Development of a methodology for the investigation of residual gases effects on gasoline compression ignition

Compression ignited engines are still considered the most efficient and reliable technology currently available for power generation in automotive applications. In this scenario, the main obstacles to the use of conventional compression-ignited engines are the increasingly stringent emission regulations, which require significant increases in engine efficiency and severely limit both NOx and particulate matter production. As a matter of fact, the combustion process that occurs in conventional compression-ignited engines, mainly characterized by the autoignition of directly injected Diesel-like fuels, is a heterogeneous process usually not compatible with modern emission regulations. To overcome the mentioned critical issues, a large amount of research is being carried out to investigate the combined use of gasoline-like fuels and compression-ignited engines, which proved to be very promising to simultaneously achieve high efficiency and low emissions. One of the main critical issues related to the auto-ignition of gasoline-like fuels is the high sensitivity to the thermal conditions of the cylinder, which results in long ignition delays strongly variable with small cylinder temperature variations. This work proposes a testing methodology suitable to investigate how the residual gases trapped inside the combustion chamber affect cylinder thermal conditions and, consequently, the gasoline auto-ignition mechanisms. The testing methodology is based on a specifically designed injection control strategy that manages the cylinders independently: one cylinder is operated using a proper pattern of gasoline direct injections, while the others are operated only to vary the intake and exhaust conditions of the first cylinder, where gasoline compression ignition is studied. The testing methodology, applied to an engine installed in a test cell, proved to be effective to highlight the effect of the residual gases on gasoline auto-ignition.