The interest in methane is lately increased due to power-to-gas tech-nologies, through which green electricity in excess could be used to produce eas-ily storable gaseous fuels. Among engines for methane exploitation, dual-fuel piston engines is a very efficient and low impact solution. Their operation, still limited by high hydrocarbons and carbon monoxide emissions at low and knock at high loads, is characterized by many parameters. Besides the ones well recog-nized in literature, like pilot quantity and substitution rate, other parameters, like engine volumetric compression ratio, intake charge conditions, pilot injection pressure and timing, engine load and speed and exhaust gas recirculation showed an impact on engine performance and emissions. This work first describes the results of a full factorial DoE in which the effects of compression ratio, intake charge pressure, pilot injection timing and pressure, and methane flow rate effect, are evaluated and discussed on combustion devel-opment, engine performance and pollutant emission levels at the exhaust. Through ANalysis of VAriance analysis, the first and second order effects were also quantified. Moreover, the factors variation ranges leading the engine to operate in or close to HCCI combustion, i.e. guaranteeing a high conversion efficiency and low emission levels at the same time, were sought and highlighted. This suggested that not only very advanced, but also retarded injection timings, combined with high intake charge pressure determine very low levels of nitrogen oxides and maximum pressure rise rate, with little or no penalty on engine efficiency and emission levels.
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