Experimental Investigation of the Compression Ignition Process of High Reactivity Gasoline Fuels and E10 Certification Gasoline using a High-Pressure Direct Injection Gasoline Injector

Gasoline compression ignition (GCI) technology shows the potential to obtain high thermal efficiencies while maintaining low soot and NOx emissions in light-duty engine applications. Recent experimental studies and numerical simulations have indicated that high reactivity gasoline-like fuels can further enable the benefits of GCI combustion. However, there is limited empirical data in the literature studying the gasoline compression ignition process at relevant in-cylinder conditions, which are required for further optimizing combustion system designs. This study investigates the temporal and spatial evolution of the compression ignition process of various high reactivity gasoline fuels with research octane numbers (RON) of 71, 74 and 82, as well as a conventional RON 97 E10 gasoline fuel. A ten-hole prototype gasoline injector specifically designed for GCI applications capable of injection pressures up to 450 bar was used. Vapor and liquid penetration from high speed optical visualizations, as well as combustion measurement were studied in an optically accessible constant volume spray and combustion chamber. Near simultaneous shadowgraph and Mie scattering images were captured to investigate the spray characteristics. OH* chemiluminescence and natural luminosity images were recorded simultaneously to characterize the ignition process through two high-speed cameras. The experiments were conducted under a wide range of ambient charge gas conditions, including temperatures from 900 to 1200 Kelvin, charge gas pressures from 50 to 100 bar, oxygen levels from 10-21% to represent 0-50% exhaust gas recirculation (EGR) levels. The fuel was injected at 300 and 450 bar injection pressure. Results show that vapor penetration of the E10 and high reactivity gasoline fuels are similar, and the liquid penetration is related to the fuel density. With the OH* chemiluminescence images analysis, the ignition delay decreases, and the flame lift-off length moves upstream towards the injector tip with increasing ambient temperature, increasing charge gas pressure, increasing cetane number and decreasing EGR level. A gasoline ignition delay correlation and a lift-off length correlation considering the charge gas conditions and the fuel properties have been achieved.