Comparison of combustion and emission characteristics under single-fueled and dual-fueled conditions with premixed compression ignition

The key point of premixed compression ignition (PCI) combustion is an ignition delay time that is sufficient to premix the air and fuel. Thus, when PCI combustion is implemented with a single fuel, a very early start of injection (SOI) is usually applied, along with heavy exhaust gas recirculation. However, if two different fuels are used simultaneously for PCI combustion, it is possible to control the in-cylinder fuel reactivity by adjusting their ratio. Because an additional ignition delay control parameter is used for dual-fueled PCI combustion, its operating strategy and combustion characteristics differ from those of single-fueled PCI combustion. In this study, single-fueled and dual-fueled PCI combustions were compared using gasoline and diesel fuel under part-load conditions (1500 rpm and a low heating value of 580 J/str). In both cases, the diesel SOI was varied from the top dead center (TDC) to 35° BTDC to analyze the combustion characteristics. Under the optimized operating conditions, the target engine-out emissions were below the gross indicated specific NOx (gISNOx) of 0.4 g/kWh and gISsmoke of 20 mg/kWh. The results showed dual-fueled combustion is more suitable for PCI conditions than single-fueled combustion in terms of both the engine-out emissions and gross indicated thermal efficiency.