Effect of ambient pressure on macroscopic and microscopic spray characteristics of gasoline-diesel blends for gasoline compression ignition engine applications

In the last decade, gasoline compression ignition technology has attracted the scientific community's attention because of its superior thermal efficiency and low soot and NOx emissions. The use of high-reactivity gasoline fuels having research Octane numbers similar to 60-80 enabled researchers to achieve low-temperature combustion with superior ignition control because of their higher resistance to ignition. A wide range of injection timings and strategies have been evaluated to extend the operating range of GCI engines. This highlights the need to characterize low-octane fuel sprays in varied ambient pressures, resembling engine conditions. Comprehensive macroscopic and microscopic spray characterization of gasoline-diesel blends vis-a-vis baseline diesel has been done under 20, 30, and 40 bar ambient pressures. This study used diffused backlit illumination and phase doppler interferometry techniques to evaluate these test fuels' macroscopic and microscopic spray characteristics respectively. Lower ambient pressures exhibited lesser air entrainment in the spray plume and higher droplet axial velocities for all test fuels. Higher droplet axial velocities enhanced droplet breakup, resulting in smaller droplets in 20 bar ambient conditions than in 30 and 40 bar for all test fuels. This indicated the possibility of overleaning the charge, while using an earlier injection in GCI engine conditions. The droplet breakup persisted for longer distances in gasoline-diesel blends, leading to superior spray atomization and mixing than baseline diesel in all ambient conditions.