Impacts of Injection Pressure on Split-Injection Energy-Assisted Compression-Ignition Combustion of Low Cetane Number SAFs with a Gaussian-Shaped Ribbed Piston Bowl Design

The impact of injection pressure on a split-injection energy-assisted compression-ignition (EACI) combustion strategy was studied in an optically accessible engine with a custom ribbed piston bowl design. Three injection pressures (600, 800, and 1000 bar) were investigated for three split-injection dwells (1.5, 2.0, and 2.5 ms) with a fixed second injection timing of -5.0 CAD. The Gaussian-shaped ribbed piston bowl design was employed to position hot combustion gases from the first injection near the centrally located injector to enable rapid ignition and mixing-controlled combustion of the second injection. At 600-bar injection pressure, as injection dwell was shortened, relocation of hot combustion gases near the injector became increasingly more difficult due to less available time for relocation and due to the higher in-cylinder densities at the start-of-injection (SOI) for the first injection. Increased injection pressure (800 and 1000 bar) improved the relocation of the first injection combusted gases and increased the number of fuel jets rapidly igniting and undergoing mixing-controlled combustion during the second injection. Injection pressures of 800 and 1000 bar for a 2.0-ms injection dwell resulted in a greater number of fuel jets rapidly igniting than for the 600-bar injection pressure with a 2.5-ms injection dwell. These results suggest there is potential to achieve EACI operation at more application-relevant engine speeds through the utilization of custom piston bowl designs which allow for stable engine operation with higher injection pressures.