Turbulent Jet Ignition Effect on Exhaust Emission and Efficiency of a SI Small Engine Fueled with Methane and Gasoline

Pollutant emission of vehicle cars is nowadays a fundamental aspect to take into account. In the last decays, the company have been forced to study new solutions, such as alternative fuel and learn burn mixture strategy, to reduce the vehicle's pollutants below the limits imposed by emission regulations. Pre-chamber ignition system presents potential reductions in emission levels and fuel consumption, operating with lean burn mixtures and alternative fuels. As alternative fuels, methane is considered one of the most interesting. It has wider flammable limits and better anti-knock properties than gasoline. Moreover, it is characterized by lower CO2 emissions. The aim of this work is to study the evolution of the plasma jets in a different in-cylinder conditions. The activity was carried out in a research optical small spark ignition engine equipped alternatively with standard ignition system and per-chamber. The engine runs at 2000 rpm at wide open throttle in standard ignition condition and slightly turbocharged in pre-chamber condition in order to overcome the decrease of compression ratio. In this activity methane and gasoline were used. Methane was always injected in the pre-chamber and ignited by spark plug; meanwhile gasoline was injected in the main chamber by port fuel injection mode. The combustion of the pre-chamber methane mixture generates four plasma jets that quickly ignite the mixture made with gasoline/air into the combustion chamber. In this condition the flame speed was much faster than the traditional ignition (gasoline injected in intake manifold without prechamber). Using optical data, significant information about the flame propagation in terms of the speeds and radius were obtained. The optical data were correlated with the engine performance and indicated measurements that showed an increase indicated mean effective pressure and coefficient of variation reduction when the pre-chamber was used. Furthermore the effect of pre-chamber ignition on the engine stability and efficiency in stoichiometric and lean-burn operation conditions was investigated.