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.