Experimental Investigation of a Fueled Prechamber Combustion in an Optical Small Displacement SI Methane Engine

The constant aim of the automotive industry is the further improvement of engine efficiency and the simultaneous reduction of the exhaust emissions. In order to optimize the internal combustion engines it is necessary to further improve the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. In this context, the application of optical diagnostic techniques permits a deep insight into the fundamental processes such as flow development, fuel injection, and combustion process. In this paper the analysis of the combustion process of gaseous fuel ignited by the plasma jets coming from a prechamber was performed. The investigation was carried out in an optically accessible small Direct Injection Spark-Ignition (DI SI) engine fueled with Methane. The ignition was obtained with a properly designed fueled prechamber prototype. It was equipped with a gas Direct Injector, used to inject the fuel into the prechamber, and a spark plug used to ignite the mixture. The combustion of the prechamber mixture generates four plasma jets that quickly ignite the mixture into the combustion chamber. The development of the combustion process was investigated for different engine operative conditions performing a cycle resolved visualization of the flame in the combustion chamber. This approach allowed the acquisition of significant information on the flame propagation. Using the prechamber, the flame speed is many times faster with respect to the traditional ignition. All the optical data were correlated with the engine performance and the exhaust emissions