Split-Injection in a Downsized Ethanol SIDI Engine Aiming to Mitigate Pre-Ignition 2017-36-0266

The abnormal combustion, such as pre-ignition and knock, are deviations from the controlled combustion process under certain operating conditions, which can result in performance losses and possible damage to the engine. In the SI engines, a pre-ignition event can take place when the flame front is started by any hot spot into the combustion chamber before ignition by the spark plug. The objective of this work is to investigate the use of the Stratified Combustion for Pre-Ignition Suppression (SCPIS) in order to reduce this undesirable phenomenon, especially under high load operating conditions. The results were obtained through dynamometric tests on a downsized ethanol SIDI engine, and considered satisfactory in terms of maximizing the fuel conversion efficiency. The split-injection was studied and adjusted so that the second injection pulse was performed in order to provide satisfactory results of charge cooling effect and, consequently, was effective for pre-ignition suppression. The strategy also lead to greater stability of the combustion process, reducing the IMEP covariance from 3.32% to 2.26%. Furthermore, the split-injection technique allowed the engine operation closer to the MBT condition, which in turn resulted in specific fuel consumption reduction from 441.3 g/kWh to 433.4 g/kWh compared to the homogeneous stoichiometric mixture condition and, consequently, an increase of 1.8% in the engine overall efficiency was achieved.