduction (mainly due to the possibility of increasing residual gas fraction), significant specific fuel consumption reduction (especially during very low load operation - brake mean effective pressure around 0.5∼1.0 bar - and during cold start operation). Finally, the paper introduces the idea of extracting from ion current signals information related to combustion instability, which can be used to activate multi-spark mode, and to identify the optimal charge-discharge sequential pattern. The main characteristics of the rapid control prototyping system that has been developed to demonstrate the feasibility and the effectiveness of the proposed solution are synthesized in the first part of the paper, while the multi-spark pattern calibration process and the main experimental results are shown next, both during test cell and on-board operation.