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 fundamentalaspect 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, toreduce the vehicle's pollutants below the limits imposed byemission regulations. Pre-chamber ignition system presentspotential reductions in emission levels and fuel consumption,operating with lean burn mixtures and alternative fuels. Asalternative fuels, methane is considered one of the most interesting.It has wider flammable limits and better anti-knockproperties than gasoline. Moreover, it is characterized bylower CO2 emissions.The aim of this work is to study the evolution of theplasma jets in a different in-cylinder conditions. The activitywas carried out in a research optical small spark ignitionengine equipped alternatively with standard ignition systemand per-chamber. The engine runs at 2000 rpm at wide openthrottle in standard ignition condition and slightlyturbocharged in pre-chamber condition in order to overcomethe decrease of compression ratio. In this activity methaneand gasoline were used. Methane was always injected in thepre-chamber and ignited by spark plug; meanwhile gasolinewas injected in the main chamber by port fuel injection mode.The combustion of the pre-chamber methane mixturegenerates four plasma jets that quickly ignite the mixturemade with gasoline/air into the combustion chamber. In thiscondition the flame speed was much faster than the traditionalignition (gasoline injected in intake manifold without prechamber).Using optical data, significant information aboutthe flame propagation in terms of the speeds and radius wereobtained. The optical data were correlated with the engineperformance and indicated measurements that showed anincrease indicated mean effective pressure and coefficient ofvariation reduction when the pre-chamber was used.Furthermore the effect of pre-chamber ignition on the enginestability and efficiency in stoichiometric and lean-burn operationconditions was investigated.