Performance Assessment of Gasoline PPC in a Light-Duty CI Engine

In the past years, stringent emission regulations for Internal Combustion (IC) engines produced a large amount of research aimed at the development of innovative combustion methodologies suitable to simultaneously reduce fuel consumption and engine-out emissions. Previous research demonstrates that the goal can be obtained through the so-called Low Temperature Combustions (LTC), which combine the benefits of compression-ignited engines, such as high compression ratio and unthrottled lean operation, with a properly premixed air-fuel mixture, usually obtained injecting gasoline-like fuels with high volatility and longer ignition delay. Gasoline Partially Premixed Combustion (PPC) is a promising LTC technique, mainly characterized by the high-pressure direct-injection of gasoline and the spontaneous ignition of the premixed air-fuel mixture through compression, which showed a good potential for the simultaneous reduction of fuel consumption and emissions in CI engines. Despite its potential, gasoline PPC might suffer from low combustion controllability and stability, because gasoline spontaneous ignition is significantly affected by slight variation of the local in-cylinder thermal conditions. This paper summarizes the work carried out to optimize gasoline PPC in a light-duty CI engine, operated in a test cell. The investigated system has been slightly modified to guarantee a stable operation, using gasoline instead of diesel, over a wide load range. The first part of the analysis has been focused on the study of gasoline auto-ignition, the goal being to define an injection strategy suitable to guarantee combustion stability. Then, further activity has been focused on performance investigation through a properly defined span of the main control parameters of interest, such as injection pressure and exhaust gas recirculation.