Impacts of Injection Pressure and Timing on Energy-Assisted Compression-Ignition Combustion with Gaussian-Shaped Ribbed Piston Bowl Design

The impacts of injection pressure with a Gaussian-shaped ribbed piston bowl design for energy-assisted compression-ignition (EACI) combustion were investigated in an optically accessible engine. Three injection pressures (600, 800, and 1000 bar) were investigated for three potential first injection timings corresponding to injection timings for injection dwells of 1.5, 2.0, and 2.5 ms of a fixed second injection timing of -5.0 CAD. Reliable positioning of the hot combusted gases from the first injection near the injector tip enables mixing-controlled combustion of the second injection. Results demonstrated the EACI capabilities of pairing high injection pressures with the Gaussian-shaped ribbed piston bowl. At higher injection pressures, the redirection of fuel vapors from the in-line fuel jet back toward the ignition assistant (IA) increased the residence time the fuel mixture was exposed to the hot zone from the ignition assistant, reducing the possibility of misfires. Results also indicate higher injection pressure accelerates the ignition process of the first injection, enabling the operation of shorter injection dwells by reducing the time it takes for the combusted gases from the first injection to reach the location of the injector. These demonstrate the ability to potentially achieve EACI operation at more application-relevant engine speeds.