The stringent emission regulations for Internal Combustion Engines (ICEs) spawned
a great amount of research in the field of innovative combustion approaches
characterized by high efficiency and low emissions. Previous research
demonstrate that such promising techniques, named Low-Temperature Combustion
(LTC), combine the benefits of Compression Ignition (CI) engines, such as high
compression ratio and unthrottled lean mixture, with low engine-out emissions
using a properly premixed air-fuel mixture. Due to longer ignition delay and
high volatility compared to diesel, gasoline-like fuels show good potential for
the generation of a highly premixed charge, which is needed to reach LTC
characteristics. In this scenario, gasoline Partially Premixed Combustion (PPC),
characterized by the high-pressure direct injection of gasoline, showed good
potential for the simultaneous reduction of pollutants and emissions in CI
engines. However, previous research on gasoline CI highlight that a key factor
for the optimization of both efficiency and pollutants is the proper management
of Exhaust Gas Recirculation (EGR). This work presents the experimental
investigation performed running a light-duty CI engine, operated with gasoline
PPC, and varying the mass of recirculated gases trapped in the combustion
chamber. To guarantee the stability of gasoline autoignition in all the tested
conditions, a specific experimental layout has been developed to accurately
quantify the amount of trapped residual gases due to the internal and external
EGR. The obtained results clearly highlight the impact of EGR on the combustion
process and emissions, demonstrating that optimization of charge dilution with
EGR is fundamental to guarantee the optimal compromise between efficiency and
emissions over the whole operating range.
