Study of Fuel Stratification on Spark Assisted Compression Ignition (SACI) Combustion with Ethanol Using High Speed Fuel PLIF
An engine can be run in Homogenous Charge Compression Ignition (HCCI) mode by applying a negative valve overlap, thus trapping hot residuals so as to achieve an auto-ignition temperature. By employing spark assistance, the engine can be operated in what is here called Spark Assisted Compression Ignition (SACI) with ethanol as fuel. The influence of fuel stratification by means of port fuel injection as well as in combination with direct injection was investigated. A high-speed multi-YAG laser system and a framing camera were utilized to capture planar laser-induced fluorescence (PLIF) images of the fuel distribution. The charge homogeneity in terms of fuel distribution was evaluated using a homogeneity index calculated from the PLIF images. The homogeneity index showed a higher stratification for increased proportions of direct-injected fuel. It was found that charge stratification could be achieved through port fuel injection in a swirling combustion system.